Invasive Hemodynamic Assessment for the Right Ventricular System and Hypoxia-Induced Pulmonary Arterial Hypertension in Mice

Summary

Here, we present a protocol to perform an invasive hemodynamic assessment of the right ventricle and pulmonary artery in mice using an open-chest surgery approach.

Abstract

Pulmonary arterial hypertension (PAH) is a chronic and severe cardiopulmonary disorder. Mice are a popular animal model used to mimic this disease. However, the evaluation of right ventricular pressure (RVP) and pulmonary artery pressure (PAP) remains technically challenging in mice. RVP and PAP are more difficult to measure than left ventricular pressure because of the anatomical differences between the left and right heart systems. In this paper, we describe a stable right heart hemodynamic measurement method and its validation using healthy and PAH mice. This method is based on open-chest surgery and mechanical ventilation support. It is a complicated procedure compared to closed chest procedures. While a well-trained surgeon is required for this surgery, the advantage of this procedure is that it can generate both RVP and PAP parameters at the same time, so it is a preferable procedure for the evaluation of PAH models.

Introduction

Pulmonary arterial hypertension (PAH) is a chronic and severe cardiopulmonary disorder with elevation in pulmonary artery pressure (PAP) and right ventricular pressure (RVP) that is caused by cellular proliferation and fibrosis of small pulmonary arteries¹. Pulmonary artery catheters, also called Swan-Ganz catheters², are commonly used in the clinical monitoring of RVP and PAP. Furthermore, a wireless PAP monitoring system has been used clinically^3,4,5. To mimic the disease for study in mice, a hypoxic environment is used to simulate human clinical manifestations of PAH⁶. In the evaluation of PAP in animals, large animals are relatively easy to monitor through pulmonary artery catheters using the same technique as for human subjects, but small animals such as rats and mice are difficult to assess because of their small body size. Hemodynamic measurement of the right ventricular system in mice is possible with an ultrasmall size 1 Fr catheter⁷. A method for measuring RVP and PAP in mice has been reported in the literature^8,9, but the methodology lacks a detailed description. RVP and PAP are more challenging to measure than left ventricular pressure because of the anatomical differences between the left and right heart systems.

To get both PAP and RVP parameters in the same mouse, we describe an open-chest surgery-based approach for right heart hemodynamic measurements, its validation with healthy and PAH mice, and how to avoid generating artificial data during the complicated open-chest surgery. Although this technique is best performed by a well-trained surgeon, it has the advantage of being able to assess PAP and RVP in the same mouse.

Protocol

The animal protocol was reviewed and approved by the Institutional Animal Care and Use Committee at Fuwai Hospital, Chinese Academy of Medical Science, Peking Union Medical College (NO.0000287). The experimental animals were housed and fed according to the guidelines of animal welfare in China. NOTE: Eight- to 12-week-old male C57BL mice were housed in an environment with a 12 h dark/ 12 h light cycle. The PAH mice were housed for 4 weeks under an oxygen concentration of 10%, maintained by an …

Representative Results

The pressure transducer catheter was inserted into the right ventricle (Figure 3A) through a tunnel expanded by a 25 G needle, and a typical RVP waveform (Figure 3C) was obtained. The catheter was continually adjusted and slowly advanced and kept in the same axis as the pulmonary artery while passing through the pulmonary valve (Figure 3B). When the pressure sensor was successfully …

Discussion

Tracheal intubation is the first important step for open-chest surgeries. The classic method of tracheal intubation for small animals, such as rats or mice, involves making a T-shaped incision on the trachea and directly inserting Y-type tracheal tubing into the trachea. In practice, we find that this method is not easy during operation. The Y-type tracheal tubing is too large for small animals and forms an angle with the trachea. Thus, it is difficult to fix the tubing in place. Additionally, once the intubation tubing …

Materials

2,2,2-Tribromoethanol	Sigma-Aldrich	T48402-5G	For anesthesia
Animal temperature controller	Physitemp Instruments, Inc.	TCAT-2LV	For temperature control
Dissection forceps	Fine Science Tools, Inc.	11274-20	For surgery
Gemini Cautery System	Gemini	GEM 5917	For surgery
Intravenous catheter (22G)	BD angiocath	381123	For intubation
LabChart 7.3	ADInstruments		For data analysis
Light illumination system	Olympus		For surgery
Mikro-Tip catheter	Millar Instruments, Houston, TX	SPR-1000	For pressure measurement
Millar Pressure-Volume Systems	Millar Instruments, Houston, TX	MVPS-300	For pressure measurement
O2 Controller and Hypoxia chamber	Biospherix	ProOx 110	For chronic hypoxia
PowerLab Data Acquisition System	ADInstruments	PowerLab 16/30	For data recording
Scissors	Fine Science Tools, Inc.	14084-08	For surgery
Small animal ventilator	Harvard Apparatus	Mini-Vent 845	For surgery
Stereomicroscope	Olympus	SZ61	For surgery
Surgery tape	3M		For surgery
Terg-a-zyme enzyme	Sigma-Aldrich	Z273287-1EA	For catheter cleaning