Reprint requests: Dr. M.Finkelstein, Department of Geophysics and Planetary Sciences of the Tel Aviv University, Tel Aviv, Israel

SUMMARY

The associations between certain geophysical conditions (magnetic storms, Hamsins [heat wave], and rain) and admission rate due to acute myocardial infarction (MI) or stroke was investigated in a major tertiary care hospital in Tel-Aviv during 1992. Admission rates were significantly higher on days with magnetic storms than on days with normal geomagnetic conditions (4.4±2 vs. 3.4±2, p <0.004, for MI; 2.7±1.5 vs 2.0±1, p <0.005 for stroke). The association (p <0.05) between MI and stroke and rainy days was less significant, while Hamsins (hot and dry climate) had no apparent effect. These findings strongly suggest that geophysical variations may have an impact on health.

Key words: myocardial infarction, stroke, magnetic storm, rain, heat wave.

INTRODUCTION

Although it is commonly accepted that certain geophysical conditions may influence human health, few studies have addressed this issue. Three recent studies, carried out in different parts of the globe, described interesting associations between unusual weather and health: the first, from Taiwan (1), showed that extreme temperature was associated with an increased incidence of cardiovascular events. The second, from southwest England (2), revealed an increase in admission rate due to asthma during thunderstorms, only when they were accompanied by high pollen counts and poor air quality. In the third study (3), conducted in Israel, geomagnetic activity was found to correlate with severity of migraine attacks.

The climate in Israel is characterized by short periods of very hot and dry weather (Hamsins) due to easterly winds and occurring mainly in the spring. There are also defined periods of heavy rain during the winter. Both the Hamsins and rain are usually limited to a few days at a time. Such clear cut interruptions of otherwise stable weather conditions facilitate the monitoring of events that can be directly associated with such changes. In the following study, we examined the possible effect of these conditions on cardiovascular morbidity as reflected by hospital admissions due to myocardial infarction (MI) or stroke. Moreover, in view of observations made mainly by Russian investigators, that solar activity correlates with mortality from cardiovascular diseases (4) and with prognosis of myocardial infarction (5), we correlated one example of this, magnetic sun storms, as well.

PATIENTS AND METHODS

All patients admitted to Ichilov Hospital in 1992 and diagnosed as having either acute myocardial infarction (ICD-9 Code 410) or stroke (ICD-9 Code 436) were included in the study. We obtained the dates of admission for MI and stroke and patients' age through the hospital registry. One investigator (M.F.), who was blinded to the hospital search, was in charge of compiling the geophysical data. Only weekdays of 1992 (Mondays to Thursdays), excluding religious holidays, were analyzed because of possible bias due to different conditions regarding hospital admissions during weekends (see Discussion for details). These were divided into "quiet", uneventful days (normal geophysical conditions), and presumed "high-risk" days (magnetic storms, Hamsins, rain). The number of daily admissions due to MI or stroke on quiet days was compared to that during high-risk days, as well as separately for each condition.

DEFINITIONS OF GEOPHYSICAL CONDITIONS

A magnetic storm was defined by an index of geomagnetic variations (Ak) of more than 30, or avariation of >10 Ak plus an anomalous electro-magnetic radio burst. Data were obtained from the Sunspot Bulletin, Brussels (6). A hamsin was defined as a combination of a temperature >29°C with a humidity level <30%. The term "rain" indicated more than 5 mm/day of precipitation, accompanied by sharp changes (> 5 millibars) in atmospheric pressure. The meteorological data (hamsins and rain) were obtained from the Israel Central Weather Bureau.

STATISTICAL ANALYSIS

Two-sample t-tests were performed for comparison of the overage daily number of admissions for either MI or stroke on "quiet" days versus the presumed "high risk" days. Days with more than one type of geophysical condition were counted separately for each condition.

RESULTS

During the 210 eligible days, there were 813 admissions due to acute MI and 453 admissions due to stroke. The overage daily number of hospital admissions was 3.9±2 and 2.1±1.5, respectively. The distribution by age groups is presented in Tab. 1.

Tab. 1 Distribution of patients by diagnosis and age groups

The 210 days were divided into 119 (57%) quiet days and 91 (43%) high risk days: 62 days (30%) with magnetic storms, 17 days (8%) with hamsins and 18% (9%) rainy days. There were 6 days in which more than one geophysical event occurred.

The overage number of admissions for MI on a quiet day was 3.4±1.9 and on a high-risk day it was 4.4±2.2 (p <0.01). The corresponding numbers for stroke were 2.0±1.4 and 2.5±1.5 (p <0.03). The distribution by the type of geophysical event and by the age groups is displayed in Tab. 2. Magnetic storms were significantly associated with an increased number of admissions due to either acute MI or stroke. This effect was recorded only in the older age group (>65 years) and not in the younger patients, possibly because of the very small sample size of patients under age 65. Periods of rain were also found to correlate with the admission rate, but the degree of statistical significance was much smaller. The occurrence of Hamsins had no apparent impact.

Tab. 2 Distribution of number of daily admissions by geophysical conditions and age groups.

DISCUSSION

Our results show that rates of hospital admissions due either to acute MI or to stroke were higher during rainy days or days with magnetic storm activity. Taken as a whole, the "high-risk" days were roughly associated with a 30% increase in acute MI admissions and a 25% increase in stroke admissions, compared to "quiet" days. Examining the distribution of data by age qroups shows that this correlation applied only to the patients above 65 years of age, probably because of the very small number of patients under this age. In spite of its being a generally accepted

phenomenon, there is a paucity of hard data on possible relationships between extraterrestrial geophysical events and human morbidity. Investigators in the USSR have claimed that 40-45% of all ischemic heart attacks occur during periods of magnetic storms, and another 25% occur just prior to the onset of these storms (7).

The higher morbidity during Hamsins, albeit not found in our study, could be explained more easily than the other phenomena since the combination of hot and dry climate has been shown to have an effect on blood pressure, hydration status, and degree of positive ionization (8). Hamsins are often accompanied by fatigue, migraines and changes in mood and well-being. A recent study from the Far East found a correlation between extreme temperatures and mortality from cardiac and cerebrovascular diseases in the elderly (1). In our cohort, the effect of Hamsins did not reach statistical significance. This could be a reflection of the widespread availability of air-conditioning in most dwellings, offices and public buildings in Tel-Aviv.

Rain is often accompanied by an abrupt change in atmospheric pressure, which may lead in low pressure conditions to enhanced release of radioactive radon gas, and positively charged particles related to radon. Radon is considered a hazardous substance because of its adverse effects on the brain, cardiorespiratory system and endocrine glands (9). Therefore, the higher morbidity recorded during rainy days could be attributed either to a direct reaction to the change in atmospheric pressure or to an event related to it, such as an increase in the concentration of gas radon and positive air ionization.

This is a preliminary study, limited to three geophysical conditions and to only two very specific diseases. Acute MI and stroke were chosen because of their high rate among hospital admissions. The study was carried on during one calendar year and in only one hospital. We excluded weekends and holidays in order to avoid possible bias since most of the community health facilities in Israel are closed from Friday afternoon until Sunday morning, as well as on holidays, with a "rebound" effect on Sundays. Moreover, public transportation does not operate on the Sabbath, making access to emergency rooms more difficult. Last and importantly is the fact that observant people (about 20% of the population) are prohibited by religious low to use any kind of transportation during the Sabbath. The above rules apply for holidays as well, which were therefore also excluded from analysis.

All the above limitations notwithstanding, our data clearly demonstrate that certain geophysical events do have an influence on health. The exact pathophysiological mechanisms have not yet been elucidated, however, one may speculate that when our knowledge on this issue will extend, the meteorological forecasts will include more geophysical information, thereby enabling the vulnerable members of the public to take special measures when such "risky" days are anticipated.

REFERENCES

1. Pan WH, Li LA, Tsai MJ. Temperature extremes and mortality from coronary heart disease and cerebral infarction in elderly Chinese. Lancet, 1995, 345: 353-355

2. Southerland A, Hall IP. Thunderstorms and asthma admissions. Lancet, 1994, 344: 1504-1505

3. Kuritzky A, Zoldan Y, Hering R, Stoupel E. Geomagnetic activity and the severity of the migraine attack. Headache, 1987, 27: 87-89

4. Gnevyshev MN, Novicova KF, Ol AE, Tokareva NV. Sadden death from cardiovascular diseases and solar activity. In: Gnevyshev MN, Ol AE (eds.) Influence of solar activity on atmosphere and biosphere of Earth. Nauka, Moscva, 1971, pp 179-186 (Russian)

5. Kondratyc IK, Baborikin AM, Emelanob AM. Prediction of prognosis of myocardial infarction by geophysical dada_analysis. In: Fokin AB, Ladkorin BN, Krasnogorskaya NV (eds.) Electromagnetic fields in biosphere. Nauka, Moscva, 1984, pp 177-184 (Russian)

6. Sunspot Index Data Center. Sunspot Bulletin, Brussels, 1992

7. Hasnulin VI. Unfavorable days due to geophysical factors. Zdorovye, 1988, @:7 (Russian)

8. Petersdorf RG. Hypothermia and hyperthermia (chapter 398). In: Harrison's Principles of Internal Medicine, 13th edition. McGraw-Nill, Inc., New-York, 1994, pp 2474-2476