Hypercapnic acidosis increases oxygen cost of contractility in the dog left ventricle.
The effect of acidosis on left ventricular (LV) mechanoenergetics was assessed in seven excised, cross-circulated dog hearts with the use of the frameworks of the contractility index (Emax) and the relationship between myocardial oxygen consumption (VO2) and pressure-volume area (PVA; a measure of the LV total mechanical energy). Acidosis was stably maintained without hypoxia by appropriately mixing CO2 and air in a membrane oxygenator in the coronary arterial perfusion circuit. Acidosis [pH: 6.98 +/- 0.09 (SD), PCO2: 91 +/- 25 mmHg in the coronary arterial blood] decreased Emax by 45 +/- 12% (P < 0.01) and PVA by 47 +/- 12% (P < 0.01) at a fixed LV volume. When the preacidosis Emax level was restored by Ca2+ infusion during acidosis, unloaded VO2 (the VO2 intercept of the VO2-PVA relation) exceeded the control value by 19 +/- 17% (P < 0.05), indicating that acidosis required higher VO2 for nonmechanical activities at a matched Emax. Moreover, the oxygen cost of enhanced contractility (the incremental ratio of unloaded VO2 to Emax) was 1.53 +/- 0.40 times higher (P < 0.01) during acidosis than preacidosis. We conclude that acidosis results in LV contractile dysfunction accompanied by an increased oxygen cost of contractility. This increased energy cost of the excitation-contraction coupling can be accounted for by a decreased Ca2+ sensitivity of the contractile proteins during acidosis.
Hata
K
K
Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan.
Goto
Y
Y
Kawaguchi
O
O
Takasago
T
T
Saeki
A
A
Nishioka
T
T
Suga
H
H
D000138:Acidosis / Q000503:physiopathology*; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood*; D002395:Catecholamines / Q000097:blood / Q000378:metabolism; D003326:Coronary Circulation; D003331:Coronary Vessels / Q000502:physiology* / Q000503:physiopathology; D004285:Dogs; D004562:Electrocardiography; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000503:physiopathology; D007773:Lactates / Q000097:blood / Q000378:metabolism; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D016277:Ventricular Function, Left / Q000502:physiology*
D002395:Catecholamines; D007773:Lactates; D002245:Carbon Dioxide; D010100:Oxygen