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. 2014:812:81-86.
doi: 10.1007/978-1-4939-0620-8_11.

Real-time, in vivo determination of dynamic changes in lung and heart tissue oxygenation using EPR oximetry

Brian K Rivera  1 , Shan K Naidu  1 , Kamal Subramanian  1 , Matthew Joseph  1 , Huagang Hou  2 , Nadeem Khan  2 , Harold M Swartz  3 , Periannan Kuppusamy  4
Affiliations

Real-time, in vivo determination of dynamic changes in lung and heart tissue oxygenation using EPR oximetry

Brian K Rivera et al. Adv Exp Med Biol. 2014.

Abstract

The use of electron paramagnetic resonance (EPR) oximetry for oxygen measurements in deep tissues (>1 cm) is challenging due to the limited penetration depth of the microwave energy. To overcome this limitation, implantable resonators, having a small (0.5 mm diameter) sensory loop containing the oxygen-sensing paramagnetic material connected by a pair of twisted copper wire to a coupling loop (8-10 mm diameter), have been developed, which enable repeated measurements of deep-tissue oxygen levels (pO2, partial pressure of oxygen) in the brain and tumors of rodents. In this study, we have demonstrated the feasibility of measuring dynamic changes in pO2 in the heart and lung of rats using deep-tissue implantable oxygen sensors. The sensory loop of the resonator contained lithium octa-n-butoxynaphthalocyanine (LiNc-BuO) crystals embedded in polydimethylsiloxane (PDMS) polymer and was implanted in the myocardial tissue or lung pleura. The external coupling loop was secured subcutaneously above chest. The rats were exposed to different breathing gas mixtures while undergoing EPR measurements. The results demonstrated that implantable oxygen sensors provide reliable measurements of pO2 in deep tissues such as heart and lung under adverse conditions of cardiac and respiratory motions.

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Figures

Fig. 11.1
Fig. 11.1
Measurement of myocardial pO2 in rat using implantable resonator (oxygen sensor). (a) Photo of an implantable resonator made of twisted copper wire (34 AWG) showing the coupling loop and sensory loop/tip holding the oxygen-sensing LiNc-BuO crystals, embedded in PDMS. (b) An expanded view of the resonator showing PDMS coating of the wire. (c) Fluoroscopy image of implantable resonator in the heart of a rat taken 10 days post-implantation. The coupling loop is buried under the skin (chest). (d) A typical EPR spectrum obtained using implantable resonator. Spectral fitting and residuals are shown at 8× amplification
Fig. 11.2
Fig. 11.2
Experimental scheme for in vivo EPR measurements in rats with bare LiNc-BuO particulates or implantable resonator. The rat is exposed to gases with different concentrations of oxygen in the chamber during EPR oximetry
Fig. 11.3
Fig. 11.3
Tissue pO2 values in the rats exposed to gases with different oxygen concentrations. Data were obtained using (a) implantable resonator in the heart (day 4 post-implantation); (b) implantable resonator in the lung (day 4 post-implantation). The breathing gases used were: carbogen (95 % O2/5 % CO2), room air (21 % O2), hypoxia (10 % O2), 40 % O2, 70 % O2, and 100 % O2
Fig. 11.4
Fig. 11.4
Peak values of myocardial (a) and lung tissue (b) PO2, values obtained using an implantable resonator during different inhaled oxygen mixtures, room air (21 % O2), 70 % O2, 10 % O2, and carbogen (95 % O2). Data are expressed as mean ± SD (N=4)
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