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  • Title: Dynamics of microvascular oxygen pressure in the rat diaphragm.
    Author: Geer CM, Behnke BJ, McDonough P, Poole DC.
    Journal: J Appl Physiol (1985); 2002 Jul; 93(1):227-32. PubMed ID: 12070209.
    Abstract:
    The relative amplitudes and rates of increase of muscle blood flow (and O(2) delivery) and O(2) uptake responses determine the O(2) pressure within the muscle microvasculature (Pm(O(2))) across the rest-to-contraction transition. Skeletal muscle function is a primary determinant of pulmonary O(2) uptake kinetics; however, it has never been determined whether the dynamics of muscle Pm(O(2)) are faster in a highly oxidative muscle [e.g., diaphragm (Dia), citrate synthase activity of 39 micromol. min(-1). g(-1)] compared with less oxidative muscles [e.g., spinotrapezius (Spino), citrate synthase activity of 14 micromol. 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 Pm(O(2)) 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, Pm(O(2)) 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 Pm(O(2)) decreased with significantly (P < 0.05) faster kinetics than reported previously for the Spino muscle (delay, 19.2 +/- 2.8 s; time constant Pm(O(2)), 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 Pm(O(2)) 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.
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