Ultrasound waves are high frequency sound waves that can render a visible image of solid structures due to their differences in tissue density and can determine blood flow using Doppler technology that reflects waves back from things in motion, such as red blood cells. This makes it ideal for non-invasive investigation into blood vessels, both arterial and venous.
Veins and Arteries–Similarities and Differences
The arterial system is a high-pressure flow of oxygenated blood to tissues throughout the body; the venous system is a low pressure return of the deoxygenated blood back to the heart. Their similarity in carrying blood sees them sharing similar conditions, but their the differences also provide them opportunities to develop abnormalities unique to each.
Veins have thin walls compared to arteries. The low pressure within veins aids in the blood return to the heart, especially with the aid of the legs acting as a compression/decompression pump during movement and ambulation. This low pressure can also fall victim to obstruction more easily than in their arterial counterparts. Failed valves (venous insufficiency) that would normally keep blood from flowing back in reverse interfere with venous function, and blood can pool as venous stasis.
Venous stasis interferes with the physiologic dynamic of gas exchange at the tissues. When the venous circulation is stalled, there is resistance to flow at the more minuscule depths of tissue and the oxygen-carbon dioxide exchange is compromised. This interference with oxygenation and nutrition can cause tissues to become ischemic, break down, become infected, and undergo gangrenous necrosis (die). In this way venous stasis contributes to ulcerations commonly seen in immobilized persons, especially at pressure points where tissue trapped between bony points and hard surfaces halt blood flow altogether.
Veins that cannot overcome the increased pressure from obstructed flow will swell as varicose veins, ranging from the small spider veins (telangectasias) to large varicosities which can become infected or burst, which is much more serious than the mere cosmetic concerns a patient may fear.
Blood can also clot, which can cause obstruction to flow as well as pose the hazard of clot separation and migration toward the heart where they can be propelled into the lung circulation as pulmonary emboli.
Ultrasound allows a non-invasive way to investigate these medical conditions. It also allows venous access for intravenous medication and fluids when veins are difficult to find, as well as aids in placing central lines into the larger veins of the body. Almost 8% of hospitalized patients need such central access to jugular, subclavian, and femoral veins and ultrasound is important in locating access points, visualizing the progress of placement in real time, and for their maintenance.