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 (/spl Delta/TD) 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 (/spl Delta/TD)(mean/spl plusmn/SD)150/spl plusmn/31 ms (p<0.001). At cuff pressures equal to diastolic blood pressure (81/spl plusmn/12 mmHg),/spl Delta/TD was 42/spl plusmn/19 ms (p<0.001), and at 50 mmHg, which is below diastolic blood pressure, (/spl Delta/TD) was still significantly positive at 6/spl plusmn/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/spl plusmn/0.41 (p<0.001) at diastolic blood pressure and 0.54/spl plusmn/0.24 (p<0.001) at 50 mmHg. The changes in (/spl Delta/TD) and AM/BL can be interpreted as originating from changes in the compliance of conduit arteries and small arteries with cuff inflation and deflation.