1. Vascular Technology Lecture 25: Venous Photoplethysmography (PPG) HHHoldorf

2. Photo-Plethysmography
Capabilities:
To document venous insufficiency / quantitate venous reflux in patients with chronic swelling, venous ulcers, and or varicose veins

4. Limitations: Patient Positioning
Contraindicated in acute deep vein thrombosis
Improper placement of PPG senor results in inaccurate information, e.g., over a varicose vein
Thickening of skin may prevent adequate penetration of infrared light
Intact skin required for sensor placement
Patient Positioning
Seated with legs dangling, i.e., non-weight bearing

5. Physical Principles Plethysmography measures volume changes
PPG not true plethysmography, but can determine changes in blood content of skin (microcirculation), which reflects intravenous volume
Photocell consists of light emitting diode and photo-sensor

6. PPG Physical Principles cont…
Diode transmits infrared light into subcutaneous tissues, which is reflected back to photo-sensor. Light is not absorbed
The cutaneous blood flow determines the reflection
Blood attenuates light in proportion to its content in tissue. Increased blood flow results in increased attenuation which decreases this reflection. However, that is displayed as a positive upstroke of the waveform.

7. Electrical coupling Method to increase gain and display signal
Only two types available: DC and AC
Allows one type of current to pass and blocks other type

8. DC Coupling Direct current
Electric voltage that is either positive or negative
Current flows in only one direction
Batteries are DC
Detects slower changes in blood content
Used for venous studies

9. AC Coupling Alternating current
Electric voltage that reverses polarity (positive or negative) 60 times a second
Current flows in both directions
Wall plugs deliver 120 volts of AC
Detects fast changes in blood content
Used for arterial studies

10. Calibration
Cannot be calibrated volumetrically as with venous plethysmography (APG)
Important to maintain the same ‘size’ or ‘gain’ setting throughout the study
Significant difference in tracing should mean a significant difference in blood volume

11. Display: tiny arterial pulsations usually evident; superimposed on tracing of venous flow

12. Technique
Sensor applied to lower leg, approximately 5 – 10 centimeters above medial malleolus (must not be over a varicosity)
Strip chart recorder
Running at slow speed (usually 5 mm/sec)
Stylus records on heat sensitive paper
Patient instructed to complete series of exaggerated dorsiflexions to empty calf veins.
Manual compressions of calf can be performed: must be done bilaterally to ensure consistency

13. Technique continued…
Tracing continues to be obtained after dorsiflexions or manual compressions to record venous refill time and or venous reactive time (VRT)
If the VRT is <20 seconds, repeat after TOURNIQUET applied to eliminate influence of superficial system

14. Venous blood runs from Superficial to Deep

15. Interpretation - Quantitative
Normal VRT: > 20 seconds without tourniquet
Superficial system incompetence: VRT of < 20 seconds without tourniquet but normalizes , i.e., > 20 seconds with tourniquet
Deep system incompetence: VRT of <20 seconds with and without tourniquet application

16. Normal VRT > 20 seconds without tourniquet

17. Superficial System incompetence: VRT of < 20 seconds without tourniquet but normalizes, i. e., > 20 seconds with tourniquet

18. NOTE:
X Axis = time
Y Axis = Volume change
Deep system incompetence: VRT of < 20 seconds with and without tourniquet application

19. Trouble - Shooting
Artifact from patient movement? Study technically impossible
Absent deflections or grossly irregular tracings? Ensure equipment on DC mode (not AC) and or on PPG setting (not Doppler)
Deflections off-the-scale or barely discernible? Adjust gain and or sensitivity and or size setting.

20. Homework Textbook: SDMS Assignments
Chapter 27: Venous Photoplethysmography
Pages: 293 – 296
SDMS Assignments