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Portex Anaesthesia, Intensive Therapy and Respiratory Medicine Unit, Institute of Child Health, and Great Ormond Street Hospital, National Health Service Trust, London WC1N 1EH, United Kingdom
Both
end-inspiratory (EIO) and end-expiratory (EEO) airway occlusions are
used to calculate the strength of the Hering-Breuer inflation reflex
(HBIR) in infants. However, the influence of the timing of such
occlusions is unknown, as is the extent to which changes in volume
within and above the tidal range affect this reflex. The purpose of
this study was to compare both techniques and to evaluate the volume
dependency of the HBIR in healthy, sleeping infants up to 1 yr of age.
The strength of the HBIR was expressed as the ratio of expiratory or
inspiratory time during EIO or EEO, respectively, to that recorded
during spontaneous breathing, i.e., as the "inhibitory ratio"
(IR). Paired measurements of the EIO and EEO in 26 naturally sleeping
newborn and 15 lightly sedated infants at ~1 yr showed no
statistically significant differences in the IR according to technique:
mean (95% CI) of the difference (EIO 
EEO) being
0.02 (0.17, 0.13) during the first week of life and 0.04 (0.14, 0.22) at 1 yr. During tidal
breathing, a volume threshold of ~4 ml/kg was required to evoke the
HBIR. Marked volume and age dependency were observed. In newborn
infants, occlusions at ~10 ml/kg during sighs always resulted in an
IR > 4, whereas a similar response was only evoked at 25 ml/kg in
older infants. Age-related changes in the volume threshold may reflect
maturational changes in the control of breathing and respiratory
mechanics throughout the first year of life.
control of breathing; vagal reflexes; pulmonary stretch receptors; occlusion technique; sedation; non-rapid-eye-movement sleep
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