mechanics of ventilation 1 Flashcards
2 integrated processes of respiration
external respiration
internal/cellular respiration
external respiration
Exchange of oxygen and carbon dioxide between the body and the external environment
internal respiration
Uptake, utilisation of oxygen by cells and release of carbon dioxide
what is ventilation driven by
mechanical forces
gas pressure
Force that the gas exerts on the walls of its container
boyle’s law
For a fixed mass of enclosed gas at constant temperature, the product of the pressure (P) and volume (V) remains constant.”
boyle’s law formula
PV = k or P1V1 = P2V2
where does pressure differential exist
exists only between pulmonary and pleural pressure
what pressure is greater pleural pressure or pulmonary pressure and why
Pleural pressure < Pulmonary pressure
keeps lungs inflated
opposing forced - lungs stretched under tension, wanting to pull inwards
chest wall wants to pull outwards
pressure of pleural sac, lung and airway before inspiration
pleural sac - 756
lungs - 760
airway - 760
pressure of pleural sac, lung and airway during inspiration
size of thorax increases
lungs stretch - less pressure
pleural sac expands - pressure decreases
intrapleural pressure decreases after intrapulmonary pressure true or false
false
8 events of inspiration
Inspiratory muscles contract
The diameter of the thoracic cage increases
Intrapleural pressure (PPL) becomes more negative
Transmural pressure (PTM) increases and causes alveoli to swell or open
Intra-alveolar pressure falls relative to atmospheric pressure
Air flows down pressure gradient from atmosphere to alveoli
Tidal volume (VT) of about 500 mls is added to resting volume or FRC
At end of inspiration – no airflow and intra-alveolar pressure = atmospheric pressure
3 types of inspiratory muscles
primary
accessory
airway
primary inspiratory muscles
diaphragm
external intercostals
accessory inspiratory muscles
contract only during forceful inspiration
sternomastoid
scalene
airway inspiratory
laryngeal
pharyngeal
genioglossus
how does diaphragm change during inspiration
dome shaped; flattens upon contraction and descends (1-10 cm); causing 75% of inspiration
how does external intercostal change during inspiration
Lift ribs upwards and outwards
how does scalenes change during inspiration
Raise the first 2 ribs
how does sternomastoid change during inspiration
Raise the sternum
Examples for respiratory diseases associated with the requirement of accessory muscle activity
Chronic bronchitis
Asthma
Emphysema
Chronic obstructive pulmonary diseases (COPD)
how do airway muscles keep inspiration occuring
- > Enlarging of the airway ->Reduced flow resistance
- > Stabilisation of the airway (esp. pharynx) -> Preventing collapse
passive expiration
Passive process, when at rest
Relaxation of inspiratory muscles sufficient
active expiration
Contraction of abdominal muscles (push up diaphragm)
Contraction of internal intercostals
expiration requires relaxation of..
external intercostal muscles
diaphragm
expiration requires contraction of.
internal intercostal muscles - flattens sternum reducing dimensions
abdominal muscles
lung volumes measured using
spirometer
reading a spirogram
FEV
Forced expiratory volume
FVC calculated
Max. inhalation followed by fast exhalation
