Effect of the shape of the cuff on blood pressure measurement in people with large arms

Purpose: Previous data suggest that tronco-conical cuffs should be used for accurate blood pressure (BP) measurement in the obese. However, not only arm size but also its shape may affect the accuracy of BP measurement when a cylindrical cuff is used. Methods: In 197 subjects with arm circumference >32 cm, and 157 subjects with arm circumference ≤ 32 cm, the upper-arm was considered as formed from two truncated cones and the frustum slant angles of the proximal (upper angle) and distal (middle angle) truncated cones were measured. Five cylindrical and five tronco-conical cuffs of appropriate size in relation to arm circumference were used. Results: In the group with large arm, the upper slant angle was greater than the middle angle (86.5 ± 1.7° versus 84.7 ± 2.3°), whereas in the group with normal arm the two angles were similar. In the former group, the cylindrical cuff overestimated BP by 2.5 ± 5.4/1.7 ± 4.7 mmHg, whereas in the latter negligible between-cuff BP discrepancies were found. In the whole sample, BP discrepancies between the cylindrical and the tronco-conical cuffs correlated with both arm size and shape, considered as the difference between the upper and middle slant angles (all p < 0.0001). Among the participants with large arm, the between-cuff BP discrepancies increased progressively with increasing upper-middle angle difference (3.75 ± 0.38/2.78 ± 0.32 mmHg for the top tertile, p < 0.001/<0.001). Conclusions: These data indicate that in people with large upper arms, the tronco-conical shape of the arm is more pronounced on the lower than the upper half, a feature that amplifies the BP measurement error when cylindrical cuffs are used.