Increased myocardial contractility during endotoxin shock in dogs.

The slope of the left ventricular (LV) end-systolic pressure-diameter relationship (Ees) was analyzed in open-chest, pentobarbital-anesthetized dogs before and after endotoxin administration. A lead II electrocardiogram, systemic arterial pressure, LV pressure, LV dP/dt, and LV minor axis diameter were measured. After control measurements were taken, dogs were given either 1 mg/kg Salmonella enteritidis endotoxin (n = 5) or an equivalent volume of saline (n = 4). Control dogs were followed for 240 min. Endotoxic dogs were monitored until death (246 +/- 44 min). There were no significant changes in Ees in control dogs (17 +/- 3 mmHg/mm), which were hemodynamically stable for 4 h. Ees was significantly increased in endotoxic dogs even into the late stages of shock (41 +/- 11 mmHg/mm, P less than 0.01). Only during the terminal phase did Ees fall significantly below control (11 +/- 2 mmHg/mm, P less than 0.05). End-diastolic diameter decreased following endotoxin administration (P less than 0.05) but returned toward control by the terminal stage. Peak + LV dP/dt was depressed following endotoxin injection. Myocardial contractility was not depressed except as a terminal event. Early depression of cardiovascular performance in endotoxic dogs was therefore due to decreased preload and not cardiac dysfunction.