Correlation between Changes in Local Earth’s Magnetic Field and Cases of Acute Myocardial Infarction

The impact of changes in the geomagnetic field on the human body remains the subject of studies across the world, yet there is no consensus. Current studies are observing effects that require further work by researchers in order to find out the mechanisms that would allow a proper assessment of the correlations between the Earth‘s magnetic field variations and changes in human organisms. The main purpose of this study was to investigate possible correlations between the strength of time-varying aspects of the local Earth’s magnetic field and incidence of myocardial infarctions. Study participants included 435 males and 268 females who had diagnosis of myocardial infarction during the period of 1 January 2016 to 31 December 2016 and attended the Department of Cardiology at the Hospital of Lithuanian University of Health Sciences (LUHS), Kauno klinikos. Time varying magnetic field data was collected at the magnetometer site located in Lithuania. After mathematical analysis, the results support the hypothesis that the Earth’s magnetic field has a relationship between the number of acute myocardial infarction with ST segment elevation (STEMI) cases per week and the average weekly geomagnetic field strength in different frequency ranges. Correlations varied in different age groups as well as in males and females, which may indicate diverse organism sensitivity to the Earth’s magnetic field.


Cell Regulation
The hypothesis that the time varying magnetic fields of the earth may be regulatory mechanism of cells acting through the ion cyclotron resonance mechanism has been proposed [1]. It is claimed that every living organism has specific sensitivity to the strength and frequency of fluctuations of magnetic fields [1,2]. Laboratory findings demonstrate the effect of ion cyclotron mechanism on extracted myocardial cell regulation [3]. However, according to recent publications, it remains unclear whether the local magnetic field of the Earth has an effect on the regulation of human heart cells. We started In the estimated power curve on the frequency range, from 0 to 65 Hz there is a series of dominant Schumann resonance frequencies, which are divided into ranges that overlap with the EEG wave classification (as related processes): 0 to 3.5 Hz-Delta waves (P1); 3.5 to 7 Hz-Theta waves (P2); 7 to 15 Hz-Alpha waves (P3); 15 to 32 Hz-Beta waves (P4); 32 to 100 Hz-Gamma waves (P5). The latter high frequency waves are believed to cause stress effects on living organisms [11,12]. As stated in [12], "It is certain that gamma, like other brain rhythms, can provide a signature of cognitive state, as well as network dysfunction". In the estimated power curve on the frequency range, from 0 to 65 Hz there is a series of dominant Schumann resonance frequencies, which are divided into ranges that overlap with the EEG wave classification (as related processes): 0 to 3.5 Hz-Delta waves (P1); 3.5 to 7 Hz-Theta waves (P2); 7 to 15 Hz-Alpha waves (P3); 15 to 32 Hz-Beta waves (P4); 32 to 100 Hz-Gamma waves (P5). The latter high frequency waves are believed to cause stress effects on living organisms [11,12]. As stated in [12], "It is certain that gamma, like other brain rhythms, can provide a signature of cognitive state, as well as network dysfunction".

Geomagnetic Field and Melatonin
Studies have shown that changes in the time varying magnetic field above 80 Nt, over three hours significantly reduces melatonin levels in the body [13,14]. Indications for the use of melatonin for treatment are not approved in cardiology, although there are many researchers who suggest that melatonin may have a positive effect on people with ischemic heart disease [15]. In addition, antiarrhythmic action of melatonin during reperfusion in acute coronary syndromes has shown promise in a study [16]. Also, under laboratory conditions, it has been found that melatonin improves myocardial microcirculation [17]. Thus, reduced levels of melatonin, along with other individual factors, may play a role in development of myocardial ischemia due to changes in geomagnetic field.

Participants
There was a total of 703 participants in the study (435 men and 268 women) with a diagnosis of new myocardial infarction (MI) event during the period from 1 January 2016 through 31 December 2016, who attended the Cardiology Department of University Hospital at Lithuanian University of Health Sciences (BEC-MF-254). Mean age of the men was 63.44 ± 11.65, (Me = 63) and 73.21 ± 10.45 (Me = 75) for women. Men group we have divided into two groups according Me-younger group with age <63 years. (N = 229, mean age ± Stdev = 54.57 ± 3.43), and older group age >63 years. (N = 206, mean age ± Stdev = 73.53 ± 4.84). The men's mean age was almost 10 years younger than the women's group, but older men group was just the same as women group age (no significant differences were observed). All the patients were admitted to the Cardiology Department with diagnosis of MI. All the patients were highly symptomatic during the time of arriving to the hospital. Figure 3 shows the number of male patients admitted for MI during each week in 2016 and Figure 4 for females.
for treatment are not approved in cardiology, although there are many researchers who suggest that melatonin may have a positive effect on people with ischemic heart disease [15]. In addition, antiarrhythmic action of melatonin during reperfusion in acute coronary syndromes has shown promise in a study [16]. Also, under laboratory conditions, it has been found that melatonin improves myocardial microcirculation [17]. Thus, reduced levels of melatonin, along with other individual factors, may play a role in development of myocardial ischemia due to changes in geomagnetic field.

Participants
There was a total of 703 participants in the study (435 men and 268 women) with a diagnosis of new myocardial infarction (MI) event during the period from 1 January 2016 through 31 December 2016, who attended the Cardiology Department of University Hospital at Lithuanian University of Health Sciences (BEC-MF-254). Mean age of the men was 63.44 ± 11.65, (Me = 63) and 73.21 ± 10.45 (Me = 75) for women. Men group we have divided into two groups according Me-younger group with age <63 years. (N = 229, mean age ± Stdev = 54.57 ± 3.43), and older group age >63 years. (N = 206, mean age ± Stdev = 73.53 ± 4.84). The men's mean age was almost 10 years younger than the women's group, but older men group was just the same as women group age (no significant differences were observed). All the patients were admitted to the Cardiology Department with diagnosis of MI. All the patients were highly symptomatic during the time of arriving to the hospital.     In our study, we divided 2016 year into two time intervals, first half of the year and second half of the year: 1 (weeks 1 through 26) and 2 (weeks 26 through 52). In a more detailed analysis we further divided the male group into two age groups (as mentioned earlier): younger than 63 and older than 63. We did not divide the female patient group due to the smaller number of females.  In our study, we divided 2016 year into two time intervals, first half of the year and second half of the year: 1 (weeks 1 through 26) and 2 (weeks 26 through 52). In a more detailed analysis we further divided the male group into two age groups (as mentioned earlier): younger than 63 and older than 63. We did not divide the female patient group due to the smaller number of females.

Magnetometer Data
The local time varying magnetic field intensity was measured using a local magnetometer located in Lithuania (Coordinates: Latitude: 55.634068 Longitude: 23.704563), which is part of the Global Coherence Monitoring Network. Two magnetic field detectors (Zonge Engineering Inc., Tucson, AZ, USA) ANT4 are positioned in north/south and east/west orientation. Data used in the analysis is from the east-west direction. Signals from the magnetometers were digitized with a 24-bit data acquisition system (Symmetric Research, Las Vegas, NV, USA) at a rate of 130 Hz and uploaded hourly to a cloud data storage site for offline processing. The overview of the magnetometer's data is available on web page [18]. Hourly data files were downloaded to a personal computer (PC) workstation for post processing where were each hourly data file was transformed into consecutive 30 s long segments. The power spectral density (PSD) was calculated for each segment. All PSD segments for each hour were then averaged together. The sum of the PSD in the frequency range from 0-66 Hz was calculated for each hour in the study period. Mean power of local magnetic field fluctuations in Lithuania, measured in pT 2 in five different frequency ranges where overlaps between the Schumann resonance and EEG frequency ranges (we named them as SDelta (0; 3.5 Hz), STheta (3.5; 7 Hz), SAlpha (7; 15 Hz), SBeta (15; 32 Hz), and SGamma (32; 66 Hz) to distinguish them from the EEG bands).

Spectral Analysis of the Magnetometer Data
In order to transform {I t } N−1 t=0 to the frequency domain the discrete Fourier transform (DFT) (Equation (1)) was used [19]. The drawback of DFT is that one cannot observe the change in spectral density over time unless sequentially computing DFT. To achieve this the discrete time short time Fourier transform (STFT) was employed.
STFT for {I t } N−1 t=0 is represented by Equation (2). In fact this is essentially the analogue for Equation (1) but applied to the function I t · ξ(t − τ). ξ(t) is a so called windowing function which has a value close to 1 in a subdomain of t centered on 0 and a value close to 0 elsewhere. The units of f (ω) and F(τ, ω) are pT·s due to the fact that the intensity of the magnetic field is measured in pT.
Spectrograms investigated in this work is the squared modulus of STFT (Equation (3)). Originally units of a spectrogram would be pT 2 · s 2 . S(τ, ω) is often referenced as power spectral density. Thus the value of S(τ, ω) is interpreted as signal power at the time interval ∆τ and at the frequency range ∆ω.
More detailed algebraic and spectral analysis of local magnetic field intensity is presented in article [20] and Schumann resonances calculated from magnetometers data are shown in Figure 2.

Statistical Analysis
Nonparametric Mann-Whitney U test for the comparison of two independent samples was used. Pearson correlation coefficient for the linear correlation between two variables was calculated. The level of p < 0.05 was considered statistically significant.

Results
We found a significant relationship between number of acute myocardial infarction with ST segment elevation (STEMI) cases per week and the average weekly geomagnetic field strength in different frequency ranges. In the female group (N = 268), we found single positive correlation coefficient P5 (SGamma) [32; 65] Hz, (r = 0.25, p = 0.037), which indicates that higher magnetic field intensity in this frequency range is significantly associated with increased number of STEMI cases. In other low frequency ranges, we observed negative correlation coefficients: P1 ( Unlike females, we observe non-significant changes in SGamma range, which may indicate slightly different sensitivity of different sexes to the changes of the Earth's magnetic field. It should be considered that all these frequencies are present at the same time, therefore, the negative SGamma frequency range effect may not outweigh the positive effects of other frequency ranges (SDelta, STheta, SAlpha, SBeta).  Unlike females, we observe non-significant changes in SGamma range, which may indicate slightly different sensitivity of different sexes to the changes of the Earth's magnetic field. It should be considered that all these frequencies are present at the same time, therefore, the negative SGamma frequency range effect may not outweigh the positive effects of other frequency ranges (SDelta, STheta, SAlpha, SBeta).     In addition, the male group was divided into two groups according to age, 63 and below and 64 and above. In both groups P5 (SGamma) [32; 65] Hz range correlations were weaker than in the other frequency ranges. However, there was no significant difference between both group correlations in all ranges (U = 10; z = −1.28, p = 0.241). Despite that, a tendency of stronger correlations in the older males group was observed.
To compare and discuss differences in correlations between all men and all women is difficult because in our country we have even 10 years' difference between our male and female patients' age we cannot say the differences are caused by gender or difference in mean age (Figures 5 and 6). We have taken the older men's group and compared year correlations with the women's group-in both those groups, there was no difference in age. In Figure 9, correlations are presented in different frequency ranges for older men and women groups. Here we see, that differences between genders appear only in higher frequencies-SBetta and SGamma (non-significant), but in lower frequencies, we see just the same correlations for both genders. For the older patient reactions, men and women, to Earth's magnetic field (EMF) different frequency bands in year interval are similar.   In addition, the male group was divided into two groups according to age, 63 and below and 64 and above. In both groups P5 (SGamma) [32; 65] Hz range correlations were weaker than in the other frequency ranges. However, there was no significant difference between both group correlations in all ranges (U = 10; z = −1.28, p = 0.241). Despite that, a tendency of stronger correlations in the older males group was observed.
To compare and discuss differences in correlations between all men and all women is difficult because in our country we have even 10 years' difference between our male and female patients' age we cannot say the differences are caused by gender or difference in mean age (Figures 5 and 6). We have taken the older men's group and compared year correlations with the women's group-in both those groups, there was no difference in age. In Figure 9, correlations are presented in different frequency ranges for older men and women groups. Here we see, that differences between genders appear only in higher frequencies-SBetta and SGamma (non-significant), but in lower frequencies, we see just the same correlations for both genders. For the older patient reactions, men and women, to Earth's magnetic field (EMF) different frequency bands in year interval are similar.
we cannot say the differences are caused by gender or difference in mean age (Figures 5 and 6). We have taken the older men's group and compared year correlations with the women's group-in both those groups, there was no difference in age. In Figure 9, correlations are presented in different frequency ranges for older men and women groups. Here we see, that differences between genders appear only in higher frequencies-SBetta and SGamma (non-significant), but in lower frequencies, we see just the same correlations for both genders. For the older patient reactions, men and women, to Earth's magnetic field (EMF) different frequency bands in year interval are similar. Based on correlation trend (Figure 10), we could see that similar ratio between the number STEMI cases and <63 y.o. males correlations was maintained in all magnetic field frequency ranges. Differences between both halves of year were significant (U = 0; z = −2.882; p = 0.002). Based on correlation trend (Figure 10), we could see that similar ratio between the number STEMI cases and <63 y.o. males correlations was maintained in all magnetic field frequency ranges. Differences between both halves of year were significant (U = 0; z = −2.882; p = 0.002).

Study Limitations
This study has several limitations. First, this study was performed about elderly hospitalized patients, making it difficult to apply the results to general population of all ages. Secondly, we did not evaluate solar activity or other weather conditions that may have additional effect besides changes in local geomagnetic field. An additional limitation of this study is that we did not evaluate the presence of other diseases or conditions which could also be affected by changes in geomagnetic field strength.

Discussion
The data we obtained by analyzing different sexes and different age group correlations with geomagnetic field strength revealed unequal relationships between these processes. Obviously, without direct influence of the field, we could not imagine the dynamics and diversity of correlations. In the first half of the year, we observed higher sensitivity to geomagnetic field of number of female MIs, which could not be explained by classical physiology. Although, we begin to understand the principal effects of the field to the living organism with circadian rhythms (The Nobel Prize in Physiology or Medicine 2017 for Jeffrey C. Hall, Michael Rosbash and Michael W. Young "for their discoveries of molecular mechanisms controlling the circadian rhythm"). Nevertheless, it is still unknown what modulates these changes in longer periods of time. The strength of our work is that we did analysis of different geomagnetic field frequencies and results revealed that different frequency ranges have different correlations with presence of myocardial infarctions. Lithuanian researchers in another study have found correlation between heart rate variability and geomagnetic field strength, their study has shown that autonomic nervous system responds to solar and geomagnetic activity [21][22][23]. Moreover, in another study which included patients from Lithuania, researchers found out that number of acute myocardial infarction events after low geomagnetic field activity and high cosmic rays days increased by a fifth, their obtained results indicate that geomagnetic field may be related to development of myocardial infarction [24,25]. Our study results indicate that the effects of changes in local geomagnetic field should be studied analyzing field's strength in frequency ranges. Ability to measure local changes of low frequency geomagnetic field provides an opportunity for researchers to begin more detailed future research.

Study Limitations
This study has several limitations. First, this study was performed about elderly hospitalized patients, making it difficult to apply the results to general population of all ages. Secondly, we did not evaluate solar activity or other weather conditions that may have additional effect besides changes in local geomagnetic field. An additional limitation of this study is that we did not evaluate the presence of other diseases or conditions which could also be affected by changes in geomagnetic field strength.

Discussion
The data we obtained by analyzing different sexes and different age group correlations with geomagnetic field strength revealed unequal relationships between these processes. Obviously, without direct influence of the field, we could not imagine the dynamics and diversity of correlations. In the first half of the year, we observed higher sensitivity to geomagnetic field of number of female MIs, which could not be explained by classical physiology. Although, we begin to understand the principal effects of the field to the living organism with circadian rhythms (The Nobel Prize in Physiology or Medicine 2017 for Jeffrey C. Hall, Michael Rosbash and Michael W. Young "for their discoveries of molecular mechanisms controlling the circadian rhythm"). Nevertheless, it is still unknown what modulates these changes in longer periods of time. The strength of our work is that we did analysis of different geomagnetic field frequencies and results revealed that different frequency ranges have different correlations with presence of myocardial infarctions. Lithuanian researchers in another study have found correlation between heart rate variability and geomagnetic field strength, their study has shown that autonomic nervous system responds to solar and geomagnetic activity [21][22][23]. Moreover, in another study which included patients from Lithuania, researchers found out that number of acute myocardial infarction events after low geomagnetic field activity and high cosmic rays days increased by a fifth, their obtained results indicate that geomagnetic field may be related to development of myocardial infarction [24,25]. Our study results indicate that the effects of changes in local geomagnetic