Capillary hemodynamics and oxygen pressures in the aging microcirculation.

Healthy aging acts to redistribute blood flow (Q) and thus O2 delivery (QO2 ) among and within the exercising muscles such that QO2 to highly oxidative muscle fibers may be compromised. Within the microcirculation of old muscles capillary hemodynamics are altered and the matching of QO2 to oxidative requirements (VO2) is impaired such that at exercise onset the microvascular O2 pressure falls below that seen in their younger counterparts. This is important because the microvascular O2 pressure denotes the sole driving force for blood-myocyte O2 transfer and any compromise may slow VO2 kinetics and reduce exercise tolerance. This review considers the microcirculatory evidence for a reduced perfusive (QO2 ) and diffusive O2 flux within aged muscle and highlights the pressing need for intravital microscopy studies of the muscle microcirculation during exercise.