Chapter 27 - Venous photoplethysmography

Question 1

Physical principles of venous photoplethysmography

Answer 1

1) must be in contact with intact skin
2) uses DC coupling for venous studies
3) blood attenuates light in proportion to its content in tissue (higher blood flow, increased attenuation)

Question 2

Technique of venous photoplethysmography

Answer 2

1) seated with leg dangling
2) PPG sensor 5-10cm above medial malleolus not over varicosity
3) serious of exaggerated dorsiflexion to empty veins
4) Record venous refill time (venous reactive time VRT)
5) repeat with tourniquet (50 mmHg) above knee and again below knee

Question 3

Interpretation of venous PPG

Answer 3

VRT > 20 sec without tourniquet = normal
VRT < 20s but > 20s when tourniquet above knee = GSV reflux
VRT < 20s but > 20s when tourniquet below knee = SSV reflux
VRT < 20s regardless of tourniquet = deep vein reflux