2.1 Mechanics of Breathing
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Questions and Answers

During expiration, what happens to the intrapleural pressure (IPP)?

  • It stays the same.
  • It decreases.
  • It increases. (correct)
  • It becomes positive.

    • What is the primary muscle of inspiration?

  • Diaphragm (correct)
  • Scalenes
  • Abdominal muscles
  • External intercostals

    • What happens when intrathoracic pressure is increased during CPR?

  • The diaphragm descends further.
  • Blood is forced out of the heart into great arteries. (correct)
  • Venous return increases.
  • The heart fills with blood.

    • In what position are patients often found post-exercise, COPD, or with epiglottitis?

    <p>&quot;Tripod&quot; position</p> Signup and view all the answers

    What causes a transient decrease in left ventricle (LV) filling?

    <p>Increased intrathoracic pressure</p> Signup and view all the answers

    What happens to alveolar pressure during forced exhalation?

    <p>It increases.</p> Signup and view all the answers

    Which lung volume/capacity measure represents the largest amount of air that can be expired after forced maximal inspiration?

    <p>Forced vital capacity (FVC)</p> Signup and view all the answers

    Which lung volume measurement is not included in calculating Vital Capacity (VC)?

    <p>Residual volume (RV)</p> Signup and view all the answers

    In measurements of forced vital capacity, what does FEV1/FVC ratio measure and represent?

    <p>Expiratory airway resistance of larger airways</p> Signup and view all the answers

    What happens to airflow as expiratory effort increases beyond a certain point according to the text?

    <p>Airflow increases up to a point, but more positive IPP does not increase airflow</p> Signup and view all the answers

    What happens to the chest wall recoil below 70% total lung capacity (TLC)?

    <p>It is outward</p> Signup and view all the answers

    In the presence of a pneumothorax, what effect does it have on the interaction between the lung and chest wall?

    <p>Interdependence ceases</p> Signup and view all the answers

    At what lung volume do both lung and chest wall elastic recoil become inward?

    <p>Above 70% TLC</p> Signup and view all the answers

    What do high lung volumes (>70%) result in terms of mouth pressure?

    <p>Positive pressure</p> Signup and view all the answers

    Which factor contributes to higher airway resistance in emphysema?

    <p>Secretions and inflammation</p> Signup and view all the answers

    What is the main cause of dynamic compression of small airways during forced expiration?

    <p>Frictional resistance</p> Signup and view all the answers

    What happens at the equal pressure point during a forced expiration?

    <p>Pressure inside the airway equals pressure outside the airway</p> Signup and view all the answers

    In emphysema, why do individuals struggle to achieve high airflow rates?

    <p>Less alveolar elastic recoil</p> Signup and view all the answers

    What is critical in generating driving pressure for airflow during forced expiration?

    <p>Alveolar pressure</p> Signup and view all the answers

    What does negative pressure breathing primarily cause in the upper airway?

    <p>Inward pulling</p> Signup and view all the answers

    What type of flow occurs in numerous small airways arranged in parallel?

    <p>Laminar flow</p> Signup and view all the answers

    What predominates in controlling the normal lung under typical conditions?

    <p>Parasympathetic control</p> Signup and view all the answers

    What mathematical expression represents Boyle's Law?

    <p>P1V1 = P2V2</p> Signup and view all the answers

    What is the significance of a pressure gradient in the movement of air?

    <p>Air moves from high pressure to low pressure areas</p> Signup and view all the answers

    In negative pressure breathing, how does air move into the lungs?

    <p>As a result of airway pressure decreasing below atmospheric pressure</p> Signup and view all the answers

    What is the functional residual capacity (FRC) of the lungs?

    <p>Volume of gas in the lungs at the end of passive expiration</p> Signup and view all the answers

    What role does intrapleural pressure play in lung expansion?

    <p>Responsible for mechanical interaction between lung and chest wall</p> Signup and view all the answers

    During inspiration, what happens to alveoli?

    <p>They collapse inward due to increased transmural pressure difference</p> Signup and view all the answers

    How does positive pressure breathing differ from negative pressure breathing?

    <p>In positive pressure breathing, ambient pressure exceeds airway pressure causing air movement</p> Signup and view all the answers

    'Alveolar pressure is considered 0 cm H2O at end-expiration' - What does this imply about airflow?

    <p>'Air moves out of the lungs'</p> Signup and view all the answers

    How does decreased lung volume affect airway pressure?

    <p>Increases airway pressure above atmospheric pressure</p> Signup and view all the answers

    Surfactant is produced in alveolar type II cells and secreted into the alveolus.

    <p>True</p> Signup and view all the answers

    Pulmonary tissue resistance is mainly caused by the friction of stationary tissues.

    <p>False</p> Signup and view all the answers

    Elastic resistance in obstructive disease increases as tidal volume increases.

    <p>False</p> Signup and view all the answers

    Friction of moving tissues causes non-elastic resistance in the lungs.

    <p>True</p> Signup and view all the answers

    What is the term used to define the mechanical interaction of the lung and chest wall and its relation to negative intrapleural pressure?

    <p>Alveolar interdependence</p> Signup and view all the answers

    Which factor contributes to alterations in airway resistance?

    <p>Constriction of bronchial smooth muscle</p> Signup and view all the answers

    What is primarily responsible for the dynamic compression of small airways during forced expiration?

    <p>Pressure difference inside and outside the airway</p> Signup and view all the answers

    Which factor does not contribute to the generation of a pressure gradient between atmosphere and alveoli?

    <p>Airway resistance</p> Signup and view all the answers

    In what physiological condition would one expect to see an increase in the work of breathing?

    <p>Emphysema with high airflow rates</p> Signup and view all the answers

    What is the significance of the equal pressure point during a forced expiration?

    <p>It represents a location where airflow ceases due to equal pressures inside and outside the airway.</p> Signup and view all the answers

    How does low lung volume contribute to the formation of dynamic compression during forced expiration?

    <p>It triggers a reduction in the cross-sectional area of small airways.</p> Signup and view all the answers

    In obstructive diseases, what is a common cause of fixed intra- or extra-thoracic obstructions?

    <p>Foreign bodies or tumors.</p> Signup and view all the answers

    Why is peak expiratory flow decreased in both obstructive and restrictive diseases?

    <p>Because of reduced airway diameter.</p> Signup and view all the answers

    What determines the movement of lungs during respiration?

    <p>Passive forces and two types of resistance.</p> Signup and view all the answers

    Which condition leads to variable extra-thoracic obstruction as described in the text?

    <p>Fat deposits or weakened pharyngeal muscles.</p> Signup and view all the answers

    What physiological event occurs when intrapleural pressure becomes equal to atmospheric pressure during a pneumothorax?

    <p>Air moves into the lungs until intrapleural pressure equalizes with atmospheric pressure</p> Signup and view all the answers

    What is the physiological significance of the outward recoil of the chest wall below 70% total lung capacity (TLC)?

    <p>Maintains equilibrium with lung elastic recoil</p> Signup and view all the answers

    How does dynamic compression affect small airways during forced expiration?

    <p>Leads to small airway collapse after the equal pressure point</p> Signup and view all the answers

    What role does alveolar elastic recoil pressure play during forced expiration?

    <p>Opposes dynamic compression of the airways</p> Signup and view all the answers

    How do high lung volumes (70%) affect mouth pressure during breathing?

    <p>Mouth pressure becomes positive</p> Signup and view all the answers

    'Laminar flow' in numerous small airways arranged in parallel is primarily due to:

    <p>'Traction' on small airways that decreases resistance</p> Signup and view all the answers

    What is the primary function of the sternocleidomastoid muscle during unilateral contraction?

    <p>Flexes the head laterally</p> Signup and view all the answers

    Which muscles assist in elevating the ribs to expand the thoracic cavity during deep and forceful respiration?

    <p>Pectoralis major, pectoralis minor, serratus anterior</p> Signup and view all the answers

    What is the normal ratio between inspiration and expiration (I:E ratio)?

    <p>1:2</p> Signup and view all the answers

    During passive expiration, what is responsible for decreasing lung volume?

    <p>Inward recoil of elastic tissue in the lung</p> Signup and view all the answers

    What is the function of abdominal muscles during expiration?

    <p>Immobilize the lower thorax and decrease thoracic dimensions</p> Signup and view all the answers

    What is the primary factor causing active expiration?

    <p>Contraction of abdominal muscles</p> Signup and view all the answers

    How does the posterior scalene muscle contribute to breathing during inspiration?

    <p>Elevate the second rib</p> Signup and view all the answers

    What is the main factor contributing to the high compliance of lungs?

    <p>Loss of elastance</p> Signup and view all the answers

    Why are alveoli less compliant at high lung volumes?

    <p>Increased elastance</p> Signup and view all the answers

    What type of compliance is measured while airflow is occurring?

    <p>Dynamic compliance</p> Signup and view all the answers

    What causes decreased lung compliance in fibrosis?

    <p>Increase in elastance</p> Signup and view all the answers

    Which condition leads to increased lung compliance due to the destruction of elastic septa?

    <p>Emphysema</p> Signup and view all the answers

    What is the role of pulmonary surfactant in alveoli stabilization?

    <p>Equalizes pressure inside smaller alveoli</p> Signup and view all the answers

    What is the main function of surfactant molecules in alveoli?

    <p>Reduce surface tension at the air-liquid interface</p> Signup and view all the answers

    Which law states the pressure within a spherical bubble is directly proportional to the surface tension and inversely proportional to the radius of the bubble?

    <p>La Place's Law</p> Signup and view all the answers

    What is the main cause of atelectasis during anesthesia?

    <p>Decreased FRC</p> Signup and view all the answers

    Study Notes

    Muscles of Inspiration

    • Sternocleidomastoid: unilateral contraction flexes head laterally, bilateral contraction pulls head forward, and assists pump-handle action of deep respiration
    • Pectoralis major, pectoralis minor, and serratus anterior: not true thoracic wall muscles, but extend from thoracic cage (axial skeleton) and help elevate ribs to expand thoracic cavity
    • Pulmonary rehab builds accessory muscles to assist breathing (lung disease)

    Accessory Muscles of Inspiration

    • Scalenes: anterior, middle, and posterior scalenes contract to lift the upper thorax
      • Anterior scalene: flexes head
      • Middle scalene: flexes neck laterally and elevates first rib
      • Posterior scalene: flexes neck laterally and elevates second rib
    • Light to moderate contraction of scalenes fixes/immobilizes upper thorax, allowing external intercostals to raise lower ribs to a greater degree

    Expiration

    • Decreased lung volume increases pressure in the airways, causing air to flow out of lungs
    • Expiration is approximately twice as long as inspiration
    • Normal I:E ratio is 1:2-1:4
    • Two lung factors decrease lung volume:
      • Inward recoil of elastic tissue of lung to resting state
      • Surface tension recoil in alveoli (more important than elastic tissue recoil)

    Muscles of Expiration

    • Abdominal muscles: attached to lower rib cage and upper portion of pelvic girdle, including pubic symphysis
    • Contraction of abdominal muscles:
      • Immobilizes the lower thorax and pulls down on the rib cage
      • Decreases all three dimensions of the thorax (transverse, anterior-posterior, vertical)
      • Increases intra-abdominal pressure, pushing up on the diaphragm and decreasing the vertical dimension of the thorax

    Summary of Events During a Eupneic Breath

    • Muscular contraction/relaxation changes thoracic volume
    • Change in IPP (intrapleural pressure) and alveolar pressure
    • Air flow and change in lung volume

    Pressure-Volume Relationships in the Respiratory System

    • Compliance (C): measure of the lung's distensibility (ease with which lungs can be inflated)
      • High compliance: lungs easily distended, low elastance
      • Low compliance: lungs difficult to distend, high elastance
    • Compliance of the lung is reflected in both elastic tissue recoil and surface tension recoil
    • Lung compliance is volume-dependent: more compliant at low volumes, less compliant at high volumes

    Non-Linear Aspects of Compliance

    • Compliance is volume-dependent
    • Lungs are more compliant at low volumes (less elastic recoil) and less compliant at high volumes (more elastic recoil)
    • At high lung volumes, lungs are already highly stretched, so an increased IPP yields a small increase in volume
    • Lungs are not compliant at very low and very high lung volumes
    • At approximately FRC (~3000 ml), the compliance curve becomes linear

    Types of Compliance

    • Static compliance: measured while no airflow is occurring
    • Dynamic compliance: measured during inspiration and expiration, with airflow
    • Dynamic compliance is measured using peak pressure and plateau pressure

    Variations in Compliance

    • Increased compliance: lungs easily distended, low elastance (e.g., emphysema)
    • Decreased compliance: lungs difficult to distend, high elastance (e.g., fibrosis)
    • Compliance changes with breathing frequency and muscle tone

    Histology of Abnormal Compliance

    • Fibrosis: decreased compliance due to excess fibrous tissue
    • Emphysema: increased compliance due to destruction of elastic septa
    • Patient with emphysema has:
      • Large lung volume due to air trapping
      • Non-compliant chest wall
      • Difficulty expiring due to loss of elasticity### Generation of a Pressure Difference
    • The objectives of mechanics of breathing include describing the generation of a pressure gradient between the atmosphere and alveoli, and the passive expansion and recoil of the alveoli.

    Interaction of Lung and Chest Wall

    • The lung and chest wall have opposing recoil forces: the lung's elastic recoil is inward, while the chest wall's elastic recoil is outward.
    • The functional residual capacity (FRC) is the volume of gas in the lungs at the end of normal tidal expiration, where the outward recoil of the chest wall equals the inward recoil of the lungs.
    • At high lung volumes (>70% TLC), the chest wall elastic recoil is inward, and at low lung volumes (<70% TLC), the chest wall elastic recoil is outward.

    Pressure-Volume Relationships in the Respiratory System

    • Compliance (C) is a measure of the lung's distensibility, defined as the change in volume (ΔV) per unit change in pressure (ΔP): C = ΔV/ΔP.
    • There are two types of compliance: static compliance (measured in the absence of gas flow) and dynamic compliance (measured in the presence of gas flow).
    • Lung compliance is reflected in both elastic tissue recoil and surface tension recoil.
    • The surface tension of the alveolar fluid-air interface contributes to the elastic recoil forces of the lung.

    Elastance

    • Elastance is the tendency to oppose stretch, and is the inverse of compliance.
    • Elastic tissue recoil and surface tension recoil both contribute to the lung's elastance.

    Surface Tension

    • Surface tension forces at the alveolar fluid-air interface attempt to collapse the alveoli.
    • Pulmonary surfactant decreases surface tension, stabilizing the alveoli and preventing collapse.
    • Surfactant deficiency can lead to respiratory distress syndrome.

    Alveolar Interdependence

    • Mechanical interdependence between adjacent alveoli stabilizes them and prevents collapse.
    • Collapsing alveoli would increase the stress on the walls of adjacent alveoli, tending to hold them open.

    Airway Resistance

    • Airways resistance decreases with increasing lung volume.
    • Small airways are compressible and traction on small airways increases at higher lung volumes.
    • Dynamic compression of small airways can cause airway collapse during forced expiration.

    Dynamic Compression of Airways

    • Dynamic compression occurs when the pressure inside the airway equals the pressure outside the airway, causing airway collapse.
    • The equal pressure point is the point during forced expiration where the driving pressure equals the surrounding peribronchial pressure.
    • Dynamic compression is affected by alveolar elastic recoil pressure and lung volume.

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    2.1 Mechanics of Breathing.pptx

    Description

    This quiz discusses the interaction between the lungs and chest wall, focusing on the elastic recoil and pressures involved. It explains how disturbances in this relationship, such as pneumothorax, can affect lung function.

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