Biomedical subjects

A Zwart

Publications and source records attributed to A Zwart.

71 records · Page 4Linked to original sources

PubMed1982

Oxygen dissociation curves for whole blood, recorded with an instrument that continuously measures pO2 and sO2 independently at constant t, pCO2, and pH.

We describe a method for recording oxygen dissociation curves for whole-blood specimens. The blood sample is placed in a thermostated measuring chamber, and pO2 and SO2 are measured continuously by polarography and by reflectometry, respectively. During the recording of an oxygen dissociation curve, the pO2 and SO2 signals are stored in a data-acquisition system, while pH, pCO2, and temperature are kept constant. Determination of precision and error discussion indicated that the coefficient of variation (CV) of the determination of the oxygen dissociation curve is mainly determined by the error in the measurement of SO2. The overall CV of pO2 values belonging to the lower, mid-, and upper parts of the SO2 range is estimated to be about 2.6, 3.1, and 2.1%, respectively. In practice the measurements are about 30% more precise than estimated. With our method, the fixed-acid-induced Bohr effect (H+ factor) can be determined over the entire SO2 range with much greater precision than hitherto.

Blood Gas Analysis↗

PubMed1982

Determination of interdependent ligand effects on human red cell oxygen affinity.

Human whole blood oxygen affinity was determined as P50, i.e. PO2 for oxygen saturation (SO2) = 0.5, in a new system which allows the measurement of SO2, PO2 and pH continuously and independently, with control of PCO2 and temperature. The influence of pH on P50 expressed as the H+ factor (delta log P50/delta pH)PCO2 was measured under conditions of varying PCO2, temperature and concentration of 2,3-diphosphoglycerate (2,3-DPG), resulting in a set of data expressing second-order inter-ligand interactions. The H+ factor appeared to be only slightly dependent on PCO2. Similarly, the CO2 factor (delta log P50/delta log PCO2)pH shows only a minor dependence on pH. The H+ factor in linearly related to the temperature: at 17 degrees C and 42 degrees C the H+ factor is about -0.53 and -0.36, respectively. Likewise, the temperature factor (delta log P50/delta T)PCO2,pH is linearly related to pH. A pilot study on the effect of varying intra-erythrocytic 2,3-DPG concentrations on the oxygen affinity showed that a very low 2,3-DPH/Hb4 ratio apparently does not influence the H+ factor. A high ratio, however, seems to lower the H+ factor considerably.

2,3-Diphosphoglycerate↗

PubMed1981

Evaluation of alveolar amplitude response technique for determination of lung perfusion in exercise.

We investigated the influence of tracer gas venous return on the determination of pulmonary perfusion (Qp) using the alveolar amplitude response technique (AART) to evaluate the applicability of this technique at rest and during exercise. The venous return influence was calculated by a computer simulation applied to a simplified body compartment model. Using the AART method, which neglects the influence of venous return, a simulation based on acetylene as a tracer gas predicted an overestimation of the actual value of Qp ranging from 0 to 10% for all work loads investigated. These theoretical results were compared with experimental results. Experiments with human subjects with acetylene as the tracer gas yielded an underestimation of Qp of about 20% at rest and an overestimation of about 7% under different exercise conditions. Experiments with anesthetized dogs showed an underestimation of Qp of about 12% for acetylene and about 6% for halothane. The theoretical and experimental results related to exercise conditions are thus in good quantitative agreement. The experimental data obtained for acetylene with human subjects at rest and with anesthetized dogs are also in good quantitative agreement. However, they deviate considerably from theoretical predictions. This discrepancy may be due to the simplified body compartment model used in the calculations, which can considerably influence the calculated results, especially for conditions at rest. The main conclusion of this paper is that recirculating tracer gas does not unduly influence results for Qp obtained with the AART method when halothane is used as the tracer gas.

Acetylene↗

PubMed1981

Helium and sulfur hexafluoride washout in asymmetric lung models.

Model calculations were carried out on extensible lung models that are characterized by asymmetries in branching pattern or cross section within the acinus. The calculations contribute to a better understanding of the intrapulmonary mixing of gases poorly soluble in blood. For single-breath washout stimulations of helium (He) and sulfur hexafluoride (SF6), only small differences were found between the results obtained from a lung model with an asymmetric branching pattern using either a local homogeneous or inhomogeneous delta V/V distribution. This indicates that the geometry of this model is the most important factor for generating realistic values for the slope of the alveolar plateau, the Bohr dead space and the end-tidal concentration ratio for SF6 and He. The calculated relation between the decrease in the slope of the alveolar plateau and postinspiratory breath-holding times showed good agreement with experimental findings in healthy adult subjects. Multiple-breath washout simulations enabled us to explain the experimentally observed high dilution of poorly soluble tracer gases in the end-tidal gas for the first few breaths during the washout procedure. Simulations of simultaneous multiple-breath washout experiments of He and SF6 showed that a shift in the crossover point of the normalized end-tidal washout curves is related in particular to cross-section asymmetry of the lung model. These asymmetric lung models are the only ones described up to now that explain many of the features of single- and multiple-breath washout experiments for gases poorly soluble in blood.

Fluorides↗

PubMed1981

Influence of variations in pH and PCO2 on scalp tissue oxygen tension and carotid arterial oxygen tension in the fetal lamb.

A description is given of the effect of hypercapnic acidaemia and hypocapnic alkalaemia on scalp tissue PO2 as measured with a subcutaneous needle-electrode and a transcutaneous electrode in 6 fetal lambs. The experiments were carried out under general anaesthesia with the fetus kept in utero. Hypocapnia was induced by hyperventilating the ewe and hypercapnia was achieved by administering extra CO2 to the ewe. Fetal carotid arterial, subcutaneous and transcutaneous PO2 were continuously recorded, and fetal and maternal arterial pH and arterial PCO2 were determined from blood samples taken at short intervals. In each experiment the H+ Bohr factor of fetal and maternal blood was measured. During hypocapnic alkalaemia, there was a fall in all fetal PO2 levels, whereas a marked rise was observed during hypercapnic acidaemia. The variations in fetal PO2 observed in vivo even exceeded the variations due to the H+ Bohr effect (measured in vitro). This was due to small variations in fetal carotid arterial oxygen saturation, which tended to fall during hypocapnic alkalaemia and to rise during hypercapnic acidaemia. The results of these findings strongly suggest that tissue PO2, as measured with the subcutaneous and transcutaneous electrodes, is dependent on the H+ Bohr effect. This adds to the uncertainty as to the value of subcutaneous and transcutaneous PO2 monitoring during labour as an early warning system for impending fetal asphyxia.

Animals↗

PubMed1981

A multi-wavelength spectrophotometric method for the simultaneous determination of five haemoglobin derivatives.

A method is described by which the concentration of deoxyhaemoglobin, oxyhaemoglobin, carboxyhaemoglobin, haemoglobin and sulfhaemoglobin in a human blood sample is determined by passing the haemolysate without air contact through a coarse filter and subsequently measuring the absorbance at lambda = 500, 569, 577, 620 and 760 nm. The ensuing set of equations is solved by matrix calculation with the aid of a simple computer program. The method has been tested by comparing it with conventional methods for the determination of the various haemoglobin derivatives separately.

Carboxyhemoglobin↗

PubMed1981

Determination of hemoglobin derivatives with IL 282 CO-oximeter as compared with a manual spectrophotometric five-wavelength method.

Hemoglobin derivatives as determined with the IL 282 CO-Oximeter correlated well with results by a manual five-wavelength method, which in turn had been checked against established methods for one or two derivatives. Measurement of total hemoglobin yielded almost identical results with both methods. As for oxyhemoglobin, carboxyhemoglobin, and hemiglobin, agreement between the two methods was fair. Although the IL 282 CO-Oximeter has not been constructed for the determination of sulfhemoglobin, it appeared that the instrument can still give a strong indication as to the presence of this hemoglobin derivative. Results from the IL 282 for fetal human blood should be used with caution, especially because of the possibility of falsely high HbCO readings.

Autoanalysis↗

PubMed1980

The sloping alveolar plateau at synchronous ventilation.

We performed model calculations on the slope of the alveolar plateau at single breath washout of helium (He) and sulphurhexafluoride (SF6). Calculations wre carried out on an extensible axis-symmetric lung model, which was synchronously ventilated either equally or unequally. The calculated slopes of the alveolar plateau were small (<0.3%), which is in agreement with the results of other investigators. However, calculations carried out on a synchronously equally ventilated axis-asymmetric lung model related to the terminal lung unit (acinus), yielded slopes for the alveolar plateau ranging from 0 up to 14% per liter between 1.2 and 1.8 1 expired volume. Even with a post inspiratory apnea of 1 s, we still found slopes ranging from 0--4%. Our findings are in contrast to the conclusions of Engel et al. (1979), who ascribe the slope of the alveolar plateau to asynchronous unequal ventilation.

Computers↗

PubMed1978

A non-invasive determination of lung perfusion compared with the direct Fick method.

In 5 young pigs (7--9 kg each) data on effective lung perfusion were obtained using a sinusoidal forcing function in the inspired halothane concentration. These data were compared with the cardiac output measured by the direct Fick method for oxygen, corrected for venous admixture. To produce different levels of cardiac output during each experiment the respiratory and circulatory conditions were changed. For the 5 experiments taken together, the mean of the ratios between the non-invasively obtained effective lung perfusion and the venous admixture corrected Fick data was 1.01 (SD = 0.14, n = 55) with r = 0.92.

Animals↗

PubMed1976

Radip induction of ether anaesthesia and controlled maintenacne by a combination of intravenous and inhalation administration without the risk of explosion.

The induction and maintenance of anaesthesia with ether using a combined intravenous infusion and a constant low inspired concentration are discribed. Predictions from a mathematical model were checked against animal experiments. Anaesthesia occurred within 5 min. The mehtod obviates the need for explosive mixtures.

Anesthesia, Endotracheal↗

PubMed1976

Ventilation-perfusion ratio obtained by a noninvasive frequency response technique.

Results of animal experiments using sinusoidal changes in inspired halothane concentration showed that the ratio of variation in end-expired concentration to the variation in inspired concentration reached a plateau in the Bode diagram. With the help of an uptake and distribution model, the interpretation of the results showed that the level of the plateau is determined by the overall ventilation-perfusion ratio. With a good selection of input frequency, tracer agent, and known ventilation, the ventilation-perfusion ratio and the lung perfusion can be consequently obtained noninvasively. Mean ventilation-perfusion ratio was determined with 20 human voluteers. At rest a mean ratio was found of 0.87 +/- 0.28 (SD). At a work load of 90 W a mean ratio was found of 1.19 +/- 0.19 (SD). In two individuals reproducibility and influence of CO2 was studied. At rest without additional CO2 the ventilation-perfusion ratio was 0.71 +/- 0.06 (SD) obtained with a constant breathing rate of 10/min. At an end-expired CO2 level of 6% the ventilation-perfusion ratio was increased almost 2.5 times. The calculated perfusion with and without increased end-expired CO2 levels under the same work load were well reproducible.

Carbon Dioxide↗

PubMed1975

A simple and non-invasive method to determine the ventilation-perfusion ratio of the lung and the effective lung perfusion.

A method is presented to obtain the ventilation-perfusion ratio non-invasively. To describe the properties of gasexchange over the lung we used the law of mass conservation. The use of sinusoidal changes in the concentration of a tracergas in the inspired mixture results in a simple formulation of the variation in the concentration in the expired mixture over the variation in the inspired mixture. A careful selection of tracergas and cycleperiod of the sinus enables us to neglect the influence of venous return leaving the ventilation-perfusion ratio as sole physiological variable in the formulation. The lungperfusion can be obtained by measuring the total ventilation and correcting this value for deadspace ventilation. The method can be used to evaluate the influences of techniques like positive end-expired pressure and increased carbon dioxyde levels on shunting. It is also suited for monitoring purposes.

Anesthesia, General↗

PubMed1973