2. Mechanics of breathing Flashcards
What is tidal volume - TV ?
Volume of air breathed in and out of lung at each breath
What is expiratory reserve volume- ERV ?
Maximum volume of air expelled from lungs at end of normal expiration
What is inspiratory reserve volume- IRV ?
Maximum volume of air drawn into the lungs at end of normal inspiration
What is residual volume- RV ?
Volume of gas in the lungs at the end of maximal expirationCannot voluntarily expire it Stops alveoli collapsing Reduces work of breathing Provides volume of air that can allow gas exchange to take place between breaths
What is vital capacity- VC ?
Total amount of air we expire TV + ERV + IRV
What is functional residual capacity- FRC ?
Volume of air that is in our lungs at the end of normal expirationERV + RV
What is total lung capacity- TLC ?
Volume of air in lungs after maximum inspiration VC + IRV
What is inspiratory capacity- IC ?
Volume breathed in from quiet expiration to maximum inspirationTV + IRV
What is forced vital capacity- FVC ?
The maximal volume of air that a subject can expel in one maximal expiration from a point of maximal inspiration
What is FEV1 -forced expiratory volume in one second ?
The maximal volume of air that a subject can expel in one second from a point of maximal inspiration
What is FEV1:FVC ?
Fraction of forced vital capacity expired in 1 second
What is Boyle’s law ?
states that the pressure exerted by a gas is inversely proportional to its volume (P a 1/V)gases move from areas of high pressure to areas of low pressure
What is Dalton’s law ?
States the total pressure of a gas is the sum of the pressures of the individual gases
What is Charles law ?
States the volume occupied by a gas is directly related to the absolute temperature
What is Henry’s law ?
states that the amount of gas dissolved in a liquid is determined by the pressures of the gas and its solubility in a liquid
How does the mechanics of breathing occur ?
Because the thoracic cavity changes volume
Based on Boyle’s law when volume increases what happens to pressure ?
When volume increases = pressure decreases
Based on Boyle’s law when volume decreases what happens to pressure ?
When volume decreases = pressure increases
What muscles are involved in normal inspiration ?
External intercostal musclesDiaphragm
What accessory muscles are used in active (forced) inspiration ?
Scalenes Sternocleidomastoids
Is expiration passive or active at rest ?
At rest expiration is passive
What muscles are involved in forced expiration ?
Internal intercostals Abdominal muscles
What happens to the diaphragm at rest ?
Relaxed
What happens to the diaphragm during inspiration ?
Contracts and flattens Thoracic volume increases
What happens to the diaphragm during expiration ?
RelaxesThoracic volume decreases
What effect does the external intercostals have on the ribcage ?
Elevates ribs and sternum upwards and outwards
What is the pump handle motion ?
During inspiration- increases anterior-posterior dimensions of the ribcage
What is the bucket handle motion ?
During inspiration- increases lateral dimensions of ribcage
What effect does the internal intercostals have on ribcage ?
Pull ribs and sternum inwards
What happens to the airways during inspiration ?
Airways are pulled open by physical forces of inspiration
What happens to airways during expiration ?
Airways are compressed by physical forces of expiration
What is intrathoracic or alveolar pressure (PA) ?
pressure inside the thoracic cavity (inside lungs), may be positive or negative compared to atmospheric pressure
What is intrapleural pressure (Pip) ?
pressure inside the pleural cavity, typically negative compared to atmospheric pressure (in healthy lungs)
What is transpulmonary pressure (PT) ?
Difference between alveolar pressure and intrapleural pressure always almost positive as intrapleural pressure is negative (in health)PT = Palv - Pip
Regarding pressure changes what does it mean if there is a volume of 0 ?
No difference between the pressure recorded and atmospheric pressure
If there is a positive value what does this mean regarding the pressure ?
pressure is greater than atmospheric pressure
What does it mean if pressure value is negative ?
Pressure is less than atmospheric pressure
During the inspiratory phase what happens to alveolar pressure ?
Always less than atmospheric pressure
During the expiratory phase what happens to alveolar pressure ?
Always greater than atmospheric pressure
What happens when alveolar pressure is the same as atmospheric pressure ?
No air movement as there is no pressure gradient to push air either way
Is intrapleural always more or less than atmospheric pressure ?
Always less
What happens to intrapleural pressure during inspiration ?
Becomes more negative
What happens to intrapleural pressure during expiration ?
Becomes less negative
What are the factors that affect breathing ?
Bulk flow of air between the atmosphere and alveoli is proportional to the difference between the atmospheric and alveolar pressures and inversely proportional to the airway resistance F = (Patm- PA)/R At the end of an unforced expiration Between breaths Patm =PA, no air is flowing and the dimensions of the lungs and thoracic cage are stable as a result of the opposing elastic forces. The lungs are streched and are attempting to recoil, whereas the chest wall is compressed and attempting to move outward. This creates a sub atmospheric intrapleural pressure and hence a transpulmonary pressure that opposes the forces of elastic recoil Airway resistance determines how much air flows into the lungs at any given pressure difference between atmosphere and alveoli. The major determinant of airway resistnace is the radii of the airways
