Simple Cause for a “Complex” Problem To the Editor: We read with great interest the recent CHEST article (February 2014) by DelRosso et al1 on complex sleep apnea syndrome (CompSAS). CompSAS is a relatively new terminology used to describe the appearance of central sleep apnea (CSA) in patients with OSA in whom airway patency has been restored with CPAP therapy. We agree with the authors that patients with CompSAS have both reduced upper airway tone and unstable central ventilatory control. However, central apnea also occurs when the patient’s ventilatory effort ceases due to several other possible reasons, including high loop gain (exaggerated hyperventilatory response to hypercarbia resulting in hypocapnea below the apnea threshold), low arousal threshold, or apnea threshold close to awake Pco2.2 Recently, in a study by Montesi et al3 regarding 310 patients with OSA who underwent either split-night or full-night CPAP titration, air leak during CPAP titration was associated with the development of acute CSA, particularly in subjects using a nasal mask. The authors postulated that air leak washing out anatomic dead space is a contributing factor in the development of CompSAS. The group with central apnea index , 5 had a median average leak of 45.5 L/min (interquartile range, 20.8 L/min) vs 51.0 L/min (interquartile range, 21.0 L/min) with central apnea index ⱖ 5 (P 5 .056). These findings might have mechanistic and therapeutic implications as the physicians involved in the management of CompSAS should be aware of this potential iatrogenic and avoidable cause of the emergence of CSA during CPAP titration. The finding of a reemergence of apneas on increasing CPAP should alert the astute physician to conduct a diligent search for air leak in the appropriate clinical setting. Lastly, although the best treatment of CompSAS remains controversial, most of the published data suggest that this form of central apnea resolves with ongoing CPAP therapy.4 Studies have also documented that adaptive servoventilation is more effective in patients with persistent central apneas.4,5 Sachin Kumar, MD, DM, FCCP Sandipan Chandra, MD New Delhi, India Affiliations: From the Department of Pulmonary Medicine, Institute of Liver & Biliary Sciences. Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article. Correspondence to: Sachin Kumar, MD, DM, FCCP, Department of Pulmonary Medicine, Institute of Liver & Biliary Sciences, C-15, Delhi Government Residential Complex, D-2 Pocket, Vasant Kunj, New Delhi, 110070, India; e-mail: [email protected] © 2014 American College of Chest Physicians. Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details. DOI: 10.1378/chest.14-0312

References 1. DelRosso LM, Harper MB, Hoque R. A man in his 50s develops 3-min central apneas during a titration study. Chest. 2014; 145(2):404-406. 2. Salloum A, Rowley JA, Mateika JH, Chowdhuri S, Omran Q, Badr MS. Increased propensity for central apnea in patients with obstructive sleep apnea: effect of nasal continuous posijournal.publications.chestnet.org

tive airway pressure. Am J Respir Crit Care Med. 2010;181(2): 189-193. 3. Montesi SB, Bakker JP, Macdonald M, et al. Air leak during CPAP titration as a risk factor for central apnea. J Clin Sleep Med. 2013;9(11):1187-1191. 4. Kuzniar TJ, Pusalavidyasagar S, Gay PC, Morgenthaler TI. Natural course of complex sleep apnea—a retrospective study. Sleep Breath. 2008;12(2):135-139. 5. Kuźniar TJ, Morgenthaler TI. Treatment of complex sleep apnea syndrome. Chest. 2012;142(4):1049-1057.

Response To the Editor: We thank Drs Kumar and Chandra for their interest in our article1 and comments regarding other postulated pathophysiologic mechanisms for complex sleep apnea syndrome. Our article illustrates the emergence of central apneas during positive airway pressure titration in a patient without any past medical history.1 This case presentation is not intended to be a complete review of the literature. As stated in the International Classification of Sleep Disorders, Third Edition, despite many postulated mechanisms, there are no definitive data regarding either the cause of treatmentemergent central sleep apnea or the optimal management strategy for these patients.2 Lourdes M. DelRosso, MD Romy Hoque, MD Shreveport, LA Affiliations: From the Division of Sleep Medicine and Department of Neurology, Louisiana State University School of Medicine. Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article. Correspondence to: Lourdes M. DelRosso, MD, Division of Sleep Medicine and Department of Neurology, Louisiana State University School of Medicine, Shreveport, LA 71130; e-mail: [email protected] © 2014 American College of Chest Physicians. Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details. DOI: 10.1378/chest.14-0604

References 1. DelRosso LM, Harper MB, Hoque R. A man in his 50s develops 3-min central apneas during a titration study. Chest. 2014;145(2):404-406. 2. American Academy of Sleep Medicine. International Classification of Sleep Disorders. 3rd ed. Darien, IL: American Academy of Sleep Medicine; 2014.

GI Symptoms in Patients With COPD To the Editor: In a recent issue of CHEST (February 2014),1 disturbed integrity of the GI system was reported in patients with COPD, implying that the GI system is affected and contributes to the systemic manifestations of COPD. These findings were detected in a wellcharacterized sample of 14 patients and compared with a matched CHEST / 145 / 6 / JUNE 2014

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