APPLICATIONS OF PULSED DOPPLER TECHNIQUES

Abstract

The comprehensive and quantitative assessment of cardiovascular anatomy and function requires a multiparameter diagnostic approach. Accomplishing this noninvasively, using ultrasound, involves utilization of a highly integrated instrument system which can be adjusted to detect and display optimally the most significant physical features of the disease process. This general approach is an outgrowth of the development of pulsed Doppler techniques for the assessment of blood flow in the heart and peripheral blood vessels. The use of an estimation of blood flow as a clinical variable means many different things to many clinicians. Volumetric blood flow, expressed in liters or milliliters per minute, is generally considered to represent a measure of tissue perfusion or an index of possible tissue viability. Volumetric flow probably has its origin as a rheologic or physiologic indicator of organ function. Commonly, it is measured concomitantly with blood pressure and is evaluated with another related parameter, the vascular blood flow resistance or impedance. This point of view is analogous to the electrical engineer's measurement of voltage, current, and resistance in an electrical circuit. Voltage corresponds to pressure, current to blood flow, and electrical resistance to hydraulic resistance caused by certain viscous effects and vessel dimensions. SUMMARY Methods of blood flow detection have undergone great advances during the last few years. However, they require further development before truly quantitative and practical methods are developed for routine clinical application. Despite these obstacles, many clinically useful applications have emerged in adult and pediatric cardiology cases as well as in the assessment of peripheral circulation. These methods have placed primary emphasis on the detection and analysis of blood flow disturbances arising from anatomic defects. The abstract nature of the flow signals is gradually diminishing with the merging of flow detection methods and imaging concepts that provide familiar anatomic landmarks for interpretation. Color-encoded displays are also being developed to cope with the ever-increasing amounts of data available. These displays help differentiate between tissue and flow defects; in fact, the spatial and temporal characteristics of flow can almost be regarded in the same sense as a tissue. More of the basic data required to calibrate the devices are being collected and methods are evolving to utilize this information in quantitative studies. The almost overwhelming flow of new information about these disease states will require a long period of careful evaluation to determine the real role and best application of these emerging methods. Fundamentally, the ability to assess and quantitate blood flow to an organ or structure in a noninvasive, atraumatic manner has great merit.