Biomedical subjects

F B Crawford

Publications and source records attributed to F B Crawford.

3 recordsLinked to original sources

PubMed1981

Myocardial contracture: the predominant causes of impeded reperfusion in simulated surgical ischemia.

"Worst-case" surgical conditions were simulated using the isolated model of a parabiotically perfused rabbit heart septum. Such conditions occur clinically in regional myocardium distal to stenosed coronary arteries and are characterized by inadequate or absent ionic influence on the myocardium by chemical cardioplegia and equilibration to room temperature. This study tested the hypothesis that ischemic contracture, rather than intracellular or extracellular edema, critical closing or delayed critical opening, was the predominant cause of impeded reperfusion that damages myocardium. In 20 reperfused ischemic septa, conductance (flow per unit pressure) decreased significantly (P less than 0.05) as ischemia at 24 degrees C was prolonged from 15 to 90 minutes and as contracture became more severe. Conductance was not decreased significantly by even large amounts of extracellular edema. Intracellular edema did not occur. In 17 normal septa, the critical closing pressure was 9.3 mm Hg. Critical opening pressures following 5 to 90 minutes ischemia at 24 degrees C did not differ significantly. Although early reflow was impeded progressively with longer ischemic intervals, it was not significant as was due to contracture rather than critical closing or delayed critical opening. This study confirmed the hypothesis that contracture is the predominant cause of impeded reperfusion in simulated surgical ischemia.

Animals↗

PubMed1977

The interventricular septum: an isolated perfused model for assessing myocardial function.

Classical models for assessing myocardial function suffer from either a potentially anoxic central core or an unsophisticated perfusion system. We have improved Langer's perfused interventricular septum model by adapting it for parabiotic resuscitation, thus achieving rapid stability and significantly less edema. The new model, which consists of a triangular piece of rabbit interventricular septum, perfused through its septal artery, first undergoes a stabilization period of 30 min during parabiotic perfusion from another rabbit. An arteriovenous shunt is then opened and the preparation remains stable for 2 h of perfusion in which fresh blood is recirculated nonparabiotically. It is proposed that during this period, experimental interventions could be undertaken using each septum as its own control. The behaviour of 66 preparations was consistent with classical concepts of myocardial function. Simple measurements were identified for beat-to-beat functional assessment. Contractility was measured by maximum active tension and maximum differential of tension. Relaxation was measured by maximum negative differential of tension and, in the presence of ischemic contracture, changes in resting tension. Compliance was measured by septal length at a specified resting tension. Perfusability was measured by the relationship between pressure and flow.

Animals↗

PubMed1976

A new model for assessment of myocardial function: I. Description and performance norms.

Use of a new isometric rabbit-heart model, a modification of Langer's original preparation, has permitted independent assessment of myocardial perfusability in addition to contractility and relaxation. In this model an isolated, paced, interventricular septum contracts against a tension transducer and is perfused from another awake rabbit. Heparinized, diluted arterial blood is warmed and pumped at 1 ml/g-min. Perfusion pressure is measured by transducer. Each preparation serves as its own control. This model was used in determining performance norms for 68 preparations. Contractility was measured by maximum active tension, maximum rate of increase of tension and time to peak tension; relaxation by resting tension, maximum rate of relaxation and relaxation time; and perfusability by mean perfusion pressure and mean conductance. The status of the parabiotic rabbit was closely monitored. These studies have shown that the model is relatively simple, clearly defined and adaptable to a variety of experimental protocols.

Animals↗