Absence Of A Slow Component Of Pulmonary VO2 Kinetics In Very Old Subjects

Abstract

0099 PURPOSE: The effects of aging on skeletal muscle oxidative metabolism, and in particular on O2 uptake (VO2) kinetics were evaluated in 28 elderly (E) (78.1±3.8 yrs, mean±SD) and 7 young (Y) (28.4±5 yrs) subjects. METHODS: After an incremental exercise to voluntary exhaustion on a cycloergometer, to evaluate peak VO2 and ventilatory threshold (VT), the subjects carried out 6 min constant-load exercises below (<VT) and above VT (>VT). Pulmonary VO2 was determined breath-by-breath. Vastus lateralis oxygenation was determined by near-infrared spectroscopy, and changes in deoxygenated hemoglobin + myoglobin concentration Δ[deoxy(Hb+Mb)] were taken as a muscle oxygenation index. Vastus lateralis surface electromyography (EMG) was also recorded. RESULTS: VO2peak in E (1.188±0.37 L·min −1) was about 50% lower (p<0.001) than in Y (2.404±0.80 L·min−1). The time constant of the primary component of VO2 kinetics was higher (p<0.05) in E than in Y, both <VT (46.29±14.8 vs. 31.59±8.3 s) and >VT (59.67±17.3 vs. 33.04±4.3 s). Differently from Y, E did not show a slow component of VO2 kinetics for >VT. The root mean square (RMS) calculated from the EMG signal was positively related to time in both groups during >VT; during <VT, RMS was positively related to time only in E. A slow component of Δ[deoxy(Hb+Mb)] kinetics, during >VT, was observed in 5 Y and in 1 E. CONCLUSIONS: We confirm the lower VO2peak and slower VO2 kinetics with aging. Elderly subjects do not show a slow component of VO2 kinetics during constant-load exercise >VT, even in the presence of EMG signs of fatigue. This could be explained by a preferential atrophy of type II fibers, or to a reduced differentiation between fiber types in aging. Financial support by EC Contract QLK6-CT-2001-00323 (“Better-Ageing”) is acknowledged.