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Published ahead of print on September 17, 2009
Am. J. Respir. Crit. Care Med. 2009, doi:10.1164/rccm.200810-1658OC
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Submitted on October 29, 2008
Accepted on September 16, 2009

Increased Propensity for Central Apnea in Patients with Obstructive Sleep Apnea: Effect of nCPAP

Anan Salloum1, James A. Rowley1*, Jason H Mateika2, Susmita Chowdhuri1, Qasim Omran1, and M Safwan Badr1

1 Sleep Research Laboratory, John D. Dingell VAMC, Division of Pulmonary, Allergy, Critical Care & Sleep, Department of Internal Medicine, Wayne State University School of Medicine, Detroit, Michigan, United States, 2 Sleep Research Laboratory, John D. Dingell VAMC, Division of Pulmonary, Allergy, Critical Care & Sleep, Department of Internal Medicine, Wayne State University School of Medicine, Detroit, Michigan, United States; Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan, United States

* To whom correspondence should be addressed. E-mail: jrowley{at}med.wayne.edu.

Rationale: There is increasing evidence of increased ventilatory instability in patients with obstructive sleep apnea but previous investigations have not studied whether the hypocapnic apneic threshold is altered in this group. Objective: To compare the apneic threshold, CO2 reserve, and controller gain between subjects with and without obstructive sleep apnea matched for age, gender, and body mass index. Methods: Hypocapnia was induced via nasal mechanical ventilation for 3 minutes. Cessation of mechanical ventilation resulted in hypocapnic central hypopnea or apnea depending upon the magnitude of the hypocapnia. The apnea threshold (PETCO2-AT) was defined as the measured PETCO2 at which the apnea closest to the last hypopnea occurred. The CO2 reserve was defined as the change in PETCO2 between eupneic PETCO2 and PETCO2-AT. Controller gain was defined as the ratio of change in VE between control and hypopnea or apnea to the {Delta}PETCO2. Results: 11 pairs of subjects were studied. There was no difference in the PETCO2-AT between the two groups. However, the CO2 reserve was smaller in the OSA subjects (2.2±0.6 mmHg) compared to the control subjects (4.5±1.4 mmHg, p=<0.001). The controller gain was increased in the OSA subjects (3.7±1.3 L/min/mmHg) compared to the control subjects (1.6±0.5 L/min/mmHg, p=<0.001). Controller gain decreased and CO2 reserve increased in seven subjects re-studied after using CPAP for 1 month. Conclusions: Ventilatory instability is increased in OSA subjects and is reversible with the use of CPAP.
Key words: control of breathing • obstructive sleep apnea • controller gain • apneic threshold • complex sleep apnea






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