Photoplethysmography

Abstract

The process of breathing occurs as a physiological cycle in which one nasal cavity is functionally active while the other is resting, i.e., breathing alternates between the nostrils according to a regular pattern referred to as the "nasal cycle" and this cycle has been found to have a profound effect on a number of brain functions. It is suspected that some cross coupling exists between the dominant nostril and the active cerebral hemisphere. It is believed that breathing has a profound effect on man's physical/psychological functioning and is the link between the body and the mind. Pranayama is a well-proven technique for controlled rhythmic breathing with beneficial effects reported both for the body and the mind. In this study the arterial blood volumetric changes from 10 normal breathing subjects and 30 subjects practicing pranayama are monitored non-invasively at the earlobes using optical sensors. This method is known as Photoplethysmography (PPG). Spectral analysis and Heart Rate Variability (HRV) studies are performed on the collected PPG data. The results show fundamental changes in the spectral components of the PPG signal in relation to the breathing brought about by pranayama. In addition, a bi-nasal respiratory airflow monitor is designed and developed for this study utilizing miniature thermistors that can be introduced into the two nostrils of the subject without causing discomfort to the subject. Another study is also reported in which changes in microcirculation in chakra points were studies as a result of concentration on these points. Results indicate the low frequency component around 0.18 Hz changes dramatically during these procedures. Concentration on heart increases the amplitude of the low frequency by about 4.5 times. Concentration on the eyebrow chakra increases the value of this component by about 3 times, but the curve is much broader showing more "power" in that band of frequencies. Since prana or chi is related to amount of blood flow, it is likely the increase in microcirculation is related to increase in prana, as suggested in ancient texts. Further work is contemplated to peruse this line of thinking through standard clinical methods.