Respiratory Phys
How does one make a static Compliance curve?
- While breathing into a spirometer, you also swallow a balloon into your esophagus. The spirometry measures volume of air in the lungs where the balloon measures transpulmonary pressure - Alveolar pressure = 0 when there is no airflow, thus a curve can be made by pausing throughout inspiration or expiration - it is termed a static compliance curve because it occurs without movement of air - decreases in compliance move the curve down and to the right, whereas increases in compliance move it to up and to the left (think of it as the expiratory arm of the PV loop)
What is the negative intrapleural pressure?
-3 to -5 cm H2O
What does surfactant do in relation to alveolar surface tension?
-Decreases elastic recoil due to surface tension in an area dependent manner - increases the compliance of the lungs above that predicted by an air-water interface and thus decreases the inspiratory work of breathing. -Because the surface tension decreased dramatically at low relative areas, it is reasonable to assume that the surface tension of different-sized alveoli is not constant and that smaller alveoli have lower surface tensions. -helps equalize alveolar pressures throughout the lung (so the end-expiratory pressure of all the alveoli is 0 cm H2O) and to stabilize alveoli. - likely responsible for hysteresis
Describe an expiratory flow volume curve with restrictive disease
-Restrictive diseases usually entail elevated alveolar elastic recoil - may have decreased PEF because the TLC (and thus the VC) is decreased - effort-independent part of the curve is similar to that obtained from a person with normal lungs since both the FEV1 and FVC are decreased because the lung has a low volume and because alveolar elastic recoil pressure may be increased
When a person shifts from sitting upright to supine positioning, describe what happens to the chest wall compliance and why
-the elastic recoil curve for the lung is relatively unchanged -the recoil curves for the chest wall and the respiratory system are shifted to the right -The reason for this shift is the effect of gravity on the mechanics of the chest wall, especially the diaphragm. When a person is standing up or sitting, the contents of the abdomen are being pulled away from the diaphragm by gravity. When the same person lies down, the abdominal contents are pushing inward against the relaxed diaphragm. This decreases the overall outward recoil of the chest wall and displaces the chest wall elastic recoil curve to the right. Because the respiratory system curve is the sum of the lung and chest wall curves, it is also shifted to the right.
What are the components of the elastic recoil of the lung?
1. Elastin (most important at low or normal lung volumes) 2. Collagen (most important at large lung volumes) 3. Surface tension at the air liquid interface of the alveoli
What are some explanations for lung hysteresis?
1. stretching on inspiration and the compression on expiration of the film of surfactant that lines the air-liquid interface in the alveoli. Surfactant has less effect on decreasing surface tension during inspiration than during expiration because of movement of surfactant molecules from the interior of the liquid phase to the surface during inspiration. 2. Another explanation is that some alveoli or small airways may open on inspiration ("recruitment") and close on expiration ("derecruitment")
respiratory zone
20th to 22nd generations lined with alveoli. These alveolar ducts and the alveolar sacs terminate the tracheobronchial tree
What is surfactant made of?
85% to 90% lipids and 10% to 15% proteins. lipid portion is about 85% phospholipid, approximately 75% of which is phosphatidylcholine, mainly dipalmitoyl phosphatidylcholine There are 4 specific surfactant proteins: SP-A, SP-B, SP-C, and SP-D
What must be established to move air into or out of the alveoli?
A pressure difference between the alveoli and atmospheric pressure
hysteresis
A second feature of the PV curve is that there is a difference between the pressure-volume curve for inflation and the curve for deflation, as shown by the arrows. Such a difference is called hysteresis
What does a pneumotachtograph measure
Airflow
What is the effective driving pressure for airflow during normal respiration?
Alveolar Pressure - atmospheric pressure
Alveolar pressure
Alveolar pressure = intrapleural pressure + alveolar elastic recoil pressure
transitional zone
Alveoli start to appear at the 17th through the 19th generations, in the respiratory bronchioles
What is the alveolar distending pressure?
As mentioned before, the alveolar-distending pressure is often referred to as the transpulmonary pressure. Strictly speaking, the transpulmonary pressure is equal to the pressure in the trachea minus the intrapleural pressure. Thus, it is the pressure difference across the whole lung. Alveolar pressure = pressure in the trachea at end inspiration or expiration (0 cmH20)
Describe transmural pressure during inhalation
As the inspiratory muscles contract, expanding the thoracic volume and increasing the outward stress on the lung, the intrapleural pressure becomes more negative. Therefore, the transmural pressure difference tending to distend the alveolar wall increases and the alveoli enlarge passively. Increasing alveolar volume lowers alveolar pressure and establishes the pressure gradient for airflow into the lung
What is the normal ratio of dynamic compliance to static compliance?
At low respiratory rates, the dynamic compliance ~ static compliance with a ratio thus of about one. In normal lungs, it stays close to one (maybe a little below making the static compliance slightly higher than the dynamic compliance). However, with obstructive disease, the ratio gradually decreases as respiratory rate increases. This indicates that changes in dynamic compliance reflect changes in airways resistance as well as changes in the compliance of alveoli
What causes negative intrapleural pressure?
At the end of expiration, when all the respiratory muscles are relaxed, the lung and the chest wall are acting on each other in opposite directions. The lung is tending to decrease its volume because of the inward elastic recoil of the distended alveolar walls; the chest wall is tending to increase its volume because of its outward elastic recoil.
Describe a flow volume curve with a fixed obstruction
Both the expiratory and inspiratory flow-volume curves are truncated, with decreased peak expiratory and peak inspiratory flows (A)
Clara cell
Clara cells secrete proteins (including surfactant apoproteins SpA, SpB, and SpD), lipids, glycoproteins, and modulators of inflammation. They also act as progenitor cells for Clara cells and for ciliated epithelial cells, metabolize some foreign material, and participate in airway fluid balance.
Compliance
Compliance is defined as the change in volume divided by the change in pressure
Constriction
Constrict Parasympathetic stimulation Acetylcholine Histamine Leukotrienes Thromboxane A2 Serotonin α-Adrenergic agonists Endothelin Decreased pCO2 in small airways
Describe the actions if the internal intercostal muscles during expiration
Contraction of the internal intercostal muscles depresses the rib cage downward in a manner opposite to the actions of the external intercostals.
How do branches of the conducting system respond to low concentrations of CO2? high concentrations? Hypoxia?
Decreased CO2 in the branches of the conducting system causes a local constriction of the smooth muscle of the nearby airways; increased CO2 or decreased O2 causes a local dilation.
Dilate
Dilate Sympathetic stimulation (β2 receptors) Circulating β2 agonists Nitric oxide Increased pCO2 in small airways Decreased pO2 in small airways
Describe a variable intrathoracic obstruction flow-volume curve
During a forced expiration, positive intrapleural pressure decreases the transmural pressure gradient across a variable intrathoracic tracheal obstruction, decreasing its cross-sectional area and decreasing the PEF (Figure 2-25C). During a forced inspiration, as large negative intrapleural pressures are generated, the transmural pressure gradient across the variable intrathoracic obstruction increases and its cross-sectional area increases. Thus, the inspiratory flow-volume curve is nearly normal or not affected.
Describe a variable extrathoracic obstruction flow-volume curve
During a forced expiration, the cross-sectional area of a variable extrathoracic obstruction increases as the pressure inside the airway increases (Figure 2-25B). The expiratory flow-volume curve is therefore nearly normal or not affected. However, during a forced inspiration, the pressure inside the upper airway decreases below atmospheric pressure, and unless the stability of the upper airway is maintained by reflex contraction of the pharyngeal muscles or by other structures, the cross-sectional area of the upper airway will decrease.
What law accounts for decreased alveolar pressure and thus airflow into the lungs?
During normal negative-pressure breathing, alveolar pressure is made lower than atmospheric pressure. This is accomplished by causing the muscles of inspiration to contract, which increases the volume of the alveoli, thus lowering the alveolar pressure according to Boyle law (P1V1=P2V2)
Describe the motion of the diaphragm during inspiration
During normal quiet breathing, contraction of the diaphragm causes its dome to descend 1 to 2 cm into the abdominal cavity, with little change in its shape. This elongates the thorax and increases its volume. These small downward movements of the diaphragm are possible because the abdominal viscera can push out against the relatively compliant abdominal wall. During a deep inspiration, the diaphragm can descend as much as 10 cm. With such a deep inspiration, the limit of the compliance of the abdominal wall is reached, abdominal pressure increases, and the indistensible central tendon becomes fixed against the abdominal contents. After this point, contraction of the diaphragm against the fixed central tendon elevates the lower ribs
How is the relationship between flow, resistance, and pressure altered during turbulent flow?
During turbulent flow, the relationship among the pressure difference, flow, and resistance changes. Because the pressure difference is proportional to the flow squared, much greater pressure differences are required to generate the same airflow. Delta P ~ V^2R
Describe Expiration
Expiration (Passive) 1. Brain ceases inspiratory command. 2. Inspiratory muscles relax. 3. Thoracic volume decreases, causing intrapleural pressure to become less negative and decreasing the alveolar transmural pressure difference.† 4. Decreased alveolar transmural pressure difference allows the increased alveolar elastic recoil to return the alveoli to their preinspiratory volumes. 5. Decreased alveolar volume increases alveolar pressure above atmospheric pressure, thus establishing a pressure difference for airflow. 6. Air flows out of the alveoli until alveolar pressure equilibrates with atmospheric pressure.
Describe expiration
Expiration is passive during normal quiet breathing, and no respiratory muscles contract. As the inspiratory muscles relax, the increased elastic recoil of the distended alveoli is sufficient to decrease the alveolar volume and raise alveolar pressure above atmospheric pressure. Now the pressure gradient for airflow out of the lung has been established.
Describe transmural pressure relating to the lungs, and relating to the chest wall
For the lungs, the transmural pressure difference is transpulmonary pressure (alveolar minus intrapleural); for the chest wall, the transmural pressure difference is intrapleural pressure minus atmospheric pressure
What does SF-B do?
Helps arrange phospholipids into lamellar bodies, form tubular myelin and surface films, and assists the entry of phospholipids into the surface monolayer as the alveoli expand during inspiration
How does hypoxia effect surfactant?
Hypoxia or hypoxemia (low oxygen in the arterial blood), or both, may lead to a decrease in surfactant production, surfactant inactivation, or an increase in surfactant destruction.
Describe alveolar interdependence
If an alveolus, such as the one in the middle of Figure 2-13, were to begin to collapse, it would increase the stresses on the walls of the adjacent alveoli, which would tend to hold it open. This process would oppose a tendency for isolated alveoli with a relative lack of pulmonary surfactant to collapse spontaneously. Conversely, if a whole subdivision of the lung (such as a lobule) has collapsed, as soon as the first alveolus is reinflated, it helps to pull other alveoli open by its mechanical interdependence with them. Thus, both pulmonary surfactant and the mechanical interdependence of the alveoli help stabilize the alveoli and oppose alveolar collapse (atelectasis).
Resistive work
Increased in asthma, bronchitis, and emphysema; upper airway obstruction, including obstructive sleep apnea; and accidental aspirations of foreign objects. Normally, most of the resistive work is that done to overcome airways resistance
What causes reflex constriction?
Inhalation of chemical irritants, smoke, or dust; stimulation of the arterial chemoreceptors; and substances such as histamine cause reflex constriction of the airways. Leukotrienes usually cause bronchoconstriction, as do some prostaglandins.
Describe Inspiration
Inspiration 1. Brain initiates inspiratory effort. 2. Nerves carry the inspiratory command to the inspiratory muscles. 3. Diaphragm (and/or external intercostal muscles) contracts. 4. Thoracic volume increases as the chest wall expands.* 5. Intrapleural pressure becomes more negative. 6. Alveolar transmural pressure difference increases. 7. Alveoli expand (according to their individual compliance curves) in response to the increased transmural pressure difference. This increases alveolar elastic recoil. 8. Alveolar pressure falls below atmospheric pressure as the alveolar volume increases, thus establishing a pressure difference for airflow. 9. Air flows into the alveoli until alveolar pressure equilibrates with atmospheric pressure.
type II alveolar cells
Interspersed among these are the cuboidal type II alveolar cells, which produce the fluid layer that lines the alveoli
barrier to gas exchange
It consists of the alveolar epithelium, the capillary endothelium, and the interstitial space between them. Gases must also pass through the fluid lining the alveolar surface and the plasma in the capillary.
What innervates the diaphragm?
It is innervated by the 2 phrenic nerves, which leave the spinal cord at the third through the fifth cervical segments.
Linear velocity
Linear velocity (cm/s) is equal to the flow (cm3/s) divided by the cross-sectional area.
Are alveoli in parallel more or less compliant together?
More compliant, compliances in parallell add together whereas in series the reciprocals add
Describe an expiratory flow volume curve with obstructive disease
Obstructive disease -high lung volumes and thus increased alveolar elastic recoil pressure -PEF and FEV1/FVC are both low - The residual volume may be increased if airway closure occurs at relatively high lung volumes - effort-independent portion of the curve is depressed inward (concave): Flow rates are low for any relative volume.
Describe the relationship between resistance, pressure, and flo
Pressure Difference = resistance x flow Q= delta Pressure/R Pressure Difference/Flow = R
Work of breathing
Proportional to the pressure change times the volume change The pressure change is the transpulmonary pressure needed to overcome both elastic work and resist work Pressure change for elastic work is equal to the change in volume/compliance Pressure change for restistance work is the airflow x the resistance The volume change in a eupnic patient is the tidal volume Thus Change in Pressure = Change in volume/compliance + flow x resistance
What causes the decreased resistance when lung volumes are large?
Resistance is proportional to radius^4, as there is little cartilage in the smaller airways, during inspiration when their airways have a increasingly positive transmural pressure they actually dilate The traction of the lower airways decreases meaning as the lung inflates the alveoli get larger and the elastic recoil in their walls increases thus pulling open the connected smaller airways
What proteins have an effect on innate immunity and what is their effect?
SP-A and SP-D bind to bacteria, viruses, mycobacteria, and fungi, and enhance phagocytosis and the release of mediators of the immune response by macrophages
Compliance in reference to PV loop
Slope of the line between two points on a pv loop; Lungs with high compliance have a steep slope on their pressure-volume curves; that is, a small change in distending pressure will cause a large change in volume.
How can you measure the volume of air entering the lungs?
Spirometry
How does stimulation of the parasympathetic nervous system effect the bronchial tree? sympathetic?
Stimulation of the cholinergic parasympathetic postganglionic fibers causes constriction of bronchial smooth muscle as well as increased glandular mucus secretion. Selective stimulation of the alpha (α) receptors with pharmacologic agents causes bronchoconstriction. The preganglionic fibers travel in the vagus. Stimulation of the adrenergic sympathetic fibers causes dilation of bronchial and bronchiolar smooth muscle as well as inhibition of glandular secretion. This dilation of the airways smooth muscle is mediated by beta2 (β2) receptors, which predominate in the airways.
How is pressure transmiitted throughout the alveoli?
Structural interdependence of alveolar units. The pressure difference across the outermost alveoli is transmitted mechanically through the lung via the alveolar septa.
Surface tension
Surface tension is a force that occurs at any gas-liquid interface (or even interfaces between 2 immiscible liquids) and is generated by the cohesive forces between the molecules of the liquid, dyn/cm. It causes a liquid to shrink to form the smallest possible surface area. the curve at left (saline inflation) represents the elastic recoil due to only the lung tissue itself. The curve at right demonstrates the recoil due to both the lung tissue and the surface tension forces. The difference between the 2 curves is the recoil due to surface tension forces.
How can intrapleural pressure be estimated?
Swallowing a balloon into the intrathoracic esophagus
How does the Bernoulli principle play a role in forced expiration?
The Bernoulli principle may also play a role in dynamic compression of the airways. For an ideal fluid with no viscosity, as the linear velocity of the fluid flow increases, the pressure exerted by the fluid on the walls of the vessel (the "lateral pressure") decreases. Therefore, as the velocity of airflow in the small compressible airways increases during a forced expiration, the pressure inside the vessel decreases. This could contribute to a decreased or more negative transmural pressure difference across the vessel wall.
What happens to the FRC when shifting from an upright to supine position?
The FRC decreases appreciably just because the person changed from the sitting to the supine position
Vital capacity
The VC is the volume of air a subject is able to expire after a maximal inspiration to the total lung capacity (TLC)
pulmonary resistance
The airways resistance plus the pulmonary tissue resistance (airway 80%, pulmonary 20% unless fibrosis etc)
What factors can decrease compliance of the chest wall?
The compliance of the chest wall is decreased in obese people, for whom moving the diaphragm downward and the rib cage up and out is much more difficult. People suffering from a musculoskeletal disorder that leads to decreased mobility of the rib cage, such as kyphoscoliosis, also have decreased chest wall compliance. Other conditions that can decrease the compliance of the chest wall include ossification of costal cartilage, skin scars from burn injuries, and abdominal distension.
Elastic work
The elastic work of breathing is the work done to overcome the elastic recoil of the chest wall and the pulmonary parenchyma and the work done to overcome the surface tension of the alveoli. Increased in obese patients, patients with no surfactant, and patients with fibrosis
What prevents alveolar collapse due to surface tension?
The first factor is a substance called pulmonary surfactant, which is produced by specialized alveolar cells, and the second is the structural interdependence of the alveoli.
Describe isovolumetric flow curves
The middle curve in Figure 2-22 demonstrates dynamic compression and supports the equal pressure point hypothesis. At this lung volume, at which elastic recoil of the alveoli should be the same no matter what the expiratory effort, with increasing expiratory effort airflow increases up to a point. Beyond that point, generating more positive intrapleural pressure does not increase airflow: It becomes effort-independent. Airways resistance must be increasing with increasing expiratory effort. Airflow has become independent of effort because of greater dynamic compression with more positive intrapleural pressures. The equal pressure point has moved to compressible small airways and is fixed there. Note that at even lower lung volumes (25% of the VC), at which there is less alveolar elastic recoil to provide traction on small airways, this occurs with lower maximal airflow rates. In other words, because alveolar pressure equals the sum of the intrapleural pressure and the alveolar elastic recoil pressure during a forced expiration at a given lung volume, the driving pressure for airflow becomes independent of expiratory muscle effort because increasing the intrapleural pressure increases the alveolar pressure by the same amount
Describe the diaphragm
The muscle fibers of the diaphragm are inserted into the sternum and the 6 lower ribs and into the vertebral column by the two crura. The other ends of these muscle fibers converge to attach to the fibrous central tendon, which is also attached to the pericardium on its upper surface
static (or "relaxation") pressure-volume curves
The relationship between lung elastic recoil and chest wall elastic recoil is illustrated in static (or "relaxation") pressure-volume curves
What law describes the wall tension within an alveolus?
The relationship between the pressure inside the alveolus and the wall tension of the alveolus would then be given by Laplace's law (units in parentheses).
How is resistance calculated in series? in parallel?
The resistance to airflow is analogous to electrical resistance in that resistances in series are added directly (r1 +r2...) Resistances in parallel are added as reciprocals (1/r1 + 1/r2...)
If surface tension is constant despite surface area, according to LaPlace's law, if 2 alveoli of different sizes are attached to eachother, what happens to the smallest alveolus?
The smallest alveolus will eventually collapse as all of it's air moves to the bigger one. This occurs because if the tension is =, then the alveolus with the smaller radius must have a high pressure and thus collapse into the larger alveolus.
Is surface tension dependent on surface area?
The surface tension of most liquids (such as water) is constant and not dependent on the surface area of the air- liquid interface.
What causes the increased resistance when lung volumes are low?
The tendency of small airways to collapse due to the positive intrapleural pressure + the positive alveolar elastic recoil pressure = a very positive alveolar pressure. The pressure gradient would typically generate flow, but without cartilage etc, the alveoli and small airways may collapse depending on the transmural pressures Furthermore, as lung volume decreases, there will be less alveolar elastic recoil pressure and the difference between alveolar pressure and intrapleural pressure will decrease.
Time constant
The time constant is equal to the resistance times the compliance and it represents the time it takes for the alveolus to fill to 63% of its final volume.
Functional Residual Capacity
The volume of gas in the lungs at the end of a normal tidal expiration, when no respiratory muscles are actively contracting, is known as the functional residual capacity (FRC)
Flow volume loop at varying intensities
There are 2 interesting points about this family of expiratory (upper portion) curves, which corresponds to the 3 curves in Figure 2-22. At high lung volumes, the airflow rate is effort-dependent, which can be seen in the left-hand portion of the curves. At low lung volumes, however, the expiratory efforts of different initial intensities all merge into the same effort-independent curve, as seen in the right-hand portion of the curve. Again, this difference is because intrapleural pressures high enough to cause dynamic compression are necessary to attain very low lung volumes, no matter what the initial expiratory effort. Also, at low lung volumes there is less alveolar elastic recoil pressure, and so there is less traction on the same airways and a smaller pressure gradient for airflow. Note that there is normally no effort independence on inspiratory curves if the subject breathes through the mouth. Patients with upper airway problems such as obstructive sleep apnea or vocal cord paralysis would demonstrate inspiratory effort independence.
What innervates the external intercostals?
These muscles are innervated by nerves leaving the spinal cord at the first through the 11th thoracic segments.
Mast cells
They contain membrane-bound secretory granules that consist of many inflammatory mediators, including histamine, proteoglycans, lysosomal enzymes, and metabolites of arachidonic acid that can induce bronchoconstriction, stimulate mucus secretion, and induce mucosal edema by increasing permeability of bronchial vessels.
dynamic compression of airways
This increased resistance during a forced expiration is called dynamic compression of airways.
What decreases the tendency of the collapse of alveoli (structure)
This tendency is partly opposed by the attachment of the alveolar septa, containing elastic tissue, to their walls
In the tracheobronchial tree where is the greatest resistance to airflow?
Under normal circumstances the greatest resistance to airflow resides in the large to medium-sized bronchi
How do you calculate total compliance?
Wall and lung are in series thus: 1/total compliance = 1/compliance of chest wall + 1/compliance of the lung
Dynamic Compliance
When PV characteristics are measured during a breath
Describe the action of the abdominal muscles during expiration
When the abdominal muscles contract, they increase abdominal pressure and push the abdominal contents against the relaxed diaphragm, forcing it upward into the thoracic cavity. They also help depress the lower ribs and pull down the anterior part of the lower chest.
Describe the results of external intercostal muscle constraction
When they are stimulated to contract, the external intercostal, parasternal intercostal, and scalene muscles raise and enlarge the rib cage. The parasternal muscles, which are usually considered part of the internal intercostals, are inspiratory muscles and may be partly responsible for raising the lower ribs. The scalene muscles appear to contract in normal quiet breathing and are therefore not accessory muscles.
terminal respiratory unit
a respiratory bronchiole and its branches
bronchioles
airways with no cartilage
type I alveolar cells
alveolar surface is mainly composed of a thin layer of squamous epithelial cells
Why are broncholoes and alveoli subject to collapse
bronchioles and alveolar ducts contain no cartilage support
acinus
contains 10 to 12 of these respiratory bronchioles and their branches
Inspiratory Muscles
diaphragm, the external intercostals, and the accessory muscles of inspiration, which include the sternocleidomastoid, the trapezius, and the muscles of the vertebral column.
What is the effective driving pressure for airflow with forced expiration and dynamic compression?
during a forced expiration, when intrapleural pressure becomes positive and dynamic compression occurs, the effective driving pressure for airflow from the lung is the alveolar elastic recoil pressure (= alveolar pressure - intrapleural pressure)
pores of Kohn
interalveolar communications
What replaces the cartilage plates in distal airways?
muscular layer completely surrounds these airways. The muscular layer is intermingled with elastic fibers
alveolar-capillary unit
site of gas exchange in the lung
dynamic compliance
the change in the volume of the lungs divided by the change in the alveolar-distending pressure during the course of a breath
What are the muscles of expiration
the muscles of the abdominal wall, including the rectus abdominis, the external and internal oblique muscles, the transversus abdominis, and the internal intercostal muscles.
What causes passive distension of alveoli?
transmural pressure difference
transmural pressure difference
transmural pressure difference is conventionally calculated by subtracting the outside pressure (in this case, the intrapleural pressure) from the inside pressure (in this case, the alveolar pressure)
