Spinotrapezius muscle microcirculatory function: effects of surgical exteriorization

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Abstract
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 O2. Surgical preparation did not alter spinotrapezius muscle blood flow in either I or EX muscle. DNP elevated muscle blood flow ∼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 O2condition, there was no difference (each P > 0.05) in microvascular Po 2 between I and EX muscles (21% O2: 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 O2 was unaffected by the EX procedure [half-time ( t 1/2) to 100% O2: 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.