The roles of the mode of contraction (i.e., dynamic or static) and the active muscle mass as determinants of the cardiovascular responses to exercise were studied. Six healthy men performed static handgrip (SHG), dynamic handgrip (DHG), static two-knee extension (SKE), and dynamic two-knee extension (DKE) to local muscular fatigue in approximately 6 min. Increases in mean arterial pressure were similar for each mode of contraction, 29 +/- 5 and 30 +/- 3 mmHg in SHG and DHG and 56 +/- 2 and 48 +/- 2 mmHg in SKE and DKE (P greater than 0.05) but larger for KE than HG (P less than 0.001). Cardiac output increased more for dynamic than for static exercise and for each mode more for KE than HG (P less than 0.001). Systemic resistance was lower for dynamic than static exercise and fell from resting levels by approximately 1/3 during DKE. The magnitude of the pressor response was related to the active muscle mass but independent of the contraction mode. However, the mode of contraction affected the circulatory changes contributing to the pressor response. Equalization of the pressor responses was achieved by proportionately larger increases in cardiac output during dynamic exercise.
The roles of absolute and relative oxygen uptake (VO2 and percent of muscle group specific VO2 max) as determinants of the cardiovascular and ventilatory responses to exercise over a wide range of active muscle mass have not previously been defined. Six healthy men performed four types of dynamic exercise--one-arm curl, one-arm cranking, and one- and two-leg cycling at four different relative work loads--25, 50, 75, and 100% of VO2 max for the corresponding muscle group. VO2 during maximal one-arm curl, one-arm cranking, and one-leg cycling averaged 20, 50, and 75%, respectively, of that for maximal two-leg cycling. Cardiac output was linearly related to VO2 with a similar slope and intercept for each type of exercise. Heart rate at a given %VO2 max was higher with larger active muscle mass. In relation to %VO2 max, systemic resistance was lower and plasma catecholamine levels were higher with larger active muscle mass. The cardiovascular responses to exercise are determined to a large extent by the active muscle mass and the absolute oxygen uptake, with the principal feature appearing to be the tight linkage between systemic oxygen transport and utilization.
Hypertensive nephrosclerosis is a progressive renal disease and the leading cause of end-stage renal disease (ESRD) in blacks in the United States. It is generally believed that hypertensive renal injury is responsible for progressive renal failure; however, it is not known whether pharmacologic lowering of blood pressure to any level prevents progression of renal disease. Accordingly, we performed a long-term prospective randomized trial to determine whether "strict" [diastolic blood pressure (DBP) 65 to 80 mm Hg] versus "conventional" (DBP 85 to 95 mm Hg) blood pressure control is associated with a slower rate of decline in glomerular filtration rate. Eighty-seven non-diabetic patients (age 25 to 73; 68 black, 58 male) with long-standing hypertension (DBP > or = 95 mm Hg), chronic renal insufficiency (GFR < or = 70 m/min/1.73 m2) and a normal urine sediment were studied. DBP was pharmacologically lowered to < or = 80 mm Hg (3 of 4 consecutive measurements at 1 to 4 weeks intervals) after which patients were randomized. DBP and GFR (renal clearance of 125I-iothalamate) were measured at baseline, at three months and every six months post-randomization. The rate of decline in GFR (GFR slope, in ml/min/1.73 m2/year), estimated by the method of maximum likelihood in a mixed effects model, was the primary outcome variable. In a secondary analysis, 50% reduction in GFR (or a doubling of serum creatinine) from baseline, ESRD and death were combined.(ABSTRACT TRUNCATED AT 250 WORDS)
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