Lecture 2 Ventilation Continued Flashcards
Why do respiratory muscles generate work?
To overcome recoil tendency of lungs and frictional resistance to airflow by airways
Elastance
A measure of the elastic recoil tendency of a balloon or lung
Compliance (C)
1/ elastance
A measure of ease of stretch
C= delta vol / delta P
How is the amount of change in PPL (transpulmonary P) determined?
By change in lung volume and lung compliance
Airflow rate (Vr)
Airway resistance (R)
Delta PPL = (delta V/C) + RVr
What happens with a decrease in PPL?
Change in the volume of air is increased (more air sucked in)
Increased compliance
Pneumothorax
At FRC, it’ll lead to collapse of lungs to their minimal volume due to elastic and collagen tissue and surface tension forces
Surface tension
Measure of the force acting to pull a liquid’s surface molcules together at an air-liquid interface
Pulmonary surfactant
A complex mix of lipids and proteins produced by Type 2 cells
Present at the alveolar air-water interface
Prevents an overstretch!!
What are the 3 major effects of pulmonary surfactant?
Reduces surface tension and increase compliance
Reduce fluid accumulation in alveoli
Keeps alveolar size uniform during respiratory cycle
What is the most abundant component of pulmonary surfactant?
DPPC and it’s hydrophilic and hydrophobic portions cause it to seek the surface of the alveolar lining
What happens to the concentration of surfactant molecules at TLC?
It becomes sparse at the alveolar surface
Surface tension will increase helping deflation
Hysteresis
Difference between inflation and deflation paths due to initial force need in surfactant’s role to stabilize the lungs
Emphysema
Destroys lung tissue and makes lungs floppy (smoking)
Lungs have high compliance but tissue architecture is lost
Fibrosis
Deposition of fibrous tissue
Restricts inflation
Lungs are poor in compliance
________ in airways slows airflow
Frictional resistance
upper respiratory tract (60%)
________ increases airflow during exercise
Mouth breathing
Obligatory nasal breathers
Horses
Flare their nostrils and can constrict BVs to shrink mucosa
Resistance
Inversely proportional to radius
Directly proportional to length (Poiseuille’s law)
How is radius altered?
Inhalation dilates airways
Contraction of smooth muscle reduces airway diameter and increases resistance to airflow
Flaring of nares
Vasoconstriction
Bronchoconstrictors/ dilators
Parasympathetic smooth muscle contractions
- Vagus releases ACH and activate muscarinic receptors (induces bronchoconstriction)
- Irritant subs induce reflex bronchoconstriction by activating PNS
- Mediators of inflammation (histamine and leukotrines from mast cells) act on muscles directly or via PNS (heaves, asthma)
Sympathetic smooth muscle contractions
Sympathetic NS inhibits airway smooth muscles (catecholamines, muscle realxation/ dilate airways)
NANC system (nitric oxide is the NT, inhibitory)
Dynamic compression of airways
The negative transmural pressure that makes airways (nares, pharynx, larynx) collapse
Adductor muscles normally prevent
When does dynamic compression occur?
During forced exhalation when PPL exceeds PA
ex: coughing air moves in high velocity in a dynamically collapsed airway facility removal of foreign material
Laryngeal Hemipegia in horse
Loss of nerve supply
Abductor muscles atrophy then fail to contract during inhalation
Vocal fold sucked into lumen producing inspiratory roaring
Idopathic
What does distribution of air depend on?
Local mechanical properties of the lung
Always uneven (esepcially in disease)
Collateral Ventilation
Movement of air between adjacent lobules (septum)
Affected by type of CT between lung lobules
Better ventilation in species without separation
Species variation of lung lobule separation
No separation (air moves between lobules): dogs and cats
Partial separation: horses and sheep
Complete separtion (obstruction dangerous): cattle and pigs
