CONICAL CUFFS SHOULD BE USED AS REFERENCE STANDARD FOR VALIDATION OF BLOOD PRESSURE MEASURING DEVICES IN OBESE PEOPLE WITH ARM CIRCUMFERENCE OF MORE THAN 42 CM

Abstract

Objective: Previous research suggested that tronco-conical cuffs and bladders should be used for accurate blood pressure (BP) measurement in the very obese. However, criteria about size and shape of the reference cuff that should be used for device validations in people with arm size > 42 cm have not yet been established by regulatory bodies. Aim of this study was to investigate the performance of a tronco-conical versus a rectangular (cylindrical) cuff in obese subjects with mid-arm circumference of 43 cm or larger. Design and method: In 90 adults with upper arm circumference > 42 cm (X-large group), 90 subjects with arm circumference between 36 and 42 cm, and 211 subjects with arm circumference < = 35 cm, cylindrical and tronco-conical cuffs were compared. Five cylindrical cuffs of appropriate size in relation to arm circumference and 5 tronco-conical cuffs having the same length and width on the midpoint were used. In the X-large group, the cuffs had 20 cm width and 40 cm length. The tronco-conical cuff had an 85.0̊ slant angle. In each subject, BP was measured in triplicate by two observers using the cylindrical and tronco-conical cuffs in a random order. Results: The mean±SEM upper arm slant angle was 84.7±0.07̊ in the X-large group, 85.6±0.07̊ in the 36-42 cm group, and 87.1±0.05̊ in the < = 35 cm group (all between-group differences, p<0.0001). In the X-large group, the cylindrical cuff overestimated BP measured with the tronco-conical cuff by 4.4±0.3/3.1±0.2 mmHg, in the 36-42 cm group by 1.5±0.3/1.6±0.2 mmHg, and in the < = 35 cm group by 0.8±0.2/0.1±0.2 mmHg (X-large versus both smaller arm subgroups, p<0.0001/<0.0001). In the whole population (1173 BP readings), both arm circumference and conical shape were independent predictors of the between-cuff SBP and DBP discrepancies. Skinfold thickness improved the predictive model for diastolic (p = 0.004) but not systolic BP. Conclusions: In obese people with arm size > 42 cm, a cylindrical cuff causes an important overestimation of BP measured with a tronco-conical cuff. We suggest that the reference cuff for validation studies in this special population should have a conical shape with an 85̊ slant angle.