Contributions of Coronary Perfusion Pressure, Metabolic Acidosis and Adrenergic Factors to the Reduction of Myocardial Contractility during Hemorrhagic Shock in the Cat

¹ Department of Pathology, Yale University School of Medicine New Haven, Connecticut 06510
² Department of Pathology, Yale University School of Medicine ,ad>New Haven, Connecticut 06510

The contributions of metabolic acidosis, coronary perfusion pressure (CPP) and adrenergic support to left ventricular performance during hemorrhagic shock at aortic pressure (AP) of 30 ± 5 mm Hg were evaluated in cats in which AP, cardiac output (CO), and heart rate (HR) were controlled, and arterial pH, Po₂ and Pco₂ were continuously monitored. After 2 hours of shock, the stroke volume (SV), ejected at end-diastolic pressure of 10 cm H₂O (SV₁₀), was irreversibly reduced to 46 ± 4% (P < .001) of initial values (arterial pH 6.93 ± .05). In control animals SV₁₀ after 2 hours was 86 ± 6% (pH 7.32 ± .07). Eight animals were subject to shock, but their CPP was held at 100 mm Hg. These showed no difference in SV₁₀ from controls after 2 hours, although the pH had fallen to 6.90 ± .05. Reduction of CPP in these animals without correction of pH resulted in a rapid fall of SV₁₀. In 10 animals subjected to shock for 2 hours, the arterial pH was maintained near 7.40 by infusion of Tris buffer. Five showed no greater reduction of SV₁₀ than the controls, and five became severely depressed. In five cats subjected to beta-receptor blockade, hemorrhagic shock (pH 7.40) produced a rapid fall of SV₁₀ which initially could be reversed by reelevation of AP. In less than 15 minutes, the SV₁₀ depression became irreversible. Thus, shock (2 hours) and associated metabolic acidosis is detrimental to ventricular contractility only if CPP is also reduced. The contribution of acidosis may be related to the amount of sympathetic support during shock. With beta-receptor blockade, shock results in a marked reduction in SV₁₀, even in the absence of metabolic acidosis.

Submitted on July 27, 1970
Accepted on September 29, 1970