Cardiac output of marmots by the thoracic impedance technique.

Baseline impedance (Z₀) and resistivity of blood were higher for marmots than reported for other species. The transthoracic impedance method was compared to dye dilution and electromagnetic flowmeter procedures for estimation of cardiac output of seven marmots at a range of flows from 40 to 400 ml/min. There was a low, positive, but significant correlation (r = 0.566) found in comparison to dye dilution at outputs measured by the impedance method exceeding 120 ml/min. Correlation was better (r = 0.905) in the comparison between impedance and flowmeter methods.It was concluded that transthoracic impedance provides data that are sufficiently accurate for chronic measurements of stroke volume and cardiac output of this species. The method has the additional advantage of supplying EGG and respiratory data without supplemental connections to the animal preparations.