Norepinephrine and phenylephrine effects on right ventricular function in experimental canine pulmonary embolism

Area of Science:

• Cardiovascular Physiology
• Pulmonary Embolism Pathophysiology
• Pharmacological Interventions

Background:

• Pulmonary embolism (PE) critically impairs hemodynamics, reducing mean arterial pressure (MAP) and cardiac output (CO).
• Restoring right ventricular (RV) function and systemic circulation is vital in acute PE management.
• Phenylephrine (PHEN) and norepinephrine (NE) are vasopressors used to manage hemodynamic instability.

Purpose of the Study:

• To compare the efficacy of NE versus PHEN in restoring hemodynamic function in a canine model of PE.
• To investigate the effects of NE and PHEN on right ventricular myocardial blood flow (RVMBF) and oxygen consumption (RVMVo2).
• To determine the impact of NE and PHEN on pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR).

Main Methods:

• A canine model of PE was induced by autologous blood clot infusion.
• MAP, CO, RV output, RV minute work, RVMBF, RVMVo2, PVR, and SVR were measured.
• Intravenous infusions of PHEN and NE were administered at equipressor concentrations.

Main Results:

• Both NE and PHEN restored MAP, but only NE normalized CO.
• NE significantly increased RVMBF and RVMVo2, restoring RV output and minute work.
• NE decreased PVR and SVR, while PHEN decreased PVR but increased SVR.

Conclusions:

• Norepinephrine's alpha and beta receptor stimulation beneficially impacts RV function and systemic hemodynamics in PE.
• Phenylephrine did not improve RV output despite maintaining coronary autoregulation.
• Judicious use of NE may be more beneficial than PHEN in treating acute PE patients.