What You Should Know About Using NIV Studies

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When NIV Studies Are Warranted

Atherosclerosis is the major cause of poor arterial flow in the foot. It decreases flow by narrowing or occluding the arterial lumen. In patients with diabetes, you’ll see occlusion in the distal bifurcation points. However, in non-diabetic patients, you’ll most often see the occlusion at proximal points.1 It is important that we are able to recognize the presence and severity of disease. Symptoms of claudication and ischemic rest pain are important warning signs that suggest the need to order NIV studies.

In addition to ordering NIVs for those with atherosclerosis, you should also order NIV studies for patients who have:
• diabetes;
• claudication;
• signs of critical ischemia, skin changes or gangrene;
• absent or diminished pedal pulses; or
• femoral bruits.

Then there’s the question of which NIV study is best for the given clinical situation. Here are some key points to keep in mind.
• The ABI/TBI/PPG have been shown to be closely associated with arterial physiology for vascular evaluation of the distal foot.
• Segmental pressure measurements and exercise testing can give you reliable information on iliac and femoral popliteal occlusive disease.
• Employing TCOM helps to determine the severity of lower extremity arterial occlusive disease and ascertain the greatest likelihood of healing ulcers or success in digital amputations.
• Dopplers are an excellent adjunctive modality in finding the exact location of stenosis/occlusion and when ABI and segmental pressures are inconclusive.

It’s also essential to pay close attention to the testing environment. Be aware of things like ambient temperature, the patient’s state of relaxation and limb positioning.

Understanding the limitations of these NIV studies is necessary for applying the results to clinical situations.

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NIV is a valuable tool in screening for peripheral arterial disease. The cost of NIV studies is substantially less in comparison to arteriography.
18
Author(s): 
By Dana Giacalone, DPM, and Khurram Khan, DPM

Getting The Lowdown On Pulse Volume Recordings And Doppler Waveforms
You can obtain the PVR by placing cuffs around the toe, midfoot, ankle, BK, AK and upper thigh. The cuffs filled to 60-65mmHg and the resulting recording reflects blood that pulses beneath a sensor cuff and produces a waveform reflective of arterial pulse. This closely corresponds to direct intra-arterial recordings at that level. The flatter the curve, the slower the flow, the less the volume.
Analyze the results for changes between segments and for differences between the contralateral limb. A normal PVR will show fast flow, dicrotic notching and a “teepee” appearance of the waveform. The absence of dicrotic notching occurs with an increase in proximal resistance that you will see when there is less than 50 percent stenosis or good collateral flow. Greater than 70 percent stenosis or low collateral flow gives an “igloo” appearance of the waveform or an oscillatory or flat line in the case of complete occlusion. In this instance, tissue necrosis is likely.
When evaluating waveforms in a limb without pathology, you will see a rapid systolic upstroke and usually a peaked appearance. The magnitude of the waveform can be affected by several factors and one should not attempt to make comparisons in the peak height. The reverse segment represents distal resistance, followed by elastic recoil of the vessel wall, which you may not see in a normal patient at the ankle level. You will see deterioration of the waveform just proximal to a lesion and it is always abnormal distal to the lesion. As flow deteriorates, waveforms become flattened and then undulating before they totally disappear. Be aware flow may exist despite absent waveforms because Doppler probes rarely detect flow at less than 6 mL/min. It is for this reason that comparing pressures with waveforms helps to avoid errors in interpretation.5
Physicians will often perform a Doppler evaluation or get an ultrasound of the lower extremity following an abnormal evaluation in cases of known arterial occlusive disease or arterial injury. The goal of the exam is to provide the location, number and severity of arterial lesions.
The frequency of the emitted beam is altered by any object moving faster than 6cm/second, such as blood flow in a vessel. The sound beam is reflected from red blood cells and the signal is used to measure segmental systolic pressure and produce flow velocity waveform patterns for analysis. The faster the blood flow, the steeper the recorded waveform and the louder the pitch.2,4,5
The results are read as triphasic, biphasic or monophasic. You can use peak systolic velocity and waveform analysis to quantify and localize the disease. You may hear two distinct sounds with the first being forward flow and the second being backward flow. Normal arteries may produce three sounds. In organic occlusive disease, the intima is disrupted, the lumen is narrowed and the vessel is calcified. This results in blood flowing slower and backward flow being damped out. The pitch will be lower and you’ll only hear one sound (i.e. monophasic).
Hoffman stated when performing elective cases like bunion surgery, it is important to do a Doppler evaluation of the deep plantar and digital arteries of the first and second toes in patients with suspected arterial insufficiency.4 This is especially important when you are dealing with diabetes patients who might have occlusive disease distal to the ankle.

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