Exercise gas transport determinants in elderly normotensive and hypertensive humans

This study examined the effect of the phenylalkylamine calcium channel bloc ker verapamil, on resting left ventricular (LV) function and O-2 uptake rat e ((V) over dot (O2)) during exercise at maximal and submaximal work rates. Nine older hypertensive (71 years; OH), 10 older sedentary normotensive (6 9 years; OS), 10 older active (71 years; OA) and 10 young (24 years; Y) ind ividuals 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 iso volumic relaxation time (IVRT)) were measured by Doppler echocardiography. Maximal oxygen uptake ((V) over dot (O2,) (max)) and, on subsequent test da ys, four transitions to and from a 6 min square wave exercise perturbation ata sub-anaerobic threshold intensity of 40 W (OH, OS, OA) or 100 W (Y) for determination of (V) over dot (O2) kinetics were performed on a cycle ergo meter. Breath-by-breath (V) over dot (O2) transients were fitted with a mon oexponential equation, starting at phase 2 of the response, while heart rat e (HR) was fitted from phase 1, for the determination of the time constant of (V) over dot (O2) (tau(V) over dot (O2)) and HR (tau HR). 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) over dot (O2, max) was higher and tau(V) over dot (O2) faster in the young (41.4 ml kg(-1) min(-1); 25.2 s) than in the older grou ps 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 59.5 s) groups (P < 0.05 ). Heart rate kinetics showed similar differences to (V) over dot (O2) kine tics among the groups. After verapamil, no significant changes in FS, E/A o r 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 0.0 7; 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) over dot (O2,) (max) tau( V) over dot (O2) or tau HR) were altered for the OA or Y groups. (V) over d ot (O2, max) increased (from 20.8 to 22.8 ml kg(-1) min(-1)) in the OH and (from 22.0 to 24.1 ml kg(-1) min(-1)) in the OS (P < 0.05). tau(V) over dot (O2) was accelerated from 71.3 to 49.2 s in the OH group and from 59.5 to 48.2 s in the OS group (P < 0.05). These results suggest that (V) over dot (O2) responses at maximal and submaximal work rates may be dependent upon t he initial cardiac pump function of the study population.