Respiratory: Pulmonary Ventilation I and II

At the functional residual capacity, the pressure inside of the system is ______.

0 mmHg * There is not increase or decrease in pressure from the push or pull of the lungs or chest wall, and pressure equals atmospheric pressure.

What are three types of dead space?

1. Anatomic Dead Space: Anatomic dead space is the volume of the conducting portions of the respiratory tract, such as the nose and trachea. These areas do not contain alveoli for gas exchange, so are considered dead space. The anatomical dead space is around 150 mL. 2. Alveolar Dead Space: Alveolar dead space is the volume of air that enters unperfused alveoli. The alveolar dead space can increase with disease. 3. Physiological (Total) Dead Space: Physiological dead space is anatomic dead space plus the volume of alveoli that do not participate in gas exchange. This is also known as functional dead space, as the system should exchange gas, but does not due to its structure.

These muscles help raise the rib cage during inspiration:

1. SCM. The SCM pulls on the sternum. 2. anterior serratus. The anterior serrati pull on the ribs. 3. scalenes. The scalenes pull on the first two rib muscles.

What are two behaviors that patients with COPD partake in to decrease lung collapse?

1. Slow Exhalation: Slow exhalation prevents a large rise in pleural pressure. With forceful exhalation, the intrapleural pressure would increase significantly, and the lungs would collapse. By a slow exhale, the intrapleural pressure would never increase so much that the lungs collapse. 2. Pursed Lips: With pursed lips, there is an increased airway (alveolar pressure). As a result, collapse is prevented.

What generates the elastic force required for normal breathing? (2)

1. The lungs are composed of elastic tissue. Elastic fibers are a part of the elastic structure of the lungs, contributing to a third of the elastic force of the structure. 2. There is fluid lining the lungs. From the nose to the terminal bronchioles, there are cilia that beat 10-20 times per second toward the pharynx to remove the fluid and entrapped particles. However, this fluid lining the system, particularly in the areas where there is no cartilage (i.e. respiratory bronchioles and below), generates an elastic force itself. This is because there is a liquid-air interface within the alveoli, generating surface tension that creates a net elastic contractile force over the entire lung. This fluid contributes to two-thirds of the elastic force.

What two things create the negative pressure within the thoracic cavity?

1. The tendency of the lungs to collapse and the chest wall to bow outward creates a negative pressure. 2. The constant suctioning and draining of pleural fluid by the lymphatics generate a negative pressure.

Four Lung Volumes

1. Tidal Volume 2. Expiratory Reserve Volume 3. Inspiratory Reserve Volume 4. Residual Volume

Ventilation can enter two places:

1. alveolar ventilation. Alveolar ventilation is useful for gas exchange. 2. dead space ventilation. Dead space ventilation is wasted ventilation.

Increased lung compliance and, therefore, an increase functional residual capacity is seen in (3):

1. emphysema (floppy lungs). In emphysema, the lung tissue structure is destroyed, making it easier to move the lung structure. There is less elasticity, but an increased compliance. There is less of a tendency for lung collapse than the chest wall to expand, which leads to a larger functional residual capacity. 2. aging. With aging, there is less elasticity of the lung tissue. With a decrease in elasticity, then there is an increase in compliance. 3. surfactant.

The muscles of expiration include: (2)

1. internal intercostals. 2. abdominal recti. The abdominal recti muscles pull down on the lower ribs.

The muscles of inspiration include: (3)

1. neck muscles. 2. external intercostal muscles. 3. diaphragm.

Decreased lung compliance and, therefore, a decrease functional residual capacity is seen in (3):

1. pneumonia. 2. pulmonary edema. With fluid around the lungs, it is more difficult for the lung to move. Therefore, there is a decrease in compliance. 3. pulmonary fibrosis. In pulmonary fibrosis, the tissue is thick and difficult to move. As a result, there is a decrease in compliance.

The length of the thoracic cavity is altered by (2):

1. the diaphragm. The diaphragm is a domed muscle at the end of the thoracic cavity. When it contracts, it pulls down, lengthening the thoracic cavity. When it relaxes, it pushes up, shortening the thoracic cavity. 2. the abdominal muscles. Contraction of the abdominal muscles can push the thoracic cavity, thereby decreasing the length of the thoracic cavity.

The diameter of the thoracic cavity is altered by (3):

1. the external intercostal muscles. With contraction of the external intercostal muscles, then there is an increase in diameter. 2. the internal intercostal muscles. When the diameter is decreased, the ribs are depressed, and the intercostal muscles contract. 3. the abdominal recti muscles. When the abdominal recti muscles contract, the ribs are depressed, thereby decreasing the diameter of the thoracic cavity.

The work of breathing involves: (3)

1. the work to overcome the elastic forces of the lung and chest wall. 2. the work to overcome the viscosity of the lung and the chest wall structures. The lungs are lubricated by the pleural fluid, but there is still movement between them. This viscosity must be overcome. 3. the work to overcome airway resistance. There is airway resistance in the lungs during inspiration. Normal respiration uses about 3-5% of total work energy, and this can increase 50x with heavy exercise.

Compliance is determined by (2).

1. volume. 2. distensibility.

Atmospheric Pressure =

760 mmHg or 0 mmHg

How are pulmonary volumes measured?

A spirometer is used to measure pulmonary volumes.

How are the lungs at rest?

At rest, the lungs have an elastic structure, so the lungs naturally, due to elastic recoil as well as surface tension, tend to collapse. The lungs are also suspended in the thoracic cavity surrounded by pleural fluid. The thoracic cavity has a negative pressure. Furthermore, the chest wall has a tendency to expand outward due to outward elastic recoil. It works in opposition to the elastic recoil of the lungs. As a result, there is an equilibrium between the elastic recoil of the lungs and the elastic recoil of the chest cavity. So, as a result, the lung is inflated, held tight to chest wall, the alveoli are not collapsed, and there is a negative pressure within the thoracic cavity.

Besides reducing surface tension, what is another major function of pulmonary surfactant? Explain.

Besides reducing surface tension, another major function of pulmonary surfactant is stabilization of alveolar structure. For example, consider fluid without surfactant, so there is water in the system. There are large and small alveoli. The small and large alveoli are interconnected. There is water lining the surface of all alveoli. Since there is one air-water interface of the alveoli, it follows LaPlace's law: the pressure of the system is equal to two times the surface tension over the radius (2T/r). The surface tension is the same throughout, as for most liquids have a constant surface tension not dependent on surface area; however, the pressure in the small alveolus is double that of the large alveolus. Pressure moves from an area of high pressure to an area of low pressure, so the pressure of the small alveolus will move to the large alveolus to equalize the pressure. As a result, the small alveolus would collapse. With surfactant, this does not occur. This is because surfactant not only lowers the surface tension in the alveoli, but also changes the surface tension with the surface area of the alveolus. So, with a small alveolus, there is lower surface tension. If the same amount of surfactant is placed in a higher surface area in a large alveolus, then water molecules have a high surface tension because the lipid molecules are not as close together, so there is more repulsion. As a result, there is a higher surface tension. With larger alveoli with higher surface tension and smaller alveoli with lower surface tension, then the pressure is more equalized, resulting in less pressure movement and collapse of small alveoli. So, overally, surfactant results in the surface tension varying with surface area of the air-liquid interface, and as a result, pressure is equalized between large and small alveoli.

Explain Bohr's method.

Bohr's method states that physiological dead space can be measured using tidal volume, CO2 exhaled, and CO2 from blood gas. Blood enters the pulmonary capillary with a CO2 concentration similar to that of the venous system of the body. Blood enters the pulmonary capillary, leaves, and enters the pulmonary veins, the left atrium, the left ventricle, and to the body via the arteries. Therefore, the pCO2 of the blood leaving the capillaries is equal to the arterial pCO2. Assuming the alveolus is functional, CO2 will leave the capillary and enter the alveolus. By the time the blood exits the capillary, there is equlirbium between the alveolar CO2 and the capillary CO2 which equals the arterial CO2. Finally, inspired air virtually has no CO2. Now, this is a perfect system. Now, say the lungs have no functional alveoli. CO2 is 0 mmHg in the inspired air, and there is no gas exchange due to dead space. So, expired CO2 would be 0 mmHg. If CO2 is not expired, then pCO2 in the blood increases, so the arterial pCO2 increases. The more dead space, the higher the CO2, and the closer that the expired CO2 reaches 0 mmHg.

What is the effect of forced exhalation on lung pressures?

During forced exhalation, the intrapleural pressure becomes positive. This compresses the airway, placing pressure of the alveoli and generating a positive pressure in the airway (higher than normal quiet breathing). This, along with elastic recoil, pushes air out, and air flows from the airways.

Exhalation Thoracic Cavity Volume: Intrapleural Pressure: Alveolar Pressure: Air Flow Direction:

Exhalation Thoracic Cavity Volume: decrease Intrapleural Pressure: less negative Alveolar Pressure: positive Air Flow Direction: out of the lungs

True or False: Dead space causes hypoxemia.

False

True or False: The residual volume can be measured via a spirogram.

False

What is the effect of dead space on pO2?

For example, there are two capillaries: both are perfused by a pulmonary alveoli. Blood enters each capillary at an oxygen saturation of 70%. After the blood passes through the alveoli, it is fully saturated at 100% on both sides. Then, blood mixes to produce arterial blood that is 100% saturated. Imagine if there is a disease process that causes flow obstruction to one of the alveoli. This causes the alveolus to turn into dead space because it is ventilated, but no longer perfused. Blood enters the alveoli at 70% oxygenation, but does not leave. So, the dead space alveolus does not contribute to oxygen concentration. The other alveolus still works, so blood is 100% saturated leaving the alveolus. Despite the formation of dead space, oxygen saturation is still 100% with no hypoxemia.

What is the effect of hypoxia on surfactant production?

Hypoxia leads to a decrease in surfactant production and increase in alveolar collapse. As a result, adult ARDS may result.

Compare and contrast a compliant lung with a non-compliant lung.

If the lungs are compliant, it takes a small amount of diaphragm effort to generate a small amount of pressure across the lungs for a large volume change. As a result, it is easy to move air in and out because the lungs easily expand and contract. If the lungs are non-compliant, it takes a large amount of diaphragm effort to generate a large amount of pressure across the lungs for a small volume change. As a result, it is difficult to move air in and out because the lungs do not easily expand and contract.

What is the effect of lung pressures on air flow?

Imagine that the atmospheric pressure is zero. Imagine the alveolar pressure is also zero. This is a change in pressure of zero, and anytime that there is no difference in pressure, there is no air flow. On the other hand, imagine that the alveolar pressure is +5 mmHg. The atmospheric pressure is still 0 mmHg. Now, the change in pressure in +5 mmHg. As a result, air flows from an area of high pressure to low pressure, so air flows out of the lungs. In contrast, imagine that the alveolar pressure is -5 mmHg. The atmospheric pressure is still 0 mmHg. Now, the change in pressure in +5 mmHg. As a result, air flows from an area of high pressure to low pressure, so air flows into the lungs.

How can anatomic dead space be measured by Fowler's method?

In Fowler's method, a person is required to be breathing in pure oxygen, and the expired air is measured using a nitrogen meter to measure the N2 level in the air. So, if a person is breathing in pure oxygen, then the conducting zone is filled with pure oxygen. Nitrogen only comes from the alveoli. During expiration, the first gas exhaled is pure oxygen. Slowly, the nitrogen concentration increases until it plateaus, and the plateau is all of the gas coming from the alveoli.

What is the effect of a pneumothorax on alveolar, intrapleural, and transpulmonary pressure?

In a pneumothorax, there is a hole in the lungs, changing the intrapleural pressure. The pressure in the intrapleural space becomes zero because there is a hole in the lungs, allowing the atmosphere to connect to the pleural space. When this occurs, the transpulmonary pressure becomes zero, and the lungs collapse. There is no force to keep the alveoli open, so they collapse.

What is the effect of bronchitis on the equal pressure point?

In bronchitis, there is a higher pressure drop than normal due to obstruction to airflow. Elastic recoil is still intact, so a high alveolar pressure can be generated. Because the walls of the bronchi and bronchioles are inflamed, the pressure drops as airflow moves out of the lungs more quickly. As a result, the EPP is reached earlier outside of the cartilaginous airways. Therefore, the lungs collapse.

What is the effect of disease on the equal pressure point?

In diseased lungs, the equal pressure point moves toward the alveoli and lead to airway compression. If the EPP moves toward the alveoli outside of the cartilaginous airways, this leads to airway collapse. This can occur in patients with airway obstruction, such as bronchitis, and emphysema, where there is a loss of elastic recoil.

What is the effect of emphysema on the equal pressure point?

In emphysema, there is a loss of elastic recoil, so when an intrapleural pressure is generated, there is a decrease in the alveolar pressure generated. This pressure drops quickly, reaching a value lower than the pleural pressure prior to the cartilaginous airways.

What causes a barrel chest?

In patients with emphysema, these patients have an increased lung compliance and therefore an increased functional residual capacity, which leads to larger volumes in the chest at all times. As a result, over time, the chest expands.

In restrictive diseases of the lung, such as interstitial fibrosis and pulmonary edema: Stiffness of the Lung: Thickness of the Lung: Work of Breathing: Standard Lung Volumes:

In restrictive disease of the lung, such as interstitial fibrosis and pulmonary edema: Stiffness of the Lung: increases Thickness of the Lung: increases Work of Breathing: increases Standard Lung Volumes: decreases

In restrictive diseases of the chest wall, such as kyphosis or scoliosis: Stiffness of the Chest Wall: Cavity Volume: Elastic Recoil: Transpulmonary Pressure: Pleural Pressure: Work in Breathing: Standard Lung Volumes:

In restrictive diseases of the chest wall, such as kyphosis or scoliosis: Stiffness of the Chest Wall: increased Cavity Volume: decreased Elastic Recoil: decreased Transpulmonary Pressure: decreased Pleural Pressure: decreased Work in Breathing: increased Standard Lung Volumes: decreased

Inhalation Thoracic Cavity Volume: Intrapleural Pressure: Alveolar Pressure: Air Flow Direction:

Inhalation Thoracic Cavity Volume: increase Intrapleural Pressure: more negative Alveolar Pressure: negative Air Flow Direction: into the lungs

What is the relationship between chest volume and pressure? How does this differ between this relationship outside of the body?

Naturally, the chest wall tends to spring outward. This creates a negative suction pressure that opens the lungs and increase the volume. So, if 0 mmHg of pressure were applied to the walls of the chest, there will still be volume present, as the chest wants to spring outward. A positive pressure can be applied to increase volume, and a negative pressure can be applied to decrease the volume. Inside of the body, the lungs never fully collapse. However, on the outside of the body, the lungs fully collapse. Further, when pressure is applied to the lungs, lung volume increases, but not as much as the volume increased outside of the body. These differences are seen because the lungs are not present alone and are also affected by the chest wall. The chest wall has its own pressure-volume relationship, which affects the volume of the lungs.

Does the pressure-volume curve for inhalation and exhalation appear the same? Why or why not?

No, the pressure-volume curve for inhalation and exhalation does not appear the same. Since the slope of the pressure-volume curve is equal to compliance, then exhalation and inhalation generates a different compliance despite similar lung structures. This is known as hysteresis. Pressure-volume hysteresis is caused by surface tension. With inspiration, the lungs begin at their smallest volume, and the molecules are close together with a strong surface tension. As a result, a high force must be exerted to break the surface tension, so there is a small change in volume with a large change in pressure. With expiration, the lungs begin at their largest volume, and the molecules are farther apart with a low surface tension. As a result, a low force must be exerted to break the surface tension, so there is a large change in volume with a low change in pressure.

Can you measure functional residual capacity?

No, you cannot measure functional residual capacity because residual volume cannot be measured.

How does surfactant affect the work of inspiration?

Pulmonary surfactant decreases the work of inspiration by decreasing surface tension and hence elastic recoil of the lung and aiding in the equalization of pressure inside alveoli of different sizes.

What is pulmonary surfactant? What is its function?

Pulmonary surfactant is a complex mix of phospholipids (85-90%), proteins, and ions (10-15%). The majority of the phospholipid component is dipalmitoyl phosphatidylcholine. There are 4 surfactant proteins (SP-A-D). The purpose of pulmonary surfactant is to decrease surface tension in the alveoli. This is because the hydrophilic component suspend in the water in the fluid lining the alveolus as well as a lipid component that is situated on the surface of the water. The lipid molecules between the surfactant phospholipids repel one another, breaking up the attraction of the water molecules. As a result, there is a decrease in surface tension, resulting in a +4 cm of water pressure.

What produces pulmonary surfactant?

Pulmonary surfactant is produced and secreted by Type II pneumocytes, which are granular cells that comprise about 10% of the surface area of the alveoli.

Functional Residual Capacity (FRC) =

RV + ERV Normal is around 2.2 L.

How do the pressures in the lungs change during the respiratory cycle?

Resting: Beginning in the resting state, the alveolar pressure is 0 mmHg, meaning it is at equilibrium with the atmosphere. The intrapleural space pressure is -5 mmHg. This creates a transpulmonary pressure of +5 mmHg. This is enough the prevent the lungs from collapsing, but not enough to expand the alveoli. Inhalation: During inhalation, the diaphragm contracts, and the chest wall expands. The intrapleural pressure becomes more negative. This force is used to drive airflow. The alveolar pressure becomes negative, and the atmospheric pressure is 0 mmHg. Air flows from an area of high pressure to low pressure, so air will flow into the alveoli. The transpulmonary pressure also increases, which causes the lungs to expand. As flows enters the lungs, it fills the lungs, and the pressure increases. The alveolar pressure increases. As a result, air flow ends. At the end of inhalation, the intrapleural pressure is even more negative, which makes the transpulmonary pressure even more positive. However, at this point, the diaphragm relaxes. Exhalation: During exhalation, the diaphragm relaxes, and the chest wall contracts. The intrapleural pressure becomes less negative. This means that the force of the lungs changes. Some of this force is transmitted to the alveoli, where the alveolar pressure becomes positive. Since atmospheric pressure is 0 mmHg, then air flows from the alveoli to the atmosphere. The transpulmonary pressure decreases, which causes the lungs to shrink. At the end of exhalation, the intrapleural pressure becomes less negative, and the pressure in the alveoli becomes 0 mmHg because air is leaving the alveoli. When there is no airflow, then there is a return back to the resting state.

What is surface tension?

Surface tension is the force acting across an imaginary line 1 cm long in the surface of the liquid. For example, when water forms an interface with air, the water molecules form a strong attraction for one another. This attraction between water molecules generates surface tension.

Inspiratory Capacity (IC) =

TV + IRV Normal is around 3.8 L.

Vital Capacity (VC) =

TV + IRV + ERV Normal is around 4.8 L.

Total Lung Capacity (TLC) =

TV + IRV + ERV + RV Normal is around 6 L.

If the intrapleural pressure becomes positive during forced exhalation, why don't the lungs collapse? Explain.

The intrapleural pressure becomes positive during forced exhalation. Under normal circumstances, the lungs would collapse; however, the equal pressure point must be taken into account. For example, during forced exhalation, the intrapleural pressure is positive, and the alveolar pressure is more positive. The atmospheric pressure is 0 mmHg. The alveolar pressure does not become 0 mmHg in one step; the pressure slowly drops from deep in the lungs to superficial in the lungs. At the point where the intrapleural pressure equals the alveolar pressure, this is known as the equal pressure point. Once beyond the equal pressure point, the pressure within the system is lower the intrapleural pressure, and the lungs collapse under normal circumstances. However, in healthy individuals, this equal pressure point occurs in cartilaginous airways, which prevents airway collapse.

How are the lungs arranged in the thoracic cavity?

The lungs are suspended in the thoracic cavity, surrounded by two layers of pleura. In between the layers of pleura, there is pleural fluid, which lubricates the movement of the lungs within the thoracic cavity. This pleural fluid is suctioned constantly into the lymphatic system, and the thoracic cavity, as a result, is maintained at a negative pressure under normal circumstances. The lungs, as a result, are suctioned against the chest wall, but are still mobile structures.

Ventilation

The movement of air in and out of the lungs

Why is the physiological dead space greater than the anatomic dead space?

The physiological dead space is greater than the anatomic dead space due to insufficient perfusion, particularly at the apex of the lungs.

How is the volume of the thoracic cavity altered? (2)

The volume of the thoracic cavity is altered by: 1. altering the length of the cavity. 2. altering the width of the cavity.

True or False: Both the lung and the chest wall have a compliance.

True

True or False: The pressure of gas in the alveoli is proportional to the sum of the force of all molecules hitting the surface.

True

Ventilation =

Volume x Respiratory Rate

How does compliance change the shape of the volume-pressure curve?

When more pressure is applied, there is less of a volume change due to non-compliance. As a result, the functional residual capacity decreases.

What is the relationship between volume and pressure outside the body?

When there is no pressure, there is no volume. The lungs are collapsed. When pressure is applied to the walls of the lungs, the lungs began to expand. The volume increases until is reaches a maximal value.

Compliance

a change in volume for a given pressure; in terms of the lungs, the extent of lung expansion per unit of increase in transpulmonary pressure

Capacity

a sum of two volumes

Transpulmonary Pressure =

alveolar pressure - intrapleural pressure

As the amount of dead space decreases, the expired CO2 approaches the ___________. As a result, there is ________ gas exchange and __________ retained CO2.

arterial CO2; more; less

Compliance (C) =

change in volume/change in pressure

The inflow of air is achieved by ______.

changing the thoracic volume * Due to Boyle's law, which states the PV is constant at a constant temperature, P1V1 = P2V2.

When the pressure in the pleural space equals the atmospheric pressure, the lungs ______, and the chest wall __________.

collapse; bow out

As lung compliance decreases, functional residual capacity _______.

decreases

In regard to the functional residual capacity, the tendency of the lungs to collapse ________ the tendency of the chest wall to spring outward.

equals

When the alveoli are small (i.e. the balloon is not blown up.), the compliance is ________.

higher

The physiological dead space can _________ in disease states.

increase

Air is driven into the lungs by a change in the __________ pressure.

intrapleural

As lung compliance increases, it takes ____ pressure to distend or inflate the lungs. This means that the pressure- volume loop shifts to the ______.

less; left

The compliance of the chest wall + lung is _______ than chest wall only.

lower

When the alveoli are large (i.e. the balloon is blown up.), the compliance is ________.

lower

As lung compliance decreases, it takes ____ pressure to distend or inflate the lungs. This means that the pressure-volume loop shifts to the ______.

more; right

The intrapleural pressure is _______ during normal quiet breathing. Why?

negative; This is because the alveoli and the lungs tend to collapse. The lungs and alveoli want to pull inward and recoil, so an outward force is required to keep the walls open. In contrast, the chest walls tend to expand. The ribs. and muscles of the chest wall tend to spring outward, creating a negative pressure in the pleural space. As a result, this negative pressure "sucks" the alveoli open, creating a positive transpulmonary pressure.

Dead Space

portions of the respiratory system that are ventilated with air, but no gas exchange occurs

Bohr's Method

states that physiological dead space can be measured using tidal volume, CO2 exhaled, and CO2 from blood gas

Residual Volume

the amount of air that cannot exit the lungs despite the force of expiration

Hysteresis

the dependence of property on its history

Transpulmonary Pressure

the difference between the alveolar pressure and the intrapleural pressure or the pressure across the walls of the alveoli

The transpulmonary pressure indicates ________.

the distension of the alveoli * If the transpulmonary pressure is positive, then the alveoli are distended.

Compliance is influenced by ___.

the elastic forces of the lung (1/3 from the tissue itself and 2/3 from the surface tension)

Pressure

the force caused by constant impact of kinetically moving molecules against a surface

At rest, the volume of gas left in the lung is determined by ________.

the functional residual capacity

Vital Capacity (VC)

the highest volume of air exhaled

Inspiratory Capacity (IC)

the highest volume of air inspired

Transmural Pressure

the pressure difference across a walls of a vessel

Intrapleural Pressure

the pressure of the pleural space open to the atmosphere

Alveolar Pressure

the pressure within the alveoli

Functional Residual Capacity

the residual volume after quiet expiration; the volume when the system is relaxed and at equilibrium with the chest wall pulling out and the lungs pulling in

Total Lung Capacity (TLC)

the sum of all lung volumes

Tidal Volume

the volume of air that enters and exits the lungs with quiet breathing

Inspiratory Reserve Volume

the volume of air that enters the lungs with forceful inspiration beyond the tidal volume where the lungs are filled to capacity * Think exercise.

Expiratory Reserve Volume

the volume of air that exits the lungs with forceful expiration beyond the tidal volume; the residual volume remains in the lungs

The ______ pressure is necessary to keep the alveoli open.

transpulmonary

As the amount of dead space increases, the expired CO2 approaches ___________. As a result, there is ________ gas exchange and __________ retained CO2.

zero; less; more