Depressed ventilatory load compensation in sleep apnea. Reversal by nasal CPAP

Abnormal inspiratory load compensation may be one factor leading to development of obstructive sleep apnea (OSA). Alternatively, abnormalities in ventilatory load compensation may be a consequence of the manifestations of OSA. This investigation was designed to determine if impairment of awake inspiratory load compensation exists in OSA and to determine if abnormalities in this parameter are reversible by nasal CPAP therapy. A new technique for assessment of awake inspiratory load compensation was devised to standardize the degree of ventilatory stimulation applied during load compensation assessment in each subject. This eliminates intersubject differences in degree of ventilatory stimulation during testing, which are inevitable with standard techniques and which have been shown to affect the measurement of load compensation. Inspiratory load compensation was assessed during resting room air ventilation and during steady state CO2 and exercise stimulation titrated to provide similar degrees of ventilatory stimulation in each subject. Impairment of awake inspiratory load compensation was found during all conditions in the patients with moderate to severe OSA studied compared with that in weight-matched control subjects. Normalization of awake inspiratory load compensation was observed after 4 wk of nasal CPAP therapy in five patients. These results indicate that impairment of awake inspiratory load compensation is a reversible consequence rather than a cause of OSA.