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 .