Cardiovascular response to treadmill exercise in untrained rats

Abstract

Oxygen consumption (Vo2), cardiac output (Q), heart rate (HR), stroke volume (SV), and oxygen extraction from blood (Cao2-Cvo2) were measured in untrained rats, both at rest and during treadmill running at various speeds (10-41 m/min). Vo2 increased linearly as a function of running speed, and maximal values (83 ml O2.kg-1 min-1) represented a five-fold increase over resting values. Q, HR, SV, and Cao2-Cvo2 increased linearly as functions of Vo2. Mixed venous oxygen content (Cao2) decreased with increasing Vo2; whereas arterial oxygen content (Cao2) remained independent of Vo2; whereas arterial oxygen content (Cao2) remained independent of Vo2, averaging 19 vol%. Maximal values of these variables and their relationship to Vo2 were as follows: Q = 4.3 Vo2 + 184; Qmax = 543 ml.kg-1.min-1, HR = 3.02 Vo2 + 340; HRmax 595 beats.min-1; SV = 0.004 Vo2 + 0.603; SVmax = 0.92 ml.kg-1.beat-1; Cao2-Cvo2 = 0.13 Vo2 + 5.62; Cao2-Cvo2max = 15.5 vol%.; Cvo2 = -0.12 Vo2 + 12.94; Cvo2min - 3.4 vol%. These data suggest that HR, SV, and Cao2-Cvo2 make significant contributions to the augmentation of Vo2 in the exercising rat.