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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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