Search PubMed⌕ Search

Biomedical subjects

J Piiper

Publications and source records attributed to J Piiper.

At least 73 records · Page 4Linked to original sources
PubMed1987

Alveolar-capillary diffusion of oxygen in dogs exercising in hypoxia.

To detect and quantify diffusion limitation in alveolar-capillary O2 transfer, measurements of pulmonary gas exchange were performed in 6 awake, chronically tracheostomized dogs (mean body weight 28.3 kg) breathing low O2 (arterial PO2 35-39 Torr), with or without CO2 added to inspired gas. From rest to exercise, with O2 uptake averaging 23 ml/(min X kg), the ideal-alveolar-to-arterial PO2 difference (PAiO2-PaO2) increased from 2.1 +/- 0.2 Torr (mean +/- SE) to 2.9 +/- 0.2 in hypoxia, and from 1.9 +/- 0.7 Torr to 3.0 +/- 0.5 in hypercapnic hypoxia. The apparent pulmonary O2 diffusing capacity (DLO2), calculated from O2 uptake, mixed-venous PO2, arterial PO2, and ideal-alveolar PO2, was found to be increased by hypercapnia and exercise. During exercise DLO2 averaged 74 ml/(min X Torr) in hypoxia and 76 ml/(min X Torr) in hypercapnic hypoxia. Because of the influence of inhomogeneity effects, these values should be considered as minimum values for the true pulmonary O2 diffusing capacity. When compared to the pulmonary CO diffusing capacity (DLCO) previously determined by C18O rebreathing in the same dogs in similar conditions, the DLO2/DLCO ratio averaged 1.2, thus being in accordance with the value predicted from the corresponding Krogh diffusion constant ratio. It is concluded that the DLO2 and DLCO values determined drug exercise in hypoxia may be considered to represent acceptable measures for alveolar-capillary diffusion conductance of lungs.

Animals↗
PubMed1987

Acid-base status immediately following rapid changes of alveolar gas composition in awake dogs.

To study the interrelationship between blood O2, CO2, and acid-base status during rapid changes of alveolar gas composition unanesthetized dogs were made to inhale high CO2 gas mixtures following air breathing or to rebreathe high CO2 and O2 mixtures following hypoxia. Before and immediately after each change in alveolar gases, sequential blood samples were taken from the carotid artery for measurement of pH, PCO2 and PO2. In the experiments at normoxia the calculated base excess (BE) decreased by about 0.7 mmol/L after 10 sec and then returned to baseline level. A smaller decrease (averaging 0.4 mmol/L) was found with hyperoxia following hypoxia. The changes in BE can be attributed to bicarbonate (or H+) exchange between blood and tissue. Lung tissue is probably responsible for the rapid initial change in BE.

Acid-Base Equilibrium↗
PubMed1986

Inert gas wash-out from tissue: model analysis.

Model simulations on variously arranged two-compartment models are performed to provide a basis for interpreting the observed non-monoexponential (or non-linear logarithmic) wash-out time courses of inert gases from tissue. The variables considered are: blood flow, tissue volume, solubility of gas in tissue and blood, and diffusive conductances (diffusing capacities) for tissue/blood gas transfer and for gas transfer between tissue compartments. The wash-out is studied in terms of both mean tissue partial pressure and effluent venous blood partial pressure. Diffusion limitation within a tissue-blood capillary unit is shown to produce logarithmic wash-out rates which increase or decrease during wash-out, depending on the functional structure of the unit. On the other hand, in a system consisting of dissimilar tissue-blood capillary units arranged in parallel, the logarithmic wash-out rate decreases with wash-out time. It is shown that the conventional analysis of nonlinear logarithmic wash-out may overestimate or underestimate tissue perfusion or the extent of its inhomogeneity.

Animals↗
PubMed1986

Cross-sectional PO2 distributions in Krogh cylinder and solid cylinder models.

Radial profiles, gradients and frequency distributions of PO2 are calculated for two cylindrical tissue models with uniform O2 diffusion properties and O2 consumption: Krogh's cylinder with O2 supplied from a central capillary (model A), and a solid cylinder with O2 supplied from the outer surface (model B). Because the O2 diffusion flux is divergent in model A, and convergent in model B, the PO2 gradient flattens with increasing distance from the supplying surface more rapidly in model A than in model B. In model A, the frequency distribution of PO2 with respect to unit cross-sectional area is highly asymmetric, being skewed to low PO2, whereas it is uniform in model B. Model A is applicable to parallel capillaries uniformly distributed across tissue cross-section. For Model B a large number of capillaries surrounding a cylindrical structure is required. Model A appears to be much more adequate than model B to describe the normal morphometry in skeletal muscle (capillary number/fiber number ratio of about 2, capillary-to-muscle fiber radius ratio of about 0.1). The experimental finding of relatively low PO2 and small PO2 gradients within muscle fiber cross-sections is in agreement with both models, but agrees better with model A than with model B.

Capillaries↗
PubMed1986

Model for analysis of counter-current gas transfer in fish gills.

The validity of previously used simplified models for the analysis of gas transfer in fish gills was tested using an integrated model which includes water flow and blood flow in counter-current arrangement. The model accounts for the resistance to diffusion of O2 both in the water-blood barrier and in the interlamellar water, which is assumed to flow with a parabolic velocity profile between the secondary lamellae. The O2 diffusing capacity (transfer factor) for this model (Dint) was compared to that (Dm + w) calculated from the diffusing capacity of the water-blood barrier (Dm), and from the effective diffusive conductance of the parabolically streaming interlamellar water (Dw) as 1/Dm + w = 1/Dm + 1/Dw. These diffusing capacities were compared with that (Dadd) calculated from Dm and diffusing capacity of a water layer of 1/4 thickness of the interlamellar space (Dw) as 1/Dadd = 1/Dm + 1/Dw. Calculations with morphometric and gas exchange parameters in the elasmobranch Scyliorhinus stellaris reveal the following features: (1) In physiological conditions, Dm + w and Dint are similar to within 10%, but Dint is always higher. (2) Dint and Dm + w increase with increasing ventilation; Dint increases with decreasing perfusion, while Dm + w remains constant. (3) Both Dint and Dm + w agree reasonably well with Dadd. In other anatomical and physiological conditions, particularly for relatively high Dm, Dw, and Dw and high ventilation, greater discrepancies between Dint and Dm + w may occur but Dm + w appears to represent a reasonable approximation of the effective O2 diffusing capacity, which is best modelled as Dint.

Animals↗
PubMed1986

Blood-gas equilibrium of carbon dioxide in lungs: a continuing controversy.

This review presents the experimental evidence that has been published in recent years both against and in support of the occurrence of negative blood-gas CO2 partial pressure differences (delta PCO2) in lungs in rebreathing equilibrium and during steady-state gas exchange in hypercapnia. Although some sources of potential experimental error can be pointed out, the reasons for the remarkably pronounced disagreement between the experimental data of the different studies cannot be definitely identified. Since a consistent and reproducible occurrence of negative blood-gas delta PCO2 in lungs in gas-blood equilibrium is not convincingly proved, it appears to be justified to continue accepting the validity of the conventional concept of equal PCO2 in blood and gas in equilibrium. Because the issue is of considerable importance in the analysis and understanding of alveolar gas exchange, pertinent evidence is expected from future work.

Animals↗
PubMed1986

Pulmonary diffusing capacity for carbon monoxide by rebreathing in awake dogs.

In order to reduce the effects of functional inhomogeneities on the determination of pulmonary diffusing capacity (transfer factor) for CO (DLCO), DLCO was measured by a rebreathing method in 5 awake chronically tracheostomized dogs (mean body weight 28 kg) during high ventilation (15-25 times above normal) induced by hypoxia, hypercapnia, exercise, or their combinations. The animals rebreathed for 15 s a mixture containing 1% He, 0.1% C18O, with CO2 and O2 concentrations adjusted to maintain end-tidal PCO2 and PO2 close to their prerebreathing values. Gas partial pressures in the trachea were continuously monitored by mass spectrometry. DLCO was calculated from C18O equilibration kinetics, effective ventilation (obtained from He mixing kinetics) and lung volume (obtained from He dilution). Each of the factors, hypoxia, hypercapnia and exercise, contributed to increasing DLCO. During exercise in combined hypoxia and hypercapnia, DLCO (mean +/- SE) was 71.7 +/- 1.8 ml/(min X Torr). The mechanisms for increases in DLCO might have involved improvement of diffusion conditions, decrease of functional inhomogeneities and reduction of the effects of functional inhomogeneities. The highest DLCO values were close to values derived from morphometry.

Animals↗
PubMed1986

Kinetics of oxygen uptake and release by red blood cells of chicken and duck.

The specific conductance (G) for O2 transfer by red blood cells (RBCs) of chicken and muscovy duck was measured using the experimental (stopped-flow) and analytical techniques (RBC model) previously applied to human RBC (Yamaguchi, Nguyen Phu, Scheid & Piiper, 1985). Avian RBCs behaved similarly to human RBCs: G values were of similar magnitude; G for O2 uptake decreased with time and increasing O2 saturation; G for O2 release at high levels of dithionite decreased slightly with decreasing O2 saturation; G for O2 release was higher than G for O2 uptake. The deoxygenation kinetics of oxyhaemoglobin in solution was similar for both avian species. The G measured for O2 release at high dithionite concentration, considered to represent a good approximation to intra-erythrocyte O2 diffusion conductance, averaged (in mmol min-1 Torr-1 ml-1 RBC) 0.33 for chicken and 0.25 for duck (at 41 degrees C, pH of the suspension = 7.5, O2 saturation range 0.4-0.8). These species differences can be explained by differences in cell size, the RBC volume averaging 104 micron3 in the chicken and 155 micron3 in the duck. Compared with human RBCs, the G estimates for avian RBCs are somewhat smaller than would be predicted from size differences, which can be explained by the discoid shape of mammalian RBCs which constitutes an advantage compared with the ovoid avian RBC.

Animals↗
PubMed1985

Kinetics of O2 uptake and release by red cells in stopped-flow apparatus: effects of unstirred layer.

Using a stopped-flow apparatus, measurements were made of the velocity of uptake and release of oxygen by red cells of man, sheep and goat, three species of widely differing red cell size. The results were used to calculate resistances to O2 uptake provided by: (1) any unstirred layer (USL) outside the cells; (2) the cell membrane; and (3) the cell substance, in which the process of simultaneous diffusion and chemical reaction occurs. For O2 release, the USL was virtually abolished by using sufficient dithionite in the reactant buffer for it to diffuse up to the cell membrane and mop up O2 as it passes out of the cell. Hence, differences in the rate of O2 uptake and release allowed estimation of the resistance and thickness of the USL. Its thickness in the three species was between 0.7 and 0.9 micron; it provided at least 70% of the resistance to O2 uptake located outside the cell interior (cell membrane plus USL). Existence of the USL slows the uptake of O2 in the stopped-flow apparatus by a factor of at least 1.8 to 2.0.

2,3-Diphosphoglycerate↗
PubMed1985

Transient PO2 and PCO2 differences between end-tidal gas and arterial blood during rebreathing in awake dogs.

O2 and CO2 partial pressures in end-tidal gas (PA) and carotid artery blood (Pa) were measured during non-steady-state gas exchange in unanesthetized dogs. In 5 experiments (A), low O2 breathing in open circuit preceded prolonged rebreathing during maintained normoxia. In 6 experiments (B), steady-state hypoxia and hypercapnia were followed by rebreathing CO2 in hyperoxia which caused PAO2 to rise and then fall while PACO2 increased. Negative (Pa-PA)CO2, averaging -5 torr, were observed 10 sec after starting rebreathing in B and values between -1 and -2 torr were noted later in A and B. (PA-Pa)O2 showed considerable transient increases for 2 min in A and 20 sec in B. This behavior of (PA-Pa)O2 could be explained by a lung model with unequal distribution of alveolar ventilation and perfusion to alveolar volume. The negative (Pa-PA)CO2 values observed during rebreathing with rapidly increasing PACO2 were in part attributable to such unequal distribution effects, in part to lung-to-carotid artery transit time effects.

Animals↗
PubMed1985

Variability of shell conductance and gas exchange of chicken eggs.

In 395 fertilized chicken eggs (strain Warren) obtained from a commercial hatchery the following coefficients of variation (SD/mean) were found: egg shell conductance for water vapor, GH2O, 22%; freshly laid egg weight, W, 8%; the specific conductance, gH2O (= GH2O/W), 22%. In 20 eggs selected for widely varying gH2O (range 57%-195% of the mean, 0.246 mg/(day X torr X g), the specific O2 uptake and the CO2 output, measured on days 16-19 of incubation, showed a maximum at medium gH2O values, decreasing at both lower and higher gH2O. The variations of gH2O in the selected eggs were shown to cause a variation of water loss up to hatching from 9 to 26% (average 15%), and a variation of the O2 tension from 84 to 123 torr, and of the CO2 tension from 18 to 54 torr, in the perichorioallantoic air space on days 16-19 of incubation. Mechanisms responsible for the observed changes in the metabolic rate and for the physiological adjustments to varied egg shell conductance are discussed.

Animals↗
PubMed1985

Model simulation of single-breath washout of insoluble gases from dog lungs.

Intrapulmonary gas mixing by convection and diffusion is analyzed on the basis of various analog lung models incorporating singly or in combination series inhomogeneity, parallel inhomogeneity, intercompartmental diffusion, sequential inspiration, and sequential expiration. The slope of the alveolar plateau of insoluble gases is used as an indicator for incomplete gas mixing. By use of the models, we have attempted to simulate experimental results obtained in artificially ventilated dog lungs with simultaneous single-breath washout of He and SF6 (Meyer et al., J. Appl. Physiol. 55: 1795-1802, 1983). Sufficient agreement with experimental data is obtained only when diffusion between serial-parallel compartments and sequential expiration are incorporated, the first being mainly responsible for separation of He and SF6, the latter for the slope of the alveolar plateau of these gases. A combined operational model comprising two parallel compartments connected to a mixing compartment, with both convective and diffusive gas transport between the compartments, could account for most of the experimental observations.

Animals↗
PubMed1985

Kinetics of O2 uptake and release by human erythrocytes studied by a stopped-flow technique.

The kinetics of O2 uptake into and release from human erythrocytes was investigated at 37 degrees C by a stopped-flow technique. From the time course of O2 saturation (SO2) change a specific transfer conductance of erythrocytes for O2 (GO2) was calculated. The following results were obtained: 1) GO2 decreased in the course of O2 uptake, but initial GO2 was nearly independent of SO2 at which uptake started; 2) addition of albumin to the medium reduced GO2; 3) increasing dithionite concentration in the medium in O2-release experiments progressively enhanced GO2, which became virtually constant for nearly the entire course of release; and 4) O2 uptake and O2 release (without dithoite) in the same SO2 range yielded very similar GO2. These results suggested that O2 uptake and release were importantly limited by diffusion through the external medium and that in the SO2 range between 0.3 and 0.8, chemical reaction exerted little limiting effect. Since O2 release at the highest dithionite concentration (40 mmol/l) appeared to be virtually unlimited by external diffusion, GO2 measured under these conditions, averaging 8.7 ml X min-1 X Torr-1 X ml erythrocytes-1, was considered to mainly reflect intracellular diffusion limitation. The corresponding specific transfer conductance for O2 transfer in whole blood (hematocrit, 0.45) is 3.9 ml X min-1 X Torr-1 X ml blood-1.

Adult↗
PubMed1985

Arterial-alveolar CO2 equilibration in exercising dogs during prolonged rebreathing.

Arterial-alveolar equilibration of CO2 during exercise was studied by normoxic CO2 rebreathing in six dogs prepared with a chronic tracheostomy and exteriorized carotid loop and trained to run on a treadmill. In 153 simultaneous measurements of PCO2 in arterial blood (PaCO2) and end-tidal gas (PE'CO2) obtained in 46 rebreathing periods at three levels of mild-to-moderate steady-state exercise, the mean PCO2 difference (PaCO2-PE'CO2) was -1.0 +/- 1.0 (SD) Torr and was not related to O2 uptake or to the level of PaCO2 (30-68 Torr). The small negative PaCO2-PE'CO2 is attributed to the lung-to-carotid artery transit time delay which must be taken into account when both PaCO2 and PE'CO2 are continuously rising during rebreathing (average rate 0.22 Torr/s). Assuming that blood-gas equilibrium for CO2 was complete, a lung-to-carotid artery circulation time of 4.6 s accounts for the observed uncorrected PaCO2-PE'CO2 of -1.0 Torr. The results are interpreted to indicate that in rebreathing equilibrium PCO2 in arterial blood and alveolar gas are essentially identical. This conclusion is at variance with previous studies in exercising humans during rebreathing but is in full agreement with our recent findings in resting dogs.

Animals↗
PubMed1985

Blood flow distribution in dog gastrocnemius muscle at rest and during stimulation.

The distribution of blood flow within the isolated perfused dog gastrocnemius muscle (weight 100-240 g) was studied by intra-arterial injection of radioactively labeled microspheres (diameter 15 micron) at rest and during supramaximal stimulation to rhythmic isotonic tetanic contractions of varied frequency against varied loads. After the experiment the muscle was cut into 180-250 pieces of approximately 0.75 g each, and the blood flow to each muscle piece was determined from its radioactivity. The inhomogeneity of blood flow was represented as the frequency distribution of the ratios of regional specific blood flow, i.e., blood flow per unit tissue weight of the piece, QR, to the overall specific blood flow of the muscle, Q. The QR/Q values for the individual pieces of a muscle were found to vary widely both at rest and during stimulation. With rising work load the frequency distribution had a tendency to broaden and flatten, indicating increasing perfusion inhomogeneity. On the average of the experiments, there was no significant difference in specific blood flow between the three anatomic components of the gastrocnemius (lateral and medial heads of gastrocnemius and flexor digitorum superficialis) nor between the superficial and deep portions within these anatomic components, only the distal third of the muscle was relatively less perfused compared with the proximal two-thirds. The considerable inhomogeneity of blood flow as revealed by microsphere embolization and by other methods is expected to exert important limiting effects on local O2 supply, particularly during exercise. Its neglect would lead to serious errors in the analysis of O2 supply to muscle tissue.

Animals↗