Anders T. Nygren

Frank LR

Haseler LJ

Lawrence R. Frank

Luke J. Haseler

Piiper J.

Russell S. Richardson

Sahlin K.

Stefan Bluml

Wong EC

 A noninvasive magnetic resonance imaging (MRI) method to assess the distribution of perfusion and metabolic demand (Q˙/V˙o 2) in exercising human skeletal muscle is described. This method combines two MRI techniques that can provide accurate multiple localized measurements of Q˙/V˙o 2 during steady-state plantar flexion exercise. The first technique,31P chemical shift imaging, permits the acquisition of comparable phosphorus spectra from multiple voxels simultaneously. Because phosphocreatine (PCr) depletion is directly proportional to ATP hydrolysis, its relative depletion can be used as an index of muscle O2 uptake (V˙o 2). The second MRI technique allows the measurement of both spatially and temporally resolved muscle perfusion in vivo by using arterial spin labeling. Promising validity and reliability data are presented for both MRI techniques. Initial results from the combined method provide evidence of a large variation in Q˙/V˙o 2, revealing areas of apparent under- and overperfusion for a given metabolic turnover. Analysis of these data in a similar fashion to that employed in the assessment of ventilation-to-perfusion matching in the lungs revealed a similar second moment of the perfusion distribution and PCr distribution on a log scale (log SDQ˙ and log SDPCr) (0.47). Modeling the effect of variations in log SDQ˙ and log SDPCr in terms of attainable V˙o 2, assuming no diffusion limits, indicates that the log SDQ˙ and log SDPCr would allow only 92% of the targetV˙o 2 to be achieved. This communication documents this novel, noninvasive method for assessingQ˙/V˙o 2, and initial data suggest that the mismatch in Q˙/V˙o 2 may play a significant role in determining O2 transport and utilization during exercise. </jats:p

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Journal of Applied Physiology

Local perfusion and metabolic demand during exercise: a noninvasive MRI method of assessment

Local perfusion and metabolic demand during exercise: a noninvasive MRI method of assessment

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