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J Piiper

Publications and source records attributed to J Piiper.

At least 55 records · Page 3Linked to original sources
PubMed1989

Cardiogenic mixing: mechanisms and experimental evidence in dogs.

Cardiogenic mixing was studied in seven anaesthetized closed-chest dogs undergoing mechanical ventilation by comparing single-breath washout of two poorly soluble inert gases of widely differing diffusivities (helium (He) and sulphur hexafluoride (SF6)) in normal conditions with the heart beating (control), and during reversible temporary myocardial arrest (heart arrest). Cardiac arrest of approximately 20 s duration was induced repeatedly (8-15 times) by intracoronary injection of acetylcholine (approximately 35 mg) facilitated by a non-occluding 7-French gauge angiographic catheter maintained in the left coronary artery. After equilibration of lung gas with 1% helium and 1% SF6, single breath, constant flow expirograms were recorded in the tracheal tube by mass spectrometry after inspiration of test gas-free air. Series deadspace (VD) and relative alveolar slope (S) (increment of expired partial pressure, normalized to mixed expired-inspired partial pressure difference per increment of expired volume (S = (delta P/(PE-P1]/delta VE litre-1], were determined as indices for intrapulmonary gas mixing. The effects attributable to the action of the heart were quantified by the heart arrest: control ratio of VD and S, which were not significantly different from unity (P greater than 0.05) (VD: 0.95 (SD 0.05) for helium and 0.94 (0.07) for SF6; S:1.03 (0.10) for helium and 1.05 (0.14) for SF6. The He:SF6 ratios of VD and S (0.90 and 0.64, respectively), indicating diffusion dependent separation of gases, also were unaffected by the mechanical action of the heart. The data indicate that convective mixing by the mechanical action of the heart did not significantly enhance intrapulmonary mixing and transport.

Acetylcholine↗
PubMed1989

Pulmonary gas exchange in panting dogs: a model for high frequency ventilation.

Panting in animals can be expected to represent a naturally occurring physiological counterpart to today's techniques of mechanical high-frequency ventilation. To analyze the mechanisms underlying the gas exchange inefficiency during ventilation with high frequencies, steady-state pulmonary gas exchange was studied in seven conscious dogs (32 kg mean body weight) during panting elicited by mild thermal stress. The animals had a chronic tracheostomy and an exteriorized carotid artery loop and were exposed to 27.5 degrees C ambient temperature for 2 h (65% relative humidity). Open-circuit techniques were used and PO2 and PCO2 from the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked gas sampling technique. PO2 and PCO2 were determined in arterial blood collected from the carotid artery. During the exposure, the following variables of steady-state gas exchange were determined (means +/- SD): breathing frequency 313 +/- 19 min-1; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l.min-1; effective alveolar ventilation, 5.5 +/- 1.3 l.min-1; partial pressures (torr; a, arterial; E', end-tidal): PaO2, 106.2 +/- 5.9; PaCO2, 27.2 +/- 3.9; (PE'-Pa)O2, 26.0 +/- 5.3; (Pa-PE')CO2, 14.9 +/- 2.5. According to the conventional lung model, parallel-dead space ventilation (ventilation of unperfused lung regions) would account for about 55% of the alveolar ventilation and for 2/3 of the (PE'-Pa)O2 difference. However, the lack of an 'alveolar plateau' in the CO2 and O2 expirograms suggests that incomplete serial mixing in peripheral airways contributes to the enhanced gas exchange inefficiency during panting as reflected in the increased blood/gas differences for O2 and CO2.

Animals↗
PubMed1989

Pulmonary gas exchange in panting dogs.

Pulmonary gas exchange during panting was studied in seven conscious dogs (32 kg mean body wt) provided with a chronic tracheostomy and an exteriorized carotid artery loop. The animals were acutely exposed to moderately elevated ambient temperature (27.5 degrees C, 65% relative humidity) for 2 h. O2 and CO2 in the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked sampling technique. PO2 and PCO2 were determined in blood samples obtained from the carotid artery. During the exposure to heat, central body temperature remained unchanged (38.6 +/- 0.6 degrees C) while all animals rapidly switched to steady shallow panting at frequencies close to the resonant frequency of the respiratory system. During panting, the following values were measured (means +/- SD): breathing frequency, 313 +/- 19 breaths/min; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l/min; effective alveolar ventilation, 5.5 +/- 1.3 l/min; PaO2, 106.2 +/- 5.9 Torr; PaCO2, 27.2 +/- 3.9 Torr; end-tidal-arterial PO2 difference [(PE' - Pa)O2], 26.0 +/- 5.3 Torr; and arterial-end-tidal PCO2 difference, [(Pa - PE')CO2], 14.9 +/- 2.5 Torr. On the basis of the classical ideal alveolar air approach, parallel dead-space ventilation accounted for 54% of alveolar ventilation and 66% of the (PE' - Pa)O2 difference. But the steepness of the CO2 and O2 expirogram plotted against expired volume suggested a contribution of series in homogeneity due to incomplete gas mixing.

Acepromazine↗
PubMed1988

Role of diffusion shunt in transfer of inert gases and O2 in muscle.

Diffusion shunt is diffusive gas exchange between arterial and venous vessels. Evidence for diffusion shunt had been obtained in washout studies in the gastrocnemius muscle of the dog. According to models, diffusion shunt is expected to be enhanced at low blood flow, and for gases of high diffusivity. Shunting of O2 should be reduced in comparison to inert gases because of chemical binding in blood.

Animals↗
PubMed1988

Dependence of O2 transfer conductance of red blood cells on cellular dimensions.

To estimate the significance of the dimensions of RBC on O2 transfer, the kinetics of O2 release from RBC into medium containing dithionite (40 mmol/l) was measured, by a stopped-flow technique, for nine different species with varying RBC size (man, llama, vicuna, alpaca, dromedary camel, pygmy goat, domestic hen, muscovy duck and turtle). The observed O2 transfer kinetics were found to be size-dependent, i.e. the O2 transfer conductance of the single RBC, gst, was lower, whereas the specific O2 transfer conductance of packed RBC, Gst, or of whole blood, theta st, was higher for smaller RBC. The ratio of surface area to effective diffusion path length which was found to be about one fourth of the mean cell thickness irrespective of cell size and cell shape, may be considered as the essential morphological factor determining O2 transfer efficiency of the single RBC.

Animals↗
PubMed1988

Elimination kinetics of acetylene and Freon 22 in resting and active lungless salamanders.

To quantify diffusion limitation in cutaneous gas exchange, the elimination of two inert gases of different diffusivity, Freon 22 (CHC1F2) and acetylene (C2H2), was measured simultaneously in exclusively skin-breathing lungless salamanders, Desmognathus quadramaculatus. In resting salamanders, elimination of both gases could be described as the sum of three exponential terms. For both the medium and the slow exponential component, the ratio of the respective rate constants (k) for acetylene and Freon averaged 1.77. This value is between the values expected for perfusion limitation (1.00) and diffusion limitation (1.94), indicating combined diffusion and perfusion limitation. In salamanders stimulated to run on a treadmill, the elimination rates and the rate constants increased more for Freon than for acetylene. During spontaneous activity, the increase in elimination of Freon was larger than that of acetylene. These findings suggest an increase in the diffusing capacity of the skin during exercise. Thus the diffusing capacity of salamander skin for gases appears to be variable and to be adjusted to meet the increased O2 requirement during exercise.

Acetylene↗
PubMed1988

Oxygen transfer of red blood cells: experimental data and model analysis.

Kinetics of O2 uptake and release by human red blood cells (RBC) as measured by stopped-flow techniques were simulated using an RBC model shaped as a spheric shell. The O2 transfer mechanisms in this model include diffusion and reaction within the RBC and diffusion and convection in the medium surrounding the RBC. Unknown model parameters were determined by comparing simulations with experimental data. The following conclusions were drawn. (1) Both diffusion and convection contribute to O2 transport in the medium surrounding the RBC, and this transport importantly limits the overall O2 transfer kinetics in stopped-flow experiments. (2) Intraerythrocyte transport mechanisms become predominant in limiting O2 transfer, and can thus be investigated by stopped-flow techniques, only when the perierythrocyte O2 transport resistance is minimized, e.g. by high levels of dithionite in measurements of O2 release from RBC. (3) Intraerythrocyte O2 transfer is shown to be mainly limited by diffusion of O2 and, to a lesser extent, by diffusion of oxyhemoglobin ('facilitated O2 diffusion') and by O2/hemoglobin reaction. The results suggest that diffusion is the main process limiting O2 uptake and release by RBC, the finite reaction kinetics of O2 with hemoglobin exerting a smaller limiting effect.

Erythrocytes↗
PubMed1988

Aeration of the shell membranes of avian eggs.

The inner and outer shell membranes (ISM, OSM) of fertile hen's eggs become aerated during the first ten days of incubation. The volume of gas in the compound membrane increases from 0 to 65% by day 11 when practically all of the space between the fibers is gas filled. The amount of gas depends on a balance between the capillary tension produced by fluid menisci in the interstices between fibers and the colloid osmotic tension of the albumen. Capillary tension, measured directly with a pressure plate apparatus, and colloid osmotic pressure, measured with a new technique, are in virtual equilibrium during aeration. These tensions increase from 0.15 bar at laying to 2.25 bar on day 11 because of evaporation from the membranes and active removal of water from the albumen by the embryo. Water leaving the membranes by evaporation is only partly replaced from the albumen. Thus the water contents of the membranes and albumen decrease (ISM: 79 to 56%, OSM: 71 to 52%, albumen: 86 to 58%). As the membranes dry, gas enters the larger pores first. Physiological estimates of effective radius show smaller (x = 1.3 micrograms), bimodally distributed pores in the ISM and larger (x = 3.4 micrograms), unimodally distributed pores in the OSM.

Animals↗
PubMed1988

Blood flow distribution and its temporal variability in stimulated dog gastrocnemius muscle.

The distribution of blood flow in skeletal muscle stimulated to rhythmic isotonic contractions was studied by injections of radioactive microspheres into the arterial supply in 8 gastrocnemius muscles (mean weight 84 g) of 6 anesthetized dogs (20-25 kg body weight). The distribution of 10 micron microspheres in regions of about 0.5 g was very similar to that of the standard 15 micron microspheres, whereas that of 25 micron microspheres was more uneven. The coefficient of variation (CV = SD/mean) of the ratio of simultaneously injected 10 micron and 15 micron microspheres, 0.12, was taken as the inherent scatter of the method. The average spatial distribution inequality of 10-15 micron microspheres corresponded to a CV of 0.45 and the specific local blood flow inhomogeneity to a CV = 0.43 ( = square root 0.45(2) - 0.12(2], but there were marked differences between muscles. At equal blood flow levels, the inhomogeneity during reactive hyperemia was similar to that observed during stimulation. The temporal variability of blood flow in individual muscle pieces was obtained from the comparison of fractional trapping of 4 to 5 differently labeled microspheres injected at intervals of 2 min into steadily stimulated muscles. The mean CV for the variations in time was 0.23 and that corrected for methodological scatter, 0.19, but the differences in the extent of temporal blood flow changes among muscle pieces within a muscle and between different muscles were large. The presence of considerable spatial and temporal variations of blood flow in exercising muscle during apparent steady state may be important in limiting and/or modulating tissue O2 supply.

Animals↗
PubMed1987

Effects of temperature on oxygen transfer conductance of human red blood cells.

The influence of temperature (varied from 37 to 7 degrees C; average pH = 7.4) on the kinetics of O2 uptake and release by human red blood cells under stopped-flow conditions was investigated by double-beam spectrophotometry. The kinetics were characterized by the specific transfer conductance for O2, G. The temperature coefficient of G, Q10(G), for O2 uptake averaged 1.17, and activation energy, Ea(G) = 2.9 kcal/mol O2. The average values for O2 release were: Q10(G) = 1.30, and Ea(G) = 4.8 kcal/mol O2. The G values for release of O2 from oxyhaemoglobin solution, Gsol, yielded Q10(Gsol) = 2.06, Ea(Gsol) = 13.4 kcal/mol O2. Comparison of these Q10 and Ea values with those for diffusion of O2 and haemoglobin in aqueous media leads to the conclusion that the kinetics of O2 uptake and release by red blood cells in the stopped-flow condition is mainly limited by diffusion of O2 and haemoglobin in the red cell interior and by diffusion of O2 in the medium, and to a lesser degree by chemical reaction kinetics.

Biological Transport, Active↗
PubMed1987

Oxygen transfer properties and dimensions of red blood cells in high-altitude camelids, dromedary camel and goat.

To estimate the advantage of the small red blood cells (RBC) of high-altitude camelids for O2 transfer, the kinetics of O2 uptake into and release from the RBC obtained from llama, vicuña and alpaca were investigated at 37 degrees C with a stopped-flow technique. O2 transfer conductance of RBC (G) was estimated from the rate of O2 saturation change and the corresponding O2 pressure difference between medium and hemoglobin. For comparison, O2 kinetics for the RBC of a low-altitude camelid (dromedary camel) and the pygmy goat were determined and previously measured values for human RBC were used. O2 transfer of RBC was found to be strongly influenced by extracellular diffusion, except with O2 release into dithionite solutions of sufficiently high concentration (greater than 30 mM). The G values measured in these 'standard' conditions, Gst (in mmol X min-1 X Torr-1 X (ml RBC)-1) were: high-altitude camelids, 0.58 (averaged for llama, alpaca and vicuña since there were no significant interspecific differences); camel 0.42; goat, 0.42; man, 0.39. The differences can in part be attributed to expected effects of the size and shape of the RBC (volume, surface area, mean thickness), as well as to the intracellular O2 diffusivity which depends on the concentration of cellular hemoglobin. The high Gst of RBC of high-altitude camelids may be considered to enhance O2 transfer in lungs and tissues. But the O2 transfer conductance of blood, theta, equal to Gst multiplied by hematocrit (in mmol X min-1 X Torr-1 X (ml blood)-1), was only slightly higher as compared to other species: 0.20 (llama, alpaca, vicuña), 0.14 (camel), 0.18 (goat), 0.17 (man).

Altitude↗
PubMed1987

Oxygen transfer conductance of human red blood cells at varied pH and temperature.

The influence of temperature (varied from 37 to 7 degrees C) and of medium pH (varied from 7.7 to 7.1) on the kinetics of O2 uptake and release by human red blood cells (RBC) under stopped-flow conditions was investigated by double-beam spectrophotometry. From the rate of O2 saturation change and the mean effective PO2 difference between the medium and the Hb of RBC, the specific transfer conductance for O2, G, was calculated. The temperature coefficient, Q10, of G for O2 uptake averaged 1.17, activation energy, Ea, 2.6 kcal/mol O2; the average values for O2 release were: Q10 = 1.32, Ea = 4.8 kcal/mol O2. The G value for release of O2 from oxyhemoglobin solution, Gsol, yielded Q10 = 2.25, Ea = 13.5 kcal/mol O2. Comparison of these Q10 and Ea values with those for diffusion of O2 and hemoglobin in aqueous media leads to the conclusion that in the stopped-flow condition the conductance for O2 transfer was mainly limited by diffusion of O2 and hemoglobin in the red cell interior and by diffusion of O2 in the medium, and to a lesser degree by chemical reaction kinetics. This was further supported by the lack of dependence of O2 transfer conductance values on pH.

Adult↗