What You Should Know About Using NIV Studies

By Dana Giacalone, DPM, and Khurram Khan, DPM
There is discrepancy with this value as Hoffman suggests 30mmHg and Pellerito suggests 20mmHg.2,4 These values can be misleading if collateral flow is so extensive that a 20-30 mmHg drop does not occur or in a situation in which there are non-compressible vessels due to calcification.1,4,5 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. When Should You Emphasize TCOM? TCOM is indicated in wound evaluation, hyperbaric oxygen therapy, plastic surgery and vascular surgery.

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