Diagnostic Medical Sonography Program Vascular Technology Lecture 8. Plethysmography of the Upper Extremity and the Lower Extremity Holdorf

A plethysmograph is an instrument for measuring changes in volume within an organ or whole body, usually resulting from fluctuations in the amount of blood or air it contains.

Plethysmography (UE, LE) Capabilities In combination with Doppler segmental pressures, helps differentiate true claudication from non-Vascular sources Detect presence/absence of arterial disease while defining its functional aspects Help localize the level of obstruction Assessment of follow-up treatment PPC mainly used fro evaluation of digits and penile vessels

Limitations Cannot be specific to one vessel. Tracing reflects all arterial flow beneath the cuff Cannot discriminate between major arteries and collateral branches (venous influence not completely eliminated) Difficult to perform volume plethysmography on obese patients

Patient Positioning Physical Principles Most exams can be done with limbs in a resting position (patient supine). The patient can be sitting for evaluation of upper limb digits Physical Principles Volume (air) Plethysmography Measurement of volume change

Pneumatic cuffs are placed around specific levels of the extremities or digits A measured amount of air is sequentially inflated into the cuff to pressure ranging from 10 to 65 mmHg, depending on the cuff size As arterial flow moves under the cuff, momentary volume changes in the limb segment occur.

These changes beneath cuff are converted to pulsatile pressure changes within the air-filled cuff bladder A pressure transducer converts the pressure changes into analog waveforms for display on strip-chart recorder. Chart paper speed = 25 mm/sec

Air-Plethysmography

Photo-Plethysmography (PPG) Consists of transducer, amplifier, strip chart recorder (paper speed = 25mm/sec Detects continuous blood flow, rather than truly measuring volume change Photocell consists of light emitting diode and photo-sensor Diode transmits infrared light into subcutaneous tissue with back-scattered light reflected back to the adjacent photo-sensor

The continuous blood flow determines the amount of 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 on the waveform.

Photo-Plethysmography (PPG)

Technique Volume Plethysmography A. Patient supine, with heels slightly elevated on cushion B. Using a 3 or 4 cuff method, appropriately sized pneumatic cuffs applied snugly to: Thigh, calf and ankle bilaterally

C. Machine performs a self-calibration when activated D C. Machine performs a self-calibration when activated D. Bilateral brachial pressures obtained during the Doppler segmental pressure exam E. Appropriate amount of air used to bring cuff pressure to predetermined levels. Begin with upper extremity, moving distally. Record at least 3 pulse cycles F. Artifacts not uncommon due to improper cuff application G. Similar “gain” setting is maintained throughout the study. If a different setting is used, mote on the recording paper. H. Volume plethysmography and pressures are complementary

Interpretation Both Volume and photo plethysmography are evaluated using qualitative criteria, Major descriptions are: Normal: fairly rapid upslope, sharp systolic peak with reflected wave. Mildly abnormal: Sharp peak, absent reflected wave, downslope is bowed away from the baseline Moderately abnormal: Flattened systolic peak, upslope and downslope more delayed; reflected wave (notch) absent Severely abnormal: low amplitude, or may be absent

Additional notes: Abnormal waveforms always reflect hemodynamically significant disease proximal to level of tracing. Severity generally underestimated. Reduced amplitude with no changes in the contour is likely to reflect insignificant disease, unless it is unilateral

Troubleshooting Can’t center the stylus? Check the “mode”. AC mode for arterial ; DC mode for venous Stylus wandering on paper? Activate the “re-set” control; and be sure correct exam function is selected. Unable to obtain clean waveform? Reapply the PPG. Patient tremors make an exam nearly impossible. No tracing? Check the exam mode, paper, and connection points

Displacement Plethysmography Any change in volume of the enclosed part will displace an equal amount of water. Displacement is measured by the height of the water in the chimney; volume change measured by spirometer Pulse plethysmography refers to transient changes in limb volume related to eh “pulse by pulse” activity of the left ventricle: the body part expands when atrial inflow exceeds venous outflow

In the example, hand is inside a surgical rubber glove (as depicted by the dotted / dashed line). The water temperature is constant

Extra Notes Chapter 8 Plethysmography (UE, LE) Measures volume changes. Has nothing to do with Ultrasound Used for Penile and digit volumes Evaluates the circulation This is not like Doppler

Volume (Air) Plethysmography uses cuffs. Cuffs have a bladder in them. When the cuffs are dilated, they can detect the pulse of the arteries. Air Plethysmography Light is reflected back into the sensor If just a little bit of blood is reflected back, this is a good thing. Blood will absorb the light. If a lot of reflection returns to the sensor, then this is bad. Not a lot of blood is available to absorb the light.

Interpretation of Photo (PPG) and AIR Plethysmography No velocity is detected No direction of blood flow Looking for volume only

The waveform Know that a proper reflection on the down slope is a normal finding. Bowed away down slope is an abnormal finding. No reflection means that there may be collateral formation (long standing disease) With the waveforms in Plethysmography, use ABIs also. Displacement Plethysmography is old school stuff. Don’t bother.

Homework Text book Chapter 9 Pages 99 – 106 SDMS assignments