Chap' 19 breathing

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Chap. 19 - breathing

• AL Mina, M.D.
• Erskine College

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Air movement

• Inspiration and expiration occur due to
  differences in air pressure
• Atmospheric pressure (sea level) 760 mmHg
• At rest (lungs), pressure in lungsatmospheric
  pressureno air movement

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Figure 19.21
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Inspiration

• Inspiratory muscles activated
• Diaphragm
• External intercostals
• Phrenic nerve stimulates contraction
• Actions expand rib cage, increase vol. of
  thoracic cavity
• As volume increases, pressure decreases
• When pressure in lungsltatm pressure, air flows in

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Figure 19.23
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• During deep inspiration, accessory muscles used,
  plus diaphragm/intercostals stimulated to
  contract further

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Figure 19.24
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Lung expansion

• Not attached to rib cage
• Moves due to interaction of pleural membranes
• Adherence due to pleural fluid
• As chest wall expands, lungs follow
• Compliance ability of lungs to expand

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Exhalation

• Muscles relax
• Elastic recoil of lungs allows them to return to
  original shape
• Abdominal organs press upward
• Increase pressure causes exhalation
• Maximal exhalation
• Internal intercostals
• Abdominal muscles

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Figure 19.25
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Spirometry

• Measurement of respiratory air volumes
• 4 volumes of air
• Combine volumes to calculate respiratory
  capacities

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Volumes

• Tidal volume (TV) air that moves during normal
  breathing
• Inspiratory reserve volume (IRV) additional air
  that can be inspired during maximal inhalation
• Exp. Res. Vol. (ERV) air moved beyond normal
  exhalation
• Residual volume (RV) air that is left after ERV

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Capacities

• Insp. Capacity (IC) total vol. inspired from
  normal exhalation (TVIRV)
• Functional residual capacity (FRC) vol. in
  lungs after normal exhalation (ERVRV)
• Vital capacity (VC) total volume of air that can
  be moved (IRVTVERV)
• Total lung capacity (TLC) VCRV

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Figure 19.26
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Dead space

• Volume of air that doesnt undergo gas exchange
• Anatomic dead space volume in trachea, bronchi,
  etc that doesnt reach alveoli
• Alveolar dead space alveoli that dont exchange
  due to poor blood flow
• Physiologic dead space total of above spaces
  (normal 150 ml)

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Dead space importance

• As dead space increases, effective TV decreases
  (or as TV decreases)
• May increase work of breathing by incorporating
  accessory muscles to breathe normally

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Nonrespiratory air movements

• Cough force air against closed glottis, then
  open suddenly
• Sneeze same thing, just comes out nose (uvula
  redirects flow upward)
• Laughing/crying series of short exhalations
• Hiccup spasm of diaphragm
• Yawn - ? May be CNS effect

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Figure 19.28
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Control of breathing

• Respiratory areas in brainstem
• Adjust rate and depth of breathing
• Medullary rhythmicity center
• Dorsal respiratory group diaphragm
• Ventral respiratory group abdominals,
  intercostals

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Contd

• Pontine respiratory group
• Contribute to rhythm

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Influences on breathing

• Partial pressures
• Central chemoreceptors
• Detect central hydrogen ions, formed from influx
  of CO2 into brain
• Peripheral chemoreceptors
• Detect O2 levels
• Minor effect deoxygenated blood at 75
  capacity, receptors activated at 50

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Alterations in breathing

• Breath-holding
• Increases CO2, stimulates respiratory center
• Hyperventilation
• Increases O2, decreases CO2
• Delays stimulation of respiratory center
• can cause alkalosis, cerebral vasoconstriction,
  fainting

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Gas exchange

• Alvoli contain respiratory pores to interact
  with each other
• Respiratory membrane
• Alveolar Epithelium
• Alveolar basement membrane
• Capillary basement membrane
• Capillary epithelium

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Figure 19.33
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Alveolar cells

• Type I epithelial cells
• Type II surfactant secreting cells
• Surfactant decreases surface tension, allows
  alveoli to remain open
• Alveolar macrophages

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Diffusion

• Gases move from high to low concentration
• Atmosphere PO2 160 mmHg, PCO2 0.3
• Alveoli PCO2 40, PO2 104
• Pulm. Venules PCO2 45, PO2 40
• Pulm. Arterioles PCO2 40, PO2 104 (same as
  alveoli)

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Figure 19.35
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Transport

• O2 bound to hemoglobin (98) or dissolved in
  plasma
• Increased PO2increased saturation of hemoglobin
• PO2 high in lungs, so O2 binds
• PO2 low in tissues, so O2 releases

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Effect of carbon dioxide on hemoglobin binding
oxygen
90
At PO2 50 mmHg
80
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As you increase PCO2, decrease saturation of
hemoglobin at any given PO2.
More oxygen is released at higher partial
pressure of CO2.
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• O2 release increases with increase in
  temperature, CO2, or acidity
• All commonly found in areas of active cell
  metabolism

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CO2 transport

• Dissolved in plasma (7)
• Bound to hemoglobin (15-25)
• Bicarbonate ions (HCO3-)
• CO2H20 --? H HCO3-