Measurement of Mitral Regurgitation by IndicatorDilution Tecirniques

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Abstract
Ethocls f o r q u a n t i f y i n g initral regurgitation that require the measurenlent only of tlie area enclosecl by the inclicator-clilution curves offer the advantage of being computationally simpler tha11 the others. Furthermore, clistortions in the shape of t h e curve will not necessarily induce significant error in the area enclosecl by the curve. Since such methocls require sampling from t h e a t r i u m as well as from the ventricle, or proximal aorta, the?- will lw successful only if meaningful samples uf indicator concentration can he obtained from these chambers. The cluestion remains to be arc$\\-erecl: 13 the mixing in the cardiac chambers sufficient to allow meaningful sampling in both atrium and rentricle? A review of the literature on this, subject 11s been inconclusive."-" MTe iwe not aware of any experiments in which all of the conclitions aftecting cardiac chamber mising have been controllecl without seriously disturbing normal carcliac physiology. Such ;in experiment shoulcl control the nature of injection (i.e., one or mauy successi\-e pulses). the number ancl placement of the orifices a t the tip of the injection catheter, ancl the timing of the i u j e c t i o ~ l with the carcliac cycle. Experiments indicate t h a t the optim~um mixing conclitions exist at the beginning of ventricular filling ancl that injection should be timed to coincide with this point in tlw cycle. I t is of interest to note that, in the clye curve e x p e r i m e ~ ~ t s by Sinclair et al.Ix in whic.11 animals were used, t h e time a t which injcctions were macle was found to be unimportant. 'I'his important difference between t11c mising characteristics of the mechanical ~noclcl and an animal lieart illustrates the cliificulties cncountered in the application of moclel results ancl observations to the human heart. It seems reasonable to conjecture, ho\vever, that the \\,ell-estal~lisl~ecl mixing properties of flows through valves ancl orifiws in ripicl systems will be enhancecl in the cleformable wall situation encountered in the h r a r t . F u r t h e r experiments using the indicator-dilution technique on both normal ancl abnormal hearts are evidently requirecl t o determine the nature ancl extent of tlie clepenclence of measurement reliability on the sanipling site location.