Understanding Advances in Perfusion

Alisha Oropallo, MD, FSVS, FACS, FABWMS began her lecture at the NYSPMA Clinical Conference by reviewing traditional methods of assessing perfusion: physical exam, doppler, duplex, ABI/TBI, pulse volume recordings, transcutaneous oxygen presure, oxygen saturation, and thermal imaging. She points out that one needs to consider both macro- and microcirculation when performing such an assessment. Macroperfusion, she says, involves arterial, venous, lymphatic circulation and is seen on all different types of imaging. However, it is important to understand that even with palpable pulses, a patient can still have insufficiency. She goes on to say that although angiography is the gold standard, it still doesn’t tell us everything.

With respect to venous disease, regardless of theory ofetiology one subscribes to, focusing on the signs and symptoms are key, as is early intervention and referral.

Lymphatic disease impacts microcirculation and microcirculation, she says. Protein-rich swelling takes place due to lymphatic malfunction, and may be at higher risk of infection. Understanding of this condition is evolving, and Dr. Oropallo cites a paper that she participated in that covers current thinking.¹

For arterial circulation, she reviews that toe indices (TBI) greater than 0.65 will most likely heal, as will pressures of 70-110 mmHg. Severely ischemic indices are usually less than 0.2 or yield pressures less than 30 mmHg.

Dr. Oropallo then presents a newer technology that focuses on microcirculation, spatial frequency domain imaging (SFDI). This method quantifies a set of chromophores using a technique to shine different patterns of light on tissue, and analyzes the effect of multiple scattering and absorption. This technique can penetrate up to 5 mm in depth and detects oxyhemoglogin, deoxyhemoglobin, and other biomarkers. It detects different variations on oxygenation and perfusion, and measures tissue oxygenation in patients with potential circulatory compromise.

This method has been the subject of ongoing research in multiple areas including wound care and oncology.²

Reviewing skin anatomy (epidermis, papillary dermis, and reticular dermis), the light in SFDI can cut through those layers, says Dr. Oropallo. The use of that structured light then identifies the key biomarkers. One can then look at trends, including underextraction, capillary shunting, and more, she says. For instance, a trend of HbT₁ decreasing and StO₂ decreasing may indicate neuropathic circulatory compromise, she says.³

Dr. Oropallo adds that one may also consider adding thermal imaging into one’s assessment, as it has evolved into a handheld device. Thermographic imaging uses infrared wavelengths to measure temperature via a heat map. Multispectral imaging, she says, uses near-infrared wavelengths (NIR) to measure

Multispectral uses NIR to measure StO₂. NIR imaging is more towards the right of the visible light spectrum, she shares, so that both tissue oxygenation and skin surface temperature can be measured at the point of care.  

She then went on to share some relevant cases illustrating the findings of some of these newer advanced perfusion assessment tools.

Reference

1.    Oropallo A, Donis-Garcia M, Ahn S, Rao A. Current concepts in the diagnosis and management of lymphedema. Adv Skin Wound Care. 2020;33(11):570-580.

2.    Gioux S, Mazhar A, Cuccia DJ. Spatial frequency domain imaging in 2019: principles application, and perspectives. J Biomed Optics. 2019;24(7):071613.

3.    Murphy GA, Singh-Moon RP, Mazhar A, Cuccia DJ, Rowe VL, Armstrong DG. Quantifying dermal microcirculatory changes of neuropathic and neuroischemic diabetic foot ulcers using spatial frequency domain imaging: a shade of things to come? BMJ Open Diab Res Care. 2020;8;e001815