Optimum criteria for the diagnosis of ventricular septal defect from measurements of blood oxygen saturation.

A LLEFT-TO-RIGHT shunnt t-hrough a veiitricular sep)tal defect is sungeste(d by a higher blood oxy geni saturatioii withiin thie right venjtriele than in the right atriun. The increased saturation inay be detected by observations at inaniv locations witlin the right ventricle, in which case the mnean of variously located observations is higher tlhani the mean of observations withinl the right atrium. Alterinatively, an iimereased blood oxyg;en saturation may be observable at only a particular region of the right -ventricle, in whibh case the left-to-right shunt is appare-nt fromn on(l the extreme values fronm this region anid may not be adequately reflected by the mean oxv o-en saturation of variously located right y-entricular blood samples. The objeetive of samplinge withinthe rigdl-t ati'iumi is to provide an accurate Avalue of rnixed atrial oxvygenl saturationl. VUJ :fortuiniately, the right atrium. is a poor mniiximlo chainber and it is urnlikelv that a point of ideal or complete mixing frequen-tly exists. It would seem, however, that a good estimnate of ideal mixed venous blood Awould be obtained from the mnore central regions of the right atriuin in an attempt to avoid those locations that predominantly contain onrle of the three enterinig streams-superior and inferior vena caval and coronarsinus streams. In eontrast to the above considerations for right atrial sampling, the optiniumn sam-lplinc locationi within the right ventriele for qualitative detection of a left-to-right shulnt