What does PPG mainly evaluate?

PhotoPlethysmography (PPG) is primarily used to evaluate the blood flow in the peripheral vascular system, particularly focusing on the small vessels found in the digits (fingers and toes) and the penile vessels. This non-invasive technique measures changes in volume within blood vessels, which can indicate variations in blood flow and vascular health.

In the context of digits, PPG helps assess conditions like peripheral artery disease or Raynaud's phenomenon, which affect blood supply to the extremities. Similarly, when evaluating penile vessels, it can be important in diagnosing erectile dysfunction or other vascular-related issues. The sensitivity of PPG to small changes in blood volume makes it especially useful for these specific areas of the body.

Other options are less relevant to the primary application of PPG. Upper limb vascularity could be assessed but is not the main focus; cardiac output typically involves more extensive measurements such as echocardiography or impedance cardiography, and respiratory function is evaluated through pulmonary function tests rather than vascular assessments.