A novel cuffless device recorded significantly higher values for both systolic and diastolic blood pressure (BP) compared with standard equipment for 24-hour ambulatory BP monitoring, in a small study from Switzerland.

Data were analysed for 71 adults recruited at the University Hospital, Basel between May and December 2017. Patients with an indication for 24-hour ambulatory BP measurement were consecutively recruited as well as healthy volunteers. The mean age of participants was 49.3 years, and 51% were male.

Cuffless BP using the Somnotouch-NIBP, a device that uses pulse transit time (PTT) for beat to beat calculation, and standard 24-hour BP measurements were performed simultaneously on the left and right arm, respectively. The first standard BP measurement was used as the calibration measurement for the cuffless BP.

The cuffless device had only been previously validated over a very short time period - 25 minutes after initial calibration in a laboratory in the absence of dynamic conditions.

Mean 24-hour BP values for cuffless BP and standard BP were 140.8 versus 134.0 mmHg (P < 0.0001) for systolic and 85.8 versus 79.3 mmHg (P < 0.0001) for diastolic BP, respectively. Mean absolute systolic and diastolic disagreements between cuffless and standard BP were 10.2 and 8.2 mmHg, respectively.

The number of absolute differences between the mean 24-hour BP values of the cuffless and standard BP within 5, 10 and 15 mmHg were 23 (32.4%), 43 (60.6%) and 53 (74.6%) for systolic and 24 (33.8%), 51 (71.8%) and 65 (91.6%) for diastolic measurements, respectively.

Current hypertension guidelines advocate the use of 24-hour ambulatory BP monitoring to secure the diagnosis of hypertension. The standard monitoring devices use an appropriately sized upper arm cuff attached to an oscillometric device. The repeated cuff inflations, particularly during the night can be poorly tolerated by some patients and potentially nocturnal readings may be artificially elevated, all of which can limit the clinical usefulness of monitoring. Novel devices which do not utilise an upper arm cuff were thought to offer a possible solution to this problem.

The study authors conclude:

‘The present analysis shows higher ambulatory BP levels by the non-invasive, cuffless, PTT-based device in comparison with a validated cuff-based device over 24 hours.

Due to the higher BP levels there is a risk of misclassification of normotensive patients into hypertensive with possible overtreatment when usual cut-off values are applied.’

‘Further studies are needed to improve the accuracy of the device or to derive device-specific cut-off points,’ they add.

This study demonstrates the importance of robust clinical evaluation for emerging medical technology to prevent the premature introduction of novel devices.

Dr Peter Savill