Differences in Cardiac Responses to Resuscitation from Burn Shock

Isolated coronary perfused hearts from guinea pigs were used to determine if aging alters left ventricular (LV) intrinsic contractile response to resuscitated burn shock. Parameters measured included LV pressure (LVP) and maximal rate of LVP rise (+dP/dt max) and fall (-dP/dt max) at a constant preload (LV enddiastolic pressure [LVEDP]). Compared with young controls (ten), aged control hearts (ten) showed significantly lower LVP (87.4 +/- 2.53 versus 76.0 +/- 1.5, p,0.001), +dP/dt max (1,351 +/- 51 versus 1,048 +/- 49, p,0.001), and -dP/dt max (1,154 +/- 34 versus 916 +/- 27, p,0.001), at an LVEDP of 10 millimeters of mercury. A 43 +/- 2 per cent third-degree burn (Walker model) was studied in ten young and ten aged guinea pigs. Burned aged hearts showed significantly lower LVP (57.1 +/- 2.1 versus 67.5 +/- 3.7, p,0.01) and -dP/dt max (707 +/- 33 versus 993 +/- 59, p,0.001) at an LVEDP of 10 millimeters of mercury. In addition, LV function curves for burned aged hearts were shifted downward and to the right of curves obtained from young burned hearts (p,0.05). Contractile defects in the aged group were not overcome by altered beating frequency, increased extracellular calcium concentration, nor maximally effective increases in diastolic stretch. Finally, we examined the effects of fluid resuscitation (4 milliliters per kilogram per percentage of burns) on contractile function in an additional ten young and ten aged burned guinea pigs. Contractile deficits persisted in both age groups despite adequate fluid resuscitation. Peak LVP and maximal rate of relaxation (-dP/dt) were uniformly depressed in aged as compared with young burned hearts (52.4 +/- 1.5 versus 63.2 +/- 2.7 and 715 +/- 42 versus 909 +/- 52, p,0.01, respectively). These data suggest that severe myocardial contractile change resulting from a major thermal insult in subjects with already compromised hearts is likely a significant limiting factor in the response to burn shock and adequate fluid resuscitation.