back | nextStroke Volume IndexStroke volume index is the volume of blood pumped by the heart with each beat (in milliliters) divided by the body surface area (square meters). This allows direct comparison of the stroke volume index of large and small patients. Show
Stroke volume index is determined by three factors:
Starling's Law is the relationship between preload and stroke volume . Recommended textbook solutions
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Visual Anatomy and Physiology3rd EditionEdwin F. Bartholomew, Frederic H. Martini, Judi Lindsley Nath, Kevin Petti, William C Ober 2,432 solutions Skip to content Preload is the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. It is related to ventricular filling. Afterload is the force or load against which the heart has to contract to eject the blood. Contractility is the intrinsic strength of the cardiac muscle independent of preload, but a change in preload will affect the force of contraction. Afterload is the ‘load’ to which the heart must pump against. Afterload goes down when aortic pressure and systemic vascular resistance decreases through vasodilation. Decreasing afterload will affect the Doppler numbers in a number of ways.
Peak velocity (PV) may increase as the heart finds it easier to pump against decreasing pressures. This will also affect corrected flow times (FTc), as the duration of aortic blood flow will increase as afterload decreases. Poor Left Ventricular FunctionThe waveform below demonstrates the response to a positive inotrope. In the first (left) screenshot, the patient had a ‘rounded’ flow waveform, with a low Peak velocity (PV) and stroke volume (SV), possibly indicating left ventricular failure. The patient was not fluid responsive and following administration of a positive inotrope, both PV and SV increase (right screenshot). Systemic Vascular ResistanceSystemic vascular resistance (SVR) is the resistance to blood flow offered by all of the systemic vasculature [2]. An increase in SVR depends on the degree of sympathetic stimulation which itself depends on the degree of sympathetic activation, responsiveness of the vasculature, the number of vascular beds involved and the relative series and parallel arrangement of these beds to each other. Changes in blood viscosity also affect SVR. SVR is an unreliable indicator of left ventricular afterload [2] since it reflects only peripheral vasomotor tone and not left ventricular systolic wall force. Discordant changes in left ventricular afterload and SVR can occur during pharmacological interventions as shown by Lang et al. They conclude “In the clinical setting, changes in SVR do not necessarily reflect left ventricular loading conditions since the true measure of ventricular afterload must consider the interaction of factors internal and external to the myocardium.” References1. Klabunde, R.E., Cardiovascular Physiology Concepts. 2005.Philadelphia. Lippincott Williams & Wilkins How does preload and afterload affect blood pressure?Increasing Preload Increases the Stroke Volume, Increasing Afterload Decreases It. The afterload for the heart is the arterial pressure into which the heart ejects its stroke volume.
What is increased cardiac output?Generally speaking, your heart beats both faster and stronger to increase cardiac output during exercise. Sufficient cardiac output helps keep blood pressure at the levels needed to supply oxygen-rich blood to your brain and other vital organs.
Which of the following factors can increase the cardiac output?The stroke volume and the cardiac output increases with the increase in the force of contraction.
Which of the following conditions would lead to an increase in the afterload for the ventricles?Afterload is increased when aortic pressure and systemic vascular resistance are increased, by aortic valve stenosis, and by ventricular dilation. When afterload increases, there is an increase in end-systolic volume and a decrease in stroke volume.
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