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

This protocol is an open chest surgery based hemodynamic assessment and it is useful for the right ventricular and pulmonary artery pressure evaluation in small animals such as mice. The advantage of this procedure is that it can generate both VP and PAP parameters at the same time. So it is preferable for evaluations of PAH models.

Begin by setting up the equipment for surgery. Soak the pressure transducer catheter in 0.9%saline at room temperature for at least 30 minutes before the hemodynamic experiment. Then, connect the catheter to a pressure volume system.

Calibrate the pressure transducer by turning the calibration knob to zero and 25 millimeters of mercury to send a verification pressure signal to the data acquisition software, then configure the calibration setting. Turn the knob to transducer, and adjust the balance valve to zero baseline. Set up a standard stereo microscope, temperature controlled small animal surgical table, and a light illumination system for microsurgery.

Once the mouse is properly anesthetized, remove the chest and neck fur using a shaver and hair removal lotion. Secure the mouse in the supine position on the temperature controlled surgical table. After ensuring that the anesthesia is in effect, make a midline incision on the neck skin.

Dissect the skeletal muscle using curved forceps and expose the trachea. Perform intubation through the mouth with a 22 gauge intravenous sheath catheter, confirming that the tubing is in the trachea with forceps. Connect the tubing to a small animal ventilator and secure it for ventilation using tape.

Then, make a midline incision on the chest skin and carefully dissect the chest muscle using a cautery tool. Cut the sternum using scissors across the middle, and expose the thoracic cavity. Make sure to prevent any bleeding using the cautery tool.

Expose the right ventricle with retractors, then insert the saline soaked pressure transducer catheter through a small tunnel created with a 25 gauge needle into the right ventricle to measure right ventricular pressure, or RVP. Hold the catheter cable and cross the pulmonary valve in a coaxial manner with the pulmonary artery. Observe the pressure waveform, and obtain a stable pulmonary artery pressure or PAP signal.

Next, record the hemodynamic data using the data acquisition software. Carefully remove the catheter from the right heart system and place it into a one milliliter syringe containing 1%digestive enzyme solution. This protocol was successfully used to obtain RVP and PAP waveforms in mice by inserting a pressure transducer catheter into the right ventricle and the pulmonary artery.

In order to avoid generating artificial data, segments with noise were excluded from the data analysis and corrections were made if the zero level of the catheter had drifted. RVP and PAP were measured in mice with induced chronic hypoxia, and the results were compared to those obtained from a control group. Systolic PAP, diastolic PAP, mean PAP, and right ventricular systolic pressure were all significantly increased in the chronic hypoxia group.

The most important thing to remember is to insert the pressure transducer catheter into the right ventricle carefully, making sure to avoid damage to the catheter and confirm the smooth RVP waveform appears on the screen.