Pulse Transit Time as an Indicator of Changes in Systemic Blood Pressure and Cardiac Output
Published on: 2018-12-27
Introduction: Pulse transit time (PuTT) is the interval between R-wave on electrocardiogram (ECG) and upstroke on peripheral arterial blood pressure (BP) waveform or pulse plethysmographic waveform. It has been suggested that changes in PuTT reflect changes in arterial BP and cardiac output (CO). The study tested the hypothesis that changes in PuTT reflect CO changes in anesthetized ventilated surgical patients. Materials and Methods: Surgical patients monitored with direct BP and non-invasive cardiac outputs were included in study. Patients with hypotension and normal CO were treated by phenylephrine (phenylephrine group, n= 41). Patients who required volume loading received bolus of colloid solution (volume loading group, n=22). Arterial and plethysmographic PuTT changes were compared with stroke volume index (SVI) and BP changes. Results: Although systolic BP increased in both groups, it increased to a greater extent following phenylephrine therapy. SVI increased following volume loading but did not change after phenylephrine administration. Arterial and plethysmographic PuTTs shortened in both groups following treatment. There was a weak but significant correlation between arterial PuTT changes and systolic BP changes (β = – 0.314; P = 0.006) and SVI (β = – 0.289; P = 0.01) as well as between plethysmographic PuTT changes and systolic BP changes (β = -0.374; P = 0.001). Correlation between changes of plethysmographic PuTT and SVI was non-significant. Conclusion: Low correlation coefficients demonstrate that PuTT changes do not correlate closely with changes either in BP or in CO. As such, we therefore conclude that PuTT changes do not reflect changes in CO or BP, and PuTT is not applicable for estimation of CO or BP changes in anesthetized ventilated patients.