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  • 1
    ISSN: 1615-2573
    Keywords: Pump function ; Systole ; Diastole ; Preload ; Afterload ; Ventricular distensibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We propose new indexes to evaluate the effects of ventricular inotropism and lusitropism on stroke volume. The end-systolic pressure-volume relationship (ESPVR) or its slope (Emax) has been employed to assess ventricular inotropism. The end-diastolic pressure-volume relationship (EDPVR) or compliance has been used to express ventricular diastolic properties or lusitropism. However, their net effect on stroke volume under a given set of preload and afterload pressures has not quantitatively been evaluated.Ejecting volume gain (Ge) was proposed to quantify the inotropic effect on stroke volume by the change in end-systolic volume between the two ESPVR curves obtained before and during an inotropic intervention at a specified ejecting pressure. Ge is a function of afterload pressure.Filling volume gain (Gf) was proposed to quantify the lusitropic effect on stroke volume by the change in end-diastolic volume between the two EDPVR curves before and during a lusitropic intervention at a specified filling pressure. Gf is a function of preload pressure. The net effect of these inotropic and lusitropic effects on stroke volume at these specified preload and afterload pressures can be expressed by the sum of Ge and Gf. We call this sumstroke volume gain (Gsv). Gsv is a function of preload and afterload pressures. Using representative examples, we demonstrate that these new indexes are conceptually useful to quantitatively understand changes in the pumping ability of the heart under simultaneous inotropic and lusitropic effects as a function of ejecting and filling pressures.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-2573
    Keywords: Inotropism ; Oxygen consumption ; Cardiac energetics ; Pressure-volume area ; Excitation-contraction coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We compared the oxygen cost of increasing ventricular contractility using Emax (slope of the ventricular end-systolic pressure-volume relation) as the index of ventricular contractility. Contractility was enhanced by calcium and epinephrine in paired experiments on dog left ventricles. Firstly, we obtained left ventricular oxygen consumption (Vo2) and systolic pressure-volume area (PVA, a measure of total mechanical energy) of contractions at different volumes in the control contractile state to determine a reference Vo2-PVA relation. PVA was obtained as the area in the pressure-volume (P-V) diagram which was bounded by the end-systolic P-V line, end-diastolic P-V curve and systolic P-V trajectory of individual contractions. Secondly, we gradually enhanced Emax with calcium and epinephrine in two consecutive runs at a fixed ventricular volume. Both Vo2 and PVA increased with enhanced Emax. From these Vo2-PVA data, we calculated the PVA-independent Vo2 values at the respective enhanced Emax levels and determined the oxygen cost of Emax as the slope of the relation between the PVA-independent Vo2 and Emax. The cost per beat and per 100g was 0.00158ml O2/ (mmHg/ml) for calcium and 0.00166 ml O2/(mmHg/ml) for epinephrine on average, values not significantly different from each other (P 〈 0.05). We conclude that epinephrine and calcium have similar oxygen costs of contractility over a wide range of Emax despite their different pharmacological mechanisms of positive inotropism.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1615-2573
    Keywords: Negative feedback ; Transfer function ; Exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In exercise training, precise control of exercise intensity would maximize the training efficacy while minimizing risks. To adjust work rate, heart rate (HR) has been used as a measure of exercise intensity. Thus, we developed a servo-controller of HR using a cycle ergometer. After estimating the transfer function from work rate to HR, we optimized feedback parameters for achieving a quick and stable HR response by means of a computer simulation. We then examined the performance of the servo-controller of HR in 55 healthy volunteers. We set the target HR at 60% and 75% of the age-predicted maximum HR. Times required for HR to reach 90% of the target HR were 136 ± 33 and 137 ± 22s in the respective protocols. Standard deviations of the steady-state difference between the target and measured HRs were 2.5 ± 0.6 and 3.8 ± 1.1 beats/min. We conclude that the developed servo-controller makes it possible to precisely regulate HR and, thereby, exercise intensity.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1615-2573
    Keywords: Cardiac performance ; Ventricular function ; Mechanical contraction ; External work ; Potential energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have theoretically proposed “systolic pressure-volume area” (PVA) as a measure of total mechanical energy generated by ventricular contraction. We then experimentally showed that PVA closely correlates with left ventricular oxygen consumption (Vo 2) regardless of ventricular loading conditions in a stable contractile state. Although Starling's law of the heart has been generally considered to describe the relation between ventricular preload as the input and the “energy of contraction” as the output, the energy of cardiac contraction has been variously identified with cardiac output, external work, contractile element work, tension-time index, etc., by different investigators. However, none of these variables has been unanimously accepted as the total mechanical energy of contraction because they do not consistently correlate withVo 2 which represents the total energy utilization for contraction. Considering the nature of PVA which has been revealed over the last decade, we now confidently propose that PVA is the most likely expression of the total mechanical energy of contraction that has been pursued for many years as the energy of contraction in Starling's law of the heart.
    Type of Medium: Electronic Resource
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