Respiratory influences on the cardiac defense response.

An investigation to examine the relationships between breathing activity and the cardiac defense response (CDR) to intense auditory stimulation is reported. 42 subjects (20 men and 22 women) underwent a physiological reaction test consisting of three trials of a distorted 400 Hz noise of 100 dB, 0.5-s duration and instantaneous risetime presented either during inspiration or expiration. The respiratory response was characterized by a specific increase in breathing amplitude both in the respiratory cycle in which the stimulus was presented and in the 80 s following stimulus onset. Significant habituation effects were observed. Manipulation of the respiratory phase did not produce any major effect on the respiratory or cardiac response. The only significant finding was observed in the inspiratory period of the cycle in which the stimulus was presented, which was longer when the stimulus was presented in expiration and shorter when it was presented in inspiration. The evocation of the cardiac defense response was dependent on the observed increase in breathing amplitude. Gender differences were also observed in the respiratory response, differences which were further increased when the CDR was elicited. These results are discussed in the context of centrally versus peripherally-mediated mechanisms and startle versus defense reflexes.