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Biomedical subjects

D W Lübbers

Publications and source records attributed to D W Lübbers.

At least 19 recordsLinked to original sources
PubMed2002

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 (tcJ(O2)). In this study the sensor was calibrated so that absolute values of tcJ(O2) could be reported. At rest, tcJ(O2) 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, tcJ(O2) was recorded at the end of a 5 min suprasystolic occlusion of the forearm. At normal skin surface partial oxygen pressure (163 +/- 9 Torr), tcJ(O2) was 0.53 +/- 0.27 ml O2 min(-1) x m(-2). A 5 min interruption of blood flow resulted in an increase of 9.5 +/- 6.3 % in tcJ(O2). The value of tcJ(O2) 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.

Adult↗
PubMed2000

Local oxygen content in the skin is increased in chronic venous incompetence.

In skin lesions of chronic venous incompetence (CVI) transcutaneous oxygen pressure (tcpO(2)) at the ankle is often reduced. However, in some CVI patients the tcpO(2) during suprasystolic occlusion remains significantly higher than in healthy subjects. The aim of the present study was to investigate which kind of CVI patients develop this phenomenon and whether the higher tcpO(2) during occlusion is caused by a smaller oxygen consumption of the skin or by an increased local oxygen content. The oxygen consumption of the skin was measured by the pO(2) decrease (DeltatcpO(2)/Deltat) after stopping the arterial oxygen supply when the hemoglobin was saturated by oxygen inhalation, i.e., at tcpO(2) values above 120-130 mmHg. By multiplying the tcpO(2) with the mean oxygen solubility coefficient of the skin the content of physically dissolved oxygen is obtained. The decrease of tcpO(2) in the 55- to 45-mmHg range indicates the consumption of oxygen physically dissolved and chemically bound to hemoglobin. It gave a parameter for estimating the local hemoglobin content of the skin. These values and the minimal tcpO(2) after a 5-min arterial occlusion were measured in 14 healthy subjects, in 13 patients with varicose veins, but no skin lesions, in 10 patients with CVI lesions like white atrophy and lipodermatosclerosis and in 16 CVI patients with open venous ulcers. During suprasystolic occlusion tcpO(2) at the ankle remained significantly higher in CVI patients with skin lesions than in the healthy control subjects (25.6 +/- 18.9 versus 8.0 +/- 7.0 mmHg). The steepness of the tcpO(2) decrease caused by cutaneous oxygen consumption in healthy subjects was not significantly different from the CVI patients. In contrast, the decrease of tcpO(2) at the ankle between 55 and 45 mmHg was 1.9 +/- 2.0 mmHg/s in the control group and 0.7 +/- 0.5 mmHg/s in the group with open venous ulcers. These results indicate a higher hemoglobin content in the skin of the CVI patients than in healthy subjects. Obviously, the hemoglobin bound oxygen content in the skin of CVI patients is increased. Thus, a lack of oxygen is unlikely to be the primary reason for the development of skin lesions in CVI.

Administration, Inhalation↗
PubMed2000

The transepidermal oxygen flux from the environment is in balance with the capillary oxygen supply.

It has been known since the nineteenth century that oxygen is taken up by the human skin. With a newly developed sensor it became possible to examine the influence of the vascular supply on the oxygen flux into the skin, tcJ(O2). tcJ(O2) was measured optically by determining the oxygen partial pressure difference, DeltapO2 across a diffusion test membrane, which itself was brought into close contact to the skin surface. Under these conditions DeltapO2 is proportional to the tcJ(O2). The skin perfusion was varied by the application of a hyperemizing ointment on the abdomen of 12 volunteers and by suprasystolic occlusion at the thigh of 20 volunteers. The tcJ(O2) was measured at a temperature of 33 degrees C of the humid skin. It was compared with the skin perfusion monitored by laser Doppler flow, and the capillary oxygen supply measured by transcutaneous partial pressure of oxygen, tcpO2, at an electrode temperature of 37 degrees C. The transcutaneous O2 flux produced a distinct DeltapO2 of 81.8 +/- 8.2 Torr (abdomen) and 72.8 +/- 12.3 Torr (ankle). In hyperemic skin on the abdomen the O2 flux was reduced (DeltapO2 = 57.7 +/- 10.6 Torr). The tcpO2 increased from 8.7 +/- 10.7 to 35.1 +/- 16.9 Torr. During suprasystolic occlusion, DeltapO2 increased by 6.4 +/- 2.3 Torr, whereas laser Doppler flow and tcpO2 decreased significantly. These results indicate that the total oxygen supply of the epidermis and the upper dermis is guaranteed even if the perfusion varies.

Adult↗
PubMed1998

Rhythmical variations of haemoglobin oxygenation in cutaneous capillaries.

The consequences of rhythmical arteriolar vasomotion for nutrition and the tissue oxygen supply to human skin are largely unknown. In the study presented here, the periodic variations of haemoglobin oxygenation in the small cutaneous vessels have been evaluated with a new reflection spectrophotometer. For the assessment of spatial variations, we examined 24 different sites in 20 healthy volunteers. For quantification of the relatively long duration of periodic variations, a Digital Fourier Transformation with a specially programmed filter was used. In 265 out of 480 spectra (55.2%), periodic variations of the haemoglobin oxygenation were found. The average of the main frequency of waves was 7.0 +/- 2.5 cycles per minute. The occurrence of variations of haemoglobin oxygenation depended on the measuring site. In the gluteal region, variations were observed in 17 out of 20 subjects, on the palms in 16 out of 20, at the foot plantar in 18 out of 20 in comparison to the cheek (8/20), the lip (5/20) and the eyelid (6/20). On the head we observed significantly more variations per minute than in the lower extremities. Because these variations, with duration of up to 30 s, have a relatively slow dynamic compared with heart rate and breathing frequency, consequences for the cutaneous diffusion and metabolism of other substrates are very likely.

Adult↗
PubMed1998

Applicability of the Kubelka-Munk theory for the evaluation of reflectance spectra demonstrated for haemoglobin-free perfused heart tissue.

Reflectance spectrometry is a useful tool for studying in vivo kinetic changes in the oxygen saturation of haemoglobin and myoglobin as well as the redox state of cytochromes. A method is given which allows the quantification of tissue reflectance spectra using multicomponent analysis. This method utilizes the Kubelka-Munk theory for modelling the measured tissue spectra. To test this approach, reflectance spectra of a haemoglobin-free perfused guinea pig heart were measured by a fast scanning spectrophotometer (100 spectra/s, spectral resolution 1.0 nm) and evaluated using the component absorbance spectra measured separately. A relative mean spectral residual error of 0.15% was achieved by least-squares fitting. Using statistical error propagation, oxygenation of myoglobin is obtained within a relative precision of 1%, and the redox state of cytochromes aa3 and c are determined simultaneously within a margin of 3%; the results for the redox-state of cytochrome b, however, are less precise. Special component error functions are presented to provide a reliability measure for the concentration prediction using this multicomponent assay. The consistency of the theory and the component absorptivity data is tested by regressing the actual concentrations obtained for each of the redox pair components during the various states of tissue oxygenation. A method is described for the recognition and reduction of systematic errors.

Animals↗
PubMed1995

Optical sensors for clinical monitoring.

Technical progresses make it now possible to monitor well known or new parameters in vivo or in the laboratory with high accuracy. Especially optical sensors can advantageously be used for many medical applications. To understand advantage and limitation of a measuring technique the basic processes will be shortly discussed. There are two types of optical sensors: 1) optical sensors which use intrinsic indicators (as for example haemoglobin or cytochromes). In this chapter tissue photometry and evaluation methods for multicomponent scattering systems are discussed; nearinfrared and NADH fluorescence measurements are shortly mentioned. 2) Optical sensors using extrinsic indicators (optodes). As extrinsic indicators absorbant as well as luminescent indicators are used. Luminescence indicators are especially sensitive. Microoptodes and two dimensional imaging is possible. From the basic molecular reactions of the sensing mechanisms follows that for most of the indicator reactions there is a non-linear, almost hyperbolic relationship between optical signal and concentration of the analyte. Consequently, accuracy as well as sensitivity of the optode is changing in a given measuring range. Therefore, the optical indicator must be carefully selected. Lifetime (or phase angle) measurements have the advantage that their accuracy is independent of indicator concentration, intensity of the light source and light transport between the sensing element and the photometric setup. Optodes can be manufactured as flexible membranes permeable for the analyte. This facilitates the construction of fibreoptic sensors. As practical examples oxygen optodes, ion optodes, optical pCO2 sensors, and bench-top as well as intra-arterial blood gas measurements are discussed in detail.

Biosensing Techniques↗
PubMed1992

Transcutaneous measurements of skin O2 supply and blood gases.

The data of the O2 exchange through the surface of the skin show that a part of the normal upper skin can be supplied with O2 from the surrounding atmosphere. This may be important in pathological situations although probably simultaneous disturbances of the substrate supply may be more serious. The noninvasive continuous registration of skin surface pO2 (and pCO2) allows to monitor skin oxygen supply under different conditions. The new optical sensing of pssO2 and of the local O2 flux into the skin opens up new promising possibilities for quantification of the skin oxygen supply.

Blood Gas Monitoring, Transcutaneous↗
PubMed1989

Oxygen supply of the blood-free perfused guinea-pig brain in normo- and hypothermia measured by the local distribution of oxygen pressure.

The O2 supply of the blood-free perfused brain cortex of the guinea pig was investigated by measuring polarographically the local distribution of tissue PO2 at 18 degrees C, 24 degrees C, and 37 degrees C. The perfusion was performed in situ, using a medium equilibrated by a gas mixture of 95% O2 and 5% CO2. Papaverine was added to prevent vasoconstriction during hypothermia. To avoid measuring artefacts thin micro electrodes with a small sharpened tip of ca. 4 microns in diameter were used and a special puncturing technique was applied. The experimental results indicate the presence of a large variation of local tissue PO2. Local mean PO2 increased up to a depth of 1000 microns, reached a plateau, and then decreased towards 3000 microns. This demonstrates that the O2 supply changes in dependence of the distance of the brain surface. This may partly be caused by the special vascularization pattern of the brain cortex. As it follows from the PO2 histograms, at 24 degrees C the tissue layer between 0-2000 microns (layer I) was well supplied with oxygen, whereas at the same time the layer between 2001-3000 microns (layer II) was hypoxic. At 37 degrees C, both layers were hypoxic, but layer III showed the more pronounced tissue hypoxia. To obtain a sufficient oxygen supply the temperature had to be reduced below 24 degrees C to sufficiently decrease tissue O2 consumption: at 18 degrees C, there was no sign of hypoxia any more. In comparison with the PO2 histogram of the tissue the PO2 histogram of the pial surface was shifted to higher PO2 values.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗