Effect of Cuff Design on Auscultatory and Oscillometric Blood Pressure Measurements

Blood Pressure Sensors: Materials, Fabrication Methods, Performance Evaluations and Future Perspectives

Advancements in materials science and fabrication techniques have contributed to the significant growing attention to a wide variety of sensors for digital healthcare. While the progress in this area is tremendously impressive, few wearable sensors with the capability of real-time blood pressure monitoring are approved for clinical use. One of the key obstacles in the further development of wearable sensors for medical applications is the lack of comprehensive technical evaluation of sensor materials against the expected clinical performance. Here, we present an extensive review and critical analysis of various materials applied in the design and fabrication of wearable sensors. In our unique transdisciplinary approach, we studied the fundamentals of blood pressure and examined its measuring modalities while focusing on their clinical use and sensing principles to identify material functionalities. Then, we carefully reviewed various categories of functional materials utilized in sensor building blocks allowing for comparative analysis of the performance of a wide range of materials throughout the sensor operational-life cycle. Not only this provides essential data to enhance the materials' properties and optimize their performance, but also, it highlights new perspectives and provides suggestions to develop the next generation pressure sensors for clinical use.

Numerical study to evaluate the effect of a surface-based sensor on arterial tonometry

Arterial tonometry is a widely used non-invasive blood pressure measurement method. In contrast to the cuff-based method, it is possible to obtain a continuous pressure profile with respect to systolic and diastolic pressures using this method. However, due to a requirement of arterial tonometry-that a sensor needs to be placed directly above a blood vessel-placement error is inevitable if the measurement device is only capable of measuring local regions. This study assumed that the plate sensor is flexible, thus reducing the placement error. We investigated the pressure distribution along the wrist surface rather than the local region through the contact simulation between the flexible plate sensor and the wrist. As a result, we concluded that there is a unique pressure distribution for any specific wrist, regardless of the length and position of the plate, and that it is possible to measure the blood pressure using the response at the wrist surface to the pressure inside the radial artery.

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.

Should patients with higher blood pressure variability be excluded from validation studies? An assessment of the '12/8' rule

To limit the inclusion of participants with increased blood pressure (BP) variability and presumably to avoid potential bias, the International Standards Organization BP device validation standard recommends exclusion of patients with a BP variability of more than 12/8 mmHg across reference readings. This '12/8 rule' is based on expert consensus and lacks empirical justification. In a post-hoc analysis of a study comparing two types of cuff designs carried out according to the International Standards Organization standard, we divided the study sample into patients who did not have (n=79) and patients who had (n=55) more than 12/8 mmHg variability. Patients with more than 12/8 mmHg variability were older and had a higher prevalence of diabetes (41.8 vs. 22.8%; P=0.02) and hypertension (43.6 vs. 29.1%; P=0.08). The mean systolic BP differences between the two cuff designs were not significantly different in participants who did not show more than 12/8 mmHg variability versus those who did (2.2±3.5 vs. 3.1±3.4; mean difference of differences -0.9±3.4; P=0.14). Similarly, the mean diastolic BP differences were not significantly different in participants who did not have more than 12/8 mmHg variability versus those who did (1.5±2.2 vs. 1.4±2.6; mean difference of differences 0.1±2.4; P=0.82). A limitation of our analysis is that the original study data focused on a comparison of different cuff designs and not formal validation of a specific device. Therefore, replication of these findings is warranted. Nevertheless, our findings do not support the use of the 12/8 rule and indicate that this rule may be promoting unnecessarily homogenous study samples, limiting external generalizability, and needlessly increasing workload and expense.