Mechanisms of myocardial depression after bolus injection of sodium bicarbonate.
OBJECTIVE
The classic model for the effects of NaHCO3 on myocardial function predicts transient myocardial depression after an intravenous bolus of sodium bicarbonate in association with myocardial acidosis.


METHODS
Five anesthetized, paralyzed, and ventilated dogs underwent midline sternotomy. Myocardial global function was assessed by cardiac output, left ventricular (LV) dp/dt, LV end-systolic, and LV end-diastolic pressures. Regional myocardial function assessed by measuring the LV regional end-systolic, LV end-diastolic lengths, and LAD coronary blood flow. Coronary sinus, intramyocardial and arterial pH were measured as was free serum Ca++. Animals were made acidemia by infusion of 0.3 N HCl and then given a bolus of sodium bicarbonate. This produced transient depression followed by recovery of myocardial function.


RESULTS
During the depression phase there was no significant decrease in interstitial pH or an increase in A-VCO2 difference as predicted by the current model. However, there was a significant decrease in the serum free Ca++ that coincided with myocardial depression.


CONCLUSIONS
We could not confirm the predictions of the classic model and hypothesize that myocardial depression may be caused by decreased availability of free Ca++ of decreased Ca++ flux rather than intracellular acidosis.
Rao
R S
RS
Division of Pulmonary and Critical Care Medicine, Long Island Jewish Medical Center, Long Island Campus for the Albert Einstein College of Medicine, New Hyde Park, New York 11042.
Graver
M L
ML
Urivetsky
M
M
Scharf
S M
SM
D000138:Acidosis / Q000097:blood / Q000503:physiopathology / Q000628:therapy*; D000818:Animals; D002118:Calcium / Q000097:blood; D002245:Carbon Dioxide / Q000097:blood; D002303:Cardiac Output, Low / Q000139:chemically induced*; D003864:Depression, Chemical; D004285:Dogs; D006334:Heart Function Tests; D007262:Infusions, Intravenous; D007275:Injections, Intravenous; D009200:Myocardial Contraction / Q000187:drug effects*; D010313:Partial Pressure; D017693:Sodium Bicarbonate / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*
D002245:Carbon Dioxide; D017693:Sodium Bicarbonate; D002118:Calcium