EFFECT OF GRADED CHANGES IN EXTRACELLULAR MUSCLE VOLUME ON CARDIOVASCULAR DRIVES DURING STATIC EXERCISE

The effects of graded changes in peripheral extracellular volume on he art rate and blood pressure during isometric exercise were studied in 12 healthy male subjects. Each subject performed four calf ergometer t ests with each calf. In all tests, static plantar flexion of one foot was performed in a supine body position with the knee joint flexed to 90-degrees. After a pre-exercise period of 18 min, during which the ca lf volume was manipulated, the subjects had to counteract a spring for ce of 120 N for 8 min. In the pre-exercise period the peripheral extra cellular volume of the calf muscle to be tested was manipulated in fou r ways. Test 1: 15 min of rest in the exercise position. During the la st 3.5 min, the calf volume was increased by venous congestion [80 mmH g (10.67 kPa) applied to the distal part of the thigh by pneumatic cuf f]. Test 2: the same protocol as in test 1 but with 7.5-min venous con gestion. Test 3: 15 min of venous congestion. Test 4: the calf volume was decreased by a negative hydrostatic pressure for 15 min (calf rais ed about 40 cm above heart level). To clamp the changed calf volume, t he thigh cuff was rapidely inflated to 300 mmHg (40.0 kPa) at the end of the volume manipulation and the subjects remained resting for a fur ther 3 min. In test 4, the leg of the subject was passively brought in to the exercise position. The occlusion was maintained until 2 min aft er exercise. The calf volume manipulation led to changes ranging from +105 ml (test 3) to -134 ml (test 4) as measured by water displacement plethysmography. The blood pressure response to exercise was inversel y related to the calf volume changes while the heart rate response dur ing exercise showed no clearcut relationship to the pretreatments.