Noninvasive methods to study autonomic nervous control of circulation.

The major findings and conclusions of this study are the following: 1. Indirect evidence suggested that nervous afferentation from the cutaneous thermoreceptors and nervous efferentation to the skin blood vessels mediated the 0.01-0.10 Hz thermally entrained response of the oscillations of the forearm skin blood flow in supine and upright subjects. 2. Postural stimulation decreased skin blood flow and oscillations of skin blood flow. The 0.10 Hz thermal stimulation interacted with the postural stimulation by increasing the oscillations of skin blood flow from sitting to standing position on the contrary to the expected postural effect. 3. The thermal entrainment of periodic heart rate variability was not constant. Both 0.01-0.10 Hz thermal and postural and sensory stimulations affected the periodic heart rate variability selectively at the frequency of the periodic stimulus or the less than 0.12 Hz frequencies. 4. The periodic thermal stimulation had a frequency-selective effect on the oscillations of the neonatal heart rate. The thermally stimulated reactivity increased with an increased maturity of a neonate. 5. Intermittent tilting had a frequency-selective influence on the oscillations of heart rate. Continuous deep breathing entrained the periodic heart rate variability. The estimation of the power spectral density function of heart rate quantified the chronotropic respiratory effects more accurately than the statistical indices of heart rate variability. 6. Response of periodic heart rate variability to intermittent tilting and deep breathing stimulation suggested normal vagal control of heart rate in children with juvenile diabetes and juvenile rheumatoid arthritis. 7. Normal vagal bradycardic response was found during the phase IV of the Valsalva manoeuvre in functionally abnormal nervous control of circulation. The simulated diving test was not found clinically useful. 8. The ratio of electrical to electromechanical systole of the heart was greater than 1.00 both at rest and during the orthostatic, Valsalva and diving reflex tests. This finding suggested constantly exaggerated sympathetic cardiac inotropic control during vagal and sympathetic stimulation of heart rate. 9. The decreased thermally stimulated heart rate variability was interpreted as an indication of inhibited vagal modulation of the sinoatrial node of the heart in subjects with dystonic symptoms and orthostatic intolerance. The exaggerated sympathetic reactivity of these subjects explained the abnormally high gain of periodic heart rate variability to 0.01-0.03 Hz periodic thermal stimulation.