CPAP machine performance and altitude.

UNLABELLED

STUDY RATIONALE AND OBJECTIVE: Sleep-disordered breathing is commonly treated with nasally applied continuous positive airway pressure (CPAP). Typically, pressures are titrated to pneumatically splint the airway to prevent its collapse in response to negative inspiratory pressure. This investigation was prompted by several patient complaints of sleep-related breathing difficulty associated with travel to high altitudes. CPAP devices create pressure with fan-generated airflow; therefore, CPAP performance should behave according to collective fan laws.

MEASUREMENTS AND RESULTS

In the present study, we examined the effect of simulated altitude change on four commercially available CPAP machines. Machines were tested using anatomic airway mannequins in an altitude chamber. We made three simulated ascents to 12,000 feet with machines set at 5, 10, and 12 cm H2O sea level pressure equivalents. We measured pressure using water manometers at 2,000-foot increments during ascent and descent. Mask pressures varied systematically with changing altitude in three machines. One machine, equipped with a pressure regulation feature, maintained pressure within 1 mm H2O at all pressure and altitude combinations.

CONCLUSIONS

Altitude significantly alters delivered pressure according to predictions made by the fan laws, unless a unit has pressure-compensating features. Clinicians should consider this factor when CPAP is prescribed for patients who live or travel to places located at significantly higher or lower elevations than the titration site.