Showing papers by "David A. Kass published in 1993"

Diminished contractile response to increased heart rate in intact human left ventricular hypertrophy. Systolic versus diastolic determinants.

Abstract: BACKGROUNDExperimental studies indicate that in addition to diastolic dysfunction, hypertrophied myocardium can display depressed contractile responses, particularly at rapid heart rates, compounding reserve limitations. This study tests whether such abnormalities exist in intact human subjects at physiological paced rates and, if so, whether they are linked to simultaneous rate-dependent deterioration in diastolic function.METHODS AND RESULTSTen subjects with left ventricular hypertrophy (LVH) and 8 normal control subjects were studied. Most LVH patients presented with dyspnea and/or pulmonary edema and had concentric hypertrophy. Since rapid pacing simultaneously alters cardiac filling volumes and pressures, pressure-volume relation analysis was used to better define changes in contractile response. Patients were instrumented with a conductance catheter and micromanometer for pressure-volume data recording and a balloon occluder at the right atrial-inferior vena caval junction to vary filling and thus g...

Ventricular stroke work and efficiency both remain nearly optimal despite altered vascular loading

Abstract: Recent clinical and animal studies have suggested that ventricular-vascular coupling normally operates at either optimal ventricular efficiency (EFF = stroke work/myocardial oxygen consumption) or stroke work (SW) and that efficiency in particular is compromised by cardiac dysfunction These distinctions between coupling states at maximal work vs efficiency are largely based on theoretical models To date, there are few direct experimental data defining optimal conditions for each parameter, respectively, in the same heart or tests of whether changes from these conditions must produce significant declines in both parameters Therefore, 10 isolated blood-perfused canine hearts were studied at varying contractilities, with the heart ejecting into a simulated three-element Windkessel model of arterial impedance For a given inotropic state [indexed by the slope of the end-systolic pressure-volume relationship (Ees)], myocardial oxygen consumption and SW were measured over a broad range of afterload resistances The latter was indexed by the effective arterial elastance (Ea) and ventricular-vascular interaction expressed by the ratio of Ea to Ees (Ea/Ees) On average, maximal SW occurred at Ea/Ees = 080 +/- 016, whereas EFF was maximal at Ea/Ees = 070 +/- 015 (P or = 90% of their respective optima over a broad overlapping range of Ea-to-Ees ratios (03-13, corresponds with ejection fractions ranging from approximately 40 to 80%) These data show that both SW and efficiency are nearly maximal under many conditions of ventricular-vascular interaction(ABSTRACT TRUNCATED AT 250 WORDS)

Diastolic compliance of hypertrophied ventricle is not acutely altered by pharmacologic agents influencing active processes

Abstract: Objective: To test, by studying the acute effects of drugs that influence active processes, the hypothesis that in humans with marked ventricular hypertrophy, reduced chamber compliance is primaril...

Validation of a method for noninvasive measurement of central arterial pressure.

Abstract: The goal of this study was to validate a newly improved noninvasive method for calibrated measurement of the ascending portion of the central arterial pressure wave in humans. Noninvasive pressure waveforms were generated by measuring the time delay between the R wave of the electrocardiogram and onset of brachial artery flow (by Doppler) during computer-controlled upper arm cuff deflation. This delay shortens with falling cuff pressure (becoming near constant at and below diastolic pressure), so that a plot of pressure versus time delay yields the ascending portion of the arterial waveform. These waveforms were compared with simultaneous invasive ascending aortic pressures in 57 adult patients (31 by fluid manometer [group A] and 26 by catheter-tipped micromanometer [group B]) during routine cardiac catheterization. Patient age ranged from 26 to 77 years. Eighty percent of group A patients and 40% of group B had coronary artery disease. Noninvasive systolic and diastolic pressures were very similar to invasive values in both groups (Pni = 0.98 x Pi, r = 0.99, p < 0.0001). Instantaneous pressure differences between waveforms were also similar in both groups, averaging between 4.5 and 5.5 mm Hg. Micromanometer and noninvasive pressure data were also obtained before and after intravenous nitroglycerin (n = 5) and isometric handgrip (n = 8) and demonstrated good agreement. A potential application of these pressures is for estimating maximal ventricular power to assess systolic function. This was tested using invasive pressure-volume data from four patients under a variety of conditions (exercise, pacing, etc.).(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular-Arterial Interaction: Cardiac Effects of Mean versus Pulsatile Arterial Load

Abstract: The influence of the two principal components of vascular loading, mean resistance and pulsatile load, on the contractile and energetic performance of the left ventricle are discussed. The data suggest that while large changes in mean resistance leading to varying ejection fraction can influence both cardiac systolic mechanics and energetic efficiency, substantial changes in pulsatile loading do not. They provide an explanation for why pulsatile loading does not necessarily result in a coronary supply/demand imbalance. By not significantly altering chamber systolic performance of elastance (i.e. stiffness), the pulsatile load results in parallel increases in coronary systolic pressure and flow, allowing adequate perfusion despite the reduced mean diastolic perfusion pressure. Future studies are required to better determine how cardiac disease alters the interplay between vascular load and cardiac performance.