PHYSICAL PRINCIPLES:

-laser Doppler uses optical (light) waves, and because of their relatively short wavelength they do not remain coherent for distances longer than a fraction of a millimeter in tissue

-low-power beam of light is delivered tot he skin through a fiber-optic cable; a volume of tissue which includes both moving red cells and stationary tissue cells in illuminated

-photons (light energy) are immediately scattered in random directions by both cell types ; photons scattered by moving RBCs are Doppler shifted in frequency; photons scattered by stationary cells are not

-portion of scattered laser light is collected by a receiving optical fiber and returned to a photodetector; photodetector converts this optical signal into an electronic signal that is processed to determine microvascular blood volume

TECHNIQUE:

-patient supine

-place extremity comfortably; movement can alter exam results dramatically so get a good position

-obtain brachial BP bilaterally

-determine test sites

-prepare skin surface with alcohol wipe prior to cuff and laser placement 

*Sample Protocol:

1. appropriate laser Doppler cuff is selected

2. PV waveform is obtained (toe cuff is inflated to 40mmHg; all other cuffs are inflated to 65mmHg); if result is abnormal it may not be possible to perform the remainder of the exam

3. skin perfusion pressure (SPP) mode is activated; cuff is inflated to 100mmHg

4. pressure is help for 10 seconds while the examiner watches for the volume indicator to drop below 0.1%; if it does not the transducer is inflated another 20mmHg and examiner waits 10 seconds

5. the process is repeated if the volume indicator had not dropped to 0.1%; if necessary elevate to approximately 60 degrees above horizontal and is held there until the volume drops to below 0.1%; once less than 0.1% SPP is obtained

6. cuff is slowly deflated using the bleed valve (10mmHg every 5 seconds

*Obtain the patient's SPP:

1. ideally you'll see a steady baseline which is followed by a doubling or more of the graph's pressure scale; this indicated patient's actual pressure; watch for artifact (patient movement) that can cause SPP level to be read too soon

2. actual SPP is confirmed by increasing size change of the bar on the scale during the deflation process

INTERPRETATION:

-Normal: PV waveform is graded similarly to the way the photoplethysmographic (PPG) waveforms are graded for the digital exam

-SPP > 40 mmHg indicates likely to heal

-SPP of 30-40 mmHg suggests marginal for healing

-Abnormal: PV waveform may be dampened or diminished 

-SPP of < 30 mmHg indicates less likely to heal

***Chapter 8: Penile Pressures and Waveforms-- Duplex/Color Flow Imaging Evaluation***

CAPABILITIES AND LIMITATIONS:

Capabilities:

-helps determine whether an individual's failure to attain or maintain a sufficient erection is related to peripheral vascular insufficiency

-combined with ergometry test may indicate pelvic steal, arterial vasospasm, or ipsilateral arterial occlusive disease

Limitations:

-only duplex and color flow imaging provide data about arterial and/or venous flow qualities and describe some anatomic pathologic conditions

-if a patient is sensitive to injectable medication or is receiving anticoagulation therapy, he may be unable to undergo the injection component

PHYSICAL PRINCIPLES:

*each of the following techniques can be used to obtain pressures and waveforms but only one would be selected for the nonimaging protocol

-CW Doppler: 8-10 MHz probe used to obtain waveforms and pressures

-volume plethysmography

-photoplethysmography (PPG): used most often

-Duplex scanning: includes B-mode imaging and Doppler spectral analysis with or without color flow imaging, often utilized before and after the injection of a medication such as papaverine and or prostaglandin

NONIMAGING TECHNIQUE AND INTERPRETATION:

Technique:

-supine, head on pillow, appropriate draping to maintain privacy

-BP cuffs placed on upper arms, ankles, and proximal shaft of penis; penile cuff sizes are 2.5x12.5cm or 2.5x9cm

-calculate ABI 

-obtain penile pressures with one of the following end-point detectors: PPG, pulse volume plethysmography, CW Doppler (obtain from two or three sites since there are nonimaging aka blind techniques)

-plethysmographic waveforms are obtained as necessary, utilizing one of the techniques mentioned above; Doppler waveforms rarely obtained

Interpretation: 

-use higher brachial pressure to calculate penile/brachial index (PBI)

    *Normal PBI: >/= 0.75

    *Marginal: 0.65-0.74

    *Abnormal: <0.65 (consistent with vasculogenic impotence)

-PBI < 0.65 considered abnormal in a young adult male with normal sexual response

-plethysmographic waveforms evaluated

    *Normal: sharp, systolic peak with prominent dicrotic wave; contour is qualitatively evaluated; emphasis on dicrotic wave is important since its presence usually excludes significant arterial disease

    *Mildly Abnormal: sharp peak, absent dicrotic wave, downslope bowed away from baseline

    *Moderately Abnormal: flattened systolic peak, upslope and downslope time increased and nearly equal, dicrotic wave absent

    *Severely Abnormal: pulse wave has low amplitude or may be absent; equal upslope or downslope time

IMAGING TECHNIQUE AND INTERPRETATION:

Technique:

-get informed consent; use 7 or 10 MHz transducer and light probe pressure

-supine with head on pillow and appropriate draping to maintain privacy

-before injection: measure cavernous arteries AP bilaterally; measure peak systolic velocities bilaterally in cavernous arteries and sometimes dorsal

-urologist injects vasodilator in lateral aspect of proximal shaft to induce erection

-repeat measurements after injection

    *peak systolic and end diastolic obtained from proximal cavernous arteries before full erection is achieved

    *deep dorsal vein flow velocity measure from dorsal approach with light probe pressure

    *sagittal and transverse approaches are used to evaluate vasculature

    *measure dimensions of cavernous arteries in AP transverse during systole

    *examiner monitor time elapsed since injection and documents when velocities are recorded

-instruct about priapism; if rigid erection is maintained for a period of 3 hours after injection, the patient is instructed to contact his urologist 

Interpretation:

-pre injection (aka pre-erection): BF in penile arteries has high-resistance quality

-post injection: BF assumes lower-resistance quality until full erection is obtained

-peak systolic velocities increase after injection

    *Normal >30cm/sec

    *Marginal: 25-29cm/sec

    *Reduced: <25cm/sec

-end diastolic velocities increase as well

-post injection, deep dorsal venous flow velocities should not increase

    *Normal: <3cm/sec

    *Moderately increased: 10-20cm/sec

    *Markedly increased: >20cm/sec

-increase to >4cm/sec may indicate a venous leak which could contribute to the erectile dysfunction

-diameter of cavernous arteries normally increases (as a result of dilation) after injection, changing previously high resistance flow to continuous, steady, low-resistance flow

VARICOCELE:

-enlargement of veins of the spermatic cord

-occurs most often in young men and adolescents; more common on left side

-B-mode imaging with 7 or 10 MHz probe

-color flow is beneficial

-Valsalva helps to document flow direction; reverse flow during Valsalva is diagnostic of varicocele

***Chapter 9: Plethysmography-- Upper and Lower Extremities***

CAPABILITIES AND LIMITATIONS:

Capabilities:

-helps differentiate true arterial claudication from nonvascular sources 

-helps document functional aspects of vascular disease

-detects presence/absence of arterial disease

-helps localize level of obstruction

-assessed results of medical and/or exercise therapy

-enhances overall accuracy when used in combination with Doppler segmental pressures

-photoplethysmography most often used to evaluate the digits and penile vasculature

Limitations:

-can't be specific to a single vessel because it measures volume changes in a large segment of a limb

-may be difficult to discriminate between major arteries and collateral branches

-obesity makes it difficult

PHYSICAL PRINCIPLES:

Volume Plethysmography:

-aka pneumo- and true plethysmography

-terms to describe are pulse volume recording, volume pulse recording, pulse contour recording

-air sequentially introduced to cup to to pressures ranging 40 to 65 mmHg

-arterial flow peaks are systolic increases in limb volume putting pressure against cuff; as arterial flow moves under cuff through arteries, branches, small vessels, and collateral branches there is a momentary increase in limb segment volume occur during systole

-pressure transducer converts pulsatile pressure changes into arterial waveforms

-more BF under cuff the greater the waveform excursion is; decrease in flow under cuff due to obstructive disease changes waveform appearance

Photoplethysmography (PPG):

-transducer, amplifier, strip-chart recorder

-detects cutaneous BF and records pulsations rather than volume changes

-sends infrared light into underlying tissue with a light-emitting diode; adjacent photodetector receives reflected backscattered infrared light and measures this reflection of light

-as light is directed into skin, tissue and blood in cutaneous vessels attenuate a portion of it; PPG uses infrared light as sensor because measurements made in infrared range have a constant but minimal attenuation

TECHNIQUE:

Volume Plethysmography:

-patient supine with heels slightly elevated 

-pneumatic cuffs placed at thigh, calf, and ankle bilaterally

-when machine is activated it self-calibrates

-brachial pressures obtained

-inflate cuffs, at least 3 pulse cycles recorded at each level

-similarly gain setting maintained; if gain setting is different, the setting must be recorded; if paper is used then the chart recording speed is set to 25mm/sec

-doppler segmental pressures obtained as previously described; volume pulse plethysmography and pressures are complementary procedures

Photoplethysmography (PPG):

-cover skin completely with PPG device and ensure proper adherence with double stick tape or velcro

-most often applied to evaluation of digital arterial disease

Troubleshooting:

-Problem: recorder stylus cannot be centered

    *Action: confirm that the machine is in the right mode

-Problem: recorder stylus is stuck at the bottom or top of the recording device (machine is in correct mode)

    *Action: activate re-set control to center the stylus

-Problem: acceptable waveform cannot be recorded (because of too much stylus movement)

    *Action: reattach the PPG is necessary; patient may have tremors and be unable to hold still

-Problem: there is no tracing at all

    *Action: ascertain that the correct mode has been selected, that the correct study has been identified, and that the proper recording method has been chosen

INTERPRETATION:

Volume Plethysmography:

-Normal: sharp systolic peak with prominent dicrotic wave

-Mildly abnormal: sharp peak, absent dicrotic reflective wave; downslope is bowed away from baseline

-Moderately abnormal: flattened systolic peak, upslope and downslope time decreased and nearly equal, absent dicrotic wave

-Severely abnormal: absent or low-amplitude pulse wave with equal upslope and downslope time

*qualitative criteria for PPG are similar to those previously listed above for volume plethysmography

***Chapter 10: Digital Pressures and Plethysmography***

CAPABILITIES AND LIMITATIONS:

Capabilities:

-helps detect presence of arterial disease

-differentiates fixed arterial obstruction from vasospasm

-assesses effects of treatment

Limitations:

-vasoconstriction greatly affects the quality of the results

-cuffs too tight can obliterate or diminish the pulse waveforms with volume plethysmography

-with PPG a photocell that is incorrectly applied to the skin will cause both artifact and poor results

-presence of ulcerations and/or gangrene may present placement of the cuff or photocell

-extensive bandages that cannot be removed make the placement of the cuffs or photocells impossible

-chronic moderate to severe arterial insufficiency often have very dry skin and/or hypertrophic skin, making good contact between the PPG photocell and skin difficult

PHYSICAL PRINCIPLES:

-refer to chapter 9 physical principles

TECHNIQUE:

Technique for Toes:

-digit cuff is at the base of the toe

-photocell is securely attached with double-stick tape tot he underside of the distal portion of the great toe

-pulse is recorded with slow recording speed

-while pulsations are being recorded, inflate cuff to suprasystolic pressure (about 20-30mmHg higher than the ankle pressure), at which point there should be no pulsations

-increase in tow volume (rise from A to B) is secondary to venous outflow obstruction; plethysmography measure all volume changes

-slowly deflate the cuff, watch for return of the first pulsation; once this pulsation is observed the pressure level at which it occurred is recorded at the toe pressure

-elevation of the recording pen after point C is likely related to a sudden slight movement of the toe and is therefore consider artifactual; look for the first small pulsation that is followed by pulsations of greater amplitude as the cuff continues to deflate

Technique for Fingers:

*Without Cold Stress*

-brachial and forearm pressures measured to rule out any proximal disease

-obtain Doppler signals of palmar arch to verify patency; palmar arch is normally supplied by radial and ulnar arteries

-two cuffs are can be applied to obtain two levels of volume plethysmographic waveforms

-pressures obtained with volume or PPG methods; same as for toes

*With Cold Stress*

-after resting study feet or hands are immersed in ice-cold water for 3 minutes or to the patient's tolerance

-towel-dry skin and obtain waveforms immediately after and 5 minutes after cold stress

-if one side has more significant disease the post-cold stress information is obtained from that side first

INTERPRETATION:

*Normal:

    -sharp upstroke during peak systole

    -prolonged downstroke with dicrotic notch approximately halfway down

    -amplitude usually greater in the fingers than in toe tracings

*Abnormal obstructive waveform quality:

    -seen with functional (intermittent) obstructive disease

    -occlusion located anywhere proximally to the end of the digit causes the pulse to assume an obstructive pattern; slow upslope to a rounded peak and a downslope that bows away from the baseline

*Abnormal peaked waveform quality:

    -upslope slower than normal

    -sharp, anacrotic notch present

    -dicrotic notch located high on the downslope

*Systolic pressure measurements:

    -finger/brachial indices of about 0.8-0.9 characterize normal digits

    -normal toes have pressures that range from 60 to 80% of the brachial pressure; significantly less signify digital arterial occlusive disease; high ankle pressures from arterial calcinosis usually negates a toe/ankle pressure index

***Transcutaneous Oximetry***

CAPABILITIES AND LIMITATIONS:

Capabilities:

-helps determine wound healing and amputation level

-reflects tissue oxygen tension, which depends on the balance between oxygen supply and consumption

Limitations:

-difficulty keeping the electrode flat on skin

-inability to place the electrode on skin that is not intact or is edematous

-inability of a patient to lie quietly for as long as 20 minutes

-technologist dependent

-findings can be difficult to interpret

PHYSICAL PRINCIPLES:

-reflects tissue partial pressure and oxygen, which depends on a balance between oxygen consumption and oxygen supply

-electrode houses heating element that heats skin to 44-45 degrees Celsius increasing BF and melting a lipid layer in the fatty tissue; since oxygen pressure on skin surface is near zero the vasodilation increases this value by increases blood flow to the capillaries which raises oxygen content and provides for the diffusion of oxygen to the surface where it can be measured

-sensor in electrode measures how much oxygen comes through the skin

TECHNIQUE:

Standard Technique:

-self adhesive molded plastic fixation ring applied to intact clean skin

-few drops of electrolyte solution put in ring

-electrode/sensor gently turned securely into the fixation ring; important that the electrode be as flat as possible against the skin so that the electrolyte solution covers the skin inside the fixation ring

-after required manual calibration, PO2 readings noted within 15 to 20 minutes of stabilization 

-obtain reference reading first, usually left upper chest then obtaining readings at other specific sites

-electrode applied near wound or at anticipated level of ambulation to determine healing potential

-sensor should not be placed on edematous skin, ulcers, areas of cellulitis or skin that is close to the bone

Technique with Oxygen Challenge:

-apply electrodes to chest for reference site and to skin site of interest

-oxygen administered by face mask

-PO2 values are obtained as described above

INTERPRETATION:

-Normal PtcO2 on the foot: >50mmHg; may increase somewhat from distal to proximal

-Poor PtcO2: <40mmHg; tissue hypoxia which prevents or impairs wound healing

-Critical limb ischemia (CLI) PtcO2 (rest pain, ulcer, gangrene): <30mmHg and more often <20mmHg