CHAPTER 7

DIAGRAMMATICAL MODEL OF THE LOBULAR KINETICS AND KINEMATICS

 

These diagrams, figs. 16 and 17 allows us to identify four stages in one lobular cycle, interpreted by comparative analysis of the following parameters:

1. The Resultants of the transmitted forces generated by pulmo-thorax dynamics and detected in the pleural space.

2. The pressure variations of the pleural content (pleural vapour).

3. The capacity variations of the pleural space, interpreted according to the equation P.V = C., according to which, capacity changes in an inverse relation to the changes in pressure of the pleural vapour and, the graph of these variations in capacity, is similar to the mirror image of the intra-pleural pressure graph.

STAGE 1. This is the point where the cycle begins, following the end of the previous lobular cycle ', when the muscular and elastic structures of the lobules are completely relaxed and the alveolo-capillary units have emptied their contents aided by the expansion of the relaxed structures. This point corresponds to the point of quasi-static equilibrium, when the graphs of all the parameters referred to have returned to their respective base levels (refer to vertical 1 in fig. 4). This moment is followed by the sudden increase of transmitted forces, due to an effective bronchiolar constriction, displacing the mass of container air to the nearest point of the alveolar complex, at the same time evoking the alveolo-capillary reflex.

This diagram shows:

1. The effect of the contraction of the intra-lobular bronchioli smooth muscles on the contained volume-mass of air carried there from the ventilatory zone, by action of the pulmonary ifrastructure.

These actions give rise to the following: 1. A decrease in the diameters of the airways, generating a force that determines the acceleration of the gas molecules directed toward the alveoli. 2. The pulling of the inter-lobular walls which traction from their points of insertion in the visceral pleura, increasing the diameters of the pleural space, and leading to a decrease in the sub-atmospheric pressure in this space.

 

STAGE 2. CENTRAL POINT

The alveolo-capillary reflex is evoked, determining strong sudden traction from the periphery of the pulmonary structure, which pulls the visceral pleura by means of the inter-lobular septum, creating maximal distance between the two pleural surfaces, and hence, maximal increase in pleural capacity during the lobular cycle. The intra-pleural pressure falls to -1.4 Hg. below base level.

STAGE 3. The present conditions, in addition to those achieved during the two previous stages, allows air and blood to arrive simultaneously to the alveolo-capillary units, which expand towards the newly-created space in the pleural cavity. The being partially occupied by the expanded alveolar hemispheres. This expansion parallels the increase in intra-pleural pressure.

STAGE 4. The previous actions are followed by the respective reactions when the retracting forces end. The structures now relax and expand by elastic forces (reaction), diminishing the potential pleural space, pressing the alveolo-capillary structure against the thorax wall, "squeezing" the contained air and blood, which then follows the path of least resistance towards its next destination. The condition for starting a new lobular cycle is now created.

 

16. Theoretical-mathematical model of the kinetics of the lobular structure, according to the Principle of independence of forces and movements. a, thorax wall. b, pleural space. c, visceral pleura (pulmonary surface). d, inter-lobular septum. e, intra-lobular airways. f, centre-lobular bronchiole. Diagram 1 corresponds to the starting point of the cycle (crossing point of the base-level line and vertical 1 in the graph). Diagram 2 corresponds to vertical 3 (respiratory pulse pressure = +1.9 mm.Hg., intra-pleural pressure = -1.4 nun. Hg.). The alveolo-capillary reflex is evoked. Diagram 3 corresponds to period 4-5, corresponding to the filling of the alveolo-capillary units for gas interchange. Diagram 4: The lobular units start to displace the oxygenated blood and waste-air towards their respective destinations.

 

DIAGRAMMATIC MODEL OF THE PULMOTHORAX KINETICS AND KINEMATICS LEADING TO PULMONARY VENTILATION

The pulmo-ventilatory dynamic-cycle has as its aim the generation of forces for broncho-constriction and pulmonary retraction, followed by elastic expansion of its structure, helped by reflex contraction of the diaphragm, finally followed by an elastic retraction to put the intra-pulmonary mass of air into circulation towards the pulmonary periphery, to store potential energy in the structure and, create space for the expansive actions and their reactions. This makes the performance of the lobular cycles possible.

 

17. Diagrammatic model of kinetics of lobular structure during one lobular-alveolo-capillary cycle, according to the theoretical model of fig. 16.This diagram has been drawn according to the interpretation of the parameters detected in the pleural space, fig. 7.

 

STARTING POINT. Vertical 1. Figs.17 and 18

This point coincides with the end of the previous cycle, when the ventilatory structures have exhausted the potentialities stored during the previous inspiration. it corresponds to the moment of quasi-static equilibrium when the graphs of the parameters detected in the pleural space reach the base level, and the costal wall reaches, maximum expansion. At this point, the primary inspiratory reflex is evoked.

 

18. Diagrammatic model of kinetics of pulmo-thorax ventilatory cycle. Diagram 2 corresponds to vertical 1 in bottom-centre graph. The primary inspiratory reflex is evoked. Diagram 3 corresponds to vertical 2. At this point, the pulmo-diaphragmatic reflex is evoked. Diagram 4 corresponds to vertical 3. At this point broncho-relaxation is initiated. Diagram 5: maximal bronchial relaxation occurs. Horizontal 1 and top-centre graph correspond to the recuperation of tone in the bronchi in order to adapt ventilation for the lobular cycles to take place during the rest of the cycle.

 

STAGE 2. Corresponds to period 2-3, fig. 18. This starts with pulmonary expansion and contraction of the diaphragm. This starting point also corresponds to the initiation of intake of the tidal volume into the lungs and their expansive axial displacement, conquering the potential space from the abdominal cavity and increasing the high of the pulmonary cone. This displacement could create potential space between the exterior surface of the lungs and the costal wall, however, this does not occur, due to a simultaneous traction from the costal wall. Axial pulmonary expansion maintains the dynamic balance in the lobular zone, whose dynamics, although correlated, obey their own 1,aws.

STAGE 3. Corresponds to period 3-4, fig. 18. The previous broncho-constriction is followed by relaxation (reaction), the elastic retraction being impeded by the contraction of the diaphragm, and slowed down by the costal wall. The gases previously pressurised now expand towards the periphery, generating suction for the penetration of the last portion of the tidal volume. The lungs then reach their maximum expansion.

STAGE 4. Period 4-5, fig. 18. This is a period permitting recuperation of the tone, exerted on the contained air mass, while this is being used by each simultaneous alveolo-capillary cycle. All this leads to exhaustion of the potentialities accumulated during the first stage, in which is reached the expansion of the costal wall and elastic retraction of the lungs, generating opposite forces to stretch pulmonary structure, which then reaches the sensitivity threshold of the specific receptor and evokes the Primary Inspiratory reflex to start a new cycle.

 


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