occurred at night in the split schedule than the consolidated schedule [F(5,795)=3.8, p > .05]. For Study 2, repeated measures ANOVA showed no differences between the three sleep strategies in night- time mean lapse count [F(2,183)=0.79, p > .05]. Discussion: The results from both studies indicate that splitting sleep episodes is not inherently harmful to performance provided the total duration is sufficient. Study 1 suggests split work-rest schedules may be preferable to traditional night shifts for sustaining perfor- mance in some industries. Study 2 suggests the timing and arrangement of daytime sleep between long 12 h nights shifts is not critical for nocturnal function. 006 EFFECTS OF 40 MG OF MORPHINE ON PHENOTYPIC CAUSES OF OBSTRUCTIVE SLEEP APNEA R. TOMAZINI MARTINS 1,2 , J. CARBERRY 1,2 , D. WANG 3,4 , L. ROWSELL 3,4 , R. GRUNSTEIN 3,4 , D. MCKENZIE 1,5 AND D. ECKERT 1,2 1 NeuRA, 2 UNSW, 3 Woolcock Institute of Medical Research, 4 University of Sydney, 5 Prince of Wales Hospital Introduction: Opioids use is common for pain management. Accidental deaths have increased in recent years. Deaths nearly always occur during sleep. Thus, people with sleep apnoea may be at greater risk. There are 4 key causes of obstructive sleep apnea (OSA). A collapsible upper airway, poor pharyngeal muscle respon- siveness asleep, a low respiratory arousal threshold and unstable ventilatory control (high loop gain). Major concerns are that morphine worsens OSA severity via respiratory depression and central reductions in neural drive to the pharyngeal muscles. However, the effects of morphine on key phenotypic causes of OSA have not been investigated. Thus, given the increasing rates of use and potential for harm, this study aimed to evaluate the effects of morphine on the 4 key causes of OSA. Materials and Methods: 21 men with OSA (AHI range=7-67 events/ h sleep), were studied on 2 separate nights (1 week wash-out) according to a randomised, double-blind, cross-over design in which patients received 40 mg of MS Contin on one visit and placebo on the other. Brief reductions in CPAP were delivered to induce airflow limitation during non-REM sleep to quantify the 4 traits that cause OSA (i.e. upper airway collapsibility [Pcrit], genioglossus muscle responsiveness [MR], respiratory arousal threshold [AT] and loop gain [LG]) at each visit. Additionally, CO 2 was administered via nasal mask to quantify hypercapnic ventilatory responses during stable non-REM sleep. Results: Compared to placebo, 40 mg of morphine did not change Pcrit (À0.1 Æ 2.4 vs. À0.4 Æ 2.2 cmH 2 O, p = 0.58), genioglossus responsiveness (À2.2 [À5.4 to À0.87] vs. À1.2 [À3.5 to À0.3] microV/ cmH 2 O epiglottic pressure, p = 0.22), or arousal threshold (À16.7 Æ 6.8 vs. À15.4 Æ 6.0 cmH 2 O, p = 0.41), but did reduce loop gain (À10.1 Æ 2.6 vs. À4.4 Æ 2.1 dimensionless, p = 0.04). Morphine also reduced ventilatory and genioglossus responses to CO 2 . Conclusions: Concordant with recent clinical findings, 40 mg of morphine does not change Pcrit, MR, or AT in patients with moderately severe OSA. However, in line with blunted chemosensitivity, 40 mg of MS Contin does reduce LG and hypercapnic ventilatory responses. These paradoxical effects may reduce unstable respiratory control in patients with high LG but could decrease breathing and worsen blood gas disturbances in others. Identification of at risk of harm patient’s characteristics with opioids remains a priority. 007 PRODROMAL OBESITY HYPOVENTILATION SYNDROME - EARLY DETECTION OF HYPOVENTILATION IN THE VERY OBESE POPULATION S. SIVAM, K. WONG, B. YEE, D. WANG, R. GRUNSTEIN AND A. PIPER Royal Prince Alfred Hospital Introduction: Prodromal obesity hypoventilation syndrome (pOHS) refers to the presence of nocturnal hypoventilation (NH) without awake hypercapnia. This study evaluates the characteristics and prevalence of prodromal OHS in the very obese population and further investigates simple measures to detect hypoventilation prior to the development of awake hypercapnia. Methods: 89 consecutive patients with a BMI >40 kg/m 2 without known lung (spirometric ratio >0.7) or neuromuscular disease were recruited from local sleep and obesity clinics. Anthropometrics, spirometry, daytime pulse oximetry, supine and upright arterialised capillary blood gases (cABG) and slow vital capacity obtained in random order, as well as in-lab polysomnography and nocturnal transcutaneous carbon dioxide monitoring (TcCO2) were performed on all patients. NH was defined by a rise in TcCO2 levels by 10 mmHg or a TcCO2 > 55 mmHg for > 10 minutes during the sleep study. Results: Twenty-one patients (24%) were diagnosed with pOHS, 54 patients (61%) with obstructive sleep apnoea (OSA) without hypoventilation, 2 patients (<1%) without sleep disordered breathing and 12 patients (13%) with OHS. In this cohort, no patient had hypoventilation without concurrent obstructive events. The mean BMI, age and gender (%male) of the overall cohort were 54 (range 40-90 kg/m 2 ), 49 (range: 26-75 years) and 37% respectively. Com- pared with OSA, patients with hypoventilation (OHS + pOHS) demonstrated significant differences in daytime pulse oximetry (SpO2), slow and forced vital capacities, waist, hip, neck, abdominal sagittal height and body mass index (BMI). The pOHS group however only showed significant differences in neck (pOHS 51 v OSA 47 cm; p = 0.01), sagittal height (31 v 28 cm; p = 0.01), BMI (57 v 51 kg/m 2 ;p = 0.008) and SpO2 (94 v 96%, p = 0.007), compared with OSA. Combining SpO2 and BMI yielded an area under the ROC curve of 0.8. Only patients with hypoventilation, including the pOHS group, showed a rise in cABG carbon dioxide levels (PaCO2) in a supine v upright position (pOHS 44 v 41 mmHg; p < 0.001). Discussion: Prodromal OHS can be recognised early with simple measures in an outpatient setting particularly with BMI and SpO2. A higher supine versus upright PaCO2 is also helpful. Further longi- tudinal studies in the pOHS cohort and subsequent awake hyper- capnia, are needed. 008 AUTOMATIC POSITIVE AIRWAY PRESSURE (APAP) MAY REDUCE WAIT TIMES FOR TREATMENT OF OSA IN PAEDIATRIC PRACTICE A. NUNEZ, R. LONGLAND, G. WILLIAMS, P. WALES AND J. CHAWLA Lady Cilento Children’s Hospital Introduction: Obstructive sleep apnoea (OSA) in children is asso- ciated adverse health outcomes including deficits in cognition, behaviour, growth and cardiovascular function. The most common ª 2017 The Authors Journal of Sleep Research © 2017 European Sleep Research Society, JSR 26 (Suppl. 1),5–33 Oral Abstracts 7