A Sensitive Respirometer for the Measurement of Rapid Changes in Metabolism of Oxygen

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Abstract
A respirometer used to study the oxygen metabolism of peripheral nerve is described. The theory of its operation and its operating characteristics are given. The respirometer consists essentially of the nerve trunk itself, placed symmetrically across the tip of a polarized platinum microelectrode which is flush with the floor of the chamber. The sides of the nerve are exposed to moist gas of known oxygen content; the top surface of the nerve is covered. The current to the platinum electrode measures the concentration of oxygen in the nerve at the electrode tip. In the steady state the oxygen concentration near the electrode is determined by: (1) the configuration of the system, (2) the oxygen content of the gas phase, (3) the diffusion coefficient of oxygen in the tissue, and (4) the rate of oxygen consumption by the tissue. Starting from the steady state, any change in rate of oxygen uptake may be followed directly during the first 45 to 60 seconds of such a change; during this time the change is equal to the negative of the rate of change of oxygen concentration at the electrode tip. Slow, prolonged changes in respiratory rate may be followed, within limitations determined by the diffusion characteristics of the system and by slow drift in electrode calibration. It is estimated that changes in rate of oxygen uptake as small as 0.3 mm3 O2/cc hr (0.6 percent of the rate of uptake by resting frog nerve) can be reproducibly detected.

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