**3. Physiology and hemodynamics of the venous circulation**

men, respectively [4–6]. Because of its clinical characteristics, it restricts individual's daily activities and has great impact on physical and psychosocial status, as well as socioeconomic status [7]. There are many treatment options such as medical, pharmacological and conservative methods used in CVI. Among these, because of being invasive and causing less adverse effects than other methods, conservative approaches are commonly used to treat CVI [8]. On account of this, we aimed to give information about the conservative approaches used in the treatment of CVI in this chapter. However, due to the different structure of the venous system, to understand the effectiveness of the treatment and how it works, it is necessary to comprehend well

The venous blood flow in the lower extremity is located at three positions, which are superficial,

More than 80% of the blood flow in the lower extremity occurs through the deep veins. The deep veins accompany the arteries and run deep to the muscles and fascia [10, 11]. It includes the posterior tibial vein, anterior tibial vein, femoral vein, profunda femoris vein and common femoral vein in the leg. It also includes the popliteal vein and femoral vein in the thigh, and the external iliac vein, internal iliac vein, common iliac vein and inferior vena cava in the pelvis [12]. The major axial veins are accompanied by matching the venae comitantes in the calf. These veins that accompany the posterior tibial and peroneal veins are particularly large (up to 10 mm in diameter in male) and participate in the muscle pump mechanism for the return of blood from the legs to the heart. In addition, the medial and lateral heads of the gastrocnemius and soleus muscles include vein pairs in these muscles (the calf) that accompany the major arteries. These usually have a large diameter and participate in the calf muscle pump. The calf veins drain into the popliteal vein. Once the popliteal vein has entered the thigh, it is known as the femoral vein. The deep femoral veins which open into the femoral veins derived from the common femoral vein in the inguinal triangle drain the thigh muscles. This drains into the great saphenous vein and is the major point of the venous return in the lower extremity [12]. The superficial compartment lies between the dermis and the deep fascia [12]. Duplex scanning has resulted in recognition of a saphenous subcompartment and saphenous fascia. The vena saphena magna and vena saphena parva are intermediate superficial veins. The VSM is

These veins connect the superficial venous system to the deep venous system. There are approximately 150 perforating veins in each lower extremity and a few of them have clinical

The perforating veins are divided into direct and indirect perforating veins. While direct perforating veins provide a connection between the superficial and deep axial veins, indirect perforating veins provide blood drainage from the superficial venous system and join other

significance. The medial calf perforators are very important at this point [12].

the anatomy and pathophysiology of the venous system.

**2. Anatomy of the venous system**

the longest vein in the human body [10, 11].

veins in the muscles [13].

deep and perforating veins [9].

122 Clinical Physical Therapy

The primary function of the venous circulation is to return blood to the heart. Effective venous return requires the interaction of a central pump, a pressure gradient, a peripheral venous pump and competent venous valves [14].

Pressures on the vessels are determined by different mechanism. While pressure in arterial vessels is generated mainly by muscular contractions of the heart, the gravity is the main factor that determines the pressure in the venous system. When the body is in a horizontal resting position, pressures in the veins of the lower limb, in the chest, abdomen and arm are similar. On the other hand, when the body goes to the upright position, significant changes occur in the values of these pressures, especially in the venous system. In presence of the upright position, there is an accumulation of approximately 500 ml of blood in the lower extremities. Venous valves play a very important role in the return of blood to the heart from the lower extremities, especially in this position. Direct observation of human venous valves has been made possible by specialized ultrasound techniques [14].

One of the important tasks of the venous valves is to be released during exercise. Supporting the antegrade flow of the venous from the superficial veins to the deep during exercise is the essential part of this important task. Muscle activity through exercise creates volume and pressure changes in the venous system, especially in the calf. While there is no apparent flow in the resting position; with the beginning of the heel strike, the venous plexus under the heel and the plantar surface of the foot (Bejar's plexus) begin to empty from the foot and ankle towards the proximal end of the calf. Then, through calf contraction the blood within the deep veins on the calf is transported into the deep veins of the thigh [14].

In the upright position, the arterial blood pressure is approximately 100 mmHg and the venous pressure is 8 mmHg. The arteriovenous pressure gradient is 92 mmHg. However, this situation changes in the upright position. After 15 min of immobilization, circulating blood volume decreases up to 20% and the velocity of the blood flow decreases. In addition, effective ultrafiltration pressure exceeds effective resorption pressure due to passive hyperemia occurring in blood capillaries. As a result, the flow moves from the blood vessel system to the interstitium in the lower extremities. This situation changes during walking. The venous blood pressure falls up to 25 mmHg in the leg due to the venous leg pump which consists of the calf muscles, joints, skin, fascia and venous valves. The contraction of the calf muscles moves the blood from the subfascial veins into the heart. The venous blood pressure of 25 mmHg is considerably lower than 100 mmHg but higher than 8 mmHg. This is called as physiological ambulatory venous hypertension. However, it can be tolerated by veins under normal conditions [15].
