Ventilation and Mechanics Flashcards
Define tidal breathing
Inhalation and exhalation during restful breathing
How do we breath in?
Active
Diaphragm contract = down
Rib cage expands by external intercostal muscles
Pressure falls below atmospheric pressure = air inflow until equal pressure
How do we breath out?
Passive
Muscle contraction ceases, muscles relax
Elastic recoil = return to resting end-expiratory level = exhalation
Define inspiratory reserve volume (IRV)
Amount you can breathe in over you tidal volume
Maximal amount of additional air that can be drawn into the lungs by determined effort after normal inspiration
Define tidal volume (TV)
Amount of air entering the ling during a normal inhalation at rest
Define expiratory reserve volume (ERV)
Maximal volume of air that can be expelled from the lungs after normal expiration
Define residual volume (RV)
Volume of air still remaining in the lungs after the most forcible expiration possible
Define total lung capacity (TLC)
Volume of air contained in the lungs at the end of maximal inspiration
Define vital capacity (VC)
Volume of air that can be expelled from the lungs after taking the deepest possible breath
Define inspiratory capacity (IC)
Total amount of air that can be drawn into the lungs after normal expiration
Define functional residual Capacity (FRC)
Volume of air remaining in the at the end of a passive expiration
Determined by = balance of elastic forces of the chest wall, favouring outward expansion, and the elasticity and surface tension of the lung, favouring a smaller lung vol
Explain what is meant by the resting end-expiratory level
volume at which the elastic forces acting to make the rib cage spring out are balanced by the elastic recoil of the lung
At end-expiration what is the pressure in the pleural space?
Slightly -ve
Due to pull outward by chest wanting to expand and lungs pulling inward wanting to collapse
What are the accessory muscles of inspiration and expiration
Inspiration = SCM, scalene, pect major/minor/trapz
Expiration = internal intercostals, muscles of abdo wall
Explain the importance of the pleural seal in respiration
~10ml pleural fluid
Seal the lungs to the chest wall
At end-expiration pleural space pressure is slightly -ve
What happens when the pleural seal is broken?
Lung can collapse
Outline the pleural pressure changes during respiratory cycle
Inhalation = pressure falls
Exhalation = pressure raises
Explain how a pneumothorax occurs and why this results in collapse of the lung
Broken pleural seal
Air fills the pleural cavity
-ve pressure lost
Lung able to collapse
Define the term ‘compliance’ of the lungs
Measure of the lungs ability to stretch and expand
C = Δvolume/Δpressure
Stiff = low compliance (fibrosis)
Slack = high compliance (emphysema)
Describe the factors which affect the compliance of the lungs
age = lungs less elastic
Fibrosis = stiffer
Surface tension
Explain the effect of surface tension in the alveoli
Water surface tension wants to collapse the alveoli
Outline the role of surfactant
acts to reduce surface tension by breaking up H-bonds
Preventing the collapse of alveoli
What is surfactant and when is produced?
Mixture of lipids and proteins
Secreted by alveolar cells
Prod begins 25-28
Adequate levels at about 35 weeks GA
What is the net effect of surfactant in a small bubble vs a big one?
Surfactant spread more thinly as bubble expands, so surfactant is less effective and surface tension increases in the bigger bubble
= same in bigger and smaller bubble so overall structure remains the same
