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Biomedical subjects

J Piiper

Publications and source records attributed to J Piiper.

At least 109 records · Page 6Linked to original sources
PubMed1981

Interpretation of inert gas retention and excretion in the presence of stratified inhomogeneity.

The effects of diffusion limitation in alveolar space (stratification) for inert gas retention and excretion by lungs with log-normal VA/Q distribution are calculated using the approach of Scheid et al. (Respir. Physiol. 44, 299-309, 1981). Since gases used in the multiple inert gas elimination technique have widely varying molecular weights (between 30 and 197), and therefore varying diffusivities, the effects of stratification are different for each gas. The result is a perturbation in the recovered VA/Q distributions that is calculated neglecting stratification effects. Application to inert gas elimination data obtained in the anesthetized rat by Truog et al. (J. Appl. Physiol. 47, 1112-1117, 1979) yields a value for the diffusion resistance in alveolar gas which would give rise to a PO2 difference of 5 Torr, suggesting that stratification may exert a significant limitation to pulmonary O2 transfer in rats.

Animals↗
PubMed1981

Changes in acid-base balance of chick embryos exposed to a He or SF6 atmosphere.

On day 16 of the chick embryo, a catheter was implanted in the allantoic vein carrying arterialized blood, and a syringe was attached to the blunt end of the shell connecting to the air cell. This technique allowed for repetitive sampling and analysis of air cell gas and arterialized blood when these eggs were exposed to a He-O2 or SF6-O2 atmosphere. Exposure to He-O2 reduced the arterial CO2 tension(PaCO2) from 36 to 17 Torr and increased pH by 0.17 units; exposure to SF6-O2 increased PaCO2 from 37 to 62 Torr and reduced the pH by 0.14 units. These responses were brought about by changes in the gas conductance of the shell, resulting in a diffusive hypocapnia and respiratory alkalosis in He-O2 and a diffusive hypercapnia and respiratory acidosis in SF6-O2. During a 4-h exposure to these foreign gases the observed pH changes were smaller than predicted because of marked shifts of HCO3- into the blood (SF6-O2) or out of the blood (He-O2).

Acid-Base Equilibrium↗
PubMed1981

Pulmonary diffusing capacity for CO independent of alveolar CO concentration.

Pulmonary diffusing capacity for CO (DCO) was measured in human subjects at various CO concentrations using a rebreathing procedure. Two stable CO isotopes, 12C18O and 13C18O, were used. These isotopes could be simultaneously and continuously recorded by a respiratory mass spectrometer. For 13C18O the initial concentration in the rebreathing bag was constant at 0.00016, whereas it was varied for 12C18O from 0 to 0.00224. DCO was calculated for both isotopes. In five normal subjects, both D12C18O and D13C18O were independent of the rebreathing CO concentration, with mean values of 31.0 and 30.2 ml . min-1 . Torr-1, respectively. These results, which are at variance with those of Mendoza et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 43: 880-884, 1977), are compatible with the assumption that diffusion is the sole mechanism of alveolocapillary CO transport; in particular, there is no evidence for facilitated transport.

Adult↗
PubMed1981

Pulmonary diffusion capacities for O2 and CO measured by a rebreathing technique.

Pulmonary diffusion capacity (D) for O2 and CO was determined from alveolar-mixed venous equilibration kinetics of 16O2, 18O2, and C18O measured during rebreathing by mass spectrometry. During the rebreathing maneuver (15 s) the ventilation was extremely high (about 100 1 X min-1) and PO2 and PCO2 in lung gas were close to their mixed venous values (aveolar hypoxia and hypercapnia). The following mean values (+/- SD) were found in six healthy males (20-33 yr) sitting on a bicycle ergometer (in ml X min-1 X Torr-1): 1) without work load, D18O2 = 54 +/- 10, Dc18O = 47 +/- 11; 2) with the highest work load tested (150 W, O2 uptake 2.1 l X min-1), D18O2 = 62 +/- 12, Dc18O = 54 +/- 8. The ratio D16O2/D18O2 averaged 1.07. The ratio D18O2/Dc18O, averaging 1.2 at rest and at all exercise levels, was close to the estimated O2/CO ratio of Krogh's diffusion constants for tissue and, therefore, was in agreement with the diffusion limitation model. An analysis of the various factors affecting the DO2/DCO ratio does not allow to reliably assess the role of diffusion in red blood cells and reaction with hemoglobin in limiting alveolar-capillary O2 transfer.

Adult↗
PubMed1980

Solubility of inert gases in dog blood and skeletal muscle.

Solubility of H2, Ar, CH4 and SF6 was determined at 310 K (37 degrees C) in water, in saline (0.154 mol NaCl/l H2O), in plasma and whole blood of dogs, and in homogenates of the dog gastrocnemius muscle. The liquids were equilibrated with pure gases, and the dissolved gases were extracted and measured by gas chromatography as described previously (Meyer, M.: Pflügers Arch. 375, 161--165, 1978). In saline, the solubilities were 4% (SF6) to 15% (Ar) lower than in water. For dog blood the following mean values for the solubility coefficient (in mumol . 1(-1) . kPa-1) were found: for H2, 6.44; for Ar, 9.94; for CH4, 11.44; for SF6, 2.62. The red cell/plasma and the muscle/blood solubility ratios were near unity for H2, Ar and CH4 (ranging from 0.9 to 1.3); for SF6, however, they were much higher (about 2.1), apparently due to the high solubility of SF6 in hydrophobic substances (lipids).

Animals↗
PubMed1980

Blood/gas equilibrium of carbon dioxide in lungs. A critical review.

(1) The scope of this review is to examine the experimental evidence for the existence of negative PCO2 differences between pulmonary capillary blood and lung gas, [delta PCO2(b-G)], which have been observed both during rebreathing, when CO2 was at equilibrium, and during steady state gas exchange, particularly in hypercapnia. (2) The mechanism that have been invoked to explain negative delta PCO2(b-G) include (i) slow equilibration of the system CO2/HCO3-/H+ in blood, and (ii) effects of a negatvely charged surface of the pulmonary capillary endothelium. While the first postulated mechanism appears to be quantitatively insufficient to explain the results, the second seems to lead to serious qualitative difficulties. (3) Existence of negative delta PCO2(b-G) in CO2 equilibrium would invalidate the basis of the conventional analysis of alveolar gas exchange. (4) A critical analysis of the experimental evidence for the existence of negative delta PCO2(b-G) is presented. It includes the identification of directional experimental errors leading to spurious negative delta PCO2(b-G), and a critical review of the literature data in this regard. (5) Results of own experiments, conducted in an attempt to consider all possible sources of error, are reported, revealing (i) perfect PCO2 equality between alveolar gas and blood in rebreathing equilibrium of CO2; (ii) absence of negative delta PCO2 (b-G) during steady state gas exchange in hypercapnia. (6)Both experiments and model calculations show that negative delta PCO2 between mixed venous blood and end-expired gas observed in birds at steady state of gas exchange are explained by a particular action of the Haldane effect in avian parabronchial lungs with cross-current arrangement of gas and blood flow. (7) It is concluded that the negative delta PCO2(b-G) reported in the literature are probably artifactual and that there is no adequate evidence to invalidate the traditional view according to which blood/gas CO2 equilibration in lungs leads to equal PCO2 in both media.

Animals↗
PubMed1980

The independent effects of atmospheric pressure and oxygen partial pressure on gas exchange of the chicken embryo.

CO2 production and air cell PCO2 were continuously measured during late development in the chicken egg while acutely exposed from one to three hours to various O2 concentrations ranging from 11 to 39%. A small but significant increase in metabolism, ca. 8%, was found when O2 concentration was above normal values, while a reduction to 70% was observed when O2 concentrations were below normal, and fell to 50% when maintained for three hours. These values were also compared with metabolic rates reported by Lokhorst and Romijn (1965, 1967)) who incubated eggs continuously at reduced O2 concentrations as well as under reduced barometric pressure, and showed that at the same ambient PO2 the metabolism was significantly higher in the eggs at reduced barometric pressure. We attribute this difference to the increased diffusion coefficient of O2 which is inversely related to the barometric pressure. It illustrates that the ambient partial pressure of O2 and ambient atmospheric pressure exert an independent effect upon gas exchange of the avian embryo.

Animals↗
PubMed1980

Carbon dioxide in the chick embryo towards end of development: effects of He and SF6 in breathing mixture.

Using an implanted CO2 electrode in the air cell of the chicken egg, its PCO2 could be followed continuously during the prenatal and paranatal period until hatching occurred. CO2 elimination rate was followed simultaneously. At various stages such eggs were subjects to 75 : 25% He/O2 and SF6/O2 atmosphere, resulting in a large decrease and increase, respectively, in air cell CO2 tension, indicating that during the prenatal stage all CO2 exchange was by gas phase diffusion transport across the pores of the shell. Measurements of the change in PCO2 as well as the CO2 output allowed one to calculate the effective diffusion coefficient for CO2 in the He and SF6 mixtures, which agreed well with the theoretical values calculated according to Wilke (1950). From the CO2 release or retention following exposure, respectively, to He or SF6 the CO2 capacitance values for blood and tissue could be calculated and agreed with values established in mammals. During the last period of development, the paranatal period, the change of PCO2 after replacement of N2 by He gradually declined, indicating that pulmonary ventilation was replacing diffusion through egg shell pores.

Animals↗
PubMed1980

Analysis of chorioallantoic gas exchange in the chick embryo.

To analyze the gas exchange mechanisms in the chorioallantois, PO2 and PCO2 were measured in air cell gas, in the allantoic artery and in the allantoic vein in chicken embryos on the 16th day of incubation. In addition, the O2 dissociation curve of blood, and O2 uptake and CO2 output of the embryo were determined. From O2 measurements performed in hypoxia (FIO2=0.14), normoxia and hyperoxia (FIO2=0.67), it was concluded that there was a sizable functional arterio-venous shunt amounting to 10-15% of the total chorioallantoic blood flow and that the diffusing capacity of the air cell-blood barrier for O2 was about 7 microliter . min-1. Torr-1. The CO2 measurements are in agreement with the model. In hypoxia, the air cell-blood transfer of O2 was markedly diffusion limited. The diffusion limitation effect was slight in normoxia, and not detectable in hyperoxia. At all oxygenation levels the effect of the shunt on blood arterialization was marked, particularly so in hyperoxia where the air cell-arterialized blood PO2 difference averaged 180 Torr.

Allantois↗
PubMed1980

Value and limits of Graham's law for prediction of diffusivities of gases in gas mixtures.

The validity of Graham's law, i.e. the inversely proportional relationship between diffusivity (diffusion coefficient) and the square root of the molecular mass, is tested for test gases and gas mixtures of physiological interest based on recent measurements of diffusivities of gases in gas phase. With gases of medium molecular mass (10 to 30 g/mol) predictions on the basis of Graham's law are reasonably accurate, deviations from experimental values not exceeding 20%. With gases of high and low molecular masses, however, larger discrepancies are encountered. The prediction of diffusion coefficients on the basis of the Chapman-Enskog theory is in most cases more accurate than that based on Graham's law.

Diffusion↗
PubMed1980

Alveolar-capillary equilibration kinetics of 13CO2 in human lungs studied by rebreathing.

Blood/gas equilibration of CO2 in lungs was studied in man by a rebreathing technique, in which the rate of uptake of the stable isotope 13CO2 in low concentration (inspired concentration about 0.07%) was measured at blood/gas equilibrium of the abundant CO2 isotope. The results were expressed in terms of overall conductance for alveolar gas-pulmonary blood equilibration (DCO2, pulmonary diffusing capacity for CO2). The following mean values of DCO2 were found in 3 healthy young men (in mmol . min-1 . Torr-1): rest, 8.0; during exercise (75 Watts), 13.7. Comparison with DO2 measured by rebreathing in the same conditions suggests equilibration of the CO2/HCO3(-)/H+ system in blood, rather than diffusion of CO2, as the limiting process in capillary/alveolar CO2 transfer. The term 'equilibration capacity' is thus suggested for DCO2. Calculations based on the experimental results show that the overall limitation of pulmonary CO2 exchange function resulting from this finite DCO2 is slight at rest, but of considerable extent in heavy exercise.

Carbon Dioxide↗
PubMed1980

Comparison of steady state pulmonary diffusing capacity estimates for O2 and CO in dogs.

In view of the fact that the inhomogeneity effects on pulmonary diffusing capacity (DL) estimates are quite different for O2 and for CO, simultaneous determinations of steady-state DLCO and DLO2 were attempted and compared. To this end, pulmonary gas exchange was measured in 17 anesthetized and artificially ventilated dogs, in hypoxia with and without carbon monoxide in inspired gas (FIO2 = 0.12, FICO = 0.0009 to 0.0016). The diffusing capacity estimates were computed by two conventional procedures, the first (Dapp) taking into account the mean alveolar partial pressures and the second (DVDA) the ideal alveolar partial pressures. It was found that the presence of COHb in blood, inevitable in the steady-state DLCO procedure, leads to a marked underestimation of DLO2; therefore DLCO values could only be adequately compared to DLO2 values obtained in the absence of CO from inspired gas. These DLO2 were 18.5 and 33.4 mumol . min-1 . Torr-1 . kg-1 for the mean DappO2 and DVDAO2, respectively, whereas the DLCO values obtained after 15 to 25 min CO inspiration were 30.0 and 83.4 mumol . min-1 . Torr-1 . kg-1 for the mean DappCO and the mean DVDACO, respectively. The salient feature is that with both procedures the mean value of DLCO estimate is higher than the corresponding DLO2 estimate. This finding suggests that in anesthetized, artificially ventilated dogs DappO2 and DVDACO estimates obtained by steady-state procedures in hypoxia are largely influenced by inhomogeneity effects and of limited value for assessment of the diffusing properties of the lung. DappCO and DVDAO2 are also affected by inhomogeneities but to a lesser degree.

Animals↗
PubMed1979

Respiratory gas transport by the incompletely separated double circulation in the bullfrog, Rana catesbeiana.

To investigate respiratory gas transport in the bullfrog, Rana catesbeiana (mean body weight 249 g. ambient temperature 25 degrees C), O2 uptake and CO2 output were determined, and blood gas parameters (PO2, PCO2, pH, O2 content, O2 capacity and hematocrit) were measured in blood samples taken from various heart cavities and blood vessels. Analysis of the data on the basis of a simplified circulatory gas transport model allowed to estimate the cardiac output and its distribution, and to describe the O2 and CO2 exchange in lungs, skin and tissues. The total cardiac output (average 20.5 ml/min) was estimated to be distributed about equally to the pulmocutaneous (56%) and systemic arterial vessels (44%), whereas the systemic venous return (62%) was larger than the pulmonary venous return (38%). The marked difference in oxygenation between aortic and pulmocutaneous arterial blood (average O2 saturation 85% and 47%, respectively) showed a highly effective separation of systemic venous and pulmonary venous blood in the ventricle and conus arteriosus. After enlargement of the ventricle produced by incision of the pericardium, the separation of arterialized and venous blood was markedly reduced, but not abolished.

Animals↗