INSTABILITY OF VENTILATORY CONTROL IN PATIENTS WITH OBSTRUCTIVE SLEEP-APNEA

Because of the oscillatory pattern of upper airway resistance and brea thing during sleep in patients with obstructive sleep apnea (OSA), we hypothesized that OSA patients have an underlying instability of venti latory drive to inspiratory muscles. To assess the stability of ventil atory drive in OSA patients and controls, we used the pseudorandom bin ary stimulation (PRBS) test and examined the closed- and open-loop res ponses to hyperoxic hypercapnia. The closed-loop response is produced by interactions of dynamic gain in controller, plant, and ventilatory feedback. The open-loop response reflects controller dynamic gain or f requency-dependent chemosensitivity. As compared with 16 non-apneic, n onobese control subjects, a group of nine obese OSA patients had a hig her peak response and a more rapid and irregular recovery phase of the closed-loop CO2 response in the PRBS test. The two groups had similar open-loop responses in the PRBS test, suggesting that central dynamic CO2 chemosensitivity was not abnormal in OSA. We conclude that the di fferences between OSA patients and controls in the closed-loop respons e in the PRBS test are not due to differences in dynamic controller ga in, but are related to differences in dynamic plant gain and/or negati ve ventilatory feedback. In addition to OSA, obesity may affect these variables and may have been responsible for our findings.