Journal of Human Hypertension (2005) 19, 559–564 & 2005 Nature Publishing Group All rights reserved 0950-9240/05 $30.00 www.nature.com/jhh
ORIGINAL ARTICLE
Home blood-pressure monitoring among hypertensive patients in an Asian population NC Tan1, LW Khin2 and R Pagi1 1
SingHealth Polyclinics, Singapore; 2Clinical Trials and Epidemiological Unit, Singapore
Hypertension is a principal cause of mortality and morbidity in Singapore. The use of home blood-pressure monitoring (HBPM) to assess hypertensive control with digital devices in the local multi-racial population is unknown. The study determined the factors associated with hypertensive patients’ use of HBPM in primary care in a multi-racial Asian population. Randomized crosssectional questionnaire survey of hypertensive patients managed in a district polyclinic. A model predicting use of HBPM was constructed by univariate and multivariate logistic regression. A total of 224 eligible subjects were randomly selected from 1943 patients. Response rate was 78.1% (n ¼ 175). In all, 61.7% of them were aware of HBPM but only 24% used HBPM. Using multivariate analysis by stepwise backward regression, the final fitted model showed that HBPM was associated with higher patients’ socioeconomic status: (adjusted OR for middle-income status ¼ 2.85, 95% CI: 1.2–6.78, P ¼ 0.018;
adjusted OR for high-income status ¼ 3.46, 95% CI: 1.22–9.87, P ¼ 0.020) and their documented diastolic BP (adjusted OR for diastolic BP480 mmHg ¼ 2.26, 95% CI: 1.06–4.82, P ¼ 0.034). Nonusers cited failure to recognize benefits (54.1%), lack of HBPM awareness (29.3%), understanding of device operation (18.8%) and perception of inaccuracy (10.5%) as deterrents. 76.2% of users were satisfied with HBPM but lacked knowledge in maintenance of devices. In conclusion, 61.7% of the study population were aware of HBPM but only 24% used it. Patients’ failure to recognize benefits, lack of awareness, cost and perception of inaccuracy were barriers. Higher socioeconomic status and patient’s documented diastolic BP correlated with HBPM usage. Journal of Human Hypertension (2005) 19, 559–564. doi:10.1038/sj.jhh.1001865 Published online 21 April 2005
Keywords: home blood-pressure monitoring; primary care
Introduction Hypertension and its related cardiovascular complications such as ischaemic heart disease and cerebrovascular disease are the second and fourth principal causes of mortality1 among the multiracial adult population (Chinese 76.8%, Malay 13.9%, Indian 7.9% and others 1.4%2) in Singapore. Because of the local fee for service healthcare system, hypertension is treated in government-subsidized hospitals and polyclinics as well as in private general practitioners’ clinics and hospitals. Patients’ blood pressure (BP) can be monitored by healthcare workers at the clinic or at home using (mercury or) automated digital BP measuring devices. In recent years, home BP monitoring (HBPM) is becoming more popular in developed Western coun-
Correspondence: Dr NC Tan, SingHealth Polyclinics, Pasir Ris, 1, Pasir Ris Drive 4, #01–11, Singapore 519457, Singapore. E-mail:
[email protected] Received 9 November 2004; revised 19 February 2005; accepted 22 February 2005; published online 21 April 2005
tries. In Singapore, there is paucity of information on HBPM usage among its hypertensive population. This could be related to lack of endorsement by medical professionals and absence of formal or structured training of the patients in HBPM in both local primary and secondary care medical institutions. This study aimed to determine the factors associated with the use of HBPM among the multiracial hypertensive patients treated in primary care. It will allow medical professionals to design suitable training programme to educate the public on the self- management of hypertension and the use of HBPM.
Methods This was a cross-sectional descriptive study of hypertensive patients, on treatment for at least two consecutive consultations at a district polyclinic in Pasir Ris in northeastern Singapore. The polyclinic provides subsidized primary care to outpatients across all socioeconomic strata. The disease codes in the polyclinic-computerized database were used
HBPM among Asian hypertensive patients NC Tan et al 560
to identify this group of patients. Patients on repeat visits within the same month were excluded. Sample size was calculated on an estimated prevalence of HBPM of 20% with 7% estimated error rate of 95%. This required a sample of 120. To allow for nonresponse, the study aimed to recruit 200 patients. Sample random sampling selected 224 hypertensive patients who satisfied the inclusion and exclusion criteria. Patient information sheet, were sent to the potential participants by post and followed up by phone contacts by the research nurses prior to the house visit to obtain a verbal consent to the study. The nurses subsequently explained the study protocol, obtained a written consent and administered a standardized questionnaire using face-to-face interview at patient’s residence. Patient’s blood-pressure was measured at sitting position thrice by the nurse using a mercury sphygmomanometer (@Accoson Metpak model). These patients’ medical records were reviewed at the study site. The average BP recorded in the preceding three visits to the clinic were compared with the mean sitting BP recorded at patients’ residence by the nurse. Patients, who refused either the verbal or written consent, were regarded as a nonresponse.
The demographic profile of the study population is shown in Table 1. Prevalence, awareness and characteristic of HBPM users
Among the 175 subjects, 108 or 61.7%. of the study population were aware of HBPM but only 42 or 24% of them were using HBPM. Among the users, about half were using HBPM for up to a year and the rest more than 1 year. They bought their devices from private pharmacy (38%), hospital or primary care clinics (29%) or obtained them as gift (33%). In all, 69% of the users did not use the device regularly or less than daily, with 45.2% did so without any fixed time, followed by measurement in the morning (35.7%). In total, 92.9% had their HBPM measured by cuff on the arm with the remaining at the wrist (Table 2). The majority did not see the need to check the device battery (78.6%) and cuff leakage (57.1%), were satisfied with the device (76.2%) and found HBPM easy (90.5%). Factors associated with the use of HBPM
The data were analyzed using SPSS statistical software. Proportions (%) were used to describe categorical variables and w2-test and Fisher’s exact test used to assess differences. w2-test for trend was applied to test for trends. Bivariate and multivariate analyses by backward stepwise logistic regression procedure were applied to determine the factors influencing the use of HBPM. Bivariate analysis was conducted to identify putative predictor variables for the HBPM use. Pp0.1 with odds ratios that exclude 1 was used as a cutoff for statistical significance for variable selection for multivariate modelling in order not to miss any potentially important predictors. Statistical significance remained the conventionally defined Pp0.05 and odds ratios that exclude 1 in the bivariate and multivariate models. To choose among competing models, the preferred logistic regression model was selected based on the clinically important variables in the model, log likelihood ratio and Hosmer and Lemeshow test (40.05).
In the multivariate analysis by stepwise backward regression, the final fitted model provided the following information: The socioeconomic status of the subjects, as reflected in their total household income was a significant determinant on the use of HBPM. The prevalence of HBPM users in the high- and middleincome groups were significantly higher when compared to low income group. Final adjusted OR for middle-income group was 2.85 with 95% CI: 1.2–6.87, P ¼ 0.018 and for high-income group was 2.26 with 95% CI: 1.06–4.82, P ¼ 0.034 (Table 3). The patients’ average diastolic BP, documented in their case notes over two consecutive consultations at the polyclinic prior to the interview, was shown to be another significant factor (Table 3). In the bivariate analysis, the prevalence of HBPM users was significantly higher in younger age group (up to 50 years old) when compared to the patients with aged 460 years (unadjusted OR: 0.40, 95% CI: 0.17–0.95, P ¼ 0.038). The value did not reach the statistical significant level in the multivariate analysis. The prevalence of HBPM users in the middleage group was 1.5 times higher when compared to the younger age group. However, this value again did not attain the statistical significance.
Results
Factors associated with the nonuse of HBPM
Demographics of study population
Among the nonusers, the majority did not see the need to carry out HBPM (56.1%), were unaware of HBPM (38.3%), did not understand how to operate the device (18.8%), were unable to afford to purchase the device (14.3%) or perceived to be inaccurate (10.5%) (Table 4).
Statistical analysis
Out of a total of 224 subjects in the sample, 175 hypertensive participants consented to the study and were interviewed by the research nurses in their residence, constituting a response rate of 78.1%. Journal of Human Hypertension
HBPM among Asian hypertensive patients NC Tan et al 561
Table 1 Factors associated with the use of HBPM using binary logistic regression analysis Variable
All respondents
Nonusers
Users
OR
95% CI
175
133 (76.0%)
42 (24.0%)
0.96
0.93–0.99
40 51 84
26 (19.5) 38 (28.6) 69 (51.9)
14 (33.3) 13 (31.0) 15 (35.7)
1 0.64 0.4
Ref: 0.26–1.57 0.17–0.95
107 68
83 (62.4) 50 (37.6)
24 (57.1) 18 (42.9)
1 1.25
— 0.62–2.52
Income Low (S$500–2000) Middle (S$2001–4000) High (4S$4000)
71 73 31
62 (46.6) 50 (37.6) 21 (15.8)
9 (21.4) 23 (54.8) 10 (23.8)
1 3.11 3.44
— 1.32–7.31 1.23–9.67
Education None and Primary Secondary Tertiary/Poly/Graduate
97 60 18
83 (62.4) 40 (30.1) 10 (7.5)
14 (33.3) 20 (47.6) 8 (19.0)
1 2.96 4.74
— 1.36–6.47 1.60–4.09
Duration of hypertension (years) Up to 5 6–10 410
86 29 60
60 (45.1) 23 (17.3) 50 (37.6)
26 (61.9) 6 (14.3) 10 (23.8)
1 0.6 0.46
— 0.22–1.65 0.20–1.05
Co-morbidity Diabetes No Yes
123 52
96 (72.2) 37 (27.8)
27 (64.3) 15 (35.7)
1 1.44
— 0.69–3.01
Coronary artery disease No Yes
162 13
125 (94.0) 8 (6.0)
37 (88.1) 5 (11.9)
1 2.11
— 0.65–6.84
High lipid profile No Yes
100 75
76 (57.1) 57 (42.9)
24 (57.1) 18 (42.9)
1 1
— 0.50–2.02
Cardiac dysarrythymia No Yes
171 4
131 (98.5) 2 (1.5)
40 (95.2) 2 (4.8)
1 0.31
— 0.04–2.23
Average systolic BP Up to 140 mmHg 4140 mmHg
120 55
91 (68.4) 42 (31.6)
29 (69.0) 13 (31.0)
1 0.97
— 0.46–2.06
Average diastolic BP Up to 80 mmHg 480 mmHg
82 93
69 (51.9) 64 (48.1)
13 (31.0) 29 (69.0)
1 2.41
— 1.15–5.03
Study population (sample size n ¼ 175) Age group (years) 20–50 51–60 460 Gender Female Male
In this study, there was no significant difference in mean BP (both systolic and diastolic) measured by the nurse at patients’ residence and patients’ average documented BP in the clinic. Based on independent samples test, the mean systolic BP difference was 2.2 mmHg (P ¼ 0.292) and that for diastolic BP was 3.1 mmHg (P ¼ 0.342).
Discussion In this study, the prevalence of HBPM was 24% of the hypertensive patients on follow-up at a
district polyclinic. Surveys in certain region in USA and Germany3–5 showed that 44–66% of individuals with hypertension measured their own BP, with 50–73% of them purchased their monitor without physician’s advice and were not trained by qualified personnel. The lower prevalence could be attributed to a population who selected the government-aided polyclinic for the management of their hypertension due partially to their socioeconomic status and the fees for service healthcare environment in Singapore. There is yet any epidemiological data pertaining to HBPM in Singapore. Journal of Human Hypertension
HBPM among Asian hypertensive patients NC Tan et al 562
Table 2 Practice and attitude of HBPM users
Table 3 Factors associated with HBPM use (final fitted model)
n ¼ 42 (%)
95% CI
Duration of use of HBPM (years) Up to 1 41
20 (47.6) 22 (52.4)
33.4–62.3 37.7–66.4
Frequency of use Frequently (4once per week) Seldom (oonce per week)
13 (31.0) 29 (69.0)
19.1–46.0 54.0–80.9
Time of day when home BP was measured Morning 15 (35.7) Afternoon and evening 8 (19.0) No fixed time 19 (45.2)
23.0–50.8 10.0–33.3 31.2–60.0
Site of limb where home BP was measured Arm 39 (92.9) Wrist 3 (7.1)
81.0–97.5 2.5–19.0
35 (83.3) 7 (16.7)
69.4–91.7 8.3–30.6
‘How often do you check the device’s battery?’ No need 33 (78.6) Every 3 months/every 6 months 8 (19.0) Every year/every 2 years 1 (2.4)
64.1–88.3 10.0–33.3 0.4–12.3
‘Do you check the cuff for any leakage?’ Yes 7 (16.7) No 24 (57.1) Don’t know 11 (26.2)
8.3–30.6 42.2–70.8 15.3–41.1
‘I am satisfied with my BP monitoring device.’ Not sure 2 (4.8) Agree 32 (76.2) Disagree 8 (19.0)
1.3–15.8 61.5–86.5 10.0–33.3
‘I find home BP monitoring easy.’ Not sure Agree Disagree
0.4–12.3 77.9–96.2 2.5–19.0
1 (2.4) 38 (90.5) 3 (7.1)
95% CI ¼ 95% confidence interval.
Average clinic (office) diastolic BP of above 80 mmHg as recorded in the subject’s case notes for consecutive two visits to the polyclinic were found to be associated with the use of HBPM. The authors postulated that emphasis on the importance of diastolic BP by doctors could have motivated the use of HBPM. Further studies are needed to investigate this HBPM and diastolic BP association, although current evidence suggested that both systolic and diastolic are probably both important factors in BP related mortality and morbidity.6 Incidentally, there was a report of end-diastolic relative cardiac wall thickness, as measured using the M-mode echocardiograms, had the highest correlation coefficient with HBPM compared to Journal of Human Hypertension
b (regression coefficient)
OR
95% CI
— 1.05 1.24
1 2.85 3.46
— 1.2–6.78 1.22–9.87
Average diastolic BP (mmHg) Up to 80 — 480 0.82
1 2.26
— 1.06–4.82
Income Low (500–2000) Middle (2001–4000) High (44000)
Table 4 Reasons for not using home BP monitoring device
‘How much must the cuff covered the limb if used on the arm?’ 1/3 cover the arm 22 (52.4) 37.7–66.6 1/2 cover the arm 2/3 cover the arm 11 (26.2) 15.3–41.1 Entire span 2 (4.8) 1.3–15.8 ‘Have you calibrated your device?’ Yes No
Variable
Can’t afford to own the device Do not understand how to operate the device Do not see the need to do so ‘Home BP monitoring is not accurate’ Other reasons No reason
n ¼ 133 (%)
95% CI
18 (13.5) 25 (18.8)
8.7–20.4 13.1–26.3
72 (54.1) 14 (10.5)
45.7–62.4 6.4–16.9
39 (29.3) 21 (15.8)
22.3–37.6 10.6–22.9
office BP and ambulatory blood pressure monitoring (ABPM) readings.7 Although the prices of HBPM devices in the market were competitive and generally affordable to the middle- and upper-income group of patients, it may appear expensive to the more elderly patients who were mostly retired or unemployed. These senior patients, in the context of the local fees for service healthcare system, may be dependent on relative’s contribution for their medical expenses. Thus, 14.3% of them reported that they could not afford to purchase the HBPM devices’s. In total, 20.3% of the nonusers claimed to be unaware of HBPM. This could again be related to their educational and socioeconomic background. Most importantly, the majority (56.4%) of the nonusers did not see the need for HBPM, although 61.7% of the entire study population were aware of such monitoring. Most of the local population relied on the healthcare professionals on health education. However, doctors and nurses were hesitant to endorse the routine use of HBPM due to perceived inaccuracy of HBPM devices and lack of strong evidence to indicate that HBPM could improve the mortality and morbidity of hypertensive patients. The BP inaccuracy could arise in many ways from the operator of the device and from the device itself.8 However, the aneroid sphygmomanometers could likewise be unreliable and operator-dependent and were discovered to be inaccurate in 80% of the units assessed at a university hospital and clinic.9 Several reports now showed that the average difference between the results of daytime ABPM and
HBPM among Asian hypertensive patients NC Tan et al 563
HBPM was –1.7/1.2 mmHg, which was not clinically important.10–13 With the establishment of strict accuracy standards by the Association for the Advancement of Medical Instrumentation (AAMI)14 and that of the British Hypertension Society,15 reports confirming accuracy were published16,17 and public buying AAMI and BHS certified devices could be assured of reliability of the monitors. The walk-in primary care services both in the public and the private sectors provide ready access to patients to consult their doctors, which offers the advantage of interaction, feedback, medical intervention and reassurance. The current HBPM does not allow for face-to-face consultation with a medical professional, which may be overcome with the advancement of telemedicine in the future. However, cost incurred by either the walk-in doctor consultation or installation of telemedicine could be substantial and was not taken into consideration in the study. There is currently lack of formal or structured training programme by healthcare professionals to educate the public on the use of HBPM. Most of the ad hoc ‘orientation’ to HBPM was conducted by the manufacturer or pharmacy sales personnel, which inevitable led to uncertainty and certain degree of skepticism. In all, 18.8% of the nonusers indicated that they did not understand the operating mode of the monitors. While there was an isolated report6 that HBPM improved prediction of hypertension-related morbidity and mortality, evidences that HBPM was costeffective,18 improved BP control18,19 and compliance with therapy20 were equivocal or conflicting. Nevertheless, there had been reports indicating benefits in each of the areas. It is important that the medical professionals must first be convinced of the clinical effectiveness of HBPM before it is introduced to the patients. In addition, doctors and nurses need to be regularly updated on the current development of HBPM so that they could advise and educate their hypertensive patients appropriately. They could review the factors motivating the patients to embark on HBPM, which could be regarded as a useful adjunct measure in their patients’ self-management of hypertension.
Conclusion Only 24% of the hypertensive patients in this study used HBPM. This was attributed to failure to see the need for HBPM, lack of awareness, cost and perception of inaccuracy. Factors influencing the use of HBPM include socioeconomic status such as education and household income, personal confidence in the use of HBPM and the average office recorded diastolic BP of the patients of 480 mmHg, which was likely perceived as a marker of BP control.
What is known about home blood pressure monitoring? Evidences suggest that HBPM can provide physicians with another reliable source of information pertaining to hypertensive patients’ blood pressure control. What does this paper add? There is increased awareness of HBPM but usage by patients remains low. Patients’ failure to recognize benefits, lack of awareness, cost and perception of inaccuracy are barriers. Higher socioeconomic status and patient’s documented diastolic BP are associated with HBPM usage.
Acknowledgements We were grateful to the nurses, Vasanti, Violet and Mary, who rendered their assistance in data entry and the team of research nurses who interviewed the subjects in their residence. The study was supported by a small research grant from CTERU/NMRC.
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