Fiberoptic ear densitometer for measurement of cardiac output.

This study presents theory, operation, and evaluation of a new earpiece method for measurement of cardiac output using the multichannel fiberoptic system recently described. The system includes an earpiece of simple design and small size suitable for applications in all subjects regardless of their age or size. The method requires no withdrawal and analysis of blood samples for calibration. Compared with earlier techniques the present method, based on measurements in three distinct absorption bands in the infrared, provides an increase in accuracy of the estimations. This accuracy was tested in children undergoing routine cardiac catheterization. Comparisons were made in 39 instances (25 subjects) between simultaneously carried out determinations by the earpiece and cuvette densitometer methods. The agreement was good (r = 0.97, p less than 0.001), with a standard deviation of the differences of 0.479 litre/min, or 10.2% of the mean values derived from the cuvette curves. The regression equation describing the values derived from ear curves in terms of values from the cuvette curves differed only slightly from unity (Y = 0.167 + 0.985X). The usefulness of the fiberoptic earpiece technique both in clinical investigations and cardiovascular diagnosis was demonstrated.