4-Respir Mechanics Flashcards
pulmonary ventilation
definition
mechanical process to initiate movement of air into/out of lungs
-to meet oxygen requirements
boyle’s law
pressure of a gas inversely related to volume of container
-inspiration = small vol > larger so dec pressure
-expiration = large vol > small so inc pressure
muscles of inspiration
act to expand vol of thorax
1. diaphragm
2. intercostal muscles-external
accessory muscles inspiration
- scalenes
- SCM
help elevate ribcage
expiration process
usually passive and driven by pressure gradient + elastic recoil of lungs/chest wall
if not passive then use internal intercostals + abdominals to force diaphragm upward
active expiration conditions
- normal if exercising
- pathologic if asthma, bronchitis, COPD
transpulmonary pressure =
alveolar pressure - intrapleural P
intrapleural should be lower than inside lung (alv)
P at end of expiration
P in lung = P in atmosphere
transpulmonary P is pos (0-neg # = pos)
elastic forces
lungs have opposite forces as chest wall
-chest wants to expand, lungs want to collapse
-forces are equally balanced at end of expir/functional residual capacity
pressures during inspiration
-elastic recoil of lungs inc (bc wants to shrink back)
-pressure in lungs less than atmospheric bc inc vol
-intrapleural pressure becomes more negative than end of expiration
alveolar pressure changes
- alveoli expand = pressure dec
- dec P so air from atmo moves down pressure gradient into lungs
- inc in gas moles counteracts the fall in P
- gas flow until alveolar and atmo are equal and no gradient
pleural pressure changes
- thorax expands = P dec
- inspiration ends and vol dec during expir so pleural P less neg
- restings size of thorax returns pleural P to baseline
why transpulmonary matters
important for work of breathing
-inc trans P with accessory muscles to expand lungs if mechanics off
compliance
measure of how much force it takes to distend an elastic structure
-inc in length or vol when a distending force applied
aka lung distensibility based on pressure-volume curve
elastance
measure of tendency to return to og length/vol when distending force removed ‘snap back ability’
shallow slope
low compliance
difficult to distend
-usually at low lung vol and maximal volume
determinants of compliance
- elastic forces of lung tissue
- elastic forces of surface tension/surfactant (more ST lower comp)
- resistance forces to airflow
hysteresis
diff b/t inspiration and expiration P-V curves
-higher levels of surface tension at low lung vol so low compliance (inspiration)
-surface tension already been overcome during expiration so curve looks diff/steeper
surface tension
generated at air-water interface
-exerts inward pressure vs walls of alveoli to resist expansion
water moles will be attracted inward and to each other
surfactant
type II alveolar cells disrupts intermolecular forces of water to dec surface tension and dec collapsing force
dipalmitoylphosphatidycoline aka lecithin mostly
neonatal rspiratory distress syndrome
infants premature have insuff lecithin so insuff surfactant = high surface tension and fluid accumulation
surfactant administered, ventilate
emphysema
normal chest wall + dec lung elastic recoil = higher functional residual capacity
steeper compliance curve bc easier to distend lungs (loss of elastic fibers) = inc compliance, barrel shape bc breathing in high volumes
pulmonary fibrosis
inc lung elastic recoil + dec chest wall = dec functional residual capacity and compliance (more diff to distend, shallow curve)
from collapsed alveoli, pulmonary edema, or lung fibrosis
chest wall abnormalities
-pectus excavatum
-kyphosis
airway resistance determined primarily by
radius of an individual airway
-small radius changes = large resist changes
airway resistance is highest
in early airway (larger diameter) bc cross sectional area smaller
