Comparisons of Oscillometric Blood Pressure Measurements at Different Sites of the Upper Limb

The importance of home blood pressure (BP) monitoring has been emphasized for achieving effective hypertension management. Currently, the most popular non-invasive BP monitors for home use are the upper-arm cuff-style oscillometric devices which determine BP from the cuff pressure oscillations during the cuff inflation/deflation induced by the pulsatile blood flow in the compressed arteries. However, the large size of the upper-arm cuff is not favorable for attachment in daily life for ambulatory BP monitoring. Therefore, the miniaturization of home BP monitors is in demand to improve their portability for frequent measurements. This work examined the oscillometric measurement of mean blood pressure(MBP) at upper arm (UA), middle forearm (MA), wrist (WR), finger proximal phalanx (FP) and finger distal phalanx (FD) on 14 young adults. The experimental results showed that the mean and standard deviation of the differences between the oscillometric MBP at UA and the other sites are 8.86±6.28 mm Hg at MA, 14.43±5.52 mm Hg at WR, 9.80±6.57 mm Hg at FP and -0.77±6.37 mm Hg at FD, respectively. Based on hand checking and literature data, the order of the ratios of the bone volume to the surrounding tissue volume from large to small is WR>MA≈FP>FD≈UA. Together with the experimental results, we infer that a larger bone-tissue volume ratio could result in a larger oscillometric MBP reading. Since the applied cuff pressure are supposed to be less effectively absorbed by the soft-tissue surrounding a larger rigid bone, it is more difficult to occlude the arteries buried in the pressure-absorbing tissue at a bonier site by the inflatable cuffs, which leads to a higher measured MBP than the real MBP. In conclusion, it is promising to develop the finger oscillometric BP monitors to be worn on the finger distal phalanx which have a compact size and provide consistent measurement results with the UA measurements.