Inspiratory duty cycle responses to flow limitation predict nocturnal hypoventilation

¹ Johns Hopkins Sleep Disorders Center, Division of Pulmonary and Critical Care Medicine

^* To whom correspondence should be addressed. E-mail: hschneid{at}jhmi.jhu.edu.

	Abstract

Upper airway obstruction can elicit neuromuscular responses that mitigate and/or compensate for the obstruction. We hypothesize 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 NREM sleep, similar degrees of upper airway obstruction were induced in healthy men and women (N=10 each). Inspiratory duty cycle, respiratory rate and minute ventilation were determined for each degree of upper airway obstruction during NREM sleep and compared to the baseline non-flow limited condition.

A dose dependent increase in the inspiratory duty cycle and respiratory rate was observed in response to increasing severity of upper airway obstruction. Increases in the inspiratory duty cycle, but not respiratory rate, helped to maintain ventilation acutely. Heterogeneity in these responses was associated with variable degrees of ventilatory compensation, allowing us to segregate 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.