Peripheral circulatory alterations in canine anaphylactic shock.

Area of Science:

• Cardiovascular Physiology
• Immunology
• Shock Pathophysiology

Background:

• Anaphylactic shock is characterized by a significant drop in cardiac output and arterial pressure.
• The precise peripheral circulatory mechanisms driving these changes remain incompletely understood.

Purpose of the Study:

• To investigate the roles of peripheral circulatory variables in the hemodynamic alterations observed during anaphylactic shock.
• To differentiate between acute plasma volume loss and other factors contributing to reduced arterial pressure.

Main Methods:

• Utilized a right heart bypass model in six dogs, administering Ascaris suum antigen to induce anaphylaxis.
• Measured cardiac output, arterial pressure, resistance to venous return, mean systemic pressure, and vascular compliance.
• Assessed plasma volume changes using protein oncotic pressure and hematocrit in intact and splenectomized dogs.

Main Results:

• Intravenous antigen administration led to a 53% decrease in cardiac output and a 58% decrease in arterial pressure.
• Resistance to venous return significantly increased, while vascular compliance remained unchanged.
• Estimates indicated small increases in plasma volume during the hypotensive phase, contradicting acute volume loss.

Conclusions:

• The primary drivers of anaphylactic shock's circulatory effects are increased resistance to venous return and a rightward shift in the systemic pressure-volume curve.
• Acute plasma volume loss is not the main mechanism responsible for the observed hypotension in anaphylaxis.