The human ventilatory response to stimulation by transient hypoxia.

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Abstract
The detailed pattern of transient changes in breathing pattern was studied following a brief hypoxic stimulus (3 breaths of N) in 9 healthy subjects. All showed an increase in ventilation of which the magnitude and relative contributions of volume and frequency varied between subjects. Ventilation, tidal volume and inspiratory, expiratory and total breath times were recorded or derived breath-by-breath; for each of these variables, several test sequences were time-averaged at 0.5 s intervals for each individual; similarly, time-averages were obtained for percentage changes from base line over all 9 subjects. An increase in inspiratory time accompanied the increasing tidal volume in all but 2 subjects. This was statistically significant for the group and in 5 individuals. Frequency changes were the resultant of alterations in the 2 phases; when total breath duration decreased it was always linked to a decrease in expiratory time. Further analysis of the initial part of the response suggested that an increase of the duration of an inspiration may be the 1st change allowing an increase in tidal volume, before the drive increases; this may be a dynamic feature of the control system whatever the nature and site of stimulus action.