Lackawanna College Vascular Technology Program Venous Hemodynamics Lackawanna College Vascular Technology Program

Special Function of Veins Capable of constricting and enlarging, storing small or large quantities of blood, making blood available when necessary Venous pump Regulating cardiac output

Right Atrial Pressure Blood from all systems flows into the right atrium (Central Venous Pressure)‏ Right atrial pressure is regulated by: the ability of the heart to pump blood out of the right atrium the tendency of blood to flow from the peripheral vessels into the right atrium

Elevated Right Atrial Pressure Weakness of the heart Any effect that causes rapid inflow on blood increased blood volume increased large vessel tone dilatation of the arterioles Increased blood volume will increase venous return, overloading the right atrium. Increased large vessel tone througout the body will increase peripheral venous pressures. Dilatation of the arterioles, which decreases the peripheral resistance and allows a rapid flow of blood from the arteries to the veins.

Cardiac Output The amount of blood pumped by the heart depends on: the ability of the heart to pump the tendency of blood to flow into the heart from the peripheral vessels

Flow patterns and venous resistance Cardiac influence Venous pressure and flow are affected by cardiac activity This effect is most pronounced in the thoracic vessels. Cardiac influence is usually not apparent or is reduced in the lower extremities Cardiac pulsatility

Flow patterns and venous resistance in lower extremities Respiratory variation During inspiration, diaphragm moves downward and increases intra-abdominal pressure. IVC is compressed and venous outflow is temporarily reduced or stopped. Flow resumes during exhalation.

Respiratory variation and cardiac pulsatility are sometimes seen in the same flow sample

Flow patterns in upper extremities- central veins Cardiac pulsatility is usually apparent and pronounced. Respiratory variation occurs, but flow during inspiration INCREASES, due to changes in thoracic pressure. Subclavian vein

Pulsatile flow due to congestive heart failure

Venous Resistance Very little muscle tone, easily collapsible The only thing to keep them open is transmural pressure Extrinsic compression will collapse vein

Venous Hemodynamics Venous Valves Hydrostatic Pressure Respiration Calf Muscle Pump

Venous Hemodynamics How does blood get back to the heart ??

Hydrostatic pressure arterial pressure gravity & gravity Venous flow V The pressure in an artery and vein when standing is high due to hydrostatic pressure. This venous flow has a long uphill battle to get back to the heart, against the effect of gravity. Venous flow distal capillary bed

Capillary bed perfusion is dependent on a pressure gradient Low pressure in venules High pressure in arterioles

Hydrostatic pressure, affect on lower veins:  transmural venous pressure distally venous distention venous pooling  in capillary perfusion  in venous return  in cardiac output Click to next slide If you stand in one place for too long without moving……

Hypotension !

We need a Pump!

Calf Muscle Pump With exercise (i.e., walking), the calf muscle will contract, forcing blood out of the sinuses in the calf muscle Blood will move towards the heart

Calf Veno-motor Pump semilunar valves are abundant in calf abundant veins in calf: PTV’s, Peroneals, ATV’s, Gastrocs, Soleal sinuses, Greater & Lesser Saphenous, Perforators abundant skeletal muscles

Venous Valves Arranged so that the only direction blood can move is towards the heart Combined with the calf muscle pump, a walking adult will maintain venous pressure at feet of about 25 mmHg

Normal Valve

Hydrostatic Pressure Weight of the column of blood When standing: right atrial pressure = 0 mmHg ankle pressure= 90 mmHg Will move proximally as pressure rises

Incompetent valve- popliteal vein

Varicose Veins Elongated, dilated, tortuous superficial veins that are usually incompetent Deep veins are surrounded and supported by muscle

Varicose Veins Primary Secondary Congenital, inherent weakness of walls May become prominent following pregnancy No abnormality of deep veins Secondary DVT Absence of deep venous valves Congenital absence or atresia of deep veins

Valvular Incompetence Congenital absence of valves When veins enlarge as in pregnancy and when collaterals enlarge (increased volume)‏ Secondary to DVT

Venous insufficiency symptoms recurrent swelling varicose veins venous claudication stasis dermatitis ulceration

Varicosities

Stasis Dermatitis

Venous ulceration etiology (theory)‏ 1. Chronic increase in intraluminal pressure. 2. Increased vein wall permeability, plasma and fibrinogen leak out into surrounding tissue. 3. Fibrinogen converts to fibrin. 4. Barrier formation between capillaries and tissue, results in a decrease of O2 and nutrient delivery. 5. Subcutaneous bacteria invasion

Venous Ulcerations

Normal Venous Flow Spontaneous Phasic Augmentation Competent Proximal compression Distal compression Competent Non-pulsatile

Spontaneous Flow Blood should be flowing consistently in all veins Spontaneity may be absent in the most distal veins (i.e., posterior tibial at ankle) due to decreased speed of blood Absence of spontaneous flow may indicate obstruction

Phasicity of Flow Should recognize a respiratory component to blood flow Decrease with inspiration (lower opposite upper) Increase with expiration (lower opposite upper ) Absence of phasic flow (continuous flow) indicates proximal obstruction Thrombus Extrinsic Compression

Normal Spontaneous Phasic Flow Respiration

Normal Spontaneous Phasic Flow Abnormal Continuous Waveform CFV No respiration variant

Augmentation Proximal Compression Distal Compression Valsalva Maneuver Flow should cease with proximal compression Upon release, significant increase in flow should be noted Flow during proximal augmentation indicates valve insufficiency Valsalva Maneuver contraindications Distal Compression Large increase in venous flow should be encountered Increase should be immediate Decreased augmentation may indicate DISTAL obstruction

Proximal Augmentation – cease flow Normal response Release

Normal response Abnormal – valve incompetence

Distal Augmentation Distal Squeeze Distal Squeeze

Squeezing the calf forces blood flow to the upper leg– we see this in the doppler as augmentation

Competence Flow should always be toward heart Proximal compression or Valsalva maneuver (VM), flow will cease in veins When abnormal, flow will be retrograde (reflux) during compression or VM, indicating incompetent valve

Pulsatility Since there is no pulsatile “venous heart” other than the calf muscle, no pulsation should be noted in venous flow When pulsatile venous is encountered, it is a good indication of right heart compromise (i.e., CHF)‏

Normal Spontaneous, Phasic, Non-Pulsatile Flow Note: pulsatility in both legs may indicate right side heart disease. One leg may indicate A-V Fistula Abnormal Pulsatile Flow