Fig. 22.1
Picture of a prototype internally calibrated pulse volume recorder (PVR). This system is controlled by a computer. The operator interfaces with the unit via a touch screen. The system also has a dedicated printer and modem for report generation
The ability to record and store data is most important to document testing for both reimbursement and certification purposes. The new PVR systems include patient interface ports (i.e., for PVR cuffs and Doppler probes), color monitor, touch screen, and color printer. Studies may be performed in a dedicated laboratory or at the patient’s bedside. It should be acknowledged that when earlier systems were making the transition from non-PC-based to PC-based units, the PC units were slow, difficult even for experienced operators to use, and inflexible. With time, technician input, and fast processors, this has changed, and the new systems are both rapid and flexible.
In our view, the major advantages of current systems over earlier PVR systems are accuracy of calibration, clarity and rapid development of data reporting, and rapid storage and transmission.
The primary purpose of performing any level of vascular laboratory testing is to provide the referring physician with information that will improve patient management. If a rapid, accurate, complete, and understandable report is not generated, this is not possible. New PVR systems provide a protocol-like format for general testing, compile the data in a logical sequence and provide guidelines for interpretation.
We compared the time taken to perform a lower extremity arterial study using a standard PVR with that using a PC-based PVR. Evaluation time was divided into three components: (1) time to obtain and record demographics, clinical history, and pulse and bruit grading; (2) time to perform ten PVR arterial tracings and six segmental limb pressures; and (3) time to prepare a final report excluding interpretation. In obtaining background information for the standard PVR, the technician recorded the data on a preprinted form that became part of the final report. The technician entered background information for the PC-based PVR directly into the system via a touch screen. Testing was performed using standard protocols for each system and included PVR tracings at the thigh, calf, ankle, metatarsal (TM), and first digital levels bilaterally and limb systolic pressures bilaterally by Doppler technique at the thigh, calf, and ankle levels. Using the standard PVR, the technician had to cut three cardiac cycles from the PVR strip charts, and using tape affix them to the final report. For the PC-based system, the technician electronically selects cycles for reporting and printing. This latter area is where the PC-based system is clearly faster (Table 22.1).
Table 22.1
Time taken to perform lower extremity arterial study using a standard PVR and a PC-based PVR
Component | Standard PVR (min) | PC-based PVR (min) |
|---|---|---|
Background | 11 | 11 |
Testing | 18 | 20 |
Report | 10 | 4 |
Total (n = 10) | 39 | 35 |
PVR vascular technicians not familiar with the PC-based systems require approximately 3 h of formal training to perform the testing and an additional 10 h of use to obtain the skills to perform the testing to the same degree of speed and confidence obtained by experienced workers.
Indications and Guidelines for Functional Lower Extremity Arterial Studies
Diagnostic technique and therapeutic methods for peripheral vascular disease have changed significantly since the development of the PVR. However, the questions posed to the vascular laboratory by referring physicians have not changed. These include the following:
1.
Is resting ischemia present?
2.
Is current perfusion adequate for lesion healing?
3.
Will a particular amputation site heal properly?
4.
Is vascular claudication present?
Further, for all of the above questions, there is an associated interest in describing as accurately as possible the anatomic location of hemodynamically significant lesions. However, it should be carefully noted that while these are the important questions in over 90% of patients referred to a vascular laboratory for lower extremity occlusion, these questions cannot be answered by knowing the anatomy.
These are purely questions of function. Later, we will discuss questions primarily of anatomy.
Before proceeding, it is helpful to describe the patient population presenting to our vascular laboratory. We have carefully reviewed our patient demographics and, when possible, have compared our figures with those of other vascular laboratories; in most cases, the numbers have been very similar. The average age of our patients is 67 years. Two-thirds are male. Over 75% are current or past cigarette smokers. Approximately 40% have a history of hypertension, and 25% are diabetic. Approximately 20% have elevated blood lipids, and 20–25% are obese by routing criteria. In our series, one-third have had a previous myocardial infarction, and one-tenth (9%) have a history of previous cerebrovascular accident.
Is Resting Ischemia Present?
Patients with rest pain as their initial presentation maybe either diabetic or nondiabetic; however, nondiabetics are more frequent in this category as will be described. Excluding patients presenting with an acute history, the majority of the remaining patients will have a history of vascular claudication. Their description of pain will also almost exclusively be limited to the forefoot. The pain will develop at rest and will transiently be relieved by dangling the foot. This temporarily decreases the local peripheral resistance, increasing local blood flow. Although ischemic pain may present more proximally, more proximal resting pain in the absence of forefoot pain is often not of vascular origin. Since ischemia is a clear indication for surgical reconstruction, its diagnosis must be made with accuracy.
In making this judgment, the following four parameters, in the limb of interest, must be obtained carefully with a PVR at the correct pneumatic gain settings:
PVR amplitude and contour at the ankle level
PVR amplitude and contour at the transmetatarsal level
PVR amplitude and contour at the first digit or most symptomatic digit
Ankle Pressure
If the ankle pressure is <40 mmHg in the nondiabetic patient and <60 mmHg in the diabetic patient, resting ischemia may be present. The difference in criteria is based on the fact that diabetics often have medial calcinosis which artificially elevates distal pressures. It should also be stated that in 10–15% of diabetic cases, distal pressures cannot be measured at all due to medial calcinosis; in these cases, PVR recordings are the only measurements available.
The diagnosis is secured on the basis of the amplitude of the PVR tracings. If a digit of interest has a flatline PVR amplitude, ischemia is very probable. The probability is further increased if the TM and ankle PVR tracings are also flatline or near flatline. It is not hemodynamically possible to have a flatline tracing proximal to a nonflatline tracing. If this occurs, the operator should look for a technical error in the testing. In the ischemic setting, all tracings should be markedly blunted with no reflected wave present in diastole.
It is possible to have transient borderline ischemia with digital amplitudes as high as 2 mm; however, this is rare.
Is Current Perfusion Adequate for Lesion Healing?
Ischemic arterial lesions are almost always present at the digit or near digit levels. More proximal foot lesions (i.e., TM level or heel) are most often secondary to a degree of ischemia and chronic trauma (pressure ulceration). In this class of patients, the initial presenters include a higher percentage of diabetics than in the rest pain group. This is due to the clinically recognized fact that diabetic patients are more prone to develop traumatic lesions due to neuropathic loss of sensation and combined large and small vessel involvement [5].
As in the rest pain case, in making this judgment, the following four parameters in the limb of interest must be obtained carefully with a PVR at the correct pneumatic gain settings:
PVR amplitude and contour at the ankle level
PVR amplitude and contour at the TM level
PVR amplitude and contour at the first digit or most symptomatic digit
Ankle Pressure
Hemodynamics tells us that local perfusion is a function of mean arterial pressure (MAP), mean venous pressure (MVP), and size and number of perfusion vessels. We use systolic pressure as a surrogate for MAP, MVP in a supine subject is near 0 mmHg, and PVR amplitude can be shown to be an adequate surrogate for size and number of perfusing vessels. Table 22.2 is a helpful guideline in determining whether a lesion will heal with the current level of perfusion in the absence of infection, chronic trauma, and microvessel diabetic disease. These stipulations are significant and require a degree of clinical judgment.
Table 22.2
Guidelines for determining whether current perfusion is adequate for healing
Nondiabetic | Diabetic | |
|---|---|---|
Ankle pressure (mmHg) | ≥60 | ≥70 |
PVR amplitude in digit of interest (mm) | ≥1 | ≥2 |
Will a Particular Amputation Site Heal Primarily?
There is a sizable group of patients with advanced arteriosclerotic peripheral vascular disease in whom arterial reconstruction is not possible and who come to amputation. Significant morbidity and mortality rates are present in these patients, particularly in those in whom a more distal amputation fails and who require a second procedure. Measurements in a vascular laboratory with a PVR are helpful in reducing this complication by predicting which amputation site is most likely to heal primarily.
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