HOW TO CHOOSE REGENERATIVE MEDICINE AND THERAPIES


lesions in the superficial digital flexor tendon, the distribution and quantification of the radioactive signal was not different from the control horses.5


3. Lateral Palmar Digital Vein Regional Limb Perfusion in Anesthetized Horses


The lateral palmar digital vein RLP was assessed in a later study with the main objective to improve distribution of MSCs to the foot when compared with cephalic vein RLP.6 A pneumatic tourniquet inflated at 450 mm Hg was placed for 30 min in the metacarpal region, proximal to the injection site. Approximately 35 million MSCs suspended in 10mL of saline and flushed with an additional 10 mL of saline were injected. Similar to the cephalic vein RLP in the anesthetized patient, the tourniquet ef- fectively retained all radioactivity within the limb. The radioactive signal was present within the foot in all 6 injected limbs; however, a marked asymmetry was identified with low to absent radioactive signal at the medial aspect of the foot and pastern. Most of the radioactive signal was located in the area of the lateral palmar digital vein and coronary band vascular plexus (Fig. 1C).6


Fig. 1. Lateral scintigraphic images of the equine distal limb acquired after administration of radiolabeled mesenchymal stem cells using different intravenous injection techniques. A, Ce- phalic vein regional limb perfusion in the anesthetized horse. The radioactive signal is mostly located in the area of the main vessels and the coronary band. B, Cephalic vein regional limb perfusion in the standing horse. The radioactive signal is mostly located proximally with poor perfusion of the distal limb. C, Lateral palmar digital vein regional limb perfusion in the anesthetized horse. Radioactive signal is present within the hoof. D, Lateral palmar digital vein regional limb perfusion in the standing horse. Radioactive signal is identified migrating proximally to the tourniquet (arrow), while the tourniquet is still in place. No radioactive signal can be observed within the hoof.


4. Cephalic Vein Regional Limb Perfusion in Standing Sedated Horses


For this study, horses were sedated with 0.01 mg/kg detomidine IV and 0.01 mg/kg butorphanol IV and a pneumatic tourniquet inflated at 225 mm Hg was placed on the forearm proximal to the injection site for 30 min.7 Approximately 40 million radiolabeled MSCs suspended in 2 mL of saline were injected and flushed with 20 mL of saline. Only 3 of 6 horses showed a radioactive signal distal to the proximal metacarpus (Fig. 1B). The quantification of the sig- nal revealed a much lower uptake than on the initial study under general anesthesia, suggesting failure of the tourniquet.


2. Cephalic Vein Regional Limb Perfusion in Anesthetized Horses


Cephalic vein RLP under general anesthesia was the first technique investigated.4,5 A pneumatic tourniquet inflated to 400 to 500 mm Hg was placed on the forearm just proximal to the cephalic vein catheter for 30 min. Twenty-five to 45 million ra- diolabeled MSCs suspended in 2 mL of saline were injected and flushed with 20 mL of saline. All of the radiolabeled MSCs remained in the limb while the tourniquet was in place and no major loss of radioactive signal was observed immediately after removal of the tourniquet. Only 3 of the 6 injected limbs had radioactive signal in the entire distal limb, whereas the other 3 limbs only had uptake in the carpal and proximal metacarpal areas.4 The maximal signal intensity was mostly in the area of the larger vessels (Fig. 1A). In horses with induced


524 2014  Vol. 60  AAEP PROCEEDINGS


5. Lateral Palmar Digital Vein Regional Limb Perfusion in Standing Sedated Horses


Horses were sedated similarly as for the cephalic vein RLP study.7 A pneumatic tourniquet inflated to 450 mm Hg was placed on the metacarpus for 20 min. Forty million radiolabeled MSCs in 10 mL of saline and flushed with an additional 10 mL of sa- line were used.7 Despite all horses tolerating the tourniquet well, very little radioactive signal was present distal to the injection site in 3 of the horses. The quantification of the signal revealed a wide range of uptake. The dynamic acquisition at the time of injection demonstrated failure of the tourni- quet with the radioactive signal proximal to the tourniquet. In the 3 horses with a better distal radioactive signal, uptake within the hoof was lower than in the anesthetized horses, suggesting poor perfusion related to the weight-bearing position (Fig. 1D).7


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