Reflex cardiovascular responses caused by stimulation of pulmonary C-fibers with capsaicin in dogs

Abstract

The purpose of these studies was to determine quantitatively the reflex cardiovascular responses to stimulation of the pulmonary C-fibers in dogs. We used a preparation in which the airway, pulmonary artery, and the pulmonary veins to the left lung were cannulated in situ. Ventilation and perfusion of the right lung maintained the animal in relatively normal homeostasis. Capsaicin, a decylenic acid amide of vanillylamine that selectively stimulates nerve endings of unmyelinated fibers (C-fibers), was injected into the left pulmonary artery in 5-ml boluses. Maximal reflex responses were obtained with concentrations as low as 0.8-1.6 X micrograms-1 X kg-1. Heart rate, hindlimb resistance, and left ventricular contractility were lowered transiently (the maximal responses showing declines of 40, 13, and 15.2%, respectively). As a result of these changes, combined with vasodilation in other resistance vessels, cardiac output fell 28% and blood pressure fell 35%. Interrupting the afferent neural pathway by severing the ipsilateral cervical vagus nerve eliminated these responses, confirming the distribution of their reflex origin. Although the role of these reflexes in homeostasis has not been decided, the results of this study suggest that the lungs of dogs, if appropriately stimulated, potentially can exert a major inhibitory influence on the neural regulation of cardiovascular function.

The cause of acute lethality of mice exposed to a laser-induced shock wave to the brainstem

“…Apnea, bradycardia and hypotension occur in thoracic blast injuries, and pulmonary C fibers may be involved 20 – 22 . Further, hypotension is caused by bradycardia but not by efferent stimulation of the vagal nerve 23 , 24 , which were not apparent here. Moreover, we expected that the vagal reflex may be induced by unilateral stimulation, such as the application of a right-dorsal LISW.…”

Cardiovascular responses to stimulation of pulmonary C fibres in the cat: their modulation by changes in respiration.

“…The systemic vascular responses to stimulation of pulmonary C fibres have been studied previously, but only in the dog, and then no attempts were made to establish the mechanisms by which they were brought about (Brender & Webb-Peploe, 1969;Cassidy, Ashton, Wead, Kaufman, Monsereenusorn & Whiteside. 1986).…”

Manual hyperinflation: consistency and modification of the technique by physiotherapists

“…Manual hyperinflation has the potential to cause cardiovascular instability (Conway, 1976;Buchanan and Baun, 1986;Cassidy et al, 1986;Stone et al, 1991a;Stone et al, 1991b;Enright, 1992;Paratz, 1992). The application of manual hyperinflation to acute head injury patients has resulted in increases in mean arterial pressure and intracranial pressure (Crosby and Parsons, 1992;Paratz and Burns, 1993) and may also cause barotrauma or volutrauma to the lung (Dreyfuss et al, 1985;Haake et al, 1987;Dreyfuss et al, 1988).…”