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J Appl Physiol 93: 227-232, 2002. First published January 18, 2002; doi:10.1152/japplphysiol.00735.2001
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Vol. 93, Issue 1, 227-232, July 2002

Dynamics of microvascular oxygen pressure in the rat diaphragm

Crystal M. Geer, Brad J. Behnke, Paul McDonough, and David C. Poole

Departments of Kinesiology, Anatomy and Physiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas 66506-5802

The relative amplitudes and rates of increase of muscle blood flow (and O2 delivery) and O2 uptake responses determine the O2 pressure within the muscle microvasculature (PmO2) across the rest-to-contraction transition. Skeletal muscle function is a primary determinant of pulmonary O2 uptake kinetics; however, it has never been determined whether the dynamics of muscle PmO2 are faster in a highly oxidative muscle [e.g., diaphragm (Dia), citrate synthase activity of 39 µmol · min-1 · g-1] compared with less oxidative muscles [e.g., spinotrapezius (Spino), citrate synthase activity of 14 µmol · min-1 · g-1, male Sprague-Dawley rats; Delp MD and Duan C, J Appl Physiol 80: 261-270, 1996]. Phosphorescence quenching techniques (porphyrin dendrimer, R2) were used to determine PmO2 across the transition to electrically stimulated contractions (1 Hz) within the rat Dia. After a delay of 10.4 ± 1.3 (SE) s at the beginning of Dia contractions, PmO2 decreased close to monoexponentially from 42 ± 2 to 27 ± 3 Torr (P < 0.05) with an extremely fast time constant of 7.1 ± 1.1 s. Thus Dia PmO2 decreased with significantly (P < 0.05) faster kinetics than reported previously for the Spino muscle (delay, 19.2 ± 2.8 s; time constant PmO2, 21.7 ± 2.1 s; Behnke BJ, Kindig CA, Musch TI, Koga S, and Poole DC, Respir Physiol 126: 53-63, 2001). With the use of two specialized muscles with similar fiber-type composition but widely disparate oxidative capacities (Delp MD and Duan C, J Appl Physiol 80: 261-270, 1996), these data demonstrate that PmO2 kinetics are significantly faster in the highly oxidative Dia compared with the low-oxidative Spino muscle and that this effect is not dependent on muscle fiber-type composition.

oxygen uptake kinetics; spinotrapezius; microvascular oxygen exchange


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