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Work, External stroke

The gas mixture inside one of the cylinders of an automobile engine expands against a constant external pressure of 0.98 atm, from an initial volume of 150 mL (at the end of the compression stroke) to a final volume of 800 mL. Calculate the work done on the gas mixture during this process, and express it in joules. [Pg.522]

Figure 13-2. Ventricular function (Frank-Starling) curves. The abscissa can be any measure of preload—fiber length, filling pressure, pulmonary capillary wedge pressure, etc. The ordinate is a measure of useful external cardiac work—stroke volume, cardiac output, etc. In congestive heart failure, output is reduced at all fiber lengths and the heart expands because ejection fraction is decreased. As a result, the heart moves from point A to point B. Compensatory sympathetic discharge or effective treatment allows the heart to eject more blood, and the heart moves to point C on the middle curve. Figure 13-2. Ventricular function (Frank-Starling) curves. The abscissa can be any measure of preload—fiber length, filling pressure, pulmonary capillary wedge pressure, etc. The ordinate is a measure of useful external cardiac work—stroke volume, cardiac output, etc. In congestive heart failure, output is reduced at all fiber lengths and the heart expands because ejection fraction is decreased. As a result, the heart moves from point A to point B. Compensatory sympathetic discharge or effective treatment allows the heart to eject more blood, and the heart moves to point C on the middle curve.
Stroke volume has long been considered a critical hemodynamic quantity in assessing ventricular function. Its product with mean blood pressure, bears a direct relation to the energy expenditure of the heart, or the external work, EW,... [Pg.277]

A larger ventricle generates a greater amount of external work. The quantity of blood that is ejected per beat (stroke volume), however, is a constant fraction of the amount contained in the heart as end-diastohc volume. Thus, ejection fraction, as it is termed, is thus an invariant among mammals. [Pg.278]

EW is also termed stroke work and is represented as the area encircled by the left ventricular pressure-volume (P-V) diagram during each heart beat. The external mechanical work generated by the heart per unit body or heart weight is constant for mammalian species [Li, 1983a, b], that is. [Pg.279]

Much of the criticism of the interpretation of Starling s original measured input-output relations was resolved by the introduction of a family of cardiac function curves [74], which accommodated neural and metabolic stimulation of the heart. Such influences manifest themselves in graphs of input (preload)-output (stroke volume, stroke work, etc.) as counter clockwise rotation (steeper) and stretch along the output (vertical) axis. Alteration in parameter c in Equation 18.1 and Equation 18.2 carries major responsibility for these modifications. In addition, it has recently been found that the cardiac function curve can be shifted along the horizontal (preload) axis [75]. This shift is effected by changes in air pressure, pe, external to the cardiac chambers, such as caused by the respiratory system, or by CPR, and modifies Equation 18.2 by approximation to... [Pg.298]

To answer the question of optimal matching between the ventricle and arterial load, we developed a framework of analysis which uses simplified models of ventricular contraction and arterial input impedance. The ventricular model consists only of a single volume (or chamber) elastance which increases to an endsystolic value with each heart beat. With this elastance, stroke volume SV is represented as a linearly decreasing function of ventricular endsystolic pressure. Arterial input impedance is represented by a 3-element Windkessel model which is in turn approximated to describe arterial end systolic pressure as a linearly increasing function of stroke volume injected per heart beat. The slope of this relationship is E. Superposition of the ventricular and arterial endsystolic pressure-stroke volume relationships yields stroke volume and stroke work expected when the ventricle and the arterial load are coupled. From theoretical consideration, a maximum energy transfer should occur from the contracting ventricle to the arterial load under the condition E = Experimental data on the external work that a ventricle performed on extensively varied arterial impedance loads supported the validity of this matched condition. The matched condition also dictated that the ventricular ejection fraction should be nearly 50%, a well-known fact under normal condition. We conclude that the ventricular contractile property, as represented by is matched to the arterial impedance property, represented by a three-element windkessel model, under normal conditions. [Pg.90]

When calculating NPSHr for the compression of liquefied gases up to supercritical pressures, account should be taken of the real fluid temperature in the working chamber during the suction stroke. This can be higher than that of the fluid stream external to the pump, thus increasing NPSHr above the value calculated from external conditions. In addition to the fluid mechanical NPSHr calculated from the external temperature there is also a thermodynamic NPSH contribution which depends on the fluid temperature in the working chamber. Local rises in the temperature can produce two effects which should be considered ... [Pg.276]


See other pages where Work, External stroke is mentioned: [Pg.943]    [Pg.94]    [Pg.1025]    [Pg.1008]    [Pg.468]    [Pg.189]    [Pg.178]    [Pg.309]    [Pg.518]    [Pg.538]    [Pg.12]    [Pg.314]    [Pg.150]    [Pg.194]    [Pg.97]    [Pg.368]    [Pg.468]   
See also in sourсe #XX -- [ Pg.94 ]




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External work

Working stroke

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