Identify whether each item would increase or decrease stroke volume Increasing afterload Increase stroke volume Increased mitral valve regurgitation Decrease stroke volume Increasing EDV Increasing preload Increasing afterload Decreased venous return Increased activity of the muscular and respiratory pumps Dehydration ok Increasing contractility Sympathetic
The correct answer and explanation is:
Here is an analysis of each item and whether it increases or decreases stroke volume, along with explanations:
- Increasing Afterload – Decrease stroke volume Afterload is the pressure that the heart must work against to eject blood during systole. When afterload increases (due to conditions like high blood pressure or aortic stenosis), it makes it harder for the heart to pump blood, which can reduce stroke volume. The heart has to generate more force to overcome the increased resistance, and this can limit the amount of blood it ejects with each beat.
- Increased Mitral Valve Regurgitation – Decrease stroke volume Mitral valve regurgitation occurs when the mitral valve does not close properly, causing blood to flow backward into the left atrium during systole. This reduces the amount of blood that is ejected into the systemic circulation, effectively reducing stroke volume, as part of the stroke volume is “lost” back into the atrium.
- Increasing EDV (End-Diastolic Volume) – Increase stroke volume EDV refers to the volume of blood in the ventricles at the end of diastole, before contraction. According to the Frank-Starling law of the heart, an increase in EDV leads to a greater stretch of the myocardial fibers, enhancing the force of contraction. This results in an increased stroke volume, as more blood is pumped out with each beat.
- Increasing Preload – Increase stroke volume Preload is the initial stretching of the cardiac muscle fibers prior to contraction, determined largely by EDV. Increasing preload enhances the force of myocardial contraction (as per Frank-Starling mechanism), thereby increasing stroke volume.
- Increasing Afterload – Decrease stroke volume (same as #1)
- Decreased Venous Return – Decrease stroke volume Venous return refers to the flow of blood back to the heart. A decrease in venous return (such as during blood loss or vasodilation) reduces the amount of blood entering the heart, which reduces EDV and thus stroke volume.
- Increased Activity of the Muscular and Respiratory Pumps – Increase stroke volume These pumps help return blood to the heart, particularly during physical activity. When the muscular and respiratory pumps are more active, venous return increases, which increases EDV and stroke volume.
- Dehydration – Decrease stroke volume Dehydration leads to a decrease in blood volume, which reduces venous return and EDV. As a result, stroke volume can decrease because there is less blood available to pump out of the heart.
- Increasing Contractility – Increase stroke volume Contractility refers to the intrinsic ability of the heart muscle to contract. Increased contractility means that the heart can eject more blood with each contraction, thereby increasing stroke volume. This can be enhanced by sympathetic nervous system stimulation and positive inotropic agents.
- Sympathetic Nervous System Activation – Increase stroke volume The sympathetic nervous system increases heart rate and contractility. Increased contractility (positive inotropy) results in a greater force of contraction, which increases stroke volume, while increased heart rate may also enhance stroke volume at higher frequencies (though the effects may be more complex at extremely high rates).
In summary, factors that increase preload, contractility, or venous return typically increase stroke volume, while factors that increase afterload or reduce venous return tend to decrease stroke volume.