Three basic concepts define the actual theory regarding respiratory mechanics which rule most of the interpretation of experimental studies in this-field of research. These concepts are: 1.The inhalation of air is determined by the active expansion of the chest walls, passively followed by the lungs, a concept previously maintained by Galen. 2. The retracting force of the lungs. 3.The intra-pleural sub-atmospheric pressure linking the lungs and the chest walls. (A wide review of these concepts can be read in reference l).
The retracting force of the lungs is a fact beyond controversy, made evident by whatever means, being relative to their tissue elasticity as well as to the fact that the lung's are permanently stretched between the trachea and larynx on one side and the thorax walls (their exterior support) on the other, an indispensable condition for the exertion of their elastic property like an elastic band.
The retraction-expansion of the lungs and the chest walls during the respiratory cycle is another incontrovertible fact, but the explanation of the actions that determine this cyclic movement, can be, and are, a matter of discussion.
The passive behaviour of the lungs is a weak argument to uphold nowadays in view of the complexity of the respiratory function, in direct connection with the cardio-circulatory function and the universal dynamics for a balanced gas interchange at the alveolo-capillary level. This interchange depends on the complex organisation and systematisation of the respiratory tree and requires balanced dynamic conditions along its structure at each point in the respiratory cycle, so as to be capable of accomplishing the function of gas exchange in the cyclic way demanded by the rhythmic action of the heart, for which an air mass has to be supplied in proportion to cardiac output.
The attribution of the determinant role in the lung and thorax wall coupling to sub-atmospheric intra-pleural pressure alone is also a matter of discussion, West's opinion15 concerning adhesion force as responsible for that attachment also merits reconsideration.
These fundamental complex-dynamics require freedom of action of the respiratory tree as a whole, and is the generator of the reflex actions of the chest walls, according to their individual requirements, under the co-ordination of the central nervous system.
Relatively recent experimental studies supply observations and conclusions which are compatible with the primary active actions of the respiratory tree; in this way, Widdicombe expresses16 that the trachea is far from being a rigid or passive gas-conducting pipe. Kilburn8 has shown that the transversal fibres of the trachealis smooth muscle are chiefly responsible for the active changes in tracheal volume. Corteau4 attributes a distensible capacity to the bronchi equal to that of the trachea, and has measured their active constriction by means of drugs and concluded that they decrease in width by up to 70% and in length by up to 10%. Miller10 observes that the smooth muscle in the bronchioli and alveolar ducts are thicker relative to the lumen diameter and; therefore, we can expect important dynamic actions. Sphincter like muscles around the openings of the atria have been shown by Shepard.13 Dubreuil,5 Miller;10 it is to be expected, as they believe, that constriction on this side should tend to trap air in the alveoli. Beinfield3 recorded spontaneous mechanic activity of the trachealis muscle, exerted primarily along an axis parallel to the transverse cervical Trachealis muscle fibres. Scarpelli12 observes constriction of the cervical trachea during inspiration.
Studies by StephensI4 relating to the force velocity contraction of the airways smooth muscle conclude that they have an analogous behaviour to that of the striated muscles which is similar from primary to secondary bronchi, while Hawkins7 notes that bronchi from the second to the fifth order behave similarly. González-Bogen6 has demonstrated the presence of forces transmitted to the pleural space whose resultant values determine a wave of impulses well above the atmospheric pressure level. This has been termed the "Respiratory Pulse Wave", and later studies by the same author deepen and widen those conclusions, constituting the subject of this book in which he tries to prove: 1. The active and primary role of lungs and airways in respiratory dynamics. 2. The reflex active role of the chest walls. 3. The intra-pleural pressure variations as a consequence of changes in the pleural capacity, relative to the dynamics of the respiratory tree in its thoracic coupling. 4. The role of the adhesion force, which results from the incontrovertible fact that the pleural membranes are two smooth and polished moist surfaces in intimate contact. 5. Finally, the correlation of the mentioned facts has allowed the author to arrive, at conclusions, which have not been foreseen up to now.
Several series of experiments in anaesthetised dogs have been performed, with and without intra-tracheal cannula and using different kinds of poligraph devices. In all cases, right thoracotomy in the sixth intercostal space has been performed; introducing a thin catheter and small water filled balloon into the pleural space.
The cannula connects the pleural space with the pressure detector device, which, supplies data on the pressure variations of the pleural content: Intra-pleural sub-atmospheric pressure. While the balloon filled with water detects the totality of transmitted pressures to that space: Respiratory Pulse. Both are recorded simultaneously.
In some cases, similar balloons are also placed between the base of the lungs and the diaphragm, at different intercostal levels, as well as in the left pleural space and the detected effects are recorded simultaneously.
The following precautions are taken:
Before performing the thoracotomy, a ventilator is connected to the trachea of the dog, in order to avoid the collapse of the lung.
The balloon is emptied of air bubbles and its pressure calibrated to that of the atmosphere before being placed in the thorax.
After the thorax wound is closed, all the air in the pleural space is extracted using the same catheter, which was formerly inserted, introducing the exterior end into a bowl of water.
Once the dog has recovered spontaneous respiration, the new state of equilibrium in the balloon, pressed between the two pleural surfaces, is determined, and this value is taken as a "base level" for cyclic inflexions.
The following simultaneous parameters have been used as comparative tests:
TIDAL VOLUME GRAPH, which indicates the very moment when air begins to enter the lungs, the, time it takes to penetrate, and the moment at which it stops, for each ventilatory cycle.
ABDOMINAL AORTIC PULSE GRAPH, which supplies data on cardiac rhythm, as well as on the influence of the impulses transmitted to the abdomen, generated by pulmo-thorax dynamics.
PNEUMOGRAM, which allows us to state the relation of costal wall expansion-retraction, to diaphragm and lung displacement.
ANALYSIS OF THE GRAPHS OF PRESSURE DETECTED IN THE PLEURAL SPACE
The general method, as described, is used in the experiment from which the graphs in figs. 1 to 7 and 13 here analysed have been chosen. Special conditions in these experimental demonstrations are the following:
Premedication: morphine hidro-clorhidrade 1 mg. Anaesthesia: a mixture of 50 mg alfa-cloralose and 500 mg Uretane. Thracheostomy and insertion of a tube connected to a balanced spirometer also connected to a closed-circuit respiratory system, to measure "tidal volume". Amplifier S. E. Laboratory Ltd. Statham S. E. strain gauge traducers.
I. INTRA-PLEURAL SUB-ATMOSPHERIC PRESSURE
|OBSERVATIONS. Fig. 1|
1. Correlation of intra-pleural sub-atmospheric pressure variations in one respiratory cycle, with simultaneous abdominal aortic pulses and with tidal volume intake.
1. A "Base level" at a maximum pressure of -6 mm. Hg. is maintained.
2. Cyclic inflexions from that base level show a decrease in sub-atmospheric pressure and a subsequent return to the initial value, giving way to a sequence of new cycles.
3. Two different types of cyclic inflexions with their own characteristics are identified.
a) A main cyclic complex of inflexions marked I, which has a gradient of pressure from -6 to -8.3 = -2.3 mm. Hg.; a duration of 1.3 sec. and a rhythm of 12-13 Cycles/min.
b) A series of minor complex inflexions, numbered from 1 to 9, with a gradient pressure of 1 mm.Hg.; a duration of 0.66 sec. and a rhythm of 90 C/min.
4. The main inflexion, as well as the minor inflexions, show a series of secondary inflexions which are present with absolute regularity, and allow themselves to be identified.
5. The rhythm of the main complex inflexions coincides with the respiratory rhythm of the animal, and corresponds to the inspiratory phase.
6. The rhythm of the minor complex inflexions coincides with the cardiac rhythm.
7. The relation between the two rhythms is 90/12-13 = 7-8 minor complex cycles in each respiratory cycle (sometimes 9 as in fig. 1)
8. The base level shows, between every two main complex inflexions, a slight slant interrupted only by the presence of minor complex inflexions.
9. The main inflexion includes some minor inflexions, as if riding over it. These are identifiable, although deformed, and marked 1 - 2 - 3. (see their relation with the aortic pulse); one of these inflexions is constant at the vertex of the main complex inflexion.
The base level of -6 mm. Hg. is the pressure of quasi static equilibrium of the content in the pleural space.
If we relate the decrease in sub-atmospheric intra-pleural pressure during inspiration to the simultaneous increase in pleural capacity (both facts are well known), it becomes evident that the pleural content behaves as gases do; i.e., its pressure changes in inverse proportion to the changes in pleural capacity and consequently follows the Boyle-Mariotte Principle according to which P.V = C.
It is well known that normally there are no gases in the pleural cavity, but there is a small amount of liquid. This has been the subject of experimental quantification and the value varies in the different species, probably in relation to the area of the pleural surface which is covered with the liquid which keeps it moist. The value for the dog has been calculated at about 0.55 ml. of liquid adherent on the pleural surface.1
It is also well-known that liquids have the property of evaporating, of changing from a liquid state to the phase of vapour, and that pure water has this property, reaching a pressure of 31.5 mm. Hg. At 30ş
The pleural liquid is watery as are all organic liquids and has a characteristic physico-chemical composition; therefore, the maximal pressure value of its vapour should be characteristic (to be determined) and relative to the function to be carried ,out between the two pleural surfaces.
The amount of pleural liquid ís maintained in physiological equilibrium, according to the functions of the pleura. From now on, we have to add to this knowledge and interpretation the fact of maintaining an amount of pleural liquid that enables its vapour to behave as a non-saturator, and for this same reason, to follow the Boyle-Mariotte Princíple, as gases do. In this, its composition and relative volume are determinant.
The circulation of the pleural liquid and/or its vapour is necessary in order that its volume and pressure in the pleural space be maintained in equilibrium, changing only in relation to the cyclic changes of the pleural capacity, in relation to the actions to be accomplished for ventilation and gas exchange. Neergard11 suggested that there is a liquid absorbing-mechanism from the cavity and another that prevents a complete removal. The pressure of this vapour could be the threshold for absorption and likewise, for circulation of the pleural liquid.
The pleural vapour, because of its property of filling up the entire space available would also be responsible for keeping the pleural surfaces moist, which is a necessary condition for the generation of a physical force of adhesion between them, as a shared responsibility in the maintenance of the functional pulmo-thorax unit.
These series of observations lead us to the following partial conclusions:
1. The sub-atmospheric intra-pleural pressure, determined by means of the cannula, is given by the pressure of the pleural vapour, which behaves as a non-saturator vapour, and its variations, in value are relates to pararle changes in volume, according to the cyclic changes in the pleural cavíty, as well as to the transmitted pressures.
2. The cyclic changes in the pleural cavity are in relation to the cyclic expansion-retraction of the walls that limit this space. Any movement translates the presence of acting forces, which in this case are transmitted to the mass of pleural vapour contained in he pleural cavity, and to the chest walls. The value of these forces cannot be determined by means of the intra-pleural cannula, because the propagation index of forces through the pleural vapour is not known. We know that the Resultant of the forces transmitted by the pleural content is very small, because it is a vapour which behaves as a non saturator and is therefore compressed.
These transmitted forces have to be taken into consideration, in any case, as a factor of correction in the interpretation of the results, and what is more important, for the interpretation of inspiratory dynamics.
3. The existence of two different types of inflexions, each one with its own characteristics, leads us to the conclusion that the pleural surface reflects two kinds of activities leading to different partial functions which determine specific cyclic changes of capacity, according to characteristic needs.
The correlation of the main inflexions with the inspiratory phase, permit us to establish a cause effect relation and to conclude that these are due to the expansion of the pleural vapour as a consequence of the increase in pleural capacity during the inspiratory phase,
The minor inflexions: Lobular-alveolo-capillary inflexions, are coincident with the cardiac cycles and hence with the pulmonary capiIlary circulation. These cycles are in relation to gas interchange at the alveolo-capillary level and therefore, with the mechanical effects which takes place there, hence, cyclic changes in intra-pleural capacity would have to be attributed to these mechanical actions, according to the performance of the phenomena which take place in the pulmonary respiratory zone.
4. The presence of the minor inflexions riding over the main ones permits us to observe that
the changes of volume relative to the actions at the alveolo-capillary level are independent and that their value is added to the value of the changes in intra-pleural capacity, relative to the actions concerned with pulmonary ventilation, and these two series of inflexions lead us to individualise two types of independent cyclic actions.
1. Cyclic actions for air renewal from the atmosphere or dynamic cycles for pulmonary ventilation.
2. Cydic actions for gas interchange at the alveolo-capillary level, or alveolo-capillary dynamic cycles.
II. THE RESPIRATORY PULSE
OBSERVATIONS. Fig. 2
2.Correlation of impulses in one respiratory cycle wi th the simultaneous abdominal aortic pulses and with tidal volume intake.
1. A "base level" at the minimum pressure of +8 mm. Hg. is maintained.
2. Cyclic inflexions from that level up to +18 mm. Hg. shows a maximum cyclic gradient pressure of +10 mm. Hg., which drops to the base level.
3. Two different types of cyclic inflexions are identified, with their own characteristics.
a) A main cyclic inflexion, marked I which has a gradient pressure of +10 mm. Hg.; a duration of about 1.3 sec. and an average rhythm of 12-13 C/min.
b) A series of minor inflexions, numbered from 1 to 9, with a maximal pressure of +9 mm.Hg. a duration of about 0.66 sec. and corresponds to the inspiratory phase.
4. Both the main inflexion and the minor ones have a series of secondary inflexions which are present with absolute regularity.
5. The rhythm of the main inflexions coincides with the respiratory rhythm of the animal, and to the inspiratory phase.
6. The rhythm of the minor inflexions coincides with the cardiac rhythm.
7. The relation between the two rhythms is 90/12-13 = 7-8 minor cycles in each respiratory cycle which is the same relation as cardiac rhythm / respiratory rhythm in the dog.
8. The base level is maintained between every two main inflexions, with only a very slight slant of about 1.2 mm. Hg. at the end of the cycle, interrupted only by the minor inflexions.
9. The main inflexions envelop some minor inflexions, which are identifiable, although deformed, (see their relation to the aortic pulse). One of these inflexions is constailt at the cusp of the main inflexion.
The nine points underlined in these series, observed in the graph of the Respiratory Pulse, as ˇt is detected in the pleural space by means of a balloon filled with water, correspond, one to one, with those observed. under the same number in the graph of the intra-pleural sub-atmospheric pressure, detected by means of the cannula, fig. 3, the only difference being the intensity of the detected forces. This coincidence shows that the two methods (balloon filled with water and empty cannula) detect simultaneous phenomena, whose dynamic effects are not detected in their totality by either one of them, because the pleural content, as we have shown, does not transmit the propagated forces in their entirety, hence, it is necessary to place a suitable agent in the pleural space, to detect the Resultant of the transmitted forces in their totality, parallel to the Resultant of intra-pleural content dynamics, which is relative to changes in pleural capacity.
The chosen method is the balloon filled with water and placed between the two pleural layers where ˇt becomes fixed, since, according to Pascal's Principle, any varlation in pressure produced at a point of a liquid mass in equilibrium is transmitted in its entirety to any point in the mass.
The intra-pleural balloon detects:
1. The Resultant of pressure variations on each side of the pleural surfaces, determined by dynamic phenomena which take place in the lungs and in the walls of the chest and beyond this, in the abdominal cavity and in the surrounding atmosphere.
2. The changes in pressure of the intrapleural medium (pleural vapour) which are relative to pleural capacity.
3. The base level of + 8 mm. Hg., which is the Resultant of the forces exerted on the liquid container in the balloon, in its new condition of equilibrium, i.e., first, the balloon placed and pressed between the two pleural surfaces, secondly, the conditions of the dog's spontaneous respiration when re-established, both of which occur after the resolution of the pneumothorax.
We should remember that the water in the balloon was balanced previously at atmospheric pressure. Therefore we may conclude that +8 mm. Hg. is the Resultant of the balanced forces
in the pleural space, in its quasi static condition. The distorting effect determines by the elastic condition of the balloon is included in this Resultant.
The following stands out among the balanced concurrent forces at the Resultant value of + 8 mrn. Hg.
1. The force of pleural adhesion as a physical Resultant between the two pleural surfaces, which are in close contact and permanently moist.
2. Forces of equal meaning between the pleural surfaces and the exterior surface of the balloon (factor of distortion).
3. The Resultant of the forces in the pleural medium (pleural vapour) detected by means of the cannula, whose value is -6 mm. Hg.
In reference to the Resultant of + 8 mm. Hg., which will be named from here on "base level" and will be made homologous to "Adhesion force" (having taken into consideration the factors of correction), cyclic variations of impulses are detected, which are not translated by means of the intra-pleural cannula. We will name these impulses, -broadly speaking, "Resultant of the transmitted forces" whose succession in time shapes the Respiratory Pulse Wave as it has been defined by the author in another study."
Among the concurrent forces of the dynamics responsible for the cyclic inflexions over the base level, we can distinguish:
1. Forces transmitted from the lungs.
2. Forces transmitted from the thorax walls.
3. The resultant of the dynamics in the intra-pleural medium (pleural vapour).
The algebraic sum of these forces determines a Resultant at each instant of the respiratory cycle, generating a wave of pressure termed "Respiratory Pulse Wave" by the writer.
The presence of two series of cyclic impulses, simultaneous and successive, during the whole respiratory cycle, each one with its own characteristics, allows us to conclude that two series of independent cyclic impulses are transmitted to the pleural space:
1. Mayor cyclic impulses, that correspond to the inspiratory phase of the respiratory cycle. This permits us to establish a cause-effect relationship and conclude that these impulses are produced by the activity of the lungs, airways and chest walls, for air circulation.
2. Minor cyclic inflexions, which coincide with the aortic pulses, are simultaneous with capillary circulation in the pulmonary area and consequently, with cycles of gas interchange. Therefore, the author has named these cyclic waves of pressure "Lobular-alveolo-capillary respiratory cycles".
The presence of these cyclic inflexions riding over the ventilatory inflexions, permits us to conclude that the movements and impulses generated to achieve pulmonary ventilation and those
developed for gas exchange at the alveolo-capillary level, are independent, and both take place according to Newton's "Principle of the Independence of Forces and Movements", which establishes that: The effect of a force over a mass is independent of the state of movement of this mass, and also of the forces that act on it, when this force is applied.
3.Simultancous graphs of five main parameters analysed here. From top to bottom: 1. Respiratory Pulse (Resultants of forces transmitted to the pleural space). 2. Tidal Volume intake. 3. intra-pleural sub-atmospheric pressure (cyclic variations in pressure of pleural vapour). Mirror image of this graph corresponds to variations in pleural capacity. 4. Abdominal aortic pulses .
This observation leads us to distinguish two kinds of biologically co-ordinated independent actions:
1. Cyclic actions for air renewal, or pulmonary ventilation, which would take place in the airways, except in the respiratory or lobular zone.
2. Cyclic actions for air injection, at the level of the lobular bronchioli and from these to the alveoli, simultaneously with blood injection through the pulmonary capillaries, identified as Lobular-alveolo-capillary dynamic cycles.
The space-time co-ordination of the two types of actions for this function, and the inter-dependency, which is co-ordinated by the central nervous system, have to be added to these parallel topographic considerations.
The coincidence of one alveolo-capillary cycle at the cusp of each inspiratory cyclic impulse is proof of a common factor in the co-ordination of the ventilatory cycles and the series of Lobular-alveolo-capillary cycles comprised in the former.
The displaced air mass and the potential energy accumulated during this displacement, by the structures of the respiratory apparatus," has to be distributed, and used proportionately during each alveolo-capillary cycle; this co-ordination needs a complex nerve network of information and responses.
The detected impulses are correlative to the mass of air displaced by the series of actions completed during each ventilatory cycle; therefore, they are correlative to the number of molecules container in each volume of air (tidal volume) and correlative to each one of its components as well as to the concentration of oxygen. The supply of oxygen during each respiratory cycle is proportional to the inspiratory impulses.
Cardiac beat is proportional to the mass of blood be displaced, and correlative to each one of their components, among which is the oxygen transporter. The mass of blood ejected by each right ventricle beat, and the corresponding mass of air ejected by the respiratory structures to the alveoli, meet at the alveolo-capillary level, where the two components generate their own impulses.
Ventilatory impulses, cardiac impulses, alveolo-capillary impulses and any kind of intermediate impulses for this function are correlated, and this correlation needs a very wide nerve network of information, some of whose stimuli are mechanical; therefore, a wide range of mechano-receptors and baro-receptors must be distributed in the working areas, whose different thresholds, together with the different conduction velocity and length of the nervous fibres modulate the information for perfect inter-actions.
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