Exercise-induced arteriovenous intrapulmonary shunting in dogs

Area of Science:

• Physiology
• Cardiovascular Research
• Comparative Anatomy

Background:

• Previous research demonstrated inducible intrapulmonary arteriovenous pathways in humans using contrast echocardiography.
• However, this method limited the assessment of shunt size and magnitude.

Purpose of the Study:

• To investigate the presence of large-diameter (over 25 micrometers) intrapulmonary arteriovenous pathways in dogs.
• To determine if these pathways are recruited during exercise.

Main Methods:

• Stable isotope-labeled microspheres (25-microm) were injected into resting (n=8) and exercising (n=6) dogs.
• Systemic arterial blood and tissue samples were analyzed; isolated dog lungs were also studied with microspheres.

Main Results:

• No microspheres were found in resting dogs, but five of six exercising dogs showed shunting.
• Exercise-induced intrapulmonary arteriovenous shunting was detected, averaging 1.4% of cardiac output.
• Intrapulmonary arteriovenous anastomoses were identified in isolated dog lungs.

Conclusions:

• Intrapulmonary arteriovenous pathways are functional in dogs.
• These pathways are recruited during high-intensity exercise, consistent with human findings.