Aim: 

The contribution of stroke volume increases to the adaptation of cardiac output (CO) to exercise in humans have not been fully document-ted. We sought to compare stroke volume (SV) and heart rate (HR) changes with changes in a group of young healthy subjects, during incre-mental cycle ergometer tests in a group of hypertensive older subjects.

Methods: 

16 older subjects (OG: 66 4 yrs) under therapy (b-blockers excluded) for diagnosed hypertension were compared with 8 healthy voluntaries (YG: 23 2 yrs). They performed an incremental test to exhaustion: after sitting still on the byke, for a control record (0 W), all subjects started pedalling at 50 W; following incremental (2 min) steps were of 10 W for OG and of 40 W for YG. Metabolic variables (Cosmed QuarkB4) and portapres finger arterial pressure were recorded; HR, SV and CO were estimated. Data are presented in percent changes over 0 W, as a function of loads; loads are normalised to the estimated HR reserve (HR_max-HR_W0); HR_max = 220-age (yrs).

Results: 

Cardiovascular changes in OG were much smaller than in YG, although HR and CO increased, as expected, in relation to the workload. In contrast, SV increased in a roughly parabolic way in YG, but did not change in OG. Even the SV increase at the first step, that accounts for the effect of muscle contraction on venous return, was absent in OG.

Conclusion: 

These results demonstrate that OG rely on HR only to increase CO during exercise, since their heart is unable to increase stroke volume. In the present research no distinction could be made between the effects of ageing and the consequences of hypertension.