Hemodynamic Assay of Hind Limb in Multiple Animal Models

Introduction: Measuring hemodynamic characteristics of injured limbs is paramount to early identification of potentially damaging ischemic conditions, but can often prove difficult attributable to a multitude of factors. Here, we present an in vivo optical imaging technique to characterize pulsatile blood flow quality through the distal extremity in multiple animal models that replicate the signs of distal extremity ischemia. The purpose of this study is to examine the feasibility of the optical imaging technique and relevance to hemodynamic complications such as acute compartment syndrome (ACS) and nonobvious hemorrhage. Materials and Methods: In one pig and six mice, three different methods were used to create ischemic conditions in the lower extremity, producing symptoms similar to what is observed in ACS. In each condition, perfusion to the distal extremity was measured with the hemodynamic detection device (HDD; Odin Technologies), an optical assessment tool for perfusion and blood flow quality. Results: We observed a profound decrease in extremity perfusion immediately after onset of ischemia in all three models. In the porcine model, the HDD’s measurements demonstrated similar characteristic flow between the various measurement locations. After the tourniquet was applied, the HDD revealed a 95% decrease in normalized perfusion value (npv) while the intracompartmental pressure rose from 5 to 52 mmHg (a 47mmHg increase). After the tourniquet was removed dur- ing reperfusion, the normalized blood flow returned to baseline and the intracompartmental pressure dropped from 20 to 6 mmHg in less than 5 minutes. For each mouse, the HDD test leg demonstrated a measurement of 0.97 npv before femoral ligation and 0.05 npv after femoral ligation, an 89% decrease (P< .01) in flow. Pulsed-wave Doppler ultra- sound (PWDU) measurements on the test leg had pre-ligation measurement of 0.84 npv and a post-ligation measurement of 0.001 npv, a 99% decrease. These PWDU measurements revealed almost complete stoppage of blood flow during ischemia, followed by a substantial increase after the femoral artery ligation was removed. Conclusions: Here, we show that a novel, optics-based sensing system can be used to diagnose and assess ACS in animal models. This technology is comparable to other standards used to monitor ACS and nonobvious hemorrhage and may also be a plausible alternative to prolonged invasive monitoring of patients with sustained extremity trauma.