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Model of Oxygen Transport through the Skin as Basis for Absolute Transcutaneous Measurement of Pa O2
Author(s) -
Kimmich H. P.,
Kreuzer F.
Publication year - 1978
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1978.tb01387.x
Subject(s) - oxygen , oxygen transport , oxygen–haemoglobin dissociation curve , dermis , electrolyte , epidermis (zoology) , blood flow , drop (telecommunication) , biophysics , electrode , anatomy , medicine , chemistry , cardiology , computer science , biology , telecommunications , organic chemistry
In the practical situation of tcP o2 , measurements, oxygen is transferred from the dermis through the epidermis, a layer of connecting fluid, and the membrane and electrolyte of the measuring system to the cathode of the polarographic cell. By application of heat the mean capillary P o2 , in the dermis (Pc o2 ,) is supposed to be equal to Pa o2 . This hyperaemization effect is influenced by many factors, e.g., the peripheral blood flow, and has therefore been the subject of major interest in recent years. But even under ideal conditions transcutaneous measurement of Pa o2 , is still influenced by several other factors. Therefore we consider hyperaemization to be ideal and investigate the P O2 , changes during oxygen transport from the arteries to the electrode with a partly well‐known model. We can distinguish three effects, namely:1 Increase of the P o2 , when travelling from the arteries to the (warmer) capillaries due to a right shift of the oxygen dissociation curve of the blood. 2 Diffusional drop of the P O2 , in the epidermis due to the oxygen flux introduced by the measuring system. 3 Diffusional drop of the P O2 , in the inner layer of the epidermis due to the oxygen flux introduced by the oxygen consumption of the living cells.With a good electrode system consuming little oxygen, the second effect is very small and can therefore be disregarded, in other words, if the resistance to diffusion in the membrane of the measuring system is large as compared to that in the epidermis we may write: tcP o2 ,±Ps O2 , = Pa o2 , + ΔPa o2 , (T1) ‐ PQ o2 where: Ps O2 , = skin P O2 , at the border of living and dead cells of the epidermis. Pa o2 , = arterial P O2 , at a body temperature of 37d̀C. ΔPa o2 , (T1) = temperature correction term for T1±37d̀C ΔPQ o2 , = P o2 , drop across the living layer of the epidermis due to cell metabolism TI = temperature of the mean capillary blood The ratio TR = tcP o2 /Pa o2 = 1 + (ΔPa o2 (T1) ‐ PQ o2 )/Pa o2 will be unity if ΔPa o2 (T1) = PQ o2. It can be shown with the aid of the model and measurements at body temperature (where P ‐ co2 is equal to PV O2 or higher) that the term PQ o2 is not small as generally assumed , but greater than 30 mmHg. If for example, at normoxia (Pa o2 = 100 mmHg) a TR of 0.7 is found, then a TR of approximately 0.5 and 0.85 may be expected for hypoxia (60 mmHg) and hyperoxia (200 mmHg) respectively. The model is also used to investigate the temperature distribution in layers parallel to the membrane of the polarographic cell as a function of the area covered by the measuring cell. Theoretically the temperature cf the mean capillary blood may be calculated from the formula for TR if TR and PQ o2 are assessed experimentally, and a t the same time calibration for absolute measurement of Pa o2 is possible if hyperaemization is such that venous admixture remains small.