In vivo microvascular structural and functional consequencesof
muscle length changes.
Poole, David C., Timothy I. Musch, and Casey A. Kindig.
Departments of Kinesiology and Anatomy/Physiology, Kansas State
University,
APStracts 3:0436H, 1996.
As muscles are stretched, blood flow and oxygen delivery are
compromised and consequently muscle function is impaired. We tested
the hypothesis that the structural microvascular sequellae associated
with muscle extension in vivo would impair capillary red blood cell
hemodynamics. An intravital spinotrapezius preparation was developed
which facilitated direct on-line measurement and alteration of
sarcomere length simultaneously with determination of capillary
geometry and red blood cell flow dynamics. The range of
spinotrapezius sarcomere lengths achievable in vivo was 2.17+0.05 to
3.13+0.11 [mu]m. Capillary tortuosity decreased systematically with
increases of sarcomere length up to 2.6 [mu]m at which point most
capillaries appeared to be highly oriented along the fiber
longitudinal axis. Further increases in sarcomere length above this
reduced mean capillary diameter from 5.61+0.03 [mu][mu] at 2.4-2.6
[mu][mu] sarcomere length to 4.12 +0.05[mu][mu] at 3.2-3.4 [mu]m
sarcomere length. Over the range of physiological sarcomere lengths,
bulk blood flow (radioactive microspheres) decreased 40% from
24.3+7.5 to 14.5+4.6 ml/100 g/ min. The proportion of continuously
perfused capillaries i.e., those with continuous flow throughout the
60 s observation period decreased from 95.9 +0.6% at the shortest
sarcomere lengths down to 56.5 +0.7% at the longest sarcomere lengths
and was correlated significantly with the reduced capillary diameter
(r = 0.711, P<0.01, n = 18). We conclude that alterations in
capillary geometry and luminal diameter consequent to increased
muscle sarcomere length are associated with a reduction in mean
capillary red blood cell velocity and a greater proportion of
capillaries in which red blood cell flow is stopped or intermittent.
Thus, not only does muscle stretching reduce bulk blood (and oxygen)
delivery, but it alters capillary red blood cell flow dynamics which
may further impair blood-tissue oxygen exchange.
Received 24 April 1996; accepted in final form 25 September 1996.
APS Manuscript Number H367-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996