A careful history and physical examination will often reveal the diagnosis of venous insufficiency with reasonable certainty. At times, however, determining the cause of leg swelling, discomfort, and ulceration proves very perplexing. The diagnostic challenge can be compounded by the presence of more than one systemic disorder. Safe and highly sensitive technologies are now available to provide reliable information on the pathophysiology of the venous system.
The scientific approach to studying the venous system in health and disease began in the early 20th century. At first, investigators relied on measurements of PRESSURE. They used intravenous manometry, a procedure that was cumbersome, patient-unfriendly, and often resulted in thrombophlebitis. Improvement came with noninvasive methods that involved changes in volume rather than pressure. Volume changes with various manual or boot compression methods were recorded with a “strain gauge,” a mercury-filled, silicone tube fitted around the limb through which an electrical current passed. Changes in limb volume causes changes in tension on the tube and consequently changes in the conductive impedance in the mercury column. While technically fussy and time-consuming, the procedures provided useful diagnostic information on venous insufficiency; it proved less reliable for identifying venous thrombosis.
Beginning in the 1940s, investigators developed an infrared signal and light-sensitive meter to assess the density of blood in the skin. Various maneuvers were performed during testing for venous filling. Excessively rapid refilling after compression or elevation of the leg indicated a defect in venous valve function.
Throughout this period of diagnostic exploration, techniques for obtaining x-ray images were under development. Venography required injecting radiopaque solutions into the veins. While the method became the gold-standard for detecting both venous thrombosis and valvular reflux, contrast venography was costly. Furthermore, the injected radiopaque solutions often caused inflammatory reactions and thromboses.
Figure 10.1 depicts injection of a radio-opaque solution. Reflux is noted through the partially closed valves.” 
Today, these approaches to venous pathophysiology have been replaced by ultrasound technologies. Ultrasonometry provides reproducible data on anatomy, obstruction, and reflux of the venous system . The advantages can be better appreciated by reviewing the history of venous diagnosis in Chapter 22.
Simply put, ultrasound technology utilizes an inaudible signal emitted from an electronic probe and receptor. When the signal strikes a solid object, it is reflected back to the probe. If the object has movement, the wavelength of the returning signal will be changed. The faster the movement, the greater is the change in frequency. The instrument converts the echo into an audible response that can be recorded graphically. Blood is highly reflective, and its rate of flow is easily evaluated by this technology.