STENOSIS AND INSUFFICIENCY 



649 



elusions from studies in animals and man. The termi- 

 nal slope of the peripheral dilution curve obtained 

 following prepulmonary injection of indicator seems 

 mainly determined by pulmonary volume. Valvular 

 insufficiency does not decrease this slope until one 

 of the downstream cardiac chamber mi.xing volumes 

 approaches the pulmonary volume or until cardiac 

 output falls. Several modifications of this method 

 hax'e been suggested by Dexter, Wood, Shillingford, 

 and Lange, among others, which consist, for example, 

 in the change of the injection site to the pulmonary 

 artery or the left heart chambers, and the use of other 

 constants for calculation. 



In the experience of most investigators, random 

 variability has been so great that the alteration in 

 curves resulting from mild regurgitation could not be 

 detected, and the \ariations in the case of severe 

 regurgitation have been so wide as to make the 

 method useless. 



Levison & Sherman (137), at the Lincoln Labora- 

 torv of the Massachusetts Institute of Technology, 

 ha\e discussed the problem of using indicator dilution 

 curves for estimation of regurgitation on a inathe- 

 matical basis. They state that the assumption of com- 

 plete and instantaneous mixing of the indicator in the 

 cardiac chambers (upon which the usefulness of all 

 the dilution techniques for regurgitation depend to 

 some degree) is the one most likely to be violated. 

 They also consider that the importance of the mixing 

 problem requires further experimental study before 

 any of the suggested methods should be used. Al- 

 though this method cannot be used for any exact 

 estimation of valvular regurgitation it has had some 

 clinical application, with a fair predicting value in 

 90 to 95 per cent of the curves (33-36, 49, 207). 



Methods have also been developed in order to 

 record dilution curves simultaneously from the left 

 atrium and systemic arterial and venous circulation, 

 following injections of indicator into the left ventricle, 

 left atrium, aorta, and \arious sites in the venous 

 circulation. These methods ha\e been used in the 

 study of mitral or tricuspid regurgitation. After 

 injection of an indicator into the left ventricle in the 

 presence of an incompetent mitral vahe, movement of 

 the resulting mixture of blood may be either back- 

 ward and into the left atrium or forward into the 

 aorta. If an indicator dilution curve is recorded from 

 the left atrium after injection of the indicator into the 

 left \entricle, the early appearance of dye in the 

 atrium indicates that regurgitation through the mitral 

 vahe has occurred. The failure to detect the earlv 



appearance of the indicator suggests that the mitral 

 valve is competent. Comparison of the area of the 

 rapidly appearing portion of such a left atrial dilution 

 curve with the areas of curves recorded from the left 

 \entricle or the pulmonary artery has been suggested 

 as an exact means of estimating the quantity of blood 

 regurgitated through the mitral valve. A necessary 

 prerequisite for this is complete mixing of indicator 

 and blood in the left heart. Studies in dogs and 

 patients with mitral valve disease have demonstrated, 

 however, that this method failed to discriminate 

 between stenosis and regurgitation in a reliable man- 

 ner, and thus cannot be used for the calculation of 

 regurgitant flow (141, 142). Incomplete mixing, both 

 in the ventricle where the indicator is injected and 

 in the atrium where it is collected, may completely 

 invalidate this method. Levison & Sherman (137), 

 who recently treated this problem mathematically, 

 stated that the importance of the mixing problem 

 requires further experimental study. 



Braunwald et al. (28) and Warner & Toronto 

 (194), among others, have also made use of indicator 

 dilution curves to estimate the regurgitant back 

 flow in aortic incompetence, with the indicator in- 

 jected distally and collected proximalh' in the aorta 

 (28, 94, 194). Too few studies have been made with 

 this method to assess its value. The lack of any figures 

 for backflow as a comparison to what is obtained with 

 the dilution methods also precludes any judgment as 

 to its validity. 



It seems safe to conclude that there is at present no 

 method for employing indicator dilution curves in 

 order to arrive at an exact es'aluation of the degree 

 of \alvular regurgitation, although several applica- 

 tions in the hands of critical investigators may have 

 limited clinical value. 



.JiTRI.^L PRESSURE PULSE 



Lejt Atrium 



Studies in laboratory animals and in man have 

 shown similar findings (fig. 2). The atrial contraction 

 causes a small pressure rise (the a wave) followed by a 

 fall. \"entricular contraction causes the mitral valve 

 to close. The positive c wa\'e in the left atrium begins 

 at this time. This wave is a function of the relative 

 pressures within the atrium and ventricle with the 

 onset of ventricular svstole. If at the start of \entricu- 

 lar contraction the ventricular pressure is less than 



