Pulse transit time, or PTT, is the time it takes a pulse pressure wave to propagate through the length of the arterial tree. The pulse pressure wave starts with the ejection of blood from the left ventricle and the PTT is estimated by subtracting the ECG R-wave peak time, which corresponds with the contraction of the left ventricle, from the time it takes the pulse pressure wave to arrive at the most distal aspect of the arterial tree. Traditionally, the distal arrival of the pulse wave is measured by photoplethysmography at the tip of the finger.
Noxturnal uses the ECG signal trace and the pleth signal trace recorded on the finger by the Nonin 3150 Oximeter to calculate PTT values. By subtracting the ECG R-wave peak time (point a in Figure 1) from the distal pleth pulse wave arrival time at the finger (point c in Figure 1) the PTT is measured. Of note, the arrival time of the pulse wave is associated with the 50% peak value of the maximum pleth pulse wave (point c in Figure 1).
Figure 1: Superimposed ECG and Pleth tracings
R-top on EKG
Pleth nadir for a single pulse
Timepoint where a pleth signal pulse has reached 50% of its peak value
|Pleth maximum for a single pulse
The ptt duration for measurement point a to c (50%)
The PTT value for each pleth signal pulse may be derived in Noxturnal after the recording has been downloaded. The PTT value is displayed in a sample and hold format where the pulse transit time is constant between each measured pleth signal pulse (see Figure 2).
Figure 2. Noxturnal display of PTT
In order to calculate the PTT signal as described above you will need Noxturnal 5.1.0 – 19071 or newer. Firmware versions supporting PTT calculations, include:
Nox T3/T3s - 184.108.40.20608 or higher
Nox A1/A1s - Any FW.
For further questions or concerns please contact us at email@example.com
NOX-PTT in Noxturnal-KBARTICLE-001-REV2