Occlusive plethysmography examines blood flow in the veins. In doing so, it is intended to detect venous circulatory disorders. The measurement method is usually risk-free with the exception of a particular form of thrombosis, phlegmasia coerulea dolens.
What is occlusion plethysmography?
Occlusive plethysmography examines blood flow in the veins. In doing so, it is designed to detect venous circulatory problems. Closure plethysmography refers to a measurement method that allows the calculation of blood flow in veins and arteries. The inflow and outflow of blood is assessed by measuring the change in leg circumference. Leg circumference depends on the volume of veins. Strain gauges are used in the measurement. The most widespread are mercury strain gauges using the strain-gauge method. These determine the increase in volume of the lower leg, while a tourniquet is tightened on the thigh. Occlusion plethysmography is also known as venous occlusion plethysmography. Venous occlusion plethysmography can be used to measure blood flow in both the arterial and venous systems. The measurement determines resting blood flow, reactive hyperemia, venous capacitance, venous outflow of blood, and capillary filtration. Occlusive plethysmography is performed when venous outflow obstruction is suspected, for example, due to thrombosis, or when therapy after thrombosis is to be accompanied by measurement.
Function, effect, and goals
The measurement principle in occlusion plethysmography is based on the determination of circumference and circumferential change at the site to be measured. The measurement is usually taken at the calf, foot, or toe. While a tourniquet is applied around the thigh, venous blood outflow stops. The arterial blood flow remains. This venous blood outflow stasis causes the lower leg to swell. The mercury strain gauges register the volume changes during this time. They correspond to arterial blood flow and are called resting blood flow measurements. After about three minutes, the tourniquet on the thigh is released. The venous blood can flow out again. The volume at the measurement sites of the lower leg decreases again. These volume changes determine the reactive hyperemia. The values of the resting blood flow measurements and the reactive hyperemia allow arterial occlusion disorders and venous outflow disorders to be distinguished. Venous outflow obstruction characterizes the patency of the vascular system. Conclusions can also be drawn about the severity of the circulatory disturbance. The poorer the blood flow, the lower the maximum peak flow and the later it occurs. Other measurement setups can be used to determine blood pressure at any limb segment. This involves inflating the tourniquet above the measurement site to supra-systolic pressure and then slowly releasing the pressure. The first recorded increase in volume corresponds to the arterial systolic blood pressure at the measurement site. During occlusion plethysmography, the patient lies down. First, the legs are elevated three minutes before the examination. Then the tourniquet is placed around the thigh. The blood accumulates for several minutes. After the cuff is opened, the strain gauge measures the change in volume at the measurement points on the lower leg. A computer program graphically displays the data. Based on the data, the physician can assess the blood flow situation. Venous capacity and venous outflow are important parameters for assessing the venous system. The venous capacity characterizes the venous volume that can be accumulated and the venous outflow characterizes the maximum passive venous outflow per unit of time. At the same time, the resting arterial blood flow is also determined, because venous capacity depends on it. The measurement is very informative with regard to the good reproducibility of the quantitative assessment of a venous outflow disorder. Therefore, the method can be used for therapy control. By means of these parameters, thrombosis, postthrombotic conditions and pronounced varicosis can be determined and assessed. The procedure of occlusion plethysmography is performed according to strictly standardized aspects. This is necessary because numerous possibilities for error can arise during the measurement procedure.
Risks, side effects and dangers
With the exception of the condition phlegmasia coerulea dolens, occlusive plethysmography involves few risks. Phlegmasia coerulea dolens is a rare particularly severe form of venous thrombosis. All the veins in a section are occluded, so that the outflow obstruction causes the tissue pressure to increase to such an extent that the arterial supply also comes to a standstill. This condition represents an emergency situation that must be treated immediately. Thrombectomy must be performed immediately to save the patient’s life. In this situation, of course, occlusive plethysmography cannot be performed. In fact, it would be counterproductive. Otherwise, the procedure is risk-free. However, a strictly standardized performance of the procedure is necessary to exclude errors. The possibilities for error are manifold. Even a room temperature that is too high or too low influences the result. Constrictive clothing should be avoided. Storage errors falsify the result. In the case of pronounced edema, the change in volume can no longer be determined correctly. Tissue changes can influence the result. In advanced arterial occlusive disease due to arteriovenous fistulas, venous capacity is no longer optimally displayed. Disease should be included in the assessment of venous outflow obstruction. A possibility of error is also too much pressure of the probe against the tissue. The same applies to incorrect placement of the probe. Furthermore, the tourniquet must not be too narrow, as this concentrates the pressure on a small area. Delayed deflation at the end of the accumulation time also represents a further source of error. When documenting the results, deviations from the applicable standardized test conditions should definitely be indicated on the curve. Despite certain limiting influencing factors, occlusion plethysmography is a good measurement technique for detecting circulatory disturbances.
