Cuff width alters the amplitude envelope of wrist cuff pressure pulse waveforms

The accuracy of noninvasive blood pressure (BP) measurement with any method is affected by cuff width. Measurement with a too narrow cuff overestimates BP and measurement with a too wide cuff underestimates BP. Automatic wrist cuff BP monitors use permanently attached narrow cuffs with bladders about 6 cm wide. Such narrow cuffs should result in under-cuffing for wrist circumferences larger than 15 cm. The objective of this qualitative study was to show that a narrow wrist cuff results in increased BP values when a cuff pulse amplitude ratio algorithm is used. According to the algorithm used in this study, systolic pressure (SBP) corresponds to the point of 50% of maximal amplitude; for diastolic pressure (DBP) the ratio is 70%. Data were acquired from 12 volunteers in the sitting position. The mean wrist circumference was 18 cm. The acquired cuff pulse data were used to compute SBP, mean pressure (MAP) and DBP. The mean values for a 6 cm cuff were SBP = 144 mmHg, MAP = 104 mmHg and DBP = 88 mmHg. The values for a 10 cm cuff were SBP = 128 mmHg, MAP = 93 mmHg and DBP = 78 mmHg. The reference BP values were SBP = 132 mmHg, MAP = 96 mmHg and DBP = 80 mmHg. All narrow (6 cm) cuff BP values were higher than wide (10 cm) cuff or reference BP values. The results indicate that wider wrist cuffs may be desirable for more accurate and reliable BP measurement with wrist monitors.