Local Regulation of Effective Blood Flow in Muscle

Abstract

The techniques of macro- and micro-tissue clearance were used to study reactive hyperemia. Clearance of radioactive iodide from gross injection sites in muscles of rabbits and clearance of micro-injected diffusible dye from the exposed, directly observed spinotrapezius of rats gave evidence for an exact quantitative repayment of effective blood flow debt. In both types of preparation a subnormal clearance followed a thermally induced hyperemia as an apparent compensation. The exact quantitative repayment and compensation support the hypothesis that local effective blood flow is in a steady-state relation to the local concentration in tissue fluid of some agent with vasodilating properties. It is suggested that an extension of this method to studies of vasodilatation induced by drugs or other chemicals might offer an approach to identification of the normal vasodilator, and to physiological proof of its exact nature.

Muscle contraction increases interstitial nitric oxide as predicted by a new model of local blood flow regulation

“…These results are consistent with long‐known data on the increased washout rate following muscle contraction (Hyman & Paldino, ; Hyman et al . ). Washout of both the DAF‐FM and DAF‐T forms of the probe from the interstitial space was one of the reasons that impaired the quality of the signal in repeated cycles of measurement.…”

“…The fluorescent probe DAF-FM cannot penetrate the cell membrane and is distributed only throughout the interstitial space of a muscle. The concentration of the low molecular weight dye in the interstitial space of a muscle decreases with time because of indicator washout (clearance), which in the spinotrapezius muscle is reported to be a simple mono-exponential process (Hyman & Paldino, 1962;Hyman et al 1963). It is important to note that both weakly and strongly fluorescent DAF-FM forms undergo washout from the interstitium, which complicates the prediction of the time course of fluorescence during a bout of muscle contraction.…”

Evidence for the shift of blood to the nutritive circulation during reactive hyperaemia

“…constriction of shunts is not sufficient to compensate for the dilatation of the other vessels. Hyman et al (1963) pointed out that 'over-payment' of ischaemic debt measured as total flow is observed more often where the initial blood flow is low, perhaps confined to nutritional vessels; the hyperaemic excess would then reflect the opening of shunts in response to the locally formed dilator. This question is not yet resolved.…”

“…However, two alternative explanations are possible: (1) because plethysmographic measurements of total blood flow include both skin and muscle perfusion, the total may be held at control level, though muscle blood flow increases to remove the local dilator by diversion from the skin. This hypothesis requires that all the measured hyperaemia occurs in muscle and that there be no reactive hyperaemia in the previously ischaemic skin; or (2) that during the period of restricted total blood flow the perfusion of the nutritional circulation in muscle increases at the expense of a shunt, or by-pass, circulation (Hyman, Paldino & Zimmermann, 1963).…”

Observations on the Role of Diminished Oxygen Tension in the Functional Hyperemia of Skeletal Muscle

“…87 When tissue clearance techniques are used, however, a quantitative relationship between blood flow deficit and repayment appears to exist. 38 Therefore, to what extent a single, as yet unidentified vasoactive agent, or a combination of humoral stimuli, perhaps including lowered oxygen tension per se, contribute to functional hyperemia remains uncertain. As recently pointed out by Zweifach, the only vessels available to local metabolites are the precapillaries and metarterioles.…”