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Use of Laser Doppler Imaging to Assess Microvascular Response to Thermal Stress

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Use of Laser Doppler Imaging to Assess Microvascular Response to Thermal Stress Evaluating Lower Limb Ischemia Use of Laser Doppler Imaging to Assess Microvascular Response to Thermal Stress Dixie R. Aragaki, MD, Min-Ning Huang, MD, PhD, Peggy Chen, MD, Peter Yeung, MD, Charles Kunkel, MD, Dorene Opava-Rutter, MD, A.M. Erika Scremin, MD, and Oscar U. Scremin, MD, PhD Assessment of cutaneous microvascular perfusion can provide important clues about wound and amputation healing in patients with diabetes. These investigators examined the practicality of laser Doppler imaging in this setting. iabetes is a major public traumatic amputation in the United venules that is not readily studied by health problem, especially States, and the disease has resulted routine ultrasonic Doppler imaging in the VA, whose patient in about 80,000 lower extremity am- or ankle-brachial index calculations. Dpopulation has a substan- putations per year since 1997.2 Three In the past, methods of estimating tially higher prevalence of the disease years after a diabetes-related lower skin perfusion included radioiso- (11.4%) compared with the general extremity amputation, the mortal- tope studies to record skin perfusion U.S. population (7.2%).1 Among ity rate is between 35% and 50%.3 pressure10 or tissue tracer uptake,11 the many complications of diabe- Furthermore, since proximal am- segmental systolic blood pressure,10 tes, lower extremity amputation is putation levels demand higher en- arteriography,12 and capillary micros- particularly distressing. Diabetes is ergy expenditure to ambulate with a copy.13 These methods are time con- currently the leading cause of non- prosthesis,4 patients who’ve had such suming, however, and have varying amputations face limited mobility degrees of reproducibility.14 In 2000, Dr. Aragaki is the assistant program director for and independence. This high cost to the Transatlantic Inter-Society Con- the physical medicine and rehabilitation (PM&R) individual health and functioning is sensus identified transcutaneous PO residency program at the Greater Los Angeles 2 VA Healthcare System (GLAVAHS) and an assis- sadly matched by the immense finan- (TcPO2) measurement, radionuclide 5 tant clinical professor in the department of medi- cial cost of associated health care. In scans, laser Doppler methods, and cine at the University of California, Los Angeles 2003, diabetes-related lower extrem- capillary microscopy as useful ad- (UCLA) David Geffen School of Medicine, both in Los Angeles, CA. Dr. Huang, Dr. Chen, and Dr. ity amputations accounted for ap- juncts in assessing critical limb isch- 2 15 Yeung are all practicing physiatrists who, at the proximately 810,000 hospital days. emia. In recent years, TcPO2 and time of this study, were PM&R residents at the Given the scope of this problem, laser Doppler methods have become GLAVAHS. Dr. Kunkel is the assistant chief of PM&R services at the GLAVAHS and an associate there is an urgent need to further our widely used to assess skin microper- 16 professor in the department of medicine at UCLA understanding of the pathophysiology fusion and oxygenation. David Geffen School of Medicine. Dr. Opava- leading to amputations in the diabetic Laser Doppler flowmetry (LDF), Rutter is the director of PM&R polytrauma at the 6–8 GLAVAHS. Dr. A. Scremin is the chief of PM&R population. Microvascular function which can monitor skin blood flow services at the GLAVAHS and a professor and the of the skin—which is important to in real time over a small area, has chair of the PM&R division of the department of wound healing, hemostasis, tempera- been used in many areas of medicine, medicine at UCLA David Geffen School of Medi- 17 cine. Dr. O. Scremin is a rehabilitation research ture regulation, and immune system including plastic surgery, vascular 18 19 and development senior research career scientist modulation—has emerged as a physi- medicine, burn management, and in the department of research at the GLAVAHS ologic variable of interest.9 dermatology.20 Additionally, some and a professor emeritus in the department of physiology at the UCLA David Geffen School of The cutaneous vasculature is a fine investigators have reported its util- Medicine. network of arterioles, capillaries, and ity in assessing amputation level and JUNE 2008 • FEDERAL PRACTITIONER • 27 LASER DOPPLER IMAGING wound healing in diabetic and non- mal and abnormal LDI values and to was approved by the VA Greater Los diabetic patients.18,21 LDF used in characterize the physiologic nature Angeles Institutional Review Board. conjunction with thermal stressing of the thermal response. To that end, (application of controlled heat) has we analyzed the microvascular re- Procedure revealed significantly lower perfusion sponse to thermal stress, as measured Participants were placed prone on in amputees than in control partici- by scanning LDI, on three cutaneous a hospital bed. Pillows were placed pants,22 and it has resulted in better calf sites of healthy individuals and strategically to offer comfort and clinical correlation with ischemia se- individuals with peripheral vascular minimize movement artifacts. Skin verity than either TcPO2 or Doppler disease and diabetes mellitus (PVD- temperature was measured with an ankle pressure measurement.23 DM). Specific aims were to identify infrared thermometer at each test site Scanning laser Doppler imaging useful microperfusion parameters that before skin heating. Circular probes (LDI) is a more recently developed can distinguish between people with that were 19 mm in diameter and technique that provides advantages and without PVD-DM and to charac- contained at their centers a heating over the LDF device—primarily the terize the spatial and temporal course element 8 mm in diameter (Transcu- ability to produce a relatively large, of heat-induced microvascular hyper- taneous CO2/O2 Monitor, Novametrix two-dimensional image with superior emic response in normal skin. Medical Systems Inc., Wallingford, spatial resolution24 and temporal re- CT) were applied with a 7-mm wide producibility25,26 without direct skin METHODS adhesive tape ribbon, concentric and contact. LDI achieves this by using external to the probe border. a continuous raster scanning laser Participants Probes were placed posteriorly beam across the skin surface. Dop- For the study, we enrolled 12 healthy at approximately 10 cm (proximal), pler-shifted light from moving blood individuals (11 men and one woman) 15 cm (middle), and 20 cm (distal) is reflected and processed to provide aged 28 to 63 years (median, 35 below the knee joint line. In order to a flux measurement expressed in ar- years) and 11 men with PVD-DM raise skin temperature to a nonpain- bitrary perfusion units (PU) propor- aged 50 to 79 years (median, 62 ful 44°C, the probes were left in place tional to tissue blood flow. years). Healthy volunteers were re- for 15 minutes and then removed. At the West Los Angeles VA Medi- cruited for the study through flyers Within one minute of removal, a laser cal Center (WLAVAMC), the Func- posted at the WLAVAMC. Among Doppler imager (Moor Instruments, tional Perfusion Laboratory team is volunteers, individuals were excluded Devon, UK) scanned the three heated called upon to evaluate patients who if they had known peripheral vascu- sites and adjacent area. In healthy are referred from various clinical ser- lar disease, diabetes, hypercholester- participants only, LDI scanning was vices, such as the limb preservation olemia, Raynaud disease, coronary repeated at five, 10, 15, 20, 25, and and amputee clinics, for diagnosis artery disease, cerebral vascular dis- 30 minutes after removal of the heat- of microcirculation abnormalities ease, prior amputation, skin diseases, ing probes. LDI measurements were and for guidance regarding wound or acute illness; had used tobacco in not repeated in participants with care, treatment of peripheral vascu- the previous six months; or were tak- PVD-DM due to concerns about par- lar disease, and surgical planning. ing medications known to alter vessel ticipants’ discomfort. Traditionally, the laboratory team re- reactivity (nitrates). lied upon TcPO2 to assess cutaneous The participants with PVD-DM Data analysis microperfusion after thermal stress in had been referred to the Functional Regions of interest (ROIs) were such patients. Recently, however, Perfusion Laboratory for vascular mapped onto the LDI photo images the staff wondered whether scanning studies and were considered candi- by tracing the outer edge of the heat- LDI technology, applied in a similar dates for lower extremity amputation. ing probes. When the probes were manner, could add valuable informa- Of these 11 participants, 10 under- removed, these ROIs were superim- tion to these assessments. went an amputation four to 98 days posed on the serial LDI images to As a first step in evaluating the after the LDI study (eight below the ensure accurate localization of the practicality and reproducibility of knee, one through the knee, and one thermally challenged skin areas. LDI technology in this setting, we transmetatarsal). Mean and peak flux levels were undertook a study to increase our All participants gave informed con- recorded, using the Moor LDI soft- understanding of the expected nor- sent to participate in the study, which ware, within ROIs at the heated sites 28 • FEDERAL PRACTITIONER • JUNE 2008 LASER DOPPLER IMAGING and in equivalent, adjacent, non- sents the difference between flux at SM analysis heated areas. Group averages, differ- the border of the heating element and Images from individual heated
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