Hering-Breuer reflex in normal adults and in patients with chronic obstructive pulmonary disease and interstitial fibrosis

Background: It has been suggested that the Hering-Breuer reflex (HBR) is unimportant in adults during normal tidal breathing and that it is elicited only if tidal volume is increased above a certain critical threshold.

Objective: The aim of this study was (1) to study the occurrence of the HBR in adults with normal pulmonary function and (2) to examine if changes in lung mechanics have any effect on the HBR.

Methods: We examined 11 adults with normal pulmonary function, 8 patients with chronic destructive pulmonary disease (COPD) and 3 with interstitial fibrosis (IF). All subjects were lightly sedated with fentanyl, intubated and ventilated with a Servo-900 ventilator. Inspiratory and expiratory flow (and after integration, volume) and mouth pressure were recorded from the endotracheal tube with a pneumotachograph and a pressure transducer. Pressure support ventilation was applied in all patients and functional residual capacity (FRC) was measured with the N(2) washout method. Mean (Te(mean)) and maximal expiratory time (Te(max)) were determined for each individual for 20 breaths. Following several breaths to establish a stable baseline the airway was occluded at end inspiration by a shutter. A positive HBR was interpreted as longer Te(occ) than Te(max) (Te(occ)/Te(max), %). Occlusion was maintained until negative airway pressure occurred and the occlusion time (Te(occ)) was measured. We attempted occlusions after the addition of 5 cm H2O positive end-expiratory pressure (PEEP) and subsequently with 10, 15 and 20 cm H(2)O PEEP. Te(occ) was measured of progressively larger lung volumes. To examine the HBR sensitivity in the three groups, we plotted the lung volumes of occlusion against the corresponding Te(occ)/Te(max).

Results: The ratio Te(occ)/Te(max) increased from 167.5 +/- 82.5 at normal FRC to 474 +/- 200.2 s (PEEP(20)). On the contrary, in patients with COPD, Te(occ)/Te(max) increased from 125.2 +/- 34 to 193.7 +/- 74.2 (p < 0.05).

Conclusions: The HBR was positive in all subjects. COPD patients were found to be less sensitive to volume changes when compared with normal controls and with IF patients.