Conditions: Sleep Apnea
Allocation: RANDOMIZED | Intervention model: CROSSOVER
Enrollment: 47
Healthy volunteers: no

Brief summary:
This study seeks to employ advanced methods to estimate the individual factors contributing to sleep apnea from standard recordings made during routine clinical sleep studies. This study focuses on breathing control or "loop gain" as one of the factors contributing to sleep apnea. Increased levels of oxygen in the air is known to make breathing more stable by lowering "loop gain". Here, our goal is to use a new method capable of detecting a reduction in loop gain with oxygen. The investigators also aim to test whether a high loop gain measured at baseline/placebo predicts a greater improvement in sleep apnea with oxygen therapy.

Detailed description:
In a single-blinded randomized crossover study, inspired oxygen/air (40%/21%) is delivered on two separate nights. Loop gain is measured from routine polysomnography using a novel mathematical method. A value of loop gain \>1 reflects unstable breathing, and a value less than but approaching 1 denotes a system more prone to oscillate. Loop gain is measured as the changes in ventilatory drive/effort that arises subsequent to changes in ventilation (e.g. due to obstructive apnea). A simple chemoreflex model (gain, time constant, delay) is fit to surrogate ventilation data (derived from airflow) during sleep. The best model is one that best matches the elevated ventilatory drive (measured as ventilation in the absence of airflow obstruction) based on the prior apneic/hypopneic fall in ventilation. Loop gain is calculated from this model. We aim to use loop gain measured on and off oxygen to determine whether a strong response (reduction in apnea severity) can be predicted by a higher loop gain (in the sham arm) using our method. We also assessed whether assessing upper airway anatomy/collapsibility, dilator muscle responsiveness, and the arousal threshold helped to predict responses to treatment.

Arms:
arm 1: Participants breathe air with additional inspired oxygen (40%) for 1 night during an overnight sleep study (15 L/min via venturi mask). 1 week later participants will crossover to Sham (sham comparator). arm 2: Participants breathe air without additional inspired oxygen for 1 night during sleep (15 L/min via Venturi mask). 1 week later participants will crossover to Inspire Oxygen (active intervention).

Interventions: intervention 1: Inspired oxygen (40%) intervention 2: Sham
Intervention descriptions: intervention 1: Supplemental oxygen at 40% inspired via venturi mask (15 L/min). Equivalent to 5 L/min via nasal cannula. intervention 2: Medical air with 21% oxygen via venturi mask (15 L/min).

Protocol document: