TY - JOUR
T1 - Biphasic changes in maximum relaxation rate during progressive hypoxia in isometric kitten papillary muscle and isovolumic rabbit ventricle
AU - St. John Sutton, M. G.
AU - Ritman, E. L.
AU - Paradise, N. F.
N1 - Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 1980
Y1 - 1980
N2 - We studied the effects of graded hypoxia on mechanical performance of cardiac ventricular muscle by producing controlled, stepwise decreases in partial pressure of oxygen (Po2) in the medium bathing the kitten papillary muscle preparation and in the perfusate of the Langendorff-prepared rabbit heart. For kitten papillary muscle at 30°C and with stimulation rate at 30/min, maximum rate of contraction (+dT/dt[max]) and maximum rate of relaxation [-dT/dt(max)] were 184 ± 10 mN/mm2 per sec, and 162 ± 12 mN/mm2 per sec, respectively, during control conditions with Po2 at 634 ± 7 mm Hg. Step decreases in Po2 from 634 mm Hg produced decreases in steady state -dT/dt(max) that were significantly greater than corresponding decreases in +dT/dt(max), except at the lowest Po2. When Po2 (mm Hg ± SE) was 411 ± 10, 218 ± 4, and 92 ±3, steady state +dT/dt(max) vs. -dT/dt(max) (expressed as % of pre-hypoxia control value ± SE) were: 97 ± 4 vs. 85 ± 7, 76 ± 5 vs. 59 ± 6, and 47 ± 5 vs. 28 ± 4, respectively. When the lowest Po2 of 34 ± 6 mm Hg was achieved, considerable shortening of the duration of the mechanical cycle occurred, and values for +dT/dt(max) and -dT/dt(max) (expressed as % of pre-hypoxia control value ± SE) of 28 ± 7 and 21 ± 7 respectively, were not significantly different. Graded hypoxia similarly affected left ventricular isovolumic pressure developed by the coronary perfused rabbit heart. In both preparations, changes in relaxation relative to changes in contraction during progressive hypoxia were biphasic: decreases in maximum relaxation rate were disproportionately greater than decreases in maximum contraction rate with intermediate hypoxia, but the proportionality was restored when severe hypoxia produced a decrease in cycle duration.
AB - We studied the effects of graded hypoxia on mechanical performance of cardiac ventricular muscle by producing controlled, stepwise decreases in partial pressure of oxygen (Po2) in the medium bathing the kitten papillary muscle preparation and in the perfusate of the Langendorff-prepared rabbit heart. For kitten papillary muscle at 30°C and with stimulation rate at 30/min, maximum rate of contraction (+dT/dt[max]) and maximum rate of relaxation [-dT/dt(max)] were 184 ± 10 mN/mm2 per sec, and 162 ± 12 mN/mm2 per sec, respectively, during control conditions with Po2 at 634 ± 7 mm Hg. Step decreases in Po2 from 634 mm Hg produced decreases in steady state -dT/dt(max) that were significantly greater than corresponding decreases in +dT/dt(max), except at the lowest Po2. When Po2 (mm Hg ± SE) was 411 ± 10, 218 ± 4, and 92 ±3, steady state +dT/dt(max) vs. -dT/dt(max) (expressed as % of pre-hypoxia control value ± SE) were: 97 ± 4 vs. 85 ± 7, 76 ± 5 vs. 59 ± 6, and 47 ± 5 vs. 28 ± 4, respectively. When the lowest Po2 of 34 ± 6 mm Hg was achieved, considerable shortening of the duration of the mechanical cycle occurred, and values for +dT/dt(max) and -dT/dt(max) (expressed as % of pre-hypoxia control value ± SE) of 28 ± 7 and 21 ± 7 respectively, were not significantly different. Graded hypoxia similarly affected left ventricular isovolumic pressure developed by the coronary perfused rabbit heart. In both preparations, changes in relaxation relative to changes in contraction during progressive hypoxia were biphasic: decreases in maximum relaxation rate were disproportionately greater than decreases in maximum contraction rate with intermediate hypoxia, but the proportionality was restored when severe hypoxia produced a decrease in cycle duration.
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U2 - 10.1161/01.res.47.4.516
DO - 10.1161/01.res.47.4.516
M3 - Article
C2 - 7408130
AN - SCOPUS:0018958423
SN - 0009-7330
VL - 47
SP - 516
EP - 524
JO - Circulation research
JF - Circulation research
IS - 4
ER -