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

OBJECTIVES: 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. DESIGN: 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. RESULTS: 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°. CONCLUSION: 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.