Snapshots of Hemodynamics by Nicolaas Westerhof & Nikolaos Stergiopulos & Mark I. M. Noble & Berend E. Westerhof

Author:Nicolaas Westerhof & Nikolaos Stergiopulos & Mark I. M. Noble & Berend E. Westerhof
Language: eng
Format: epub
ISBN: 9783319919324
Publisher: Springer International Publishing

with g f a geometry factor accounting for the (local) radius of curvature and myocardial wall thickness. By the chain rule, differentiating with respect to time, we obtain:

This shows that it is important to determine dP lv /dt max during isovolumic conditions so that g f may be assumed constant, i.e., dg f /dt = 0, and

With changes in filling the geometric factor g f will change limiting its use as contractility index. At low volumes, such as during cardiac surgery with open chest, a change in dP lv /dt max , may result both from changes in muscle function and filling. In the closed chest, and in the catheter laboratory the geometric factor does, in general, not change so that dP lv /dt max gives useful information on averaged global muscle function. At very large ventricular volumes an increase in the factor g f may even result in a decrease in dP lv /dt max . Thus dP lv /dt max can be used only as a convenient volume independent index for changes in cardiac contractility in the catheter laboratory. In Fig. 20.2 the record on the left was obtained with the patient in head-up tilt and the record on the right with the patient in head-down tilt. It can be seen that the left ventricular end-diastolic pressure is higher in the right hand record due to the increase in ventricular volume, but dP lv /dt max is unchanged [2].

Fig. 20.2Time derivative of left ventricular pressure, dP lv /dt max , when falling before valve opening (left panel) is used as a measure of contractility. The right panel shows that increased filling, resulting in an increase in end-diastolic pressure (LVEDP, dashed line) does not affect dP lv /dt max since this index is sensitive to inotropic interventions and not, in this range, depending on filling pressure. The rate of ventricular relaxation is defined by the time constant tau, and relates with left ventricular end-diastolic pressure. The dP lv /dt min is a measure of ventricular relaxation. (Right panel adapted from Ref. [2], by permission)

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