Determinants of diastolic cardiac filling during exercise

Aim. To examine relative contributions of factors responsible for cardiac diastolic filling during exercise by investigating changes in systemic venous; return (as indicated by alterations in cardiac output) after abrupt cessation of skeletal muscle pump function. Methods. Two cycle exercise studies differing in subject population (men, boys), intensity (submaximal, maximal), and technique for assessing cardiac output (thoracic bioimpedance, Doppler echocardiography). Study 1 involved 12 healthy boys (mean age 12.0+/-1.3 years) and study 2 was composed of 9 young adult men (mean age 27.0+/-3.7 years). Results. Decline in cardiac output averaged 15.8% within the first 15 see of passive recovery in study 1, while a decrease of 10.9% was observed at 20 sec of passive recovery in study 2. Active pedaling recovery in study 2 slowed the decrease in cardiac output. Conclusion. Factors other than the skeletal muscle pump, particularly forward cardiac flow, are capable of maintaining high levels of systemic venous return during early passive recovery. However, this model is unlikely to reflect hemodynamics during exercise, since skeletal muscle contractions impede arterial inflow but augment systemic venous return by increasing the arterial-venous pressure gradient.