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 noninvasive 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.