Relationships Between Eupnoeic Pattern of Breathing and Ventilatory Control in Man

Abstract The apnoeic response following interruption of the air flow at different levels of the inspiratory capacity (ΔVL) was studied in conscious children and adults. Changes in mouth pressure were used to measure the duration of the apnoea. The total duration of the interrupted breath (T1) was compared to mean value of the ventilatory period of the five preceding breaths (T0). A monoexponential regression could be fitted to the relationship between T1/T0 ratio and change in lung volume (ΔTL) measured at the onset of interruption : T1/T0 = k ·exp ·(S · ΔTL), S begin the sensitivity of the response to lung inflation. When T1/T0 = 1, the intrathoracic lung volume was called threshold volume (TTh.L.). The parameters S and TTh.L. were used for characterization of the individual importance of the Breuer-Hering inspiratory-inhibitory reflex (B.H. reflex). The high reproducibility of the T1/T0 vs. ΔTL relationship in many subjects showed the light influence of voluntary control on apnoea's duration. In each subject, S and TTh.L. were compared with ventilatory variables measured during eupnoea. A fast pattern of breathing (i.e., small inspired volume and short inspiratory duration) was associated with high value of S and low TTh.L.. Moreover TTh.L. was near the tidal volume range in subjects where the B.H. reflex was the more potent. Thus, vagal afferents relating to this reflex could modulate the eupnoeic pattern of some subjects.