D. W. Lübbers

Optical Fluorescence and Its Application to an Intravascular Blood Gas Monitoring System

Optical fluorescence has an extensive history of application in the laboratory to the measurement of ionic concentrations and the partial pressures of oxygen and carbon dioxide. The use of optical fluorescence based sensors to fulfill a recognized need for continuous invasive monitoring of arterial blood gases offers a number of inherent advantages. However, the requirements placed upon a blood gas probe and supporting instrumentation appropriate for use in the clinical environment result in significant design challenges in selection of suitable fluorescent dyes, maintenance of mechanical integrity while obtaining required miniaturization of sensors, and in the transmission, acquisition, and processing of low level light signals. An optical fluorescence based intravascular blood gas monitoring system has been developed which is particularly suited for the critical care and surgical settings and which has a sensor probe that can be introduced into the patient via a radial artery catheter. This system has shown an excellent agreement of measured with true values of pH, pCO2, and P02 in both in vitro and animal studies. Linear regression analysis of typical in vitro data, where true levels were established via tonometry and standardization to a high accuracy laboratory pH measuring instrument, shows slope/intercept values very close to 1.0/0.0 and correlation coefficients of greater than 0.99 for all three parameters.

The oxygen supply of the rat kidney: Measurements of intrarenalpO2

SummaryUsing a newly developed platinum-O2-microeletrode [30] based on the design ofSilver [37] the construction and properties of which are described,pO2-measurements in the parenchyma of the blood-perfused and the cell-free perfused rat kidney were carried out.By continuous recording of thepO2 during slow (150 μ×min−1) insertion of the O2-electrode into the respiring tissue two regions of distinctly different meanpO2-values were found. In the outer region which extends from the renal surface to a depth of about 3–4 mm (corresponding anatomically with the renal cortex) largepO2-differences exist close to each other. In the blood-perfused kidney the maximum corticalpO2-values lie in the range of arterialpO2 the lowest values at about 10 Torr. In the cortex of the cell-free perfused kidney the maximumpO2-values lie considerably below the arterialpO2.In both the blood perfused and in the cell-free perfused kidney at centripetal movement of the O2-electrode the cortical region of high and fluctuatingpO2 is followed by a narrow zone (≈200 μ radial extension) of a steep decrease of the meanpO2. At further insertion in both preparations thepO2 remains at lowpO2-values of ca. 10 Torr. Anatomically, this latter region of low and constantpO2 corresponds to renal medulla and pelvis.By recording the decrease of parenchymalpO2 after sudden stop of the perfusion attempts were made at measuring the critical local O2-supply pressure. In the cortex of the cell-free perfused kidney critical local O2-supply pressures between 6 and 28 Torr with a maximum abundance at 8 Torr were found.The qualitative and quantitative implications of the presented data on the conditions of parenchymal O2-supply are discussed. The results are interpreted as an indication for the arteriovenous shunt (bypass)-diffusion of considerable amounts of oxygen, especially under the conditions of the cell-free perfusion. Furthermore, it follows from the data presented that even at high venous O2-pressures and high meanpO2-values in the parenchyma regions of local anoxia may exist.

The cutaneous uptake of atmospheric oxygen contributes significantly to the oxygen supply of human dermis and epidermis

It has been known since 1851 that atmospheric oxygen is taken up by the human epidermis. The contribution to total respiration is negligible. Until now the significance for the local oxygen supply of the skin has remained unknown. With a newly developed sensor, the oxygen fluxoptode, it has become possible to make local measurements of the transcutaneous oxygen flux (tcJO2). In this study the sensor was calibrated so that absolute values of tcJO2 could be reported. At rest, tcJO2 was determined on normal, humidified skin on the volar forearm of 20 volunteers of different age groups. In order to evaluate the contribution of the blood flow to the oxygen supply of the skin, tcJO2 was recorded at the end of a 5 min suprasystolic occlusion of the forearm. At normal skin surface partial oxygen pressure (163 ± 9 Torr), tcJO2 was 0.53 ± 0.27 ml O2 min−1 m−2. A 5 min interruption of blood flow resulted in an increase of 9.5 ± 6.3 % in tcJO2. The value of tcJO2 was unaffected by the age of the subject. Published data on the oxygen diffusion properties of skin and simulations of intracutaneous profiles of oxygen partial pressure indicated that under these conditions, the upper skin layers to a depth of of 0.25–0.40 mm are almost exclusively supplied by external oxygen, whereas the oxygen transport of the blood has a minor influence. As a consequence, a malfunction in capillary oxygen transport cannot be the initiator of the development of superficial skin defects such as those observed in chronic venous incompetence and peripheral arterial occlusive disease.

Time course of changes of extracellular H+ and K+ activities during and after direct electrical stimulation of the brain cortex

The kinetics of H+ and K+ activities were recorded during and after direct electrical activation of the brain cortex (cat). H+ activity was measured with H+-sensitive glass microelectrodes (tip diameters of 1–4 μm) and K+ activity was registered with double-barrelled ion-sensitive microelectrodes (tip diameters of 1–3 μm). It could be shown that extracellular H+ activity initially decreased for a few seconds and increased only after the 7.s. Maximum acidosis was always noticed after stimulation ended. Alkalotic as well as acidotic changes were the higher the stronger the stimulation parameters were. K+ activity increased very rapidly after stimulation began, reached its maximum when stimulation ended and then decreased to its initial value with an undershoot.It is concluded that the functional hyperemia of microflow could be triggered by the rapid increase in K+ activity, whereas the initial alkalotic change of extracellular pH means that H+ activity does not play a role in the first phase of this kind of hyperemia. The alkalotic shift is interpreted to be caused by the washout of CO2 due to the rapid increase in microflow. In the further course, H+ activity obviously contributes to the maintenance of functional hyperemia. In this later period K+ activity is always below the control value.

Quantitative continuous measurement of partial oxygen pressure on the skin of adults and new-born babies

SummaryIt is possible to perform continuous quantitativePO2 measurements on vasodilated skin by means of surface Pt electrodes according to Clark when the electrode is fixed to the skin with a synthetic plastic material and in situ calibration is performed. A new in situ calibration of thePO2 electrode is described. At first the skinPO2 increases with O2 inspiration. After perfusion stop the skinPO2 shows a linear decrease because of the skin respiration, down to aPO2 at which hemoglobin liberates chemically bound O2. As thisPO2 value of hemoglobin is known it is possible to use it for calibrating the electrode. ThePO2 of normal skin is about 0–7 Torr. After vasodilation obtained by rubbing with a nicotinic acid derivate (Finalgon®, Anasco, Wiesbaden),PO2 increases to a mean value of 38.1 (±8.1) Torr (n=77). Under these conditions, skinPO2 reaches arterial values never in adults and rarely in new-born babies.

The oxygen supply of the dog kidney: Measurements of intrarenal pO2

The platinum O2-microelectrode of Lubbers and Baumgartl (1967) [11] has been used for the measurement of the intrarenal distribution of pO2 values in the dog kidney in situ. By continuous recording of the pO2 during slow (150 μ × min−1 insertion of the O2-electrode into respiring tissue two regions of distinctly different mean pO2 values were found. In the cortical region large pO2-differences exist close to each other. The maximum cortical pO2 values lie in the range of arterial pO2, the lowest values at about 1–2 Torr. At centripetal movement of the O2-electrode the cortical region of high and fluctuating pO2 is followed by a narrow zone (≈200 μ radial extension) of a steep decrease of the mean pO2. At further insertion the pO2 remains at low pO2 values at ca. 10 Torr. Anatomically this latter region of low and constant pO2 corresponds to renal medulla and pelvis. The results fully confirm the conclusions drawn on the oxygen supply of the mammalian kidney which we have derived from previous experiment on the isolated and the in situ rat kidney (Leichtweiss et al. 1969) [7]. Strong indications are found for the efficient a-v oxygen shunting by diffusion. Even at high O2 pressures in the renal vein and high mean pO2 values in the renal parenchyma regions of local anoxia may exist.

Behavior of microflow and localP O 2 of the brain cortex during and after direct electrical stimulation

SummaryMicroflow was continuously recorded at four sites of the brain cortex (cat) during and after direct electrical stimulation of the brain. In some experiments local oxygen partial pressure (Po2) was additionally measured with a new combined element in the same capillary area where microflow was determined. This simultaneous measurement of both microflow and localPo2 in the tissue enabled us to analyze the kinetics of microflow and its dependence on localPo2 during activation. Microflow increased at all sites measured, in most cases within 1–2 s after the beginning of stimulation, reached the maximum of hyperemia after the end of stimulation and then gradually returned to the initial level within 30 s up to several minutes according to the intensity of the stimulation. The reaction pattern of microflow was uniform. As localPo2 normally did not decrease and did not even show an initial decrease after the onset of stimulation, the hyperemia could not be caused by local hypoxia. On the contrary, localPo2 always increased with the increase of microflow. ThisPo2 increase is necessary, because the tissue which consumes more oxygen needs higherPo2 gradients to transport the oxygen to the mitochondria.

Regulation of local tissuePo 2of the brain cortex at different arterial O2 pressures

SummaryLocal tissue oxygen pressure (Po2)was recorded with a platinum multiwire surface electrode at adjacent sites of the cat cortex under steady-state conditions and with different arterial oxygen supply. SimultaneouslyPo2in the sinus sagittalis was continuously recorded through the vascular wall in some experiments. Under normoxic and steady-state conditions localPo2values varied between 0 Torr and almost arterial levels of 90 Torr. This was in accordance with the assumption of a diffusive transport of oxygen in tissue. With increased arterial oxygen supply local tissuePo2reacted quite differently at adjacent sites. Linear increases in local tissuePo2as compared to arterialPo2as well as constant levels, very small increases and even small decreases were recorded. Constancy or small changes, respectively, of localPo2(=localPo2regulation) may be caused by changes in microflow, but changes in oxygen consumption cannot be excluded completely. The regulation of localPo2could be abolished by adding CO2 to the gas mixture or by producing tissue anoxia. With severely reduced arterial oxygen supply local tissuePo2dropped down to hypoxic or anoxic levels at all sites measured.

Limiting section thickness of guinea pig olfactory cortical slices studied from tissuepO2 values and electrical activities

The relationship between tissue oxygen partial pressure (pO2) values and electrical activities of guinea pig olfactory cortical slices was investigated as the slices were superfused with Krebs-Ringers solution equilibrated with different gas mixtures. ThepO2 values were measured in the slices with oxygen microelectrodes (tip diameter <1 μm). 1. Studies ofpO2 measurements showed the variability of minimumpO2 value of oxygen profiles in the tissue slice. The profile depends on thepO2 value of the superfusate and on the thickness and the oxygen consumption of the slice. With our experimental conditions an anoxic area developed in the middle layers of the slice when the thickness of the slice exceeded ca. 430 μm; in thinner slices there was no anoxic area. In our case the limiting section thickness of the slice was ca. 430 μm from the viewpoint of tissuepO2 value. 2. The N potential (extra-cellularly recorded EPSP) showed a tendency to decrease in amplitude, for slices being thicker than ca. 430 μm. It would seem reasonable to think that the decrement of the N potential was brought about by the existence of the anoxic area. 3. When the slice was bubbled with 25, 45 or 95% O2, the tissuepO2 value changed, and the N potential height also changed. The N potential was higher in amplitude when bubbled with 95% O2 than with 25% O2. On the other hand, the amplitude of the IS potential (the lateral olfactory tract potential) was not influenced as much as that of the N potential by the change of tissuepO2 value in the slice. 4. The tissuepO2 value was continuously measured during the electrical stimulation of the lateral olfactory tract. The steady state level of tissuepO2 value obtained during the stimulation diminished as the frequency of stimulation increased from 5–30 Hz.

Die Messung des Kohlensäuredruckes in Gasen und Flüssigkeiten mit der pCO2-Elektrode unter besonderer Berücksichtigung der gleichzeitigen Messung von pO2, pCO2 undph im Blut

Die direkte ~Iessung des Kohlens£uredruckes (pC02) ist nuch einem MeBprinzip mSglich, das unabh~ngig voneinander yon STow u. ~A~DALL (1954) und yon GE]~Tz u. LOESC~CKE (1958) angegeben wurde. Diffundier~ CO 2 in Wasser oder in eine BicarbonatlSsung, so £ndert sich dabei gesetzmiiBig in Abh~ngigkeit yon der C02-Konzentration der p~ dieser LSsung. Sorgt man durch Zwischenschaltung einer Membran dafiir, d~l~ nur C0~ in die BicarbonatlSsung dringcn kann, so ist diese p~-J~nderung spezifisch fiir C02. S~ow u. Mitarb. benutzten eine Gla~elektrode, die mit einer Gummimembran bezogen war, G ~ T Z u. LOESCKCKE arbeiteten mit einer Poly~thylenmembran. S ] ~ v ~ n ~ a ~ v s u. B ~ D L n ¥ (1958) entwickelten dies Verfahren besonders fiir Blutmessungen weiter. Sie benutzten eine Teflonmembran und fiigten zur Stabilisierung des Fliissigkeitsspaltes eine Cellophanmembran yon 12 tt Dicke zwischen Teflonund Glasmembran ein. tt]¢RTZ u. S~s55 (1959) verwandten ffir oberfl~chliche Gewebemessungen eine flachkonl~ave Elektrode, fiber welchc die Teflonmembran ohne Zwischenlage gespannt wurde. Bei der gleichzeitigen Messung yon Sauerstoffund Kohlens~uredruck im Blur wirkt es sich nachteilig aus, dal~ die Elektrode yon S ~ v ~ x ~ ~ v s u. ] ~ n ~ ) ~ ¥ eine relativ lange Einstellzeit (2--4 min fiir 99 °/0 des Endwertes in Gas) hut, w~hrend sich bei der Elektrode yon H ~ T z u. SI~S55 durch mechanische Belastung leich~ die Eichkurve verschiebt, da der Bicarbonatspal~ nicht durch eine Zwischenschicht stabilisiert ist. Die Verwendung yon Plexiglas als Geh~useoder Analysengefiil~material (siehe S ~ v ~ G ~ v s u. B~AI)L~¥ 1958) hat wegen der LSslichkei~ fiir CO 2 die gleichen Nachteile wie bei der P02-Messung.