Mechanics Of Breathing Flashcards
(47 cards)
What is the mechanics of breathing?
How air is moved in + out of lungs
Physics/physiology of chest wall, airways + lungs
What happens to the lungs in inhalation and exhalation?
Lungs expand in response to muscle work, chest wall expansion + changes in pleural pressure
Air moves by bulk flow down a pressure gradient from more positive atmospheric to more negative peripheral airways pressure creating by lung expansion
Exhalation is passive + does not require muscular work as lungs are elastic + constrict on own
What provides resistance to air flow?
Airway diameter + contents
What is lung compliance and what does it depend on?
Lung stretchability
Depends on size + physical state
What occurs during quiet respiration? What changes if tidal volume increases?
Inhalation: lungs pulled open by muscle action against elastic tissue promoting recoil + resistance of airways to air flow (active)
Exhalation: lungs return due to elastic recoil to FRC where the opposing elastic forces of lung + chest wall are in balance
If tidal volume increases, exhalation must use elastic recoil AND muscular work to complete exhalation of larger volume in same 2/3rds of respiratory cycle of unchanged length
What are the mechanical components of respiration? What are their functions?
Chest wall tissues + ribcage: respiratory muscles/diaphragm act here
Pleural space: provides lubrication + transfer of expansile force to lung
Respiratory muscles:
- External intercostals: elevate ribs + increase both anteroposterior + left (right dimensions) - bucket handle effect in inspiration
- Diaphragm: dome becomes depressed in contraction increasing thorax height
Diaphragm is principle muscle of respiration. What does it do? What is its innervation?
Diaphragm moves down ~ 1 cm during quiet respiration in inspiration as muscles will shorten, dome of diaphragm goes flat, pulling base of lung down increasing thorax height + volume expanding the lungs
Innervated by phrenic nerve C3-5
The position of the first rib is stabilised by __ ___ so the rib is not very ___. This impacts upon movement of ___ in breathing.
Scalene muscles
Mobile
Sternum
What is the work of breathing and its 3 components?
Energy expended during respiration, 3 components:
- That required to expand lungs against lung/chest elastic forces (compliance/elastic work)
- That required to overcome viscosity of lung/chest wall structures (tissue resistance work)
- That required to overcome airway resistance to movement of air into lungs (airway resistance work)
Constitutes 5% of total energy expenditure at rest but can increase up to 50x during strenuous exercise
What is Functional Residual Capacity?
Lung volume where opposing forces of expansile skeletal structure of chest wall (with muscles at rest) + contractile lung are in balance with each other -> combined forces reach equilibrium volume
OR
The amount of air left in the lungs after passive exhalation
What muscle work is done in forced exhalation?
- Extracartilaginous portion of internal intercostals moves rib downwards
- Abdominal wall muscles
contract + increase pressure in abdomen pushing diaphragm up beyond FRC position - Pectoral girdle muscles
-> depress ribs + decrease ribcage volume
What muscles are used in inhalation? What do aim to do?
- Mainly external intercostal muscles
- Intercartilaginous portions of internal intercostals
- Diaphragm
- > elevate ribs + enlarge ribcage volume
In extremes of respiratory effect, accessory muscles become important in inhalation. What 2 muscles are these and what do they do?
- Scalenes: elevate first 2 ribs
2. Sternocleidomastoid muscles: raise sternum
Describe the layout + features of the lungs pleural membranes.
Visceral pleura: pleural membrane covering lung surface
Parietal pleura: pleural membrane attached to inside of thoracic cage/chest wall
Thin layer of pleural fluid between the 2 lubricates the pleural interface/space creating a seal effect
Why do movements of the diaphragm + chest wall permit expansion of the lung?
2 opposing forces of chest wall + lung -> negative pressure of ~-0.5kPa in pleural space
During inhalation, chest wall expands stretching pleural space decreasing the intrapleural space further
Pleural seal have suction effect on visceral pleura + attached lung causing them to expand with chest wall as force of lungs elastic recoil is exceeded
What lung volume is represented when the forces inflating + deflating the lungs are equal? At what phase of the respiratory cycle does this occur?
FRC
At end of exhalation of quiet breathing
The lungs are not adherent to the inside of the thoracic cavity. What stops them from collapsing away from the chest wall?
The negative pressure within the pleural space i.e. pleural seal
What is the commonest mechanism allowing lung collapse away from the chest wall?
Pneumothorax = puncture of lung surface or chest wall letting air into the pleural space (may lead to cardiac arrest + death if not recognised quickly)
Why do the lungs collapse in a pneumothorax?
Integrity of pleural seal broken raising the intrapleural pressure -> suction effect between 2 pleurae removed -> disconnection of lung from expansile force of chest wall -> lungs collapse away from chest wall under unopposed force of its elastic recoil
What will a pneumothorax on one side of the lungs look like on a scan?
- Hemithorax black due to air in pleural cavity
- Wont see any spidery capillaries as lung is completely collapsed
- Hemidiaphragm depressed
- Trachea may be pushed to one side (deviated)
- Heart/border of heart may be pushed to one side
What are the 2 important factors in the energy ‘cost’ of breathing?
- Resistance to flow
2. Compliance (how stretchy/stiff the combination of elastic lungs + semi-rigid chest wall are)
What is compliance of the lungs?
Volume change of lung (or length change of a substance) per unit of force (or pressure) applied
A measure of disposition of lungs to expand under traction or pressure i.e. stiffness of respiratory system
What is elastance of lungs?
Measure of disposition of lungs to return to resting position due to their intrinsic elasticity
What is Hooke’s law?
The force needed to extend or compress a spring by some distance, is proportional to that distance (if elasticity of lung + thorax were only factor)BUT the lung is stiffer at high + low lung volumes
Can be presented by a lung inflation curve where a hysteresis curve of inhalation + exhalation would be shown (slope of curve is compliance of whole system at that moment)
