Validity of thermal dilution technique for measurement of cardiac output in rats

Abstract

The validity of the thermal dilution technique for the measurement of cardiac output was verified in experiments on a circulation model and on anesthetized rats under open- and closed-chest conditions. In the circulation model thermal dilution was compared with direct (Fdir) and electromagnetic (F(elm)) flowmetry. Flow values measured in the circulation model with the thermal dilution (Fth) technique correspond well with direct flowmetry (Fth = 0.92 Fdir + 7.0; r = 0.888) and with electromagnetic flowmetry (Fth = 0.95 F(elm) + 1.2; r = 0.990). In the anesthetized rat cardiac output was determined with thermal dilution and simultaneously with Fick's method and/or with electromagnetic flowmetry. Fick's method and electromagnetic flowmetry resulted in identical cardiac output values (COFick = 0.95 COelm; r = 0.865), whereas the thermal dilution technique yielded unequivocally higher values. The extent of overestimation is much more pronounced at low cardiac output than at a high output. The study clearly demonstrates that this overestimation is due to heat diffusion, which is obviously of greater significance in small animals than in large animals or humans. Therefore, the thermal dilution technique is not appropriate for the measurement of cardiac output in the rat.

Validation of high-resolution echocardiography and magnetic resonance imaging vs. high-fidelity catheterization in experimental pulmonary hypertension

“…Kissling et al (17) measured CO with thermal dilution and simultaneously with Fick method and/or with electromagnetic flowmetry. Although all three techniques correlated well, and the Fick method and electromagnetic flow techniques yielded identical results, the thermodilution technique yielded higher CO values under conditions of low CO (17). Our study demonstrates excellent correlations in CO as determined by noninvasive techniques and thermodilution over the wide range of values seen in normal and pulmonary hypertensive rodents (Supplemental Fig.…”

“…Thermodilution has been successfully used to measure CO in rats (17,31). The technique is based on detection of changes in aortic temperature by a thoracic aortic thermistor in response to venous injections of saline (Fig.…”

Quantitative blood flow measurements in the small animal cardiopulmonary system using digital subtraction angiography

“…5,6,8,12,51,52 The cardiac output in the rat can range from 25 ml/min in a deeply anesthetized rat 29 to 50 ml/min in a conscious rat. 4 In previous work using the Fick's method, CO measurements in the same animal yielded Ͻ5% variation between measurements.…”

“…The focus of this work is mapping the relative flow metrics in DSA to an absolute metric through physiologic-based measurements-the Fick and thermodilution techniques. Fick's method, the gold standard for measuring cardiac output, [28][29][30] is the ratio of the total blood oxygen uptake by the peripheral tissues to the arterial-venous blood oxygen concentration difference. [30][31][32][33] The thermodilution technique is an indicator-dilution method where the regional blood flow is measured by noting temperatures changes induced at specific points through the injection of a cold liquid.…”

Validation of transit-time flowmetry for chronic measurements of regional blood flow in resting and exercising rats

“…The transit-time technology for measuring dynamic changes of regional blood flow has several advantages over other methods such as electromagnetic, microsphere and Doppler system flowmetry: 1) small probe size permitting easy implantation; 2) continuous measurement of absolute blood flow representing an enormous advantage over phasic (microspheres, dye dilution) (3,22,23) or relative measurements (3,4,8-10); 3) probes are nonconstrictive and therefore do not interfere with the pulse pressure or percentage of diastolic flow as electromagnetic devices do (7,14); 4) the probes are suitable for long-term studies (17) since the quality of the received signal improves with reactive infiltrating tissue growth around the probe/ vessel, providing the necessary acoustic conduction (3,15), and 5) the flowmeter zero offset function permits frequent calibration in conscious freely moving rats. The perivascular transit-time probe has been successfully used for continuous assessment of flow in coronary (17), mesenteric (13,(15)(16)(17), renal (13,14,17,24), carotid (13), gastric (11,12), hindlimb (13,17,25,26) and pulmonary arteries (7) and also for measurement of cardiac output (3,8,13,15,24).…”