Chapter 20 - Vascular lab - arterial physiologic Flashcards
Transmitting frequency of pocket doppler
5-10 MHz
Tip of the probe of a doppler
Piezoelectric crystal - converts electrical energy into ultrasound waves - detects reflected ultrasound waves
Impedance mismatch in duplex
Difference in density causing significant reflection of ultrasound waves - prevent further tissue penetration
Doppler equation
ABOVE FIGURE 20.1 delta f = frequency shift V = blood velocity f0 = transmitted frequency theta = angle between velocity and path of beam C = velocity of sound through blood
Loudness/amplitude is proportional to
Volume of RBC
Earliest change at site of stenosis on doppler waveform
Widening of waveform (spectral broadening) in early diastole
Name of the analysis to turn frequency into picture
Fourier analysis
Indirect measures of waveform from doppler
Peak to peak pulsatility index = (Vmax - Vmin) / Vmean
Frequency most sensitive to stenosis
Higher frequency components decrease in systolic pressure more sensitive
What type of energy loss is caused by turbulence
Kinetic energy loss
When does turbulence occur
Reynold number > 2500 Re = Vd/viscosity V = velocity d = diameter vessel
ABI measurement interpretation
> 1.3 = noncompressible 1-1.29 = normal 0.91-0.99 = borderline (equivocal) 0.41-0.9 = mild to moderate PAD 0-0.4 = severe PAD
Percentage higher pressure in normal ankle compared to arm
10%
Causes of normal person to have higher pressure in ankle
1) increased intraluminal pressure from gravity 2) thickened arterial wall and stiffness
Sen and SPE of ABI to detect PAD PPV/NPV
Sen 80-95% Spe 95-100% ppv and npv 90%
How does automated BP cuff work
Detects oscillations of pressure caused by changes in volume in extremity
Using oscillometry to detect ankle pressure
Overestimate pressure when there is moderate disease and cannot detect severe disease
Positive test for popliteal entrapment
ABI change > 0.5 with dorsi or plantar flexion flattening of plethysmography
Ankle pressure in relation to height difference from right atrium to cuff
0.74 x increase with every cm
cuff bladder length requirements to be used
length 80% of circumference width 40% of circumference
Signs of a falsely elevated ABI
1) quality of doppler waveform 2) nonpalpable pulse when one expected 3) clinical picture does not fit 4) doppler diminish with ankle elevation
Typical segmental systolic arterial pressure
TABLE 20.1
Profundapopliteal collateral index (PPCI) interpretation
Difference between above knee and below knee pressure divided by above knee low index = good collateral < 0.25 = good result from profundaplasty > 0.5 = no improvement with profundaplasty alone
Normal toe pressure
20-40 mmHg less than ankle pressure TBI > 0.7 normal
Exercise test protocol
1) super 20 min 2) ABI measured 3) walk 2 mile/ehr on treadmill at 12 degree for 5 min 4) note time of symp, nature and time until stop 5) lie down and remeasure ABI q2min for 10 min
Cut off for potential benefit of revascularization in mmHg drop from exercise test
20 mmHg
Why is exercise not good for detecting infra popliteal disease
Sural branches to gastrocnemius come off proximally
Reactive hyperemia
Occlusion of blood flow to extremity by tourniquet with BP cuff x 3-5 min Release and monitor ankle pressure q2-3min for 6 min Normal = returns to half within seconds then doubles compared to baseline PAD = half of resting value delayed; does not go above baseline drops like in exercise but comes back faster - less oxygen debt
Which penile artery is for erectile function
Cavernosal artery proximal occlusion responsible for vasculogenic impotence
Penile-brachial index for normal erectile function
0.75-0.8 < 0.6 = diagnostic vasculogenic impotence
Brachial-penil pressure gradient thats normal
20-40 > 60 is arterial insufficiency
Plethysmography
Measurement of change in volume of extremity caused by cyclic nature of arterial inflow
Impedance plethysmography
Monitors electrical impedance = inversely proportional to volume
Air plethysmography
monitors pressure in cuff placed around extremity and inflated to 65 mmhg
Pulse volume recording normal appearance
1) rapid upslope 2) sharp systolic peak 3) dicrotic notch 4) downslope bows towards baseline
Definition of pulse volume recorder categories at different levels
TABLE 20.2
Photo plethysmography how it works
1) infrared light into tissue 2) detector for backscattered light 3) corresponds to variation of blood volume over time
Pulse reappearance time after release of arterial occlusion based on location of lesion
TABLE 20.3
Reactive hyperemia is a good test for what
Predicting response to sympathectomy since it requires sympathetic tone
Other way to test if sympathetic innervation is intact
Decrease in pulse volume in response to a deep breath
Transcutaneous oxygen tension key points
1) TcPO2 2) electrode at dorsal foot, AM aspect calf below and above patella, supraclavicular chest as reference 3) requires O2 sat to drop 80% before detection
Factors affecting TcPO2
1) temperature 2) sympathetic tone 3) cellulitis 4) hyperkeratosis 5) obesity 6) edema 7) metabolic activity 8) oxygen diffusion through tissue 9) oxyhemoglobin curve 10) increased venous pressure 11) vertical position of site of measurement relative to heart 12) age
Cut off for wound healing in TcPO2
> 40 mmHg same for skin pressure pressure
Laser doppler key points
1) monochromatic light to detect RBC 2) depth 1.5 mm from skin
