What are the factors affecting pulmonary ventilation
Resistance of the airway
Pressure relationship in the thoracic cavity
Chest and lung compliance
Surfactant
What are the factors affecting airway diameter (resistance)
Nervous
Chemical
Irritants
Explain the nervous factors affecting the airway diameter
1- Sympathetic adrenergic innervation; Direct symp. stimulation
bronchodilatation.
2- Parasympathetic cholinergic innervation; rich innervation of
airways, so when stimulated bronchoconstriction & increase in
mucus secretion of sub-mucosal glands
bronchomotor tone
3- Non adrenergic Non cholinergic(NANC) innervation; e.g.
• VIP → bronchodilatation.
• Substance P, Neurokinin A →bronchoconstriction.
Describe the chemical factors affecting airway diameter
1.Circulating catechoalmines: adrenaline &NA act on β2
adrenoreceptors in bronchial smooth muscle
marked bronchodilatation.
2.Local mediators:
a. Histamine (H1 receptors)→ bronchoconstriction.
b.Slow reactive substance of anaphylaxis (SRS, allergic
response to pollen)→ bronchoconstriction.
c. PG F
→ bronchoconstriction.
d. PGE2
→ bronchodilatation
Explain how irritants affect airway diameter
such as dust, smoke, air pollution,
cold air → Airway constriction.
Mediated by
1-parasympathetic reflexes.
2-local responses
Define lung and chest compliance
Def: Ability of the lung and chest to expand.
Or the extent to which the lung expands for each
unit increase in its transmural
pressure(distensibility pressure).
Explain tranpulmonary and transthoracic pressures
❖ transmural pressure for the lung =
intrapulmonary pressure – intrapleural
pressure, called “transpulmonary pressure”.
❖ transmural pressure for the lung& thorax =
intrapulmonary pressure – atmospheric
pressure, called “transthorathic pressure
Define lung compliance
the measurement of the lungs’ ability to
stretch and expand
• It refers to the ease with which the lungs can
expand and contract in response to changes in
pressure
Explain what high and low compliance mean
• High compliance means that the lung can expand
and contract easily
• Low compliance: the lung is stiff and resist
change in pressure
What is the normal lung compliance in adult human
200 ml/cm of water pressure
What is the combined compliance of the lung and thorax
130 ml/cm of water pressure
Define lung elasticity
tendency of the lung tissue to returen to
its original shape after it has been stretched or compressed
What is the importance of lung elasticity
maintain the lung function during
respiratory cycle?? Without elasticity lungs
can’t expel air during expiration or be filled
with air during inspiration
Factors in the Lung decrease compliance
Pulmonary congestion
Pulmonary edema
Pulmonary fibrosis
Dec surfactant
What disease increases lung compliance
Emphysema
Factors in the chest wall that Dec lung compliance
Deformities of the chest wall
Skeletal muscle disease like poliomyelitis
Obesity
Define surfactant
Def: it is a complex substance secreted by the alveolar epithelium
and acts mainly to decrease the surface tension inside the alveoli
What is the chemical structure of surfactant
Phospholipids and proteins
From where is surfactant secreted
Type 2 alveolar cells
The main stimulus for Surfactant synthesis
is:
: Stretch of the alveoli (distortion of
alveolar type II cells by inspired air) , B
adrenergic stimulation and cortisol
Functions of surfactant
a) prevent lung collapse
b)↓ muscle effort to expand lung
c) ↓ work of breathing
d) Has antibacterial action: stimulant for macrophages,
assists ciliary movement
Factors decrease surfactant:
1-Resp. distress syndrome (in infants)
2-Cigarette smoking (destruction of type II cells)
3-Heart-lung bypass (prolonged pulmonary artery occlusion)
4-Long term inhalation of 100% O2
Explain work of breathing
• Energy utilized during respiration.
• Inspiration is active process.
• Expiration is passive. So, it is the
work done during inspiration.
• It is about 1-2% of the total body
energy expenditure during quiet
breathing. During heavy exercise,
work is about 3-5%.
