Exercise gas transport determinants in elderly normotensive and hypertensive humans

Abstract

This study examined the effect of the phenylalkylamine calcium channel blocker verapamil, on resting left ventricular (LV) function and O2 uptake rate (V(O2)) during exercise at maximal and submaximal work rates. Nine older hypertensive (71 years; OH), 10 older sedentary normotensive (69 years; OS), 10 older active (71 years; OA) and 10 young (24 years; Y) individuals volunteered. Studies were completed in the control condition and 4-6 h following 240 mg verapamil SR per os. Resting LV systolic (fractional shortening; FS) and diastolic (early:late (E/A) flow velocity ratio and isovolumic relaxation time (IVRT)) were measured by Doppler echocardiography. Maximal oxygen uptake (V(O2,max)) and, on subsequent test days, four transitions to and from a 6 min square wave exercise perturbation at a sub-anaerobic threshold intensity of 40 W (OH, OS, OA) or 100 W (Y) for determination of V(O2) kinetics were performed on a cycle ergometer. Breath-by-breath V(O2) transients were fitted with a monoexponential equation, starting at phase 2 of the response, while heart rate (HR) was fitted from phase 1, for the determination of the time constant of V(O2) (τV(O2)) and HR (τHR). Baseline left ventricular FS was significantly greater in the OS (32%), OA (34%) and Y (34%) than in the OH (23%) groups, while E/A was significantly greater in the OA (1.16) and Y (2.34) than in the OH (0.9) and OS (0.82) groups (P < 0.05). Baseline V(O2,max) was higher and τV(O2) faster in the young (41.4 ml kg-1 min-1; 25.2 s) than in the older groups and in the OA (28.8 ml kg-1 min-1; 44.3 s) than in both OH (20.8 ml kg-1 min-1; 71.3 s) and OS (22.0 ml kg-1 min-1; 59.5 s) groups (P < 0.05). Heart rate kinetics showed similar differences to V(O2) kinetics among the groups. After verapamil, no significant changes in FS, E/A or IVRT were observed in the OA and Y groups. In the OH group, FS (32%) and E/A (1.15) increased while IVRT decreased significantly (from 0.103 to 0.07; P < 0.05). In the OS group, only E/A increased significantly (0.82 to 1.0; P < 0.05). None of the exercise variables (V(O2,max), τV(O2) or τHR) were altered for the OA or Y groups. V(O2,max) increased the OS group responses at maximal and submaximal work rates may be dependent upon the initial cardiac pump function of the study population.