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Blood flow and pressure relationships which determine VO2max

BRECHUE WILLIAM F.; AMEREDES, BILL T.; BARCLAY, JACK K.; STAINSBY, WENDELL N.
Medicine & Science in Sports & Exercise: January 1995
BASIC SCIENCES/REGULATORY PHYSIOLOGY: Symposium: Mechanisms Which Control JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2 Near JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2max: PDF Only

ABSTRACT

The role of O2 delivery in regulating JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2max has been studied in an isolated gastrocnemius-plantaris muscle preparation contracting in situ; recent data addressing this issue are presented. JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2 increases nonlinearly with stimulation frequency reaching a peak at 5 twitches·s−1 or 1 tet·s−1 (200 ms trains, 50 imp·s−1). Further increases in stimulation frequency result in a lower JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2. Measured JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2 maxima are less than predicted JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2 capacity, and peak JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2 during tetanic contractions is greater than that during twitches. Above 150 imp·min−1, JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2 is directly related to the level of blood flow attained as JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2/JOURNAL/mespex/04.02/00005768-199501000-00008/ENTITY_OV0422/v/2017-07-20T222434Z/r/image-png (arterial-venous O2 difference) is fixed by some unknown mechanism. Increasing blood flow, with a pump, during 1·s−1 tetanic contractions increases O2 diffusive conductance and peak JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2. When O2 delivery is reduced, ischemic hypoxia appears to result in more rapid reductions in muscle performance than hypoxic hypoxia because of decreases in perfusion pressure and JOURNAL/mespex/04.02/00005768-199501000-00008/ENTITY_OV0422/v/2017-07-20T222434Z/r/image-png. 31P-NMR studies reveal that reductions in creatine phosphate and energy charge are similar between ischemia and hypoxia suggesting a common regulator, O2. We conclude that JOURNAL/mespex/04.02/00005768-199501000-00022/ENTITY_OV0312/v/2017-07-20T222434Z/r/image-pngO2max is limited by O2 delivery as a result of a limited and uneven distribution of muscle blood flow. These limitations appear secondary to mechanical restraints imposed by contraction duty cycle and vascular compression.

©1995The American College of Sports Medicine