Measurement of cardiac output by impedance cardiography under various conditions

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Abstract
The suitability of impedance cardiography as a method to follow changes in cardiac output (CO) was studied by comparing it with thermodilution and by measurements in conditions with predictable effects on CO. The correlation between absolute CO values obtained by impedance and thermodilution techniques was moderate (r [correlation coefficient] = 0.61), but the percentage changes showed a good correlation (r = 0.84). Headup tilting decreased CO by 25% in 5 normal subjects. Bloodletting in 3 subjects caused a 20% decrease, reinfusion in 1 subject a 16% increase. Occlusion of artificial large flow arteriovenous shunts in 6 dialysis patients caused a 12% decrease in CO, but the effect was less with moderate and absent with small flow shunts. Ultrafiltration caused a 28% decrease in 2 dialysis patients. In 20 hypertensive patients CO dropped 25% after salt depletion; propranolol given i.v. gave a 15% decrease (no. = 13), diazoxide i.v. a 30% increase (no. = 6). Apparently impedance cardiography is a reproducible method and suitable for the measurement of intrapatient changes in CO.