Which characteristic best describes a normal photoplethysmography (PPG) waveform?

• A. Absent dicrotic notch
• B. Rounded systolic peaks with low amplitude
• C. Very low amplitude
• D. Readily visible dicrotic notch, sharp systolic upstroke

Answer: (D)

Photoplethysmography reflects how blood volume in the microvasculature changes with each heartbeat. A normal waveform has a rapid, sharp systolic upstroke as arterial volume increases during contraction, reaching a distinct peak. After the peak, you see the dicrotic notch—an inflection caused by the brief backflow and the closure of the aortic valve—which signals normal arterial dynamics. This combination of a sharp upstroke and a readily visible dicrotic notch is typical of well-perfused, compliant peripheral arteries. If the waveform were damped with a rounded, low-amplitude peak or lacked the notch, it would suggest poor contact, low perfusion, or vascular damping. Therefore, a readily visible dicrotic notch with a sharp systolic upstroke best describes a normal PPG waveform.