Time-invariant oxygen cost of mechanical energy in dog left ventricle: consistency and inconsistency of time-varying elastance model with myocardial energetics.
We studied whether the oxygen cost of mechanical energy is time-invariant in the excised, cross-circulated canine heart. The total mechanical energy generated by ventricular contraction can be quantified by the total pressure-volume area (PVA) according to the time-varying elastance model. In this model, mechanical energy generated until a specified time (t) during systole can be quantified by the partial pressure-volume area, PVA(t). PVA(t) was obtained by quickly releasing ventricular volume at a varied time during isovolumic contraction. The quick release aborted further development of mechanical energy. We found that PVA(t) at a constant end-diastolic volume linearly correlated with myocardial oxygen consumption (VO2). This indicates that the oxygen cost of mechanical energy is time-invariant. However, we also found that the slope of the VO2-PVA(t) relation decreased with increasing quick-release speed. This indicates a decrease in VO2 by the quick release despite the same PVA(t). The time-invariant oxygen cost of mechanical energy is consistent with the time-varying elastance model of the ventricle, but the decreased VO2 with increasing quick-release speed despite the same PVA(t) is not.
Yasumura
Y
Y
Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan.
Nozawa
T
T
Futaki
S
S
Tanaka
N
N
Suga
H
H
D000818:Animals; D001696:Biomechanical Phenomena; D004285:Dogs; D004548:Elasticity; D006321:Heart / Q000502:physiology*; D008954:Models, Biological; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption; D013997:Time Factors