Mechanics of Breathing Flashcards
Movements of breathing
ventilation = inspiration and expiration
inspiration - air going in (needs a suction pressure (negative pressure within alveoli))
expiration - gas going out (needs a blowing pressure (positive pressure in the alveoli))
respiratory muscles are able to generate the sucking and blowing pressure automatically
Muscles of inhalation
- sternocleidomastoid (moves up - elevates sternum)
- scalenes (anterior, middle and posterior - moves up - elevate and fix upper ribs)
- external intercostal muscles (move up - elevates ribs, increasing width of thoracic cavity)
- interchondrial part of internal intercostals (elevates ribs)
- diaphragm ( moves down and flattens, increasing vertical dimension of thoracic cavity and elevates lower ribs)
this combined action increases the volume of the chest cavity and thus creating a negative pressure
muscles of exhalation
- internal intercostals, except the interchondrial part (move down)
- abdominals (depress lower ribs, compress abdominal contents, pushing up diaphragm)
- external oblique (down and in)
- internal oblique (down and out)
- transversus abdominus (out)
- rectus abdominus (down)
what are the two described actions with breathing
- pump action (up and down like a water pump)
- bucket-handle action (up and out, down and in)
elastic recoil of the lungs
- quiet breathing
- expiration depends on lung elasticity (elastin in lungs)
- elastic recoil resists stretch - makes inspiration harder but expiration automatic - similar to balloon
- lungs tend towards their smallest volume
- big feature of COPD is when this breaks down
the pleura
- bi lavered pleura (parietal and visceral) ‘sticks’ lungs to rib cage
- pleural fluid in between - for lubrication and ease of movement
- negative intrapleural pressure ‘holds’ lungs to chest wall
pressures before inspiration - referenced to atmospheric
atmospheric - 0mmHg
intra-alveolar - 0mmHg
intrapleural - -4mmHg
pressures during inspiration
air flows in
atmospheric - 0mmHg
intra-alveolar - -1mmHg
intrapleural - -6mmHg
what is total lung capacity?
volume at the end of a maximal inhalation
TLC = RV + VC
what is functional residual capacity?
volume at the end of a normal exhalation
what is the residual volume?
volume at the end of a maximal exhalation
RV = TLC - VC
what is the inspiratory capacity?
volume between FRC and TLC
IC = TLC - FRC
what is the expiratory reserve volume?
volume between FRC and RV
ERV = FRC - RV
what is the vital capacity?
volume of gas exhaled for TLC to RV
VC = TLC - RV
airway pressure flow relationships
flow = (air pressure at mouth) - (air pressure in alveoli) / (resistance to flow of air in airways)
AWR: pressure required in the alveoli to drive one unit of flow ~ 1L/s
Conditions of expiration
- COPD (and asthma)
- work of breathing increases (dyspnoea, difficulty breathing, shortness of breath)
- mucous, inflammation and constriction increasing resistance (wheeze)
- elastic fibres breaking down so expiration no longer passive (barrel chest)
- eventually respiratory controller has to make a decision, type II failure respiratory muscle fatigue
- asthma reversible, COPD not!!!
conditions of inspiration
- fibrotic lung diseases leading to small ‘stiff lungs’
