A Study of Heart Rate and Heart Rate Variability During Rapid Decompression to 50,000 FT.

Abstract : A previous study of the heart rate (HR) response to positive pressure breathing (PPB), anxiety and hypoxia during rapid decompression (RD) revealed a consistent pattern in the beat-to-beat or interbeat interval variability of HR, known in the literature as heart rate variability (HRV). One method of analyzing HRV is a noninvasive measure of the respiratory-cardiac neural reflex known as vagal tone monitoring. This method is based on the amplitude of respiratory sinus arrhythmia (RSA) as a manifestation of vagal cardioinhibitory influence on the heart. The RD/HR data were interpreted by two HRV analysis methods, vagal tone monitoring (VTM) and a method developed in-house based on maximum entropy method (MEM) (spectral analysis), as a means of studying the heart rate regulating mechanisms during RD. A significant drop in vagal tone in both HRV measures was shown during the PPB and hypoxia profiles. Conflicting results regarding the anxiety profile during RD leave room for questions as to the use of these HRV measures as a tool for assessing anxiety or emotional stress. However, these measures only examined a subset of the HRV frequency spectrum (the respiratory frequency range) which provides information only on the parasympathetic autonomic contributions. Investigation of other frequency bands may provide more complete data on the autonomic regulation of the cardiovascular system. (AN)