O₂microsensors for minimally invasive tissue monitoring

Abstract

Tissue oxygenation is a key factor ensuring normal tissue functions and viability. Continuous real-time monitoring of the partial pressure of oxygen, pO 2 , in tissues gives insight into the dynamic fluctuations of O 2 supplies to tissues by blood circulation. Small oxygen sensors enable investigations of the spatial variation of pO 2 in tissues at different locations in relation to local microvessels. In this paper, pO 2 measurement using microelectrodes and biocompatible sensors is discussed and recent progress of their application in human skin is reviewed. Emphasis is given to working principles of a number of existing oxygen sensors and their potential application in vivo and in tissue engineering. Results on spatial and temporal variations of the pO 2 in human skin introduced by localized ischaemia-reperfusion are presented when the surface of the skin is covered by an oxygen-free paraffin oil layer and the range of the tissue pO 2 is deduced to be between 0 and 60 mmHg. In the study, pO 2 increases from 8.0 ± 3.2 mmHg (n = 6) at the surface of the skin to 35.2 ± 8.0 mmHg (n = 9) at a depth just above the subpapillary plexus. Temporal decay in pO 2 following tissue compression and rise in pO 2 following pressure release can be described using mono-exponential functions. The time constant for the exponential decay, τ = 8.44 ± 1.53 s (n = 7) is consistently greater than that for the exponential rises, τ = 4.75 ± 0.82 s (n = 6). The difference in pO 2 change with the time following tissue compression and pressure release reveals different dynamic mechanisms involved in the two transient phases. The elevated steady state pO 2 following reperfusion, which is approximately 20% higher than the pre-occlusion value, indicates localized reactive hyperaemia. Possible applications of O 2 microsensors in diseases, e.g. tumours, pressure ulcers, are also discussed.

Influence of Different Anesthetics on Skin Oxygenation Studied by Electron Paramagnetic Resonance in vivo

“…The variability in the position of the LiPc implants in the skin was approximately 0.4 mm. It has been shown in previous studies that the gradients in pO 2 across the skin exist [20][21][22] . However, these gradients are only seen at the superficial layers of the skin (region between the surface of the skin and the upper dermis), while the deeper dermis and hypodermis are well oxygenated and the pO 2 dependence on the depth is not as significant as in upper layers [21,22] .…”

Single photon counting fluorescence lifetime detection of pericellular oxygen concentrations

“…Invasive probes, such as the Clark's electrodes 5,8 or optrodes, 6,9,10 are able to derive oxygen measurements from within a three-dimensional cell system. The invasive nature of the probe causes damage to the surrounding site and, in the case of the electrode, directly consumes oxygen at a rate of 0.4 5 pmol∕h thereby influencing the measured oxygen environment.…”

“…Methods that have been used to examine oxygen gradients in tissue or three-dimensional constructs include computational modeling, 1 photo-acoustic microscopy, 2 electron paramagnetic resonance combined with magnetic resonance imaging, 3,4 invasive probes, and non-invasive luminescence. 5,6 Modeling approaches rely heavily on experimental data using the Michaelis-Menten equation to describe the maximum oxygen consumption rate of cells 7 combined with Fick's 2nd law governing diffusion to estimate macro-gradients in tissues or constructs. 1 However, estimation of macro-environmental conditions may not be representative of the pericellular microenvironment that is influenced by microgradients directly around individual cells.…”

Clinical Chemistry: Challenges for Analytical Chemistry and the Nanosciences from Medicine

“…These include sensors that can be implanted in a blood vessel for permanent monitoring of, for example, the pH value, blood-glucose levels, temperature, and oxygen partial pressure. [193,194] A further development is measuring systems that are implantable and provide long-term stability, and which can be recalibrated in vivo. One example makes possible permanent glucose determination for diabetics.…”