MOUTH LEAK WITH NASAL CONTINUOUS POSITIVE AIRWAY PRESSURE INCREASES NASAL AIRWAY-RESISTANCE

Nasal congestion, dry nose and throat, and sore throat affect approxim ately 40% of patients using nasal continuous positive airway pressure (CPAP). The mechanisms causing nasal symptoms are unclear, but mouth l eaks causing high unidirectional nasal airflow may be important. We co nducted a study to investigate the effects of mouth leak and the influ ence of humidification on nasal resistance in normal subjects. Nasal r esistance was measured with posterior rhinomanometry in six normal sub jects who deliberately produced a mouth leak for 10 min while using na sal CPAP. Nasal resistance was measured regularly for 20 min after the challenge. A series of tests were performed using air at differing te mperatures and humidities. There was no change in nasal resistance whe n subjects breathed through their noses while on CPAP, but a mouth lea k caused a large increase in resistance (at a flow of 0.5 L/s) from a baseline mean of 2.21 cm H2O/L/s to a maximum mean of 7.52 cm H2O/L/s at 1 min after the challenge. Use of a cold passover humidifier caused little change in the response (maximum mean: 8.27 cm H2O/L/s), but a hot water bath humidifier greatly attenuated the magnitude (maximum me an: 4.02 cm H2O/Us) and duration of the response. Mouth leak with nasa l CPAP leads to high unidirectional nasal airflow, which causes a larg e increase in nasal resistance. This response can be largely prevented by fully humidifying the inspired air.