Diaphragmatic responses to graded stimulation of pulmonary C-fibers with capsaicin

Publisher Website
Google Scholar
Abstract
It has been suggested that pulmonary C-fiber stimulation is responsible for the rapid shallow breathing that accompanies pulmonary edema. However, pulmonary C-fiber stimulation also causes apnea. To determine whether it was possible for both responses to occur from one stimulus, we infused varying concentrations of capsaicin (a compound that selectively stimulates C-fiber receptors in the dog) into an in situ vascularly isolated dog lung and measured rates and strengths of diaphragmatic contractions with a strain gauge sutured to the diaphragm and electromyogram electrodes implanted in the diaphragm. There was a dose response to capsaicin in that increased doses were related directly with the duration of cessation of diaphragmatic contractions (2–100 s) and inversely with the latency from the start of stimulation to the beginning of the cessation of diaphragmatic contractions (100–5 s). There was no evidence, however, of rapid shallow breathing in this set of experiments. Either a gradual return to normal rate from prolonged contraction intervals or no change in contraction rate was seen, depending on capsaicin concentration. We conclude that the primary diaphragmatic response to pulmonary C-fiber stimulation is a cessation of diaphragmatic contractions rather than rapid shallow contractions.