The changes in pulse transit time at specific cuff pressures during inflation and deflation.

The changes in pulse transit time (PTT) during the continuous slow deflation of brachial cuff were early reported; however, the PTTs obtained for specific cuff pressures during inflation or deflation have not been compared before. Therefore, the objective of this study is to examine the differences in PTT when cuff pressure (P(cuff)) was raised or deflated to the desired level. Sixteen subjects participated in this study and according to their systolic blood pressure (SBP) and diastolic blood pressure (DBF), 8 levels of P(cuff) were predetermined for them individually. P(cuff) was directly raised to each predetermined level while 20 seconds of electrocardiographic and photoplethysmographic signals were recorded for the calculation of PTT. Another set of recordings were taken when P(cuff) was raised above the SBP and deflated to the predetermined levels. The results of this study showed that PTT increase significantly when P(cuff) was larger than 80% of DBF, regardless of whether P(cuff) was reached by inflation or deflation. Overall, no significant difference was found between PTT obtained during inflation and deflation for 12 out of the 16 subjects. To conclude, changes in PTT are mainly induced by the level of cuff pressure when there is no prolonged period of artery occlusion.