DEPRESSED VENTILATORY LOAD COMPENSATION IN SLEEP-APNEA - REVERSAL BY NASAL CPAP

Abnormal inspiratory load compensation may be one factor leading to de velopment of obstructive sleep apnea (OSA). Alternatively, abnormaliti es in ventilatory load compensation may be a consequence of the manife stations of OSA. This investigation was designed to determine if impai rment of awake inspiratory load compensation exists in OSA and to dete rmine if abnormalities in this parameter are reversible by nasal CPAP therapy. A new technique for assessment of awake inspiratory load comp ensation was devised to standardize the degree of ventilatory stimulat ion applied during load compensation assessment in each subject. This eliminates intersubject differences in degree of ventilatory stimulati on during testing, which are inevitable with standard techniques and w hich have been shown to affect the measurement of load compensation. I nspiratory load compensation was assessed during resting room air vent ilation 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 al l conditions in the patients with moderate to severe OSA studied compa red with that in weight-matched control subjects. Normalization of awa ke inspiratory load compensation was observed after 4 wk of nasal CPAP therapy in five patients. These results indicate that impairment of a wake inspiratory load compensation is a reversible consequence rather than a cause of OSA.