Local perfusion and metabolic demand during exercise: a noninvasive MRI method
of assessment.
Richardson, Russell S., Luke J. Haseler, Anders T. Nygren, Stefan Bluml, and Lawrence
R. Frank.
1Department of Medicine, University of California, San Diego, La Jolla, and 2San
Diego Veterans Administration Health Care System and Department of Radiology,
University of California, San Diego, La Jolla, California 92093«hyphen»0623; and
3Huntington Medical Research Institute, Pasadena
APStracts 8:0322A, 2001.
A noninvasive magnetic resonance imaging (MRI) method to assess the distribution of
perfusion and metabolic demand («odot»Q/«vo2») in exercising human skeletal muscle is
described. This method combines two MRI techniques that can provide accurate multiple
localized measurements of «odot»Q/«vo2» 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 («vo2»). 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 «odot»Q/«vo2», 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
SD«odot»Q and log SDPCr) (0.47). Modeling the effect of variations in log SD«odot»Q
and log SDPCr in terms of attainable «vo2», assuming no diffusion limits, indicates that
the log SD«odot»Q and log SDPCr would allow only 92% of the target «vo2» to be
achieved. This communication documents this novel, noninvasive method for assessing
«odot»Q/«vo2», and initial data suggest that the mismatch in «odot»Q/«vo2» may play a
significant role in determining O2 transport and utilization during exercise.
Received 5 October 2000; accepted in final form 16 April 2001
APS Manuscript Number A0956-0.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001