CPPS 302 Venous Return and the Length-Tension Relationship

Flashcards covering the effects of venous return and the length-tension relationship on stroke volume within the cardiovascular system, including definitions of key terms like preload, compliance, contractility, and Frank-Starling mechanism.

Venous Return

The rate of blood flow back to the heart from the vena cavae into the right atrium, a key determinant of preload.

Length-Tension Relationship

The biophysical basis for Starling's law, illustrating the relationship between the initial length of a myocyte (preload) and the contractile force (tension) developed by the heart muscle.

Preload (EDV)

The ventricular end-diastolic volume (EDV), often determined by venous return, length-tension relationship, ventricular compliance, and to a lesser extent, heart rate

Ventricular Compliance

The ability of the ventricle to stretch and fill, measured as the change in volume per unit change in pressure (ΔV / ΔP).

Cardiac Output

The volume of blood pumped by the heart per minute, calculated as heart rate multiplied by stroke volume.

LVEDPVR

Left Ventricular End-Diastolic Pressure-Volume Relationship, showing the relationship between pressure and volume in the left ventricle during diastole.

End-Diastolic Volume (EDV)

The maximum amount of blood contained in the ventricles at the end of diastole (isovolumic relaxation), before systole begins.

End-Diastolic Pressure (EDP)

The pressure within the ventricles at the end of diastole

What does the Frank-Starling Mechanism ensure?

That the outputs of both ventricles match over time and to prevent the shifting of blood between pulmonary and systemic circulations

Optimal Resting Length

The muscle length at which the thick and thin filaments have the ideal overlap for producing maximal tension development upon contraction.

End-Systolic Volume (ESV)

The volume of blood remaining in the ventricles at the end of systole, after isovolumic contraction.

What is the relationship between dilated ventricles and venous return?

Dilated ventricles indicates an increase in compliance, the slope of the LVEDPVR will be less steep, which implies an enhanced venous return due to reduced pressure required to fill the ventricles adequately. This also means that the heart experiences a smaller rise in EDP than it normally does.

What is the relationship between hypertrophied ventricles and venous return?

Hypertrophied ventricles indicates a decrease in compliance, the slope of the LVEDPVR is steeper, which implies a decrease in venous return due to a much higher pressure within the ventricles prior to systole. The rise in EDP experienced by the heart is much higher than normal.

How does increased venous return effect EDV?

an increase in venous return always indicates an increase in EDV, due to increased ventricular filling

When you have an observed increase in venous return (and EDV), how would contractility of the heart be influenced?

It wouldn’t be, such an increase has no influence over the intrinsic ability of the heart to contract (its contractile status), as an increase in venous return doesn’t imply any changes in parasympathetic or sympathetic activity

When you have an increase in preload, what can be observed about the length-tension relationship?

An increase in preload will increase active tension of the muscle (through increased stretching of sarcomeres), this will be accompanied by an increase to the force of contraction through an increased velocity of muscle fiber shortening

Why does the length-tension relationship explain why you have an observed increase in stroke volume and EDV, but no change in ESV?

Because the contractility of the heart has had no change, the ability of the heart to forcefully contract matches the increased venous return