Flexible valinomycin electrodes for on-line determination of intravascular and myocardial K+

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Abstract
Flexible electrode systems capable of monitoring in vivo changes in venous and myocardial extracellular potassium activity were constructed using valinomycin-polyvinyl chloride matrix membrane and polyvinyl chloride tubing. Electrode impedance was 1-30 m.OMEGA., time constant 10-200 ms, drift < 1 mV/h, and shelf life .apprx. 3 days (intramyocardial electrode) and .apprx. 6 wk (venous electrode). In vitro and in vivo accuracy were determined in 5 dogs and 18 pigs, anesthetized with sodium pentobarbital (35 mg/kg i.v.), with normal and elevated K+ levels. Serum and venous K+ concentration, determined using a K+ electrode with tip diameter of 1.5 mm, correlated well to serum K+ values determined by flame photometry (r [correlation coefficient] = 0.997). Steady-state myocardial extracellular K+ concentration determined using double-barrel electrodes with total tip diameter of 0.6 mm correlated well to the serum K+ concentration (r = 0.992). These electrode assemblies permit on-line, virtually instantaneous in vivo determination of intravascular and local myocardial extracellular K+ activity, a capability not previously available.

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