COMPARISON OF ARTERIAL-OCCLUSION AND ISCHEMIC EXERCISE FOR THE STUDY OF VASODILATATION IN THE HUMAN CALF

1. Calf blood flow was measured by venous occlusion plethysmography to compare two stimuli for eliciting maximal calf vascular conductance: (i) 10 min of arterial occlusion and (ii) isolated exhaustive calf exe rcise with ischaemic occlusion, The subjects were semi-supine with the calf in position for immediate blood flow measurements after release of the occluding cuff, Three groups of subjects were studied: young [3 5 years (SD 9, n=9)], old [57 years (SD 5, n=10)] and patients with co ngestive heart failure [63 years (SD 7, n=7)]. 2. Occlusion and ischae mic exercise were equally effective in producing maximal calf vascular conductance in each of the subject groups, Maximal calf vascular cond uctance (ml min(-1) 100 ml(-1)mmHg(-1)) was equivalent in the young [i schaemic exercise 0.54 (SEM 0.03), occlusion 0.54 (SEM 0.05)] and old [ischaemic exercise 0.47 (SEM 0.05), occlusion 0.48 (SEM 0.04)] subjec ts, However, patients with congestive heart failure exhibited signific antly reduced maximal calf vascular conductance [ischaemic exercise 0. 20 (SEM 0.02), occlusion 0.20 (SEM 0.01)]. 3. Analysis of the curves, generated by plotting serial calf vascular conductance values obtained immediately and every 15s after occlusion cuff release for 165s, reve aled differences in the pattern of vasodilatation after occlusion and ischaemic exercise, Maximal calf vascular conductance was more sustain ed after ischaemic exercise, and the shape of the calf vascular conduc tance curve was similar in all subject groups, After occlusion in the patients with congestive heart failure, maximal calf vascular conducta nce occurred at 6s (SEM 3) after cuff release and declined rapidly, wh ereas, in the healthy subjects, calf vascular conductance increased af ter the first measurement, with maximal calf vascular conductance at 2 0s (SEM 4) in the old and 27s (SEM 6) in the young groups, The time de lay for maximal calf vascular conductance in the healthy subjects is c onsistent with a velocity-mediated proximal arterial dilatation, and t he rapid decline in the patients with congestive heart failure may ref lect sympathetic vasoconstriction and endothelial dysfunction. 4. In c onclusion, both occlusion and ischaemic exercise are equally useful fo r the determination of vasodilatory capacity of the human calf, The pr olonged vasodilatation after ischaemic exercise allows more time for t he measurement of maximal calf vascular conductance. However, analysis of the entire calf vascular conductance recovery curve after occlusio n provides more information on the relative contributions of factors w hich sustain vasodilatation after a maximal stimulus.