Blood flow kinetics at the onset of moderate exercise in the elderly

Abstract

The age-related effects on the time course of the rapid increase in blood flow at the onset of exercise are largely unknown. In addition, whether this time course is altered with training in older people is also unclear. It appears that this dearth of information was partly due to the lack of non-invasive methods of measurements that could present high temporal resolution and could be used during the exercise. Another difficulty that might also have contributed to this lack of information was that the mechanisms involved in blood flow kinetics regulation in humans are not well understood. It is also not clear how these mechanisms are affected by age or physical training. In order to address the questions about whether blood flow kinetics were altered by aging or physical activity, three studies were developed. In all three studies, forearm mean blood velocity and mean arterial perfusion pressure were measured on a beat-by-beat basis, using pulsed Doppler ultrasound and a plethysmographic finger cuff, respectively. This allowed calculation of forearm vascular conductance also on a beat-by-beat basis. The diameter of the brachial artery was measured at several points in time and during exercise. Since the exercise mean diameter was not different from the resting values, it was assumed that mean blood velocity kinetics represented the blood flow kinetics.

The results showed that forearm blood flow and vascular conductance kinetics were not impaired with age. Regarding the effects of increased physical activity on blood flow kinetics, the results were more difficult to interpret. While a longitudinal study showed improved blood flow and vascular conductance kinetics in response to a training protocol, a cross-sectional study showed only a tendency for 20% faster kinetics (p>0.05), in the very active older people compared to their less active counterparts. Since the kinetics values presented a large variability with overlap between the groups, it is possible that the small sample size might have compromised significant differences.

The findings of the three studies are confined to dynamic contractions of a small muscle mass with moderate workload.