A comparison among oscillometric waveforms in healthy nonpregnant women, pregnancy and hypertensive disorders of pregnancy.

OBJECTIVE: Understanding of how oscillometric waveforms (OMW) vary between pregnant and nonpregnant individuals remains low. An exploratory analysis was completed to assess for quantitative and qualitative changes in OMW and oscillometric envelope features in pregnancy. DESIGN AND METHODS: Eighteen pregnant individuals (over 20 weeks gestational age) and healthy, nonpregnant (HNP) women were recruited. Six HNP were matched to six healthy pregnant (HP) women, and six pregnant women with a hypertensive disorder of pregnancy (HDP) by age, arm circumference, and cuff size. Blood pressure measurements were completed per the International Organization for Standardization (ISO) protocol using a custom-built oscillometric device as the test device and two-observer mercury auscultation as the reference measurement. Auscultatory blood pressure and blood pressure derived from slope-based and fixed ratio algorithms were determined. OMW and envelope features were compared among groups. RESULTS: In HNP, HP, and HDP groups respectively: mean auscultatory blood pressure (systolic mean ± SD/diastolic mean ± SD) was 103.4 ±â€…12.2/67.1 ±â€…7.9; 109.5 ±â€…3.1/58.1 ±â€…6.4; 135.6 ±â€…18.9/85.1 ±â€…14.2 mmHg. HDP had significantly higher auscultatory systolic and diastolic blood pressure than the HP group (P = 0.001). The pregnant groups had a lower average pulse width (mean ± SD: HNP = 0.8 ±â€…0 s, HP = 0.6 ±â€…0.1 s, HDP = 0.6 ±â€…0.1 s; HP vs. HNP mean difference [adjusted P value]: 0.2 [P = 0.004], HDP vs. HNP 0.1 [P = 0.018]) compared with the HNP group. The HDP group had a larger area under the OMW envelope than the HNP group (mean ± SD: HNP = 22.6 ±â€…3.4; HDP = 28.5 ±â€…4.2; HDP vs. HNP mean difference [adjusted P value]: 5.9 P = 0.05). CONCLUSION: In this exploratory work, differences in the OMW morphology and parameters were found in pregnancy and in hypertensive disorders of pregnancy compared with healthy controls. Even small differences may have important implications in algorithm development; further work comparing OMW envelopes in pregnancy is needed to optimize the algorithms used to determine blood pressure in pregnancy.

Automated blood pressure measuring devices: how are they clinically validated for accuracy?

Accurate blood pressure (BP) assessment is essential for the optimal diagnosis and management of hypertension. Contemporary clinical practice guidelines strongly endorse use of automated cuff blood pressure measuring devices (BPMD) as the preferred means of measuring and monitoring BP in the office, at home and with ambulatory blood pressure monitoring. To ensure that they are accurate, automated BPMDs should undergo clinical validation testing, performed using an established clinical validation standard. Unfortunately, most BPMDs sold on the global market have not been clinically validated. Furthermore, in the last thirty years, several different clinical validation protocols have been published, with major differences apparent between these standards, causing controversy with respect to which standard is considered acceptable for clinical validation. Complexly worded standards, multiple revisions, and firewalled access also contribute to a lack of understanding and use of clinical validation standards and the number of expert centers performing clinical validations is small. Recently, joint society collaborations have led to creation of the AAMI/ESH/ISO universal standard for the clinical validation of automated cuff BPMDs. Not only is this unified standard a necessary step, but oversight from regulators and influential stakeholders to ensure that only clinically validated BPMDs can be marketed is additionally needed.

Effect of Elevated Ambient Temperature on Simulator-Derived Oscillometric Blood Pressure Measurement.

BACKGROUND: Oscillometric blood pressure (BP) devices are typically labeled for use up to 40 °C. Many geographic regions have ambient temperatures exceeding 40 °C. We assessed the effect of increased ambient temperature (40-55 °C) on simulator-derived oscillometric BP measurement. METHODS: Three Omron BP769CAN devices, 3 A&D Medical UA-651BLE devices, and accompanying cuffs were used. A custom heat chamber heated each device to the specified temperature. A noninvasive BP simulator was used to take 3 measurements with each device at differing temperatures (22, 40, 45, 50, and 55 °C) and BP thresholds: 80/50, 100/60, 120/80, 140/90, 160/110, and 180/130 mm Hg. Using each device as its own control (22 °C), we determined the relative differences in mean BP for each device at each temperature and BP setting, assessed graphical trends with increasing temperature, and examined variability. RESULTS: Graphical trends of mean simulator-subtracted BP differences from room temperature showed no discernable pattern, with differences clustered around zero. Overall mean difference in BP (combined elevated temperatures minus room temperature) was -0.8 ± 2.1 (systolic ± SD)/1.2 ± 3.5 (diastolic ± SD) mm Hg for the A&D device and 0.2 ± 0.4 (systolic ± SD)/-0.1 ± 0.1 (diastolic ± SD) mm Hg for the Omron. All individual elevated temperature differences (elevated temperature minus room temperature) except A&D diastolic BP at 50 °C were within 5 mm Hg. CONCLUSIONS: In this simulator-based study assessing within-device differences, higher ambient temperatures resulted in oscillometric BP measurements that were comparable to those performed at room temperature.

Impact of choosing the closest rather than the mean auscultatory blood pressure value on the European Society of Hypertension International Protocol device validation results.

OBJECTIVE: When calculating the difference between alternating auscultatory reference standard (ARS) and the automated device-under-test (DUT) blood pressure (BP) measurements, the European Society of Hypertension International Protocol (ESH-IP) allows investigators to choose the closest ARS value to the DUT value, rather than using the mean of the ARS readings [which is mandated by the International Organization for Standardization (ISO)]. The impact of this rule on ESH-IP validation study results is unknown and was assessed. DESIGN AND METHODS: Nine alternating BP measurements performed according to the ISO protocol were obtained in 94 subjects. The impact of using the closest rather than the mean ARS reading on mean error, SD of the difference, and proportion of readings with DUT-ARS differences within 5, 10, and 15 mmHg was determined. RESULTS: Mean age was 58.6 ± 18.3 years, screening BP was 126.4/77.7 mmHg, and arm circumference was 32.0 ± 4.7 cm. DUT-ARS difference was 0.0 ± 5.3/-0.5 ± 5.0 mmHg using the closest ARS and -0.2 ± 6.5/-0.7 ± 5.9 mmHg using the mean ARS. When using the closest rather than the mean ARS value, the proportion of systolic readings with absolute DUT-ARS differences ≤5 mmHg was 73% (vs. 60% for the mean ARS method), ≤10 mmHg was 93% (vs. 88%), and ≤15 mmHg was 99% (vs. 98%). Corresponding values for diastolic BP were 73% (vs. 62%) for differences ≤5 mmHg, 94% (vs. 91%) for ≤10 mmHg, and 99% (vs. 99%) for ≤15 mmHg. CONCLUSION: Using the closest rather than the mean ARS value results in more favourable validation study results and increases likelihood of passing.

Validation of the BIOS BD240 home blood pressure monitor in a multi-racial, multi-morbid Canadian population according to the International Standards Organization 2018 Protocol.

OBJECTIVE: Assess the accuracy of the BIOS BD240 home blood pressure (BP) monitor and wide-range cuff according to the International Organization for Standardization (ISO) 2018 standard. METHODS: Eighty-five subjects (aged ≥18 y) with arm circumferences between 24 and 43 cm were studied. Blinded, two-observer, mercury-based auscultation performed using a two-piece cuff chosen for upper arm size was used for reference measurements. Accuracy criteria 1 and 2 of the ISO standard were determined and Bland-Altman plots generated. RESULTS: Sixty percent of the study sample was female and 42% had hypertension. Mean device-to-reference standard differences in SBP/DBP were 0.0 ± 6.2/-0.2 ± 6.3 for criterion 1 and 0.0 ± 4.8/-0.2 ± 5.8 for criterion 2. CONCLUSION: The BIOS BD240 passed the requirements of the American National Standards Institute/Association for the Advancement of Medical Instrumentation/ISO standard for both SBP and DBP and can be recommended for use.

Patient perceptions of ambulatory blood pressure monitoring testing, tolerability, accessibility, and expense.

Use of 24-hour ambulatory blood pressure monitoring is strongly endorsed by contemporary hypertension guidelines. The objective of this study was to assess patient perceptions of ambulatory blood pressure testing, tolerability, accessibility, and expense. A convenience sample of 50, consenting patients undergoing ambulatory blood pressure monitoring at the University of Alberta Hypertension Clinic in Edmonton, Canada was studied. A 16-item structured questionnaire was administered in person or electronically. Questions regarding the tolerability of ambulatory monitoring were evaluated using a 5-point Likert scale and wait times, expenditures, and willingness to pay were evaluated by direct questioning. Mean age was 53.1 ± 15.4 years, 32 (64%) were female, and 23 (46%) were employed. Mean 24-hour ambulatory BP was 134 ± 12/79 ± 8 mmHg. Ambulatory monitoring caused discomfort in 40 (80%) patients and disturbed sleep in 39 (78%). Forty-one (82%) patients perceived that the home (vs pharmacy, primary care clinic, and speciality care clinic) would be the easiest venue to access future testing. On average, patients waited 27.3 ± 23.7 days for testing; they felt that a wait time of 21.3 ± 12.3 days was appropriate. Mean time taken off work was 8.6 ± 10.8 hours. Twelve (24%) patients indicated that they would be willing to pay out-of-pocket to undergo testing sooner, at a mean expenditure of $120 ± 69. Nineteen (62%) patients were willing to buy a monitor and felt that a mean purchase cost of $125 ± 89 was appropriate. These findings extend current knowledge of patient perceptions of ambulatory monitoring and may help to refine and optimize future delivery of this essential test.

Comparability of oscillometric to simultaneous auscultatory blood pressure measurement in children.

OBJECTIVE: Uncertainty exists regarding the accuracy of automated blood pressure (BP) measurement in children. We recorded oscillometric waveforms in children, derived oscillometric BPs using two standard algorithms, and compared the results to simultaneous auscultation. PATIENTS AND METHODS: Twenty children aged 2-12 years were recruited from a tertiary-care Pediatric Nephrology Clinic. Sex, height, weight, arm circumference, history of hypertension, and clinic BP were recorded. Two, simultaneously measured, oscillometric and auscultatory BP readings were obtained 30-60 s apart. The first reading was discarded and, the second, used for analyses. Fixed-ratio and slope-based algorithms were used for BP derivation. RESULTS: Mean age was 7.95±2.82 years, 40% were female, mean arm circumference was 21.86±4.06 cm, and 50% had hypertension or a history of hypertension. Mean auscultatory BP for all participants (systolic±SD/diastolic±SD) was 93.40±11.80/50.50±9.04 mmHg, oscillometric fixed-ratio BP was 99.20±11.90/57.35±7.15 mmHg and oscillometric slope-based algorithm was 91.60±13.94/60.65±7.71 mmHg. Compared to auscultation, the fixed-ratio method differed by 5.80±12.72/6.85±7.51 mmHg (P=0.06 and <0.01) and the slope-based method differed by -1.80±13.59/10.15±8.07 mmHg (P=0.56 and <0.01). Differences from auscultation were statistically significant for diastolic BP with both fixed-ratio and slope-based methods for all age categories but of greatest magnitude in the youngest children. CONCLUSION: Oscillometric BP derived using two commonly used algorithms differed by more than 5 mmHg in either systolic BP or diastolic BP from simultaneous auscultatory BP in children aged 2-11. These findings emphasize the need for greater understanding of the functionality and accuracy of oscillometry in children.

Accuracy of oscillometric blood pressure algorithms in healthy adults and in adults with cardiovascular risk factors.

BACKGROUND: Fixed-ratio and slope-based algorithms are used to derive oscillometric blood pressure (BP). However, a paucity of published data exists assessing the accuracy of these methods. Our objective was to determine the accuracy of fixed-ratio and slope-based algorithms in healthy adults and in adults with cardiovascular risk factors. PATIENTS AND METHODS: Overall, 85 healthy adults (age≥18 years) and 85 adults with cardiovascular risk factors were studied. Three oscillometric and four two-observer mercury-based auscultation measurements were performed in each, according to International Standards Organization 2013 methodology. Two fixed-ratio algorithms and one slope-based algorithm were applied to process oscillometric waveform envelopes and derive oscillometric BP. Paired and unpaired t-tests were used to compare mean oscillometric BP within and between each group, respectively. RESULTS: For healthy adults, mean age was 50.3±17.8 years, mean arm circumference was 30.4±3.8 cm, and 62% were female. In the cardiovascular risk group, mean age was 63.8±12.4 years, mean arm circumference was 31.9±4.2 cm, and 62% were female. For systolic BP, the fixed-ratio algorithms produced the lowest mean error and narrowest SD. For diastolic BP, mean errors were similar for all three algorithms, but the fixed-ratio algorithms had higher precision. The comparison of healthy adults and those with cardiovascular risk factor showed high variability for systolic and diastolic BP (SD: 8.113.9 mmHg). CONCLUSION: In both healthy adults and in those with cardiovascular risk factors, the fixed-ratio technique performed better than the slope-based algorithm. High between-group variability indicates that subject-specific algorithms may be needed.

Comparability of Automated Office Blood Pressure to Daytime 24-Hour Ambulatory Blood Pressure.

BACKGROUND: Clinical practice guidelines endorse automated office blood pressure (AOBP) measurement as the preferred in-office measurement modality. However, recent data indicate that this method may underestimate daytime ambulatory BP. The objective of this study was to further assess the comparability of mean AOBP and daytime ambulatory BP in clinical practice. METHODS: A retrospective cross-sectional chart review was conducted of 96 consecutive patients referred from primary or specialty care practices to a tertiary care ambulatory BP monitoring service. Six AOBP readings were taken using an appropriately cuffed BpTRU (BpTRU Medical Devices, Coquitlam, Canada) device on the nondominant arm and no rest period (first reading discarded). Twenty-four-hour ambulatory BP monitoring was then performed. Between-group means were compared with paired t tests. The proportion of patients with differences of ≥ 5, 10, and 15 mm Hg was tabulated. RESULTS: Mean age was 52.6 ± 16.7 years, 60% were women, and 79% had previously diagnosed hypertension. Mean AOBPs were 130.8 ± 15.5/82.3 ± 10.7 mm Hg, and mean daytime ambulatory BPs were 142.8 ± 14.9/83.9 ± 11.2 mm Hg (difference of -11.9 ± 13.5/-1.6 ± 7.6; P < 0.001 for systolic BP and P < 0.04 for diastolic BP). Between-group differences were greater in patients with previous hypertension and in those with daytime ambulatory BP levels ≥ 135 mm Hg. The proportions of patients with systolic or diastolic BP differences of ≥ 5, 10 and 15 mm Hg were 89%, 52%, and 33%, respectively. CONCLUSIONS: Mean AOBP underestimates daytime ambulatory BP. Variability between the 2 methods is high. These findings do not support the premise that AOBP closely approximates daytime ambulatory BP.

The effect of back and feet support on oscillometric blood pressure measurements.

BACKGROUND/OBJECTIVE: Recommendations to support the back and feet during blood pressure (BP) measurement are not always followed in clinical practice. Our objective was to determine to what extent back and feet support affects mean oscillometric BP measurements. PARTICIPANTS AND METHODS: Eighty-five consecutive, consenting participants 18 years or older with systolic BP readings 80-220 mmHg and diastolic BP readings 50-120 mmHg and arm circumferences of 25-43 cm were recruited. BP was measured using an Omron HEM 907 oscillometric device. Back and feet support were examined independently. First, while the feet were supported, two sets of three BP readings were taken in random order: one with the back supported and one with the back unsupported. Next, with the back supported, two sets of three BP readings were taken in random order: one with the feet dangling and one with feet supported. RESULTS: The mean age of the participants was 52.0±20.7 years and the mean arm circumference was 31.0±3.2 cm; 62% were women and 49% had hypertension. The mean BP levels with the back unsupported were slightly higher than those with the back supported (119.8±15.5/69.9±8.9 vs. 119.2±16.4/68.2±8.8 mmHg; difference of 0.7±4.9/1.8±3.0; P=0.21 for systolic and <0.0001 for diastolic comparisons). The mean BP levels with feet dangling were slightly lower than with feet supported (120.3±16.3/72.6±8.9 vs. 121.2±16.1/72.9±8.6 mmHg; difference of -0.9±4.1/-0.3±2.8; P=0.04 for systolic and <0.36 for diastolic comparisons). Systolic BP differences were greater than or equal to 5 mmHg in 34% (back phase) and 23% (feet phase) of the participants. CONCLUSION: Provision of back and feet support has a small effect on the mean oscillometric BP. The magnitude of effect is greatest on diastolic BP when the back is unsupported.

An Assessment of the Accuracy of Home Blood Pressure Monitors When Used in Device Owners.

OBJECTIVE: To examine the accuracy of home blood pressure (BP) devices, on their owners, compared to auscultatory reference standard BP measurements. METHODS: Eighty-five consecutive consenting subjects ≥18 years of age, who owned an oscillometric home BP device (wrist or upper-arm device), with BP levels between 80-220/50-120 mm Hg, and with arm circumferences between 25-43 cm were studied. Pregnancy and atrial fibrillation were exclusion criteria. Device measurements from each subject's home BP device were compared to simultaneous 2-observer auscultation using a mercury sphygmomanometer. Between-group mean comparisons were conducted using paired t-tests. The proportion of patients with device-to-auscultatory differences of ≥5, 10, and 15 mm Hg were tabulated and predictors of systolic and diastolic BP differences were identified using linear regression. RESULTS: Mean age was 66.4 ± 11.0 years, mean arm circumference was 32.7 ± 3.7 cm, 54% were female and 78% had hypertension. Mean BPs were 125.7 ± 14.0/73.9 ± 10.4 mm Hg for home BP devices vs. 129.0 ± 14.7/72.9 ± 9.3 for auscultation (difference of -3.3 ± 7.3/0.9 ± 6.1; P values <0.0001 for systolic and 0.17 for diastolic). The proportion of devices with systolic or diastolic BP differences from auscultation of ≥5, 10, and 15 mm Hg was 69%, 29%, and 7%, respectively. Increasing arm circumference was a statistically significant predictor of higher systolic (parameter estimate 0.61 per cm increase; P value 0.004) and diastolic (0.38; 0.03) BP. CONCLUSIONS: Although mean differences from 2-observer auscultation were acceptable, when tested on their owners, most home BP devices were not accurate to within 5 mm Hg. Ensuring acceptable accuracy of the device-owner pairing should be prioritized.

Effect of Cuff Design on Auscultatory and Oscillometric Blood Pressure Measurements.

BACKGROUND: Two-piece blood pressure (BP) cuffs are the historical cuff standard. Use of 1-piece cuffs is increasing. Substituting 1-piece for 2-piece cuffs has an unknown effect on measurement accuracy. We compared these cuff types in a 2-phase study using auscultatory and oscillometric techniques. METHODS: Consenting subjects (aged ≥18 years) with BP levels between 80 and 220mm Hg/50 and 120mm Hg and arm circumferences between 25 and 43cm were studied using the International Standards Organization (ISO) 2013 protocol (modified). A Baum 2-piece cuff was used as the reference standard. A 1-piece Welch Allyn cuff was the comparator. In phase 1 (2-observer auscultation with a mercury sphygmomanometer), 88 subjects were required to obtain 255 paired BP determinations. In phase 2 (oscillometric measurement with a Spacelabs 90207 device), 85 subjects were studied. Each phase was analyzed separately using paired t-tests. RESULTS: Phase 1 mean age was 54.2±20.5 years, mean arm circumference was 29.9±3.7cm, 60% were female, and 32% had hypertension. One-piece cuff mean BPs were lower than the 2-piece cuff means (115.5±15.5/66.4±9.3 vs. 117.8±15.2/67.9±9.2; difference of -2.4±3.6/-1.5±2.4; P values <0.0001 for systolic and diastolic comparisons). Phase 2 mean age was 52.8±20.8 years, mean arm circumference was 29.4±3.9cm, 67% were female, and 38% had hypertension. Mean BPs were lower for the 1-piece compared to the 2-piece cuff (116.5±12.8/67.1±8.1 vs. 120.8±13.5/70.4±8.5; difference of -4.4±3.6/-3.3±2.7; P values <0.0001 for both). CONCLUSIONS: Mean BP is lower with 1-piece cuffs vs. 2-piece cuffs. Differences are greater with oscillometry. When performing validation studies and measurements for clinical purposes, cuff type should be taken into account.

Detecting latent tuberculosis infection during anti-tumor necrosis factor therapy.

OBJECTIVES: There is little information regarding the reliability of repeat tuberculin skin tests (TSTs) and interferon gamma release assays (IGRAs) in detecting latent tuberculosis infection (LTBI) in people on anti-tumour necrosis factor (TNF) medication. METHODS: We conducted a prospective, observational study of patients referred to the Saskatoon Tuberculosis (TB) Clinic prior to starting anti-TNF medication. A chest x-ray (CXR), 2-step TST and IGRA (QuantiFERON-TB Gold In-Tube Method) were performed at baseline. Those patients with a baseline TST ≥10 mm and/or a positive IGRA were followed with a clinic visit, CXR, TST and IGRA at 3 and 6 months after starting anti-TNF medication. RESULTS: Of 106 potential patients, 91 consented to participate. Twenty-six patients had a positive (≥ 10 mm) TST or IGRA at baseline; twelve started and stayed on anti-TNF medication through the 6-month follow-up and completed both planned follow-up visits. The baseline mean TST measurement for the 12 participants was 13.9 mm (SD 11.4), increasing to a mean of 16.8 mm (SD 9.3) post-booster. At 3 months post-anti-TNF initiation, there was an overall decrease in TST measurement (mean=10.0 mm; SD 9.3; p=0.013), with measurements <5 mm in 3 of the 12 patients. By the 6-month TST, a response recovery was observed with a mean TST measurement of 14.5 mm (SD 7.7), with 11/12 ≥5 mm. The IGRA was unchanged throughout the study period in all patients. The overall agreement between TST and IGRA was poor (kappa coefficient = 0.180, p=0.020). CONCLUSIONS: We demonstrated a transient but significant decrease in TST response in the first six months of anti-TNF therapy.

Vitamin D and hypertension in pregnancy.

PURPOSE: Vitamin D Deficiency is common, particularly in northern latitudes. We examined the association between vitamin D status and hypertension in late pregnancy. METHODS: A case-control study was conducted during two time periods: September-October, 2008, and January-March, 2009, in women near term. A case was defined as having two or more documented blood pressure readings above 140/90 (either/or) at any time during pregnancy (n=78). Controls had at least two blood pressure readings, with none above 140/90 during pregnancy (n=109). Serum 25-hydroxyvitamin D (25(OH)D) was measured in all participants. RESULTS: In the summer, 13% of controls and 29% of the cases had 25(OH) D levels < 50 nmol/L. During the winter, these numbers rose to 44% and 49% respectively. Both cases and controls were more likely to be vitamin D deficient in the winter (p=0.002). There was a negative correlation between BMI and 25(OH)D (r=-0.202, p=0.002). In univariate analysis, cases had lower 25(OH)D (p=0.046), but also higher body mass index, so that in multivariate analysis 25(OH)D status was no longer significant. There was no difference in mean oral daily vitamin D intake (dietary intake and supplements, 746 and 785 IU respectively). Controls gained less weight in pregnancy. There was a negative correlation between the highest blood pressure measured in pregnancy and 25(OH)D levels (r= -0.118; p=0.012). CONCLUSION: There is a high prevalence of vitamin D deficiency in pregnant women recruited in Saskatoon, Saskatchewan. Women with low circulating vitamin D concentrations are more likely to have hypertension.