Papaverine injection into the hindlimb circulation stimulates ventilation in sheep

Area of Science:

• Physiology
• Respiratory Control
• Cardiovascular Physiology

Background:

• The control of breathing is complex, involving multiple sensory inputs.
• A previous hypothesis suggested that peripheral microvascular distention could directly stimulate ventilation.

Purpose of the Study:

• To investigate if muscular vasodilation, induced by papaverine, can stimulate ventilation independently of systemic effects.
• To test the hypothesis that peripheral vasodilation contributes to respiratory control via a neural pathway.

Main Methods:

• Ten anesthetized sheep underwent surgical preparation for reversible hindlimb circulation isolation.
• Papaverine was injected intra-arterially into the isolated hindlimbs to induce vasodilation.
• Ventilatory changes (VE) and systemic arterial pressure were monitored, with control injections into the jugular vein.

Main Results:

• Intra-arterial papaverine caused a significant increase in ventilation (VE) with a short latency (13 ± 6 sec) and decreased peripheral vascular resistance without altering systemic blood pressure.
• Control injections into the jugular vein resulted in a larger VE increase with a longer latency (21 ± 2 sec) and a decrease in systemic arterial pressure.
• The results indicate that papaverine-induced vasodilation in the hindlimbs stimulates ventilation independent of arterial baro- or chemoreceptor activation.

Conclusions:

• Muscular vasodilation can stimulate ventilation through a neural mechanism.
• This study provides evidence supporting a peripheral neural link in the control of breathing.
• The findings contribute to understanding the complex interplay between the cardiovascular and respiratory systems.