Chapter 22 - Vascular lab - venous physiologic

Question 1

Ambulatory venous pressure

Answer 1

Venous pressure in dorsal foot vein after execution of 10 tiptoe maneuvers in standing position gold standard for venous hemodynamics

Question 2

Techniques for measuring ambulatory venous pressure

Answer 2

1) catheter/butterfly needle placed in dorsal pedal vein 2) connect pressure transducer 3) baseline standing pedal venous pressure recorded 4) perform 10 tiptoe maneuvers at 1/sec to empty calf veins 5) return to standing position 6) pressure recorded defined as AVP 7) refill measured as time required to return 90% of venosu pressure after cessation of calf contraction

Question 3

Interpretation of ambulatory venous pressure measurements

Answer 3

1) failure of pressure to fall with exercise = calf pump defective 2) AVP returns too quickly = reflux of veins 3) pressure rise rather than fall = deep vein occlusion

Question 4

Plethysmography types

Answer 4

1) strain-gauge plethysmography 2) impedance plethysmography 3) photoplethysmography 4) air plethysmography

Question 5

Techniques for all plethysmography steps

Answer 5

1) patient supine with leg elevated 20-30 degrees 2) heel supported to enable venous drainage 3) knee flexed 10-20 degrees to prevent obstruction of popliteal vein outflow 4) plethysmographic sensor applied 5) thigh occlusion cuff inflated 50-60 mmHg 6) cuff released rapidly

Question 6

Plethysmography Venous volume and venous outflow

Answer 6

Venous volume = rise in recording to plateau during cuff inflation Venous outflow = fall in recording after rapid deflation

Question 7

Strain-gauge plethysmography

Answer 7

Change in calf volume stretches a mercury-filled silastic conductor tube with proportional change in its resistance = results in corresponding change in voltage output signal

Question 8

Impedance plethysmography

Answer 8

Measure changes in electrical resistance in tissue of extremity in response to change in volume two electrodes on calf and voltage output used to derive resistance thigh occlusion cuff inflated then rapidly deflated to estimate venous outflow use for diagnosis of acute DVT

Question 9

Photoplethysmography key concept steps

Answer 9

Tranducer that emits infrared light from light-emitting diode into dermis - HGB absorbs light and is the most abundant chromophore in skin 1) sit with legs hanging 2) transducer to leg 3) 5 consecutive ankle flexion/extension 4) tracing drops as calf empty the veins 5) time to recover to 90% of baseline is called venous refill time (VRT)

Question 10

Photoplethysmography interpretation

Answer 10

Normal venous refill time > 20 s < 20 s is significant venous reflux

Question 11

Typical outflow fraction tracing from air plethysmography

Answer 11

FIGURE 22.5

Question 12

Important indices with air plethysmography

Answer 12

1) venous filling index = defines rate of increase in volume ons tanding - measures mean filling rate of the dependent leg and is slow in normal limbs 2) ejection fraction = percentage of volume removed from leg with one calf contraction 3) residual volume fraction = residual volume expressed as percentage of baseline volume of leg

Question 13

Prevalence of the sequelae of venous disease in relation to venous filling index

Answer 13

TABLE 22.1

Question 14

Interpretation of EF, RVF and AVP

Answer 14

EF + RVF = efficacy of calf muscle to pump blood out of leg Lower RVF = better calf pump function normal RVF < 35%

Question 15

Outflow fraction on air plethysmography

Answer 15

Divide 1 second venous outflow by venous volume Outflow fraction > 38% is normal 30-38% = partial venous outflow obstruction < 30% severe obstruction

Question 16

Prediction of VFI on venous ulcers recurrence

Answer 16

VFI > 4 ml/s = increase risk of recurrence each 1 ml/s higher = increase recurrence by 17%

Question 17

Limitations of plethysmography in certain patients

Answer 17

CEAP 5-6 reduced ankle ROM Change in EF and RVF may be due to intrinsic dysfunction of calf pump pt inability to activate pump cuff limitation in obese patients