title: Two zero-flow pressure intercepts exist in autoregulating isolated skeletal muscle.
abstract: The autoregulating vascular bed of the isolated canine extensor digitorum longus muscle was investigated for the possible existence of two positive zero-flow pressure axis intercepts, a tone-dependent one and a tone-independent one. An isolated preparation, perfused with autologous blood, was used to exclude effects of collateral flow and nervous and humoral regulation while autoregulation was left intact [mean autoregulatory gain 0.50 +/- 0.24 (SD)]. In a first series of experiments, the steady-state (zero flow) pressure axis intercept [mean 8.9 +/- 2.6 (SD) mmHg, tone independent] and the instantaneous (zero flow) pressure axis intercept [mean 28.5 +/- 9.9 (SD) mmHg, tone dependent] were determined as a function of venous pressure (range: 0-45 mmHg) and were independent of venous pressure until the venous pressure exceeded their respective values. Beyond this point the relations between the venous pressure and the steady-state and instantaneous pressure axis intercept followed the line of identity. The findings agree with the predictions of the vascular waterfall model. In a second series it was shown by means of administration of vasoactive drugs that the instantaneous pressure axis intercept is tone dependent, whereas the steady-state pressure axis intercept is not. It is concluded that there is a (proximal) tone-dependent zero-flow pressure at the arteriolar level and a (distal) tone-independent zero-flow pressure at the venous level.
authors.affiliation: Laboratory for Physiology, Free University, Amsterdam, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Braakman
authors.forename: P
authors.initials: P
authors.lastname: Sipkema
authors.forename: N
authors.initials: N
authors.lastname: Westerhof
mesh_terms: D000818:Animals; D001794:Blood Pressure; D004285:Dogs; D004864:Equipment and Supplies; D006706:Homeostasis / Q000502:physiology*; D066298:In Vitro Techniques; D009132:Muscles / Q000098:blood supply* / Q000502:physiology; D010827:Physiology / Q000295:instrumentation; D012039:Regional Blood Flow; D014661:Vasoconstriction; D014664:Vasodilation; D014690:Venous Pressure