The interaction of the upper airway and thermo-metabolism on respiratory rhythm during non-REM sleep in the developing lamb.

This study investigates the role of metabolic rate and of vagal airway mechanisms in sustaining rhythmic breathing in the developing lamb. Fifteen lambs were prepared, at 2 days of age under fluothane anaesthesia, for sequential studies at 4, 14, 30, 45, and 55 days of age. At each age they were maintained at an ambient temperature of 5, 10, 15, 20, 25 and 30 degrees C for at least one hour before measurements were made during N-REM sleep. In 6 lambs at 4 days and in all lambs at older ages the upper airway was by-passed (by opening a tracheal window) for 10-15 minutes at each ambient temperature. Oxygen consumption was unaffected by upper airway by-pass and there were no consistent changes in mean breathing frequency or amplitude, with the exception of shifts to panting at warm ambient temperatures. Breathing pattern was unaffected by upper airway by-pass in lambs at 4 days of age, but at older ages loss of regularity of breathing frequently occurred (up to 47% of 30 days-old lambs at 25 degrees C). This was related to the fall in oxygen consumption with age and to basal values at thermoneutrality, and coincided with lower respiratory rates and increased use of expiratory laryngeal braking. Periodic breathing (and apnea) of a fixed cycle length (9.3 +/- 0.36 s) was a common feature (62%) of the observed breathing dysrhythmia. In young lambs high metabolic rate sustained high frequency rhythmic breathing which was unaffected by upper airway by-pass.(ABSTRACT TRUNCATED AT 250 WORDS)