A Race-neutral Approach to the Interpretation of Lung Function Measurements.

Rationale: The use of self-reported race and ethnicity to interpret lung function measurements has historically assumed that the observed differences in lung function between racial and ethnic groups were because of thoracic cavity size differences relative to standing height. Very few studies have considered the influence of environmental and social determinants on pulmonary function. Consequently, the use of race and ethnicity-specific reference equations may further marginalize disadvantaged populations. Objectives: To develop a race-neutral reference equation for spirometry interpretation. Methods: National Health and Nutrition Examination Survey (NHANES) III data (n = 6,984) were reanalyzed with sitting height and the Cormic index to investigate whether body proportions were better predictors of lung function than race and ethnicity. Furthermore, the original GLI (Global Lung Function Initiative) data (n = 74,185) were reanalyzed with inverse-probability weights to create race-neutral GLI global (2022) equations. Measurements and Main Results: The inclusion of sitting height slightly improved the statistical precision of reference equations compared with using standing height alone but did not explain observed differences in spirometry between the NHANES III race and ethnic groups. GLI global (2022) equations, which do not require the selection of race and ethnicity, had a similar fit to the GLI 2012 "other" equations and wider limits of normal. Conclusions: The use of a single global spirometry equation reflects the wide range of lung function observed within and between populations. Given the inherent limitations of any reference equation, the use of GLI global equations to interpret spirometry requires careful consideration of an individual's symptoms and medical history when used to make clinical, employment, and insurance decisions.

Effects of adopting the Global Lung Function Initiative 2017 reference equations on the interpretation of carbon monoxide transfer factor.

The recently published Global Lung Function Initiative (GLI) carbon monoxide transfer factor (T LCO) reference equations provide an opportunity to adopt a current, all-age, widely applicable reference set. The aim of this study was to document the effect of changing to GLI from commonly utilised reference equations on the interpretation of T LCO results.33 863 T LCO results (48% female, 88% Caucasian, n=930 aged <18 years) from clinical pulmonary function laboratories within three Australian teaching hospitals were analysed. The lower limit of normal (LLN) and proportion of patients with a T LCO below this value were calculated using GLI and other commonly used reference equations.The average T LCO LLN for GLI was similar or lower than the other equations, with the largest difference seen for Crapo equations (median: -1.25, IQR: -1.64, -0.86 mmol·min-1·kPa-1). These differences resulted in altered rates of reduced T LCO for GLI particularly for adults (+1.9% versus Miller to -27.6% versus Crapo), more so than for children (-0.8% versus Kim to -14.2% versus Cotes). For adults, the highest raw agreement for GLI was with Miller equations (94.7%), while for children it was with Kim equations (98.1%). Results were reclassified from abnormal to normal more frequently for younger adults, and for adult females, particularly when moving from Roca to GLI equations (30% of females versus 16% of males).The adoption of GLI T LCO reference equations in adults will result in altered interpretation depending on the equations previously used and to a greater extent in adult females. The effect on interpretation in children is less significant.

Reference values for spirometry and their use in test interpretation: A Position Statement from the Australian and New Zealand Society of Respiratory Science.

Traditionally, spirometry testing tended to be confined to the realm of hospital-based laboratories but is now performed in a variety of health care settings. Regardless of the setting in which the test is conducted, the fundamental basis of spirometry is that the test is both performed and interpreted according to the international standards. The purpose of this Australian and New Zealand Society of Respiratory Science (ANZSRS) statement is to provide the background and recommendations for the interpretation of spirometry results in clinical practice. This includes the benchmarking of an individual's results to population reference data, as well as providing the platform for a statistically and conceptually based approach to the interpretation of spirometry results. Given the many limitations of older reference equations, it is imperative that the most up-to-date and relevant reference equations are used for test interpretation. Given this, the ANZSRS recommends the adoption of the Global Lung Function Initiative (GLI) 2012 spirometry reference values throughout Australia and New Zealand. The ANZSRS also recommends that interpretation of spirometry results is based on the lower limit of normal from the reference values and the use of Z-scores where available.

Optimizing respiratory function assessments to elucidate the impact of obesity on respiratory health.

There is an increasing prevalence of obesity worldwide and its impact on respiratory health is of significant concern. Obesity affects the respiratory system by several mechanisms, including by direct mechanical changes due to fat deposition in the chest wall, abdomen and upper airway, as well as via systemic inflammation. The increased mechanical load in obese individuals leads to reduced chest wall and lung compliance and increased work of breathing. While there is generally minimal effect on spirometric values, as body mass index increases, the expiratory reserve volume, and hence functional residual capacity, reduces, often approaching residual volume in more severe obesity. The majority of evidence however suggests that obese individuals free from lung disease have relatively normal gas exchange. The link between asthma and obesity, while initially unclear, is now recognized as being a distinct asthma phenotype. While studies investigating objective markers of asthma have shown that there is no association between obesity and airway hyper-responsiveness, a recent working group identified obesity as a major risk factor for the development of asthma in all demographic groups. Although the temptation may be to attribute obesity as the cause of dyspnoea in symptomatic obese patients, accurate respiratory assessment of these individuals is necessary. Lung function tests can confirm that any altered physiology are the known respiratory consequences of obesity. However, given that obesity causes minimal changes in lung function, significant abnormalities warrant further investigation. An important consideration is the knowledge that many of the respiratory physiology consequences of obesity are reversible by weight loss.

Grading the severity of airways obstruction: new wine in new bottles.

The objective of this study was to redesign the current grading of obstructive lung disease so that it is clinically relevant and free of biases related to age, height, sex and ethnic group. Spirometric records from 17 880 subjects (50.4% female) from hospitals in Australia and Poland, and 21 191 records (53.0% female) from two epidemiological studies (age range 18-95 years) were analysed. We adopted the American Thoracic Society(ATS)/European Respiratory Society (ERS) criteria for airways obstruction based on an forced expiratory volume in 1 s (FEV1)/(forced) vital capacity ((F)VC) ratio below the fifth percentile and graded the severity of pulmonary function impairment using z-scores for FEV1, which signify how many standard deviations a result is from the mean predicted value. Using the lower limit of normal for FEV1/(F)VC and z-scores for FEV1 of -2, -2.5, -3 and -4 to delineate severity grades of airflow limitation leads to close agreement with ATS/ERS severity classifications and removes age, sex and height related bias. The new classification system is simple, easily memorised and clinically valid. It retains previously established associations with clinical outcomes and avoids biases due to the use of per cent predicted FEV1. Combined with the Global Lung Function prediction equations it provides a worldwide diagnostic standard, free of bias due to age, height, sex and ethnic group.

Measurement of FEF25-75% and FEF75% does not contribute to clinical decision making.

The aim of this study was to determine the added value of measuring the forced expiratory flow at 25-75% of forced vital capacity (FVC) (FEF25-75%) and flow when 75% of FVC has been exhaled (FEF75%) over and above the measurement of the forced expiratory volume in 1 s (FEV1), FVC and FEV1/FVC ratio. We used spirometric measurements of FEV1, FVC and FEF25-75% from 11 654 white males and 11 113 white females, aged 3-94 years, routinely tested in the pulmonary function laboratories of four tertiary hospitals. FEF75% was available in 8254 males and 7407 females. Predicted values and lower limits of normal, defined as the fifth percentile, were calculated for FEV1, FVC, FEV1/FVC ratio, FEF25-75% and FEF75% using prediction equations from the Global Lung Function Initiative. There was very little discordance in classifying test results. FEF25-75% and FEF75% were below the normal range in only 2.75% and 1.29% of cases, respectively, whereas FEV1, FVC and FEV1/FVC ratio were within normal limits. Airways obstruction went undetected by FEF25-75% in 2.9% of cases and by FEF75% in 12.3% of cases. Maximum mid-expiratory flow and flow towards the end of the forced expiratory manoeuvre do not contribute usefully to clinical decision making over and above information from FEV1, FVC and FEV1/FVC ratio.

Cardiorespiratory responses to 6-minute walk test in interstitial lung disease: not always a submaximal test.

BACKGROUND: The 6-minute walk test (6 MWT) is used to measure exercise capacity and assess prognosis in interstitial lung disease (ILD). Although the 6 MWT is usually considered to be a test of submaximal exercise capacity in ILD, the physiological load imposed by this test is not well described and 6 MWT outcomes are poorly understood. This study aimed to compare cardiorespiratory responses to 6 MWT and cardiopulmonary exercise test (CPET) in people with ILD. METHODS: 47 participants with ILD (27 idiopathic pulmonary fibrosis (IPF), mean age 71 (SD 12) years, diffusing capacity for carbon monoxide (TLCO) 49(15) %predicted) undertook CPET and 6 MWT on the same day in random order. Oxygen uptake (VO(2)), ventilation (VE) and carbon dioxide production (VCO2) were assessed during each test using a portable metabolic cart. RESULTS: The VO(2)peak during the 6 MWT was lower than during CPET (1.17(0.27) vs 1.30(0.37) L.min-1, p = 0.001), representing an average of 94% (range 62-135%) of CPET VO(2)peak. Achieving a higher percentage of CPET VO(2)peak on 6 MWT was associated with lower TLCO %predicted (r = -0.43, p = 0.003) and more desaturation during walking (r = -0.46, p = 0.01). The VEpeak and VCO(2)peak were significantly lower during 6 MWT than CPET (p < 0.05). However, participants desaturated more during the 6 MWT (86(6)% vs 89(4)%, p < 0.001). The degree of desaturation was not affected by the percent of peak VO2 achieved during the 6 MWT. Responses were similar in the subgroup with IPF. CONCLUSIONS: On average, the 6 MWT elicits a high but submaximal oxygen uptake in people with ILD. However the physiological load varies between individuals, with higher peak VO2 in those with more severe disease that may match or exceed that achieved on CPET. The 6 MWT is not always a test of submaximal exercise capacity in people with ILD.

Implications of adopting the Global Lungs Initiative 2012 all-age reference equations for spirometry.

The aim of this study was to determine the diagnostic and interpretative consequences of adopting the Global Lungs Initiative (GLI) 2012 spirometric prediction equations. We assessed spirometric records from 17 572 subjects (49.5% females), aged 18-85 years, from hospitals in Australia and Poland. We calculated predicted forced expiratory volume in 1 s (FEV1), forced expiratory volume (FVC), FEV1/FVC and lower limits of normal (LLN) using European Community for Steel and Coal (ECSC), National Health and Nutrition Examination Survey (NHANES) III and GLI 2012 equations. Obstruction was defined as FEV1/FVCLLN and FVC20% underdiagnosis of airway obstruction up to the age of 55 years and to 16-23% overdiagnosis in older subjects. GLI 2012 equations increase the prevalence of a "restrictive spirometric pattern" compared to ECSC but decrease it compared to NHANES.

Effect of singing on respiratory function, voice, and mood after quadriplegia: a randomized controlled trial.

OBJECTIVE: To explore the effects of singing training on respiratory function, voice, mood, and quality of life for people with quadriplegia. DESIGN: Randomized controlled trial. SETTING: Large, university-affiliated public hospital, Victoria, Australia. PARTICIPANTS: Participants (N=24) with chronic quadriplegia (C4-8, American Spinal Injury Association grades A and B). INTERVENTIONS: The experimental group (n=13) received group singing training 3 times weekly for 12 weeks. The control group (n=11) received group music appreciation and relaxation for 12 weeks. Assessments were conducted pre, mid-, immediately post-, and 6-months postintervention. MAIN OUTCOME MEASURES: Standard respiratory function testing, surface electromyographic activity from accessory respiratory muscles, sound pressure levels during vocal tasks, assessments of voice quality (Perceptual Voice Profile, Multidimensional Voice Profile), and Voice Handicap Index, Profile of Mood States, and Assessment of Quality of Life instruments. RESULTS: The singing group increased projected speech intensity (P=.028) and maximum phonation length (P=.007) significantly more than the control group. Trends for improvements in respiratory function, muscle strength, and recruitment were also evident for the singing group. These effects were limited by small sample sizes with large intersubject variability. Both groups demonstrated an improvement in mood (P=.002), which was maintained in the music appreciation and relaxation group after 6 months (P=.017). CONCLUSIONS: Group music therapy can have a positive effect on not only physical outcomes, but also can improve mood, energy, social participation, and quality of life for an at-risk population, such as those with quadriplegia. Specific singing therapy can augment these general improvements by improving vocal intensity.

Effects of adopting the new global lung function initiative 2012 reference equations on the interpretation of spirometry.

BACKGROUND: The recently generated spirometry reference equations from the Global Lung Function Initiative (GLI2012) provide a long-awaited opportunity for the adoption of a globally applicable set of normal reference values. OBJECTIVE: The aim of this study was to document the likely interpretative effects of changing from commonly used current spirometry reference equations to the GLI2012 equations on interpretation of test results in a clinical spirometry dataset. METHODS: Spirometry results from 2,400 patients equally distributed over the age range of 5-85 years were obtained from clinical pulmonary function laboratories at three public hospitals. The frequency of obstruction [FEV1/FVC below the lower limits of normal (LLN)] and spirometric restriction (FVC below the LLN) was assessed using the GLI2012, the National Health and Nutrition Assessment Survey (NHANES III), the European Community of Steel and Coal (ECSC) and the Stanojevic all-ages reference equations. RESULTS: The rates of obstruction (range 20.0-28.5%) and spirometric restriction (range 14.2-25.8%) were similar across the four sets of reference equations. The highest level of agreement with the new GLI2012 equations was seen with the NHANES III equations (97.6% for obstruction and 93.6% for spirometric restriction) and the lowest with those from the ECSC (96.0 for obstruction and 92.0% for restriction). These data can be used to estimate likely diagnostic spirometry interpretation effects in the clinical setting when switching to GLI2012 spirometry reference data. CONCLUSIONS: We have found the effects on interpretation of changing to GLI2012 reference data to be minimal when changing from NHANES III and most significant when changing from ECSC reference data.

Prescribing walking training in interstitial lung disease from the 6-minute walk test.

INTRODUCTION AND OBJECTIVE: Endurance training during PR requires exercise prescription at sufficient intensity to achieve physiological benefits. This analysis sought to investigate whether walking training prescribed from 6-minute walk test (6MWT) average speed provides an appropriate training intensity for people with ILD during PR. METHODS: Individuals with ILD completed cardiopulmonary exercise test (CPET) and 6MWT in random order. A 10-minute constant speed treadmill walk test (10MTW) was undertaken at 80% of the average 6MWT speed. Oxygen uptake (VO2) was measured during all tests. Percentage VO2peak during 10MTW was main outcome measure. RESULTS: Eleven people with ILD (age 71 (8) years; forced vital capacity 73 (18) %predicted, 6-minute walk distance 481 (99) meters, and VO2peak during CPET 1.3 (0.2) L.min-1) undertook testing. Average VO2peak during 10MTW was 91 (18) % of CPET VO2peak [range 67-116%]. Participants who achieved a greater VO2peak during CPET walked at a smaller %VO2peak during 10MTW (r = -0.6; p = .04). CONCLUSIONS: For people with ILD, walking training prescribed at 80% of 6MWT average speed can provide adequate exercise training intensity for PR.

'Is it okay for me to ... ?' Assessment of recreational activity risk in patients with chronic lung conditions.

BACKGROUND: Recreational activities, including travel, can be associated with risks to health. Assessing and advising on these risks can be an important part of travel planning for a person with a chronic lung condition when they ask, 'Is it okay for me to ...?' OBJECTIVE: This article discusses the respiratory considerations important in the assessment of, and advice for, a proposed activity in a person with a chronic lung condition. DISCUSSION: Patients with chronic lung disease can safely engage in a range of recreational, sporting and other activities. However, there are a number of general factors that should be taken into account, including access to, and the standard of, medical care available and the travel destination and medication availability. Guidelines based on limited evidence and expert opinion are available for some activities, but not all. Simple precautions and a common sense approach guided by knowledge of the particular risks in each setting should ensure a satisfactory outcome for the patient who asks, 'Is it okay for me to ... ?'

Impact of smoking status and chronic obstructive pulmonary disease on pulmonary complications post lung cancer surgery.

INTRODUCTION: Smoking and chronic obstructive pulmonary disease (COPD) are associated with an increased risk of post-operative pulmonary complications (PPCs) following lung cancer resection. It remains unclear whether smoking cessation reduces this risk. METHODS: Retrospective review of a large, prospectively collected database of over 1000 consecutive resections for lung cancer in a quaternary lung cancer centre over a 23-year period. RESULTS: One thousand and thirteen patients underwent curative-intent lobectomy or pneumonectomy between 1995 and 2018. Three hundred and sixty-two patients (36%) were ex-smokers, 314 (31%) were current smokers and 111 (11%) were never smokers. A pre-operative diagnosis of COPD was present in 57% of current smokers, 57% of ex-smokers and 20% of never smokers. Just over 25% of patients experienced a PPC. PPCs were more frequent in current smokers compared to never smokers (27% vs 17%, p = 0.036), however, no difference was seen between current and ex-smokers (p = 0.412) or between never and ex-smokers (p = 0.113). Those with a diagnosis of COPD, independent of smoking status, had a higher frequency of both PPCs (65% vs 35%, p<0.01) and overall complications (60% vs 40%, p<0.01) as well as a longer length of hospital stay (10 vs 9 days, p<0.01). CONCLUSION: Smoking and COPD are both associated with a higher rate of PPCs post lung cancer resection. COPD, independent of smoking status, is also associated with an increased overall post-operative complication rate and length of hospital stay. An emphasis on COPD treatment optimisation, rather than smoking cessation in isolation, may help improve post-operative outcomes.

A randomised trial of domiciliary, ambulatory oxygen in patients with COPD and dyspnoea but without resting hypoxaemia.

BACKGROUND: Patients with chronic obstructive pulmonary disease (COPD) who are not severely hypoxaemic at rest may experience significant breathlessness on exertion, and ambulatory oxygen is often prescribed in this circumstance despite a lack of conclusive evidence for benefit. This study aimed to determine whether such patients benefit from domiciliary ambulatory oxygen and, if so, which factors may be associated with benefit. METHODS: This was a 12 week, parallel, double-blinded, randomised, placebo-controlled trial of cylinder air versus cylinder oxygen, provided at 6 l/min intranasally, for use during any activity provoking breathlessness. Patients underwent baseline measurements of arterial blood gases and lung function. Outcome measures assessed dyspnoea, health-related quality of life, mood disturbance, functional status and cylinder utilisation. Data were analysed on an intention-to-treat basis, p≤0.05. RESULTS: 143 subjects (44 female), mean±SD age 71.8±9.8 years, forced expiratory volume in 1 s (FEV(1))1.16±0.51 litres, Pao(2) 9.5±1.1 kPa (71.4±8.5 mm Hg) were randomised, including 50 patients with exertional desaturation to ≤88%. No significant differences in any outcome were found between groups receiving air or oxygen. Statistically significant but clinically small improvements in dyspnoea and depression were observed in the whole study group over the 12 weeks of the study. CONCLUSION: In breathless patients with COPD who do not have severe resting hypoxaemia, domiciliary ambulatory oxygen confers no benefits in terms of dyspnoea, quality of life or function. Exertional desaturation is not predictive of outcome. Intranasal gas (either air or oxygen) may provide a placebo benefit. CLINICAL TRIAL NUMBER: ACTRN12605000457640.

Assessment of breathing patterns and respiratory muscle recruitment during singing and speech in quadriplegia.

OBJECTIVES: To explore how respiratory impairment after cervical spinal cord injury affects vocal function, and to explore muscle recruitment strategies used during vocal tasks after quadriplegia. It was hypothesized that to achieve the increased respiratory support required for singing and loud speech, people with quadriplegia use different patterns of muscle recruitment and control strategies compared with control subjects without spinal cord injury. DESIGN: Matched, parallel-group design. SETTING: Large university-affiliated public hospital. PARTICIPANTS: Consenting participants with motor-complete C5-7 quadriplegia (n=6) and able-bodied age-matched controls (n=6) were assessed on physiologic and voice measures during vocal tasks. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Standard respiratory function testing, surface electromyographic activity from accessory respiratory muscles, sound pressure levels during vocal tasks, the Voice Handicap Index, and the Perceptual Voice Profile. RESULTS: The group with quadriplegia had a reduced lung capacity (vital capacity, 71% vs 102% of predicted; P=.028), more perceived voice problems (Voice Handicap Index score, 22.5 vs 6.5; P=.046), and greater recruitment of accessory respiratory muscles during both loud and soft volumes (P=.028) than the able-bodied controls. The group with quadriplegia also demonstrated higher accessory muscle activation in changing from soft to loud speech (P=.028). CONCLUSIONS: People with quadriplegia have impaired vocal ability and use different muscle recruitment strategies during speech than the able-bodied. These findings will enable us to target specific measurements of respiratory physiology for assessing functional improvements in response to formal therapeutic singing training.

Effects of changing reference values and definition of the normal range on interpretation of spirometry.

BACKGROUND AND OBJECTIVE: Recent spirometry reference studies are arguably the most valid ever performed and the ATS/ERS now recommend the National Health and Nutrition Assessment Survey (NHANES) equations for North America. It is timely to consider adopting these reference values in Australasia; however, an evaluation of the consequences of such a change is required. METHODS: We analysed data from 1108 patients tested in two pulmonary function laboratories in public hospitals. Lower limits of normal (LLN) were calculated using European Community for Steel and Coal (ECSC) (1993), Knudson (1983), NHANES (1999) and Health Survey of England (HSE) (2004) equations and used to define restriction (FVC < LLN) and obstruction (FEV(1)/FVC < LLN). This interpretative strategy was also compared with the GOLD definition of obstruction (FEV(1)/FVC < 70%). RESULTS: Average age for all patients (50% female) was 60 years (range: 20-91). The mean predicted FVC from NHANES and HSE were similar and consistently higher than those from ECSC and Knudson (average 270 mLs). This translates into a 76% increase in the incidence of 'restrictive' interpretations using NHANES data compared with ECSC and Knudson, and a smaller increase of 40% for HSE. Using FEV(1)/FVC < 70% to diagnose obstruction in those over 65 years would result in false positive rates of approximately 28%. Using the same definition in a younger group (<50 years old) results in a false negative rate of approximately 14%. CONCLUSIONS: Changing to either NHANES or HSE predicted values will significantly increase the rate of 'restrictive' interpretation, and alter the rate of obstructive findings. The NHANES and HSE data confirm that using FEV(1)/FVC < 70% to define obstruction causes misdiagnosis in elderly and younger subjects.

Acute effects of hyperoxia on resting pattern of ventilation and dyspnoea in COPD.

BACKGROUND AND OBJECTIVE: Hyperoxia has been shown to reduce resting ventilation, hyperinflation and dyspnoea in patients with severely hypoxaemic COPD. This study assessed the effects of hyperoxia on these resting measures in patients with COPD of varying disease severity and characterized those patients who responded. METHODS: Measurements of dyspnoea (Borg score), oxyhaemoglobin saturation (SpO(2)), inspiratory capacity (IC), minute ventilation, tidal volume, breathing and cardiac frequency were performed at rest in 51 patients with COPD while they breathed air and 44% oxygen, in a randomized double-blinded fashion. RESULTS: Hyperoxia induced significant reductions in cardiac frequency and dyspnoea and a significant increase in SpO(2). No significant change was noted in IC for the group overall, and there was substantial inter-subject variation in this measurement. No significant changes were found in ventilation, and there was no correlation between change in dyspnoea and change in IC. In patients with moderate to severe airflow obstruction (FEV(1) < 70% predicted), a significant association was found between the degree of airflow obstruction and change in IC induced by hyperoxia. CONCLUSIONS: Hyperoxia improved dyspnoea but did not significantly alter resting pulmonary hyperinflation in a group of patients with COPD of varying severity. However, in a subset patients with moderate to severe airflow obstruction a relationship existed between the severity of airflow obstruction and volume response to hyperoxia.

The effect of sex and body weight on lung volumes during sleep.

STUDY OBJECTIVES: Low lung volumes are thought to contribute to obstructive sleep apnea (OSA). OSA is worse in the supine versus lateral body position, men versus women, obese versus normal-weight (NW) individuals and REM versus NREM sleep. All of these conditions may be associated with low lung volumes. The aim was to measure FRC during wake, NREM, and REM in NW and overweight (OW) men and women while in the supine and lateral body positions. METHODS: Eighty-one healthy adults were instrumented for polysomnography, but with nasal pressure replaced with a sealed, non-vented mask connected to an N2 washout system. During wakefulness and sleep, repeated measurements of FRC were made in both supine and right lateral positions. RESULTS: Two hundred eighty-five FRC measures were obtained during sleep in 29 NW (body mass index [BMI] = 22 ± 0.3 kg/m2) and 29 OW (BMI = 29 ± 0.7 kg/m2) individuals. During wakefulness, FRC differed between BMI groups and positions (supine: OW = 58 ± 3 and NW = 68 ± 3% predicted; lateral OW = 71 ± 3, NW = 81 ± 3% predicted). FRC fell from wake to NREM sleep in all participants and in both positions by a similar amount. As a result, during NREM sleep FRC was lower in OW than NW individuals (supine 46 ± 3 and 56 ± 3% predicted, respectively). FRC during REM was similar to NREM and no sex differences were observed in any position or sleep stage. CONCLUSIONS: Reductions in FRC while supine and with increased body weight may contribute to worsened OSA in these conditions, but low lung volumes appear unlikely to explain the worsening of OSA in REM and in men versus women.