Abstract
We examined the contribution of afferent vagal A- and C-fibers on abdominal expiratory muscle activity (EMA). In seven spontaneously breathing supine dogs anesthetized with α-chloralose we recorded the electromyogram of the external oblique muscle at various vagal temperatures before and after the induction of a pneumothorax. When myelinated fibers were blocked selectively by cooling the vagus nerves to 7°C, EMA decreased to 40% of control (EMA at 39°C). With further cooling to 0°C, removing afferent vagal C-fiber activity, EMA returned to 72% of control. On rewarming the vagus nerves to 39°C, we then induced a pneumothorax (27 ml/kg) that eliminated the EMA in all the dogs studied. Cooling the vagus nerves to 7°C, during the pneumothorax, produced a slight though not significant increase in EMA. However, further cooling of the vagus nerves to 0°C caused the EMA to return vigorously to 116% of control. In three dogs, intravenous infusion of a constant incrementally increasing dose of capsaicin, a C-fiber stimulant, decreased EMA in proportion to the dose delivered. These results suggest that EMA is modulated by a balance between excitatory vagal A-fiber activity, most likely from slowly adapting pulmonary stretch receptors, and inhibitory C- fiber activity, most likely from lung C-fibers.
Original language | English (US) |
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Pages (from-to) | 1795-1800 |
Number of pages | 6 |
Journal | Journal of Applied Physiology |
Volume | 71 |
Issue number | 5 |
State | Published - 1991 |
Keywords
- C-fibers
- external oblique
- pneumothorax
- slowly adapting pulmonary stretch receptors
- vagus nerve
ASJC Scopus subject areas
- Endocrinology
- Physiology
- Orthopedics and Sports Medicine
- Physical Therapy, Sports Therapy and Rehabilitation