Tissue oxygen concentration represents the balance between the delivery of oxygen by the blood vessels and oxygen utilization in the tissue. Tissue oxygen concentration can alter with changes in metabolic demands (e.g. skeletal muscles during exercise) and alterations to blood flow to the region (e.g. after an ischemic stroke).
Tissue oxygen concentrations can be measured by electrochemical sensors such as carbon paste electrodes. Oxygen is reduced to water on the surface of the electrode generating an electrical current in the process, which can be measured. The tip of the carbon paste electrode used in the Kaha Sciences TR57Y Oxygen telemeter (formerly sold by Millar) is approximately 200µm in diameter and measures from an area of approximately 300µm. The measurable range of oxygen using the TR57Y Oxygen telemeter is up to 300µM, well exceeding normal physiological values.
Tissue oxygen can be measured under normal physiological conditions as well as in pathologic studies. Oxygen concentrations in the brain, kidney and liver have been measured using Kaha Sciences Telemetry.
An example of tissue oxygen concentration measured in the rat kidney using the TR57Y telemeter is shown below.
Measurement of tissue oxygen concentrations can be useful in the fields of physiology, neuroscience, trauma medicine and safety pharmacology and toxicity studies.
The autonomic nervous system adjusts and maintains homeostasis by modulation of parasympathetic and sympathetic nervous activity (SNA). Together, parasympathetic nerve activity and sympathetic nerve activity regulate the respiratory system, digestive system and the stress response. In the cardiovascular system, sympathetic nerve activity maintains vascular tone (there are no parasympathetic nerves innervating blood vessels), heart rate and renal function by a basal firing rate. Sympathetic nerve activity has been shown to increase in cardiovascular pathologies such as hypertension and heart failure.
Chronic SNA has been reported to be measured in the rat from the lumbar, splanchnic and renal sympathetic nerves. SNA is usually recorded in conjunction with arterial pressure, which provides a means of distinguishing between recorded SNA, background noise and electrical artefacts such as ECG. The data is usually filtered and integrated to obtain an averaged signal and/or burst amplitudes and frequencies. For more information on quantifying the SNA and distinguishing the SNA signal, see the paper by Guild et al., 2010, "Quantifying sympathetic nerve activity: problems, pitfalls and the need for standardization".
An example of raw renal SNA, arterial pressure and filtered integrated renal SNA recorded in a rat using the TRM56SP telemeter is shown below.
Chronic recordings of SNA and arterial pressure can be useful in the study of autonomic-cardiovascular physiology.