Voluntary cardiorespiratory synchronization: Heart rate variability as a function of age, tidal volume and body position

A technique of voluntary cardiorespiratory synchronization (VCRS), where the respiration rate is synchronized at a sub-multiple of the heart rate (1:5), was used to investigate heart rate variability (HRV) in 14 subjects as a function of age, body position, and respiratory tidal volumes of 500ml and 1000ml. Following a tone, the subjects inspired for two heart beats and expired for three beats. Subjects were grouped according to age into two groups (20 to 30 and 46 to 57). The results showed no statistically significant change with tidal volume but a significant decrease in HRV with age. Changing from sitting to supine showed a slight increase in HRV for the younger group whereas the older group showed a decrease. Because a constant phase relationship between respiration and the heart beats is maintained, VCRS is an easy to use method to measure the influence of each phase of the respiratory cycle on the HR and blood pressure due to the mechanical action of respiration.