Spinotrapezius muscle microcirculatory function: effects of surgical exteriorization

Intravital microscopy facilitates insights into muscle microcirculatory structural and functional control, provided that surgical exteriorization does not impact vascular function. We utilized a novel combination of phosphorescence quenching, microvascular oxygen pressure (microvascular Po-2), and microsphere (blood flow) techniques to evaluate static and dynamic behavior within the exposed intact (I) and exteriorized (EX) rat spinotrapezius muscle. I and EX muscles were studied under control, metabolic blockade with 2,4-dinitrophenol (DNP), and electrically stimulated conditions with 1-Hz contractions, and across switches from 21 to 100% and 10% inspired O-2. Surgical preparation did not alter spinotrapezius muscle blood flow in either I or EX muscle. DNP elevated muscle blood flow similar to 120% (P< 0.05) in both I and EX muscles (P> 0.05 between I and EX). Contractions reduced microvascular Po-2 from 30.4 +/- 4.3 to 21.8 +/- 4.8 mmHg in I muscle and from 33.2 +/- 3.0 to 25.9 +/- 2.8 mmHg in EX muscles with no difference between I and EX. In each O-2 condition, there was no difference (each P> 0.05) in microvascular Po-2 between I and EX muscles (21% O-2 :I = 37 +/- 1; EX = 36 +/- 1; 100%: I = 62 +/- 5; EX = 51 +/- 9; 10%: I = 20 +/- 1; EX = 17 +/- 2 mmHg). Similarly, the dynamic behavior of microvascular Po-2 to altered inspired O-2 was unaffected by the EX procedure [half-time (t(1/2)) to 100% O-2 :I = 23 +/- 5; EX = 23 +/- 4; t(1/2) to 10%: I = 14 +/- 2; EX = 16 +/- 2 s, both P> 0.05]. These results demonstrate that the spinotrapezius muscle can be EX without significant alteration of microvascular integrity and responsiveness under the conditions assessed.