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Purpose: Beyond the initial cardiodynamic "Phase I," pulmonary oxygen uptake ([latin capital V with dot above]O2) kinetics are dictated largely by, and resemble closely, the [latin capital V with dot above]O2 of the exercising muscles ([latin capital V with dot above]O2m). Within those muscles, the microcirculation is responsible for affecting almost all blood-myocyte O2 transfer, and thus, observations at this site may provide key insights into muscle oxidative function in health and dysfunction in disease.

Methods: Recently, a novel combination of microscopy and phosphorescence quenching techniques has been utilized to understand the dynamics of microvascular O2 delivery ([Latin capital letter Q with dot above]O2m) and muscle O2 utilization ([latin capital V with dot above]O2m) at the onset of muscle contractions.

Results: These experiments have addressed longstanding questions regarding the site of control of [latin capital V with dot above]O2m kinetics and provide a first look at capillary hemodynamics at exercise onset in healthy muscle and their derangements resulting from chronic diseases such as heart failure and diabetes.

Conclusion: This paper will review these novel findings within our current understanding of microcirculatory control and blood-myocyte O2 transfer.

(C)2005The American College of Sports Medicine