Non-invasive vascular tests
Non-invasive vascular tests can be divided into those that employ ultrasound and those that use plethysmography.
Plethysmography tests are used almost exclusively to identify and define pathological physiology. Ultrasound based tests can be used to defined anatomical and physiological processes.
Ultrasound based testing
Ultrasound based testing involves continuous wave (CW) ultrasound. This shows direction of flow and waveform and pressure measurement. B-mode scanning gives anatomical information with respect to the area scanned. Combinations of these two , in the form of colour flow Doppler and power domain based flow give very accurate images of the vascular system.
CW Doppler is used in the arterial system is used to measure segmental blood pressure in conjunction with the position of a blood pressure cuff. The most common form of this is when the highest systolic BP in either the right or left arm is measured and pressure reading is used as the denominator to calculate ankle/brachial systolic pressure (ABPSI) index. The numerator in this calculation is the systolic pressure found by placing the blood pressure cuff around the ankle and measuring the blood pressure in the dorsalis pedis artery or the posterior tibial artery. The ABSPI can be measured before and after graded treadmill exercise to assess intermittent claudication and atypical claudication syndromes.
CW testing in the venous system can be used to detect sights of venous incompetence such as at the saphenofemoral junction or saphenopopliteal junction or perforator vein incompetence when varicose veins are present.
B-mode scanning in both the arterial and venous systems can give anatomical information concerning stenosis , occlusion or incompetence when combined with colour flow Doppler and power domain scanning at a given site in the vascular system.
Plethysmographically based testing
Plethysmographically based testing can involve photoplethysmograhy , used to measure 1st toe or digital arterial pressures in the hand or venous refill times in the lower limb in the presence of venous hypertensive disease.
Air plethysmography can be used to measure arterial pulse volume or lower limb venous emptying time to detect the presence of venous occlusive disease.
In general plethysmographically based testing is infrequently used with the exception of photoplethysmgraphy to measure digital arterial pressures in the upper or lower limbs. This modality can also be useful in assessing vasospastic conditions such as a Reynaud’s Disease.