Validation of Noninvasive Measurements of Cardiac Output in Mice Using Echocardiography

doi:10.1016/j.echo.2010.12.019

Journal of the American Society of Echocardiography

Volume 24, Issue 4, April 2011, Pages 465-470

https://doi.org/10.1016/j.echo.2010.12.019 Get rights and content

Background

Although multiple echocardiographic methods exist to calculate cardiac output (CO), they have not been validated in mice using a reference method.

Methods

Echocardiographic and flow probe measurements of CO were obtained in mice before and after albumin infusion and inferior vena cava occlusions. Echocardiography was also performed before and after endotoxin injection. Cardiac output was calculated using left ventricular volumes obtained from an M-mode or a two-dimensional view, left ventricular stroke volume calculated using the pulmonary flow, or estimated by the measurement of pulmonary velocity time integral (VTI).

Results

Close correlations were demonstrated between flow probe-measured CO and all echocardiographic measurements of CO. All echocardiographic-derived CO overestimated the flow probe-measured CO. Two-dimensional image-derived CO was associated with the smallest overestimation of CO. Interobserver variability was lowest for pulmonary VTI-derived CO.

Conclusion

In mice, CO calculated from two-dimensional parasternal long-axis images is most accurate when compared with flow probe measurements; however, pulmonary VTI-derived CO is subject to less variability.

Section snippets

Protocol

C57BL/6 male mice (25 ± 2 g) were anesthetized with an intraperitoneal injection of ketamine (0.1 mg/g) and xylazine (0.01 mg/g) and placed supine on a heated operating table. After tracheotomy, mice were ventilated and a custom-made catheter (PE10, Becton Dickinson, Franklin Lakes, NJ) was inserted via the right carotid artery to monitor mean arterial pressure. A venous line was inserted in the left jugular vein. A thoracotomy was performed, and a flow probe (1.5SL; Transonic Systems, Ithaca,

Hemodynamic Measurements at Baseline

At baseline with all catheters and flow probe in place, systolic arterial pressure was 70 ± 4 mm Hg and heart rate was 366 ± 19 bpm in the mice used for M-mode measurements, 72 ± 6 mm Hg and 445 ± 24 bpm in the mice used for two-dimensional measurements, and 72 ± 7 mm Hg and 373 ± 22 bpm in the mice used for pulmonary measurements.

Relationship between Echocardiographic- and Flow Probe-Measured CO

CO measured by flow probe correlated closely to CO calculated using M-mode (flow probe-measured CO = [0.38 M-mode-calculated CO] + 0.78, r² = 0.78, P < .0001, Figure 2

Discussion

The present study demonstrates that CO can be accurately estimated using echocardiography. Four echocardiographic methods were tested, including M-mode-, two-dimensional-, and pulmonary flow-calculated CO, and pulmonary VTI-derived CO. All echocardiographic methods correlated closely with flow probe-measured CO. Echocardiographic measurements overestimated CO measured by flow probe. The overestimation was greatest using the M-mode and lowest using two-dimensional images. Intraobserver

Conclusions

Echocardiography can noninvasively measure CO in the mouse, with close correlations to flow probe measures. Although overestimation of the flow probe-measured CO is noted regardless of the echocardiographic method used, the close correlations noted between each echocardiographic method and flow probe-measured CO allow an acceptable estimation of CO and, more important, an accurate assessment of its changes within and between mice. Investigators may choose to report CO calculated from the

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However, PF consistently provided a greater number of usable images for analysis (Table 1), so that any potential variability bias would more likely influence other more frequently excluded measures of CO. The comparison of echocardiographic CO values with flow probe CO values was additionally limited by the inability to simultaneously obtain values (as was the case in previous studies8). This was the result of the placement of the flow probe in the upper mediastinum, directly atop the greater vessels, which made concurrent visualization of the pulmonary trunk impossible.
Echocardiography is a valuable noninvasive technique to estimate cardiac output (CO) from the left ventricle (LV) not only in clinical practice but also in small-animal experiments. CO is used to grade cardiac function and is especially important when investigating cardiac injury (e.g., myocardial infarction [MI]). Critically, MI deforms the LV, invalidating the assumptions fundamental to calculating of cardiac volumes directly from the LV. Thus, the purpose of this study was to determine if Doppler-derived blood flow through the pulmonary trunk (pulmonary flow [PF]) was an improved method over conventional LV–dependent echocardiography to accurately determine CO after MI.
Variations in CO were induced either by transverse aortic constriction or MI. Echocardiography was performed in healthy (n = 27), transverse aortic constriction (n = 25), and MI (n = 41) mice. CO calculated from PF (pulsed-wave Doppler) was internally compared with CO calculated from left ventricular images using M-mode (Teichholz formula) and the single-plane ellipsoid two-dimensional (2D) formula and externally compared with the gold standard, flow probe CO.
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PF CO calculated from pulsed-wave Doppler through the pulmonary trunk was an improved method of estimating CO over LV–dependent formulas after MI.
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In the latter 2 groups, CO was measured during isoflurane inhalation by transthoracic pulsed wave Doppler-echocardiography. For PC-DOB group, mice were placed on continuous intravenous infusion of DOB administered via a tail vain [17] initially at low dose of 3 μg/kg/min and then increased in 3 μg/kg/min increments (maximum 15 μg/kg/min) to maintain supra-normal levels (target CO range: 35 ± 10 mL/min) [18]. Cardiorespiratory variables (echocardiography-derived parameters, respiratory rate, and SpO2) were assessed 1.5 h and 2 h after SAH surgery (corresponding to 0.5 h and 1 h after postconditioning).
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: F.T., B.P., and H.T. participated equally to this work.

: Funding: This study was supported by a Shared Equipment Grant (National Institutes of Health/National Heart, Lung, and Blood Institute 1S10RR022586-01A1, to M.S.C.), the Claflin Award (to M.S.C.), and fellowship grants from the Fédération Française de Cardiologie (to F.T., H.T., and B.K.).

: Disclosures: None.

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Pre-Clinical InvestigationsValidation of Noninvasive Measurements of Cardiac Output in Mice Using Echocardiography

Background

Methods

Results

Conclusion

Section snippets

Protocol

Hemodynamic Measurements at Baseline

Relationship between Echocardiographic- and Flow Probe-Measured CO

Discussion

Conclusions

J Am Soc Echocardiogr

J Am Soc Echocardiogr

J Am Soc Echocardiogr

Ultrasound Med Biol

J Am Coll Cardiol

Determination of right ventricular structure and function in normoxic and hypoxic mice: a transesophageal echocardiographic study

Circulation

Pulmonary vasoconstriction and hypertension in mice with targeted disruption of the endothelial nitric oxide synthase (NOS 3) gene

Circ Res

Chronic measurement of cardiac output in conscious mice

Am J Physiol Regul Integr Comp Physiol

Effects of anesthetics on systemic hemodynamics in mice

Am J Physiol Heart Circ Physiol

In vivo murine left ventricular pressure-volume relations by miniaturized conductance micromanometry

Am J Physiol

Validation of a mouse conductance system to determine LV volume: comparison to echocardiography and crystals

Am J Physiol Heart Circ Physiol

Pre-Clinical Investigations
Validation of Noninvasive Measurements of Cardiac Output in Mice Using Echocardiography