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Increased Propensity for Central Apnea in Patients with Obstructive Sleep Apnea

Effect of Nasal Continuous Positive Airway Pressure

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

James A. Rowley, M.D., Wayne State University School of Medicine, Division of Pulmonary, Allergy, Critical Care & Sleep, Harper University Hospital, 3 Hudson 3990 John R, Detroit, MI 48201. E-mail: jrowley{at}med.wayne.edu

Rationale: There is increasing evidence of increased ventilatory instability in patients with obstructive sleep apnea (OSA), but previous investigations have not studied whether the hypocapnic apneic threshold is altered in this group.

Objectives: To compare the apneic threshold, CO₂ reserve, and controller gain between subjects with and without OSA matched for age, sex, 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 (PET_CO2–AT) was defined as the measured PET_CO2 at which the apnea closest to the last hypopnea occurred. The CO₂ reserve was defined as the change in PET_CO2 between eupneic PET_CO2 and PET_CO2–AT. Controller gain was defined as the ratio of change in VE between control and hypopnea or apnea to the PET_CO2.

Measurements and Main Results: Eleven pairs of subjects were studied. There was no difference in the PET_CO2–AT between the two groups. However, the CO₂ reserve was smaller in the subjects with OSA (2.2 ± 0.6 mm Hg) compared with the control subjects (4.5 ± 1.4 mm Hg; P < 0.001). The controller gain was increased in the subjects with OSA (3.7 ± 1.3 L/min/mm Hg) compared with the control subjects (1.6 ± 0.5 L/min/mm Hg; P < 0.001). Controller gain decreased and CO₂ reserve increased in seven subjects restudied after using continuous positive airway pressure for 1 month.

Conclusions: Ventilatory instability is increased in subjects with OSA and is reversible with the use of continuous positive airway pressure.

Key Words: control of breathing • obstructive sleep apnea • controller gain • apneic threshold • complex sleep apnea • central sleep apnea

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Ventilatory instability, manifested by increased chemoresponsiveness is observed in subjects with obstructive sleep apnea and when combined with unfavorable upper airway mechanics, explains the propensity to sleep-disordered breathing in such individuals. However, the role of continuous positive airway pressure in affecting the parameters of central apnea in such patients has not been completely defined. What This Study Adds to the Field In subjects with obstructive sleep apnea, ventilatory instability is manifested by a lower CO2 reserve and increased controller gain, both of which are reversed by the use of continuous positive airway pressure.

 

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