Standards for blood pressure measuring devices

Practical Application of a New Cuffless Blood Pressure Measurement Method

It would be useful to develop a reliable method for the cuffless measurement of blood pressure (BP), as such a method could be made available anytime and anywhere for the effective screening and monitoring of arterial hypertension. The purpose of this study is to evaluate blood pressure measurements through a CardioQVARK device in clinical practice in different patient groups.

METHODS

This study involved 167 patients aged 31 to 88 years (mean 64.2 ± 7.8 years) with normal blood pressure, high blood pressure, and compensated high blood pressure. During each session, three routine blood pressure measurements with intervals of 30 s were taken using a sphygmomanometer with an appropriate cuff size, and the mean value was selected for comparison. The measurements were carried out by two observers trained at the same time with a reference sphygmomanometer using a Y-shaped connector. In the minute following the last cuff-based measurements, an electrocardiogram (ECG) with an I-lead and a photoplethysmocardiogram were recorded simultaneously for 3 min with the CardioQVARK device. We compared the systolic and diastolic BP obtained from a cuff-based mercury sphygmomanometer and smartphone-case-based BP device: the CardioQVARK monitor. A statistical analysis plan was developed using the IEEE Standard for Wearable Cuffless Blood Pressure Devices. Bland-Altman plots were used to estimate the precision of cuffless measurements.

RESULTS

The mean difference between the values defined by CardioQVARK and the cuff-based sphygmomanometer for systolic blood pressure (SBP) was 0.31 ± 3.61, while that for diastolic blood pressure (DBP) was 0.44 ± 3.76. The mean absolute difference (MAD) for SBP was 3.44 ± 2.5 mm Hg, and that for DBP was 3.21 ± 2.82 mm Hg. In the subgroups, the smallest error (less than 3 mm Hg) was observed in the prehypertension group, with a slightly larger error (up to 4 mm Hg) found among patients with a normal blood pressure and stage 1 hypertension. The largest error was found in the stage 2 hypertension group (4-5.5 mm Hg). The largest error was 4.2 mm Hg in the high blood pressure group. We, therefore, did not record an error in excess of 7 mmHg, the upper boundary considered acceptable in the IEEE recommendations. We also did not reach a mean error of 5 mmHg, the upper boundary considered acceptable according to the very recent ESH recommendations. At the same time, in all groups of patients, the systolic blood pressure was determined with an error of less than 5 mm Hg in more than 80% of patients. While this study shows that the CardioQVARK device meets the standards of IEEE, the Bland-Altman analysis indicates that the cuffless measurement of diastolic blood pressure has significant bias. The difference was very small and unlikely to be of clinical relevance for the individual patient, but it may well have epidemiological relevance on a population level. Therefore, the CardioQVARK device, while being worthwhile for monitoring patients over time, may not be suitable for screening purposes. Cuffless blood pressure measurement devices are emerging as a convenient and tolerable alternative to cuff-based devices. However, there are several limitations to cuffless blood pressure measurement devices that should be considered. For instance, this study showed a high proportion of measurements with a measurement error of <5 mmHg, while detecting a small, although statistically significant, bias in the measurement of diastolic blood pressure. This suggests that this device may not be suitable for screening purposes. However, its value for monitoring BP over time is confirmed. Furthermore, and most importantly, the easy measurement method and the device portability (integrated in a smartphone) may increase the self-awareness of hypertensive patients and, potentially, lead to an improved adherence to their treatment.

CONCLUSION

The cuffless blood pressure technology developed in this study was tested in accordance with the IEEE protocol and showed great precision in patient groups with different blood pressure ranges. This approach, therefore, has the potential to be applied in clinical practice.

Comparing blood pressure measurements between a photoplethysmography-based and a standard cuff-based manometry device

Repeated blood pressure (BP) measurements allow better control of hypertension. Current measurements rely on cuff-based devices. The aim of the present study was to compare BP measurements using a novel cuff-less photoplethysmography-based device to a standard sphygmomanometer device. Males and females were recruited from within the general population who arrived at a public BP screening station. One to two measurements were taken from each using a sphygmomanometer-based and the photoplethysmography-based devices. Devices were considered equal if the mean difference between paired measurements was below 5 mmHg and the Standard Deviation (SD) was no greater than 8 mmHg. Agreement and reliability analyses were also performed. 1057 subjects were included in the study analysis. There were no adverse events during the study. The mean (± SD) difference between paired measurements for all subjects was -0.1 ± 3.6 mmHg for the systolic and 0.0 ± 3.5 mmHg for the diastolic readings. We found 96.31% agreement in identifying hypertension and an Interclass Correlation Coefficient of 0.99 and 0.97 for systolic and diastolic measurements, respectively. The photoplethysmography-based device was found similar to the gold-standard sphygmomanometer-based device with high agreement and reliability levels. The device might enable a reliable, more convenient method for repeated BP monitoring.

The changing distribution of arm circumferences in NHANES III and NHANES 2000 and its impact on the utility of the ???standard adult??? blood pressure cuff

BACKGROUND

Accurate blood pressure measurement is dependent on using a blood pressure cuff that is appropriate to the patient's arm circumference.

OBJECTIVE

This study identifies the change in distribution of arm circumferences in the United States and its impact on usage of the 'standard adult' cuff.

METHOD

The most current National Health and Nutritional Examination Survey (NHANES) data, available on the website (http://www.cdc.gov/nchswww/nchshome.htm), covers NHANES III (Cycle 1, 1988-1991; 8381 subjects and Cycle 2, 1991-1994; 8566 subjects) and NHANES 2000 (1999-2000; 4,444 subjects). The weighted change in arm circumference between NHANES III as a whole and NHANES 2000 was calculated. Correlates for increased arm circumference were obtained via multivariate analysis. The predicted change in blood pressure cuff usage based on the changing prevalence of arm circumferences was calculated.

RESULTS

The mean arm circumference for the whole population increased significantly from NHANES III to NHANES 2000 (31.83 +/- 0.08 cm versus 32.86 +/- 0.15 cm, p < 0.001) and in the hypertension population without reaching statistical significance (33.07 +/- 0.16 to 33.61 +/- 0.30 cm, p = 0.11). When adjusted regressions were performed, the increases in arm circumference were due to increasing weight in both the whole population and the hypertensives. The numbers of Americans predicted to require the 'standard adult' cuff to accurately measure blood pressure decreased from 76.2% to 66.3% while the number of Americans increased from 42.2% to 45%.

CONCLUSIONS

The increasing prevalence of overweight and obese Americans found in NHANES III and NHANES 2000 has led to larger mean arm circumferences in hypertensives and the total population. This increased frequency of larger arm circumferences predicts that the 'large adult' cuff will be increasingly required in clinician's offices for accurate blood pressure measurement.