The Occlusion plethysmography examines the flow of blood in the veins. It is supposed to detect venous circulatory disorders. The measurement method is usually risk-free with the exception of a special form of thrombosis, phlegmasia coerulea dolens.
What is occlusive plethysmography?
The occlusion plethysmography is 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. The leg circumference depends on the volume of the veins.
Strain gauges are used for the measurement. Mercury strain gauges based on the strain gauge method are most widely used. These determine the increase in volume of the lower leg, while a tourniquet is tightened on the thigh. The occlusion plethysmography is also called Vein occlusive plethysmography designated. With venous occlusion plethysmography, blood flow measurements can be carried out on both the arterial and venous systems.
The measurement determines the resting blood flow, the reactive hyperemia, the venous capacity, the venous outflow of the blood and the capillary filtration. An occlusive plethysmography is performed if there is a suspicion of a venous outflow disorder caused by a thrombosis or if the therapy is to be accompanied by measurements after a thrombosis.
Function, effect & goals
The measuring principle in occlusion plethysmography is based on determining the circumference and change in circumference at the point to be measured. The measurement is usually taken on the calf, foot or toe. While a tourniquet is placed around the thigh, the venous blood flow stops.
The arterial blood flow continues. This congestion of the venous blood makes the lower leg swell. The mercury strain gauges register the volume changes during this time. They correspond to the arterial blood flow and are known as 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 measuring points on the lower leg decreases again. These changes in volume determine the reactive hyperemia. The values of the resting blood flow measurements and the reactive hyperemia allow a distinction to be made between arterial occlusive disorders and venous outflow disorders.
The venous outflow disorder characterizes the patency of the vascular system. Conclusions can also be drawn about the severity of the circulatory disorder. The worse the blood flow, the lower the maximum peak flow and the later it occurs. With other measuring arrangements, the blood pressure can be determined on any part of the limb. The cuff above the measuring point is inflated to over-systolic pressure and the pressure is then slowly released. The first registered increase in volume corresponds to the arterial systolic blood pressure at the measuring point. During occlusion plethysmography, the patient lies down.
First, the legs are raised three minutes before the examination. Then the tourniquet is placed around the thigh. The blood builds up for several minutes. After opening the cuff, the strain gauge measures the change in volume at the measuring points on the lower leg. The data is displayed graphically using a computer program. The doctor can use the data to assess the blood flow situation. The venous capacity and the venous outflow are important parameters for assessing the venous system. The venous capacity characterizes the accumulative vein volume and the venous outflow the maximum passive venous outflow per unit of time.
At the same time, the resting arterial blood flow is also determined, because the venous capacity is dependent on it. The measurement is very meaningful with regard to the good reproducibility of the quantitative assessment of a venous outflow disorder. The method can therefore be used for therapy control. These parameters can be used to determine and assess thromboses, post-thrombotic conditions and pronounced varicose veins. The occlusion plethysmography procedure is carried out according to strictly standardized criteria. This is necessary because numerous possible errors can arise during the measurement.
Risks, side effects & dangers
With the exception of Phlegmasia coerulea dolens, occlusive plethysmography hardly carries any risks. Phlegmasia coerulea dolens is a rare, particularly severe form of venous thrombosis.
All veins of a section are closed, so that the outflow disturbance causes the tissue pressure to rise so much that the arterial supply also comes to a standstill. This condition is an emergency situation that must be treated immediately. A thrombectomy must be performed immediately to save the patient's life. Obviously, occlusive plethysmography cannot be performed in this situation. It would even be counterproductive. Otherwise the process is risk-free. However, a strictly standardized implementation of the procedure is necessary in order to rule out errors.
There are many possible errors. A room temperature that is too high or too low already influences the result. Clamping clothing should be avoided. Positioning errors falsify the result. In the case of pronounced edema, the change in volume can no longer be correctly determined. Tissue changes can influence the result. In the case of advanced arterial occlusive disease caused by arteriovenous fistulas, the venous capacity is no longer optimally displayed. The disease should be included in the assessment of venous outflow disorders. Another possibility of error is excessive pressure on the sensor against the tissue.
The same applies to the incorrect installation of the measuring probe. Furthermore, the tourniquet must not be too narrow, as this will concentrate the pressure on a small area. Another source of error is the delayed deflation at the end of the accumulation period. When documenting the results, deviations from the applicable standardized test conditions should be indicated on the curve. Despite certain limiting influencing factors, occlusion plethysmography is a good measurement method for determining circulatory disorders.
