Effects of acid-base changes, hypoxia, and catecholamines on ventricular performance

Area of Science:

• Cardiovascular Physiology
• Acid-Base Balance
• Pharmacology

Background:

• Extracellular pH significantly impacts cardiac function.
• The role of buffering agents in modulating ventricular performance during acidosis is complex.
• Beta-adrenergic pathways are crucial in regulating myocardial contractility.

Purpose of the Study:

• To investigate the effects of tris (hydroxymethyl)-aminomethane (Tris) and sodium bicarbonate (NaHCO3) on ventricular performance (VP) during induced acidosis in dogs.
• To determine if hypoxemia influences VP during acidosis.
• To evaluate the impact of beta-adrenergic blockade on the response to buffering agents.

Main Methods:

• Utilized a canine right heart bypass preparation with controlled hemodynamic parameters.
• Induced extracellular pH changes using Tris or NaHCO3, with and without hypoxemia.
• Administered propranolol for beta-adrenergic blockade.
• Measured maximal rate of rise of left ventricular pressure (dp/dt max) and left ventricular end-diastolic pressure to assess VP.

Main Results:

• Low extracellular pH diminished VP.
• Tris increased VP significantly more than NaHCO3 at elevated pH.
• Beta-adrenergic blockade reduced the VP response to Tris.
• Prior reserpine administration abolished the inotropic effect of Tris, indicating a role for endogenous catecholamines.

Conclusions:

• Tris (hydroxymethyl)-aminomethane (Tris) influences ventricular performance (VP) independently of its pH-altering effects.
• The observed inotropic effect of Tris is likely mediated through interaction with myocardial beta-adrenergic receptors and endogenous catecholamines.
• These findings highlight a potential direct myocardial action of Tris beyond simple acid-base correction.