B.G. Min

Sensitivity and afterload independence of zero-load aortic flow.

The computed zero-load flow is the expected aortic flow when the aortic pressure is zero, thus eliminating the effect of afterload on ventricular ejection. Zero-load flow was computed in 15 anesthetized dogs (sodium pentobarbital 25 mg/kg, iv) by studying the response of left-ventricular pressure or aortic pressure, and aortic flow to the change in aortic input impedance induced by partial snare occlusion of the aorta. The waveform and peak value of zero-load flow were computed from a theoretical model of the left ventricle and verified by measurements of aortic flow in the first beat after transection of the aorta. To study the sensitivity, changes of zero-load flow were computed under the enhanced inotropic state produced by isoproterenol (0.1 μg/kg/min), and under the depressed contractile state induced by propranolol (0.15 mg/kg). Administration of isoproterenol resulted in an increase in the peak zero-load flow by 143.9% (p<0.001), compared with a 50.6% increase (p<0.05) in peakdp/dt. The difference of the variations was statistically significant in a pairedt test. After injection of propranolol, peak zero-load flow decreased by 32.0% (p<0.005). Afterload independence of zero-load flow was studied by computing zero-load flow before and after increasing arterial pressure by partial aortic occlusion or injection of 5 mg methoxamine. After injection of methoxamine in denervated dogs, the peak zero-load flow increased by 11.2% (N.S.), while input resistance increased by 153% (p<0.025). The peak zero-load flow decreased by 8% (N.S.) after partial aortic occlusion, while cardiac output decreased by 26.7% (p<0.001). These results may suggest that the computed peak zero-load flow is an afterload independent index of the pumping capability of the left ventricle in the intact heart.

Significance of Left Ventricular Power Waveform on Changes in Stroke Work During Pulsatile Left Ventricular Bypass

Abstract The object of this paper is to introduce the “peakedness” of the left ventricular power waveform as an index of the effectiveness of the pulsatile ventricular bypass (LVBP). The “peakedness” is determined by the position of the peak and the rate of ascent and decline of the instantaneous left ventricular power waveform. In eight open-chested dogs with coronary artery ligation, it has been found that the “peakedness” of the LV power waveform during assistance is important in determining the efficacy of LVBP. When the LV power waveform, the instantaneous product of LV pressure and aortic flow, has a broad width about the peak with an early rise to peak (low value of “peakedness” factor), the chance of improvement in stroke work after bypass is greater than when the waveform is sharply peaked with a delayed rise (high value of “peakedness”). Improvement in stroke work (SW) occurred when the percentage bypass flow was between 45 and 60%. Among the pumping runs with improved SW and CO, there was no consistent relationship between the percentage changes in SW and CO and the percentage bypass flow. The data suggest that “peakedness” may be of importance, because it evaluated the effect of left ventricular bypass on the performance of the native ventricle during postischemic periods.

Relation between computed zero-load aortic flow and cardiac muscle mechanics☆

Abstract Computed zero-load flow, qs(t), is the expected aortic flow at zero aortic input impedance, thus eliminating the effect of afterload on ventricular ejection. It is computed from an equivalent model of the ventricle using the Fourier components of left ventricular (LV) pressure and aortic flow, qa(t), of two consecutive beats with different input impedance produced by partial aortic occlusion. Actual qs(t) may be measured during the first beat after transection of the aorta. In animal experiments computed qs(t) was similar to the waveform and magnitude of actual qs(t) and was sensitive to inotropic interventions. A relationship between zero-load flow and parameters of cardiac muscle mechanics is derived from the Thevenin equivalent model of the pumping function of the ventricle and the three dimensional force-velocity-length diagram. The present analysis indicates that aortic flow can be expressed as the difference of afterload-independent zero-load flow and externally-controlled afterload-dependent internal flow.

Dynamic optimization of in-series cardiac assistance by means of intra-aortic balloon pumping.

Analytical techniques are developed which permit objective control of assist device driving systems. In addition to being objective, the techniques described in this paper are optimal in the sense of minimizing a performance index which consists of a term involving left ventricular power and a term involving deviations of aorta hemodynamic parameters from normal values. Comparisons are included of off-line computations and measurements on dogs with experimentally induced myocardial infarctions undergoing intra-aortic balloon pumping.

Frequency analysis of time-varying elastance model of the left ventricle

Zadehs transfer function method for linear time-variable systems is used to apply frequency-domain analysis to a periodically time-varying elastance model of the left ventricle. Left ventricular pressure computed from the system function of the time-varying elastance and the phasors of aortic flow shows a typical waveform of the measured ventricular pressure.

Frequency-Domain analysis of oxygen stores during hypoxia in the goat

AbstractSinusoidal variations of expired oxygen fraction (FEO2) and arterial blood oxygen saturation (SaO2) were measured in three paralyzed and anesthetized goats after producing sinusoidal changes in inspired oxygen fraction (FIO2) under controlled ventilation. These frequency-domain data were used to evaluate the quantitative dynamic relations amongFIO2,FEO2, oxygen uptake at the lung

Performance criteria for optimization of cardiac assistance.

\dot VO_2

The Interraction of Mechanical Left Ventricular Assistance and the Physiological Control System

andSaO2 using the material balance equation at the lung and the Fourier transform of this equation. The overall transfer function betweenFIO2 andFEO2 wasT(s)=0.07/(s+0.075) with a time constant of 13.3 sec, and