Inspiratory duty cycle responses to flow limitation predict nocturnal hypoventilation.

Upper airway obstruction (UAO) can elicit neuromuscular responses that mitigate and/or compensate for the obstruction. It was hypothesised that flow-limited breathing elicits specific timing responses that can preserve ventilation due to increases in inspiratory duty cycle rather than respiratory rate. By altering nasal pressure during non-rapid eye movement (non-REM) sleep, similar degrees of UAO were induced in healthy males and females (n = 10 each). Inspiratory duty cycle, respiratory rate and minute ventilation were determined for each degree of UAO during non-REM sleep and compared with the baseline nonflow-limited condition. A dose-dependent increase in the inspiratory duty cycle and respiratory rate was observed in response to increasing severity of UAO. Increases in the inspiratory duty cycle, but not respiratory rate, helped to acutely maintain ventilation. Heterogeneity in these responses was associated with variable degrees of ventilatory compensation, allowing for the segregation of individuals at risk for hypoventilation during periods of inspiratory airflow limitation. Upper airway obstruction constitutes a unique load on the respiratory system. The inspiratory duty cycle, but not the respiratory rate, determine the individual's ability to compensate for inspiratory airflow limitation during sleep, and may represent a quantitative phenotype for obstructive sleep apnoea susceptibility.