The concept of preload and its evaluation in the intact left ventricle.
Preload affects left ventricular pump function through the Frank-Starling curve by changing sarcomere length. However, common indices of preload, such as end-diastolic volume, or pressure, or stress, do not necessarily reflect sarcomere length. Ultimately, this depends on the elastic stiffness constant (k) and end-diastolic stress (sigma), which are not in simple relation with the above mentioned indices. An index of preload is proposed, (k sigma)(1/k). This index has been evaluated in 148 patients with different degrees of hemodynamic overload, and in 24 normal subjects. The preload index was found to be 1.448 +/- 0.034 in normal subjects. However, in the other patients evaluated preload index increased in mitral insufficiency (1.490 +/- 0.035), in decompensated aortic insufficiency (1.490 +/- 0.89) and in dilated cardiomyopathy (1.52 +/- 0.125), and markedly decreased in aortic stenosis (1.367 +/- 0.039) and in hypertrophic cardiomyopathy (1.41 +/- 0.034). It was always positively related to the afterload, measured as peak systolic stress. No positive relationship was found with end-diastolic volume nor pressure. Therefore, preload as a compensatory mechanism is differently recruited in response to various degrees of hemodynamic overload and parallels the afterload, in agreement with the concept of preload-afterload mismatch.
Razzolini
R
R
Department of Clinical Medicine, University of Padova Medical School, Italy.
Boffa
G M
GM
Ramondo
A
A
Daliento
L
L
Stritoni
P
P
Chioin
R
R
Dalla-Volta
S
S
D001022:Aortic Valve Insufficiency / Q000503:physiopathology; D001024:Aortic Valve Stenosis / Q000503:physiopathology; D001794:Blood Pressure; D002302:Cardiac Output; D002306:Cardiac Volume; D002311:Cardiomyopathy, Dilated / Q000503:physiopathology; D002312:Cardiomyopathy, Hypertrophic / Q000503:physiopathology; D006439:Hemodynamics; D006801:Humans; D008944:Mitral Valve Insufficiency / Q000503:physiopathology; D008955:Models, Cardiovascular; D009200:Myocardial Contraction; D013318:Stroke Volume; D016276:Ventricular Function