RESEMBLANCE AND DIFFERENCES BETWEEN AIR AND BLOOD CIRCULATION AS INTEGRATED BALANCED PROCESSES OF FLUID MECHANICS FOR RESPIRATION
My contribution to scientific knowledge of the pulmonary lobe's mechanics, added to my most recent observations on air circulation throughout the extra-pulmonary airways have led me to reflections on the possible conceptual and factual analogy between the air and blood circulation, since they are two cyclical integrated processes of fluid balanced mechanics leading to complementary simultaneous results.
The steady circulation of the fluids, air and blood, makes evident the presence of cyclical displaced masses, throughout appropriated circuits, accelerated by proportional forces able to guarantee their simultaneous arrival to the proper areas of the physiological procedure.
The fluid blood is an organic tissue that behaves as other liquids do, hence, it circulates throughout a closed circuit, being primarily impelled by forces generated by contraction-relaxation of the cardiac muscle..
The fluid intra-pulmonary air is a gaseous mass derived from the mass of air per volume unit offered by the environment. The atmospheric air is taken by the organism and displaced throughout a circuit in communication with the Atmosphere although it is physiologically opened for air renovation and closed for adaptation and displacement, since atmospheric air needs to be adapted: acclimatised and balanced in pressure, "organised" before being apt for conditions demanded at the alveolo-capillary units, for gas exchange with the blood. The whole process corresponds to what I have named Dynamic-functional Integration of the Living Beings with the Atmosphere, a process commanded by the Vagus nerve
The blood circuit, mechanically described, is only one, which is always full with the totality of the blood. This circuit disposes of an intermediate system of pumps and valves, for impulsion and derivation, by fractions, towards two similar areas, for alternating gas exchange: delivery of Oxygen and load of carbon dioxide at tissue level and load of Oxygen and discharge of carbon dioxide at the alveolar-capillary units.
These objectives are complementary and the latter named one needs a complex circuit to enable the atmospheric air intake, adaptation and transportation up to the alveoli, with the rhythm demanded by the blood arrival at the alveoli. This complex process is known as Pulmonary Respiration
The pulmonary air circuit is conceptually also only one, conceptually, although divided into five similar circuits: the pulmonary lobes, each one filled with the corresponding fraction of the total air mass into the Lung.
This circuit also disposes, by analogy, of a system of pumps and sphincters for derivation and simultaneous, fractionated distribution among the proper areas of the total alveolar surface. The named system of pumps and sphincters is composed of the smooth muscles of the airways, the fibres of which are distributed as a geodesic net (Miller- Mason) and circular fibres around the dichotic divisions (sphincter-like of Miller)
The final program for air distribution is designed for delivery to the alveoli, of air masses per volume unit proportional to the simultaneous arrival and passing masses of blood. The achievement of these physiological conditions poses new problems to be solved and interpreted.
This final objective is performed by different structures developing simultaneous dynamics for partial processes integrated for this goal. These structures are worth recalling here.
Each pulmonary lobe is a complex circuit of airways with decreasing diameters after each dichotic division (bronchi and bronchioli), all innervated by Vagal and Sympathetic fibres in different proportion.
The wider air ways correspond to the first divisions of the lobar bronchial trees, being provided with cartilage structures to prevent them from being completely closed by muscular contraction, guaranteeing a permanent filling with a correlative volume-mass of air. The finest bronchia and bronchioli do not have cartilage and dispose of a relatively greater number of muscular fibres, and as a likeness with the arterioles eject the total mass of contained air.
All the above said, plus the successive dichotic divisions of the bronchia and bronchioli into approximately sixteen generations approximately for the lobar trees and more or less eight for the lobular trees, announces the progressive division and distribution of the air mass ejected by each cyclic bronchoconstriction. This structural design also shows the potential active role of the segments as proportional pneumatic pumps to achieve different partial results and complementary actions.
Therefore. Each nerve discharge of the Vagus generates contraction of its commanded muscles, followed by broncho-constriction-retraction and closure of sphincters, in accordance with the general and local distribution of the muscle fibres. This role is similar to that of the cardiac systole, although with a different rhythm. The following muscle relaxation has its analogy with the cardiac diastole.
As in blood circulation, the forces generated by bronchial muscle contraction-relaxation, eject the contained mass of air, followed by aspiration of a similar contiguous mass of air, always in the direction of lower resistance. This air mass will circulate or be retained and pressurised, depending on whether the air passages are opened or not at the moment of the generation of forces.
Contraction of the bronchial muscles under Vagus command shows a vagal rhythm, which corresponds to the known Respiratory rhythm.
As I have demonstrated in my analysis of the graphs of the Respiratory Pulse, which starts with a sudden increase in pressure corresponding to bronchoconstriction that I have interpreted as effect of an air mass ejection towards the lobar periphery, since this zone offers the lower resistance at the end of the previous cycle, being practically empty of air and because the same muscle contraction produces the closure of the sphincters at the insertion point of the lobar bronchial trees in the corresponding right or left bronchus,
The lobar periphery represents in this moment a functional cul de sac, consequently retaining the displaced air and proportionally increasing its mass per volume-unit
On the other hand, the above named functional closure of the right and left bronchia, added to simultaneous general muscle contraction and closure of the Glottis, converts this air sector to a transitorily closed cavity. The consequence is an increase in pressure of the contained air mass, as a physical condition for the following processes, simultaneous and complementary of those in the lobes.
This is the moment to recall that the air mass contained in the sector comprised by main bronchi, trachea and larynx, have two origins, two destinations and two particular physical conditions:
Once the effects produced by the programmed muscle contraction are completed, relaxation begins, for proper simultaneous and progressive effects, finishing the cycle, but also preparing conditions for the next one.
The long lasting relaxation period of the Vagus innervated muscles of the lobes gives place to complementary performances in the two specific sectors of the lobar structure:
This is the moment to emphasise the special functional mechanics of the lobular structure to enable blood circulation throughout the alveolar capillaries: The lobular structure repeats the cyclic mechanical procedure of the lobar structure formerly explained. The bronchiolar muscular contraction produces bronchiolo-constriction-retraction thus ejecting the contained small masses of air at the same time that they retract, to widen the pleural virtual lumen, thus acting as a floodgate for the blood circulation by the alveolar capillaries. The following expansion, due to muscle relaxation, works now as a press to displace the used air in the converse direction, towards the extra-pulmonary airways and the blood, with its load of Oxygen towards the pulmonary veins and left auricle.
Each "Ventilatory" cycle known as Respiratory cycle repeats the functional scheme here described, with a slight difference among the successive cycles of each series of four or six cycles. The difference is the following: The air mass inspired in each cycle fills up the naso-pharynx up to the next cycle, while the similar mass from the previous cycle enters the trachea to remain there until the next cycle. It is now displaced and distributed among the immediate empty spaces in the lobes, for another cycle, when it will be ejected towards the lobules at the lobar peripheries to be used in gas exchange.
This air displacement during several ventilatory cycles before being used in gas exchange, is a process like the blood displacement by the known vis a tergo during several cardiac cycles, before being used in gas exchange. The great difference lies in the fact that the whole lobar air circuit comprises two sectors of different capacity with different rhythms for different complementary objectives:
The lobar bronchial tree is mainly innervated by the Vagus nerve, consequently performing its role of pulmonary ventilation with vagal rhythm, and several cycles are needed for the once-inspired air mass to arrive in the lobules, to be used in gas exchange. This long-lasting period is used in "organisation" of the atmospheric air, in other words, in adaptation of the natural atmospheric air to conditions demanded by the blood for physiological gas exchange. This air adaptation means a rhythmical, cyclical adaptation of the Living being to the Atmosphere for a permanent integration as the primary condition for Life on Earth.
The lobar capacity and rhythm are a multiple of the lobular capacity and rhythm, as the blood vessels capacity is a multiple of the ejected blood by each cardiac systole.
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