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Natural HazardsJournal of the International Societyfor the Prevention and Mitigation ofNatural Hazards ISSN 0921-030XVolume 69Number 1 Nat Hazards (2013) 69:25-37DOI 10.1007/s11069-013-0686-y
Solar and geomagnetic activity effects onheart rate variability
S. Dimitrova, I. Angelov & E. Petrova
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ORI GIN AL PA PER
Solar and geomagnetic activity effects on heart ratevariability
S. Dimitrova • I. Angelov • E. Petrova
Received: 31 July 2012 / Accepted: 3 April 2013 / Published online: 10 April 2013� Springer Science+Business Media Dordrecht 2013
Abstract Investigation into possible space weather hazards on cardiovascular system has
been performed. A group of 14 healthy volunteers was examined in the spring of 2009 and
2 healthy persons performed electrocardiograph records for a period of 1 year everyday in
the morning and in the evening. Results revealed that heart rate variability (HRV)
parameters of the group varied strongly from the day before till 3 days after the registered
weak storms during the time of investigation. Blood pressure and subjective psycho-
physiological complaints increased statistically significantly from 0 day till ?2nd day.
Heart rate (HR) of the group showed a trend for decrease. It was established that morning
measurements were more sensitive to space weather variations in comparison with evening
measurements. Both persons with prolonged registrations for a period of year did not
reveal graded response to geomagnetic storms with different intensities. Both of them
decreased HR during moderate storms, but they increased HR during major storms and on
the days before and after these storms. HRV parameters varied significantly on these days.
Keywords Space weather � Cardiovascular system � Blood pressure � Heart rate
S. Dimitrova (&)Space Research and Technology Institute, Bulgarian Academy of Sciences, Sofia, Bulgariae-mail: svetla_stil@abv.bg
I. AngelovDepartment of Physics, South West University ‘‘Neofit Rilski’’, Blagoevgrad, Bulgaria
I. AngelovInstitute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia,Bulgaria
E. PetrovaInstitute of Experimental Morphology, Pathology and Anthropology with Museum, BulgarianAcademy of Sciences, Sofia, Bulgaria
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1 Introduction
Numerous scientific studies indicate possible influence of physical environmental factors
such as solar activity, geomagnetic storms, cosmic rays and climate changes on human
physiology and psychophysiology and different diseases, especially on cardiovascular and
nervous system. At the same time, other studies do not confirm these effects or the results
are inconsistent or controversial because different medical, physical and statistical methods
are used, and the studies have been performed during different solar activity cycle phases.
Analysis of heart rate variability (HRV) is the most commonly used measure of the
cardiovascular autonomic regulatory system, reflecting both sympathetic and parasympa-
thetic functions (Malliani et al. 1991; Ori et al. 1992). HRV is determined based on the
length of successive RR intervals in electrocardiogram (ECG). RR interval is the peak of
one QRS complex to the peak of the next QRS complex in ECG. HRV is the variation in
the beat-to-beat (RR) interval. HRV is different from heart rate (HR) as the HR is the
number of the heartbeats per unit of time. HRV is an important indicator of the activity of
the autonomous (vegetative) nervous system. Reduced HRV is a negative prognostic
factor, often preceding and/or accompanying various cardiovascular diseases, including
fatal diseases as well as cases of sudden cardiac death (Task Force 1996).
There are investigations which have shown that space weather changes are associated
with variations in HRV. Cornelissen et al. (2002) established reduced HRV during geo-
magnetic storms. Baevsky et al. (1998) used HRV parameters and demonstrated a specific
impact of geomagnetic perturbations on the vegetative nervous system in cosmonauts
during space flight. Variations in autonomic regulation were more pronounced on 1–2 days
after a storm. Oinuma et al. (2002) performed 7-day Holter measurements of 5 clinically
healthy men in subarctic area, and graded alteration of HRV endpoints was found in
association with increased geomagnetic activity (GMA). Similar investigation was per-
formed by Otsuka et al. (2001) on 8 healthy persons in the same region. Results revealed a
5.9 % statistically significant increase in the HR and a 25.2 % decrease in HRV on days of
high geomagnetic disturbance.
The aim of this study is to assess cardiovascular variations to geomagnetic activity. For
that purpose, HRV parameters derived from ECG recordings and data about blood pressure
and psychophysiological complaints of healthy persons were analyzed.
2 Materials and methods
Two healthy volunteers recorded their ECGs for a period of 1 year (April 2008–April
2009). The first person was 35-year-old female and the second one 39-year-old male. The
volunteers recorded two 5-min ECGs everyday—in the morning after awakening and in the
evening before falling asleep.
Additionally, a group of 14 healthy persons with an average age of 47.2 (±12.3) years
was also examined from 23.03.2009 to 30.04.2009 in the same region (Sofia, Bulgaria).
Data about their ECGs, systolic and diastolic blood pressure (SBP and DBP) and subjective
psychophysiological complaints (SPPC) were gathered. Volunteers filled in a questionnaire
with three groups of questions: one concerned complaints related to the common functional
state (general condition, working ability, sleep disturbances, weakness, absent-minded-
ness); another concerned cardiovascular system (heart thumping, arrhythmia, tachycardia);
and a third concerned nervous system (headache, dizziness, vertigo, nausea), Dimitrova
et al. (2004).
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None of the examined persons was informed about current space weather conditions
before and during measurements.
ECGs were processed by custom software, and HRV parameters in time domain and
frequency domain were derived. Description of the ECG devices and software for RR
intervals detection and HRV estimation are presented in Angelov and Dimitrova (2009).
The following HRV parameters in time domain were assessed from ECGs:
– RRavg, RRmin, RRmax—these values are, respectively, the average length of RR
intervals, minimal and maximal value of the length of R–R intervals. This index is
directly related to the heart rate (HR): high values of RRavg correspond to low values
of HR and on the opposite;
– SDNN—standard deviation of normal sinus RR intervals;
– RMSSD—the square root of the mean squared differences of successive RR intervals;
– pNN50—percentage of adjacent RR intervals that vary by more than 50 ms.
Spectral analyses (Lomb–Scargle periodogram) (Clifford et al. 2006; Lomb 1976) were
used to analyze the RR interval series in frequency domain. Power spectral density (PSD)
represents power as a function of frequency. Usually, interest is directed toward two
frequency bands of the spectrum: LF band (0.04–0.15 Hz) and HF band (0.15–0.4 Hz).
LF and HF powers and the ratio of LF/HF were calculated. The relation between LF and
HF components of HRV represents the balance between the two branches of the autonomic
nervous system (sympathetic and parasympathetic). The HF component reflecting sinus
arrhythmia has been attributed to the modulation of the parasympathetic output. The LF
component has been referred to both sympathetic and parasympathetic activity (Task Force
1996).
Cardiovascular parameters were analyzed regarding variations in GMA, estimated by
daily planetary Ap-index. Gradation of GMA levels and the number of days with different
GMA levels during examination periods are presented in Table 1.
The spring period was chosen because of the high probability for geo-effective solar
storms during spring and autumn equinox. It was characterized by minimal solar and
GMA. There were 7 days with unsettled GMA conditions during the time of examination
of the group from March 23, 2009, to April 30, 2009 (Table 1). The registrations of the two
individuals for a whole-year period provided data for 12 moderate and 3 major geomag-
netic storms (Table 1).
It is quite difficult to plan such prospective study and envisage space weather variations,
especially during a period of minimal solar and geomagnetic activity as years 2008–2009
were. The measurements of the two individuals for 1-year period were to examine the
individual HRV variations of everyday cardiological variations under different GMA
Table 1 GMA levels and the number of days
GMA levels Ap-index values Number of eventsfor the group(23.03.2009–30.04.2009)
Number of events forthe two persons(08.04.2008–08.04.2009)
10—Quiet GMA Ap \ 8 32 277
I—Unsetteled (weak storms) 8 B Ap \ 15 7 74
II—Moderate storms 15 B Ap \ 30 0 12
III—Major storms 30 B Ap \ 50 0 3
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changes expecting (and eventually occurred) geomagnetic storms for a whole-year period
during minimal solar activity. Actually, the observed variations in their HRV parameters
and the results obtained about the dynamic of arterial blood pressure and subjective
complaints of a group of 86 healthy volunteers examined by the team in the autumn of
2001 and spring of 2002 (years of maximal solar and geomagnetic activity), Dimitrova
et al. (2004), provoked this planned study of a group of healthy persons during declining
phase of solar activity and posed the question to study cardiological parameters like HRV,
which are not as dynamic as blood pressure is.
The statistical method of the analysis of variance (ANOVA) was applied to establish a
statistical significance of the influence of GMA levels on HRV parameters, BP and SPPC.
The effect of GMA up to 3 days before and after the respective events on the examined
physiological parameters was also investigated by the help of ANOVA and superimposed
epoch method.
3 Results
Table 2 shows statistically significant effects (p \ 0.05) and trends for significant effects
(p \ 0.1) of GMA levels on the examined physiological parameters of the group. There
was a trend for statistically significant decrease (p = 0.097) in HR of the group on the day
of weak geomagnetic storms (0 day), Fig. 1. Vertical bars in the figure denote 0.95 con-
fidence intervals (CI). RRmin, RRmax and RRavg increased statistically significantly
(p \ 0.05) on these days.
Although the other HRV parameters of the group were not statistically significantly
(p [ 0.05) affected by the weak storms, they varied significantly on the days of weak
storms:
– SDNN increased on the day before the storm and after that decreased, Fig. 2;
– RMSSD increased on -1st and 0 day;
– pNN50 increased on the days before the storms and after that decreased;
– LF increased on -2nd, -1st, ?2nd and ?3rd day;
– HF increased on -1st and 0 day;
– The ratio of the two frequency components LF/HF decreased on 0 day and then
increased gradually up to ?3rd day, Fig. 3.
Table 2 Significance levels (p values) of GMA effect on parameters of the group for the days before (?),during (0) and after (-) geomagnetic storms
Days HR RRmin RRmax RRavg SBP SPPC
-3 – – – – 0.024
-2 – – – – – –
-1 – – 0.062 – – –
0 0.097 0.016 0.021 0.055 – –
?1 – – – – – 0.010
?2 – – – – 0.074 0.002
?3 – – – – – –
Not significant results are denoted as ‘‘–’’
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SBP (Fig. 4), DBP and SPPC (Fig. 5) increased from 0 day till ?2nd day. The effects
were statistically significant on ?1st day for SPPC and on ?2nd day for SBP and SPPC
(Table 2).
Personal everyday measurements of the two volunteers for a period of 1 year revealed
that morning measurements were more sensitive to space weather variations in comparison
with evening measurements. It is probably due to the accumulation of other social factors’
effects during the course of everyday activities such as physical and/or psychic load, stress,
emotional responses and anthropogenic electromagnetic fields, which ‘‘mask’’ adaptation
reactions to natural physical factors. Evening variations were similar to morning variations
although the effects were in a smaller degree. That is why results only for morning
measurements are presented. Tables 3 and 4 show statistically significant effects of GMA
on HRV parameters of both persons.
GMA levels: I0 I
-3 -2 -1 0 +1 +2 +3
Day
68
70
72
74
76
78
80
Hea
rt r
ate,
bea
ts/m
in
Fig. 1 GMA effect on HR of thegroup before (-), during (0) andafter (?) geomagnetic storms(±95 % CI)
GMA levels: I0 I
-3 -2 -1 0 +1 +2 +3Day
30
32
34
36
38
40
42
44
SDN
N
Fig. 2 GMA effect on SDNN of the group before (-), during (0) and after (?) geomagnetic storms (±95 %CI)
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It is interesting that both persons reacted in different way to geomagnetic storms with
different intensities. Both persons increased HR during major storms and on the days
before and after the respective major storms, and the 1st person increased HR also during
weak storms. However, both persons decreased HR during moderate storms. Morning HR
variations for the 1st person are shown in Fig. 6 upper panel and for the 2nd person in
Fig. 6 bottom panel. RRmin, RRmax and RRavg, respectively, decreased on the days of
weak and major storms and increased during moderate geomagnetic storms. Only for
RRmin values of both persons for evening measurements, peak increases (which corre-
sponds to HR decreases) were established on 0 day and ?1st and ?2nd day of major
storms.
GMA levels: I0 I
-3 -2 -1 0 +1 +2 +3
Day
2.0
2.5
3.0
3.5
4.0
4.5
5.0
LF/
HF
Fig. 3 GMA effect on LF/HF of the group before (-), during (0) and after (?) geomagnetic storms(±95 % CI)
GMA levels: I0 I
-3 -2 -1 0 +1 +2 +3
Day
122
124
126
128
130
132
134
136
Syst
olic
BP,
mm
Hg
Fig. 4 GMA effect on SBP of the group before (-), during (0) and after (?) geomagnetic storms (±95 %CI)
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For the 1st person, SDNN decreased on -1st and 0 day of major storms and increased
on ?3rd day of the same GMA level as well as on -2, -1, ?1 and ?2nd day of moderate
storms (Fig. 7 upper panel). SDNN for the 2nd person decreased for all of geomagnetic
storms except on ?2nd and ?3rd day of major storms (Fig. 7 bottom panel).
GMA levels: I0 I
-3 -2 -1 0 +1 +2 +3
Day
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Subj
ectiv
e co
mpl
aint
s, %
Fig. 5 GMA effect on SPPC of the group before (-), during (0) and after (?) geomagnetic storms (±95 % CI)
Table 3 Significance levels (p values) of GMA effect on HRV parameters of 1st person for the days before(?), during (0) and after (-) geomagnetic storms
Days HR SDNN RMSSD pNN50 LF/HF LF HF RRmin RRmax RRavg
-3 0.011 – – – – – – – – 0.017
-2 0.004 – – – 0.049 0.023 – – 0.090 0.005
-1 0.001 0.038 0.108 – – 0.038 0.061 – 0.024 0.001
0 0.000 – – 0.060 – – – 0.012 0.007 0.000
?1 0.004 – – – – – – 0.075 0.046 0.005
?2 0.000 – – – – – – 0.000 0.004 0.000
?3 0.003 – – – – – – – – 0.004
Not significant results are denoted as ‘‘–’’
Table 4 Significance levels (p values) of GMA effect on HRV parameters of 2nd person for the daysbefore (?), during (0) and after (-) geomagnetic storms
Days HR SDNN LF/HF LF RRmin RRavg
-3 – – – – – –
-2 – 0.098 0.018 – – –
-1 – 0.015 – – – –
0 – 0.054 – – 0.059 –
?1 0.099 – 0.013 – 0.096 0.110
?2 – – – 0.084 – –
?3 – – – – – –
Not significant results are denoted as ‘‘–’’
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RMSSD and pNN50 for the 1st person had similar variations as SDNN. For the 2nd
person, RMSSD and pNN50 had peak decreases on -1st and ?1st day and peak increases
on -2nd and ?2nd day of major storms. The 2nd person decreased these parameters on
-2nd day of moderate storms and after that increased them up to ?1st day.
LF component of the 1st person varied significantly during moderate and major storms
(Fig. 8 upper panel). It had peak increases on -2nd and ?1st day of major storms as well
as on -2, -1, ?1 and ?2 day of moderate storms. LF decreased on 0 and ?2 day of major
storms. For the 2nd person, LF increased from 0 day up to ?3rd day of major storms
(Fig. 8 bottom panel).
Fig. 9 shows an example of a power spectral density of two morning measurements of
the 1st person, respectively, on a day with quiet GMA (Ap = 3)—the upper panel—and on
GMA levels: I0 I II III
Day
61
62
63
64
65
66
67
68
69
70
Hea
rt r
ate,
bea
ts/m
in
GMA levels: I0 I II III
-3 -2 -1 0 +1 +2 +3
-3 -2 -1 0 +1 +2 +3
Day
60
62
64
66
68
70
72
74
Hea
rt r
ate,
bea
ts/m
in
Fig. 6 GMA effect on HR before (-), during (0) and after (?) geomagnetic storms (1st person—upperpanel—2nd person—bottom panel)
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a day with major storm (Ap = 37)—the bottom panel. It is seen that LF component
decreased during geomagnetic storms.
HF of the 1st person decreased on 0 day of major storms and increased on -2, ?1, ?2
and ?3 day of these GMA levels. It increased from -2nd till ?2nd day of moderate
storms. For the 2nd person after the decrease of HF on -2nd day of moderate storms, it
increased up to ?1st day. Regarding major storms, this person had peak decreases of HF
on -1st and ?1st day and increments on -3, -2 and ?3 day.
The ratio LF/HF for the 1st person was maximal on -2nd day of all intensity types of
geomagnetic storms and minimal on ?2nd day of major storms as well as on the day of
development of different geomagnetic storms. The second person increased HF on -1st,
?1st and ?2nd day of major storms as well as on -2nd day of moderate storms and after
that gradually decreased the values up to ?2nd day of moderate storms.
GMA levels: I0 I II IIIDay
48
51
54
57
60
63
66
SDN
N
GMA levels: I0 I II III
-3 -2 -1 0 +1 +2 +3
-3 -2 -1 0 +1 +2 +3
Day
30
32
34
36
38
40
42
44
46
48
SDN
N
Fig. 7 GMA effect on SDNN before (-), during (0) and after (?) geomagnetic storms (1st person—upperpanel—2nd person—bottom panel)
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Different responses of the two persons to GMA changes reveal that individuals try to
accommodate to space weather variations. It supposes that the type of adaptation reaction
depends on the personal features and initial state of the persons’ functional state, which can
vary from day to day according to everyday activities, and suggests that even healthy persons
could be adversely affected from sharp environmental factors variations in some cases (when
they are more physically and/or psychically loaded and, respectively, more vulnerable).
4 Discussion and conclusions
Results revealed strong variations of HRV parameters of the group from the day before
(-1st day) till 3 days after (?3rd day) weak storms, which were registered during the time
GMA levels: I0 I II III
-3 -2 -1 0 +1 +2 +3
Day
0.00020
0.00025
0.00030
0.00035
0.00040
0.00045
0.00050
0.00055
0.00060
LF
Pow
er, s
^2
GMA levels: I0 I II III
-3 -2 -1 0 +1 +2 +3
Day
0.00016
0.00018
0.00020
0.00022
0.00024
0.00026
0.00028
0.00030
0.00032
0.00034
LF
Pow
er, s
^2
Fig. 8 GMA effect on LF before (-), during (0) and after (?) geomagnetic storms (1st person—upperpanel—2nd person—bottom panel)
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of investigation. Unfortunately, there were no geomagnetic storms with higher intensity
from March 23, 2009, to April 30, 2009. BP and SPPC increased statistically significantly
from 0 day till ?2nd day. There was a trend for decrease in heart rate on 0 day.
Personal everyday measurements of the two volunteers for a period of 1 year revealed
that morning measurements were more sensitive to space weather variations in comparison
with evening measurements. It is interesting that both persons reacted in different way to
geomagnetic storms with different intensities. They decreased heart rate during moderate
storms but increased this parameter during major storms and on the days before and after
the respective storms. HRV parameters varied significantly also on these days.
Variations of the measured physiological parameters on the days before geomagnetic
storms, which usually occur 1–3 days after solar events, show that potential biophysical
effects are probably related to some of the precursors of geomagnetic storms like extremely
low-frequency electromagnetic fields. Similar results for healthy persons at different
0
0.01
0.02
HRV - power spectral density, Lomb
Frequency , Hz
Pow
er, s
^2
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
0 0.05 0.1 0.15 0.2 0.25 0.3 0.350
0.01
0.02
HRV - power spectral density, Lomb
Frequency , Hz
Pow
er, s
^2
Fig. 9 Example of spectralanalysis of HRV of the 1st personon a day of quiet GMA, Ap = 3(12.06.2008)—upper panel—andon a day of major storm,Ap = 37 (11.10.2008)—bottompanel)
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latitudes and geographical regions like Sofia, Baku, Kosice, Moscow for parameters like
blood pressure, heart rate, subjective psychophysiological complaints and electrical
characteristics of acupunctural points have been established (Dmitrieva et al. 2001;
Dimitrova et al. 2004, 2009a; Khabarova and Dimitrova 2009; Papailiou et al. 2011).
These results show that GMA should be used as an indirect indicator of geo-effective solar
storms, but further studies for establishing the exact space weather factors linked to the
effects of human cardiovascular state should be performed.
This hypothesis is supported by the fact that physiological response to storms with dif-
ferent intensity is not consistent with gradation of GMA levels. Similar results were obtained
about heart rate and arterial blood pressure of Slovak aviators (Papailiou et al. 2011, 2012).
Geomagnetic storms have different origin. It is quite probable that physiological reactions are
not related directly to GMA and, respectively, to intensity of the storms, but depend on the
sources of solar events. Previous studies have revealed that geomagnetic storms caused by
magnetic clouds were related to significant increase in acute myocardial infarctions in Sofia
and Baku in comparison with the storms caused by high-speed solar wind streams (Dimitrova
et al. 2009b). These new results about HRV dynamic indicate that further studies are needed
to clarify the possible relationship and biophysical mechanisms through which helio-geo-
physical factors and their variations affect cardio-health state.
The results suggest that healthy people manifest an adaptation reaction to accommodate
to space weather variations, which is within their normal physiological range and not
threatening to their health status. However, persons with decreased compensatory abilities
are more vulnerable to environmental factors’ variations. It could be useful for such
individuals to be aware of them and to take precaution measures in time to avert negative
physiological reactions and to diminish the probable clinically significant effects. The
strong increase as the decrease in the HRV indices is related to increased risk of incidences
like arrhythmia, infarctions, other cardiovascular diseases and also sudden cardiac death.
The results show that further investigations should be performed in this direction. Another
study with greater number of subjects and over longer period of time is planned to be
performed in the following spring and autumn when maximal solar and geomagnetic
activity are expected. However, this study cannot be performed for as big group as in the
previous study when 86 persons were examined. It will be impossible per a day to register
so many persons’ ECGs (ECG record of each of the persons must be at least 5 min to
derive HRV parameters, and there is a necessity of technical time to put electrodes and
start recording programme), to measure BP of each subject at least 3 times to take the
average value of this dynamic parameter, and to fill in a questionnaire. It requires attention
to each of the examined persons at least about 30 min, which limits the number of the
persons who can be examined per a day. Finding serious, responsible persons who would
make self-recordings everyday is also a difficult task or payment for additional self-
motivation to the volunteers must be assured. Persons with cardiovascular diseases would
be motivated; however, one of the important tasks in these studies is to find out whether
healthy persons react to environmental factors variations and is the physiological reaction
of a normal adaptation reaction. The determination of the impact degree of the solar
activity factors on the cardiovascular parameters will make it possible to recommend under
which changes of the respective factors it would be desirable to apply countermeasures.
More investigations are needed to confirm these adverse effects and to determine those
helio-geophysical factors’ features which most strongly affect human physiology state. If
the effects of space weather are confirmed in different examinations at various latitudes
and longitudes, then it would help for timely applying a prophylactic measures to avert
unfavorable reactions of vulnerable persons.
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Acknowledgments We thankfully acknowledge the contribution of all volunteers who took part in theexaminations.
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