Fig. 3

A Time to the trough of the pulse wave originally measured as a fraction of the cardiac cycle and converted to seconds by multiplication by the cardiac cycle time. The harmonic regression wave fit of three consecutive cardiac cycles is shown at 3 horizontal points along the venous wall nasal, central, and temporal at two locations proximal (A) and distal (B) to the optic disc spanning the visible pulsatile segment distance spatially calibrated to a vertical disc diameter of 1.65 mm was 0.34 mm. Pulse transit time was calculated by subtracting the time to trough of the harmonic regression wave at the proximal (T\(_{\text {a}}\)=0.334377) and distal point (T\(_{\text {b}}\)=0.349660) along the vessel, each computed from the average of T\(_{\text {A1-3}}\) and T\(_{\text {B1-3}}\) respectively, located on the nasal, central and temporal vein wall. Pulse Transit Time = 0.349660 - 0.334377 = 0.015283 s. Pulse wave velocity = Distance / Pulse Transit Time = 0.34/0.015283 \(\approx\) 22.24694 mm/s. B Schematic of the time to trough measured as the distance between the pulse oximetry audio and the foot of the pulse wave at two points along the path of pulse wave propagation