Comparison of noninvasive pulse transit time estimates as markers of blood pressure using invasive pulse transit time measurements as a reference

Pulse transit time (PTT) measured as the time delay between invasive proximal and distal blood pressure (BP) or flow waveforms (invasive PTT [I-PTT]) tightly correlates with BP. PTT estimated as the time delay between non-invasive proximal and distal arterial waveforms could therefore permit cuff-less BP monitoring. A popular noninvasive PTT estimate for this application is the time delay between ECG and photoplethysmography (PPG) waveforms (pulse arrival time [PAT]). Another estimate is the time delay between proximal and distal PPG waveforms (PPG-PTT). PAT and PPG-PTT were assessed as markers of BP over a wide physiologic range using I-PTT as a reference. Waveforms for determining I-PTT, PAT, and PPG-PTT through central arteries were measured from swine during baseline conditions and infusions of various hemodynamic drugs. Diastolic, mean, and systolic BP varied widely in each subject (group average (mean +/- SE) standard deviation between 25 +/- 2 and 36 +/- 2 mmHg). I-PTT correlated well with all BP levels (group average R-2 values between 0.86 +/- 0.03 and 0.91 +/- 0.03). PPG-PTT also correlated well with all BP levels (group average R-2 values between 0.81 +/- 0.03 and 0.85 +/- 0.02), and its R-2 values were not significantly different from those of I-PTT. PAT correlated best with systolic BP (group average R-2 value of 0.70 +/- 0.04), but its R-2 values for all BP levels were significantly lower than those of I-PTT (P < 0.005) and PPG-PTT (P < 0.02). The pre-ejection period component of PAT was responsible for its inferior correlation with BP. In sum, PPG-PTT was not different from I-PTT and superior to the popular PAT as a marker of BP.