Assessment of tissue perfusion in the lower limb: current methods and techniques under development

Peripheral arterial disease (PAD) affects 27 million individuals in Europe and North America.1 This condition causes a severe restriction of blood flow that can lead to critical limb ischemia (CLI), a condition characterized by rest pain, ulceration, or gangrene, which is associated with limb loss in ≈25% of cases.2 The ischemic limb can be revascularized by endovascular techniques (angioplasty/stenting) or surgical bypass. Imaging modalities, including duplex ultrasound, MR angiography, computer tomographic angiography, or intra-arterial angiography, are used to assess the extent of disease, plan intervention, and confirm the patency of major blood vessels after intervention. These techniques do not provide information about perfusion at the tissue level. An early relatively crude method for assessing ischemic limbs, venous occlusion plethysmography3 relies on the principle that the volume of the limb is dependent on the arterial inflow when venous drainage is occluded. Under resting conditions, ≤70% of blood flow to the limb is directed to skeletal muscle, with the remainder to the skin circulation.4 Venous occlusion plethysmography provides a global indication of limb perfusion but gives no anatomic information and cannot delineate segmental perfusion deficits. It is influenced by numerous factors, such as ambient temperature and arteriovenous shunting that may lead to erroneous readings. Objective measurement of limb perfusion would particularly benefit patients with CLI but most attempts at addressing this have used patients with claudication. The latter can lead to CLI but is a less severe form of PAD that is often treated conservatively and is characterized by pain only when walking as opposed to pain at rest or gangrene. An accurate, noninvasive method of measuring limb perfusion would aid the diagnosis and treatment of PAD and could be combined with conventional angiography to provide both functional …