Ethnicity and socioeconomic status predict initial continuous positive airway pressure compliance in New Zealand adults with obstructive sleep apnoea

Ethnicity and socioeconomic status predict initial continuouspositive airway pressure compliance in New Zealand adultswith obstructive sleep apnoeaimj_2360 95..101

A. Campbell, A. Neill and R. Lory

WellSleep, Department of Medicine, Otago University, Wellington, New Zealand

Key wordsobstructive sleep apnoea, continuous positive

airway pressure, patient compliance, ethnic

group, social class.

CorrespondenceAngela Campbell, WellSleep, Bowen Hospital,

Churchill Drive, Crofton Downs, Wellington

6035, New Zealand.

Email: [email protected]

Received 19 April 2010; accepted 30 July 2010.

doi:10.1111/j.1445-5994.2010.02360.x

Abstract

Background: Understanding factors that contribute to low continuous positive airway

pressure (CPAP) compliance will lead to improvements in the long-term outcome of

patients with obstructive sleep apnoea (OSA) syndrome. Both cultural and socioeco-

nomic factors are likely to be important but have not been systematically studied.

Aim: To examine the effect of ethnicity and socioeconomic status on initial CPAP usage

for people with OSA in New Zealand.

Methods: We retrospectively collected demographic, clinical and CPAP treatment-

related data on patients undergoing a 1-month CPAP trial for a 10-month period. We

compared objectively measured CPAP usage (by ANOVA) with self-identified ethnicity;

levels of socioeconomic deprivation (NZDep06 index), Epworth Sleepiness Scale (ESS)

and Apnoea-Hypopnoea Index (AHI).

Results: A total of 214 patients with a mean age of 52.7 (�11.8) years, mean AHI 57.3

(�35.8) events per hour and mean ESS 13 (�5.58)/24 made up the cohort. CPAP usage

which averaged 5.13 � 2.34 h per night was significantly lower in patients of non-

European ethnicity (P = 0.019 univariate) and remained significant after socioeconomic

status was added to the model (P = 0.048). Patients living in the most socioeconomically

deprived areas showed significantly lower compliance with CPAP on univariate analysis

(P = 0.024, NZDep06 scores 1&2, average 5.3 per night compared to score NZDep06

scores 9&10, average 4.3 h per night), but this effect was no longer significant once

ethnicity was added to the model (P = 0.28).

Conclusion: CPAP usage in New Zealand is affected by both ethnicity and level of

socioeconomic deprivation. We recommend further research to unravel specific cultural

and socioeconomic reasons for the variance reported.

Introduction

Obstructive sleep apnoea (OSA) is a disorder of recurringpartial (or complete) airway obstruction during sleepassociated with an increased respiratory effort, oxyhae-moglobin desaturation and frequent arousals. Symptomstypically include loud snoring interrupted by apnoea, andaetiological risk factors including age, obesity, malegender, smoking and alcohol consumption.

Untreated OSA results in an unrefreshing sleep,daytime somnolence and is associated with increased risk

of hypertension,1–3 heart disease,4 stroke5,6 and motorvehicle accidents.7,8

The international literature reports that OSA iscommon in adults, affecting 2% of women and 4% ofmen.9,10 A number of studies report ethnic differences inthe prevalence of OSA,11–14 with the increased preva-lence in certain populations thought to be explainedprimarily by established anthropomorphic risk factorsparticularly increasing body mass index (BMI) and necksize.12–14

In a national survey, OSA symptoms (snoring always,observed apnoea and excessive daytime sleepiness)15

and prevalence measured by sleep study14 were higherin Maori compared to non-Maori (men 12% and 8%,women 8.5% and 2.3% respectively). Significant inde-pendent risk factors for reporting observed apnoea

Funding: R. Lory is receiving payment for the research projectfrom the Asthma and Respiratory Foundation of New Zealand.Conflict of interest: None.

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© 2010 The AuthorsInternal Medicine Journal © 2010 Royal Australasian College of Physicians e95

included being male, increasing age, increasing socio-economic deprivation, increasing neck size and higheralcohol consumption. Evidence from sleep clinics inNew Zealand indicates that Maori and Pacific IslandNew Zealanders present with more severe OSA16,17 andhence the need for good compliance with treatment toreduce long-term risks.

Continuous positive airway pressure (CPAP), deliv-ered through a nasal or oronasal mask18 is first linetherapy for moderate to severe OSA.19 When deliveredas part of a comprehensive sleep apnoea treatmentprogramme in New Zealand, CPAP therapy is highlycost-effective;20 however, CPAP adherence remains asignificant issue for many patients. Common side-effectsimpacting on compliance include mask leakage,machine noise and pressure, dry mouth and nasal symp-toms such as stuffiness.21 Technological advances aimingto reduce side-effects from CPAP have had mixedresults. Heated humidification is beneficial in selectedpatients,22–24 but flexible pressure has been shown to notimpact compliance.25–28

Optimum treatment outcomes occur when CPAP isused for �4 h per night, every night of the week.29 CPAPtreatment improves quality of life, including reducingdaytime sleepiness30,31 and improving vigilance andgeneral productivity.32

The majority of CPAP adherence studies have beenfocused on patients of European descent. Given the highprevalence of OSA in Maori and Pacific peoples and theirdisproportionate burden of cardiovascular disease33,34 anddiabetes,35 it is essential that CPAP adherence andoutcome studies be undertaken in these groups.

Socioeconomic status is a social and economic measureof an individual’s position relative to others, consideringfactors such as income, education and occupation.36

Socioeconomic status in New Zealand is commonlymeasured by the New Zealand Deprivation Scale(NZDep06),37 which is a small-area measure based onvariables obtained from the five-yearly census data36 (thisincludes: education; number of people per household;access to telephones and vehicles; employment andsupport and currently relates to the 2006 census). Inhealth it is well accepted that some conditions are morecommon in lower socioeconomic areas.38 The demo-graphics of New Zealand show a greater proportion ofMaori and Pacific peoples live in lower socioeconomicareas.37

This study investigated if socioeconomic status as mea-sured by the NZDep06 impacts on initial CPAP usage,with the hypothesis that there is variation in initial CPAPuse that is best predicted by socioeconomic status ratherthan ethnicity for patients with OSA, in a New Zealandsetting.

Materials and methods

Sample

The study population comprised 214 consecutive, clinicalpatients with polysomnographically confirmed OSAundergoing a trial period of CPAP at home throughWellSleep, Otago University, Wellington, Sleep Investiga-tion Centre from January to October 2008. Paediatricsubjects, patients who were from out of town areas andtherefore not followed up by WellSleep or who werereceiving bi-level ventilation were excluded. Patientsundergoing a trial of CPAP met usual local clinical guide-lines for receiving treatment for OSA with CPAP whichinclude: Apnoea-Hypopnoea Index (AHI) > 30/h orAHI > 20/h plus sleepiness and/or comorbidity.

Protocol

Consecutive data were collected both retrospectively andprospectively from patient records held at WellSleepand entered into a database. Age, self-identified ethnicgroup(s), study type undertaken, OSA severity (AHI),Epworth Sleepiness Scale (ESS), objectively measuredCPAP usage and the level of socioeconomic deprivation(NZDep06 measured on a scale of 1–10, with 10 being themost deprived) were recorded.

Ethnic group

Patients self-identified the ethnic group(s) with whichthey identified. For analysis purposes ethnicities weregrouped into six different categories – European (definedas any of New Zealand European, European, Australianand American), New Zealand Maori, Pacific Island, Asianand Other. Those who did not supply an ethnic groupwere grouped as Unknown.39

Those who identified two or more ethnic groups wereassigned to the minority ethnicity in an attempt to addstatistical power to these smaller groups. For example thefive patients who identified themselves as New ZealandEuropean/New Zealand Maori were assigned to theMaori ethnicity.

CPAP titration

CPAP titration was either a full or split night attendedlaboratory study or through auto-positive airway pressure(autoPAP) at home (over seven nights).40 All pressurelevel determinations were confirmed by a Sleep Physician.

OSA severity

AHI was calculated from diagnostic polysomnography.

Campbell et al.

© 2010 The AuthorsInternal Medicine Journal © 2010 Royal Australasian College of Physicianse96

Subjective sleepiness

Measured by the ESS,41 it assesses sleepiness in eightsituations and has a possible range of 0–24.

Objective adherence

CPAP usage data included mask type (nasal or full face),number of nights on CPAP and average usage per night(hours). These data (measured as a real-time clock,downloaded on to a computer through specialised soft-ware) were obtained from the CPAP machine at thepatients’ final follow-up appointment conducted atWellSleep, which typically occurs 4 weeks after com-mencing CPAP.

NZDep06 score

Deprivation was measured by the New Zealand Depriva-tion Scale (NZDep06) adapted from the 2006 censusdata.37 Participants’ addresses were provided on admis-sion to WellSleep. This, in combination with a map of thesuburbs, allowed determination of the small area valuerepresenting deprivation level. Levels of deprivation weregrouped into quintiles to add statistical power to thesmaller groups.

Analysis

Data were entered into Microsoft Excel 2003 and SPSS forWindows (version 15.0, SPSS, Chicago, IL, USA). Thepopulation data were summarised by calculating meansand standard deviations. ANOVA was performed on thecompliance data with ethnicity and NZDep06 level addedas univariate variable and multivariate variables. AP-value of �0.05 was considered to be statistically signifi-cant. The usage data for those patients undergoing aCPAP trial were tested for normality of distribution.

Results

A total of 221 CPAP trials was undertaken in the datacollection period. Small numbers in the unknown (n = 6)and other (n = 1) groups resulted in their exclusion fromfurther analysis. Final dataset comprised 214 subjectswith ethnicity, deprivation index and compliance datacomplete. CPAP trial patient demographics are shown inTable 1. As expected they were on average middle aged,male, with severe OSA and sleepy during the day.

The ethnic grouping for CPAP trial included: Asian 8patients (3.7%), Maori 47 patients (22%), Pacific peoples33 patients (15.4%) and a European group comprising126 patients (58.9% of the study population).

The NZDep06 distribution showed a predominance ofEuropean ethnicities in the higher socioeconomic areas.In the lower socioeconomic areas Maori and Pacificpeoples predominated (Fig. 1).

CPAP usage showed a normal distribution around themean (5.13 � 2.34 h per night). In total 70.1% ofpatients were compliant with CPAP treatment (�4 h pernight). There was a significant difference in adherencebetween ethnic groups (F(3,210) = 3.79, P = 0.01,r = 0.23, Fig. 2) with non-European ethnicities usingCPAP on average 1 h less per night.

Low levels of deprivation (NZDep06 levels 1&2)showed increased usage of CPAP compared with thoseliving in higher deprivation areas (NZDep06 levels 9&10,F(4,209) = 15.2, P = 0.024, r = 0.23, Fig. 3). Once ethnic-ity was added to the model, NZDep06 index was notsignificantly related to usage (P = 0.28, r = 0.19).

CPAP usage was not related to type of CPAP titration(full night (29%), split night (57.4%), autoPAP (13.6%):F(2,211) = 0.93, P = 0.83, r = 0.04), AHI (F(1,210) =2.12, P = 0.15, r = 0.10), patient referral base (private vspublic vs research; F(2,211) = 0.93, P = 0.40, r = 0.09) orsex (F(1,219) = 2.41, P = 0.12, r = 0.10).

Discussion

This study found that self-identified ethnicity and socio-economic status as estimated by the NZDep06 predicted alower level of CPAP use for patients with OSA. Consistentwith higher OSA prevalence and disease severity14 ahigher proportion of Maori and Pacific peoples (22.1%and 15% respectively) commenced CPAP trials comparedto Wellington region estimates of population ethnicity(12.8% Maori and 8.1% Pacific peoples).42

Adherence to long-term medical therapy is complex. Anumber of factors has been previously shown to influ-ence patient adherence with CPAP therapy, includingmotivation, severity of the symptoms, particularlydaytime sleepiness,43 the complications and discomfort

Table 1 Demographics of continuous positive airway pressure trial

subjects

Demographic variable Mean � SD

Age (years) 52.7 � 12

Epworth Sleepiness Scale/24 13 � 5.58

Apnoea-Hypopnoea Index (events per hour) 57.3 � 35.8

Neck size (cm) 43.6 � 5.0

% male 73

% auto-positive airway pressure titration versus

attended manual titration split study versus

attended manual titration full night

13.6, 57.4, 29

Ethnicity and CPAP compliance in OSA


which result from CPAP usage, including incorrect maskfit, machine noise and side-effects such as nasal stuffi-ness,44,45 education level and understanding the patienthas about OSA and its complications.46 There has beenmuch research looking at behavioural measures andCPAP adherence. Studies show that a patient’s self-efficacy and attitude to health can be predictive of adher-ence at 647 and 1 month.48 These data have not beencollected in different ethnic groups and is the subject ofcurrent research with both Maori and Pacific people.

WellSleep uses a structured CPAP education pro-gramme with a face to face discussion, video education,hands-on demonstration of the equipment and mask fitfollowed by early phone contact, regular one-on-onefollow-up appointments over a 4-week trial period andtrouble shooting of machine and mask issues. The

programme is delivered in English without specific use ofinformation sheets in other languages. Adherence isobjectively measured by downloading usage informationfrom the CPAP machine and discussing the resultsdirectly with the patient. This overcomes the well-recognised overestimate by patients of their CPAP usage.Previous research clearly shows that higher CPAP usage(i.e. the longer usage per night and the more nights usedper week) results in a greater improvement in OSA

Figure 1 NZDep06 by ethnic group for

study population. ( ) Asian; (�) European;

( ) Maori; ( ) Pacific Island.

Figure 2 Continuous positive airway pressure (CPAP) usage (hours per

night) of CPAP trial patients by ethnic group.

Figure 3 Continuous positive airway pressure (CPAP) usage (hours per

night) of CPAP trial patients by NZDep06 Score quintile.

Campbell et al.


symptoms such as snoring and excessive daytimesleepiness.49

Few other studies have looked exclusively at theadherence–ethnicity relationship. Scharf et al. investi-gated racial differences in the clinical presentation ofCaucasians and African Americans, finding no differencein compliance with CPAP therapy.12 Platt et al. also foundno difference in initial CPAP usage between white andblack Americans during the first week post titration.50

Minority ethnic groups and those in lower socioeco-nomic areas have greater difficulty accessing a range ofhealth services, including sleep services.14 There areseveral steps required before receiving a sleep study,including consulting a family doctor about the sleepproblem, which is followed by a referral and appointmentto a sleep physician. The physician then decides if a sleepstudy is required, and referral made to the sleep labora-tory. This represents multiple levels at which barriers tocare can occur. Other potential barriers include nothaving a regular GP, language and communication prob-lems and transport difficulties. Outpatient clinics havebeen established in an effort to improve access to diag-nostic and treatment services.

A recent American paper investigating the associationbetween socioeconomic status and CPAP compliance in apopulation of mainly male patients found a similar asso-ciation with socioeconomic status with those in highersocioeconomic areas being more compliant with treat-ment in the initial week of CPAP therapy, but they werenot able to provide an explanation or mechanism forthis.50 Recently Simon-Tuval reported that patients fromlow socioeconomic status backgrounds are less receptiveto CPAP treatment after controlling for age, BMI, ESS andAHI.51

NZDep06 is an area-based measure of deprivation, andbecause of this there will be some anomalies between anindividual’s actual level of deprivation and the NZDep06level assigned to individuals based on the small areawhere they live.36 Recently, NZiDep has been developedwhich is a deprivation level based on an individual.52 Itconsiders eight factors in the last 12 months, includingfeeling cold to save on heating costs and inability topurchase fresh fruit and vegetables. Because of the ret-rospective nature of this study we were unable to collectNZiDep as a measure of an individual’s socioeconomicstatus relying instead on the NZDep06 area measures.Collecting these data for future studies of CPAP

compliance and socioeconomic status would be useful. Itis worth noting that NZiDep also has limitations. NZiDepfocuses on those in the highest levels of deprivation, andtherefore around 50% of the population receive a scoreof 0, therefore providing no information on their level ofdeprivation.52

There is likely a level of bias in this study because of thefact that those people who are incorporated are sobecause they were motivated to do something about theirhealth, and therefore are more likely to adhere to CPAPtreatment than those who were not represented, that is,those people in the community with OSA who have notsought assistance for this health problem. It should benoted that all ethnic and NZDep06 groups had meanCPAP usage of >4 h per night, a commonly used cut-offfor being ‘compliant’. Research has found that the mostlikely predictor of long-term adherence is the nightly usein the first 1–3 months of CPAP therapy.53,54

A nationwide study including a greater number ofpeople in minority ethnic groups would increase the sta-tistical power and help validate our hypothesis or not. Itwould also allow for investigation of regional differencesand variations in treatment methods and protocolsbetween Sleep Clinics.

Conclusion

The results of this study show a definitive differencebetween ethnic group and adherence to CPAP therapy inthose with diagnosed OSA. Future research is required toinvestigate these relationships further to discover whichfactors of ethnicity and socioeconomic status drive thisdifference and what type of intervention packages couldbe structured to address these issues.

Acknowledgements

The authors would like to thank Ms Karyn O’Keeffe(Otago University) for providing the follow-up care anddownloading CPAP compliance data. Dr Sarah-JanePaine (Massey University) contributed informationregarding the grouping of ethnicity data for analysis. DrClare Salmond, Professor Peter Crampton and Ms JuneAtkinson (Otago University) provided informationaround the NZDep06 and NZiDep, as well as demo-graphic breakdowns of the Wellington Region. GordonPurdie, Biostatistician Otago University Wellington.

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Ethnicity and socioeconomic status predict initial continuous positive airway pressure compliance in New Zealand adults with obstructive sleep apnoea