Rectangular cuffs may overestimate blood pressure in individuals with large conical arms

Although the upper arm has the shape of a truncated cone, cylindrical cuffs and bladders are currently used for blood pressure (BP) measurement. The aim of this study was to ascertain whether cylindrical and tronco-conical cuffs provide different readings according to arm size and shape.

We studied 220 individuals with arm circumference ranging from 22 to 42.5 cm. Four different cylindrical and four different tronco-conical bladders of appropriate size were used. Sequential same-arm measurements were performed in triplicate by two observers using the two cuffs in a random order. In 100 individuals, the actual pressure transmitted to the arm surface by the two cuffs at the central point was also measured.

Upper arm shape was tronco-conical in all of the individuals. In a multiple regression, conicity was related to arm circumference (P < 0.001) and length (P = 0.001). Arm conicity and size were independently related to the between-cuff SBP (P = 0.001 and 0.002, respectively) and DBP (P = 0.001 and <0.001, respectively) discrepancies. In the group with arm circumference of 37.5-42.5 cm, the cylindrical cuff overestimated BP measured with the tronco-conical cuff by 2.0 ± 0.4/1.8 ± 0.3 mmHg (P = 0.001 and <0.001). In this group, 15% of individuals found hypertensive with the cylindrical cuff were normotensive when assessed with the conical cuff. Differences as great as 9.7/7.8 mmHg were found in individuals with large arms and slant angle equal to or less than 83°.

In obese people, the upper arm may have a pronounced tronco-conical shape and cylindrical cuffs may overestimate BP. Tronco-conical cuffs should be used for BP measurement in individuals with large arms.