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J Piiper

Publications and source records attributed to J Piiper.

At least 91 records · Page 5Linked to original sources
PubMed1984

Diffusion-perfusion relationships in skeletal muscle: models and experimental evidence from inert gas washout.

In order to study the dependence of blood-tissue gas exchange upon diffusion, the simultaneous washout of two inert gases of differing diffusivity was investigated in isolated-perfused dog gastrocnemius preparations. The muscles were equilibrated with CH4 and SF6 via arterial blood. The washout kinetics were determined from venous blood samples analyzed by gas chromatography. The results revealed the following features: The washout of the test gases was pronouncedly multi-exponential, and could be described by three exponential components when analyzed to 5% of the initial value. The non-exponential washout was attributed to unequal distribution of capillary blood flow to tissue volume. The mean ratio of washout rate constants CH4/SF6 was within 1.10-1.25 and was even smaller than the ratio expected for pure perfusion limitation (1.46). Therefore, no evidence for effective tissue-blood diffusion limitation was obtained. The observed washout rate constant ratio could be explained by a model with veno-arterial back diffusion which more strongly retards washout kinetics of the better diffusible gas (CH4) as compared to the less diffusible gas (SF6).

Animals↗
PubMed1984

Elements for modeling inert gas washout from heterogeneous tissues.

Inert gas washout from tissue may be analyzed using Krogh's cylinder or a simplified model thereof, represented by a series arrangement of compartments. In particular with limited axial diffusion in tissue, washout from this model is multi-exponential, the rate of washout accelerating with time. To explain the experimentally observed multicomponent washout, in which washout retards with time, heterogeneity of flow and/or diffusing capacity to volume is required, either in series or in parallel compartments. While there appears to be a structural basis for both types of heterogeneity, parallel and series, a distinction between both on the basis of washout curves alone is impossible.

Animals↗
PubMed1984

Dual role of diffusion in tissue gas exchange: blood-tissue equilibration and diffusion shunt.

The role of diffusion in inert gas washout from tissue is investigated using simple mathematical models incorporating diffusive blood-tissue equilibration and diffusion shunt due to diffusive gas transfer between precapillary and postcapillary vessels with counter-current blood flow. With increasing diffusivity blood-tissue equilibration is improved, but simultaneously the diffusion shunt by veno-arterial back diffusion is increased. Similarly, with decreasing blood flow, the extent of diffusion limitation in blood-tissue transfer is diminished, but at the same time veno-arterial diffusive shunting is enhanced. Diffusion shunt slows inert gas washout (local tissue clearance) and thus, if not taken into account, leads to an underestimation of capillary blood flow calculated from the washout rate constant. Diffusion shunting of O2 diminishes the efficacy of blood-tissue transfer, but its extent is predicted to be smaller compared to that for inert gases, because the chemical combination of O2 in blood decreases diffusive shunting.

Animals↗
PubMed1984

Carbon dioxide dissociation and buffering in chicken blood during development.

Carbon dioxide dissociation curves of oxygenated and deoxygenated bloods, the Haldane effect, the buffer value and other blood and true plasma buffering indices, O2 capacity and hematocrit were determined in bloods withdrawn from chicks before, during and after hatching and 8-month-old hens. Blood CO2 dissociation curves shifted upwards in the developing embryo till pipping, and moved downwards after pipping and hatching. In accordance with the position of the CO2 dissociation curves, the true plasma bicarbonate and red cell CO2 standardized to PCO2 = 40 torr changed. The Haldane factor at standard PCO2 increased from 0.12-0.13 on days 10-14 of incubation to 0.34 in young hens. The buffering power changed in parallel with O2 capacity and hematocrit, increasing steadily during incubation, dropping at hatching and then increasing again to the adult value. The observed changes in the CO2 dissociation curves and buffering variables during the development enable the chick to minimize the changes in the acid-base status and are favorable for coping with the increasing demand for CO2 transport and buffering of the developing bird.

Acid-Base Equilibrium↗
PubMed1984

Dual role of diffusion in tissue gas exchange: blood-tissue equilibration and diffusion shunt.

The role of diffusion in tissue gas exchange is investigated using a simple mathematical model which incorporates both tissue-blood equilibration and gas transfer between arterial and venous vessels with counter-current flow, leading to 'diffusion shunt'. Both increasing the diffusion coefficient of the gas considered or decreasing the blood flow results in two antagonistic effects: (i) improvement of blood/tissue equilibration, (ii) increase in extent of diffusion shunt. The diffusion shunt retards inert gas wash-out (local tissue clearance) and leads thus, if not taken into account, to an underestimation of capillary blood flow calculated from the wash-out rate constant. For O2 (and CO2) the diffusion shunt reduces the efficacy of blood/tissue transfer, but its extent is expected to be only moderate because of the chemical combination of these gases in blood.

Diffusion↗
PubMed1984

Blood flow in exercising muscles by xenon clearance and by microsphere trapping.

The accuracy of muscle blood flow measurement by the 133Xe clearance method (QXe) was assessed against direct venous outflow (Qv) and microsphere trapping flow (Q mu) determinations in isolated perfused dog gastrocnemius both at rest and during graded stimulation [O2 consumption (VO2) up to 12 ml X 100 g-1 X min-1] and in the gastrocnemius, vastus lateralis, and triceps of intact dogs at rest and while running on a treadmill at varied speeds up to maximum VO2. In 29 measurements performed in 11 isolated muscles, Q mu was in good agreement with Qv at rest and at all stimulation levels (Q mu/Qv = 1.0; r = 0.98). 133Xe clearance yielded much lower blood flows than the venous outflow and the microsphere trapping methods. In 43 measurements in 11 muscles, the mean QXe/Qv ratio was 0.57 +/- 0.03 (SE), independent of blood flow. Similarly, in 65 measurements in 2 intact dogs, the mean QXe/Q mu ratio in all tested muscles was 0.49 +/- 0.02 (SE), independent of blood flow. These results show that the 133Xe clearance method considerably underestimates blood flow in dog muscles.

Animals↗
PubMed1984

Blood-gas equilibration of CO2 and O2 in lungs of awake dogs during prolonged rebreathing.

To reinvestigate the blood-gas CO2 equilibrium in lungs, rebreathing experiments were performed in five unanesthetized dogs prepared with a chronic tracheostomy and an exteriorized carotid loop. The rebreathing bag was initially filled with a gas mixture containing 6-8% CO2, 12, 21, or 39% O2, and 1% He in N2. During 4-6 min of rebreathing PO2 in the bag was kept constant by a controlled supply of O2 while PCO2 rose steadily from approximately 40 to 75 Torr. Spot samples of arterial blood were taken from the carotid loop; their PCO2 and PO2 were measured by electrodes and compared with the simultaneous values of end-tidal gas read from a mass spectrometer record. The mean end-tidal-to-arterial PO2 differences averaging 16, 4, and 0 Torr with bag PO2 about 260, 130, and 75 Torr, respectively, were in accordance with a venous admixture of about 1%. No substantial PCO2 differences between arterial blood and end-tidal gas (PaCO2 - PE'CO2) were found. The mean PaCO2 - PE'CO2 of 266 measurements in 70 rebreathing periods was -0.4 +/- 1.4 (SD) Torr. There was no correlation between PaCO2 - PE'CO2 and the level of arterial PCO2 or PO2. The mean PaCO2 - PE'CO2 became +0.1 Torr when the blood transit time from lungs to carotid artery (estimated at 6 s) and the rate of rise of bag PCO2 (4.5 Torr/min) were taken into account. These experimental results do not confirm the presence of significant PCO2 differences between arterial blood and alveolar gas in rebreathing equilibrium.

Animals↗
PubMed1983

Blood gases and acid-base status in chicken embryos with naturally varying egg shell conductance.

In chicken eggs selected for widely varying values of specific water vapor conductance, gH2O (= water vapor conductance per freshly laid egg mass), PCO2, pH, PO2 and hematocrit were measured in arterialized blood sampled from an allantoic vein (after 16 days of incubation) or in blood termed 'venous', sampled from an allantoic artery (after 18 days of incubation). Both arterialized and 'venous' PCO2 were inversely related to gH2O. Since the variations of blood plasma pH with PCO2 were smaller than predicted for true plasma, partial compensation by appropriate non-respiratory changes of plasma bicarbonate concentration must have occurred. Only with extremely high and low gH2O a definite alkalosis and acidosis, respectively, were observed. Both arterialized and 'venous' PO2 tended to diminish with decreasing gH2O. The hematocrit value showed a tendency to increase with decreasing gH2O and with decreasing arterialized PO2.

Acid-Base Equilibrium↗
PubMed1983

Gas exchange, blood gases and acid-base status in the chick before, during and after hatching.

To study the transition from chorioallantoic to pulmonary gas exchange in birds, blood gases and acid--base variables were measured in chicks of domestic fowl before, during and after hatching. Measurements were made in samples of 'venous' blood (from allantoic arteries or the right ventricle, respectively) entering the gas exchanger (chorioallantois or lungs, respectively) and arterialized blood (from allantoic veins or the left ventricle, respectively) leaving the gas exchanger. Also, O2 uptake was measured and blood flow of the gas exchanger was determined according to the Fick principle. During the last days of incubation PO2 decreased PCO2 increased in both arterialized and 'venous' blood, but the changes of pH were small due to a concomitant increase in bicarbonate concentration, in accordance with the results of previous studies. After external pipping and hatching pronounced hypocapnia developed, but the respiratory alkalosis was partiallY compensated by a transitory non-respiratory reduction of bicarbonate. In spite of arterial hypoxia at the end of incubation and some loss of blood during hatching, blood O2 transport was not seriously impaired during pipping and hatching as revealed by 'venous' blood gases. The blood gases and pH of 17-day-old chicks were close to those of adult chickens.

Acid-Base Equilibrium↗
PubMed1983

Gas mixing in dog lungs studied by single-breath washout of He and SF6.

Simultaneously measured helium (He) and sulfur hexafluoride (SF6) single-breath washout was studied in 16 anesthetized paralyzed dogs ventilated with a special hydraulically operated ventilatory servo system. After equilibration of lung gas with 1% He and 1% SF6, the maneuver consisting of inspiration of a test gas-free mixture at constant rate (VI), a variable time of breath holding, and an expiration at constant rate (VE), was performed. Fractional concentrations of He and SF6, recorded against expired volume, were analyzed in terms of slope of the alveolar plateau (S) and series (Fowler) dead space (VD). In control conditions (VI = 0.5 l/s, VE = 0.1 l/s) S was about 10% of alveolar-to-inspired concentration difference per liter expirate both for He and SF6. Both SHe and SSF6 were inversely related to VI and VE, the relative changes being more pronounced with varying VE. SHe/SSF6 was higher or lower than unity depending on VI and VE. Both SHe and SSF6 decreased with increasing preinspiratory lung volume. Breath holding up to 10 s slightly decreased SHe and SSF6 while SHe/SSF6 was unchanged. The contribution of continuing gas exchange to S assessed from comparative measurements using the reversed (single breath washin) technique ranged from 6 to 23% in the various conditions. The VDHe/VDSF6 ratio was 0.84 and was little affected in the various settings. Results indicate that the substantial alveolar gas inhomogeneity in the dog lung and the mechanism accounting for S are little diffusion dependent. By exclusion sequential filling and emptying of lung units is believed to constitute the most important mechanism responsible for the sloping alveolar plateau.

Animals↗
PubMed1982

Blood-gas CO2 equilibration in lungs of unanesthetized dogs during hypercapnia.

We have reinvestigated the problem of blood-gas equilibration of CO2 in lungs during hypercapnia. Six dogs with chronic tracheostomy and exteriorized carotid artery were subjected in acute experiments to hypercapnic inspired mixtures [CO2 fraction of expired gas (FICO2) = 0.06; 0.08; 0.10]. Expired CO2 partial pressure (PCO2) was continuously measured with a respiratory mass spectrometer and compared with arterial PCO2 determined in blood samples that were collected during apparent steady-state conditions. Particular care was taken in using continuously recorded temperature in the right heart for correction of blood PCO2 measured by CO2 electrodes. In no animal was there a significant difference between arterial and alveolar PCO2. On the average, this difference was -0.1 Torr at FICO2 = 0.06; 0.0 Torr at FICO2 = 0.08, and -0.2 Torr at FICO2 = 0.10. The results are in agreement with the conventional view that PCO2 in pulmonary capillary blood approaches PCO2 in alveolar gas.

Animals↗
PubMed1982

Models for a comparative functional analysis of gas exchange organs in vertebrates.

The analysis of external gas exchange in the various respiratory organs of vertebrates is based on models with gas transport properties determined by ventilatory, diffusive, and perfusive conductances and by the geometric arrangement of medium and blood flows. The following factors are examined: water vs. air as external medium; gas transport properties of blood; diffusive gas transfer between medium and blood; problems in assessing diffusion limitation in fish gills, amphibian skin, avian lungs, and mammalian lungs. Finally the limitations to the analysis imposed by various physiological and anatomical complexities are discussed.

Amphibians↗
PubMed1982

Respiratory gas exchange at lungs, gills and tissues: mechanisms and adjustments.

(1) A general model for external gas exchange organs of vertebrates is presented, in which the main parameters are the ventilatory, diffusive and perfusive conductances for O2 and CO2. The relevant properties of the external medium (air or water) and of the internal medium (blood) are analysed in terms of capacitance coefficients (effective solubilities) for O2 and CO2. The models for the main types of gas exchange organs (fish gills, amphibian skin, and avian and mammalian lungs) are compared in terms of their intrinsic gas exchange efficacy. The adjustments to increased metabolic rate or to hypoxia are achieved by increasing the conductances. (2) The gas exchange at tissue level is analysed using the Krogh cylinder and a simplified model containing a diffusive and a perfusive conductance. The adjustments to increased load (exercise, hypoxia) consist in both increased local blood flow and in improvement of diffusion conditions (enlargement and recruitment of capillaries). (3) Some particular features of respiration in transitional (unsteady) states, such as occurring at the beginning of exercise and of hypoxia, are examined. The additional physical variables are the O2 (and CO2) stores acting according to their capacitances and partial pressure changes. Delayed increase in O2 uptake at the beginning of exercise is due to the limited speed of physiological adjustments. The ensuing O2 debt is energetically covered by anoxidative energy releasing processes (hydrolysis of high-energy phosphates and anaerobic glycolysis). Finally, the reduction of metabolic rate as adjustment to hypoxia is discussed.

Amphibians↗
PubMed1982

Diffusion in the interlamellar water of fish gills.

The role of diffusion limitation in interlamellar water of fish gills can be studied on simplified gill models consisting of slits bounded by trapezoidal plates and perfused by water. The main factors determining the degree of O2 equilibration of gill water are shown to be interlamellar distance, length of the secondary lamellas, water velocity, and diffusion coefficient of O2 in water. Estimations indicate that a considerable part of the resistance to O2 transfer in fish gills is attributable to diffusion limitation in water, particularly with increased ventilation provoked by hypoxia or swimming.

Animals↗
PubMed1981

Energy sources and mechanical efficiency of anaerobic work in dog gastrocnemius.

Thermally isolated dog gastrocnemii were stimulated to exhaustion by rhythmic isotonic tetani of 0.2s duration (30 min-1) in complete occlusion of blood flow. Total enthalpy change, H = heat + work, work output, w, (kJ . kg-1) and average mechanical efficiency over the working period, n = w/H, were determined from deep muscle temperature increase and amount of shortening, and lactate produced, La, (mol . kg-1) from washout curves, respectively. Under these conditions H is the sum of the enthalpies due to a) alactic sources (Hal), i.e., net approximately P depletion and muscle O2 stores utilization, and b) formation: H = Hal + "delta HLa" . La. Thus, as "delta HLa", the molar enthalpy of La formation, amounts to 76 kJ . mol-1, Hal could be calculated. It was observed that: i) n ranged from 0.2-0.5 and was higher the lower H, this inverse relationship being essentially due to the dependence of n on Hal as described by: Hal = Ho . 10-kn + a (where Ho = 9.3, k = 3.7 and a = 0.15), and ii) the shortening speed of the first few tetani (vi, mm . s-1), was directly related to Hal as described by: vi = 63.3 + 30.7 Hal. Hal is essentially proportional to the approximately P content of resting muscle. These findings suggest therefore that the efficiency of contraction and the shortening speed are both affected by the approximately P concentration, the efficiency increasing, and the speed decreasing with decreasing approximately P.

Anaerobiosis↗
PubMed1981

Inert gas elimination from lungs with stratified inhomogeneity: theory.

The effects of diffusion limitation in alveolar space (stratified inhomogeneity) on steady state inert gas elimination by the lung from blood are studied in theory. The lung models used for the calculations are characterized by a diffusion barrier in the alveolar space, which is quantified by a diffusive conductance (diffusing capacity), D'. In both homogeneous and inhomogeneous lung models (with log-normal distribution of VA, Q and D') increasing stratified inhomogeneity (decreasing D') is shown to diminish inert gas elimination. The effect, which depends on the solubility of the gases, is similar to the effect of alveolar dead space ventilation.

Lung↗