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  • The lungs are a remarkable feat of engineering. They receive the entire right ventricular cardiac output and they are called upon at birth to function without cessation. The lungs are contained in a space with a volume of approximately 4 L, but they have a surface area for gas exchange that is the size of a tennis court (∼85 m2). This large surface area is comprised of myriads of independently functioning respiratory units. Unlike the heart, but similar to the kidneys, the lungs demonstrate functional unity; that is, each unit is structurally identical and functions just like every other unit. a marathon runner who staggers across the 26-mile finish line in less than 3 hours or someone who swims the English Channel in record time is rarely limited by the amount of oxygen taken up by the lungs. The reason is that gas exchange can increase more than 20-fold to meet the body's energy demands. These examples of human activity not only underscore the functional capacity of the lungs but also illustrate the important role respiration plays in our extraordinary adaptability.
  • Explain Pip, Palv and Ptp (transpulmonary)
  • Values after a quiet expiration
  • Explain static & dynamic lung components..
  • *The component which only causes change in volume is refered to as static component. E,g. transpulmonary P and compliance determine lung volume only……whereas the parameter that causes air flow is refered to as dynamic component. E.g. alveolar pressure (Palv)The key message in Figure 26-15 is that during inspiration, the negative shift in PIP has two effects. Thebody invests some of the energy represented by %PIP into transiently making PA more negative (dynamiccomponent). The result is that air flows into the lungs, and VL increases. But this investment in PA is onlytransient. Throughout inspiration, the body invests an increasingly greater fraction of its energy in makingPTP more positive (static component). The result is that the body maintains the new, higher VL. By the endof inspiration, the body invests all of the energy represented by %PIP into maintaining VL and none intofurther expansion. The situation is not unlike that faced by Julius Caesar as he, with finite resources,conquered Gaul. At first, he invested all of his resources in expanding his territory at the expense of thefeisty Belgians. But as the conquered territory grew, he was forced to invest an increasingly greater fractionof his resources in maintaining the newly conquered territory. In the end, he necessarily invested all of hisresources into maintaining his territory, and was unable to expand further.
  • Ptp = Palv – Pip
  • What would happen if, having inflated the lungs to TLC, we allowed PIP to increase to 0 cm H2O onceagain? Obviously, the VL would decrease. However, the lungs follow a different path during deflation (seeFig. 26-5B, upper blue curve). The difference between the inflation and the deflation paths is known ashysteresis, and it exists because a greater pressure difference is required to open a previously closedairway than to keep an open airway from closing. As an example, the horizontal line in Figure 26-5B showsthat inflating collapsed lungs to FRC requires a PIP of -12 cm H2O, whereas maintaining previously inflatedlungs at FRC requires a PIP of only -5 cm H2O. During normal respiration, the lungs exhibit much lesshysteresis, and the hysteresis loop (see Fig. 26-5B, green loop) lies close to the deflation limb of the blueloop.Green small compliance curves – Dynamic Compliance
  • *In emphysema, the situation is reversed. The disease process, a common consequence of cigarettesmoking, destroys pulmonary tissue and makes the lungs rather floppy. An important part of the diseaseprocess is the destruction of the extracellular matrix, including elastin, by elastase released frommacrophages Normal mice that are exposed to cigarette smoke develop emphysema rapidly, whereas thedisease does not develop in "smoker" mice lacking the macrophage elastase gene. The same increase inPTP that produces a 500-ml VL increase in normal lungs produces a substantially larger VL increase inlungs with emphysema. In other words, static compliance is much greater (i.e., much less elastic recoil). Because it requires work to inflate the lungs against their elastic recoil, one might think that a littleemphysema might be a good thing. Although it is true that patients with emphysema exert less effort toinflate their lungs, the cigarette smoker pays a terrible price for this small advantage: The destruction ofpulmonary architecture also makes emphysematous airways more prone to collapse during expiration,drastically increasing airway resistance. Hence in emphysema, static compliance increases – since volume is increasing; but dynamic compliance decreases – decreased airflow.
  • Transcript

      Dr. Faraz A. Bokhari
    • 2. If you cant breathe, nothing else matters!
      (American Lung Association)
    • 3. Introduction
      Why respire?
      Gas exchange
      Host defense (barrier b/w outside and inside)
      Metabolism (produces/metabolizes compounds)
      Gas exchange
      Pulmonary ventilation
      Diffusion of O2 and CO2 b/w alveoli and blood
      Transport of O2 and CO2 in blood and body fluids to & from body's tissue cells
      Regulation of ventilation
    • 4. Physiological Anatomy
      Upper airway
      All structures from nose to the vocal cords, including sinuses and the larynx
      Conditioning of inspired air
      Lower airway
      Trachea, airways & alveoli
    • 5.
    • 6.
    • 7. The Airway Tree:Conducting zone
      Consists of trachea and first 16 generations of airway branches
      First four generations are subjected to changes in -ve and +ve pressures, & contain a considerable amount of cartilage (to prevent airway collapse)
      Cartilage present up to lobar and segmental bronchi
      Disappears in bronchioles
      Bronchioles are suspended by elastic tissue of lung parenchyma
      This elasticity keeps them patent
      Blood supply: Bronchial vessels
      No gas exchange
    • 8. The Airway Tree:Respiratory zone
      Composed of last seven generations
      Consists of respiratory bronchioles, alveolar ducts and alveoli
      Blood supply: pulmonary circulation
      Pulmonary circulation receives all of CO
    • 9. The Airway Tree:Respiratory zone
      Adult lungs contain 300 to 500 million alveoli
      Combined internal surface area: 75 m2
      Represents one of the largest biological membranes in the body
      With age number and size increases till adolescence!
      after adolescence, alveoli only increase in size
      Smoking induced damage can be reversed in a limited way only!
    • 10. Physiological Anatomy
      Lung are covered by the visceralpleura and are encased by the parietal pleura
      Potential space b/w these 2 layers
      Layer of fluid allows for smooth gliding of lung as it expands in the chest
      Pressure within this space is normally kept negative
    • 11. Lung-Chest Wall Interaction
    • 12.
    • 13. Mechanics of Pulmonary Ventilation
      Lungs can be expanded and contracted in 2 ways:
      By downward and upward movement of the diaphragm
      To lengthen or shorten the chest cavity
      By elevation and depression of the ribs
      To increase and decrease the anteroposterior diameter of the chest cavity
      Physical events
      Pump Handle movement
      Bucket-handle movement
    • 14. Pump Handle – AP Diameter
    • 15. Bucket Handle – Lateral Expansion
    • 16. Muscles of Respiration
      Diaphram (domes descend – increase longitudinal aspect)
      External intercostals (elevate ribs – increase AP aspect)
      Sternocleidomastoid muscles (lift upward on the sternum)
      Scaleni (lift the first two ribs)
      Quiet breathing
      Passive recoil of lungs
      Active breathing
      Internal intercostals (depress ribs)
      Abdominal recti (depress lower ribs, compress abdominal contents)
      External/internal oblique
    • 17. Inspiratory Sequence – General Concept
    • 18. Quiet Inspiratory Sequence -General Concept
    • 19. Quiet Expiratory Sequence -General Concept
    • 20. Pressures Involved in Breathing
      Barometric pressure (Pb)
      Intrapleural pressure (Pip)
      Alveolar pressure (Palv)
      Transpulmonary pressure (Ptp)
    • 21. Pressures Involved in Breathing
      Barometeric P
      P exerted by the air we breathe
      @ sea level: 760 mmHg
      Dalton’s law:
      Pb is equal to sum of partial pressures of individual gases
      Pb = PN+PO2+PH2O+PCO2
      Changes in respiratory pressures during breathing are often expressed as pressure relative to atmospheric P
      When relative pressures are used, Pb = zero
    • 22. Partial pressures and percentages of Respiratory Gases at Sea Level (PB = 760 mm Hg)
    • 23. Pressures Involved in Breathing
      Intrapleural Pressure
      Less than Pb
      Since the 2 elastic recoils are opposite
      Pip in fact is intrathoracic pressure
      In upright subject:
      Greatest vacuum (least Pip) – lung apex
      Lowest vacuum (highest Pip) – lung base
      Average (Resting) value = -5 cm water
    • 24. Pressures Involved in Breathing
      Alveolar pressure (Palv)
      Pressure inside the alveoli
      Decreases during inspiration
      Atmospheric air fills in
      Transpulmonary pressure (Ptp)
      Distending pressure
      Ptp = Palv – Pip
    • 25. Interaction of Pressures Involved in Breathing
    • 26. Pneumothorax
    • 27. Static Vs Dynamic Lung
      Cadaver lung
      Collapsed lung
      Initially pressure is required to ‘regain’ original lung & chest wall volume (static component)
      The lung is now expanded
      In vivo, over and above ‘static P’, more pressure is required to overcome inertia and resistance of tissues (airways) & air molecules (dynamic component)
    • 28. Static Vs Dynamic Lung
      Ptp = Palv – Pip
      Pip = (-Ptp) + Palv
      Thus, Pip has 2 aspects*:
      Transpulmonary pressure (Ptp) – Static component
      Alveolar pressure (Palv) – Dynamic component
      Compliance (dV/dP) varies
      Static compliance
      Change in volume for a given change in Ptp with zero gas flow
      Dynamic compliance
      Measurements made by monitoring TD used
      While intra thoracic pressure (Pip) measured during the instance of zero air flow occurring at the end inspiritory and expiratory levels with each breath
    • 29. Compliance*
      Extent to which lungs will expand for each unit increase in Ptp
      Stages of compliance:
      Stage1 [Stable VL):
      Less volume change for pressure change
      Surface tension makes it difficult to open an airway
      Stage2 (airway start opening):
      Stepwise decreases in PIP beyond -8 - produce dV
      dV first small, then larger
    • 30. Compliance
      Linear expansion of open airways
      Limit of airway inflation
      Mostly due to surface tension
      Less due to elastic forces
    • 31. Compliance Vs Elastance
      Compliance is a measure of distensibility
      Elastance is a measure of elastic recoil
      These both oppose each other!
      Compliancedecreases as Elastanceincreases:
      Pulmonary fibrosis (restrictive lung disease)
      Pulmonary hypertension/congestion
      Decreased surfactant – increased surface tension (prematurity, artificial ventilation)
      Complianceincreases as Elastancedecreases
      Normal ageing (alteration in elastic tissue)
      Asthma (unknown reason)
      Emphysema* (obstructive lung disease)
    • 32. Compliance - Emphysema
    • 33. Compliance & Surface Tension
      ELASTIC FORCES of the lungs:
      (1) Lung tissue elastic forces
      (elastin& collagen fibers)
      (2) Elastic forces caused by surface tension
      (Tension created by fluid-air interface)
      Lung tissue elastic
      forces (air-filled lung) I/3
      of total
      Surface tension forces - 2/3
    • 34. Surfactant
      Surface active agent
      Greatly reduces surface tension of water
      Secreted by Type II alveolar epithelial cells
      Most important components:
      Surfactant apoproteins
      Calcium ions
      Premature babies lack surfactant
    • 35. Lung-Thoracic CageCompliance
      Thoracic cage has its own compliance!
      Compliance (lung-cage): 110 ml/cm water
      Compliance (lung): 200 ml/cm water
      When the lungs are expanded to high volumes/ compressed to low volumes - checked by chest compliance limitations