Increasing humidity blocks continuous positive airflow-induced apnea responses in rats

Background: The aim of this study was to investigate the role of temperature and humidity in positive continuous pressure flow-induced apnea. Methods: Forty-two adult male Sprague-Dawley rats were used in a functionally isolated laryngeal animal model. In study 1, animals were challenged with laryngeal stimulation for 1 minute to detect the possibility of adaptation. In study 2, different airflow conditions (25°C dry-25°C dry, 25°C dry-25°C wet, 25°C dry-37°C dry and 25°C dry-37°C wet) were delivered to determine the role of temperature and humidity in the flow-induced apneic response of the larynx. The apneic index was calculated by prolonged expiratory time/baseline expiratory time. Results: Laryngeal dry room temperature air exposure induced an apneic response, and this response was reproducible and could be eliminated by humidification. In contrast, this apneic response could not be inhibited by increasing temperature alone. In addition, prolonged cold dry air stimulation did not evoke a tachyphylactic effect to normalize the breathing pattern. Conclusion: Laryngeal cold dry air stimulation triggered an apneic response, which could be eliminated by humidification but not by the heating of air. These results suggest that using continuous positive airway pressure (CPAP) with humidified air decreases CPAP-induced apnea.