Peripheral Arterial
Physiologic, not anatomic
Segmental pressures, plethysmography and Doppler waveform analysis are physiologic tests. They prove a lesion exists and roughly localize it; they do not depict the plaque.
ABI technique and pitfalls
Use a cuff about 20 percent wider than the limb; a cuff that is too narrow falsely elevates pressure. Rest the patient supine for about 10 minutes, measure both brachial pressures and use the higher, then measure dorsalis pedis and posterior tibial at each ankle and use the higher pressure per ankle. ABI equals highest ankle pressure divided by highest brachial pressure. Interpretation: above 1.4 is non-compressible (medial calcinosis in diabetes or end-stage renal disease); 1.0 to 1.4 normal; 0.9 to 1.0 borderline; 0.5 to 0.9 typical of claudication; below 0.4 suggests rest pain or tissue loss. Trap: a normal-looking ABI in a diabetic patient with rest pain. Calcified vessels invalidate the ratio, so go to toe pressures or waveforms.
Waveforms and velocity
Normal lower-extremity Doppler is triphasic: sharp upstroke, brief early reversal, small forward diastolic component. Proximal to a stenosis the waveform dampens and becomes monophasic. At the stenosis the PSV roughly doubles with spectral broadening; downstream flow is turbulent. A systolic pressure drop of 20 to 30 mmHg between adjacent segments is significant.
Worked example
ABI of 1.5 in a patient with rest pain is not reassurance. Obtain toe pressures (normal above 60 mmHg, toe-brachial index above 0.7) or plethysmographic waveforms to evaluate the truly compressible distal bed.