Depression of papillary muscle contractility by plasma incubated with pneumococci.

Mechanisms of death in pneumococcal disease are poorly understood. We have previously shown that intravenous pneumococcal products in dogs caused a mean decrease in cardiac output of 58%. The present study used measurements of the force and rate of contraction of isolated rabbit papillary muscle to determine whether pneumococci (PNC) altered myocardial contractility. Nine papillary muscles were superfused with various solutions including Tyrode's, Tyrode's incubated with sonicated type 1 PNC, normal rabbit plasma, and rabbit plasma incubated with PNC. Compared to untreated Tyrode's solution, PNC-treated Tyrode's solution did not alter papillary muscle contractility. However, compared to untreated rabbit plasma, plasma incubated with PNC caused a mean decrease of 18% in the force of contraction and 16.7% in the maximum rate of force development in nine studies. We conclude that PNC do not directly affect papillary muscle contractility. However, the interaction of PNC and plasma does cause a decrease in rabbit papillary muscle contractility.

Oxygen extraction ratio: a valid indicator of transfusion need in limited coronary vascular reserve?

We have described whole body oxygen (O2) extraction ratio (ER) as a reliable indicator of transfusion need in acute normovolemic anemia. In normal hearts, myocardial lactate production (-LACT), indicating anaerobic metabolism, does not occur until the ER greater than 50% and Hct less than 10%. It is not known if the ER is valid in the setting of limited coronary vascular reserve. This study assesses the effect of a critical left anterior descending (LAD) coronary stenosis on the compensation to acute blood loss anemia. Adult dogs were anesthetized, paralyzed, and mechanically ventilated. A critical LAD stenosis was created in seven animals (STEN). There were seven controls (CON). Animals underwent isovolemic exchange transfusion with 6% HES until cardiac failure (CF). Catheters were placed in the aorta, pulmonary artery, and anterior interventricular coronary vein. Cardiac failure occurred at Hct = 8.6% +/- 0.4% in the CON and 17.0% +/- 0.5% in the STEN animals. Cardiac output increased in the CON, but not in the STEN animals. Blood flow in the LAD increased in the CON but not the STEN animals. -LACT began in the CON and STEN animals at Hct less than 20% and coincided with an ER greater than 50% in both groups. We conclude that CF occurs at a higher hematocrit with a critical LAD stenosis. The whole body ER greater than 50% remains a valid indicator of myocardial metabolism in anemia in the presence of limited coronary vascular reserve. The ER may be a useful guide to transfusion therapy.