Influence of breathing on variation in cardiac stroke volume at the onset of cycling.

PURPOSE

During cycling, the variation in cardiac stroke volume (SVV) is similar to that at rest. However, SVV may be influenced by ventilation at the start of cycling, e.g., by a Valsalva-like maneuver used to stabilize the body. This study evaluated the influence of ventilation on SV during initiation of cycling.

METHODS

Ten healthy recreationally physical active males (mean ± SD: age 26 ± 3 years, height 184 ± 9 cm, weight 85 ± 9 kg) cycled on an ergometer for four 30 s intervals at submaximal workloads while synchronizing ventilatory and cardiovascular variables derived from gas exchange and arterial pulse contour analysis, respectively.

RESULTS

At exercise onset, cardiac output increased by an instantaneous rise in heart rate and SV (P < 0.05). In contrast, blood pressure increased only after 15 s (P < 0.05), reflected in a decline in total peripheral resistance from exercise onset (P < 0.05). SVV was similar at rest (20 ± 6%) and during exercise (21 ± 5%) except for the first 5 s of exercise when a ~ 2.5-fold elevation (47 ± 6%; P < 0.05) was correlated to variation in respiratory frequency (= 0.71, P = 0.02) and tidal volume (R = 0.66, P = 0.04) but not to variation in heart rate or blood pressure. Stepwise multiple regression analysis indicated a respiratory frequency influence on SVV at the onset of ergometer cycling.

CONCLUSION

The data provide evidence for a ventilatory influence on SVV at the onset of cycling exercise.