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Biomedical subjects

G P Armstrong

Publications and source records attributed to G P Armstrong.

5 recordsLinked to original sources
PubMed2000

Exercise echocardiographic assessment in severe mitral regurgitation.

In chronic severe mitral regurgitation, minimum morbidity and mortality is achieved by applying surgical correction before left ventricular dysfunction becomes irreversible. This requires detection of subtle signs of early ventricular decompensation, for which isotonic stress echocardiography is more accurate than is use of resting indices of contractile function alone. We perform serial 6-monthly stress echocardiography for patients with severe mitral regurgitation, and recommend surgery when the exercise end-systolic volume index or ejection fraction reaches the cutoff values in Table 4 or if there is a clear adverse trend. Exercise echocardiography is more accurate than is exercise electrocardiography for detecting concomitant coronary disease prior to revascularization. Stress testing is also an objective measure of symptoms. Color-Doppler stress echocardiography can detect those patients whose mitral regurgitation worsens (or even develops de novo) with exercise, which can explain unexpected symptoms. Stress echocardiography, therefore, provides a comprehensive and cost-effective evaluation of patients with mitral regurgitation that combines functional, diagnostic, and prognostic information.

Echocardiography, Doppler, Color↗
PubMed1999

Estimation of cardiac reserve by peak power: validation and initial application of a simplified index.

OBJECTIVES: To validate a simplified estimate of peak power (SPP) against true (invasively measured) peak instantaneous power (TPP), to assess the feasibility of measuring SPP during exercise and to correlate this with functional capacity. DESIGN: Development of a simplified method of measurement and observational study. SETTING: Tertiary referral centre for cardiothoracic disease. SUBJECTS: For validation of SPP with TPP, seven normal dogs and four dogs with dilated cardiomyopathy were studied. To assess feasibility and clinical significance in humans, 40 subjects were studied (26 patients; 14 normal controls). METHODS: In the animal validation study, TPP was derived from ascending aortic pressure and flow probe, and from Doppler measurements of flow. SPP, calculated using the different flow measures, was compared with peak instantaneous power under different loading conditions. For the assessment in humans, SPP was measured at rest and during maximum exercise. Peak aortic flow was measured with transthoracic continuous wave Doppler, and systolic and diastolic blood pressures were derived from brachial sphygmomanometry. The difference between exercise and rest simplified peak power (Delta SPP) was compared with maximum oxygen uptake (VO(2)max), measured from expired gas analysis. RESULTS: SPP estimates using peak flow measures correlated well with true peak instantaneous power (r = 0.89 to 0.97), despite marked changes in systemic pressure and flow induced by manipulation of loading conditions. In the human study, VO(2)max correlated with Delta SPP (r = 0.78) better than Delta ejection fraction (r = 0.18) and Delta rate-pressure product (r = 0.59). CONCLUSIONS: The simple product of mean arterial pressure and peak aortic flow (simplified peak power, SPP) correlates with peak instantaneous power over a range of loading conditions in dogs. In humans, it can be estimated during exercise echocardiography, and correlates with maximum oxygen uptake better than ejection fraction or rate-pressure product.

Animals↗
PubMed1996

Left ventricular function in scleroderma.

Scleroderma affects the left heart directly and indirectly via the effects of systemic hypertension. Using transthoracic echocardiography, we evaluated 35 patients with scleroderma and compared them with matched control subjects. Compared with controls, there were no differences between left ventricular dimensions, wall thickness, calculated mass or fractional shortening. However, the left atrium was enlarged (P = 0.006) and the mitral deceleration time was prolonged (P = 0.0005) in patients with scleroderma; suggesting abnormal diastolic function. After adjusting for potential confounders, duration of Raynaud's was found to be an independent predictor of deceleration time (P = 0.04), E/A peak velocity ratio (P = 0.04), A peak velocity (P = 0.004) and A velocity time integral (P = 0.0001), all measures of diastolic function. This group of individuals with scleroderma have evidence of abnormal diastolic function of the left ventricle despite normal left ventricular size and systolic function, and in the absence of hypertrophy. This finding is independent of the use of vasoactive medications and history of systemic hypertension, and thus may be due to primary myocardial involvement by scleroderma. The tendency to abnormal diastolic function of the left ventricle correlated with the duration of Raynaud's phenomenon.

Adolescent↗
PubMedDate not supplied

Numeric modeling of the cardiovascular system with a left ventricular assist device.

A numeric model consisting of a lump-parameter cardiovascular system (CVS) model and a model for the Cleveland Clinic Implantable Ventricular Assist System (IVAS), a nonpulsatile rotary pump designed to augment the failing left ventricle, are described in this paper. The purposes of this study were to 1) observe the hemodynamic interactions between CVS and IVAS under various physiologic and pathophysiologic conditions running at different speeds; and 2) allow testing and optimization of various IVAS control algorithms. An existing numeric model of CVS (24 coupled differential equations, representing all cardiac chambers and systemic and pulmonary vasculature) was modified to add the IVAS pump as an auxiliary chamber between the left ventricle and aorta with pressure-flow-speed characteristics derived from in vitro testing. Simulations were conducted for ventricles with normal and abnormal systolic and diastolic dysfunction at different exercise levels with the pump running at various speeds. Computer simulations show that 1) numeric modeling is useful for predicting hemodynamic response of CVS to IVAS in various circumstances; 2) IVAS results in normalization of cardiac output, especially in failing hearts, although with reduced pulse pressure; and 3) various control algorithms allowing adaptation of IVAS to physiologic demands of CVS could be developed based on the simulation study.

Blood Pressure↗