Influence of contractility on myocardial water distribution during cardiopulmonary bypass.

Water equilibrium within heart muscle during cardiopulmonary bypass is an important aspect of ventricular physiology which must be considered in efforts to optimize myocardial protection. This study focuses on the influence of the inotropic state of the ventricle in determining the amount of heart water and its regional distribution within the free wall of the left ventricle. Experiments involving cardiopulmonary bypass were performed in 57 dogs. Three spontaneous levels of myocardial contractility were identified under conditions of standard preload, afterload, and heart rate. Each increase in level (grade) was associated with a significantly higher myocardial wet weight/drug weight (W/D) ratio. In addition, higher levels of contractility were associated with a marked shift in water distribution within the left ventricular wall; water tended to accumulate in the inner half of the better contracting left ventricular wall, the reverse of the distribution seen at lower levels of contractility. These three grades of contractility and myocardial water content were not associated with any significant differences in total or regional myocardial blood flow, as determined by the use off radioactive microspheres. Maintenance of low levels of contractility during cardiopulmonary bypass may be desirable in order to prevent the occurrence of subendocardial edema.