ABSTRACT
Cardioventilatory coupling (CVC) is a temporal alignment between the heartbeat and inspiratory activity caused by pulsatile baroreceptor afferent activity. However, although first described over a century ago, the functional significance of CVC has yet to be established. One hypothesis is that baroreceptor triggering of inspiration positions heartbeats into phases of the respiratory cycle that may optimize pulmonary gas exchange efficiency. To test this hypothesis, we recruited ten patients with permanently implanted fixed-rate cardiac pacemakers and instructed them to pace breathe at heart rate-to-respiratory rate (HR/f) ratios of 3·8, 4·0 and 4·2. This breathing protocol enabled us to simulate heartbeat distributions similar to those seen in the presence (4·0) and complete absence (3·8, 4·2) of CVC. Results showed that heart rate, mean arterial pressure, end-tidal carbon dioxide and tidal volume remained unchanged across the three conditions (P> 0·05). Pulmonary gas exchange efficiency, as determined by the ventilatory equivalents of carbon dioxide (V·E/V·CO2) and oxygen (V·E/V·O2) did not differ significantly by HR/f ratio (P = 0·29 and P = 0·70, respectively). These data suggest that CVC does not play a significant role in optimizing pulmonary gas exchange efficiency in humans.
