Effects of external pressure on arteries distal to the cuff during sphygmomanometry

The aim of this study was to examine the effect on distal arteries of external pressure, applied by upper arm sphygmomanometer cuff. Photoplethysmographic (PPG) signals were measured on the index fingers of 44 healthy male subjects, during the slow decrease of cuff air pressure. For each pulse the ratio of PPG amplitude to its baseline (AM/BL) and its time delay (ΔTD) relative to the contralateral hand were determined as a function of cuff pressure. At cuff pressures equal to systolic blood pressure, pulses reappeared with the pulse time delay in the cuffed arm significantly greater than in the noncuffed arm, with (ΔTD)(mean±SD)150±31 ms (p<0.001). At cuff pressures equal to diastolic blood pressure (81±12 mmHg),ΔTD was 42±19 ms (p<0.001), and at 50 mmHg, which is below diastolic blood pressure, (ΔTD) was still significantly positive at 6±9 ms (p<0.001). AM/BL relative to its initial value rose at cuff pressures between systolic and diastolic blood pressure, then deceased to 0.6±0.41 (p<0.001) at diastolic blood pressure and 0.54±0.24 (p<0.001) at 50 mmHg. The changes in (ΔTD) and AM/BL can be interpreted as originating from changes in the compliance of conduit arteries and small arteries with cuff inflation and deflation.