Assessment of pulse transit/arrival time as noninvasive blood pressure predictors in finger and earlobe sites

Development of wearable medical devices to measure noninvasive blood pressure (NIBP) has recently been evolving at finger/wrist and earlobe locations. The study investigates the predictive power of pulse transit time (PTT) and pulse arrival time (PAT) measured at finger and earlobe sites for BP measurement during two unique physiological interventions: handgrip test (HGT) and modified Valsalva test (mVT). Single-lead electrocardiogram, impedance cardiogram, infrared photoplethysmogram (PPG) from finger and earlobe, and CNAP® NIBP were simultaneously acquired in 14 heathy subjects (39±11 years); beat-to-beat BP, PAT and PTT were extracted; linear regression, correlation and statistical analyses were carried out. The results show that both the BP interventions caused significant increase (P<;0.05) in diastolic blood pressure (DBP), but concurrent significant decrease (P<;0.01) in PTT was observed only during mVT in both finger and earlobe sites. On the other hand, PAT did not change significantly during both the BP interventions. PTT showed highest correlation (R2) of 0.47±0.26 and negative regression slope of - 0.39±0.31 with DBP in finger during mVT compared to earlobe. Thus, the predictive power of PTT for NIBP monitoring vary broadly in distinct BP regulation mechanisms, and found to be moderate in finger site and relatively weak in earlobe site.