Pulmonary Mechanics Flashcards
What muscles are used for expiration?
Quiet - none, it’s passive.
Forced - abdominal muscles and internal intercostals
What muscles are used in inspiration?
Quiet - diaphragm and external intercostals
Forced - as above, and sternocleidomastoid, scalenes
What makes up the alveolar pressure?
Alveolar pressure = pressure on outside of alveoli + pressure generated by elastic recoil of alveoli
What is compliance?
The stretchiness of the lung tissue
What is maximal expiratory flow limited by?
Resistance!
Increased effort causes an increase in resistance as the airways are compressed by the raised external pressure.
This means that increasing effort may increases expiratory flow to a certain point!
What keeps the bronchioles open?
Radial traction (the outwards pull of surrounding tissue)
What keeps the upper airway open?
Cartilage
What happens when the pressure on the outside of the bronchioles is more negative than the inside?
They may collapse
What is dynamic airway compression?
In diseases which decrease the elasticity of lung tissue, muscular effort cannot compensate for lack if recoil as the muscles compress the airway, making it harder to expire.
In what conditions is dynamic airway compression a problem?
COPD and Emphysema
Can muscular effort compensate for increased airway resistance?
No.
Asthma and Bronchitis
What is surfactant?
Mostly lipid. Lowers surface tension allowing easy expansion or lungs
What is respiratory distress syndrome?
Lack of surfactant. Common in premature babies.
What receptors control ventilation?
Mechanoreceptors and chemoreceptors
What do mechanoreceptors detect?
Inflation and deflation of the lungs
What are central chemoreceptors?
Detect pH changes.
Desensitised by prolonged periods of high CO2
What is hypoxic drive?
When central chemoreceptors are desensitised by prolonged periods of high CO2 so ventilation is now being controlled by the detection of hypoxia (peripheral chemoreceptors)
What is the problem with treating hypoxic drive?
Giving O2 treats the hypoxia, and so the chemoreceptors think conditions are normal again. Patient may stop ventilating. CO2 levels are dangerously high.
What are peripheral chemoreceptors?
In carotid and Aortic bodies. Detect pH.
ESSENTIAL when CO2 sensitivity is lost. Most sensitive during hypercapnia.
What are ‘restrictive’ diseases?
Decreased compliance
What are obstructive diseases?
Impaired airflow
What is Asthma?
An obstructive airway condition caused by bronchoconstriction and airway inflammation in response to an allergen.
What is bronchitis?
Mucus overproduction and periods of infection.
What is Emphysema?
A respiratory condition caused by the destruction of alveoli due to excessive protease activity.
Chronic over inflation.
What is COPD?
Chronic obstructive pulmonary disorder.
Features of bronchitis and emphysema.
What is Henry’s law?
[gas] = partial pressure x solubility coefficient
What is Dalton’s law?
The total pressure is the sum of all of the constituent partial pressures.
Where is the respiratory centre?
Medulla
What are the 2 groups of the respiratory centre?
Dorsal respiratory group and the ventral respiratory group
What does the dorsal respiratory group do?
Causes inspiration (expiration is passive)
What does the ventral respiratory group do?
Involved in inspiration and expiration when there is an increased demand to breathe
Where does the dorsal respiratory group receive its stimuli from?
Mechanical stretch receptors in the lung.
How does the ventral respiratory group cause forced inspiration and expiration?
Signals for the usage of accessory muscles (scalenes, sternocleidomastoid, internal intercostals etc) for inspiration and abdominal muscles for expiration.
What is the pontine respiratory group?
The pons!
Limits ventilation by controlling the rate and depth of breathing.
What do central chemoreceptors respond to?
Increased CO2 and decreased pH
What do peripheral chemoreceptors respond to?
Increased CO2, decreased pH and decreased oxygen
Where are peripheral chemoreceptors?
Aortic and carotid bodies
Where are central chemoreceptors?
Medulla
How are central chemoreceptors stimulated?
H+ can’t cross BBB so the bicarbonate buffering system converts it to CO2 which diffuses across and forms H2CO3. This lowers the pH or cerebral spinal fluid and so stimulates chemoreceptors.
How else can respiration be controlled?
Higher centre afferents (muscles controlled during pain and emotion)
Proprioceptors - joint movement stimulates respiration (exercise)
What is congenital hypoventilation syndrome (Ondine’s curse)?
Breathing is absent during sleep.
What is type 1 respiratory failure?
Low PaO2
Normal or low PaCO2.
What is type 2 respiratory failure?
Low PaO2
High PaCO2
When is respiratory adaptation necessary?
Exercise
Altitude
Depth
Illness
What is the forced vital capacity (FVC)?
Total volume of air that can be exhaled from total lung capacity, measured in litres.
What is the forced expiratory volume (FEV1) ?
The volume of air that can be forcefully expired in one second.
What is a normal FVC?
80+%
What is a normal FEV1?
Over 75%
What is the forced expiratory flow (FEF25-75) ?
Mean forced expiratory flow in the middle half of the FVC
Over 60% is normal
What impact do obstructive airway conditions have on FEV1?
Decrease
What impact do obstructive conditions have on total lung capacity?
No effect.
What impact do restrictive airway conditions have on total lung capacity?
Decreased
What impacts do restrictive airway conditions have on FEV1?
Very little
