Received December 13, 2006
Revised December 14, 2006
Accepted after revision December 14, 2006
Human, Environmental & Exercise [250]
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Oxygen exchange in the young and old:
muscle-vascular-pulmonary coupling
D.C. Poole 1*
Leonardo F. Ferreira 1
1 Kansas State University
* To whom correspondence should be addressed. E-mail: poole{at}vet.ksu.edu.
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Abstract |
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Sustained performance of muscular exercise is contingent upon increasing muscle O2 delivery [QO2; the product of blood flow and arterial O2 content, i.e., QxCaO2) and utilization (VO2m) rapidly at exercise onset and sustaining necessary conductive and diffusive O2 fluxes throughout exercise. A tight coordination of pulmonary, cardiovascular and muscle system responses is therefore required to prevent muscle microvascular O2 pressures (PO2mv) from falling to levels that impair blood-muscle O2 exchange and/or impact metabolic control and reduce exercise tolerance. Microvascular O2 pressures are determined by the balance between QO2 (QCaO2) and VO2m and emerging evidence indicates that this balance is regulated differently across muscle fibre types and also in aged muscle. Moreover disease states such as diabetes (Type I and II) and chronic heart failure (CHF) also impact PO2mv. This brief review examines primarily evidence obtained in animals for ageing: 1. redistributing exercising QO2 (QCaO2) away from highly oxidative muscles and muscle fibers, 2. altering muscle capillary hemodynamics, and 3. reducing the O2 pressure head within the microcirculation (PO2mv) that serves to facilitate blood-muscle O2 transfer. In many respects, these alterations found in healthy ageing bear a striking resemblance to those present in some chronic diseases (e.g. diabetes, CHF) and may help explain the compromised exercise tolerance present in aged individuals. Putative mechanistic insights are explored within the context of current knowledge and future investigative approaches.
Key Words:
Exercise, Microcirculation, Oxygen
