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Biomedical subjects

C E Hahn

Publications and source records attributed to C E Hahn.

11 recordsLinked to original sources
PubMed1992

In vitro performance test system for pulse oximeters.

An in vitro system was developed capable of testing the accuracy and reproducibility of pulse oximeter readings. The pulse oximeter probe receives signals through a pulsating blood cuvette. The development of the design of the cuvette is described. Using the final design (or 'model finger'), a comparison is made between readings from a Datex Satlite pulse oximeter (SpO2) and saturation values obtained by use of a multi-wavelength bench oximeter (SaO2). Linear regression analysis of the data gives SpO2 = 0.88 SaO2 + 11.2 (r = 0.979, p < 0.001).

Fingers↗
PubMed1992

Response of 10 pulse oximeters to an in vitro test system.

Pulse oximeters are often used in situations in which severe hypoxaemia may occur. We have developed an in vitro system to test the accuracy of pulse oximeter calibration. The probe of 10 different oximeters was attached to a model finger in an in vitro blood circuit, and pulse oximeter readings (SpO2) were compared with multi-wavelength in vitro oximeter readings (SO2) over a range of SO2 values from 50 to 100%. The oximeters tested varied widely in their accuracy and linearity. We conclude that the system can test the accuracy, reproducibility and linearity of response of pulse oximeter readings at low oxyhaemoglobin saturations.

Calibration↗
PubMed1979

Continuous measurement of blood gases in vivo by mass spectrometry.

Continuous analysis of oxygen and carbon dioxide tension in the blood phase, over periods of 4-5 h, was carried out in the pulmonary artery (93 determinations in six anesthetized dogs) and in the aorta (29 determinations in four anaesthetized dogs). Silastic-covered stainless steel catheters attached to a mass spectrometer were used. The mass spectrometer signals were linearly related to the blood-gas tensions measured by conventional analysis. The mass spectrometer signals were calibrated in vivo by exposing the animals to high and low oxygen and carbon dioxide tension. With such in vivo calibration the slopes of the straight line regressions for mass spectrometer PO2 or PCO2 on PO2 or PCO2 by conventional analysis were comprised between 0.944 and 1.031 while the standard error of the slopes were between 0.019 and 0.031. Deliberate reductions of cardiac output had little effect on the mass spectrometer readings.

Animals↗
PubMed1979

O2 and N2O analysis with a single intravascular catheter electrode. An in-vitro study.

The simultaneous measurement of O2 and N2O in liquid, using a single polarographic catheter electrode, is described. It is shown that commercial PO2 intravascular electrodes, with silver cathodes, produce separate and distinct polarograms for O2 and N2O, and that these electrodes can be used for the measurement of both PO2 and PN2O.

Blood Gas Analysis↗
PubMed1978

An electrode for PN2O and PO2 analysis in blood and gas.

The development of a new polarographic sensor for measuring simultaneously both N2O and O2, in either gas or blood, is described. The cathode is made of silver, and it is shown that silver deposition on normal platinum or gold cathode electrodes can result in an enhancement of a PO2 signal, when measured in the presence of nitrous oxide. Silver can be deposited on the cathode by means of Ag+ ions diffusing through the electrolyte from an Ag/AgCl reference electrode. The use of an Ag cathode enables both O2 and N2O signals to be measured.

Blood Gas Analysis↗
PubMed1977

Properties of blood oxygen transport in the turtle Pseudemys scripta and the tortoise Testudo graeca: effects of temperature, CO2 and pH.

Properties of oxygen-haemoglobin binding have been investigated in the aquatic turtle Psuedemys scripta and the terrestrial tortoise Testudo graeca. Haematocrit (30-35%) and haemoglobin concentration (12-14 g/100 ml blood) were similar in both species. P50 at physiological levels of PCO2 (20-25 mm Hg) was 21 mm Hg in Pseudemys, compared with 23 mm Hg in Testudo. The Bohr shift of the blood of both the turtle and the tortoise was almost identical at -0.28. The heat of oxygenation, deltaH, reflecting the temperature sensitivity of O2-Hb affinity, was -10.55 in Pseudemys and -8.12 kcal/mol in Testudo. These data on whole blood do not support previous generalizations in the literature suggesting marked differences in oxygen-haemoglobin binding between aquatic and terrestrial chelonian reptiles.

Animals↗
PubMed1976

A development of the oxyhemoglobin dissociation curve analyzer.

The development and improvement of an oxyhemoglobin dissociation curve analyzer is described. PO2 electrode performance was improved by electrochemical means and circuits are described for processing the PO2 and pH signals from the analyzer. A circuit for automatically correcting the curve for Bohr shifts from pH 7.40 is described, and the performance of the Bohr shift unit is verified by experiment. The analyzer produces curves under standard conditions of PCO2 40 mmHg, pH 7.40, and 37 degrees C.

Electrodes↗
PubMed1975

Electrochemical improvement of the performance of PO2 electrodes.

Rotating ring-disc electrode studies have indicated that relatively large quantities of hydrogen peroxide ion, HO2-, are produced when oxygen is reduced at a platinum or gold polarographic electrode surface. The electrochemical reduction processes are improved and the quantity of HO2- is reduced by using alkaline buffer electrolytes (pH 10 to 11) and by polarising the electrode at voltages more negative than -0.9 V. The presence of HO2- in the electrolyte has been shown to be the cause of excessively long time response in both blood-gas and respiratory polarographic PO2 electrodes; electrode alinearity on micro-blood-gas PO2 electrodes has also been shown to be due to the absence of a plateau on the polarogram of electrodes when used with conventional electrolytes. The use of a high pH buffer and high negative voltage results in a long, flat plateau and a marked improvement in both electrode linearity and response time. This two-fold improvement in electrode performance holds true for both platinum and gold polarographic respiratory gas and blood-gas PO2 electrodes.

Blood Gas Analysis↗
PubMed1975

Studies with the "Severinghaus" PCO2 electrode I: electrode stability, memory and S plots.

A study of the Radiometer "Severinghaus" Pco2 electrode has been made in order to investigate its stability and reproducibility when exposed to a series of inknown gas samples of various carbon dioxide concentrations. Electrodes were found to exhibit a pronounced memory effect, which depended upon the Pco2 of the last sample to which they had been exposed if the exposure had been for more than a few minutes. When a number of electrodes were exposed to a single reference gas at all times, except for the few minutes required to measure the Pco2 of an unknown sample, the electrical output of the electrode was unexpectedly stable and reproducible. This implies a high degree of measurement accuracy. If the reference gas to which the electrode is usually exposed is of low carbon dioxide concentration, the electrode displays its highest degree of stability and reproducibiltiy. The use of low carbon dioxide content reference gases is not always convenient, however, because they increase the response time of the electrode. Reference gases of high carbon dioxide content induce unstable electrode behaviour, and so it is recommended that gases higher than 5% v/v Co2 are not chosen for this purpose.

Carbon Dioxide↗
PubMed1975

Studies with the "Severinghaus" Pco2 electrode II: CO2 measurement using a single control analyser.

A simple, single calibration point, single control Pco2 analyser is described. Results are presented to show that such an analyser will provide extremely accurate and reproducible results over a limited range around the calibration point, and this technique has been applied to the measurement of the apparent blood-gas and water-gas difference for a Pco2 electrode. The accuracy and working range of this simple system has been compared with a two-calibration-point, two-control analyser similar to commercial systems and results are presented to show that the more complicated system, although accurate over a wider range of Pco2, did not produce accurate results when the Pco2 of test samples lay outside the calibration range. Reasons are presented to explain this unexpected behaviour.

Carbon Dioxide↗