Corneal epithelial oxygen uptake rate in diabetes mellitus

Corneal epithelial oxygen uptake rate (CEOUR) has been measured using a non-invasive polarographic electrode technique in patients with diabetes mellitus (DM), all with varying degrees of retinopathy. CEOUR was found to be significantly reduced in diabetic patients when compared to age-matched non-diabetic controls--Type I diabetics p less than 0.001; Type 2 diabetics p less than 0.01. Known duration of DM and assay of instantaneous, medium and long term glycaemic control showed no significant correlation with CEOUR in the patients studied. These results give further evidence of abnormal corneal metabolism in DM. Reduced CEOUR may be a contributory factor in the pathogenesis of diabetic corneal epitheliopathy.

[Tissue pO2 measurement in taut back musculature (m. erector spinae)]

Measurements with polarographic needle probes in fibromyalgic muscles (mm. erectores spinae) revealed an elevated mean tissue-pO2. The total mean tissue-pO2 in the patient group was significantly higher than that in the control group. Greater pathological tension in fibromyalgic muscles increases the mean tissue-pO2. The distribution of local tissue-pO2 values was normal; there was no evidence of small hypoxic areas in the muscle. The elevated tissue-pO2 in fibromyalgic muscles could either be explained by an increase in local blood flow or by disturbance of oxygen-utilization of the muscle cells. The mean tissue-pO2 in patients treated with NSAD was lower than in patients without this treatment. Myogelosises (i.e., circumscript tautness in muscles, that, contrary to fibromyalgic muscles, do not relax under general anesthesia) showed low tissue-pO2 values and even hypoxia in the core. In myogelosises, pain could be hypoxic in nature. However, in fibromyalgic muscles no evidence for hypoxia or hypoxia-related pain could be found.

Determination of oxygen profiles in biocatalyst particles by means of a combined polarographic oxygen microsensor

When studying the effect of immobilization of enzymes or whole cells on the conversion of substrate, more information is gained if measurements of substrate inside the biocatalyst particles are possible. With the methods used until now, only measurements outside the particle can be performed. In this article a method for measuring oxygen profiles in a biocatalyst particle under steady state conditions is described. The biocatalyst particle was made of agarose and contained the enzyme L-lactate 2-monooxygenase. This enzyme decarboxylates lactic acid to acetic acid in the presence of oxygen. The experiments were carried out in a flow chamber with the use of a micromanipulator and a stereomicroscope. The data were sampled by means of a computer. Four different profiles were measured using four different enzyme concentrations. The measured oxygen profiles were reproducible and the signal was very stable. It was also possible to measure the boundary layer around the particle. With the use of the oxygen microsensor, measurements in a biocatalyst particle could be performed accurately, giving way for model validation.

Comparative study of vitreous oxygen tension in human and rabbit eyes

For the first time, vitreous oxygen tension in the human vitreous body was measured using a polarographic oxygen electrode during vitreous surgery. The same method was used in a rabbit experimental model. In the human eye, the mean oxygen tensions of the anterior peripheral vitreous body, central vitreous body and posterior vitreous body were 16.7 +/- 3.7 mm Hg (mean +/- 1 SD), 15.9 +/- 2.8 mmHg and 19.9 +/- 4.8 mm Hg, respectively, while the preretinal oxygen tension of the detached retina was 30.0 +/- 4.8 mm Hg. In the rabbit eye, the mean oxygen tensions of the anterior peripheral vitreous body, central vitreous body and posterior vitreous body were 13.9 +/- 4.3 mm Hg, 16.0 +/- 3.5 mm Hg and 22.5 +/- 2.1 mm Hg, respectively. The preretinal oxygen tension of the attached retina in the rabbit eye was 39.5 +/- 3.4 mm Hg, while that of the detached retina decreased to 4.3 mm Hg. When comparing human with rabbit eyes, it appears that the vitreous oxygen tensions are similar, except over the detached retina, even though the ocular circulation differs. We believe that human retinal vasculature plays an important role in perfusing the detached retina with relatively high levels of oxygen.

Intraocular oxygen tension measured with a fiber-optic sensor in normal and diabetic dogs

A new fiber-optic O2 sensor was used to measure the O2 tension in the living dog eye, and the results were compared with simultaneous O2 tension measurements with polarographic electrodes. The fiber-optic sensor and the polarographic electrodes gave similar readings of anterior chamber O2 tension and gave an identical response to elevation of inspired O2 levels. In the preretinal vitreous, the fiber-optic probe measured the O2 tension 26 +/- 5 mmHg (means +/- SD, n = 5), whereas the polarographic electrode showed 23 +/- 7 mmHg (means +/- SD, n = 5) in the contralateral eyes. Breathing 100% O2 raised the preretinal O2 tension similarly with both systems. Preretinal O2 tension was measured with the fiber-optic sensor in seven alloxan diabetic dogs and was 26 +/- 7 mmHg, which is not significantly different from normal dogs. The fiber-optic sensor has some advantages over the polarographic electrodes. The fiber-optic sensor does not consume O2 and is not dependent on the diffusion characteristics of the medium or changes due to stirring or fluid currents.

Polarimetric detection in high-performance liquid chromatography

Chiroptical detection for HPLC is particularly useful as a selective detection method for chiral molecules, and in enantiomeric purity determination with partial chiral separation or without chiral separation. The recent development of laser-based polarimeters with microdegree sensitivity has increased the applicability of optical rotation detection in HPLC. The detection limit of these instruments is submicrogram on-column for many chiral compounds in analytical HPLC. A variety of applications of the selective detection of optically active molecules are reviewed. The use of polarimetric detection with partial chiral separation is considered, both as an aid to method development and for enantiomeric purity determination. Finally applications to enantiomeric purity determination without chiral separation are reviewed, with the dual use of nonchirally selective and chiroptical detectors to determine the total amount and optical purity of the analyte. Determinations of chiral purity for samples of high enantiomeric excess are described, which with laser-based instrumentation may give accuracies of better than +/- 1% with sample loadings of 50 micrograms on an achiral column. Applications to the study of enantioselective reactions are also considered, with determination of enantiomeric excess in near-racemates to better than +/- 0.1%.

Postoperative monitoring of conjunctival oxygen tension and temperature

To define the utility of conjunctival temperature (Tcj) and conjunctival oxygen tension (PcjO2) monitoring during rewarming in the postoperative period, we measured serial Tcj, PcjO2 and PcjO2 index (PcjO2/PaO2) values in 10 patients after cardiac surgery. PcjO2 and PcjO2 index were markedly depressed at the low conjunctival temperatures recorded during the immediate postoperative period. As the patients' core and conjunctival temperatures increased, there was a concomitant, linear increase in PcjO2 and PcjO2 index for Tcj less than 33.5 degrees C. Two patients showed deviation from this temperature-related rise in PcjO2 and PcjO2 index, and both of these patients demonstrated physiologic deterioration associated with cardiac arrest or hypotension. These results indicate that monitoring of PcjO2 and Tcj can provide a continuous assessment of the adequacy of peripheral perfusion and oxygenation in the postoperative period.

Oxygen tension measurements using an oxygen polarographic electrode sealed in an implantable silastic tonometer: a new technique

Our new method is comparable to the standard, "open-end" tonometer system and incorporates all its abilities to monitor oxygen tension and perfusion. The new device has the advantage of being completely sealed, providing a true, continuous direct measurement over several days, with freedom of movement for the patient without operator attention and with improved stability of the electrode, which minimizes the drift artifacts previously encountered. These improvements will facilitate routine clinical monitoring of tissue oxygen tension.

Tissue oxygen uptake from the atmosphere by a new, noninvasive polarographic technique with application to corneal metabolism

A standard Clark electrode has been modified to continuously monitor the PO2 in a thin, disk shaped reservoir membrane mounted on the electrode membrane surface. In vitro tests were conducted to determine the proportionality constant between the rate of change of reservoir PO2 and the flux of O2 out of the reservoir. The device was then used to determine the corneal O2 uptake on proptosed eyes of previously sacrificed rabbits. Our average measured uptake at 20 degrees C, 1.7 microliter/cm2.hr, agrees with the value 2.3 microliters/cm2.hr calculated from a diffusion analysis of the cornea utilizing literature values of the parameters at 37 degrees C for the three component layers of the cornea when they are adjusted for temperature to 20 degrees C.

Long-term implantation of voltammetric oxidase/peroxide glucose sensors in the rat peritoneum

Methods for designing, fabricating, testing in vitro and in vivo, and improving chronically implantable oxidase/peroxide-type polarographic glucose sensors are described. Voltammetric means to evaluate oxygen supply to the sensor and to measure the nearby microcirculation with hydrogen washout techniques using the implanted glucose sensor are outlined. Because some peritoneally implanted sensors have, perhaps surprisingly, remained functional for months, such devices may prove with further development to be useful as the sensing components in artificial pancreatic beta cells for the control of diabetes.

Altered tissue oxygen tension responsiveness in diabetes

Subcutaneous oxygen tension (tissue PO2) was measured by a polarographic method in the legs of insulin-dependent diabetics (IDDM) and controls. Current flow was measured continuously using a five-stage protocol: baseline; 4 min of complete arterial occlusion; during recovery from ischemia; baseline approximately re-established; induction of hyperemia by local application of heat. Eleven patients with IDDM of 4-32 years of duration, without peripheral arterial disease, were studied and compared with 10 controls. The mean baseline subcutaneous PO2 in diabetics was less than controls; however, the difference was not statistically significant. At the end of arterial occlusion the mean decrease in tissue PO2 was less (P less than 0.025) in diabetics (4.7 +/- 0.9 mm Hg, SEM) compared to controls (10.2 +/- 1.6 mm Hg). With induction of hyperemia the increase in tissue PO2 was lower (P less than 0.001) in diabetics (7.4 +/- 0.4 mm Hg) than in controls (18.6 +/- 1.7 mm Hg). The observed differences provide for the first time direct evidence of altered tissue PO2 responses in diabetes.

Measurement of oxygen tension in the ischemic myocardium using encased polargraphic oxygen electrodes

The ability to continuously monitor the delicate balance between blood flow and oxygen consumption would be a great asset in the study of myocardial ischemia. The present study was performed, in anesthetized dogs, to validate the use of encased polargraphic oxygen electrodes in the study of myocardial ischemia. Polargraphic oxygen electrodes were placed in the area to be rendered ischemic at fixed tissue depths of 3 mm (epicardium) and 9 mm (endocardium). Endocardial and epicardial oxygen tensions as well as the ratio of endocardial to epicardial oxygen tension and left circumflex coronary flow were monitored. Ischemia was induced by decreasing left circumflex coronary flow by 50%. Upon completion of a 20-min poststenotic period, endocardial pO2, endocardial/epicardial ratio, and coronary flow were significantly decreased (59 +/- 7, 52 +/- 7, and 55 +/- 4%, respectively) whereas epicardial pO2 was slightly decreased. Nitroglycerin (10 micrograms/kg, i.v.) markedly increased endocardial pO2 and endocardial/epicardial ratio above poststenotic control (13 +/- 5 mmHg and 64 +/- 10%, respectively) whereas epicardial pO2 was not significantly decreased. The increases in endocardial pO2 occurred at a point where coronary flow and mean arterial pressure were not significantly changed. Conversely, dipyridamole (125 micrograms/kg, i.v.) significantly increased coronary flow (26 +/- 2 ml/min/100 g) although it did not appreciably alter endocardial or epicardial pO2. It is concluded that encased polargraphic oxygen electrodes provide a quantitative method for determination of oxygen tension in the ischemic myocardium.

Electrodes in clinical chemistry

On theoretical grounds it would appear preferable to use calibrants which are not adjusted to a constant ionic strength, whether concentration or activity is being estimated directly. For indirect methods, when sample and calibrant are diluted in an ionic strength adjusting buffer, there is probably little difference between adjusted and unadjusted calibrants. In this case a simple calculation of concentration is possible. A simple algorithm may be used for activity estimation. The algorithm for direct concentration estimation is more complex. If concentration, rather than activity, is required an indirect method must be used. If activity is required a direct method must be used. The quantitative effects of variations in calibration procedure may be smaller than variations in junction potential.

Microelectrode for measuring local cortical oxygen tension and blood flow in the same microareas of cat cortex

The purpose of this study is to investigate the relationship between changes in cortical Po2 (bPo2) and cortical blood flow when inhalating different oxygen mixtures. Experiments were performed on 31 cats anaesthetized with N2O/O2 plus supplemental drugs for immobilization and analgesia. Cortical Po2 was measured by the polarographic method using 25 microns Pt electrode (coated) and a 250 micron Ag-AgCl2 indifferent electrode, especially designed to rest lightly on the cortex by means of coiled spring support. Using the same electrode but with opposite tip polarization; local cortical blood flow (lCoBF) was measured at the same site by the H2-clearance method. The change of bPo2 in going from FiO2 25% to FiO2 75% was measured at 58 different sites. (Table 2). At 25% FiO2 the mean bPo2 was 24 +/- 16 mm Hg, with a range from 4 to 92 mm Hg. With increased FiO2 to 75% local bPo2 responded quite differently at adjacent sites. At 75% FiO2 the mean bPo2 was 42.7 +/- 32 mm Hg with a range from 10 mm Hg to 198 mm Hg. The bPo2 and lCoBF were both measured at 44 of the 58 different sites. Cortical sites with a resting bPo2 greater than 30 mm Hg at 25% FiO2 had a lCBF = 57 +/- 12 ml/100g m; whereas sites with resting normoxic bPO2 less than 20 mm Hg had a mean ICoBF = 56 +/- 14 ml/100g min.(ABSTRACT TRUNCATED AT 250 WORDS)

Transcutaneous PO2 monitoring during a Himalayan ascent

Transcutaneous PO2 (PtcO2) measurements were taken daily on seven subjects during two nine day ascents of the Himalayas to an altitude of 4,579 meters. Five of the subjects lived in areas under 450 meters (Group I), while two subjects lived at an altitude of 3,100 meters (Group II). The PtcO2 values decreased with increasing altitude. The Group II subjects had PtcO2 values greater than the Group I subjects and the difference became greater with increasing altitude. The linear regression lines of PtcO2/pbO2 to Group I during ascent and decent were lower than the regression line for Group II (PbO2 is the barometric oxygen partial pressure). The regression line for Group I data during the second half of the trek approached the data for Group II. We conclude that acclimatization to high altitude is possibly associated with increasing peripheral tissue oxygenation as assessed by PtcO2 values.