Respiratory System Module Second semester

2020-2021

Respiratory physiology

References

• Guyton and Hall Textbook of Medical Physiology. Author : John E. Hall, 14th Edition, 2021

• Physiology . Author : Linda s. Costanzo , Sixth Edition, 2018.

• Ganong's Review of Medical Physiology. Authors Kim E. Barrett, Susan M. Barman, Heddwen L. Brooks, Jason X.-J. Yuan. 26 Edition, 2019

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Teaching style and office hours

• On line lectures according to module schedule via MS team

• Recorded lectures will be posted on MS team

• PPT slides will be posted on MS team

• Discussion and office hours : 2 hours ( Twice weekly)

• office hours will be announced weekly daily based on schedule or by appointment via tram

• Office hours can also be requested by appointment through MS team or by emailing me at zuheirakh@hu.edu.jo

• A practice quiz will be posted on team as informative assessment in due course before the midterm exam

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Lecture 1 MECHANICS OF PULMONARY VENTILATION

Zuheir A Hasan

Professor of physiology

College of Medicine

HU

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Lecture objectives

• Review the structures and the of the conducting airways, the alveolar–capillary unit, and the chest wall.

• List the functions of the lungs

• Describe the generation of a pressure gradient between the atmosphere and the alveoli.

• Define the mechanical interaction of the lung and the chest wall.

• Identify the respiratory muscle and describe their function during tidal breathing as well as during forced inspiration and expiration

• Define pulmonary pressure (alveolar pressure) , intrapleural pressure , transpulmonary pressure and elastic recoil pressure

• Describe the passive expansion and recoil of the alveoli.

• Describe the pressure changes and air flow during the respiratory cycle

• Describe the events involved in a normal tidal breath.

• Define pneumothorax and describe respiratory system pressure changes in pneumothorax

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Anatomical components of the respiratory system• The respiratory system is composed of the

• conducting airways

• Lungs

• muscles of respiration, and the chest wall.

• The chest wall consists of the muscles of respiration— the diaphragm, the intercostal muscles, and abdominal muscles Rib cage.

• Parts of the central nervous system concerned with the control of the

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Functional anatomy of the respiratory system

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Respiratory airways

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Air ways

• The airways are divided into two functional zones:

▪ conducting zone : First 16 generations of branches comprising the and functioning to conduct air to the deeper parts of the lungs.

▪ Respiratory zone• The last 7 generations participate in gas exchange

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The conducting zone

• Functions :• Warm and humidify inspired air• Distribute air evenly to all regions of the lungs• Serve as part of the body’s defense system

(removal of dust, bacteria, and noxious gases from the lungs).

• No gas exchange occurs in the conducting zone.• Constitute the anatomic dead space

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Respiratory Zone

• The respiratory zone is the location of the blood–gas interface where gas exchange occurs in thin-walled air sacs called alveoli.

• The respiratory zone (generations 17–23).

• comprising the respiratory bronchioles, alveolar ducts, and alveolar sacs

• Large cross-sectional area even as the passages narrow .

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Alveolar sacs

• Alveoli are thin-walled with internal diameters of 75–300 um

• Adult lungs contain 300 to 500 million alveoli, connected via with pores of Kohn

• internal surface area of ~75 m2

• In adults, alveoli, if damaged, have limited ability to repair themselves.

• It comprises two types of respiratory epithelial cell, or pneumocyte.

• Type I pneumocytes . :

• Type II, or granular, pneumocytes are

➢Synthesis pulmonary surfactant.

➢are capable of rapid division, which allows them to repair alveolar wall damage.

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Type I cell

(epithelial cell

in alveolar wall)

Alveoli

Alveolar basement

membrane

Deoxygenated

blood

Oxygenated

blood

Endothelial cell

in capillary wall

Capillary basement

membrane

Respiratory

membrane

Alveolar

air space

Capillary

O2

CO2

Alveolar capillary unit

Alveolus and associated pulmonary capillaries and alveolar capillary membrane

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Respiratory Functions

• The main functions of respiration are to provide oxygen to the tissues and remove carbon dioxide.

• The four major components of respiration are (1) pulmonary ventilation, which means the inflow and outflow of air between the atmosphere and the lung alveoli; (2) diffusion of oxygen (O2) and carbon dioxide (CO2) between the alveoli and the blood (3) transport of oxygen and carbon dioxide in the blood and body fluids to and from the body’s tissue cells(4) regulation of ventilation and other aspects of respiration.

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Gas Laws and Applications to Respiratory Physiology

Law Formula Application

Boyle’s P1V1=P2V2 Basis of gas flow during ventilation,Derivation of residual volume

Charles’ V1/V2=T1/T2 Gas volume varies in proportion to temperature; air expands during inspiration

Dalton’s Ptotal=∑P(gas) x For atmospheric: PB=PN2+PO2

Estimate of Inspired O2: PIO2=(PB-PH2O)* FIO2

Henry’s Cx=KPx Volume of dissolved gas is proportional to partial pressure

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Standard Notations

Symbol Definition Example

Px Partial pressure of x PCO2: partial pressure of CO2

Fx Fractional volume or pressure FN2: nitrogen fraction of pressure

Sx Saturation, decimal fraction or %

SO2: % saturation of hemoglobin with oxygen

Cx Concentration (content) CO2: total oxygen content

Locations

a Arterial blood PaCO2: carbon dioxide partial pressure of arterial blood

v Mixed venous PvCO2: carbon dioxide partial pressure of venous blood

c Pulmonary capillary blood PcO2: oxygen partial pressure of arterial blood

A Alveolar gas PAO2: alveolar oxygen partial pressure

I Inspired gas FIO2: oxygen fraction of inspired gas

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External and cellular respiration.

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External respiration and Internal respiration

External Respiration :

Refers to the entire sequence of events in exchange of O2 and CO2 between n the external environment and tissue cells. This achieved through the following events

• Pulmonary ventilation• Transfer of gas across the respiratory membrane to the

blood • Transport of gas by the blood to and from the body cells.

Internal respiration

Refers to the intracellular metabolic processes carried out within the mitochondria which use O2 and produce CO2 while deriving energy from nutrient molecules

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The respiratory quotient (RQ)

• RQ = ml of O2 used/ml CO2

• For carbohydrate utilization RQ is =1

• For fat utilization, the RQ is 0.7

• For f protein utilization , is 0.8.

• On a typical diet consisting of a mixture of these three nutrients, resting O2 consumption averages about 250 mL/min, and CO2 production averages about 200 mL/min

• RQ = 0.8

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Respiratory mechanics and pulmonary ventilation

Key words

• Atmospheric pressure

• Alveolar pressure

• Intrapleural pressure

• Transpulmonary pressure

• Elastic recoil pressure

• Lung volume

• Respiratory muscle

• Respiratory cycle

• Boyle's law

• Tidal normal breathing

• Inspiration

• Expiration

• Pneumpthorax

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Pleural sac and lung relationship

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Schematic diagram of the lung and chest-wall system.

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Absolute and relative pressures in the respiratory system

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Schematic diagram of the lung and chest-wall system.

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Respiratory system pressures important in ventilation

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Transmural Pressure

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Relationship between transpulmonary pressure (PL) and the pleural (Ppl), alveolar (PA), and elastic recoil (Pel) pressures of the lung.

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Alveolar pressure is the sum of pleural pressure and elastic recoil

pressure. Transpulmonary is the difference between alveolar pressure and

intrapleural pressure

Representation of the interaction of the lung and chest wall

At end expiration,

• The muscles of respiration are relaxed.

• The inward elastic recoil of the lung is balanced by the outward elastic recoil of the chest wall.

• Intrapleural pressure is –5 cm H2O

• alveolar pressure is 0.

• The transmural pressure gradient across the alveolus is therefore 0 – (–5) cm H2O, or 5 cm H2O.

• Since alveolar pressure is equal to atmospheric pressure, no airflow occurs.

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Intrapleural pressure in a normal person and in a person

with a pneumothorax.

• The arrows show expanding or collapsing elastic forces.

• Normally, at rest, intrapleural pressure is −5 cm H2O because of equal and opposite forces trying to collapse the lungs and expand the chest wall.

• With a pneumothorax, the intrapleural pressure becomes equal to atmospheric pressure, causing the lungs to collapse and the chest wall to expand.

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Pneumothorax

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CLINICAL CORRELATION

Pneumothorax.

• A 26-year-old man comes to the emergency department because of sudden dyspnea (a feeling that breathing is difficult, also called “shortness of breath”) and pain in the upper part of the left side of his chest. He has no history of any medical problems. He is 183-cm (6′2″) tall and weighs about 63.5 kg (140 lb). Blood pressure is 125/80 mm Hg, heart rate is 90/min, and respiratory rate is 22/min( usually12–15/min in a healthy adult). There are no breath sounds on the left side of his chest, which is hyperresonant (louder and more hollow-sounding) to percussion (the physician tapping on the chest with his or her fingers). The patient has a pneumothorax. Air has entered the pleural space on the left side of his chest and he is unable to expand his left lung. Therefore, there are no breath sounds on the left side of his chest and it is hyperresonant to percussion

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CLINICAL CORRELATION Pneumothorax

In this case, the pneumothorax is a primary spontaneous pneumothorax because it occurred suddenly, and is not attributable to an underlying pulmonary disease (secondary spontaneous pneumothorax) or trauma (traumatic pneumothorax).

The inability to ventilate his left lung, combined with pain and anxiety, explains his high respiratory rate

Primary spontaneous pneumothorax is most common in tall, thin males between 10 and 30 years of age, although the reason for this is not known. It is believed to occur when overexpanded alveoli rupture, perhaps as a result of a cough or sneeze. If the pneumothorax is mild and the patient is not in too much distress, it may resolve without treatment other than observation. More severe pneumothorax is treated by inserting a catheter or chest tube through the skin and intercostal muscles into the pleural space to allow removal of the air by external suction.

A tension pneumothorax is a potentially life-threatening disorder that most commonly occurs as a result of trauma or lung injury. Air enters the pleural space on inspiration but cannot leave on expiration, progressively increasing intrapleural pressure above atmospheric. This can compress the structures on the affected side of the chest (e.g., blood vessels, heart,

etc.) and eventually the structures on the other side of the chest as well.

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Boyle's law,

• P1V1 = P2V2 constant

• PV = Pressure multiplied by volume equals some constant k

•

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Mechanics of Respiration

Patmospheric

Palveolar

Rest

Patmospheric

PalveolarPalveolar

Rest Inhalation

↓ Pleural Pressure

Patmospheric

Muscles that cause lung expansion and contraction during inspiration and expiration

The lungs can be expanded and contracted in two ways:

• (1) by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity

• (2) by elevation and depression of the ribs to increase and decrease the anteroposterior diameter of chest wall

• Normal quiet breathing is accomplished almost entirely by the first method, that is, by movement of the diaphragm.

• During inspiration, contraction of the diaphragm pulls the lower surfaces of the lungs downward.

• Then, during expiration, the diaphragm simply relaxes, and the elastic recoil of the lungs, chest wall, and abdominal structures compresses the lungs and expels the air

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Muscles of respiration

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Function of respiratory muscles

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Action of expiratory muscle during forceful breathing

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Intra-alveolar and intrapleural pressure changes throughout the respiratory cycle

Movement of Air in and Out of Lungs During Tidal Breathing

Changes in pressure

• Pleural Pressures• Resting -5 cm

H20• Inspiration -8 cm

H20

• Alveolar Pressure• Resting 0 cm

H20• Inspiration

-1 cm H20• Expiration 1 cm

H20

Volume pressure curves

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Duration of inspiration = 2 secLength of expiration 3 sec

Changes of pressure and volume during Eupneic Respiratory Cycle

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Pleural pressure

• Pleural pressure is the pressure of the fluid in the thin space between the lung pleura and the chest wall pleura.

• It is slightly negative pressure compared to atmospheric pressure .

• The negative pressure is because of the balanced forces generated by the chest wall (tends to increase lung volume) and the lungs (tends to shrink, i.e. elastic recoil).

• The normal pleural pressure at the beginning of inspiration is about −5 centimeters of water,

• During normal inspiration, expansion of the chest cage pulls outward on the lungs with greater force and creates more negative pressure, to an average of about −7.5 centimeters of water.

Alveolar pressure

• Is the pressure of the air inside the lungalveoli. It is equal to 0 cm H2O when no air is flowing into or out of the lungs.

• During the respiratory cycle alveolar pressureranges between -1 cm H2O to +1 cm H2O. The quiet cycle is made of inspiration (2 seconds) and expiration (2-3 seconds).

Transpulmonary Pressure

• Is the alveolar-distending pressure is

often referred to as the

transpulmonary pressure

• It is pressure difference between that

in the alveoli and that on the outer

surfaces of the lungs (pleural

pressure)

• It is a measure of the elastic forces

in the lungs that tend to collapse the

lungs at each instant of respiration,

called the recoil pressure.

Changes in transpulmonary pressure of pressure and volume during tidal (Eupneic ) Respiratory Cycle

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Intra-alveolar and intrapleural pressure changes throughout the respiratory cycle.

• During inspiration, intra-alveolar pressure is less than atmospheric pressure.

• During expiration, intra-alveolar pressure is greater than atmospheric pressure.

• At the end of both inspiration and expiration, intra-alveolar pressure is equal to atmospheric pressure because the alveoli are in direct communication with the atmosphere, and air continues to flow down its pressure gradient until the two pressures equilibrate.

• Throughout the respiratory cycle, intrapleural pressure is less than intra-alveolar pressure.

• Thus, a transmural pressure gradient always exists, and the lung is always stretched to some degree, even during expiration.

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Pulmonary ventilation: Summary of events during inspiration (Tidal Breathing)

1. Inspiration is an active process, normally produced by contraction of the inspiratory muscles (negative-pressure breathing).

2. 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 expand

5. Intrapleural pressure becomes more negative

6. Alveolar transmural pressure gradient increases

7. Alveoli expand (according to their individual compliance curves) in response to the increased transmural pressure gradient.

8. Alveolar pressure falls below atmospheric pressure as the alveolar volume increases, thus establishing a pressure gradient for airflow

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Pulmonary ventilation: Summary of events during

inspiration (Tidal Breathing)

• Expiration (passive)

• Brain ceases inspiratory command

• Inspiratory muscles relax

• Thoracic volume decreases, causing intrapleural pressure to become less negative and decreasing the alveolar transmural pressure gradient

• Decreased alveolar transmural pressure gradient allows the increased alveolar elastic recoil to return the alveoli to their pre inspiratory volumes

• Decreased alveolar volume increases alveolar pressure above atmospheric pressure, thus establishing a pressure gradient for airflow

• Air flows out of the alveoli until alveolar pressure equilibrates with atmospheric pressure

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Representation of alveolar, intrapleural pressures at end expiration (left) and during a strong inspiratory effort

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Maximal inspiratory intrapleural pressures can be as low as –80 cm H2O.

Pressures across the alveoli and conducting airways during forced expiration in a normal person and a person with

emphysema and dynamic compression of airways

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Alveolar pressure is the sum of the pleural pressure and

elastic recoil pressure of the lung

Schematic diagram illustrating dynamic compression of airways and the equal pressure point hypothesis during a forced expiration. Left: Passive (eupneic) expiration. Intrapleural pressure is –8 cm H2O, alveolar elastic recoil pressure is +10 cm H2O, and alveolar pressure is +2 cm H2O. Right: Forced expiration at the same lung volume. Intrapleural pressure is +25 cm H2O, alveolar elastic recoil pressure is +10 cm H2O, and alveolar pressure is +35 cm H2O. (

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Increasing effort during forced expiration can generate a positive intrapleuralpressure, which can be as high as 120 cm H2O during a maximal forced expiratory effort

Schematic diagram illustrating dynamic compression of airways and the equal pressure point hypothesis during

Alveolar elastic recoil is also important in opposing dynamic compression of the airways because of its role in the traction of the alveolar septa on small airways,

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Additional notes

• Expiratory muscle contraction is required when respiration is increased during exercise or in the presence of severe respiratory disease

• Obesity, pregnancy, wall can impede the effectiveness of the diaphragm in enlarging the thoracic cavity.

• Damage to the phrenic nerves can lead to paralysis of the diaphragm.

• When a phrenic nerve is damaged, that portion of the diaphragm moves up rather than down during inspiration

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Additional Notes

• Muscular dystrophy, poliomyelitis Neuromuscular disorders (ALS , Myasthenia gravis can lead to respiratory failure

• Such patients require mechanical respirators (positive-pressure breathing)

• Spine Curvature Disorders disorders decrease lung and chest wall compliance • Lordosis. Also called swayback, the spine of a person with

lordosis curves significantly inward at the lower back.• Kyphosis. Kyphosis is characterized by an abnormally rounded

upper back• Scoliosis. A person with scoliosis has a sideways curve to their

spine. The curve is often S-shaped or C-shaped.

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