Cardiopulmonary adjustments during operant heart rate control.

Twenty-three healthy men and women participated in a 5-session experiment in which they attempted to increase and decrease their heart rate with the assistance of visual analogue biofeedback. As a group subjects did successfully raise and lower heart rate from resting baseline. These changes in heart rate were closely paralleled by changes in V, a measure of cardiac vagal tone. Heart rate slowing was associated with increases in V, and heart rate speeding was associated with decreases in V. Respiration rate and amplitude did not differ significantly between heart rate slowing and speeding trials, and covariance analysis indicated that respiratory changes did not account for the heart rate or V effects. The weighted coherence between respiration and heart rate showed that cardiopulmonary coupling increased during heart rate slowing and decreased during heart rate speeding. Individual differences in cardiac vagal tone and cardiopulmonary coupling were unrelated to heart rate speeding and slowing performance.