RR and R wave to finger pulse interval changes as a function of respiration rate and body position using VCRS

A technique of voluntary cardiorespiratory synchronization (VCRS), where the respiration rate is synchronized at a sub-multiple of the heart rate, was used to investigate the RR wave interval change and R to finger pulse interval change as a function of respiration in 6 subjects. Data were collected with subjects breathing at 4, 8, 12 beats per respiratory cycle in the supine and standing position. Following a tone, the subjects inspired for two, four or six heart beats and expired respectively for two, four, or six beats. The results showed a significant decrease in the RR interval with inspiration and an increase in the R to finger pulse time. This produces an approximate 180 degree phase difference between the pulse time interval change and the RR interval. It is unclear whether R-pulse interval change is due to blood pressure changes, other vasomotor factors or a change in the inotropic state of the heart.