Interstitial muscle fluid
Springer Online Journal Archives 1860-2000
Summary The volume of interstitial fluid in the limbs varies considerably, due to hydrostatic effects. As signals from working muscle, responsible for much of the cardiovascular drive, are assumed to be transmitted in this compartment, blood pressure and heart rate could be affected by local or systemic variations in interstitial hydration. Using a special calf ergometer, eight male subjects performed rhythmic aerobic plantar flexions in a supine position with dependent calves for periods of 7 min. During exercise heart rate, blood pressure, oxygen uptake (VO2) and blood lactate concentrations were measured in two different tests, one before and after interstitial calf dehydration through limb elevation for 25 min, compared to the other, a control with unaltered fluid volume in a maintained working position. Impedance plethysmography showed calf volume to be stabilized in the control position. Leg elevation by passive hip flexion to 90° resulted in a fast (vascular) volume decrease lasting 〈2 min, followed by a slow linear fluid loss from the interstitial compartment. Then, when returned to the control position, adjustment of vascular volume was completed within 2 min and exercise could be performed with dehydration remaining in the interstitium only. Cadiovascular response was identical at the start of both tests. However, exercising with dehydrated calves elicited a significantly larger increase in heart rate compared to the control, whereasVO2 was identical. The blood pressure response was shown to be only slightly enhanced. Structural interstitial features varying with hydration, most likely chemical or mechanical ones, may have been responsible for this amplification of signals.
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