Effects of experimental cochlear thrombosis on oxygenation and auditory function of the inner ear

To elucidate the etiology and pathogenesis of sudden hearing loss, the effect of experimental cochlear thrombosis on oxygenation and the auditory function of the inner ear was investigated in anesthetized guinea pigs. Impairment of cochlear blood flow (CBF) was induced by ferromagnetic obstruction of cochlear blood vessels at lowered body temperature. Perilymphatic oxygen partial pressure (PO2) in the basal scala tympani (about 200 microm below the round window membrane) was measured polarographically using micro-coaxial needle electrodes. Auditory function was examined by recording cochlear microphonic (CM) frequency responses, compound action potentials (CAP) and auditory evoked brainstem responses (ABR). Findings demonstrated a considerable decrease in the mean perilymphatic PO2 of 40%, 2 h after the start of the experiment. Mean CM and N1 CAP amplitudes were reduced by about 25% each and ABR by 18%. No significant changes were observed in the latencies of either CAP or ABR. Mean basal CBF was found to decrease by 35%, as measured by laser Doppler flowmetry in a parallel study. The present findings demonstrate that vascular impairment in the inner ear results in a considerable drop in intracochlear oxygenation, causing a significant loss in the auditory response.

Adverse effects of hyperoxemia during cardiopulmonary bypass

OBJECTIVE

Aiming at elucidating the effects on capillary blood flow and tissue oxygenation of hyperoxemia during cardiopulmonary bypass, we studied skeletal muscle surface oxygen tensions in 10 patients undergoing elective cardiac operations.

METHODS

In a prospective investigation each patient was exposed to normoxemia (arterial oxygen tension 75 to 115 mm Hg) and hyperoxemia (arterial oxygen tension > 185 mm Hg, inspired oxygen fraction = 1.00) during normal anesthetized conditions before and after cardiopulmonary bypass, as well as during normothermic and hypothermic continuous-flow bypass. In each state hemodynamic variables and arterial and mixed venous blood gas and acid base values were measured. From these data oxygen transport variables were calculated. Tissue oxygenation was studied with the use of a multiple-point polarographic oxygen microelectrode, known to provide measures of oxygen tensions at the capillary level. The oxygen distribution profile of such a sample is also indicative of capillary blood flow distribution changes.

RESULTS

In all patients and at each occasion of the investigation markedly low mean surface oxygen tensions in skeletal muscle were registered. When hyperoxemia was instituted, a significant decrease in these surface oxygen tensions together with an increase in distribution heterogeneity was seen during all stages. Contrary to prebypass, postbypass, and hypothermic bypass, where vascular resistance, oxygen delivery, and oxygen consumption remained similar during hyperoxemia and normoxemia, a significant (p < 0.05) increase in vascular resistance together with a decline in oxygen consumption was seen during hyperoxemic normothermic (35 degrees to 36 degrees C) cardiopulmonary bypass.

CONCLUSION

These findings show that the microcirculatory response to hyperoxemia, seen under other circumstances, persists during continuous-flow cardiopulmonary bypass, normothermic as well as hypothermic. If these adverse effects on tissue oxygenation by hyperoxemia can be further verified and shown to be valid for other organs than skeletal muscle, we would suggest that hyperoxemia should be avoided, especially during normothermic cardiopulmonary bypass.

[Follow-up of contralateral intratesticular oxygen pressure in unilateral testicular torsion]

The intratesticular tissue oxygen tension (= IT-pO2) depends on the testicular perfusion. Polarographic microcatheter probes have recently become available and are suitable for continuous measurements of the tissue oxygen tension. In 20 adult albino rats flexible Clark-type oxygen electrodes (1.5 F) were used for simultaneous monitoring of IT-pO2 of the ipsi- and contralateral testicle during unilateral torsion. A counterclockwise 720 degrees torsion caused a decrease of IT-pO2 from 21 mm Hg (+/- 5 mm Hg) to 5 mm Hg (+/- 1.5 mm Hg) in the twisted testicle within 5-7 min. After detorsion the IT-pO2 returned to normal level in the following 25 min. The IT-pO2 of the contralateral testicle showed no significant changes during torsion for 1 h or after detorsion. Thus, if the oxygen utilization is unchanged a unilateral acute torsion for 1 h does not cause a decrease in perfusion in the contralateral testicle. It will probably also prove possible to use oxygen tissue tension measurements to improve our understanding of testicular perfusion in humans.

Evaluation of the polarographic technique for assay of the viability of freeze-dried BCG vaccine: I. The polarographic technique

In this paper, a new assay based on oxygen uptake assessed by polarography was evaluated with the aim of establishing the viability of freeze-dried BCG vaccine. An oxygen electrode possessing a temperature sensor was designed for this purpose. The polarographic method used had several advantages, particularly its rapidity and use of small amounts of biological material. These advantages are ideal for quality control of BCG vaccine.

The effect of the perflubron emulsion Oxygent on the calibration characteristics of polarographic oxygen electrodes

The perfluorocarbon emulsion Oxygent improves normal tissue oxygenation. A clinical trial is planned to evaluate this effect in tumors. Polarographic oxygen electrodes were calibrated in solutions of saline +/- perflubron to assess whether Oxygent influenced probe behavior. Calibrations were linear under both conditions. There were no major differences in estimated oxygen tensions.

[The potentials of polarography in predicting the effect of a reconstructive operation in patients with severe ischemia of the lower extremities]

Possibilities to prognose the effect of reconstructive operation on the lower extremity vessels are shown on the basis of transcutaneous of oxygen on the dorsal surface of the foot in complex with ultrasonic Dopplerometry in patients with severe ischemia of lower extremities. Effectiveness of the test with the orthostatic growth of Po is proved. An examination of 60 patients with severe ischemia of lower extremities and 10 patients without pathology of main vessels (control group) was performed. Operations were performed on 48 patients, in 35 of them reconstructive operations were made. No correlation was found between preoperative value of Po and a result of the reconstruction. A correlation was found between the value of the orthostatic growth of Po and outcome of the reconstructive operation. The average growth of Po in the group of patients with a negative outcome of the reconstruction made up 9.93 + 2.78 mm Hg, with a positive outcome it was 14.137 + 2.30 mm Hg (p < 0.05). In patients with malleolus index of the regional systolic pressure > 0.3 with the orthostatic growth of Po > 20 mm Hg the probability of positive prognosis of the reconstruction made up 88.8%.

[Continuous measurement of peripheral oxygen availability in skeletal muscle of patients with infection]

In patients with sepsis, a pathologic oxygen uptake supply dependence due to an oxygen extraction defect was suggested to result in tissue hypoxia--a hypothesis which is discussed controversially. In order to determine more directly whether the oxygen transport to tissue was reduced in patients with sepsis, the distribution of skeletal muscle pO2 was measured intermittently by polarographic needle electrodes in 28 patients with sepsis for 7 days. Comparison of intermittent with continuous measurements by pO2 catheters showed a close linear relation (r = 0.88; p < 0.001) and acceptable agreement. Therefore, continuous measurement of skeletal muscle pO2 by pO2 catheters can be used as an estimate of mean skeletal muscle pO2. Neither by intermittent nor by continuous measurements, skeletal muscle hypoxia was detected in patients with sepsis. In contrast, the skeletal muscle pO2 was statistically significantly higher on days with septic state (44.1 +/- 10.3 mm Hg) than on days with intermediate (30.1 +/- 8 mm Hg) and nonseptic (26.8 +/- 5.1 mm Hg) states. From our data we infer that the hypothesis of tissue hypoxia in sepsis must be questioned at least for the skeletal muscle. The increase of skeletal muscle pO2 in sepsis, however, suggested that oxygen utilization within skeletal muscle decreased the more severe the stage of sepsis was. A decreased oxygen utilization within tissue, which may result from a 'downregulation' of oxygen-dependent metabolic pathways, might account for a decreased oxygen extraction of peripheral tissue in sepsis.

Monitoring cerebral oxygenation: experimental studies and preliminary clinical results of continuous monitoring of cerebrospinal fluid and brain tissue oxygen tension

Cerebral ischaemia is considered to be the central mechanism leading to secondary brain damage in patients with severe head injury. It would therefore seem appropriate to monitor cerebral oxygenation in these patients. The possibilities of continuous monitoring of brain tissue and CSF oxygen tension as parameters for cerebral oxygenation were evaluated. In experimental studies the influence of changed oxygen offer and decreased cerebral perfusion pressure on CSF and brain tissue pO2 were investigated. Fast changes in CSF pO2 were observed in response to decreasing oxygen offer. Slower changes were noted in response to hypo- and hyperventilation. An autoregulatory mechanism regulating CSF pO2 is postulated. Reducing cerebral perfusion pressure decreased both brain tissue and CSF pO2, but in the reperfusion phase after complete ischaemia a dissociation occurred between brain tissue and CSF pO2, CSF pO2 being restored, but brain tissue pO2 remaining low or even decreasing further. From these studies it is concluded that both CSF pO2 and brain tissue pO2 reflect changes in cerebral oxygenation caused by changes in oxygen offer as well as by changes in cerebral blood flow. Brain tissue pO2 is also sensitive to oxygen demand from the tissue. Preliminary studies of continuous monitoring of brain tissue pO2 in patients with severe head injury are reported.

The influence of different levels of PEEP on peripheral tissue perfusion measured by subcutaneous and transcutaneous oxygen tension

OBJECTIVE

To compare subcutaneous (PscO2) and transcutaneous (PtcO2) oxygen tension measurements in relation to hemodynamic variables at different levels of PEEP, and to evaluate the usefulness of these measurements as monitors of peripheral tissue perfusion.

DESIGN

Prospective trial.

SETTING

Intensive care unit in a university hospital.

PATIENTS

Seven patients with gastric cancer who where undergoing total gastrectomy.

INTERVENTIONS

Silicone catheter was placed in the upper arm and transcutaneous oxygen monitor was placed on the upper part of the chest. A pulmonary artery catheter was placed in the right pulmonary artery.

MEASUREMENTS AND RESULTS

PscO2 and PtcO2 together with hemodynamic variables were measured at different levels of PEEP. Progressive increase of PEEP reduced cardiac index (CI) (p < 0.05) with a concomitant decrease of PscO2 (p < 0.05) and oxygen delivery (DO2) (p < 0.05). Changes in PtcO2 paralleled changes in arterial oxygen tension (PaO2), but no correlation was found between PtcO2, CI and DO2.

CONCLUSION

PscO2 is a sensitive indicator of subcutaneous tissue perfusion, which can be used to identify the PEEP level, with optimum peripheral perfusion. PscO2 seems to be a more reliable indicator of tissue perfusion than PtcO2.

[The distribution of oxygen pressure in the pial arterioles of the rat under normobaric hyperoxia]

Breathing with air revealed that oxygen tension in arterioles practically does not depend on the diameter of vessels under study in rats. Whereas in breathing with oxygen, oxygen tension sharply decreased along the course of the microvessel bed. The above decrease seems to be due to exclusion of hemoglobin's dumping function and the effect of such factors as the ratio of arterioles surface's extension to the volume of their blood and the velocity of blood flow in pial arterioles.

Photothrombosis in rabbit brain cortex: follow up by continuous pO2 measurement

Continuous recording of changes in local pO2 during and after brain infarction in surviving animals which can be followed for months or years, may provide interesting information concerning pathophysiology and treatment of stroke and thrombosis. We performed such measurements before, during and till 4 weeks after photochemical induction of a cerebrocortical infarction in three rabbits. Rose bengal--a photosensitive dye which sticks to endothelial cells and gives rise to endothelial damage and thrombosis when illuminated--was injected intravenously. After injection, a circular area (diameter 3 mm) of the brain cortex was illuminated using an optic fiber conducting light from a halogen lamp, whether or not filtered by heat and colour filters. In order to enable pO2 measurement in and near the infarct zone, we constructed a transparent plastic frame in which pO2 electrodes were fixed beneath and 1 mm besides a shaft permitting mounting of the optic fiber. A black adhesive ring (inner diameter 3 mm) was attached to the bottom of the frame providing a perfectly demarcated illumination area. After fixation the electrodes were calibrated and the frame was implanted in the rabbit's skull. Ten days later an infarction was induced; pO2 was monitored continuously before, during and till 4 hours after this induction. Furthermore, pO2 was recorded 24 hours, 48 hours, 5 days, 14 days and 4 weeks after infarction. Parameters describing the time course of pO2 were determined. In the illuminated area pO2 decreased after a certain latency time to reach a very low level, probably zero level, where it remained for at least 24 hours. Gradually, recovery was observed during the following days, and four weeks after infarction both level and pattern of electrode current appeared to be normal again. In the border zone pO2 decreased but did not reach zero level. Recovery was observed earlier than in the illuminated area.

Feasibility of measuring oxygen tension in uterine cervix carcinoma

Cellular hypoxia is a cause of radioresistance. The oxygen tension (pO2) in normal tissues and in tumours can be measured by polarography. In this feasibility study we have measured the tissue pO2 of 10 patients suffering from uterine cervix carcinoma, using the Eppendorf histograph. The measurements were performed at the time of the brachytherapy after external radiotherapy. The machine was found to be reliable and no adverse effect was noted. The mean pO2 values in tumours were lower than those of normal tissues.

Does the direct measurement of oxygen tension in tumors have any adverse effects?

A new polarographic histograph was tested in tumors to assess its potential adverse effects in mice. The tumor cell lines used were: the lewis lung carcinoma (3LL) and two human xenografts (Na11+ and HRT18). The C57BL/6 mice survival and number of pulmonary metastases were not altered after pO2 measurements. Whatever the cell line, tumor doubling times were not changed after pO2 measurements. The new polarographic histograph was found to be reliable.

Construction, calibration and evaluation of pO2 electrodes for chronical implantation in the rabbit brain cortex

Aiming at continuous polarographic measurement of the mean pO2 in the rabbit brain cortex before, during and after photochemically induced infarction, we designed and constructed monopolar platinum oxygen electrodes of the open type for chronical implantation. The measuring tip (length 1 mm, diameter 0.1 mm) is covered with a homogenous membrane of cellulose acetate. The electrode currents are measured by a four-channel amplifier of proper design; the device permits accurate and stable polarisation, identical for each channel. Moreover, a calibration device has been constructed. It consists of a Buchner funnel filled with Ringer solution and mounted in a temperature-controlled bath. In order to create a specific partial pressure of oxygen in the calibration chamber, predetermined gasmixtures are bubbled through the solution using computer controlled mass flow regulators. The calibration device thus permits the determination of primary and secondary electrode parameters, i.e. linearity, oxygen sensitivity and residual current, and polarisation dependency, temperature dependency, sensitivity to CO2, electrode stability, dynamic behaviour and oxygen consumption. Three groups, each of them containing ten electrodes, have been tested with regard to electrode parameters: the first group contains bare electrodes, the second and the third group contain membrane covered electrodes, with a membrane thickness of 10 and 20 microns respectively. In order to evaluate acute and long-term effects of implantation on the brain cortical tissue and on the sensors' measuring qualities, electrodes have been implanted for different time periods (51 days, 30 days, 9 days, 5 min). pO2 was recorded regularly and polarograms have been registered. The effects on cortical tissue have been studied with the aid of light microscopy.

Cell growth experiments using a microcalorimetric vessel equipped with oxygen and pH electrodes

A method is described for simultaneous measurements of heat production rate, oxygen activity and pH, using a 3-ml stirred microcalorimetric titration/perfusion vessel fitted with a polarographic oxygen sensor and a combination pH-electrode. Heat production rate (+/- 0.3 microW), pH (+/- 0.01) and oxygen concentration (+/- 4 mumol/l) could be measured without any cross interference between the three signals. Results from measurements on suspensions of T-lymphoma cells and E. coli are presented.

Measurement of blood flow in rat eyes by hydrogen clearance

Intraocular measurements of blood flow have been made in the rat eye using hydrogen-clearance polarography. Hydrogen was delivered by a bolus injection of hydrogen-saturated saline via a cannula in the lingual artery of the anesthetized rat. An intraocularly placed hydrogen-sensitive microelectrode monitored the arrival and clearance of hydrogen preretinally adjacent to retinal arteries, veins, and intervascular areas. The effect of stepwise penetration through the retina and into the choroid was also determined, and a map of hydrogen distribution in the retina during hydrogen delivery and clearance was produced. Intraocular measurements, which have the advantage that the electrode location can be clearly visualized, together with computer control of the bolus injection and data collection, have allowed highly repeatable measurements of local blood flow to be made. The mean blood flow in retinal tissue was 373 +/- 51 ml.min-1.100 g-1 (values are means +/- SD, n = 32). The correlation between the nature of the hydrogen clearance curve and the location of the electrode helps explain data from other studies in which the position of the electrode with respect to the vasculature was unknown.

[The effect of tobacco smoking on tissue oxygen balance]

Oxygen tension (pO2) in the muscles was studied in 90 healthy young males: 60 were tobacco (cigarette) smokers and 30 were non-smokers. In the smokers pO2 in the muscles was higher than in the non-smokers. Functional tests revealed worsening of O2 to the tissues and reduced tissue metabolism intensity. The latter occurred against the background of quantitative and qualitative compensatory reactions of pO2 regulation mechanisms directed for improvement of O2 transport and tissue aeration indicating a negative effect of smoking on the capacity of tissue cells to utilize O2 in aerobic breathing.

[The diagnostic and prognostic significance of transcutaneous PO2 dynamics during a functional test in "pretoxicosis" and the initial stage of gestosis]

This study has simultaneously examined the kinetics of oxygen metabolism (KOM) and clinical symptoms of "pretoxemia" and edema of pregnancy. It was found out that estimates of KOM obtained before and after the hypoxia test may allow identification of abnormal tissue respiration typifying "pretoxemia", differentiation between "pretoxemia" and early-stage late toxemia (edema of pregnancy), and prediction of the risk and time of late toxemia, and potential of the body to adapt to hypoxia. Evaluation of KOM before and after the hypoxia test may be employed as a test for subclinical late toxemia.