Biomedical subjects

M B Ratcliffe

Publications and source records attributed to M B Ratcliffe.

24 records · Page 2Linked to original sources

PubMed1989

Measurement of end-systolic pressure-volume relations by intra-aortic balloon occlusion.

A new situ technique has been developed for measuring peak end-systolic elastance, Emax, that does not alter intrinsic or reflex-stimulated cardiac contractility. Afterload is varied by the inflation of an intra-aortic balloon catheter positioned in the ascending aorta. Balloon inflation is timed to interrupt ventricular ejection transiently at different times during the ejection phase, therefore, producing contraction at different ventricular volumes. Simultaneous measurement of left ventricular pressure and aortic flow during the occlusion sequence allows pressure versus ejected volume loops to be generated, from which the end-systolic pressure-volume relation is determined. End-systolic pressure-volume relation (ESPVR) was measured in six anesthetized Dorsett sheep with normal and enhanced contractile states. ESPVR was analyzed using both linear and nonlinear techniques. Although nonlinear components were seen in ESPVR, for the pressure-volume data range produced by the transient occlusions, linear approximations of ESPVR fit the end-systolic data points well. In the normal state, Emax, the slope of the linear ESPVR, was 1.01-5.08 mm Hg/ml in animals with body weights of 23-32 kg. After epinephrine infusion, Emax increased from 3.07 +/- 1.49 to 5.79 +/- 1.97 mm Hg/ml, which is consistent with previous investigations. Linear and nonlinear volume intercepts had a small increase with positive inotropic stimulation. Furthermore, serial measurements of Emax tracked cardiac function in depressed hearts with rapidly changing contractility.

Animals↗

PubMed1989

Surgery for left ventricular aneurysm. Early survival with and without endocardial resection.

In the past 3 years, 86 patients had left ventricular aneurysms resected or plicated. Sixty-eight had recurrent sustained ventricular tachycardia as the indication for surgery and had preoperative and intraoperative electrophysiologic mapping. There were 14 hospital deaths (16%). Eight preoperative potential risk factors for early hospital mortality were analyzed by multivariate analysis. Only acute myocardial infarction within 30 days before surgery correlated with hospital death at the p less than 0.05 level. History of previous heart surgery and advanced New York Heart Association functional class were important risk factors at the p less than 0.1 level. Hospital mortality was 17.6% for patients who had intraoperative mapping and endocardial resection and 11.1% for the others. Patients who had aneurysm repair for ventricular tachycardia had a significantly higher incidence of low cardiac output early after surgery (p less than 0.025).

Adult↗

PubMed1988

Open-heart surgery in octogenarians.

One hundred consecutive patients 80 years of age or older consented to and subsequently underwent open-heart operations at our institution between July 1976 and May 1987. Fifty of the patients had aortic valvular disease (28 with coexisting coronary artery disease), and 41 had isolated coronary artery disease. Eight patients had mitral valvular disease, and one had a dissecting aortic aneurysm. Ninety had Class IV disease that was functional, ischemic, or both. The most compelling indications for operation in 85 patients were unstable or postinfarction angina, syncope, acute pulmonary edema, or cardiogenic shock. Twenty-nine patients died soon after operation (within 90 days). New York Heart Association Class IV disease, previous myocardial infarction, cachexia, and emergency operation were preoperative variables associated with early death. Forty-three patients had no complications except for atrial arrhythmias and were discharged from the hospital a mean (+/- SD) of 11.5 +/- 3.7 days after operation. Low cardiac output, acute myocardial infarction, reoperation for bleeding, renal insufficiency, pneumonia, and prolonged endotracheal intubation were the most common serious postoperative complications. Twenty-eight patients who survived postoperative complications were discharged 24.9 +/- 19.6 days after operation. Seventeen patients died 2 to 104 months after discharge from the hospital. Actuarial calculation predicts the survival of 59 percent of patients at three years and 54 percent at five years. Of the 54 patients still alive at this writing, 53 have disease within New York Heart Association and Canadian Cardiovascular Society Classes I or II. For selected octogenarians with unmanageable cardiac symptoms, operation may be an effective therapeutic option.

Aged↗

PubMed1988

Changes in left ventricular systolic wall stress during biventricular circulatory assistance.

Extracorporeal membrane oxygenation (ECMO) reduces the systolic stress integral (SSI) in the normal left ventricle. We tested the hypothesis that the SSI does not decrease in poorly contracting, dilated, ejecting hearts during ECMO. In 14 sheep, four pairs of ultrasonic crystals measured changes in left ventricular (LV) wall thickness and three LV diameters. Volume calculations were validated by balloon distention of the ventricles after death (slope = 0.85; r = 0.85). SSI was measured during ECMO flows of 20 to 100 ml/kg/min in both normal and dilated, poorly contracting hearts produced by 30 minutes of warm ischemia. After warm ischemia, end-systolic elastance, an index of contractility, decreased from 8.3 +/- 0.6 mm Hg/ml to 2.9 +/- 0.4 mm Hg/ml (p = 0.001) and peak systolic pressure decreased from 47.4 +/- 0.7 mm Hg to 37.5 +/- 0.08 mm Hg (p = 0.01). In normal hearts, as ECMO flow increased, SSI decreased from 10.5 +/- 2.2 mm Hg.sec to 7.7 +/- 0.8 mm Hg.sec at 60 ml/kg/min (p = 0.001). However, in postischemic hearts, SSI progressively increased from 6.6 +/- 0.3 mm Hg.sec before ECMO to 12.4 +/- 1.8 mm Hg.sec at ECMO = 100 ml/kg/min. These studies indicate that the initial effect of ECMO on the poorly contracting, dilated heart increases LV wall stress and that the increase in stress is proportional to ECMO flow. The increase in stress is primarily due to an increase in afterload, which more than offsets decreases in systolic and diastolic volumes.

Animals↗

PubMed1988

Flow dynamics of peripheral venous catheters during extracorporeal membrane oxygenation with a centrifugal pump.

Extracorporeal membrane oxygenation uses peripherally placed cannulas and a streamlined circuit without a venous reservoir. This study tests the flow dynamics of venous catheters connected without a reservoir directly to a centrifugal pump. During in vitro testing, a 30 cm segment of collapsible tubing interposed between the reservoir and pump simulates the vein. In five sheep, flow was measured between catheters placed in the right atrium and inferior vena cava from peripheral sites. Catheter tip design (four types) does not affect flow within a simulated vein in vitro. Maximum pump flow is independent of filling pressures (6 to 21 mm Hg) in vitro and in vivo when the catheter tip is in a tank reservoir or the right atrium. However, when the catheter tip is within a collapsible segment or in the inferior vena cava, maximal flow is significantly influenced by filling pressure (6 to 18 mm Hg) and by the ratio of catheter outer diameter to venous diameter. At all filling pressures, maximal flow in vivo is significantly reduced when this ratio is greater than 0.5. During extracorporeal membrane oxygenation, central venous pressure and catheter/vein ratio, not catheter size alone, control flow through peripheral venous catheters.

Adult↗

PubMedDate not supplied

The effect of diastolic stiffness on ventricular function after partial ventriculectomy: a finite element simulation.

Partial ventriculectomy (PV) has been proposed by Batista and colleagues to improve cardiac function in patients with dilated cardiomyopathy (DCM); however, results have been mixed. We tested the hypothesis that preoperative diastolic function affects the stroke volume/end-diastolic pressure (Starling) relationship after PV. A previously described finite element simulation of DCM and PV was used. Diastole and end systole were represented by separate elastic finite element models with different unloaded shapes and nonlinear material properties. Left ventricular (LV) end-systolic elastance (E(ES)), diastolic compliance (DC), and Starling relationships were calculated. DC was varied by changing Ogden material property alpha(i) from 12 (compliant) to 20 (stiff). PV was simulated at 20% LV mass reduction. The slope of the Starling relationship increased from 1.82 to 1.21 as alpha(i) increased from 12 to 20. Partial ventriculectomy increased the Starling relationship in each case from 1.34 to 1.01 respectively. However, the net result in each case is a decrement in the Starling relationship with resection, and the smallest decrement was associated with the highest diastolic stiffness (alpha(i) = 20). Partial ventriculectomy depressed the Starling relationship for all values of diastolic compliance. It is expected that patients with a higher diastolic stiffness should do better.

Cardiomyopathy, Dilated↗