Respiratory Physiology Flashcards

1
Q

Overview

A

3 Processes involved in exchange of air:

1) Pulmonary Ventilation
a) Inspiration
b) Expiration
2) External Respiration
3) Internal Respiration

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2
Q

Pulmonary Ventilation

A
  • Results of pressure gradients caused by changes in thoracic cavity volume
  • Boyle’s Law
  • Gas volume is inversely proportional to pressure
  • As vol increases, P decreases (+ vice versa) - for the same # of molecules of air (gas amount remains constant)
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3
Q

Pulmonary Ventilation Pressures Involved

A

a) Atmospheric pressure = Patm = 760 mmHg (sea level)
b) Intrapulmonary Pressure = Ppul = air pressure inside lungs (= Patm between breaths)
c) Intrapleural Pressure = Pip = fluid pressure in pleural cavity
- always < Ppul (healthy individual)
- Usually < Patm = ~4mmHg less = 756 mmHg at rest
- Thoracic wall recoils out, lungs recoil in - but fluid holds them together = Pip lowers slightly

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4
Q

Pulmonary Ventilation Processe

A

1) Quiet Inspiration
2) Forced Inspiration
3) Quiet Expiration
4) Forced Expiration

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5
Q

Quiet Inspiration

A
  • Active process (muscle contract)
  • At start Patm = Ppul (760 mmHg) - no air moves, then:
    1) Diaphragm, ext intercostals contract (active), higher volume of thoracic cavity
    2) Lungs resist expansion = Pip lowers (756 -> 754 mmHg)
    3) Higher pressure difference between Ppul and Pip pushes lungs out –> lungs expand = Ppul lowers –> 758 mmHg)
    4) Air moves in down P gradient (until Ppul = Patm)
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6
Q

Forced Inspiration

A
  • Active process
  • diaphragm, external intercostals + sternocleidomastoids, pectorals minors, scalene contract (active)
  • Great increase in volume of thoracic cavity - pressure gradient higher, and more air moves in
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7
Q

Quiet Expiration

A
  • Relax diaphragm, ext. intercostals = lungs to resting size = lower thoracic cavity size (passive process)
  • Vol lower, Pip higher (754 -> 756 mmHg) = Ppul increased (760–> 762 mmHg) –> air moves out down pressure gradient
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8
Q

Forced Expiration

A
  • Laboured or impeded (e.g. asthma) breathing
  • Relax diaphragm, ext. intercostals + contract internal intercostals, abdominals (active process)
  • Pip increased –> lung volume decreased = Ppul increased and air moves out
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9
Q

Stretch in Lungs Determined by

A
  • Compliance = effort needed to stretch lungs; low = much effort
  • Recoil = ability to return to resting size after stretch
  • both = result of elastic CT + surfactant
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10
Q

Lungs Collapse Prevented by

A

1) Pip is always below Ppul
- Pneumothorax = air in pleural cavity
- Patm = Pip = Ppul : lungs collapse, thoracic wall expands
2) Presence of Surfactant
= lipoprotein/phospholipid mixture
- in watery fil coating alveoli - decreased surface tension
- Allows easier stretch of lungs (increases compliance)
- Prevents alveolar collapse

  • Respiratory Distress Syndorme
  • newborns <7 months gestation
  • inadequate surfactant : alveoli tend to collapse (low compliance)
  • Effort high –> exhaustion, death
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11
Q

Air Flow and Airway Resistance Formula

A
F = P/R
F= air flow
P = Patm - Ppul
R= airway resistance
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12
Q

Resistance of Airway Determined by:

A

Resistance determined by diameter of bronchi, bronchioles

  • Asthma, bronchitis, emphysema increased airway R - more difficult to expire than to inspire
  • Inspiratory mechanics open airways/ expiratory close airways
  • SNS - dilates bronchiolar smooth muscle (bronchodilation)
  • PSNS - contracts it (bronchoconstriction)
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13
Q

Respiratory Volumes

A
  • Measured using a spirometer ; 1 respiration = 1 inspiration + 1 expiration
  • Volumes:
    a) Tidal Vol (TV) - inspired or expired air during quiet respiration (~500ml)
    b) Inspiratory Reserve Volume (IRV) - excess air over TV taken in on a max inspiration (~3000 ml)
    c) Expiratory Reserve Volume (ERV) - excess air over TV pushed out on max expiration (~1200 ml)
    d) Residual Vol (RV) - volume of air in lungs after maximal expiration (~1200 ml)
    e) Minute Respiratory Vol = TV X Respiratory Rate e.g. = 500mL X 12 breaths/minute = ~6 L/min (on average)
    f) Forced Expiratory Volume in 1 second (FEV1) - volumes expired in 1 sec., with max. effort, following max. inspiration
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14
Q

Respiratory Capacities

A
  • 2 or more volumes
    a) Inspiratory Capacity (IC) = TV + IRV
    b) Vital Capacity (VC) = TV + IRV + ERV - largest volume in and out of lungs
    c) Total Lung Capacity (TLC) - max amount of air lungs can hold = TV + IRV +ERV + RV (=VC + RV)
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15
Q

Clinical Application

A
  • FEV1 is measured while measuring VC + expressed as %VC (allows correction for body size)
  • Usually FEV1 = ~80% VC
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16
Q

Measurements Allow Diagnoses of

A

1) Obstructive Disorders
- e.g. emphysema, asthma, cystic fibrosis
- Hard to expire = Increased R
- RV increased, VC decreased, FEV1 <80% VC
2) Restrictive Disorders
- e.g. scoliosis, pneumothorax
- Restrict lug expansion
- Hard to inspire
- IC decreased, VC decreased, FEV1 decreased (but FEV1 = 80% VC)