H. Slama

Intrapulmonary CO2 receptors in the duck: I. Stimulus specificity☆

Single unit vagal recordings were made from intrapulmonary CO2 receptors in five domestic ducks. Gas, containing various concentrations of CO2, was unidirectionally passed through the respiratory system either from the trachea to the surgically opened, right caudal thoracic air sac or vice versa. Intrapulmonary gas pressure (Pip) and CO2 concentration in the ventilatory gas (FiCO2 were varied independently. The units were identified and studied during unidirectional ventilation and during phasic ventilation with a Starling pump. The static discharge frequency of these receptors increased as Fico, decreased. In most receptors, step changes in FICO2 also produced dynamic responses. The static discharge frequency at various levels of FiCO2 did not significantly diner when Pip was low (about 2 cm H2O) or high (about 10–20 cm H2O). Likewise, the peak dynamic discharge frequency, elicited when FICO2 was suddenly decreased to 0%, was not affected by these levels of Pip. The receptor discharge frequency was also unaltered by transient changes in Pip provided FiCO2 and gas flow remained constant. All receptors exhibited cyclic discharge patterns during pump ventilation and peak frequencies occurred either during inspiration, or during expiration or during both phases of the respiratory cycle. Their discharge frequency decreased when CO2 was added to the inhaled gas. The results indicate that intrapulmonary CO2 receptors are not stretch-sensitive and therefore are not mechanoreceptors. Their cyclic discharge patterns during pump ventilation were similar to those seen during spontaneous breathing and appear to result from changes in intrapulmonary CO2 concentration at the receptor site. These receptors may be able to monitor alterations in intrapulmonary CO2 concentration resulting from changes in the metabolic activity of the bird, and may thereby be involved in the control of breathing.

Mechanisms of unidirectional flow in parabronchi of avian lungs: Measurements in duck lung preparations☆

Abstract To investigate the pathway of respired air in birds, lungs of ducks, fixed by means of glutaraldehyde, were separated from the air sacs and from all other organs. When this isolated lung was ventilated by applying pressure or suction to the main bronchus, the dorsobronchial flow was shown to be unidirectional in both respiratory phases, leading from the mesobronchus through the dorsobronchi to the parabronchi, as has previously been shown for the living duck. Flow direction could also be measured in other parts of the bronchial tree including ventrobronchi where the measurements were not in agreement with the hypothesis of Hazelhoff (1943). To analyze the mechanisms of this rectification of flow, the aerodynamical properties of some structures of the bronchial tree, especially the openings of the secondary bronchi into the mesobronchus, were investigated. These openings offered a direction-dependent resistance to air flow, presumably due to detachment of flow at sites of sharp edges. These results lend support to the hypothesis that the particular pathway of respired air in duck lungs is effected by “aerodynamical valving”.

Intrapulmonary CO2 receptors in the duck: II. Comparison with mechanoreceptors☆

Single-unit recordings from vagal afferents exhibiting discharge patterns in phase with pump ventilation were made in domestic ducks to determine if receptors, other than intrapulmonary CO2 receptors, discharge in phase with the pump. After identification of the units during pump ventilation, the units were tested during unidirectional ventilation for their response to changes in inspired CO2 concentration (FiCO2) and to changes in mechanical distortion resulting from increases in intrapulmonary pressure (Pip). Two types of receptors with distinct differences in discharge pattern were encountered: (1) Receptors which responded rapidly to changes in FICO2 but which were insensitive to mechanical deformation (18 receptors out of 22). These receptors were located in the lung and were similar to those described by Fedde et al. (1974). (2) Receptors that were insensitive to changes in FICO2 but increased their discharge frequency parallel to increases in Pip (4 receptors out of 22). These receptors appear to be slowly adapting mechanoreceptors. Their location could not be determined. The results suggest that with cyclic ventilation, spontaneous or artificial, only two types of receptors with vagal afferents are stimulated, both of which are highly stimulus-specific. Whereas the intrapulmonary CO2 receptors are very likely to be involved in control of breathing, the role played by mechano-receptors is unknown.

Intrapulmonary CO2 receptors in the duck:III. Functional localization

Abstract Single-unit activity in the right vagus nerve was recorded from 67 intrapulmonary CO 2 receptors in anesthetized ducks. The right caudal thoracic air sac was cannulated and the mesobronchus was blocked in the right lung between the origins of ventrobronchi and dorsobronchi. The lung could be unidirectionally ventilated in either direction. Two different tests were applied to each receptor in an attempt to determine its location within the lung. 1. (1) Gross localization of receptors in cranial or caudal parts of the lung was assessed on the basis of differences in discharge frequency when gas flow direction was air sac to trachea vs. trachea to air sac. More than 95% of the receptors were in caudal parts of the lung. 2. (2) For finer localization , pure CO 2 or O 2 was insufflated via catheters into the ventilatory gas stream either proximal or distal to the blocking balloon during gas flow in both directions. In this way, the location of 60 receptors (90%) could further be specified. Of these receptors 56% were found to be in the caudal ends of paleopulmonic parabronchi, 27% in neopulmonic parabronchi, and 12% in dorsobronchi or in parabronchial tissue near the dorsobronchi; only 5% were located in the cranial ends of paleopulmonic parabronchi; none were in the ventrobronchi or extrapulmonary air ways. Thus, CO 2 receptors are located in those parts of the lung that experience marked fluctuations in CO 2 concentration during the respiratory cycle. Differences in location permit satisfactory explanation of differences in discharge pattern of CO 2 receptors observed during spontaneous breathing.

Volume and ventilation of air sacs in ducks studied by inert gas wash-out

Abstract Volume and ventilation of the air sacs were determined in spontaneously breathing domestic ducks by an inert gas wash-out technique. A known quantity of helium was injected via a catheter into an air sac and initial concentration as well as time course of subsequent wash-out were monitored by a mass spectrometer. Data were analyzed on the basis of single-compartment or two-compartment models according to whether the wash-out curves showed one or two exponentials. Whereas all air sacs studied (interclavicular, prethoracic, postthoracic and abdominal) had similar volumes, the prethoracic and the postthoracic sacs were found to receive about 3 times as much ventilation as the interclavicular sac or the abdominal sacs. The functional inhomogeneity, as indicated by bi-exponential wash-out kinetics, was most pronounced in the interclavicular air sac. During artificial ventilation the total air sac volume was increased, both volume and ventilation were shifted towards the caudal (postthoracic and abdominal) air sacs, and inhomogeneity of the air sacs was reduced. The physiological significance of the results, particularly with respect to gas exchange, will be discussed.

Zeitabhängige Veränderungen des Filmdruckes alveolärer Oberflächenfilme im Langmuir-Trog

SummaryElastic properties as well as time depending properties of surface films are responsible for the effects of surface active substances on the stabilization of the lung alveoli. Lung alveolar surfactant (LAS) obtained from rat lungs was spread in a rhomb-formed trough and the surface tension was recorded during rapid changes of the surface area using the Wilhelmy method. — Immediately after rapid compression of the surface area by 75% the surface tension is very low increasing again to a higher level during the following minutes. Expansion of the surface area to its initial size was at first accompanied by a high surface tension which afterwards decreased to a lower value. In comparative experiments using Dipalmitoyllecithin a similar behaviour with, however, some quantitative differences was found. Following compression lecithin shows higher final values of surface tension than LAS. After expansion the surface tension decreases more when LAS is spread in the through than when Lecithin is used. This last difference is due to the better spreading qualities of LAS on the hypophasis. In this respect LAS seems to be more efficient in preventing atelectasis of the lung than Dipalmitoyllecithin. If LAS is spread on a hypophasis containing protein the values of the surface tension following compression are only slightly increased while the values following expansion are distinctly decreased. If Lecithin is spread on such protein solutions the values after compression and after expansion are very similar to those obtained when pure protein solutions are used.ZusammenfassungFür die Wirksamkeit von oberflächenaktiven Substanzen als Stabilisatoren der Lungenalveolen sind nicht nur elastische, sondern auch zeitabhängige Eigenschaften der von ihnen gebildeten Oberflächenfilme verantwortlich. In einem rhombusförmigen Trog wird oberflächenaktives Material aus Rattenlungen (LAS) gespreitet und die Oberflächenspannung bei raschen Änderungen der Trogfläche mit der Methode von Wilhelmy gemessen. Nach rascher Verkleinerung der Trogfläche um 75% stellt sich die Oberflächenspannung zunächst auf einen sehr niedrigen Wert ein, steigt dann aber wieder in einigen Minuten auf einen höheren Wert an. Bei Vergrößerung der Trogfläche auf den Ausgangswert stellt sich zunächst eine sehr hohe Oberflächenspannung ein, die aber dann auf einen niederen Wert zurückgeht. Vergleichende Untersuchungen mit Dipalmitoyllecithin zeigen ein ähnliches Verhalten, jedoch gewisse quantitative Unterschiede. Im Anschluß an die Kompression stellen sich bei Lecithin endgültig höhere Oberflächen-spannungen ein als beim LAS. Im Anschluß an die Expansion sinkt bei der Beschickung des Trogs mit LAS die Oberflächenspannung stärker ab als bei Lecithin-Versuchen. Der letztgenannte Unterschied beruht darauf, daß das LAS besser als das Lecithin auf der Hypophase spreitet. In dieser Hinsicht scheint LAS besser geeignet zu sein, Atelektasen in der Lunge zu verhindern, als Dipalmityllecithin. Spreitet man LAS auf Eiweißlösungen, so sind die Werte der Oberflächenspannung nach der Kompression leicht erhöht, die nach der Expansion deutlich erniedrigt. Spreitet man Lecithin auf Eiweißlösungen, erhält man bei Kompression und Expansion des Films Werte, die denen der reinen Eiweißlösung sehr ähnlich sind.

Lung surfactant: film kinetics at the surface of an air bubble during prolonged oscillation of its volume.

Abstract These investigations were designed to provide a better understanding of the behaviour and action of surface-active materials in the alveolus of the lung. The bubble method was used to generate area/surface tension diagrams (ASD) for films of lung alveolar surfactants and of dipal-mitoyllecithin. If one rhythmically enlarges or reduces a bubble covered with a film of lung surfactant or lecithin, supplied in excess, the ASD changes as though surface-active substance was disappearing. This alteration in successive ASDs occurs very rapidly at first but later is much slower. After ca 1000 cycles practically no further change can be seen; this final or “equilibrium” ASD is approached asymptotically as the number of cycles increases. The equilibrium ASD is to a large extent independent both of the amount of surfactant applied and of whether the material has been applied to the bubble surface or to the hypophase. For films of lung surfactant, with oscillatory surface-area changes of 75% at 37 °C, the maximal surface tensions obtained with the largest area lie between 67–69 dyne/cm and the minimal values, with the smallest area, between 19–22 dyne/cm. For lecithin films under the same conditions, a maximal surface tension of, 70 dyne/cm and a minimal value of less than O.5 dyne/cm are found. If the bubble area is changed by less than 75%, the difference between maximal and minimal surface tension in the equilibrium ASD decreases, for both kinds of film, by an amount corresponding to the reduction in change of area, the minimal surface tension remaining the same. These results can be explained in part by an exchange of surfactant between the aqueous phase and the interface, and in part by the behaviour of the material at the interface durins ranid chanses of area.

Bestimmung der Oberflächeneigenschaften von Stoffen aus den Lungenalveolen mit einer Blasenmethode

SummaryA method for study of dynamic and static surface properties of small bubbles in liquids is described.An air bubble, remaining in communication with the atmosphere, is sucked into a cuvette, filled with an aqueous solution through a circular opening in its bottom. Surface active material is brought on to the surface of the bubble by means of a micro-pipette. The volume of the bubble is changed by corresponding displacements of liquid into and out of the cuvette with varied time patterns and amplitudes. The transmural pressure of the bubble is measured by means of a pressure transducer, and the radius and surface area of the bubble are derived from photocell recordings. The surface tension is instantaneously obtained, according to the Laplace equation, using an analog computer. The method has been applied to the study of the behavior of lung surfactant. The film-lined air bubble is considered to represent a good model for the lung alveolus covered with the surfactant film.ZusammenfassungEs wird eine Methode beschrieben, mit der statische und dynamische Oberflächeneigenschaften von kleinen Blasen in Flüssigkeit untersucht werden können.Durch eine kreisförmige Öffnung können in eine mit einer wäßrigen Lösung gefüllten Cuvette Gasblasen mit einem Radius von 250–380 μ eingesogen werden. Sie stehen durch die Öffnung mit der Außenluft in Verbindung und können in ihrer Größe planmäßig verändert werden. Aus dem Blasenradius und der Druckdifferenz zwischen dem Blaseninnern und der umgebenden Flüssigkeit läßt sich mit Hilfe eines Analogrechners die jeweilige Oberflächenspannung an der Blasenoberfläche berechnen und registrieren. Auf die Oberfläche der Blase kann man oberflächenaktive Substanzen bringen und das Verhalten der dadurch gebildeten Oberflächenfilme bei Änderung der Blasenfläche untersuchen. Mit Hilfe dieser Methode wurde das Verhalten von Filmen aus alveolären oberflächenaktiven Stoffen bei verschieden rascher Flächenänderung untersucht. Die mit Film bedeckte künstliche Blase ist ein gutes Modell für die mit oberflächenaktiver Substanz bedeckte Lungenalveole.

Remote-controlled device for sampling arterial blood in unrestrained animals

SummaryA device is described that allows remote-controlled sampling of arterial blood in unrestrained animals. An artery and a vein are dissected in local anesthesia and connected by a plastic catheter, the sampling catheter. The flow of arterial blood in this artificial shunt can be blocked by kinking the sampling catheter by a remote-controlled device. The blood thus trapped in the sampling catheter, of 0.45 ml volume, is analyzed forPo2,Pco2 and pH using electrodes. The technique has been used in ducks and hens but can be applied to other vertebrate classes and to species of smaller body size.

Zeitabhängiges Verhalten von Filmen von oberflächenaktivem Material aus Lungenalveolen

SummaryUsing a special bubble method, the behaviour of lung alveolar surfactant (LAS) films was studied during rapid changes of the surface area covered by the film.Upon a rapid decrease of the surface area by 75%, the surface tension at first reached a very low value, but thereafter returned to a higher value. Upon a rapid increase of the surface area the surface tension at first reached a high level, decreasing thereafter.The behaviour of the surface tension during and after increases in surface area was dependent upon temperature. At 45°C and 37°C the peak surface tension reached immediately after an increase in film surface area was lower than that observed at 24°C. Also the final value reached after an increase in surface area was lower and practically coincident with the final value attained after compression of the film. Furthermore, at the higher temperatures the time constants for attainment of the final value were shorter than at 24°C.Films of dipalmitoyl-lecithin (DPL) showed a behaviour similar to that of LAS films. However, after an increase of the surface area the surface tension reached very high values and thereafter decreased less rapidly and to a lesser extent when compared with LAS films. In this respect a DPL film appears to be less suited for stabilization of lung alveoli than the LAS film.ZusammenfassungMit einer Blasenmethode wurde das Verhalten von Filmen aus alveolärer oberflächenaktiver Substanz (LAS=lung alveolar surfactant) bei rascher Änderung der von dem Film bedeckten Fläche untersucht. Bei rascher Verkleinerung einer mit einem Film bedeckten Luftblase um 75% der Ausgangsfläche findet man zunächst eine sehr niedrige Oberflächenspannung, die dann wieder auf einen höheren Wert ansteigt. Bei rascher Vergrößerung der Fläche stellt sich zunächst eine hohe Oberflächenspannung ein, die aber dann wieder auf einen niederen Wert zurückgeht. Das Verhalten der Oberflächenspannung während und nach der Flächenvergrößerung ist temperaturabhängig. Bei 45 und 37°C liegt die Oberflächenspannung direkt nach der Flächenvergrößerung niedriger als bei 24°C. Auch der in Anschluß daran sich einstellende Endwert liegt tiefer und stimmt praktisch mit dem Endwert überein, der sich im Anschluß an die Kompression des Films einstellt. Auch sind die Einstellzeiten für diesen Wert bei hohen Temperaturen kürzer als bei 24°C. Filme aus Dipalmitoyllecithin (DPL) zeigen ein ähnliches Verhalten wie LAS-Filme. Jedoch stellen sich direkt nach der Oberflächenvergrößerung sehr hohe Oberflächenspannungen ein, die auch im Anschluß daran langsamer und weniger stark absinken. In dieser Hinsicht scheint der DPL-Film für die Stabiliserung der Lungenalveolen weniger geeignet als der LAS-Film.