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ORIGINAL ARTICLE
Blood pressure and thermal responses to repeated whole bodycold exposure: effect of winter clothing
Yue Li Æ Hisham Alshaer Æ Geoff Fernie
Accepted: 13 August 2009 / Published online: 29 August 2009
� Springer-Verlag 2009
Abstract The effect of outdoor clothing and repeated cold
exposure on blood pressure, heart rate, skin temperature, and
thermal sensation was studied in 16 young (18–34 years)
and 8 middle-aged (35–51 years) normotensive participants.
Four winter clothing ensembles were used: regular winter
clothing without a hat, with a hat, with an extra pair of pants,
and with a hat and an extra pair of pants. The participants
were exposed four times to -5�C for 15 min wearing dif-
ferent clothing ensembles in counterbalanced order and each
cold exposure was followed by 25 min of rewarming at
25�C. The results showed that systolic and diastolic blood
pressure increased in cold and increased more when a hat
was not used. Wearing hats not only reduced the blood
pressure response during cold exposure, but also promoted
faster recovery of forehead skin temperature and blood
pressure. These findings are encouraging and warrant further
investigations to better understand the benefits of wearing
appropriate clothing in the winter, especially among older
people and patients with cardiovascular diseases.
Keywords Winter � Cold exposure � Blood pressure �Skin temperature � Hat � Warm clothing
Introduction
It is well known that an increase in mortality is associated
with exposure to low outdoor temperatures, primarily due
to cardiovascular diseases, in particular from myocardial
infarction and stroke (Marchant et al. 1993; Nayha 2002;
Schneider et al. 2008). Though the associations between
cardiovascular diseases and temperature are well docu-
mented, the underlying mechanisms behind these associa-
tions are in general not very well understood. One
mechanism could be that these exposures act on the car-
diovascular system by elevating blood pressure. Cold
exposure is known to increase blood pressure by activation
of the sympathetic nervous system (Young 1996). Since
elevated blood pressure is a major risk factor for a range of
cardiovascular diseases (Jackson et al. 2005; Kim et al.
2003), it seems reasonable to explore how environmental
exposure affects blood pressure both experimentally and on
the population level.
The results of several large population studies of the
effects of the season and temperature on systolic blood
pressure show strong, statistically significant effects for
both factors (Madsen and Nafstad 2006). The effect of
season, however, disappeared in a model that also con-
tained outdoor temperature, which suggests that a major
component of the seasonal change in blood pressure, and
hence cardiovascular disease risk, is due to temperature
(Barnett et al. 2007). Improvements in central indoor
heating are not consistently associated with a reduction in
seasonal differences in mortality from cardiovascular dis-
ease (Keatinge et al. 1989; Wilkinson et al. 2004; Barnett
et al. 2005). Therefore, Keatinge et al. (1989, 1997) place
more emphasis on personal behaviors and have argued that
many excess winter mortalities are related to exposure to
cold from ‘‘brief excursions outdoors rather than to low
indoor temperatures’’. A study by Perez-Lloret et al. (2006)
contributed further supporting evidence that seasonal dif-
ferences in blood pressure do exist, but are largely confined
to the daytime. Causative mechanisms, such as the time
Y. Li (&) � H. Alshaer � G. Fernie
iDAPT Technology R&D Team,
Toronto Rehabilitation Institute,
550 University Avenue,
Toronto, ON M5G 2A2, Canada
e-mail: [email protected]
123
Eur J Appl Physiol (2009) 107:673–685
DOI 10.1007/s00421-009-1176-5
course of increases in blood pressure in response to chan-
ges in ambient temperature, individual differences in these
responses, and the potential importance of improved out-
door clothing during winter all require further experimental
study.
Donaldson et al. (2001) surveyed more than 6,500 par-
ticipants from two age groups (50–60 and 65–74 years) and
found that there was large variation between regions in the
wearing of gloves, hats, and scarves. Furthermore, their
data showed that regional variations in the average wearing
of these three items (gloves, hats, and scarves) were sig-
nificantly related to excess winter mortality in those
regions. People do not always wear a hat during winter.
According to Donaldson et al. (2001), of the 6,583 people
who were interviewed, 2,678 (41%) wore a hat, and only
1,042 (16%) wore all three items. Furthermore, little is
known regarding the extent to which differences in the
thermoregulatory function mirror clothing effectiveness,
especially the insulation of the head.
According to an epidemiological survey, in North
America, people spent approximately 10% of their time
outdoors in summer and about 2–4% of their time outdoors
in winter (Leech et al. 2002). Numerous studies have been
conducted to demonstrate the effects of long-term exposure
to cold (Leppaluoto et al. 2001; Makinen et al. 2006;
Reynolds et al. 2007). On the other hand, investigations of
the effects of short-term repeated cold exposures on health
and physiological responses are limited in number (Ozaki
et al. 1998, 2001; Tochihara 2005; Kim et al. 2007).
However, these short cold exposures are very common in
daily life during winter and have become more increasingly
common in industry. In general, people are not exposed to
severe cold for long periods of time in the winter, but
instead, they have to go in and out of the cold environment
frequently.
To date, only one study conducted by Gavhed (2003),
has attempted to examine the extent to which personal
protection (e.g., wearing hats) is related to the cold-induced
rise in blood pressure in controlled laboratory conditions.
Gavhed (2003) found that wearing headgear with ear pro-
tection tended to reduce the systolic blood pressure
response among young healthy male participants. This
study was initiated to verify the findings of Gavhed, as well
as to investigate the effect of repeated brief cold exposures
on physiological responses across a broader range of ages
by including middle-aged participants. Accordingly, the
purpose of the present study was to examine the combined
effects of wearing different winter clothing and repeated
cold exposure on thermophysiological responses in 18
young (18–34 years) and 6 middle-aged (35–51 years)
normotensive participants under controlled laboratory
conditions.
Methods
Participants
A total of 24 adults (8 male, 16 female), mainly university
students and staff, participated in this study. Participants
were self-selected in response to printed advertisements.
The average and standard deviation of their baseline
characteristics are provided in Table 1. All participants
were normotensive, nonsmokers, and not taking any med-
ications that might alter the cardiovascular or thermoreg-
ulatory responses to cooling. The protocol was approved by
the Toronto Rehabilitation Institute Research Ethics Board.
Prior to data collection, each participant was provided a
clear description of what was required for participation and
thereafter was asked to carefully read and sign the consent
form. Participants were given the right to withdraw from
the study at any stage.
Instrumentation
After giving informed consent, physiological recording
devices and sensors were attached for the measurements of
blood pressure, heart rate and skin temperature. Systolic
blood pressure (SBP), diastolic blood pressure (DBP) and
heart rate were measured every 2.5 min before, during and
after cold exposure by a validated oscillometric BP monitor
(PhysioLogicTM Auto Inflate Blood Pressure Monitor,
AMG Medical Inc., Canada). The cuff was placed on the
left upper arm and worn throughout the trial. The skin
temperatures were measured using thermistors (Mon-a-
therm Temperature Probe, Nellcor Puritan Bennett Inc.,
Pleasanton, CA, USA) from seven sites: forehead, lower
back, right forearm, back of right hand, right thigh, right
lower leg, and right foot instep. Skin temperature values
were recorded throughout the experiment at 8-s intervals
Table 1 Demographic and
baseline hemodynamic
characteristics of the 24
participants
Age
(years)
Height
(cm)
Body
mass (kg)
Body
mass index
SBP
(mmHg)
DBP
(mmHg)
HR
(bmp)
Average 27.1 165.9 63.1 22.4 111.5 69.3 71.1
SD 9.0 9.2 13.3 3.1 9.6 7.6 8.0
Range 18–51 152–183 42–91 18–31 94–129 55–85 54–85
674 Eur J Appl Physiol (2009) 107:673–685
123
with a data logger (Smartreader 8?, ACR Systems,
Canada). The tip of each thermistor was in direct contact
with the participant’s bare skin. Each thermistor tip was
covered with a 3-cm strip of 3 M TransporeTM tape (3 M
Health Care, USA) to help minimize the effect of the
ambient air on the reading. The system (data logger and 7
thermistors) was calibrated in accordance with ISO 17025
by an accredited calibration facility (Alpha Controls
And Instrumentation, Markham, Canada) with an accuracy
of ± 0.1�C over the temperature range of -30 to 40�C.
The mean skin temperature was calculated using an area-
weighting formula: mean skin temperature Tsk = 4.655 ?
0.114 forehead ? 0.027 lower arm ? 0.068 hand ? 0.262
lower back ? 0.152 thigh ? 0.172 lower leg ? 0.076 foot
temperature. (Nielsen and Nielsen 1984).
Clothing ensembles
The present study was aimed at simulating normal winter-
time outdoor cold exposure in Southern Ontario, Canada.
Clothing plays an important role in adjusting thermal
comfort and it is classified according to its insulation value.
The unit normally used for measuring clothing insulation is
the clo unit (1 clo = 0.155 m2 K/W). A regular Toronto-
nian winter ensemble normally includes a shirt, trousers and
a winter coat, which has a total insulation of 1.3 clo, in
agreement with a survey study that showed the average
clothing insulation to be 1.3 ± 0.3 clo in South Finland
(Donaldson et al. 2001). A total of four different ensembles
that correspond to normal winter clothing were evaluated.
The ensembles included a base-ensemble and four winter
clothing ensembles. The base-ensemble consisted of a vest
(knitted lycra material), long-sleeved shirt, briefs (for
female participants: panties and bra), trousers, ankle socks,
and running shoes. As shown in Table 2 and Fig. 1, the four
winter clothing ensembles were base-ensemble plus varied
winter items. None-ensemble consisted of the base-
ensemble, a thigh length coat, a scarf, and a pair of fleece
gloves. In the tuque-ensemble, a tuque (knitted hat) was
added to the none-ensemble. In the pants-ensemble, a pair
of tear-away pants (windpants with metal snaps running the
length of both legs) was added to the none-ensemble. In the
both-ensemble, a tuque and a pair of tear-away pants were
added to the none-ensemble. The total dry insulation was
calculated from these garments (ISO 1994; Donaldson et al.
2001) and was expressed in clo units. The estimated clo
values for each ensemble are listed in Table 2. The tuque-
ensemble corresponded to normal winter clothing, which
included all three items (hat, scarf, gloves) (Donaldson et al.
2001). To control for the repeated exposure effect that can
Table 2 Characteristics of experimental clothing ensembles
Base-ensemble None-ensemble Tuque-ensemble Pants-ensemble Both-ensemble
Items Clo Items Clo Items Clo Items Clo Items Clo
Briefsa 0.03 Baseb 0.605 Base 0.605 Base 0.605 Base 0.605
Vest 0.09 Coat 0.6 Coat 0.6 Coat 0.6 Coat 0.6
Shirt 0.2 Gloves 0.025 Gloves 0.025 Gloves 0.025 Gloves 0.025
Socks 0.025 Scarf 0.02 Scarf 0.02 Scarf 0.02 Scarf 0.02
Shoes 0.02 Hat 0.02 Pants 0.24 Hat 0.02
Trousers 0.24 Pants 0.24
Total clo 0.605 1.250 1.270 1.490 1.510
a For female participants: panties (0.02 clo) and bra (0.01 clo)b Base is base-ensemble
Fig. 1 Line drawing
illustrations of base-ensemble
(a) and the four winter clothing
ensembles (b–e) (illustration by
Jamie Ibbett, MFA)
Eur J Appl Physiol (2009) 107:673–685 675
123
result from repeated testing, we used a counterbalancing
technique in which the order of the clothing ensembles was
counterbalanced for order across participants.
Experimental protocols
The study was performed during the winter from January to
April 2008 (mean monthly outdoor air temperature -2.1,
-5.3, -1.7 and 9.5�C) in the climate chamber at the
Toronto Rehabilitation Institute in Toronto. Each partici-
pant evaluated the four clothing ensembles under the same
environmental conditions (air temperature, Ta -5.8 ±
0.2�C, relative air humidity 72 ± 4%). Trials were con-
ducted on the same day to minimize between-day varia-
tions and were conducted during the winter/early spring
months to minimize the effects of cold acclimatization. The
testing for each participant was conducted by the same
investigators and started at the same time of day to reduce
possible confounding effects. Attempts were made to
standardize pre-trial behaviors of participants (i.e., general
exercise; timing and content of the meal (own choice) and
water consumed at mealtimes preceding the test session;
refraining from drinking alcoholic and caffeinated bever-
ages the day before trial). On the test day, participants
reported to the laboratory fully hydrated, having completed
their lunch 2.0–2.5 h prior to the starting time of the test.
The laboratory protocol involved four 15-min cold
exposures (C1–C4) in different winter ensembles in
counterbalanced order. Before each cold exposure, there
was a 10-min baseline period (B1–B4). Each cold exposure
was followed by a 15-min recovery period (R1–R4). The
total time of exposure to cold was 60 min. The total
rewarming time between two successive cold exposures
was 25 min. The experimental protocol is described in
Fig. 2. During the baseline period, the participants wore
the base-ensemble. They sat quietly for 10 min on a chair
in a thermally neutral room with air temperature at
24.4 ± 1.0�C, air velocity less than 0.2 m/s, and relative
air humidity of 25 ± 6%. Thereafter, the participants wore
one of the four winter ensembles and walked slowly 10 m
to a climatic chamber. The participants sat quietly in the
climatic chamber (air temperature at -5.8 ± 0.2�C, air
velocity less than 0.2 m/s, and relative air humidity of
72 ± 4%) on a chair for 15 min. The walls, ceiling and
floor of the climatic chamber were at the same temperature
as the air. After the cold exposure, the participants walked
slowly back to the thermally neutral room and removed
their winter ensemble. Then they sat quietly for 25 min
(15-min recovery period plus 10-min baseline period for
the next trial) wearing base-ensemble. Subjective ratings of
temperature sensation and thermal comfort were made at
the end of each baseline, cold exposure, and recovery
periods. Temperature sensations for the whole body were
assessed using a 9-degree subjective judgment scale (ISO
1995), ranging from very hot to very cold. Thermal com-
fort was assessed using a 5-degree scale ranging from
extremely uncomfortable to comfortable (ISO 1995) (as
shown in Fig. 3). Participants were asked to report each
temperature sensation separately by marking on a linear
100-mm line rating scale. A vertical line drawn at the
center of the scale indicated ‘‘neutral’’. The temperature
sensation and thermal comfort scales were labeled with
warm 25 min
cold 15 min
Base ensemble
Winter ensemble
Base ensemble
Winter ensemble
Base ensemble
Winter ensemble
Base ensemble
Winter ensemble
Base ensemble
C1R1
warm25 min
cold 15 min
C2R2
warm25 min
cold 15 min
C3R3
cold 15 min
C4R4B2 B3 B4
warm 10 min
warm15 min
B1
Trial 1 Trial 2 Trial 3 Trial 4
Fig. 2 Study design. A total of
24 participants performed the
tests in four consecutive trials at
cold (-5�C) and warm (?24�C)
conditions
(a) Temperature sensation scale
(b) Thermal comfort scale
Very cold
Very hot
Cold Cool Slightlycool
Neutral Slightlywarm
Warm Hot
Extremely uncomfortable
ComfortableSlightly uncomfortable
UncomfortableVery uncomfortable
Fig. 3 Illustration of (a)
temperature sensation and (b)
thermal comfort scale
676 Eur J Appl Physiol (2009) 107:673–685
123
descriptions as shown in Fig. 3. The length from the left
end point to the point marked by the participant was
measured and quantified as the rating score of either tem-
perature sensation or thermal comfort. Participants repe-
ated the cold exposure wearing different winter ensembles
and the whole experiment lasted for about 4 h, including
setup of devices and electrodes.
Statistical analysis
All skin temperature data were stored as 5-min averages.
All index values were expressed as mean ± standard
deviation. Trial baseline values were computed for each
physiological response by averaging data from the 10-min
baseline period (B1–B4). The effect of repeated cold
exposure on baseline values of BP, HR, skin temperatures
and thermal response was tested by a one-way repeated-
measures ANOVA (within factor: trial 1–4) to test whether
the order of presentation of clothing ensembles had a sig-
nificant impact on thermophysiological responses. If the
impact was negligible for any of the measurements, the
analyses were collapsed over order and the effect of
clothing ensemble on that measurement was examined by a
one-way repeated-measures ANOVA (within factor: four
winter ensembles). Data from each of the 15- min of cold
exposure (C1–C4) and the 15 min of recovery (R1–R4)
were averaged to compute means for BP, HR, and skin
temperatures in each trial. Temperature sensation and
thermal comfort rating scores were also obtained after each
cold exposure and recovery period. Changes due to cold
exposure were calculated as the difference between trial
baseline value and the mean cold exposure period values,
C1–C4. For example, the change in SBP in trial i during
cold exposure was calculated as:
CDSBPðiÞ ¼ SBPCðiÞ � SBPBðiÞ:
Changes during recovery were defined as the difference
between trial baseline value and the mean recovery period
values R1–R4. For example, the change in SBP in trial i
during recovery was calculated as:
RDSBPðiÞ ¼ SBPRðiÞ � SBPBðiÞ:
The effect of clothing ensemble and repeated cold
exposure on changes in BP, HR, skin temperatures, and
thermal response was tested by a two-way ANOVA (four
ensembles 9 four trials) for cold exposure and recovery
period separately. Tukey’s HSD post hoc test was
employed if significant main effects were observed.
For each cold period (C1–C4) and baseline period (B1–
B4), the maximal and minimal values of SBP and DBP
were calculated. The BP surge due to cold exposure was
calculated as the difference between the maximal BP
during cold exposure and the minimal BP obtained during
the baseline period. For example, the SBP surge in trial
i was calculated as:
DSBPðiÞ ¼ SBPmax CðiÞ � SBPmin BðiÞ:
The effect of clothing ensemble on SBP and DBP surge
was examined by a one-way repeated-measures ANOVA
(within factor: four winter ensembles). Tukey’s HSD post
hoc test was employed if significant main effects were
observed.
All BP and HR data during the 15-min cold exposure
and recovery were also calculated as 5-min averages,
which were then compared with the trail baseline value to
examine how fast BP and HR reacted to cold and whether
BP returned to trial baseline level after 5, 10, or 15 min of
rewarming using paired sample t tests. The same test was
performed on 5-min averages of skin temperature data.
Results
Effect of repeated cold exposure on baseline values
There was no repeated cold exposure effect on baseline
values of SBP, DBP, and thermal comfort TC (p [ 0.11).
As shown in Fig. 4, repeated cold exposure had a sig-
nificant effect on baseline HR (p = 0.002), mean skin
temperature Tsk (p \ 0.001) and temperature sensation TS
(p = 0.01). Baseline HR was significantly higher before
the first cold exposure than before the third and fourth
exposures (p = 0.03 and p = 0.002, respectively). Base-
line Tsk decreased significantly through the repeated cold
exposures, from 33.7 ± 0.4�C before the first cold expo-
sure to 31.9 ± 0.6�C before the fourth cold exposure
(p = 0.0001). Baseline TS was significantly higher
before the first cold exposure than before the fourth cold
exposure (p = 0.006), decreased from 56 ± 11 (between
neutral and slightly warm) to 46 ± 9 (between slightly
cool and neutral). Further analysis confirmed that there
were no significant differences between clothing ensem-
bles in any of these baseline measures (p [ 0.54). Table 3
presents trial baseline values (SBP/DBP, HR, Tsk, TS, and
TC) for each clothing ensemble trial before cold
exposure.
Blood pressure and heart rate during cold exposure
and recovery period
Overall, cold exposure resulted in a significant increase in
SBP and DBP (p \ 0.0001). Mean baseline SBP/DBP
was 113.8 ± 9.5/72.0 ± 7.6 mmHg, which increased to
124.5 ± 9.8/82.0 ± 8.0 mmHg during cold exposure and
then returned to the trial baseline level during recovery
(116.3 ± 9.5). There were significant differences in
Eur J Appl Physiol (2009) 107:673–685 677
123
average BP between trial baseline and cold exposure
(p \ 0.0001), and between cold exposure and recovery
(p \ 0.0001). However, there was no significant difference
between trial baseline and recovery (p [ 0.07). SBP reac-
ted to the cold in the first 5 min and did not change sig-
nificantly through the rest of the cold exposure across all
four clothing ensemble groups (Fig. 6). DBP showed
similar pattern. Clothing ensembles and repeated cold
exposure had no significant effect on average increases in
SBP and DBP during cold exposure (p [ 0.05) (Table 4).
Since there was no repeated cold exposure effect on
baseline and cold exposure values of SBP and DBP through
the four trials, the BP surges due to cold exposure were
compared among the four winter ensemble conditions. The
SBP surge was significantly higher in none-ensemble
condition (22.9 ± 6.5 mmHg) than in pants-, tuque- and
both-ensemble conditions (19.7 ± 6.5 mmHg, p = 0.03;
18.7 ± 5.6 mmHg, p = 0.03; and 19.3 ± 7.1 mmHg,
p = 0.04, respectively) (Fig. 5). Clothing ensembles had
no significant effect on DBP surge. Although the partici-
pants were all wearing base-ensemble during the recovery
period, the evidence suggests that the effect of different
clothing ensembles that they wore during the cold exposure
still tended to have an impact on the recovery of their SBP
and DBP (p = 0.06). Wearing hats during cold exposure
resulted in a faster recovery in SBP and DBP than wearing
no hats during cold exposure. The results showed that
blood pressure reached the trial baseline level after 5 min
of rewarming in tuque- and both-ensemble trials and after
10 min of rewarming in pants-ensemble trials (Fig. 6).
When the participants were not wearing a hat or extra pair
of pants (none-ensemble trial) during cold exposure, it took
20 min of rewarming for SBP and DBP to reach the trial
baseline level. Overall, during the 15-min recovery period,
the average RDSBP/DBP in tuque- and both-ensemble
trials was only 1.0 ± 5.7/0.2 ± 5.4 and 1.3 ± 5.7/1.1 ±
5.6 mmHg higher than the baseline level (Table 4). But
the average RDSBP/DBP in none-ensemble trial was
4.6 ± 5.9/3.8 ± 5.2 mmHg higher than the baseline level.
There was no interaction between clothing ensemble and
repeated cold exposure on changes in BP during cold
exposure and recovery.
Heart rate decreased slightly from 66.1 ± 8.2 to
64.4 ± 7.6 bpm during the cold exposure and then to
62.4 ± 7.3 bpm during recovery. There were no significant
differences in average HR between trial baseline and cold
exposure (p = 0.15) or between cold exposure and recov-
ery (p = 0.06). However, there was a significant difference
0
10
20
30
40
50
60
70
80
90
HR (bpm) mean skin temperature (°C) temperature sensation
* *
* **
*
# #
$
B 1 B 3 B 2 B 4 B 1 B 3 B 2 B 4 B 1 B 3 B 2 B 4
Fig. 4 Baseline values through
four trials. *p \ 0.05: in
comparison to B1, #p \ 0.05:
in comparison to B2, $p \ 0.05:
in comparison to B3
Table 3 Trial baseline values for each clothing ensemble trial
Clothing ensemble Systolic BP Diastolic BP HR Mean skin temperature Temperature sensation Thermal comfort
Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD
None 112.8 9.8 71.3 7.4 65.6 7.0 32.6 0.8 51 10 80 21
Pants 113.1 9.5 71.3 8.4 65.9 8.8 32.7 0.8 52 13 82 20
Tuque 114.9 10.1 72.9 8.2 66.4 9.6 32.6 0.9 50 8 74 20
Both 114.2 9.2 72.4 6.8 66.4 7.6 32.5 0.8 49 10 81 18
Total 113.8 9.5 72.0 7.6 66.1 8.2 32.6 0.8 50 11 79 20
678 Eur J Appl Physiol (2009) 107:673–685
123
Ta
ble
4C
han
ges
inth
erm
op
hy
sio
log
ical
resp
on
ses
du
rin
gco
ldex
po
sure
per
iod
and
reco
ver
yp
erio
dfo
rea
chcl
oth
ing
ense
mb
letr
ial
Co
ldex
po
sure
Rec
ov
ery
No
ne
Pan
tsT
uq
ue
Bo
thN
on
eP
ants
Tu
qu
eB
oth
Sy
sto
lic
BP
Mea
n1
0.9
9.5
8.4
8.1
3.2
1.0
1.3
2.5
SD
7.6
6.1
5.0
8.1
3.9
5.7
5.7
6.2
Ran
ge
-7
.5to
26
.7-
3.3
to2
4.0
-0
.7to
18
.9-
4.2
to2
9.3
-2
.0to
18
.7-
2.8
to1
1.3
-1
3.0
to1
1.8
-1
0.3
to1
1.7
Dia
sto
lic
BP
Mea
n9
.47
.97
.56
.83
.82
.90
.21
.1
SD
6.3
3.4
4.7
75
.22
.95
.45
.6
Ran
ge
-0
.3to
23
.80
.5–
13
.5-
3.6
to1
4.0
-4
.7to
21
.2-
3.0
to1
4.2
-1
.8to
9.2
-1
0.5
to9
.8-
8.3
to1
1.8
HR M
ean
-1
.3-
1.4
-1
.0-
2.5
-3
.6-
2.8
-3
.1-
4.4
SD
5.1
5.5
4.0
4.9
4.1
6.1
4.6
4.4
Ran
ge
-1
0.3
to1
3.3
-1
1.8
to1
0.8
-7
.5to
8.9
-1
1.3
to8
.3-
11
.5to
4.0
-1
1.8
to3
.5-
12
.3to
6.5
-1
2.0
to3
.2
Mea
nsk
inte
mp
erat
ure
Mea
n-
3-
2.3
*#
-2
.4*
#-
1.9
*-
1.7
#-
1.4
*-
1.5
#-
1.2
SD
0.6
0.4
0.6
0.5
0.3
0.4
0.5
0.4
Ran
ge
-4
.6to
-2
.3-
3.4
to-
1.7
-3
.8to
-1
.1-
3.0
to-
1.1
-2
.4to
-1
.1-
2.5
to-
0.8
-2
.6to
-0
.6-
1.8
to-
0.5
Tem
per
atu
rese
nsa
tio
n
Mea
n-
36
-3
6-
34
-3
2-
4-
4-
2-
1
SD
15
15
13
15
13
10
91
0
Ran
ge
-6
9to
-1
2-
69
to0
-6
0to
0-
63
to1
-5
0to
13
-2
5to
14
-1
3to
22
-1
8to
24
Th
erm
alco
mfo
rt
Mea
n-
52
-5
3-
45
-4
5-
1-
52
-4
SD
30
24
27
25
14
13
22
19
Ran
ge
-1
00
to0
-1
00
to3
-1
00
to2
4-
98
to-
7-
44
to2
5-
27
to2
5-
78
to5
1-
48
to2
6
*p\
0.0
5:
inco
mp
aris
on
ton
on
e-en
sem
ble
,#p
\0
.05
:in
com
par
iso
nto
bo
th-e
nse
mb
le
Eur J Appl Physiol (2009) 107:673–685 679
123
between trial baseline and recovery (p = 0.001). It took
25 min of rewarming for HR to reach the trial baseline
level. No effects of clothing ensemble on average changes
in HR were observed during cold exposure and recovery.
However, repeated cold exposure had a significant effect
on HR decreases. The cold-induced decreases of HR
were greater during the first cold exposure (CDHR =
-3.5 ± 3.4 bpm) than during the fourth cold exposure
(CDHR = -0.7 ± 4.9 bpm) (p = 0.02) (Table 5). The
decreases of HR during the 15-min recovery were greater
in the first trial (RDHR = -6.3 ± 4.0 bpm) than in the
second (RDHR = -2.7 ± 3.9 bpm, p = 0.02) and fourth
trials (RDHR = -1.9 ± 4.3 bpm, p = 0.003) (Table 5).
There was no interaction between clothing ensemble and
repeated cold exposure on changes in HR.
Skin temperature during cold exposure and recovery
period
Tsk showed a significant decrease from 32.6 ± 0.8 to
30.2 ± 1.0�C (p \ 0.01) during cold exposure. There were
significant clothing ensemble effects in mean skin tem-
perature (p \ 0.0001) during cold exposure. Overall, the
decrease of Tsk was significantly greater in the none-
ensemble condition than in tuque-, pants- and both-
ensemble conditions (p \ 0.002) (Table 4). The decrease
in Tsk was significantly smaller in the both-ensemble con-
dition than in the tuque- and pants-ensemble conditions
(p \ 0.03). The repeated cold exposure had no significant
effect on CDTsk (p = 0.80).
During the recovery period, Tsk increased significantly
compared to the cold exposure period, but was still
significantly lower compared to the baseline value
(p \ 0.001). The effect of different clothing ensembles that
participants wore during cold exposure had significant
impact on the recovery of their Tsk during the 15-min
recovery period. The decreases in mean skin tempera-
ture were significantly greater in none-ensemble trials
(CDTsk = -1.7 ± 0.3�C) than in both-ensemble trials
(CDTsk = -1.2 ± 0.4�C) (p \ 0.008) (Table 4). The repe-
ated cold exposure also had significant effect on the recovery
of Tsk. The recovery of Tsk was smaller in the first
trial (CDTsk = -1.8 ± 0.4�C) than in the second, third,
and fourth trials (CDTsk = -1.4 ± 0.5�C, CDTsk =
-1.4 ± 0.4�C, and CDTsk = -1.2 ± 0.3�C, respectively)
(p \ 0.002) (Table 5). There was no interaction between
clothing ensemble and repeated cold exposure on CDTsk.
There were significant clothing ensemble effects on
changes in forehead skin temperature (RDTfh) during cold
exposure and recovery (p \ 0.0001), but there was no
difference in the changes in Tfh between trials. During cold
exposure, the decreases in forehead skin temperature were
significantly smaller while wearing a hat (tuque-ensemble:
0
5
10
15
20
25
30
35
None Tuque Pants Both
Winter ensemblesS
BP
su
rge (
mm
Hg
) * **
Fig. 5 SBP surge due to cold
exposure across four winter
clothing ensembles. *p \ 0.05:
in comparison to none-ensemble
-4
-2
0
2
4
6
8
10
12
14
trialbaseline
5 min 10 min 15 min 5 min 10 min
Ch
ang
e in
SB
P (
mm
Hg
)
-None
-Pants
-Both
-Tuque
*
$
* *
# # #
Cold exposure Recovery
15 min
Fig. 6 Systolic blood pressure after 5-, 10, and 15-min of cold
exposure and recovery across four winter clothing ensembles (values
are mean differences between 5-min averages and trial baseline
values). #p \ 0.05: 5-min average value in comparison to baseline
value in all four cloth ensembles. *p \ 0.05: 5-min average value in
comparison to baseline value in none-ensemble. $p \ 0.05: 5-min
average value in comparison to baseline value in pants-ensemble
680 Eur J Appl Physiol (2009) 107:673–685
123
Ta
ble
5C
han
ges
inth
erm
op
hy
sio
log
ical
resp
on
ses
du
rin
gco
ldex
po
sure
per
iod
and
reco
ver
yp
erio
dfo
rea
chtr
ial
Co
ldex
po
sure
Rec
ov
ery
Tri
al1
Tri
al2
Tri
al3
Tri
al4
Tri
al1
Tri
al2
Tri
al3
Tri
al4
Sy
sto
lic
BP
Mea
n1
0.4
9.7
7.8
9.0
4.0
2.6
1.0
2.5
SD
7.6
5.9
7.6
6.0
5.3
4.9
5.1
6.2
Ran
ge
-3
.3to
29
.3-
1.0
to2
6.7
-7
.5to
26
.0-
4.2
to1
9.8
-6
.3to
18
.7-
4.8
to1
4.0
-1
3.0
to1
1.5
-1
0.3
to1
3.5
Dia
sto
lic
BP
Mea
n9
.08
.06
.77
.83
.11
.91
.31
.6
SD
5.5
5.0
6.4
5.3
5.0
4.5
4.9
5.8
Ran
ge
-2
.7to
21
.20
.0–
23
.8-
4.5
to2
0.0
-4
.7to
15
.3-
8.0
to1
4.2
-7
.5to
11
.8-
10
.5to
10
.0-
10
.1to
11
.9
HR M
ean
-3
.5-
1.7
-1
.7-
0.7
*-
6.3
-2
.7*
-3
.6-
1.9
*
SD
3.4
6.6
3.1
4.9
4.0
3.9
4.3
4.3
Ran
ge
-1
0.3
to3
.3-
11
.3to
13
.3-
7.5
to6
.0-
11
.8to
9.1
-1
2.3
to2
.5-
9.2
to4
.0-
11
.5to
6.5
-1
1.8
to3
.5
Mea
nsk
inte
mp
erat
ure
Mea
n-
2.5
-2
.4-
2.5
-2
.3-
1.8
-1
.4*
-1
.4*
-1
.2*
SD
0.8
0.6
0.5
0.6
0.4
0.5
0.4
0.3
Ran
ge
-4
.6to
-1
.1-
3.7
to-
1.1
-3
.8to
-1
.7-
3.4
to-
1.3
-2
.6to
-1
.1-
2.2
to-
0.5
-2
.4to
-0
.8-
1.7
to-
0.6
Tem
per
atu
rese
nsa
tio
n
Mea
n-
36
-3
5-
34
-3
4-
60
-3
-1
SD
17
15
15
12
91
07
14
Ran
ge
-6
9to
0-
63
to0
-6
9to
1-
60
to-
9-
24
to1
3-
25
to1
4-
18
to1
3-
50
to2
4
Th
erm
alco
mfo
rt
Mea
n-
42
-4
8-
51
-5
5-
1-
3-
51
SD
27
25
28
27
18
18
19
14
Ran
ge
-7
5to
24
-9
6to
-1
2-
10
0to
-1
-1
00
to-
13
-3
7to
26
-4
8to
51
-7
8to
25
-4
4to
26
*p\
0.0
5in
com
par
iso
nto
tria
l1
Eur J Appl Physiol (2009) 107:673–685 681
123
RDTfh = -3.5 ± 0.7�C; both-ensemble: RDTfh = -3.6 ±
1.0�C) than when no hat was worn (none-ensemble:
RDTfh = -8.7 ± 1.5�C; pants-ensemble: RDTfh = -8.8 ±
2.1�C) (p \ 0.0002). During recovery, although the mean
and forehead skin temperature did not reach the trial
baseline level after 15 min of rewarming in any of the
winter ensemble trials, Tfh was higher in the tuque- and
both-ensemble trials than in the pants- and none-ensemble
trials. There was no interaction between clothing ensemble
and repeated cold exposure on RDTfh.
Temperature sensation and thermal comfort during cold
exposure and recovery period
At 15 min after exposure to -5�C, temperature sensation
and thermal comfort decreased significantly from 50 ± 11
(neutral) to 16 ± 12 (cold) and from 79 ± 20 (slightly
uncomfortable) to 31 ± 22 (very uncomfortable), respec-
tively. By the end of the 15-min recovery period, TS and
TC increased to 48 ± 12 (neutral) and 77 ± 21 (slightly
uncomfortable), respectively, which were not significantly
different from the baseline values. No effects of clothing
ensemble and repeated cold exposure on overall changes in
temperature sensation and thermal comfort were observed
(Tables 4, 5).
Discussion
Effect of wearing a hat on cold responses
The present study provides for the first time information
about the effects of winter clothing and repeated cold
exposure on BP responses in normotensive participants
exposed to cold in a way that is similar to normal outdoor
exposure in winter. Our results show that wearing a
hat reduced SBP surge from 22.9 ± 6.5 mmHg (none-
ensemble) to 18.7 ± 5.6 mmHg (tuque-ensemble) and
19.3 ± 7.1 mmHg (both-ensemble) during the cold expo-
sure period. These results are consistent with a previous
study, which showed that the magnitude of the blood
pressure response was attenuated by wearing hats (Gavhed
2003). Gavhed (2003) reported that wearing headgear with
ear protection tended to reduce the systolic blood pressure
response, but heart rate was similar with and without a hat.
A study in Europe found that the geographical variation in
cold-related mortality may be explained by differences in
the outdoor clothing worn (Donaldson et al. 2001). The
authors suggested that gloves, hats, and scarves are the
most important clothing items, because they cover those
areas of the body most involved in determining the blood
pressure response to cold. Stevens and Choo (1998) ana-
lyzed the detection thresholds for heating and cooling in 13
body regions of 60 adults between the ages of 18 and
88 years. They found that thermal sensitivity varies
100-fold over the body surface, the face being most sen-
sitive and the extremities least sensitive. Cutaneous ther-
mal receptors are not distributed equally throughout the
body surface. In primates, including humans, non-hairy
skin on the face and hands contains many more thermal
receptors than other skin areas (Pittman 2003). The fifth
cranial nerve, the trigeminal nerve, supplies all of the
anterior sensory fibers to the skin of the head. Various
types of noxious stimuli to the trigeminal region were
shown to result in a reflex pattern characterized by rises in
muscle sympathetic nerve activity, blood pressure, and
bradycardia (Heindl et al. 2004; Smith et al. 1997; Collins
1990): a pattern of both sympathetic and parasympathetic
activation similar to our findings in subjects who did not
wear a hat during cold exposure. Our data are also con-
gruent with previous works showing that local cooling of
the forehead provoked a fast increase of sympathetic acti-
vation, and high levels of diastolic blood pressure (LeBlanc
and Mercier 1992; Trouerbach et al. 1994; Walsh et al.
1995) that are even more profound than with cooling of the
hand (Heindl et al. 2004). Our results demonstrate that
wearing a hat during cold exposure kept the forehead skin
temperature at a higher level. Therefore, the skin of the
forehead represents an important region for the adaptation
of the cardiovascular system to cold exposure. The sym-
pathetic activation observed during cold exposure is
probably mediated by trigeminal cold-sensitive afferents in
the skin (Heindl et al. 2004; Collins 1990). The present
study showed that HR decreased during cold exposure and
decreased further during the recovery period in young
adults. However, no significant differences were observed
in the heart rate for different clothing conditions, sug-
gesting that wearing hats per se did not influence the
parasympathetic responses to the cold. It can be concluded
that wearing a hat that covers the forehead and ears could
alleviate the sympathetically mediated surge in BP in
young adults.
It is worth noting that the impact of wearing a hat during
cold exposure lasted through the recovery period when the
participants were all wearing the same base clothing
ensemble. The results showed that blood pressure reached
the trial baseline level faster when a tuque or a pair of
overpants was worn singly or in combination. During
recovery, the forehead skin temperatures were higher in
tuque- and both-ensemble trials than in pants- and none-
ensemble trials. Therefore, the higher forehead skin tem-
perature during rewarming may be responsible for the
faster recovery of blood pressure. Compared to wearing
hats, the effect of wearing an extra pair of pants on low-
ering SBP surge and speeding up BP recovery was less
prominent, but was still significant. Since wearing an extra
682 Eur J Appl Physiol (2009) 107:673–685
123
pair of pants increased lower extremity skin temperatures
but not forehead temperatures, these results suggest that
keeping the legs warm could also play an important role in
hemodynamic responses to cold exposure. These findings
are encouraging and warrant further investigations to better
understand the benefits of wearing appropriate clothing in
the winter.
The effect of wearing a hat on attenuating cold-induced
SBP surge and encouraging faster recovery was significant
in the young and middle-aged normotensive individuals in
the present study. Since only healthy, young, and middle-
aged participants were included in the present study, the
results cannot be extrapolated to patients with various
disorders or to the general older population. However,
Keatinge et al. (2000) have indicated that the enhanced
pressor response to cold stress with other circulatory
reflexes might be one mechanism explaining the excess
winter mortality in the elderly population. Aging is asso-
ciated with many changes in autonomic nervous system
function that often lead to impairments in the normal
ability to respond to physiological stressors commonly
encountered in daily life (Collins et al. 1985; Sheth et al.
1999; Smith and Fasler 1983; Smolander 2002). One of the
most serious complications in older people is the tendency
toward hypertension in cold ambient temperatures (Wagner
and Horvath 1985). In healthy elderly people, whole body
cooling has been shown to produce a greater increase in
arterial blood pressure and a reduced bradycardia com-
pared to younger adults (Collins 1990; Collins et al. 1995).
Since the risks of cardiac strain after exposure to the cold
probably increase with age, sufficient winter clothing that
includes head covering should be a recommended practice
in cold environment for older people, especially for older
people with underlying cardiac conditions. Further studies
on the effect of keeping head and lower extremities warm
in cold temperatures are needed to examine the role of
winter clothing on thermoregulatory and non-thermoregu-
latory responses (hemodynamics, cardiac function, respi-
ration, autonomic nervous function) to cold stress in older
people. The second stage of this project is currently
underway to examine whether wearing a hat would have
similar effect on older adults.
Effect of repeated cold exposures
on thermophysiological responses
The present study simulated normal wintertime outdoor
cold exposure in Southern Ontario, Canada. The effect of
repeated cold exposure on blood pressure was not signi-
ficant in this study. The results showed that SBP and
DBP were 121.9/78.3, 122.1/79.1, 123.4/80.0, and 124.5/
82.0 mmHg after the first, second, third, and fourth cold
exposures, respectively. The level of maximal blood
pressure was reached 5 min after the starting of the cold
exposure, and blood pressure stayed almost at the same
level during the 15-min cold exposure. SBP and DBP
responses in the present study were in accordance with
previous studies (Ozaki et al. 1998, 2001), which have been
carried out with normotensive participants in warmer
winter clothing (2.3 clo) under colder test conditions. SBP
has been reported to increase from 118 to 126, 129, and
128.5 mmHg after the first, second and third 20-min
exposure to -25�C with 20-min warm up in 30�C between
two cold exposures (Ozaki et al. 1998).
Previous studies suggested that chronic and repeated
cold exposures causing marked whole body cooling result
in more pronounced physiological responses, including
enhanced vasoconstriction and metabolic rate (Hammel
et al. 1959; Young 1996). However, repeated brief expo-
sures to cold not involving marked whole body cooling are
suggested to result in habituation (Leppaluoto et al. 2001).
When being habituated to cold, shivering and the vaso-
constrictor response are blunted, stress responses are
reduced, and the sensations of cold are less intense. These
responses can develop even after only a few repeated cold
exposures to cold air (Leppaluoto et al. 2001). Leppaluoto
et al. (2001) demonstrated that the thermal sensations
became habituated after the first or second daily cold air
exposure, but the other responses became variably habit-
uated as late as after four daily exposures, and hemocon-
centration was not affected until the end of the 11-day
experiment. In the present study, the changes in blood
pressure, skin temperatures, and thermal sensations were
similar through the four cold exposures. Hence, no habit-
uation process was observed, which may be due to the short
durations of our cold exposures. However, the measure-
ments from this study showing that the decreases in heart
rate in the fourth cold exposure were less pronounced
compared to the first (Table 5). Therefore, when the cold
exposures were repeated, the reduction in heart rate was
slightly blunted. A recent study suggested that the reduc-
tion in heart rate could be an indicator for increased
parasympathetic activity in the cold (Makinen et al. 2008).
The same study also suggested that at the sinus node level,
the sympathetic activation due to cold exposure was
blunted during cold acclimation, and replaced to some
extent by increased parasympathetic influence. Thus, the
brief moderate cold air exposure in this study was not a
sufficient stimulus to achieve a general habituation to cold,
but might have elicited a shift in the autonomic nervous
system toward parasympathetic activity to some extent.
Autonomic nervous system response can be further studied
by assessing heart rate variability (HRV) while being
exposed to repeated cold, which may also provide further
insight into the assessment of autonomic cardiovascular
regulation and the mechanisms that are involved.
Eur J Appl Physiol (2009) 107:673–685 683
123
Conclusions
The present study has shown that protection of the head
from cold reduces the sympathetically mediated surge in
BP in young adults. Systolic and diastolic blood pressures
increased more profoundly when a hat was not worn by
normotensive individuals during cold exposure. Wearing
hats also promoted faster recovery of forehead skin tem-
perature and blood pressure during the recovery period.
This is an important finding, since elevated blood pressure
is a major risk factor for a range of cardiovascular diseases.
This defensive measure against cold-induced surges in BP
might be even more important in susceptible populations,
such as older people with and without underlying cardio-
vascular diseases. More studies should be carried out to
determine whether a positive health outcome could be
achieved by such lifestyle interventions. Our ongoing
projects are examining the effective use of warm clothing,
especially headgear to protect older and at-risk populations
in controlled laboratory conditions.
Acknowledgments This research was funded by the National
Institute on Disability and Rehabilitation Research (NIDRR) through
the Rehabilitation Engineering Research Centre on Universal Design
and the Built Environment (grant #H133E050004-08A), a partnership
with the Centre for Inclusive Design and Environmental Access
(IDEA). The authors acknowledge the support of the Toronto Reha-
bilitation Institute, which receives funding under the Provincial
Rehabilitation Research Program from the Ministry of Health and
Long-Term Care in Ontario. Equipment and space were funded, in
part, with grants from the Canada Foundation for Innovation and the
Province of Ontario. The authors wish to express their gratitude to
Jennifer Hsu, Stephanie Soo, and Christine Yen for their invaluable
assistance in data collection. The authors would also like to thank all
the participants for their time and effort.
References
Barnett AG, Dobson AJ, McElduff P, Salomaa V, Kuulasmaa K, Sans
S (2005) Cold periods and coronary events: an analysis of
populations worldwide. J Epidemiol Community Health 59:551–
557
Barnett AG, Sans S, Salomaa V, Kuulasmaa K, Dobson AJ (2007)
The effect of temperature on systolic blood pressure. Blood Press
Monit 12:195–203
Collins KJ (1990) Age-related changes in autonomic control: the use
of beta blockers in the treatment of hypertension. Cardiovasc
Drugs Ther 4:1257–1262
Collins KJ, Easton JC, Belfield-Smith H, Exton-Smith AN, Pluck RA
(1985) Effects of age on body temperature and blood pressure in
cold environments. Clin Sci 69:465–470
Collins KJ, Abdel-Rahman TA, Goodwin J, McTiffin L (1995)
Circadian body temperatures and the effects of a cold stress in
elderly and young subjects. Age Ageing 24:485–489
Donaldson GC, Rintamaki H, Nayha S (2001) Outdoor clothing: its
relationship to geography, climate, behaviour and cold-related
mortality in Europe. Int J Biometeorol 45:45–51
Gavhed D (2003) Human responses to cold and wind. Karolinska
Institutet, Stockholm
Hammel HT, Elsner RW, LeMessurier DH, Anderson HT, Milan FA
(1959) Thermal and metabolic responses of the Australian
aborigine exposed to moderate cold in summer. J Appl Physiol
14:605–615
Heindl S, Struck J, Wellhoner P, Sayk F, Dodt C (2004) Effect of
facial cooling and cold air inhalation on sympathetic nerve
activity in men. Respir Physiol Neurobiol 142:69–80
Jackson R, Lawes CMM, Bennett DA, Milne RJ, Rodgers A (2005)
Treatment with drugs to lower blood pressure and blood
cholesterol based on an individual’s absolute cardiovascular
risk. Lancet 365:434–441
Keatinge WR (1997) Cold exposure and winter mortality from
ischaemic heart disease, cerebrovascular disease, respiratory
disease, and all causes in warm and cold regions of Europe.
Lancet 349:1341–1346
Keatinge WR, Coleshaw SRK, Holmes J (1989) Changes in seasonal
mortalities with improvement in home heating in England and
Wales from 1964 to 1984. Int J Biometeorol 33:71–76
Keatinge WR, Donaldson GC, Bucher K, Jendritzky G, Cordioli C,
Martinelli M, Katsouyanni K, Kunst AE, McDonald C, Nayha S,
Vuori I (2000) Winter mortality in relation to climate. Int J
Circumpolar Health 59:154–159
Kim JY, Jung KY, Hong YS, Kim JI, Jang TW, Kim JM (2003) The
relationship between cold exposure and hypertension. J Occup
Health 45:300–306
Kim TG, Tochihara Y, Fujita M, Hashiguchi N (2007) Physiological
responses and performance of loading work in a severely cold
environment. Int J Ind Ergon 37:725–732
LeBlanc J, Mercier I (1992) Cold wind stimulation reflex. J Appl
Physiol 73:1704–1707
Leech JA, Nelson WC, Burnett RT, Aaron S, Raizenne ME (2002)
It’s about time: a comparison of Canadian and American time-
activity patterns. J Expo Anal Environ Epidemiol 12:427–432
Leppaluoto J, Korhonen I, Hassi J (2001) Habituation of thermal
sensations, skin temperatures, and norepinephrine in men
exposed to cold air. J Appl Physiol 90:1211–1218
Madsen C, Nafstad P (2006) Associations between environmental
exposure and blood pressure among participants in the Oslo
Health Study (HUBRO). Eur J Epidemiol 21:485–491
Makinen TM, Palinkas LA, Reeves DL, Paakkonen T, Rintamaki H,
Leppaluoto J, Hassi J (2006) Effect of repeated exposures to cold
on cognitive performance in humans. Physiol Behav 87:166–176
Makinen TM, Mantysaari M, Paakkonen T, Jokelainen J, Palinkas
LA, Hassi J, Leppaluoto J, Tahvanainen K, Rintamaki H (2008)
Autonomic nervous function during whole-body cold exposure
before and after cold acclimation. Aviat Space Environ Med
79:875–882
Marchant B, Ranjadayalan K, Stevenson R, Wilkinson P, Timmis AD
(1993) Circadian and seasonal factors in the pathogenesis of
acute myocardial infarction: the influence of environmental
temperature. Br Heart J 69:385–387
Nayha S (2002) Cold and the risk of cardiovascular diseases.
A review. Int J Circumpolar Health 61:373–380
Nielsen R, Nielsen B (1984) Measurement of mean skin temperature
of clothed persons in cool environments. Eur J Appl Physiol
Occup Physiol 53:231–236
Ozaki H, Enomoto-Koshimizu H, Tochihara Y, Nakamura K (1998)
Thermal responses from repeated exposures to severe cold with
intermittent warmer temperatures. J Physiol Anthropol Appl
Human Sci 17:195–205
Ozaki H, Nagai Y, Tochihara Y (2001) Physiological responses and
manual performance in humans following repeated exposure to
severe cold at night. Eur J Appl Physiol 84:343–349
Perez-Lloret S, Toblli JE, Vigo DE, Cardinali DP, Milei J (2006)Infradian awake and asleep systolic and diastolic blood pressure
rhythms in humans. J Hypertens 24:1273–1279
684 Eur J Appl Physiol (2009) 107:673–685
123
Pittman Q (2003) The autonomic nervous system and thermoregu-
lation. In: Bolis CL, Licinio J, Govoni S (eds) Handbook of the
autonomic nervous system in health and disease. Marcel Dekker,
New York, pp 247–276
Reynolds L, Mekjavic I, Cheung S (2007) Cold-induced vasodilata-
tion in the foot is not homogenous or trainable over repeated cold
exposure. Eur J Appl Physiol 102:73–78
Schneider A, Schuh A, Maetzel FK, Ruckerl R, Breitner S, Peters A
(2008) Weather-induced ischemia and arrhythmia in patients
undergoing cardiac rehabilitation: another difference between
men and women. Int J Biometeorol 52:535–547
Sheth T, Nair C, Muller J, Yusuf S (1999) Increased winter mortality
from acute myocardial infarction and stroke: The effect of age.
J Am Coll Cardiol 33:1916–1919
Smith SA, Fasler JJ (1983) Age-related changes in autonomic
function: relationship with postural hypotension. Age Ageing
12:206–210
Smith JC, Stephens DP, Winchester PK, Williamson JW (1997)
Facial cooling-induced bradycardia: attenuating effect of central
command at exercise onset. Med Sci Sports Exerc 29:320–325
Smolander J (2002) Effect of cold exposure on older humans. Int J
Sports Med 23:86–92
Stevens JC, Choo KK (1998) Temperature sensitivity of the body
surface over the life span. Somatosens Mot Res 15:13–28
Tochihara Y (2005) Work in artificial cold environments. J Physiol
Anthropol Appl Human Sci 24:73–76
Trouerbach J, Duprez D, De Buyzere M, De Sutter J, Clement D
(1994) Cardiovascular responses elicited by different simulated
diving manoeuvres. Eur J Appl Physiol Occup Physiol 68:341–
344
Wagner JA, Horvath SM (1985) Cardiovascular reactions to cold
exposures differ with age and gender. J Appl Physiol 58:187–192
Walsh JT, Andrews P, Batin PD, Cowley AJ (1995) Haemodynamic
and hormonal response to a stream of cooled air. Eur J Appl
Physiol 72:76–80
Wilkinson P, Pattenden S, Armstrong B, Fletcher A, Kovats RS,
Mangtani P, McMichael AJ (2004) Vulnerability to winter
mortality in elderly people in Britain: population-based study.
Br Med J 329:647–651
Young AJ (1996) Homeostatic responses to prolonged cold exposure:
human cold acclimatization. In: Fregly MJ, Blatteis CM (eds)
Environmental physiology, vol 1, Handbook of physiology, Sect.
4. Oxford University Press, New York, pp 419–438
Eur J Appl Physiol (2009) 107:673–685 685
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