Measuring Cardiac Output in a Swine Model

Summary

Thermodilution, pressure-volume loop catheters, and contrast ventriculography are reliable and accurate methods for determining cardiac physiology such as stroke volume and cardiac output in a laboratory setting in swine.

Abstract

Swine are frequently used in medical research given their similar cardiac physiology to that of humans. Measuring cardiac parameters such as stroke volume and cardiac output are essential in this type of research. Contrast ventriculography, thermodilution, and pressure-volume loop (PV-loop) catheters can be used to accurately obtain cardiac performance data depending on which resources and expertise are available. For this study,five Yorkshire swine were anesthetized and intubated. Central venous and arterial access was obtained to place the necessary measurement instruments.A temperature probe was placed in the aortic root. A cold saline bolus was delivered to the right atrium and temperature deflection curve was recorded. Integration of the area under the curve allowed for the calculation of the current cardiac output.A pigtail catheter was percutaneously placed in the left ventricle and 30 mL of iodinated contrast was power injected over 2 seconds. Digital subtraction angiography images were uploaded to volumetric analysis software to calculate the stroke volume and cardiac output. A pressure volume-loop catheter was placed into the left ventricle (LV) and provided continuous pressure and volume data of the LV, which allowed the calculation of both stroke volume and cardiac output.All three methods demonstrated good correlation with each other. The PV-loop catheter and thermodilution exhibited the best correlation with a 3% error and a Pearson coefficient of 0.99, with 95% CI=0.97 to 1.1, (p=0.002). The PV-loop catheter against ventriculography also showed good correlation with a 6% error and a Pearson coefficient of 0.95, 95% CI=0.96 to 1.1 (p=0.01). Finally, thermodilution against ventriculography had a 2% error with r=0.95, 95% CI=0.93 to 1.11, (p=0.01). In conclusion, we state that the PV-loop catheter, contrast ventriculography, and thermodilution each offer certain advantages depending on the researcher’s requirements. Each method is reliable and accurate for measuring various cardiac parameters in swine such as the stroke volume and cardiac output.

Introduction

Swine are frequently used in hemorrhage control and resuscitation research due to their similar physiology to humans. Integral to resuscitation research is continuous cardiac output monitoring to assess the physiological response to interventions. Several clinical systems exist such as pulmonary artery (PA) catheters and pulse contour analysis-based systems¹. Additionally, echocardiography (echo), computed tomography (CT) and magnetic resonance imaging (MRI) can all be used to capture hemodynamic data. Images obtained during end-diastole and systole can be used to determine the volume of blood ejected during that cardiac cycle. While these techniques are minimally invasive, they only present data acquired at the time of imaging and do not provide continuous measures². They are also either largely operator dependent (echo) or require advanced, expensive equipment (CT and MRI). Given different laboratories’ capabilities and resources, there are various alternative methods to measure the cardiac output optimally in each instance.

Thermodilution is a common method of measuring cardiac output in the clinical setting using a Swan-Ganz catheter³. This method can be recreated in a laboratory setting in swine to directly measure the cardiac output. Contrast ventriculography can also be utilized if the fluoroscopic capability is readily available⁴. Finally, pressure-volume loop catheters offer a means of directly measuring the ventricular pressure and volume on a beat-to-beat basis and can generate more nuanced data⁵. This method utilizes electrical admittance and Wei’s equation to measure the chamber volume. Compared to older conductance-based catheters, admittance catheters eliminate the parallel conductance phenomenon between the blood and the cardiac muscle, thereby producing more accurate measurements without requiring repeated calibration⁶.

The aim of this study is to validate the accuracy of these three methods against each other in terms of measuring cardiac stroke volume and output in a healthy swine model. Ultimately, each investigator can choose which approach suits their needs the best, depending on their study requirements and what resources are available to them.

Protocol

Procedures were approved by the University of Maryland, Baltimore Institutional Animal Care and Use Committee (Approval #0320017) and conformed to National Institutes of Health guidelines for ethical animal research. Five adult male Yorkshire swine weighing between 50 and 70 kg were enrolled into the study. This study utilized a digital data collection system and paired software to record all hemodynamic and temperature data. Measuring cardiac parameters in the swine model consisted of the following steps: preparation, t…

Representative Results

The weight of the swine ranged from 51.4 kg to 61.5 kg with a mean weight of 56.6 ± 3.6 kg. The average stroke volumes measured by PV-loop catheter, ventriculography, and thermodilution across all five subjects were 58.0 ± 12.0 mL, 57.6 ± 8.5 mL, and 53.0 ± 9.8 mL, respectively. The average cardiac outputs measured by a PV-loop catheter, ventriculography, and thermodilution across all five subjects were 5.0 ± 1.1 L/min, 5.3 ± 1.2 L/min, and 5.2 ± 1.0 L/min,…

Discussion

This study details a standardized method of three different ways to accurately measure cardiac output in swine. Swine has analogous cardiovascular anatomy and physiology to humans and is commonly used as a model for human cardiac physiology, specifically for pre-clinical evaluations of surgical and interventional processes¹⁰. This allows swine to serve as the primary model for cardiovascular physiology, pathology, and emerging biotechnology¹¹. In order to assess these …

Materials

0.9% sodium chloride injection	Hospira	0409-4888-50
7 Fr Introducer Kit	Terumo	RCFW-5.0-35
Anesthesia Machine	Drager	Fabius Tiro
Contrast Power Injector	GEHealthcare	E8004N
Fluoroscope	GEHealthcare	OEC 9800
Heating/Cooling T/pump	Gaymar	Tp-700
Isoflurane	Baxter	10019-360-40
Jackie catheter	Terumo	40-5023
Omnipaque	GEHealthcare	559289
PowerChart	ADinstruments	ML866/P	Software
PowerLab	ADinstruments	PL3516
PV-loop catheter	Transonic		Prefer pigtail tip to straight tip
PV-loop module	Transonic	FFS-097-A004
Surgical suture, black braided silk, 3.0	Surgical Speciaties Corp.
Thermocouple probe	ADinstruments	MLT1401
Ultrasound probe	Philips	L12-4
Various-sized syringes
ViewPlus	Sanders Data Systems		Software