Maximal muscular vascular conductances during whole body upright exercise in humans

Abstract

That muscular blood flow may reach 2.5 l kg(-1) min(-1) in the quadriceps muscle has led to the suggestion that muscular vascular conductance must be restrained during whole body exercise to avoid hypotension. The main aim of this study was to determine the maximal arm and leg muscle vascular conductances (VC) during leg and arm exercise, to find out if the maximal muscular vasodilatory response is restrained during maximal combined arm and leg exercise. Six Swedish elite cross-country skiers, age (mean +/-s.e.m.) 24 +/- 2 years, height 180 +/- 2 cm, weight 74 +/- 2 kg, and maximal oxygen uptake (VO(2,max)) 5.1 +/- 0.1 l min(-1) participated in the study. Femoral and subclavian vein blood flows, intra-arterial blood pressure, cardiac output, as well as blood gases in the femoral and subclavian vein, right atrium and femoral artery were determined during skiing (roller skis) at approximately 76% of VO(2,max) and at VO(2,max) with different techniques: diagonal stride (combined arm and leg exercise), double poling (predominantly arm exercise) and leg skiing (predominantly leg exercise). During submaximal exercise cardiac output (26-27 l min(-1)), mean blood pressure (MAP) (approximately 87 mmHg), systemic VC, systemic oxygen delivery and pulmonary VO2(approximately 4 l min(-1)) attained similar values regardless of exercise mode. The distribution of cardiac output was modified depending on the musculature engaged in the exercise. There was a close relationship between VC and VO2 in arms (r= 0.99, P < 0.001) and legs (r= 0.98, P < 0.05). Peak arm VC (63.7 +/- 5.6 ml min(-1) mmHg(-1)) was attained during double poling, while peak leg VC was reached at maximal exercise with the diagonal technique (109.8 +/- 11.5 ml min(-1) mmHg(-1)) when arm VC was 38.8 +/- 5.7 ml min(-1) mmHg(-1). If during maximal exercise arms and legs had been vasodilated to the observed maximal levels then mean arterial pressure would have dropped at least to 75-77 mmHg in our experimental conditions. It is concluded that skeletal muscle vascular conductance is restrained during whole body exercise in the upright position to avoid hypotension.

Figure 1. Position and function of the catheters

All catheters were sutured to the skin.

Figure 2. Experimental protocol

Speed and inclination of the treadmill during roller skiing. The order in which the different skiing techniques were applied is illustrated in the lower part of the figure.

Figure 3. Oxygen delivery and oxygen uptake

Systemic (horizontally hatched bars), leg (filled bars) and arm (diagonally hatched bars) O₂ delivery and V̇_O2 during exercise with arms and legs (Diagonal), with double poling (predominantly arms: P. Arms), with only legs (Legs) and maximal exercise with the diagonal technique (Diagonal Max). §P < 0.05 compared to double poling; ‡P < 0.05 compared with leg skiing.

Figure 4. Blood flow, arterial pressure and vascular conductances

A, cardiac output (white bars), leg blood flow (grey bars) and arm blood flow (black bars). B, arterial blood pressures at the level of the right atrium: systolic (white bars), mean (grey bars) and diastolic (black bars). C, systemic vascular conductance (white bars), leg vascular conductance (grey bars) and arm vascular conductance (black bars), during exercise with arms and legs (diagonal), with double poling (predominantly arms: P. Arms), with only legs (legs) and maximal exercise with the diagonal technique (Diagonal Max). §P < 0.05 compared to double poling; ‡P < 0.05 compared with leg skiing.

Figure 5. Relationship between limb vascular conductance and V̇_O2

Vascular conductance values adjusted for V̇_O2 were significantly higher for the upper than for the lower extremity. This difference disappeared after accounting for differences in O₂ extraction between upper and lower extremities.