The effects of CPAP therapy withdrawal in patients with obstructive sleep apnea: a randomised controlled trial. Online Data Supplement

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1 The effects of CPAP therapy withdrawal in patients with obstructive sleep apnea: a randomised controlled trial Malcolm Kohler, Anne-Christin Stoewhas, Lisa Ayers, Oliver Senn, Konrad E. Bloch, Erich W. Russi, John R. Stradling Online Data Supplement 1

2 Methods Sleep studies and CPAP Attended polysomnographic sleep studies were performed and analysed according to standard methods (see online data supplement). 1 Measurements comprised 2 EEG, 2 EOG and 1 EMG channels, calibrated respiratory inductance plethysmography, 2 pulse oximetry, ECG, body position, and audio-visual recordings by a low-light infra-red video camera. Apnoea were defined as a reduction in amplitude of chest wall motion by >90% from baseline over the previous 2 min for >10 s, hypopnoea were defined as a reduction in amplitude of chest wall motion by >50% from baseline over the previous 2 min for >10 s, associated with a 4% drop in oxygen saturation. 3 In addition, pulse-oximetry was performed every night at home during the 14 days study period using the S8 TM Res-Link device (ResMed Ltd, Switzerland) from which the number of nocturnal oxygen desaturations 4% per hour (ODI) was derived and the number of apnea/hypopnea was downloaded from the internal memory of the CPAP device (S8 TM, ResMed Ltd, Switzerland) to calculate the apnoea/hypopnoea index per hour (AHI). In patients randomized to subtherapeutic CPAP, the subtherapeutic pressure was achieved by setting the CPAP machine to the lowest pressure, inserting a flow-restricting connector at the machine outlet, and inserting six extra holes in the collar of the main tubing at the end of the mask to allow air escape and to prevent rebreathing of carbon dioxide as previously described. 4,5 Endothelial function assessed by flow-mediated dilatation Patients were asked to abstain from alcohol, tobacco or caffeine on the day of the measurements. Room temperature and lighting were set at the same level for all measurements. Flow-mediated dilatation (FMD) measurements were performed by 2

3 ultrasound according to the method originally described by Celermajer. 6 Longitudinal images of the brachial artery were obtained using a high frequency (10.0 MHz) ultrasound scanning probe (Acuson Sequoia S512, Siemens AG, Switzerland) proximal to the antecubital fossa. Two-dimensional images, acquired with electrocardiogram gating, were obtained at baseline with Doppler ultrasound imaging to assess arterial diameter and flow velocity. Reactive hyperaemia was then induced by inflation of a pneumatic tourniquet around the forearm to 200 mmhg for 5 minutes, and repeated arterial diameter and flow velocity measurements were made at maximal dilatation seconds after cuff deflation. To assess endothelial independent vasodilation, we measured maximal brachial artery diameter 3 minutes after a single sublingual dose of 0.5 mg nitroglycerin (NTG). All measurements were stored digitally and analysed offline. Brachial artery diameter was measured automatically at the onset of the R wave with dedicated software (Vascular Research Tools 5, Medical Imaging Applications LLC, Coralville, USA) as previously described and validated. 7,8 The mean values of at least 3 cardiac cycles were averaged for each time point and results of endothelial dependent (FMD) and independent (nitroglycerin, GTN) vasodilation were expressed as percent change in arterial diameter from the baseline diameter. FMD measurements were performed at baseline and after 1 and 2 weeks, respectively. Blood markers of systemic inflammation Blood was drawn in all patients in the morning between 7 and 8 am at baseline and at 14 days. Measurements of hscrp, IL-6, IL-10 and TNF-α were performed from plasma samples which were stored at -80 C. 3

4 The Dade Behring BN method (particle-enhanced immunonephelometry, measuring range mg/l) was used to measure hscrp as previously described and validated. 9 IL-6, IL-10 and TNF-α were measured by ELISA with commercially available kits (BMS213HS, BMSF0004 and BMS223HS, Bender MedSystems GmbH, Vienna, Austria). The lower limit of detection for IL-6, IL-10 and TNF-α were 0.03 pg/ml, 0.05 pg/ml and 0.13 pg/ml respectively. The intra- and interassay coefficients of variation were 4.9 % and 6.0 %, respectively for IL-6 and 6.8 % and 7.5 % for IL-10, and 8.5 % and 9.8 % for TNF-α. All blood markers of systemic inflammation were measured in duplicate and in the same batch. Urinary catecholamines Urine was collected for 12 hours from 7 pm to 7 am at baseline and at 14 days. For analysis of urinary catecholamines 10 ml of urine were sampled and acidified with 0.5 ml 20% HCl. Urinary catecholamines were measured by high-performance liquid chromatography as previously described. 10 Results were corrected for creatinine excretion and expressed as nmol/mmol of creatinine. 4

5 References E1. Rechtschaffen A, Kales A. A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects NIMH Publication 204. Washington, DC: U.S. Government Printing Office E2. Bloch KE, Li Y, Sackner MA, Russi EW. Breathing pattern during sleep disruptive snoring. Eur Respir J 1997;10: E3. Peppard PE, Young T, Palta M, Skatrud J. Prospective study of the association between sleep-disordered breathing and hypertension. N Engl J Med 2000;342: E4. Jenkinson C, Davies RJ, Mullins R, Stradling JR. Comparison of therapeutic and subtherapeutic nasal continuous positive airway pressure for obstructive sleep apnoea: a randomised prospective parallel trial. Lancet 1999;353: E5. Pepperell JCT, Ramdassingh-Dow S, Crosthwaite N, Mullins R, Jenkinson C, Stradling JR, Davies RJO. Ambulatory blood pressure after therapeutic and subtherapeutic nasal continuous positive airway pressure for obstructive sleep apnoea: a randomised parallel trial. Lancet 2002;359: E6. Celermajer DS, Sorensen KE, Gooch VM, Spiegelhalter DJ, Miller OI, Sullivan ID, Lloyd JK, Deanfield JE. Non-invasive detection of endothelial dysfunction in children and adults at risk of atherosclerosis. Lancet 1992;340: E7. Tounian P, Aggoun Y, Dubern B, Varille V, Guy-Grand B, Sidi D, Girardet JP, Bonnet D. Presence of increased stiffness of the common carotid artery and endothelial dysfunction in severely obese children: a prospective study. Lancet. 2001;358: E8. Sonka M, Liang W, Lauer RM. Automated analysis of brachial ultrasound image sequences: early detection of cardiovascular disease via surrogates of endothelial function. IEEE Trans Med Imaging 2002;21: E9. Roberts WL, Moulton L, Law TC, Farrow G, Cooper-Anderson M, Savory J, Rifai N. Evaluation of nine automated high-sensitivity C-reactive protein methods: implications for clinical and epidemiological applications. Part 2. Clin Chem 2001;47: E10. Peaston RT. Routine determination of urinary catecholamines by high performance liquid chromatography with electrochemical detection. J Chromatogr 1988;424: