Flashcards in Lecture 2 - Mechanics of breathing Deck (37)
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1
definition of breathing
bodily function that leads to ventilation of the lungs
also known as external respiration
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Ventilation definition
Process of moving gases in - inspiration and out (expiration) of the lungs
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Mechanics of breathing involves...
describes the structural and physiological bases of ventilation
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in what 2 ways do diseases affect ventilation
obstructive conditions: asthma, COPD, lung cancer
Restrictive:
Intrinsic : pulmobary fibrosis
extrinsic: pneumothorax, disorders of thoracic skeleton
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How will gas flow?
through patent airways according to the pressure gradient between atmosphere (barometric pressure) and alveoli
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Pressure during inspiration
Pb (atmospheric pressure) is greater than alveolar pressure
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Pressure during expiration
Aloveolar pressure (variable - Pa) is greater than the atmospheric pressure
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Why does airway obstruction have a major effect on flow? describe in terms of the equation
flow = (k x delta PX r^4)/ (L)
As flow depends on the radius, airway obstruction would majorly affect it.
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How is generation of Delta P brought about
atmospheric pressure is constant
therefore difference in pressure generation is dependent on the pressure changes in the chest
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How does alveolar pressure changes related to thoracic volume
Change in pressure is inversely proportional to thoracic volume. The pressure is higher when the volume is low and vice versa
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What are inspiratory muscles used in quiet breathing and when there is an increasing effort
quiet breathing: diaphragm
external intercostals stabilise rib cage
Increasing effort:
diaphragm
, external intercostals lift and expand rib cage, accessory muscles, neck muscles, shoulder girdle muscles
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Expiratory muscles during quiet breathing and increasing effort
quiet breathing: elastic recoil of tissues
increasing effort: internal intercostals, abdominal wall muscles
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what physical changes happen in inspiration
increased vertical diameter
increase A-P diameter
elevated rib cage
external intercostals contracted
internal intercostals relaxed
neck muscles contract
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Expiration: physical changes
abdominals contracted
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Innervation of diaphragm and intercostals
phrenic nerve - C3,4,5
Intercostals: segmental thoracic nerves
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What can a spinal cord injury cause
ventricular muscle paralysis
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What are the pleura responsible in doing
transmitting thoracic cage expansion into lung volume expansion
thoracic cage expansion exerts an increasing negative pressure on the intrapleural space
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What does a spirometer measure
Volume of air moving in and out of the lungs
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What is tidal volume
the volume of air moved in or out of the lungs during normal breathing.
at rest - 6-7 ml/kg
during exercise - 15 ml/Kg
Volumes dependent on age, sex and height
typical value of an adult male is 500 ml
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Inspiratory reserve volume
after normal expiration, take as deep a breath as possible
typical value for 70 kg male - 3000 ml
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Expiratory reserve volume
after normal inspiration, breath out as deeply as possible
1,500 ml for 70 kg male
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What is residual volume
even after maximal expiration, air remains in the lungs. this is because of rigid nature of thorax and pleural attachments of the lungs to the chest wall that prevent complete emptying.
this volume left is residual volume
cannot be measured by spirometry
typical value is 1000 ml
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Lung capacities
combinations of lung volumes
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Total lung capacity
TV+IRV+ERV+RV
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Vital capacity
TV+IRV+ERV
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Functional residual capacity
ERV+RV
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What is vital capacity
after a maximal inspiration, make a maximal expiration
typical value - 5,000 ml
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Examples of chest diseases affecting lung volumes and capactities
Restrictive lung diseases - pulmonary fibrosis - reduced Residual volume, FRC, VC, TLV
Obstructive - asthma, copd, emphysema,
increased RV, TLC may be reduced or increased
FRC increased in emphysema
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what is measured clincally using a vitalograph spirometer
forced expiratory measurements
FVC, Forced expiratory volume in 1 second (FEV1)
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