DETERMINATION OF THE MEAN CROSS-SECTIONAL AREA OF THE THORACIC AORTA USING A DOUBLE INDICATOR DILUTION TECHNIQUE

A double indicator dilution technique for determining the mean cross-s ectional area (CSA) of a blood vessel in vivo is presented. Analogous to the thermodilution method, dilution of hypertonic saline was measur ed by an electrical conductance technique. Because the change in condu ctance rather than absolute conductance was used to calculate CSA, pul satile changes in shear rate of blood and conductance of surrounding t issues had no effect on the data. To calculate CSA from an ion mass ba lance, cardiac output was needed and estimated from the thermodilution curve using the same ''cold'' (hypertonic) saline injection. The mean CSA, obtained from this double indicator dilution method (CSA(GD)), w as compared with the CSA obtained from the intravascular ultrasound me thod (IVUS) in 44 paired observations in six piglets. The regression l ine is close to the line of identity (CSA(GD) = -1.83 + 1.06 . CSA(IVU S), r = 0.96). The difference between both CSAs was independent of the diameter of the vessel, on average -0.99 mm(2) +/- 2.64 mm(2) (mean C SA(GD) = 46.84 +/- 8.21 mm(2), mean CSA(IVUS), = 47.82 +/- 9.08 mm(2)) and not significant. The results show that the double indicator dilut ion method is a reliable technique for estimating the CSA of,blood ves sels in vivo.