title: Dynamics of microvascular oxygen pressure in the rat diaphragm.
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.
authors.affiliation: Department of Kinesiology, College of Veterinary Medicine, Kansas State University, Manhattan 66506-5802, USA.
authors.forename: Crystal M
authors.initials: CM
authors.lastname: Geer
authors.forename: Brad J
authors.initials: BJ
authors.lastname: Behnke
authors.forename: Paul
authors.initials: P
authors.lastname: McDonough
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
mesh_terms: D000465:Algorithms; D000818:Animals; D002196:Capillaries / Q000502:physiology; D003964:Diaphragm / Q000098:blood supply* / Q000502:physiology*; D004558:Electric Stimulation; D004912:Erythrocytes / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006400:Hematocrit; D008163:Luminescent Measurements; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000502:physiology; D012121:Respiration, Artificial