THE LOBULAR-ALVEOLO-CAPILLARY CYCLES
To begin our analysis, we have identified (arrows A and B., fig. 4), the starting and ending points of the respiratory cycle shown in this graph, and the lobular cycles numbered 1 to 8, that are embraced in the respiratory cycle.
We have traced a plotted line between the two lowest points in the graph which correspond to both ends of the inspiratory pulse falling down, and belong to the two contiguous inspiratory impulses that frame the graph. This line is horizontal.
We have traced a continuous line, tangent to the lowest point of the graph and have identified ¡t as "base line" which is a slanted line and permits us: 1. To follow the evolution of the general pulmonary tension variations during the period of a ventilatory cycle. 2. To measure the amplitude of the inflexions that are produced over and below it. 3. To interpret the reason for the differences among each one of the lobular cycles comprised in one ventilatory cycle and later on, other dynamic problems, which are the object of another study.
As a model for the analysis we have chosen the cycle numbered 6 in the series, because this is the longest cycle and, have circumscribed it with a circumference whose centre corresponds to the most outstanding inflexion.
From a dynamic point of view, this inflexion possibly reflects the most important phenomenon for the necessary co-ordination of actions to be achieved for the accomplishment of the function.
The diameter of the circumference has been limited by other inflexions to which the writer has attributed the referential value of being the finishing and starting common points of the neighbouring cycles in the sequence.
Six verticals have been drawn and numbered from 1 to 6; the first and last are tangents to the circumference, the fourth passes along its centre, and the other three limiting different stages of the cycles which merit special attention.
The centre of this circumference has been taken as a point of reference to circumscribe the other cycles, making their individual analysis possible. This circumscription of each cycle is also useful because it clarifies the differences of each one in relation to the others in the series.
As the alveoli-capillary cycles ride over the wave of the ventilatory cycle, those cycles that appear displaced because of the inspiratory impulse, have been projected to the line of the general tendency, so as to complete the sequence.
I have projected the circumferences and the six verticals onto the graph of the intra-pleural pressure curve, using identical criteria and with the proposal of establishing the relationship between simultaneous phenomena evident in each graph, attributing to them the same purpose, which is to achieve gas interchange.
Finally, similar projections have been made onto the graph of the aortic pulse wave to relate the chronology of the facts to those of the cardiac cycle.
ANALYSIS OF THE CYCLE
Fig 4. Analysis of dynamic lobular-alveolo-capillary cycles comprised in one respiratory cycle. Integration of the heart and lungs as a dynamic unit.
PERIOD 1-2. Duration: 0.20 seconds.
LOBULAR PULSE. IS characterised by a slow progressive ascending slope during which the transmitted impulses reach a value of + 1.5 mm.Hg. over the base level.
INTRA-PLEURAL PRESSURE. A descending slope during which the intra-pleural sub-atmospheric pressure increases by -0.7 mm. Hg. below the base level.
AORTIC PULSE. Shows the relation between the starting point of the two above mentioned phenomena and the dicrotic notch (beginning of the diastole)
This period is the initial phase of the lobular cycle; it is also a preparatory stage of the conditions for the development of the phenomena that properly define the dynamics at the alveolo-capillary level, riding over the pulmonary ventilator "infra-structure" dynamics.
The increase of the impulses observed in the graph of the lobular cycle can be interpreted as the effect of the penetration of a new volume mass of air from the pulmonary "ventilatory zone" to the intra-lobular bronchioles, this acquires an acceleration as a result of the tone increase of the bronchiolar structures which shorten simultaneously. This dynamic activity determines a simultaneous traction of the visceral pleura by means of the inter-lobular septum's with the consequence of widening the pleural cavity and simultaneously increasing the sub-atmospheric pressure. These facts coincide with the very beginning of the cardiac diastole (proto-diastole).
PERIOD 2-3. Duration: 0.7 seconds.
LOBULAR PULSE. Characterised by a sudden increase of the transmitted impulses, reaching its highest value during the cycle about + 1.9 mm. Hg., over the base level.
INTRA-PLEURAL PRESSURE. Shows a parallel increment of the sub-atmospheric pressure, reaching the lowest value during the cycle, i.e., about -1.4 mm. Hg. under the base level.
AORTIC PULSE. Shows the correspondence of this period to the last moment of the cardiac diastole (tele-diastole).
This period means the culmination of the autonomic air-filling of the intra-lobular bronchioles, up to the nearest point of the alveolar complex, generating the maximal impulse for air displacement into the lobuli during the lobular cycle, which could be attributed to the contraction of the muscles of the terminal bronchioles which are rich in smooth muscles and next to the alveolar complex.
The intra-pleural sub-atmospheric pressure decreases in the same proportion as the pleural space increases (according to the Boyle-Mariotte Principle) favouring the air displacement towards the alveolar complex.
Periods 1-2 and 2-3, can be reduced to only one phase, for the filling of the intra-lobular bronchioles with air at a physiological pressure, as well as to increase the necessary 1 'tone" for the next events. This phase is parallel to the cardiac diastole.
PERIOD 3-4. Duration: 0.04 seconds.
LOBULAR PULSE. The transmitted pressure has dropped suddenly to its lowest level during the cycle, i. e., to the base level. This very moment corresponds to the centre of the whole cycle.
INTRA-PLEURAL PRESSURE. At this moment, which corresponds to vertical 3, a sudden decrease of the sub-atmospheric intra-pleural pressure begins, preceding the fall equally sudden of the respiratory impulses. The sequence of the two curves, as a mirror image, is now broken and the sense of the vector pressure re-inverts, as a signal of a sudden new widening of the pleural cavity, during which the pleural pressure reaches -0.4 mm.Hg.
AORTIC PULSE. This shows the correspondence to the pre-systolic moment.
This outstanding moment of the lobular cycle is its centre and possibly the most important one from a dynamic point of view; it is the most noticeable in the graph. This is also the most delicate dynan-iic moment because of the synchronisation at the pre-alveolo-capillary level of the phenomena of autonomic lobular-ventilatory origin and those of the cardio-vascular origin in relation to elastic properties of the surrounding area under control of the central nervous system, by means of specific receptors.
The rupture of the previous sequence of events and the crossing of the sense of the lobular pulse vectorial forces and that of the intra-pleural 'sub-atmospheric pressure can be interpreted as follows: at vertical 3, the lobular impulses drop without a parallel decrease of the sub-atmospheric intra-pleural pressure (which means without a parallel widening of the pleural capacity) as could be expected from our previous observations. It is inferred, therefore, the necessary increase of the lobular cápacity to explain the decrease of the intra-lobular air pressure. This would take place near the surface of the lungs and leads us to conclude that this expansion takes place in the nearest cavities to the respiratory bronchiole; that is to say, in the alveolar cavities which. would expand towards the pleural space; therefore, when the volume of the pulmonary respiratory zone increases, the pleural capacity decreases.
The respiratory impulses continue to decrease while the cavities next to the alveoli expand and at this very moment there is a new and sudden change of relation: a new increase of the pleural capacity, testified by the decrease of the sub-atmospheric intra-pleural pressure which coincides with the moment of the lowest drop of the lobular impulses, all of which means that an important
retraction of the pulmonary periphery (lobular zone) is initiated. This retraction, when separating the two-pleural surfaces, widens the pleural cavity for the alveolar expansion.
The widening of the pleural space at this moment is greater than the increased volume of the alveoli that expand to fill ¡t up; therefore, the sub-atmospheric pressure remains lower and the pleural cavity remains wider.
The traction of the visceral pleura from the insertion points of the interlobular walls elastic fibres, are reflected in two simultaneous facts:
1. The sudden drop of the transmitted impulses (Respiratory Pulse)
2. The decrease of the sub-atmospheric intra-pleural pressure as a consequence of the pleural capacity increases.
The objectives of these consequences are:
1. To decrease the resistance at the surface of the lungs, in view of the alveolo-capillary expansion.
2. To create a potential space for the alveolo-capillary expansion. The physical conditions for the alveolo-capillary filling with blood and gas are given: creation of a temporary space with decreased resistance, to favour gas expansion into the alveoli and the alveolar-capillary "flood" related to the cardiac pump action, all of which makes possible the necessary simultaneous concurrence of the air elements and the blood transport to take and deliver the material. This characterises the second half of the lobular cycle.
PERIOD 4-5. Duration: 0.25 sec.
LOBULAR PULSE. (Corresponds, from now on to the alveolo-capillary cycle).
Shows a slope that starts from the previous depression to reach an intensity of + 1.2 mm Hg. over the' base level, to then decrease slowly to 0.9 mm Hg. during a period of 0.04 sec. and to regain the base level.
INTRA-PLEURAL PRESSURE. Shows a simultaneous drop of the intrapleural pressure, to -1 mm Hg. below the base level to maintain a global pressure of -7mm Hg.
AORTIC PULSE. Shows the correspondence of the alveolo-capillary cycle with the cardiac systole.
This period corresponds to the culmination, the utmost purpose of the whole Pulmo-cardio-thorax
cycle: The simultaneous arrival of blood and air, each one in its own compartment, in order to exchange the gas elements as well as to transfer heat.
This stage demands a previous total pulmonary surface retraction, creating space of low resistance for circulation of the blood arriving from the low-pressure pulmonary artery, to achieve gas exchange.
This newly made space is also needed for the alveolar filling, since the volume-mass of air previously displaced for this purpose is trapped at a pressure of about + 1.2 mm. Hg. (period 3-4) at the entrance of the alveoli. This mass of air should expand now, adding an impulse that helps the alveolo-capillary expansion at the low-pressure environment.
Period 3-4 corresponds to the conditioning for the present events characterised by simultaneous entrance and passage of the balanced masses of blood and air through their own spaces, where diffusion will take place.
The physiological equilibrium of the pulmothorax dynamics in this zone and specifically at this moment depends upon the physiological equilibrium in the pulmonary arterial area in one direction, farther on in the right ventricle and even farther on, in the tissue area. In the opposite direction, the carrying of blood to the left ventricle also depends on these dynamics simultaneously, all of that allows us to think about the importance of these dynamics to interpret the phenomena of organic unbalance.
The mechanical events during this period are characterised by the following figures:
ALVEOLO-CAPILLARY PULSE: average + 1.2 to 0.9 mm Hg. with a mean about + 1mm Hg.
INTRA-PLEURAL SUB-ATMOSPHERIC PRESSURE decrease: -1 mm Hg.
Total intra-pleural pressure: -7 mm Hg.
Intra-pleural capacity increases relative to the sub-atmospheric pressure decrease.
Pressure gradient for alveoli-capillary circulation: Mean pulmonary arterial pressure: 13 mm Hg.
Pressure of alveolar-capillary bed environment intra-pleural pressure) -7 mm Hg.
Capillary bed: widens in relation to the intrapleural space width.
PERIOD 5-6. Duration: 0.15 sec.
ALVEOLO-CAPILLARY PULSE. The impulses drop to the base level.
AORTIC PULSE. Coincides with the proto-diastolic point,
This is the final stage of the lobular cycle, and the second phase of the alveoli-capillary cycle, which corresponds to the emptying of the pulmonary respiratory zone after having accomplished its objective of air-blood gas exchange: The blood will flow towards the tissues with its useful acquired load, after the gas waste of the metabolism has been discharged into the atmosphere.
When the fluid currents for gas exchange cease, the respiratory zone structure relaxes (reaction) which means that the pulmonary structure expands towards the space from which these had retracted previously, and because this, the alveoli-capillary zone is "squeezed" to help the flow of blood towards the left auricle, and the current of used air towards the atmosphere.
These dynamics increase the sub-atmospheric pressure, which means that the pleural capacity decreases in relation to the narrowing of its diameter and the respiratory impulses decrease because the fluid circulation has inverted its sense, ending the alveoli-capillary cycle as well as the lobular cycle.
The end of this stage coincides with the beginning of the next lobular cycle, in the new conditions of the thorax and pulmonary structures adaptation and, is related to the remaining volume-mass of air (residual volume) and to the achieved degree of retraction to repeat the events up to exhaustion of the potentialities accumulated during the correspondent inspiration to this respiratory cycle.
COMPARATIVE ANALYSIS OF THE CYCLES COMPRISED IN ONE VENTILATORY CYCLE
We are now prepared to identify any inflexion of those which are characteristic of the lobular pulses embraced into the ventilatory cycle and hence in any lobular cycle we propose to study. As we now know the relationship of those inflexions to each studied event on the thorax-pulmonary dynamics. we can also make their comparative analysis to define how the transient conditions of the ventilatory dynamics influence each one of the lobular cycles and therefore, the cyclic dynamics of the heart and thereafter, it is possible to infer the results at the tissue level.
Cycle number 6 has a period which can be considered equal to those of the cycles number 5 and 7.
Cycles 4 and 3 have a segment in the common space limited by the intersection of the two circumferences that circumscribe them, in whose central part, we can identify the starting and ending points of each cycle; and conclude that both are shortened at the expense of their respective starting and ending points.
A similar observation can be made in relation to cycles 1 and 2 and furthermore to observe that cycle number 2 is deformed over the descending slope of the respiratory pulse on which it rides. Cycle number 1 is also shortened at each end, but its central part is not deformed.
The comparative analysis of the lobular pulse waves and the corresponding inflexions of the intra-pulmonary pressure curve and those of the aortic pulse wave, as we have studied them, allow us to identify the similar inflexions of any cycle, being especially useful to identify them when deformed by the stronger inspiratory impulse.
Following this method, we have identified and shown by arrows the Centre of each lobular cycle graph deformed by the inspiratory impulses (the same can be made with any other point) and their corresponding centres in the intra-pleural pressure and aortic pulse waves.
it is important to note that the small differences in the period of the series of cycles take place at their ends, which coincides with the cardiac diastole; the same diastolic relationship is observed in the aortic pulse wave as well as in the intra-pleural pressure wave.
This analysis also makes evident that:
1. The cardiac rhythm and the lobular rhythm are parallel.
2. The difference of period between each of them is at the expense of the diastolic period.
3. The systolic period is always of the same duration and ¡t is equal to the required time for gas exchange and oxygen saturation.
4. The inspiratory impulse and the following ventilatory dynamics influence and determine the differences we have observed during the corresponding lobular cycles along the ventilatory cycle (because the dynamic conditions at the thorax level are determined by a parallel reflex phenomenon).
5. We can also see that the tension in the pulmonary "infra-structure" increases steadily from cycle number three (which corresponds in this series to the beginning of the post-inspiratory" period) up to the last one of the series.
6. This tension of the pulmonary structure is also evident during a similar period in the general tendency of the aortic pulse wave. The aortic pulse increases from the lowest part of the inspiratory inflexion up to three more cycles, to decrease steadily, all of which shows that the variations of the pulmonary ventilatory pressure during one ventilatory cycle influences the ventilatory zone, the lobular cycles and also the heart and blood circulation, and furthermore by extension, the whole organism.
The Lobular Cycle is composed of two phases of equal lengths and different meaning, separated by sudden drop in the transmitted impulses, which define two slopes of a different mechanism of generation.
This is a ventilatory phase at the lobular level, shown by a slope that translates the transmitted impulses by the air mass displaced along the lobular bronchioli, to be used for gas exchange during the next alveolo-capillary cycle.
These lobular mechanics are performed by parallel actions of two simultaneous processes, which generate a pair of forces:
1. Contraction of the bronchiolar smooth muscles, which decrease the bronchiolar capacity and increase its tone over the air mass displaced from the pulmonary ventilatory zone.
2. The fibre-elastic structure, and especially that of the interlobular walls, is simultaneously shrunk; therefore, it exerts forces opposite in direction and sense to the vector of the air displacement and, when pulling from its insertion points at the visceral pleura stretches the pleural -adhesion medium with the consequent increase in the pleural capacity.
These dynamics lead to the following results:
1. The creation of potential space in the proximity of the pulmonary surface, to enable the potential expansion of the tiny alveoli, due to the expansive force of the displaced air.
2. The decrease of the pleural vapour pressure, as a consequence of the pleural space width, which is an important simultaneous factor in alveolar expansion.
3. The ejection, of the air volume-mass towards the alveoli, to be used during this cycle.
The detected forces in the pleural cavity must be interpreted as the Resultant of the transmitted forces due to the acceleration of the air mass from the intra-lobular bronchioli, whose muscle contraction narrows and shortens their cavities.
The narrowing of the bronchioli and the 'flattening" of the lobular surface, due to the simultaneous shrinking of the interlobular walls, determines the diminishing of intra-lobular airways capacity,
consequently, the pressure increase of the container volume-mass of air up to a physiological limit would be the threshold for the relaxation of the "sphincter like" muscles around the alveolar mouth. This would happen simultaneously to sudden lobular retraction to create space in the pleural cavity, for the alveolar expansion, as previously analysed. This very moment would coincide with the transitional moment between the first and the second half of the cycle.
The displaced volume-mass of air from the ventilatory zone has now acquired new conditions: Its volume has been reduced and its pressure has increased in a converse relationship. Consequently, the alveoli open up and are filled up and expanded, due to expansive force of the retained air mass, just at the alveolar mouth. The alveolar expansion is also a pre-requisite for capillary circulation and gas exchange.
These dynamics are made evident in the slope that characterises the beginning of the second half of the lobular cycle. which identifies itself with the alveoli-capillary cycle, as well as in its mirror image in the intra-pleural sub-atmospheric pressure curve, which translates the pleural capacity increase in inverse proportion. The coincidence of these dynamics with the capillary circulation can be demonstrated by the synchronous presence of the cardiac systole, as shown in the aortic pulse wave.
It is important to keep in mind that the slope of the impulses in the first phase of the lobular cycle is higher than that of the second phase, determined by the alveoli-capillary air-blood interaction (alveoli-capillary pulse) which is further evidence of the overwhelming role of the primary pulmonary activity at the lobular level to enable pulmonary circulation, which in its absence would meet resistance to flow with the consequent hypertension.
The alveoli-capillary cycle has a double relationship:
1. With the lungs, which eject the required air volume-mass needed for the mechanics of the gas interchange and the exchange per se.
2. With the heart, which injects the blood volume-mass for the gas exchange.
These two factors converge at the alveoli-capillary complex, expand their own contents towards the newly enlarged pleural space, being in contact during the required time for the gas exchange. This period of the cycle coincides with the cardiac systole.
When the lobular structure relaxes and expands against the thorax walls, it empties the alveoli-capillary content, with the necessary impulse required for the blood flow towards the left auricle and the air to the atmosphere.
The above description leads us to a very important conclusion, the interpretation of which leads to a better understanding of pulmo-cardiac distresses:
The potential variations of the pleural capacity during each lobular cycle, relative to its diameter variations, are correlative to the cardiac stroke, to pulmonary capillary capacity, and also correlative to the capillaries of the rest of the organism, since they receive a similar blood volume during successive moments, with a similar purpose which is not other than the supply of material to be interchanged, with the special differences demanded by the "regional" biological behaviour.
The pleural cavity, which is the object of reflex dynamics, accomplishes one expanding-retracting cycle of its cavity, alternating with the contracting expanding cycle of the heart, since they have the same dynamic meaning, i.e., the pleural cavity is widened to give place to the capillary expansion when filled up by the volume of blood that is ejected by the right ventricle, allowing the huge alveoli-capillary surface to be flooded.
In this sense, the widened pleural cavity permits blood flow, while the gas exchange is accomplished in only 0.2 sec. during each alveoli-capillary cycle, which would not be possible without perfect division and co-ordination of the work which balances the strength of each sector represented by one lobule and in it, each sector represented by one alveoli-capillary unit, in relation to the dynamic conditions offered by the pulmo-thorax structure and the cardiac activity.
Only in this way is the pulmonary-capillary circulation, the gas exchange, and the uniform oxygen saturation of the blood possible, as well as the progression of the blood towards the auricle.
The transcendental fact signified by the pulmonary circulation and the gas exchange of blood with the natural atmosphere, is not due to a pressure gradient between the right ventricle and the left auricle as is currently believed. lt is performed by a programme executed by the complex pulmonary structure, attached to the thorax walls by means of the pleura. The unit works like a hydro-pneumatic pump whose expansion-compression chamber between the right and left cavities of the heart is represented by the pleural cavity.
When analysing the facts in this way, to attribute the role of "chamber" of the hydro-pneumatic pump to the pleural cavity, it is necessary to keep in mind that the pleural membrane are an integral part of the lungs and thorax walls, lining their surfaces and linking them together by means of an elastic medium, which is the pleural adhesion; and the event in this closed space is the result of the pulmo-cardio-thorax dynamics, as it is being interpreted by the writer.
The pleural membrane and its cavity are now identified as having a very important role as an "inter-system" between the vegetative and somatic systems.
1. The blood-gas interchange with the air is accomplished during small cycles synchronous with the cardiac systole, which take place in the entirety of the alveolo-capillary units.
2. The air volume-mass and dynamic conditions for each alveolo-capillary cycle are supplied by a previous cycle synchronous with the cardiac diastole, which takes place in the lobular unit.
3. The first half of the lobular cycle is concerned with the displacement of the air volume mass from the ventilatory zone up to the mouth of the alveoli, as well as the preparation of the mechanical conditions for the alveolo-capillary cycle.
4. The second half of the lobular cycle identifies itself with the alveolo-capillary cycle.
5. The retraction of the lobular zone structure (action) and its consequent elastic expansion (reaction) in relation to the pleural space at the beginning and end respectively of each alveolo-capillary cycle works as a "suction and impelling force pump" to drive the blood and air forward, to the alveolo-capillary level and then to impel both currents to their proper destination.
6. The lobular cycle is performed in relation to the mechanical conditions and supply offered by the ventilatory cycle in which they are comprised.
7.Each lobular cycle uses the corresponding fraction of the potentialities accumulated by the ventilatory cycle in which it is comprised.
8. Each lobular cycle adapts itself to the new general dynamic conditions created by the progressive consumption of those potentialities accumulated during inspiration.
9.This adaptation is reflected in the whole organic dynamics (evidence of this can be seen in the effects on the sequence of the aortic pulses).
10.The pleural cavity is widened when the lobular zone retracts during the first half of the lobular cycle. This newly created space is then occupied by the alveolo-capillary expansion.
11.The pleural cavity is narrowed again when the lobular zone expands as soon as the retracting force ends.
12.The widening and narrowing of the pleural cavity makes it similar to the chamber of a suction and impelling force pump to which we can compare the work of the lobular zone on the ventilatory infra-structure assembled in the thorax.
13. These co-ordinated actions and reactions need a very precise system of information, processing of data and delivery of orders as action potential, which is the special role of the central nervous system.
14.This correlation is not only relative to the events at the pulmonary level, but also to the organic needs and to environmental adaptation.
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