Natural fluctuations of air pressure (FAP) of very low frequencies are considered as potential causal agents of health effects of weather on humans. This study by means of exposure chamber tests examines the effects of artificially generated oscillations of air pressure (OAP), simulating FAP, on the regulation processes of the cardiovascular system.

Changes in end points characterising central haemodynamics, caused by OAP, were studied in 10 healthy women, 20-21 years of age. Exposure to sinusoidal OAP with an oscillation period of 30 s and amplitude of 50 Pa during 15 min caused a reduction in systolic blood pressure by 7% (p<0.05) and an increase in the cardiac output by 10 % (p<0.05). These changes were attributed to a reduction (approximately by 11%) in the peripheral resistance of circulatory system.

In the second series of experiments, effects of sinusoidal OAP (45 s, 50 Pa) on the rhythm of cardiac contractions of another group of subjects (4 men and 6 women aged 21 to 64, supine position) were studied. 15 minutes long records of R-R-intervals of ECG were analysed by multicomponent cosinor, superposed epochs and spectral filtering. Exposure to OAP in all subjects caused constrained oscillations of R-R with an amplitude of 3-10 ms (P < 0,001). In 5 subjects OAP synchronised the physiological (periods »10 s) fluctuations of R-R (P < 0,0001) as a result of the baroreflex loop, which stabilises arterial pressure. The amplitude and the phase of the constrained oscillations of R-R induced by OAP fit the baroreflex sensitivity data available from the literature.

The results shown above together with the OAP effect on the smooth muscle of peripheral vessels indicate that OAP is perceived by baroreceptors of the baroreflex loop. This process may be a link between symptoms in weather sensitive persons (the so called Atmosphere Related Syndrome) and changes in weather, which are associated with changes in the air pressure oscillation pattern. Most probably, OAP swing periodically the reference point of baroreceptors of the carotid sinus located just underneath the skin of the neck. As a result, constrained oscillations of R-R are induced, which modify considerably the time structure of spontaneous fluctuations in the baroreflex loop. The baroreceptor mechanism can explain why the cardiovascular system responds to OAP with changes in peripheral resistance, arterial pressure and cardiac output. Besides, the baroreceptor signal through the cardiovascular centre in medulla oblongata via ascending ways influences both hypothalamus and brain-cortex. This also can explain the activating effect of OAP on the mental process, reported earlier [1].

[1] Delyukov A., Didyk L. The effects of extra-low-frequency atmospheric pressure oscillations on human mental activity. Int. J. Biometeorol. 1999, 43: 31-37