Functional tests of the lower extremities

Measurement of arterial pressure at the ankle at rest to detect arterial insufficiency of the lower extremities is a sufficient test in many clinical observations. A major problem is presented by patients with complaints of intermittent claudication with normal or borderline values at rest. In such cases, it is necessary to study peripheral hemodynamics under load, or so-called stress test, which is based on the effect of vasodilation in response to physical exertion, post-occlusive hypoxia or the use of pharmacological agents, in particular, nitroglycerin.

The value of stress tests is determined by the ability to detect hemodynamically significant arterial lesions that are not detectable at rest and to assess the functional state of the blood circulation in the extremities.

The effect of the stress test is best demonstrated by analyzing measurements in a patient with one healthy limb and the other limb affected by the occlusive process. Arterial blood flow in the healthy leg is determined by the resistance of the outflow vessels (terminal arteries, arterioles, capillaries, and venous bed); in the affected limb, blood flow is determined, along with the resistance of the outflow bed, by the resistance in the proximal parts at the level of the stenosis. At rest, both limbs have the same basal blood flow to maintain the exchange in muscle, skin, and bone. On the affected side, the effect of proximal resistance is compensated by moderate vasodilation so that blood flow becomes comparable to that on the normal side. However, the stenosis causes turbulence with loss of kinetic energy and leads to a decrease in distal pressure.

During exercise, the increasing metabolic demands lead to marked dilation of muscular arterioles and an increase in arterial blood flow. On the healthy side, it can increase by 5 times compared to the baseline level. In the affected limb, the increase in blood flow is limited by the proximal resistance at the level of stenosis. When the metabolic demands of the working muscles are not met by the limited arterial blood flow, symptoms of claudication develop. In addition, there is a further drop in arterial pressure at the level of arterial stenosis, since the resistance there increases with increasing blood flow velocity. This drop in pressure is measured as a drop in systolic pressure at the ankle. The degree of its decrease and the duration of its recovery are closely related to the severity of arterial insufficiency.

The simplest form of stress testing involves walking up and down stairs until symptoms of claudication occur and the palpable resting pulse disappears; the "pulseless" phenomenon indicates the presence of arterial occlusive disease.

In clinical practice, two types of loads are widely used as stress tests: dosed walking on a treadmill (treadmill test) and a test of flexion and extension of the lower limb.

Treadmill test. The treadmill is installed next to a couch on which the patient can lie down after the test. The treadmill is inclined at an angle of 12°, and the speed is about 3 km/h. The test lasts until signs of claudication appear or 5 minutes if they are absent. After the load is completed, the ankle segmental systolic pressure is measured every 30 seconds for the first 4 minutes and then every minute until the initial data are restored. The test is assessed by three indicators:

1. load duration;
2. maximum drop in ankle pressure index;
3. the time required to return to the original level.

Recovery usually occurs within 10 minutes. However, in severe cases of ischemia, it can last 20-30 minutes.

Limb flexion and extension test. The subject, lying on his back, performs full flexion and extension of the lower limb at the knee joint (30 times per minute) or maximum dorsiflexion and extension of the foot (60 times per minute) separately for each limb at 10-15 minute intervals. The exercises are continued until the patient is forced to stop them due to pain in the limb. If clinical symptoms of ischemia do not occur within 3 minutes, the test is considered normal and stopped. The test is assessed by the same indicators as in the treadmill test.

At the same time, when performing stress tests, it is necessary to have ECG monitoring, special equipment and trained personnel to provide assistance in cases of acute cardiac dysfunction. In addition, the use of the test is limited by a number of general and local factors: neurological disorders, absence of one limb, severe limb ischemia, etc. Stress tests are also not without subjectivity in assessing the maximum walking time, which significantly complicates their standardization.

Post-occlusion reactive hyperemia (POHR) is a common and alternative to the load "stress" test - it causes changes similar to post-load ones. Being equivalent to physical exercise, POHR has an undeniable advantage over it, as it is an objective, easily reproducible test that does not have the above limitations. In addition, POHR allows you to assess the state of blood circulation in each limb separately, does not require much time and can be performed in the early postoperative period.

Like exercise tests, PORG allows the presence of hemodynamically significant lesions that are not evident during resting examination to be established and helps in early diagnosis of the disease, making this test mandatory in patients with suspected occlusive disease.

PORG can be used in two ways.

Option I. Pneumatic cuffs are applied to the shoulder, the upper third of the thigh and the lower third of the shin at the ankle. The pressure at these levels is measured using the previously described method. Then, a pressure exceeding the initial pressure for this level by 40-50 mm Hg is applied to the thigh cuff for 4 minutes. After decompression of the thigh cuff, the pressure at the ankle is measured and the pressure index is calculated after 30, 60 seconds and then every minute for 9 minutes. The reaction of the vessels of the healthy limb is manifested in an insignificant drop in ankle pressure relative to the initial pressure and its rapid (within 1 minute) restoration.

Changes in monofocal stenosis are more pronounced. Proximal monofocal occlusion leads to more pronounced changes compared to distal. The most pronounced changes occur in patients with lesions in all three segments of the vascular system of the lower extremities and reach extreme degrees when GBA is involved in the process.

Option II. Reactive hyperemia is obtained similarly to Option I. Before the procedure, the average blood flow velocity in the OBA is recorded at rest. After decompression, the average blood flow velocity in the OBA is continuously recorded until the amplitude values of the velocity return to the pre-occlusion level. The Dopplerogram obtained during the test is assessed by two parameters:

• by the relative increase (6V) of the average speed during hyperemia in relation to rest (in percent);
• by the time interval during which the average blood flow velocity returns to 50% of its peak value ( _T 1/2 _index ).

The nitroglycerin test is used as one of the main tests of pharmacological vasodilation in order to improve the detection of blood flow in the distal sections of the leg arteries. The patency of the distal sections of the lower limb vessels is one of the factors determining the success of reconstructive surgery. On radiocontrast angiograms, especially with the most commonly used translumbar method, the arteries of the leg and foot are poorly visualized, due to which the role of ultrasound Doppler imaging increases in assessing the distal bed. The main issue is the differential diagnosis of anatomical damage and functional hemodynamic insufficiency of peripheral vessels. The latter is associated with the fact that damage to the proximal sections of the vascular system (especially multisegmental, with poorly developed collateral blood flow) and the occurrence of vasospastic reactions, in particular, Kholodov's, lead to insufficient perfusion of unaffected distal vessels. The location of vessels during ultrasound Doppler imaging becomes impossible, since the blood flow parameters decrease to values that are beyond the resolution of the method (BFV < 1 cm/s, SVD (10-15 mm Hg). In such cases, a vasodilation test (warming of the limb, pharmacological agents) may be indicated, when an increase in peripheral blood flow is achieved by reducing peripheral resistance.

Pharmacological vasodilation with nitroglycerin (1 tablet sublingually) is often used in patients with varying degrees of ischemia with blood flow localization (before taking nitroglycerin and 1-3 minutes after taking it) in the ZBBA and ATS.

The frequency of arterial localization progressively decreases depending on the degree of limb ischemia. Nitroglycerin administration increases the frequency of arterial localization regardless of the degree of ischemia.

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