Respiration and measurement of cardiac output by thermodilution and central or peripheral dye dilution.

Cardiac output as measured by indicator dilution methods during artificial ventilation shows differences up to +/- 35%. We studied the influence of spontaneous breathing on measurement of cardiac output by thermodilution (TD) and central (CDD) and peripheral dye dilution (PDD) in seven anesthetized dogs. Injection of indicator was timed at one of five chosen moments in a respiratory cycle. The indicator for TD was also used as solvent for indocyanine green. Results were normalized by the value obtained with injection at inspiratory onset. Results of the central dilution methods showed a slight but not significant difference between values measured with injection at 25 and 75% of the respiratory cycle: 105.7 and 98.0%, respectively, (TD) and 102.3 and 97.2% (CDD). Mean cardiac output determined by TD, CDD, or PDD was not significantly different. We conclude that 1) a reasonable estimate of cardiac output may be obtained by means of a single indicator-dilution curve and 2) the choice of the dilution method may be determined by practical considerations.     

A technique of measuring cardiac output and peripheral resistance in the conscious rat

A technique for the measurement of cardiac output in the conscious rat by cardiac catherization and application of the Fick principle, with simultaneous measurement of oxygen consumption and aortic pressure, is described. In conscious rats, the cardiac index was found to be 1.5 1/min/m² and the total peripheral resistance 0.8 mm Hg/ml/min per 100g body weight.     

Cardiac output measurement in mice by thermodilution

Traditional methods for measuring cardiac output in mice are invasive and traumatic. The authors discuss using the less-invasive thermodilution method, which is widely accepted in humans and other animals.     

Cardiac output by rebreathing in patients with cardiopulmonary diseases

Noninvasive estimates of cardiac output by rebreathing soluble gases (Qc) can be unreliable in patients with cardiopulmonary diseases because of uneven distribution of ventilation to lung gas volume and pulmonary blood flow. To evaluate this source of error, we compared rebreathing Qc with invasive measurements of cardiac output performed by indicator-dilution methods (COID) in 39 patients with cardiac or pulmonary diseases. In 16 patients with normal lung volumes and 1-s forced expiratory volumes (FEV1), Qc measured with acetylene [Qc(C2H2)] overestimated COID insignificantly by 2 +/- 9% (SD). In subjects with mild to moderate obstructive lung disease, Qc(C2H2) slightly overestimated COID by 6 +/- 15% (P = 0.11). In patients with restrictive disease or combined obstructive and restrictive disease, Qc(C2H2) underestimated COID significantly by 9 +/- 14% (P less than 0.04). The magnitude of the discrepancy between Qc and COID correlated with size of the volume rebreathed and an index of uneven ventilation calculated from helium mixing during rebreathing that determined a dead space to inspired volume ratio (VRD/VI). Rebreathing volumes less than 40% of the predicted FEV or VRD/VI of 0.4 or greater identified all subjects with a discrepancy between Qc(C2H2) and COID of 20% or greater.