Chapter 8: Plethysmography (UE and LE) Flashcards
purpose of plethysmography
in combination with doppler segmental pressures it helps differentiate true claudication from non vascular sources
plethysmography can
detect presence or absence of arterial disease while defining its functional aspects
plethysmography helps to
localize the level of obstruction
assess follow-up treamenet
PPG is mainly used for
eval of digits and penile vessels
limitations of plethysmography
not specific to one vessels
tracing reflects all arterial flow beneath cuff
cannot tell major arteries vs collateral branches
limited due to body habitus
plethysmography patient positioning
patient supine limbs in resting position
pt can also be sitting for eval of upper limb digits
Volume air plethysmography
measurement of volume change
volume air plethysmography technique
pneumatic cuffs placed around specific levels of extremities or digits
a measured amount of air is inflated into cuff ranging from 10 to 65mmHg depending on cuff size
volume air plethysmography how does it work
as arterial flow moves under the cuff, volume changes in the limb segment occur
these changes re converted to pulsatile pressure changes within the air-filled cuff
how are results gathered with volume air plethysmography
a pressure transducer converts the pressure changes into analog waveforms and display on strip-chart recorder
chart paper speed
25mm/sec
during diastole
fixed amount of air pressure in cuff
during systole
air pressure in cuff increases as arteries expand
Photo-phlethysmography (PPG) consists of
transducer, amplifier, strip chart recorder (paper speed 25 mm/sec)
PPG detects
cutaneous blood flow rather than truly measuring volume change
photocell in PPG consists of
light emitting diode and photo sensor
PPG diode
transmits infrared light into subcutaneous tissue with backscattered light reflected back to the adjacent photo sensor
the cutaneous flow in PPG deteremines
the amount of reflection
the PPG the blood attentuates
light in proportion to its content in tissue
increased blood flow results in
increased attenuation
decreases reflection
this is displayed as positive upstroke waveform
volume plethysmography technique
pt supine
heels slightly elevated on cushion
use 3 or 4 cuff method penumatic cuffs applied snugly to thigh calf and ankle bilaterally
machine performs self calibration when activated
bilat brach pressures obtained during segmental pressure exam
start at upper extremity and move distally
record at least 3 pulse cycles
volume plethysmography air pressures are
predetermined
volume plethysmography artifacts
not uncommon due to improper cuff application
gain should be kept
similar throughout the study
if different setting is used note it on recording paper
both PPF and volume plethysmography are evaluated usuing
qualitative criteria described by DE strandness and J Raines
PPG results: normal
fairly rapid upslope, sharp systolic peak with reflective wave
PPG results: mildly abnormal
sharp peak
absent reflected wave
downslope is bowed away from baseline
PPG results: moderately abnormal
flattened systolic peak upslope and downslope more delayed reflected wave (notch) absent
PPG results: severely abnormal
low amplitude or may be absent
abnormal waveforms during PPG reflect
hemodynamically significant disease proximal to level of tracing
reduced amplitude with no changes i the contour of wave is likely to reflect
insignificant disease unless its unilateral
a fair waveform with abnormal segmental pressures means
collaterals which underestimate significance of obstruction
if you 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 PPG
pt must remain still, tremors make it impossible
if you’re not getting a tracing
check exam mode, paper, and connection points
Displacement plethymography
any change in volume of the enclosed part will displace an equal amount of water
Displacement plethymography : displacement is measured by
the height of the water in the chimney
Displacement plethymography :volume change is measured by
spirometer
Pulse plethysmography refers to
transient changes in limb volume related to the pulse by pulse activity of left ventricle; the body part expands when arterial inflow exceeds venous outflow
