Background and objective Currently there is paucity of evidence in the literature in relation to normative values for diffusing capacity of carbon monoxide (DLCO) and total lung capacity (TLC) among Indigenous Australians. Hence, in this study we assessed the DLCO and TLC parameters among Indigenous Australians in comparison to Australian Caucasian counterparts. Methods DLCO and TLC values were assessed and compared between Indigenous Australians and Australian Caucasians matched for age, sex and body mass index, with normal chest radiology. Results Of the 1350 and 5634 pulmonary function tests assessed in Indigenous Australian and Australian Caucasian adults respectively, a total of 129 Indigenous Australians and 197 Australian Caucasians met the inclusion criteria. Absolute DLCO and TLC values for Indigenous Australians were a mean 4.3 ml/min/mmHg (95% CI 2.86, 5.74) and 1.03 L (95% CI 0.78, 1.27) lower than Australian Caucasians (p<0.01). Percentage predicted values were 15.38 (95% CI 11.59, 19.17) and 16.63 (95% CI 13.59, 19.68) points lower for DLCO and TLC, respectively. Lower limit of normal (LLN) values did not significantly differ between groups, however a significantly greater proportion of Indigenous Australians recorded values below the LLN in comparison to Australian Caucasians for DLCO (64 vs. 25%, p<0.01) and TLC (66 vs. 21%, p<0.01). Significant differences for the interaction of sex on DLCO and TLC were noted in Australian Caucasians, with reduced or absent sex differentiation among Indigenous Australians. Conclusions There are significant differences in DLCO and TLC parameters between Indigenous Australian compared to Australian Caucasians. Appropriate DLCO and TLC norms need to be established for Indigenous Australians.

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Objective Obstructive sleep apnoea (OSA) is reported to be highly prevalent among Aboriginal Australians. However, no studies have assessed the implementation and efficacy of Continuous Positive Airway Pressure (CPAP) therapy in this population. Hence, we compared the clinical, self-reported perception of sleep quality and polysomnographic (PSG) characteristics among Aboriginal patients with OSA. Methods Adult Aboriginal Australians who underwent both diagnostic (Type 1 & 2) and in-lab CPAP implementation studies between were included. Results Total of 149 patients were identified (46% female, median age 49 years, BMI 35 kg/m 2). The OSA severity was 6% mild, 26% moderate & 68% severe on the diagnostic PSG. On application of CPAP there were significant improvements in; Total Arousal Index (diagnostic 29 to 17/hour on CPAP), Total Apnoea Hypopnea Index (AHI) (diagnostic 48 to 9/hour on CPAP), Non-rapid eye movement (NREM) AHI (diagnostic 47 to 8/hour on CPAP), Rapid eye movement (REM) AHI (diagnostic 56 to 8/hour on CPAP) and oxygen saturation (SpO2) nadir (diagnostic 77% to 85% on CPAP) (p&lt;0.001 for each). Following a single night of CPAP, 54% of patients reported sleeping “better than normal” compared to 12% following the diagnostic study (p=0.003). In multivariate regression models, males had a significantly lesser change in REM AHI than females (5.7 events/hr less change (IQR 0.4, 11.1), p=0.029). Conclusion There is substantial improvement in several sleep related domains on application of CPAP among Aboriginal patients with a good initial acceptance of treatment. Whether the positive impact observed in this study translates to better sleep health outcomes with long-term adherence to CPAP therapy is yet to be assessed.