The importance of load-independent analysis in assessment of the inotropic effect of prostaglandin E1 in vivo.

Load-independent pressure-dimension analysis was applied in 13 open-chest, anesthetized dogs during either left atrial (n = 7) or right atrial (n = 6) infusion of prostaglandin E1. Right atrial infusion of prostaglandin E1 in doses from 31 to 500 ng/kg/min resulted in no change in any parameters studied, including mean arterial pressure, cardiac output, and systemic and pulmonary vascular resistances. Left atrial infusion of prostaglandin E1 produced dose-dependent reductions in mean arterial pressure and systemic vascular resistance but no change in the slope of the relationship of left ventricular stroke work to end-diastolic length, a load-independent index of ventricular performance. In contrast to findings obtained with load-dependent parameters, these results suggest that prostaglandin E1 has no positive inotropic effect in vivo.

Quantification of the contractile response to injury: assessment of the work-length relationship in the intact heart.

We used a sonomicrometric determination of ventricular dimension to examine the effect of ischemia and reperfusion on the work-length relationship in the intact heart to develop a useful and precise variable of ventricular contractile response to injury. Twenty anesthetized dogs were instrumented with epicardial ultrasonic dimension transducers to record right ventricular free wall chord length and left ventricular minor-axis length, micromanometers to record ventricular pressures, and an electromagnetic probe to record pulmonary arterial (n = 8) or aortic (n = 7) flow. Dogs were subjected to either 20 min (n = 7) or 30 min (n = 13) of global cardiac ischemia supported by cardiopulmonary bypass. Data were acquired over a range of end-diastolic volumes produced by transient (5 to 10 sec) vena caval occlusion before and after ischemia. In both ventricles, systolic epicardial dimensional shortening correlated with flow probe-measured stroke volume (mean r = .969) and regional stroke work calculated as the integral of instantaneous ventricular pressure and epicardial dimension correlated with measured global stroke work (mean r = .960), confirming the validity of dimensional measurements. Regression analysis demonstrated a highly linear relationship between calculated regional stroke work and end-diastolic length in the right ventricle (mean r = .973) and left ventricle (mean r = .967), quantifiable by a slope (Mw) and x intercept (Lw). Change in afterload produced by pulmonary arterial or aortic constriction resulted in no significant changes in Mw or Lw in either ventricle. Ischemia and reperfusion decreased Mw and shifted Lw to the right in both ventricles. The decrease in Mw with 30 min ischemia exceeded the decrease with 20 min ischemia by 29% in the right ventricle and by 32% in the left (p less than .04) with up to 1 hr of reperfusion. Changes in Lw were not related to severity of injury. After ischemia, infusion of calcium increased Mw by 177% in the right ventricle and by 67% in the left (p less than .03) without significant changes in Lw. Independent of load conditions, the slope Mw, of the linear stroke work vs end-diastolic length relationship is a valid and precise index of right and left ventricular contractile response to global ischemia in the intact circulation. This variable may be useful in evaluating therapies designed to limit myocardial injury and enhance ventricular functional performance.

Private medical insurance in New Zealand: issues of membership and growth.

Questions concerning ownership of private medical insurance were included in a recent Department of Statistics' survey of a random sample of almost 7000 New Zealanders. The results indicated that 35% of those surveyed owned private medical insurance and such ownership was significantly related to various social, demographic and health related variables. The findings are discussed in terms of the possibilities for growth of private medical insurance and the implications of such growth for both the public and the private health care sectors.