Rachel Schembri

Neuropsychological function in patients with acute tetraplegia and sleep disordered breathing

&NA; Sleep disordered breathing is highly prevalent following spinal cord injury and likely caused by the injury. Beyond the devastating physical consequences of spinal cord injury, neuropsychological dysfunction is also common. In both the able‐bodied and chronic spinal cord injury patients, sleep disordered breathing impairs many areas of neuropsychological function. However, this has not been investigated in patients with acute injury. Study objectives: To investigate the relationship between apnea severity and neuropsychological function in patients with acute‐onset tetraplegia and sleep disordered breathing. Methods: Polysomnography and neuropsychological testing were performed on 104 participants (age M = 45.60, SD = 16.38; 10 female) across 11 international sites, 2 months postinjury (M = 60.70 days, SD = 39.48). Neuropsychological tests assessed attention, information processing, executive function, memory, learning, mood, and quality of life. Results: More severe sleep apnea was associated with poorer attention, information processing, and immediate recall. Deficits did not extend to memory. Higher preinjury intelligence and being younger reduced the associations with sleep disordered breathing; however, these protective factors were insufficient to counter the damage to attention, immediate recall, and information processing associated with sleep disordered breathing. Conclusions: These data suggest that new spinal cord injury may function as a model of “acute sleep apnea” and that more widespread sleep apnea‐related deficits, including memory, may only be seen with longer exposure to apnea. These findings have important implications for functioning and skill acquisition during rehabilitation and, as such, highlight the importance of sleep health following tetraplegia.

Subjective sleep disturbances and quality of life in chronic tetraplegia

Study design:This is a cross-sectional survey.Objectives:The objective of this study was to evaluate the subjective sleep disturbances and quality of life in chronic tetraplegia.Setting:This study was conducted in a community sample from Victoria, Australia.Methods:People with tetraplegia were mailed a survey battery including the following: demographic questions; Karolinska Sleepiness Scale (KSS); Basic Nordic Sleepiness Questionnaire; Functional Outcomes of Sleep Questionnaire (FOSQ); Multivariate Apnoea Prediction Index and Assessment of Quality of Life (AQoL) Questionnaire. Scores were compared with the best available normative data.Results:A total of 163 of 424 (38%) surveys were returned (77% male; 39% sensory and motor complete; mean age±s.d.=46±14 years; mean years since injury=11±8 years). The AQoL health utility score (0.31±0.29) was significantly lower than published population norms. FOSQ total (17.55±2.57) and KSS (3.93±2.27) scores were no different from the best available population data. People with tetraplegia reported worse sleep habits, symptoms and quality than a normal population, as indicated on 17 of 21 questions on the Basic Nordic Sleep Questionnaire. Multivariate analysis found that greater injury severity (coefficient (95% CI)=0.14 (0.10, 0.18)), increasing age (−0.004 (−0.008, −0.001)) and worse sleep symptoms (−0.005 (−0.009, −0.0003)) were all significantly associated with reduced quality of life.Conclusion:People with chronic tetraplegia experience more subjective sleep problems and worse quality of life than their able-bodied counterparts. Quality of life is related to injury severity, age and sleep symptoms. Treating the sleep disorders experienced by people living with tetraplegia has the potential to improve their health and well-being.

Diagnostic accuracy of a two-stage model for detecting obstructive sleep apnoea in chronic tetraplegia

Background Obstructive sleep apnoea (OSA) is highly prevalent in people with spinal cord injury (SCI). Polysomnography (PSG) is the gold-standard diagnostic test for OSA, however PSG is expensive and frequently inaccessible, especially in SCI. A two-stage model, incorporating a questionnaire followed by oximetry, has been found to accurately detect moderate to severe OSA (MS-OSA) in a non-disabled primary care population. This study investigated the accuracy of the two-stage model in chronic tetraplegia using both the original model and a modified version for tetraplegia. Methods An existing data set of 78 people with tetraplegia was used to modify the original two-stage model. Multivariable analysis identified significant risk factors for inclusion in a new tetraplegia-specific questionnaire. Receiver operating characteristic (ROC) curve analyses of the questionnaires and oximetry established thresholds for diagnosing MS-OSA. The accuracy of both models in diagnosing MS-OSA was prospectively evaluated in 100 participants with chronic tetraplegia across four international SCI units. Results Injury completeness, sleepiness, self-reported snoring and apnoeas were included in the modified questionnaire, which was highly predictive of MS-OSA (ROC area under the curve 0.87 (95% CI 0.79 to 0.95)). The 3% oxygen desaturation index was also highly predictive (0.93 (0.87–0.98)). The two-stage model with modified questionnaire had a sensitivity and specificity of 83% (66–93) and 88% (75–94) in the development group, and 77% (65–87) and 81% (68–90) in the validation group. Similar results were demonstrated with the original model. Conclusion Implementation of this simple alternative to full PSG could substantially increase the detection of OSA in patients with tetraplegia and improve access to treatments. Trial registration number Results, ACTRN12615000896572 (The Australian and New Zealand Clinical Trials Registry) and pre-results, NCT02176928 (clinicaltrials.gov).

Light sensors for objective light measurement in ambulatory polysomnography

Ambulatory polysomnography (PSG) does not commonly include an objective measure of light to determine the time of lights off (Loff), and thus cannot be used to calculate important indices such as sleep onset latency and sleep efficiency. This study examined the technical specifications and appropriateness of a prototype light sensor (LS) for use in ambulatory Compumedics Somte PSG.Two studies were conducted. The first examined the light measurement characteristics of the LS when used with a portable PSG device, specifically recording trace range, linearity, sensitivity, and stability. This involved the LS being exposed to varying incandescent and fluorescent light levels in a light controlled room. Secondly, the LS was trialled in 24 home and 12 hospital ambulatory PSGs to investigate whether light levels in home and hospital settings were within the recording range of the LS, and to quantify the typical light intensity reduction at the time of Loff. A preliminary exploration of clinical utility was also conducted. Linearity between LS voltage and lux was demonstrated, and the LS trace was stable over 14 hours of recording. The observed maximum voltage output of the LS/PSG device was 250 mV, corresponding to a maximum recording range of 350 lux and 523 lux for incandescent and fluorescent light respectively. At the time of Loff, light levels were within the recording range of the LS, and on average dropped by 72 lux (9–245) in the home and 76 lux (4–348) in the hospital setting. Results suggest that clinical utility was greatest in hospital settings where patients are less mobile. The LS was a simple and effective objective marker of light level in portable PSG, which can be used to identify Loff in ambulatory PSG. This allows measurement of additional sleep indices and support with clinical decisions.

Long-term change in respiratory function following spinal cord injury.

Study design:Retrospective study.Objectives:To model the effect of time since injury on longitudinal respiratory function measures in spinal cord injured-individuals and to investigate the effect of patient characteristics.Setting:A total of 173 people who sustained a spinal cord injury between 1966 and April 2013 and who had previously participated in research or who underwent clinically indicated outpatient respiratory function tests at the Austin Hospital in Melbourne, Australia, were included in the study. At least two measurements over time were available for analysis in 59 patients.Methods:Longitudinal data analysis was performed using generalised linear regression models to determine changes in respiratory function following spinal cord injury from immediately post injury to many years later. Secondly, we explored whether injury severity, age, gender and body mass index (BMI) at injury altered the time-dependent change in respiratory function.Results:The generalised linear regression model showed no significant change (P=0.276) in respiratory function measured in (forced) vital capacity ((F)VC) after the spinal cord injury. However, significant (P<0.05) differences in respiratory function over time were found when categorising age and BMI.Conclusion:This clinical cohort with long-term, repeated measurements of respiratory function showed no significant overall change in respiratory function over 23 years. However, a decline in respiratory function over time was observed in subgroups of individuals older than 30 years at the onset of injury and in those with a BMI>30 kg m−2.

Validation of the Dutch clinical prediction rule for ambulation outcomes in an inpatient setting following traumatic spinal cord injury.

Study design:Retrospective study.Objectives:To determine the accuracy of a previously described Dutch clinical prediction rule for ambulation outcome in routine clinical practice.Setting:Adult (⩾18 years) patients who were admitted to the Austin Hospital with a traumatic spinal cord injury between January 2006 and August 2014.Methods:Data from medical records were extracted to determine the score of the Dutch clinical ambulation prediction rule proposed by van Middendorp et al. in 2011. A receiver-operating characteristics (ROC) curve was generated to investigate the performance of the prediction rule. Univariate analyses were performed to investigate which factors significantly influence ambulation after a traumatic spinal cord injury.Results:The area under the ROC curve (AUC) obtained during the current study (0.939, 95% confidence interval (CI) (0.892, 0.986)) was not significantly different from the AUC from the original Dutch clinical prediction model (0.956, 95% CI (0.936, 0.976)). Factors that were found to have a significant influence on ambulation outcome were time spent in the ICU, number of days hospitalised and injury severity. Age at injury initially showed a significant influence on ambulation however, this effect was not apparent after inclusion of the 24 patients who died due to the trauma (and therefore did not walk after their injuries).Conclusion:The Dutch ambulation prediction rule performed similarly in routine clinical practice as in the original, controlled study environment in which it was developed. The potential effect of survival bias in the original model requires further investigation.

Periodic limb movements in tetraplegia

Objective: To establish the prevalence of Periodic Limb Movements during Sleep (PLMS) in patients with tetraplegia, controlling for obstructive sleep apnea. To explore whether demographic and injury characteristics affect PLMS. Study Design: Retrospective cohorts. Setting and Participants: One hundred seventy-three participants with acute (<12 months) and 92 with chronic (>12 months) tetraplegia who underwent full overnight diagnostic sleep studies. Interventions and outcome measures: Two hundred sixty-two sleep study recordings were included. A randomly selected subgroup of 21 studies was assessed for PLM during wakefulness. Data were analysed according to the current American Academy of Sleep Medicine guidelines. Results: Of the participants, 41.6% (43(15.7) years and 14.9% female) had a motor and sensory complete lesion. Sleep was poor with both OSA (87.8% with apnea hypopnoea index ≥ 5) and PLMS (58.4% with PLMS per hour PLMSI > 15) highly prevalent. There was no difference in the PLMSI between those with OSA (36.3(39.8)) or without (42.2(37.7), P = 0.42). PLMS were evident during REM and NREM sleep in all of the 153 patients with PLMSI > 15. All 21 participants in the subgroup of studies analysed for the PLM during quiet wakefulness, exhibited limb movements. None of the modelled variables (injury completeness, gender, OSA severity or time since injury) significantly predicted a PLMSI > 15 (P = 0.343). Conclusion: In conclusion, this study confirms the high prevalence of PLM in tetraplegia and the presence of leg movements in NREM and REM sleep along with wakefulness after controlling for OSA. No associations between the presence of PLMS and patient characteristics or injury specific aspects were found.

AB003. Validation of a two-stage screening model to predict moderate to severe obstructive sleep apnea in chronic tetraplegia

Institute for Breathing and Sleep, Austin Health, Melbourne, Victoria, Australia; The University of Melbourne, Department of Medicine Melbourne, Victoria, Australia; National Spinal Injuries Centre, Stoke-Mandeville Hospital, Aylesbury, Buckinghamshire, UK; The University of Miami, Miller School of Medicine, Miami, Florida, USA; University of British Columbia, Department of Medicine, Vancouver, BC, Canada; Monash University, School of Public Health and Preventive Medicine, Melbourne, Victoria, Australia

The Effects of Experimental Sleep Fragmentation and Sleep Deprivation on the Response of the Genioglossus Muscle to Inspiratory Resistive Loads

STUDY OBJECTIVES Poor upper airway dilator muscle function may contribute to obstructive sleep apnea (OSA). Sleep deprivation reduces dilator muscle responsiveness, but sleep fragmentation, which is most characteristic of OSA, has not been assessed. This study compared the effects of sleep deprivation and fragmentation on dilator muscle responsiveness during wakefulness. METHODS Twenty-four healthy individuals (10 female) participated in two consecutive overnight polysomnography (PSG) sessions. The first was an adaptation PSG of normal sleep. The second was an experimental PSG, where participants were allocated to groups of either normal sleep, no sleep, or fragmented sleep. Inspiratory resistive loading assessment occurred the morning following each PSG. Four 10 cmH2O and four 20 cmH2O loads were presented in random order for 60 seconds while participants were awake and supine. Sleep (electroencephalogram, electrooculogram, electromyogram [EMG]), intramuscular genioglossus activity (EMGGG), and ventilation were measured throughout the loading sessions. RESULTS Five controls, seven sleep deprivation participants, and seven sleep fragmentation participants provided data. Contrary to expectations, neither EMGGG nor ventilation showed significant interaction effects (group × session × load) during resistive loading. There was a main effect of load, with peak EMGGG (mean % max ± standard error) significantly higher for the 20 cmH2O load (4.1 ± 0.6) than the 10 cmH2O load (3.3 ± 0.6) across both sessions and all groups. Similar results were observed for peak inspiratory flow, duty cycle, and mask pressure. CONCLUSIONS Upper airway function was not affected by 1 night of no sleep or poor-quality sleep. This raises doubt as to whether fragmented sleep in OSA increases disorder severity via reduced upper airway dilator responses.

Light sensors for determination of lights off time in home polysomnography

Introduction: Polysomnography (PSG) in the home has advantages over in-laboratory PSG, but one important disadvantage is the inability of current devices to record lights off (Loff) and on times and thus important indices such as sleep onset latency and sleep efficiency cannot be determined. This study evaluates the characteristics of a prototype light sensor (Compumedics) used with a portable PSG device (SomtePSG, Compumedics), and its utility in the home where light conditions are uncontrolled and it is impractical to calibrate the light sensor to the conditions in each individual home. Methods: Three examples of the light sensor were exposed to incandescent light at a range of controlled light levels to determine their signal characteristics. Twenty-four home PSGs were analysed to explore the characteristics of the light sensor signal in the home. Results: The table below shows the results for the sensor signal characteristics. The light sensor allowed a discernable Loff to be identified in 19 of 24 home PSGs, and in these 19, the mean difference between patient reported and light sensor Loff was 1.2 min (SD 16.6, range -23 to +50). Discussion: The light sensor signals were found to have good sensitivity and linearity, low drift and record a range of lux appropriate for the home setting. When used in home PSG, these light sensors were able to establish Loff in the majority of PSGs. The wide range of differences between patient reported and sensor Loff demonstrates the importance of objective determination of Loff in home PSG, particularly for studies where accurate measurements of Loff dependant indices such as sleep onset latency are needed.Po01 Understanding pharyngeal airflow and upper airway collapse in OSA: use of computational fluid dynamics and fluid-structure interaction M. ZHAO, G. ROSENGARTEN, K. SUTHERLAND, T. BARBER and P. CISTULLI School of Mechanical Engineering, University of New South Wales, Sydney, NSW, Australia, Centre for Sleep Health and Research, Royal North Shore Hospital, Sydney, NSW, Australia, NHMRC Centre for Sleep Health (CIRUS), Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia Introduction: Understanding pharyngeal airflow and the mechanisms of upper airway collapse in OSA is important and has implications for developing new treatment modalities . Three-dimensional imaging techniques provide an accurate model of airway geometry which can be combined with computational techniques to simulate regional flow and pressure profiles in the airway. This study aimed to replicate pharyngeal airflow in a collapsing airway in OSA using computational fluid dynamics (CFD) and fluid-structure interaction (FSI). Methods: A male with severe OSA (AHI 41.5 h) and magnetic resonance imaging of the upper airway was selected to obtain airway geometry for computational analysis. The pharyngeal airway was segmented and used to construct a computational model. CFD simulation of airway flow was performed at a maximum flow rate of 166 mL s corresponding to maximum inspiration. A uniform 2 mmthick airway computational model was designed for FSI with material properties of 13 000 Pa in Young’s modulus and 0.45 in Poisson’s ratio. Physical upper airway models (rigid and flexible) were fabricated to validate the results of both the CFD and FSI. Results: CFD indicated that in the upper airway flow was restricted by the soft palate with a maximum velocity of 11 m s found at the level of the uvula. This flow restriction induced a 45 Pa pressure drop across velopharynx. The pressure distribution in the rigid airway experimental model closely matched that from CFD, validating the CFD methodology. FSI results showed the largest deformation of the airway was located at the base of the tongue on the left posterior airway wall. The physical flexible airway model produced collapse of the airway wall in the same region as the FSI simulations. Conclusion: CFD was effectively employed to replicate upper airway flow patterns in a typical OSA patient. The results of the simulation were replicated using a rigid physical model, thus validating the methodology. A FSI model demonstrated airway collapsibility, with findings validated in a flexible physical model. This demonstration of upper airway collapse using FSI is an important step and potentially useful tool for understanding mechanisms of airway collapse in OSA. Such computational techniques have potential for clinical application in the understanding of pharyngeal airflow and responses to OSA treatments in a patient-specific manner. Po02 Does increasing the ventilatory response to arousal induce genioglossus muscle hypotonia on the resumption of sleep? J. CORI, C. NICHOLAS, S. BAPTISTA, P. ROCHFORD, F. O’DONOGHUE, J. TRINDER and A. JORDAN University of Melbourne, Melbourne, Vic., Australia, Institute for Breathing and Sleep, Heidelberg, Vic., Australia Arousals from sleep are thought to predispose to obstructive sleep apnea (OSA) by causing hyperventilation and hypocapnia, which reduces airway dilator muscle activity on the return to sleep. Despite this suggestion, studies of brief auditory arousals in patients with and without OSA have not induced hypotonia of the genioglossus (GG) airway dilator muscle. This may have occurred because airway resistance was low prior to arousal in these studies, resulting in a small ventilatory response to arousal (VRA) and minimal hypocapnia. Thus we aimed to increase the VRA in healthy subjects by resistive loading prior to auditory arousal in order to determine whether GG hypotonia on return to sleep then occurs. Methods: Healthy men and women were instrumented with sleep staging and GG muscle electrodes, an epiglottic pressure catheter and a mask/pneumotachograph. Auditory tones (45-100dB, 0.5 s, 1000 Hz) were played to induce brief (3–15 s) ASDA arousal following either resting breathing or five breaths through an inspiratory resistive load (5–15 cmH2O L )1 s). Results: Adequate data have been obtained in four of seven subjects studied to date. Subjects were normal weight (BMI = 20.5 ± 1.2 kg m) and were aged 21 ± 0.4 years. Ventilation (VI) and GG responses to arousal in the two conditions are shown in the figures below.