Novel injectable biosensors were used to measure interstitial oxygenation before, during, and after transient ischemia. It is well known that reactive hyperemia occurs following a period of ischemia. However, increased blood flow does not necessarily mean increased oxygen tension in the tissue. Therefore, the purpose of this study was to test the hypothesis that tissue reactive hyperoxia occurs following release of hind-limb tourniquet occlusions. Rats were injected with bilateral hind-limb biosensors and were simultaneously subjected to a unilateral femoral vessel ligation. After approximately one and three months, the rats underwent a series of oxygenation challenges, including transient hind-limb tourniquet occlusion. Along with the biosensors, near infrared spectroscopy was used to measure percent oxyhemoglobin in capillaries and laser Doppler flowmetry was used to measure blood flow. Post-occlusion reactive hyperemia was observed. It was accompanied by tissue reactive hyperoxia, affirming that the post-occlusion oxygen supply must have exceeded the expected increased oxygen consumption. The measurement of the physiologic phenomenon of reactive hyperoxia could prove clinically beneficial for both diagnosis and optimizing therapy.

functioning as expected. In comparison, of the 5 patients with negative patch test results, 3 patients kept their devices, which demonstrated that the negative patch test result had important diagnostic value. The remaining patients had their devices extracted prior to testing, and reimplantation was not indicated.Discussion | This study included 11 patients who underwent cardiac implant patch testing. The majority of patients had history of erythema at the implant site. Concern for infection was common, and more than half of patients had devices extracted prior to presentation. Culture results, with 2 exceptions, were negative.More than half of the patients had relevant positive patch test results, and the most common allergens were metals, rubber accelerators, and silicone. Cardiac device allergy to metals, silicone-based components, and thiuram rubber accelerators has been published previously. 5 To our knowledge, there are previous reports of allergy to carbamate rubber accelerators, diphenylguanidine rubber accelerators, and lidocaine, though not in the setting of cardiac devices. The majority of patients with relevant positive patch test reactions underwent device extraction and successful reimplantation. In a majority of cases, electrophysiologists were able to avoid allergens. For those patients in which we have follow-up data, new cardiac devices were functioning well.One limitation of this study is the lack follow-up data for 2 subjects. In addition, the duration of follow-up was limited to a maximum of 36 months. Cardiac device allergy should be considered when there is clinical concern for infection, history of device extraction, history of erythema at the implant site, or negative culture results. When cases are identified, positive outcomes may be obtained when allergen-guided reimplantation is performed. Contact allergy to cardiac devices is an uncommon but important phenomenon.

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