Exam
Preload
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Preload
, Ventricular Preload, Frank-Starling Curve
See Also
Ventricular Afterload
Blood Volume
Cardiac Output
(and
Stroke Volume
)
Definitions
Preload (right atrium Preload)
Determined by venous return and right ventricular compliance
End-diastolic wall tension (and end-diastolic volume) of the right ventricle
Ventricular muscle stretches in response to increased pressure
Physiology
Frank-Starling Curve
Normal heart
Diastolic volume is the key determinent of ventricular contraction strength in the normal heart
As end-diastolic volume (and pressure) increases, peak systolic pressure (contraction strength) increases
Augmented contractility (e.g. inotrope infusion)
Frank-Starling Curve shifts up and to the left
For any given end-diastolic volume, the ventricular contraction (
Stroke Volume
) is increased
Congestive Heart Failure
Frank-Starling Curve shifts downward and flattens
For any given end-diastolic volume in CHF
Ventricular contraction (
Stroke Volume
) is less than in a normal patient
Increasing end-diastolic volume in CHF has adverse effects
Stroke Volume
increases minimally (flat part of Frank-Starling Curve)
Peak systolic pressure increases significantly and results in vascular congestion
Maladaptive long-term compensatory mechanisms develop to maintain
Stroke Volume
Ventricle dilates (
Cardiomyopathy
) to allow for increased filling
Ventricle becomes stiff (
Diastolic Dysfunction
)
Diagnostics
Right Preload
Central Venous Pressure
(see precaution below)
IVC Ultrasound for Volume Status
(
Caval Aorta Index
)
Left Preload
Pulmonary Artery
Occlusion
pressure or wedge pressure (see precaution below)
Symptoms (
Orthopnea
or
Dyspnea
on exertion)
Signs (
Pulmonary Edema
, rales)
Imaging (
Lung Ultrasound
)
Precautions
End diastolic pressure (e.g. CVP and Wedge Pressure) correlates poorly with end diastolic volume even in healthy patients
Hence CVP and Wedge Pressure are unreliable markers of ventricular filling and volume status
References
Killu and Sarani (2016) Fundamental
Critical Care
Support, p. 93-114
Marino (2014) ICU Book, 4th Ed Wolters-Kluwer p. 151-7
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