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Left ventricular volume measurement in mice by conductance catheter: evaluation and optimization of calibration

¹Department of Cardiology, ²Magnetic Resonance Centre, and ³Medical Research Laboratories, Medical Department M, Aarhus University Hospital, Skejby, Denmark; and ⁴Hospital for Sick Children, Toronto, Ontario, Canada

Submitted 20 November 2006 ; accepted in final form 21 March 2007

The conductance catheter (CC) allows thorough evaluation of cardiac function because it simultaneously provides measurements of pressure and volume. Calibration of the volume signal remains challenging. With different calibration techniques, in vivo left ventricular volumes (V_CC) were measured in mice (n = 52) with a Millar CC (SPR-839) and compared with MRI-derived volumes (V_MRI). Significant correlations between V_CC and V_MRI [end-diastolic volume (EDV): R² = 0.85, P < 0.01; end-systolic volume (ESV): R² = 0.88, P < 0.01] were found when injection of hypertonic saline in the pulmonary artery was used to calibrate for parallel conductance and volume conversion was done by individual cylinder calibration. However, a significant underestimation was observed [EDV = –17.3 µl (–22.7 to –11.9 µl); ESV = –8.8 µl (–12.5 to –5.1 µl)]. Intravenous injection of the hypertonic saline bolus was inferior to injection into the pulmonary artery as a calibration method. Calibration with an independent measurement of stroke volume decreased the agreement with V_MRI. Correction for an increase in blood conductivity during the in vivo experiments improved estimation of EDV. The dual-frequency method for estimation of parallel conductance failed to produce V_CC that correlated with V_MRI. We conclude that selection of the calibration procedure for the CC has significant implications for the accuracy and precision of volume estimation and pressure-volume loop-derived variables like myocardial contractility. Although V_CC may be underestimated compared with MRI, optimized calibration techniques enable reliable volume estimation with the CC in mice.

contractile function; ventricular function; hemodynamics; magnetic resonance imaging