Different roles of two subgroups of lung vagal C-fiber afferents in the tachypneic response to pulmonary air embolism in dogs.
It is known that lung vagal C-fiber afferents play an important role in eliciting the tachypneic response to pulmonary air embolism (PAE), and can be subgrouped as those with low resistance (LRC) and those with high resistance (HRC) to perivagal capsaicin. In this study, we investigated the relative contributions of vagal LRC and HRC C-fiber afferents to the PAE-induced tachypneic response. Phrenic activity was recorded from 10 anesthetized, paralyzed, and artificially ventilated dogs. PAE was induced by infusion of air into the vein (2 ml/min, 1 ml/kg). During control conditions, induction of PAE produced a shortening in expiratory duration with no significant change in inspiratory duration, resulting in tachypnea. The PAE-induced tachypneic response was totally abolished by perivagal capsaicin treatment with a method (capsaicin concentration, 6 mg/ml; treatment duration, 25-30 min) that blocks the conduction of LRC C-fiber afferents, but not that of HRC C-fiber afferents. This tachypneic response was not affected by cooling of both vagi to a temperature (4.5 degrees C) that blocks the conduction of HRC C-fiber afferents, but not that of LRC C-fiber afferents. A bilateral cervical vagotomy virtually eliminated this tachypneic response. These results suggest that LRC C-fiber afferents are responsible for eliciting the reflex tachypneic response to PAE, whereas HRC C-fiber afferents play no vital role.
Chen
H F
HF
Department of Early Childhood Care and Education, Cheng Shiu Institute of Technology, Kaohsiung, Taiwan, ROC.
Lee
B P
BP
Kou
Y R
YR
D000758:Anesthesia; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D003080:Cold Temperature; D004285:Dogs; D004618:Embolism, Air / Q000503:physiopathology*; D008168:Lung / Q000294:innervation* / Q000503:physiopathology; D009412:Nerve Fibers / Q000502:physiology*; D010791:Phrenic Nerve / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology*; D014630:Vagus Nerve / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D002211:Capsaicin