Introduction People with co-morbid insomnia and sleep apnoea (COMISA) have worse symptoms and require a tailored therapy approach for their sleep disorders. The relationship between the respiratory arousal threshold, a key OSA non-anatomical contributor and insomnia symptoms is unclear. This study investigated the relationship between insomnia symptoms using the insomnia severity index (ISI) and the respiratory arousal threshold in people with OSA. Methods 46 people with OSA (11 female, age=50±15years, BMI=29±6kgm-2, AHI=33±20events/h) participated in a physiology sleep study to predict response to oral appliance therapy and completed the ISI. Standard polysomnography, an epiglottic airway pressure sensor, bipolar intramuscular electrodes inserted into the genioglossus and a nasal mask with a pneumotachograph to quantify airflow were used. The respiratory arousal threshold was measured as the nadir epiglottic pressure during a respiratory event prior to a cortical arousal. Following this, participants trialled mandibular advancement therapy. Results There was no relationship between ISI (average=12±6) and the arousal threshold (-24±10cmH₂O) in participants with OSA (r=0.1, p=0.42, n=46). However, in the 59% of people with COMISA (ISI ≥11), there was a positive relationship between ISI and arousal threshold, with increasing insomnia severity associated with lower arousal threshold (r=0.5, p=0.017, n=27). People with a BMI<30kgm-2 (n=27), also had a positive linear relationship between ISI and improvement in oral appliance therapy (r=0.49, p<0.01, n=27). Conclusion Greater insomnia symptoms in people with COMISA is associated with a lower respiratory arousal threshold. In non-obese people with OSA, higher ISI values are related to poor response to oral appliance therapy.

Background Unplanned hospital readmissions (HRA), which have been used as key performance index of healthcare quality, are becoming more prevalent. They are associated with substantial financial burden to hospital systems and considerable impacts on patients' physical and mental health. Patients with frequent readmissions are not well studied. Aims To determine the prevalence, characteristics and risk factors associated with frequent readmissions (FRA) to an internal medicine service at a tertiary public hospital. Method A retrospective observational study was conducted at an internal medicine service in a tertiary teaching hospital between 1 January 2010 and 30 June 2016. FRA was defined as four or more readmissions within 12 months of discharge from the index admission (IA). Demographic and clinical characteristics and potential risk factors were evaluated. Results A total of 50 515 patients was included; 1657 (3.3%) had FRA and were associated with nearly 2.5 times higher in 12‐month mortality rates. They were older, had higher rates of indigenous Australians (3.2%), more disadvantaged status (index of relative socio‐economic disadvantage decile of 5.3) and more comorbidities (mean Charlson comorbidity index 1.4) in comparison, to infrequent readmission group. The mean length of hospital stay during the IA was 6 days for FRA group (21.4% staying more than 7 days) with higher incidence of discharge against medical advice (2.0% higher). Intensive care unit admission rate was 6.6% for FRA group compared with 3.9% for infrequent readmission group. Multivariate analysis showed mental disease and disorders, neoplastic, alcohol/drug use and alcohol/drug‐induced organic mental disorders are associated with FRA. Conclusion The risk factors associated with FRA were older age, indigenous status, being socially disadvantaged, having higher comorbidities and discharging against medical advice. Conditions that lead to FRA were mental disorders, alcohol/drug use and alcohol/drug‐induced organic mental disorders and neoplastic disorders.