Age and cardiac output during cycle exercise in thermoneutral and warm environments
Minson, C.T.; Kenney, W.L.
Medicine and Science in Sports and Exercise 29(1): 75-81
1997
ISSN/ISBN: 0195-9131 PMID: 9000158 Document Number: 474793
To determine whether chronological age, independent of changes in aerobic capacity, alters cardiac output ( ovrhdot Q-c), the central hemodynamic responses to intermittent incremental cycle exercise were studied in two groups of men. ovrhdot Q-c was measured at rest and during exercise at 35%, 60%, 75%, and 85% peak aerobic capacity ( ovrhdot VO-2peak) using a CO-2 rebreathing method in seven trained older (65 +- 2 yr) and eight normally active but untrained young men (26 +- 1 yr) matched for ovrhdot VO-2peak and anthropometric measures. Subjects were tested in both a thermoneutral (22 degree C) and a warm (36 degree C) environment to investigate possible differential cardiovascular responses to exercise in the heat. Only subjects with no history of pulmonary, cardiac, neuromuscular, or endocrine disease and a normal electrocardiogram were studied. The older men had significantly lower (P lt 0.05) ovrhdot Q-c relative to the younger men at intensities greater than 60% ovrhdot VO-2peak in both environmental conditions. At these higher intensities, the older men had a significantly higher stroke volume (SV) and lower heart rate (HR) (P lt 0.05). A higher arteriovenous oxygen difference ((a- hivin v)O-2)) compared with their younger counterparts enabled the older men to exercise at the same absolute intensity, most likely because of training induced changes in left-ventricular performance and oxygen extraction. The addition of an exogenous heat source did not alter the ovrhdot Q-c response in either group of men; however, a higher HR (P lt 0.05) and smaller SV (P gt 0.05) were observed in the young men during exercise in the heat. This may reflect previously reported differences in the skin blood flow response of ovrhdot VO-2peak-matched young and older men during exercise. It is suggested that endurance trained older men can enhance left-ventricular performance to augment SV, but not sufficiently to maintain ovrhdot Q-c in light of an attenuated HR response during exercise at intensities above 60% ovrhdot VO-2peak.