Apg Measurement; Apg Defined - Vetland V1410 User Manual

V1410 / V1412 User Manual

36. APG Measurement

APG Defined

The plethysmogram waveform represents pulsatile peripheral blood flow, which reflects both
peripheral and central hemodynamics. Photoplethysmography (PPG) uses infrared light transmitted
through the skin to non-invasively measure hemodynamic parameters. Photoplethysmography is
thus a useful measure of vascular dysfunction and heart rate variability.
Digital photoplethysmography uses infrared light transmitted through a well diffused body part such
as tongue or ear to measure arterial pressure noninvasively, continuously, and in real time. Digital
volume pulse (DVP), an output of digital photoplethysmography, estimates pulse wave velocity
(PWV), which in turn reflects aortic stiffness and blood pressure.
Pulse transit time (PTT) is defined as the interval between the electrocardiogram (ECG) R wave and
the foot of the PPG wave, or the elapsed time of a pulse wave between two arterial sites; altered
PTT is an indirect indicator of various hemodynamic pathologies associated with aging, hypertension,
cardiovascular disease, and diabetes mellitus.
Accelerated plethysmography (APG) uses the second derivative of the photoplethysmograph
(SDPTG), which allows more detailed analysis of the primary plethysmogram. SDPTG consists of
four systolic waves (the "a" or early positive wave, "b" or early negative wave, "c" or late reincreasing
wave, and "d" or late redecreasing wave) and one diastolic wave ("e" or early positive wave). Wave
analyses are generally made using the ratios of waves b-e to the a-wave (b/a, c/a, d/a, and e/a).
Commercially available photoplethysmographs can continuously record arterial pressure, through a
well diffused body part such as tongue or ear, to 0.25kPa accuracy compared to direct (albeit
invasive) intra-arterial recordings.
APG Measurement
1
2
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To view the APG waveform, press the
Menu button one time and select
SpO2  APG  APG ON.
The APG waveform on the right is
described below:
a: Differential Rising Index
e
b: Pressure Descent Index
c: Reflex Rising Index
d: Elastic Descent Index
e: Early Positive Wave