Airways resistance Flashcards
(30 cards)
what is the biggest source of resistance to the movement of air?
the friction encountered between air and the airway walls
what is the calibre and airway resistance of the trachea and first 7 generations?
large calibre (diameter) and low airway resistance
where is the highest resistance and why?
7th - 13th generation, small calibre (diameter) and only 72 branches per generation (few)
what happens to calibre and airway resistance after the 14th generation?
airways become smaller and smaller in calibre, but there are 1m branches per generation. larger cross sectional area -> more airflow and less resistance
what innervates the airways?
automatic nervous system (ANS)
what are the two branches of the automatic nervous system?
sympathetic (SNS) and parasympathetic (PNS) nervous systems
where is the PNS and what does it do?
the PNS directly innervates the bronchial smooth muscle which will cause bronchoconstriction and a decrease in arirway calibre which increases airway resistance and decreases airflow
where is the SNS and what does it do?
the SNS receptors are sited in the airway walls of small bronchi / bronchioles. they are responsive to catecholamines released by the body (fight or flight hormones). this causes bronchodialtion and an increase in airway calibre, reducing airway resistance and increasing airflow
what happens to airways resistance and lung volume increases in health?
airways resistance decreases because the airways distend as the lungs inflate, and the wider the airways the lower the resistance and the greater the airflow
what is poiseuille’s law?
the flow of gas through an airway is:
* directly proportional to the fourth power of its internal radius
*inversely proportional to its length
* inversely proportional to viscosity of gas
what intraluminal pathologies reduce airway calibre?
bronchoconstriction (PNS activation)
bronchial secretions (infection, inflammation)
mucosal oedema (inflammation)
airway remodelling (thickening of the basement membrane in response to chronic inflammation)
tumour / mass
inhaled foreign body
what extraluminal pathologies reduce airway calibre?
bronchial tumour / mass
loss of radial traction (emphysema)
what is an obstructive disease?
respiratory disease characterised by increased airways resistance
what are SABAs and what do they do?
short acting beta2 agonist
stimulate B2 receptors in the airway walls, causing relaxation of bronchial smooth muscle and therefore bronchodilation
what are SAMAs and what do they do?
they have anti secretory properties and when administered inhibit secretions from mucus glands lining the nasal mucosa. it inhibits acetylocholine from being released at parasympathetic sites in bronchial smooth muscle resulting in bronchodilation
what do corticosteroids do?
decrease inflammatory response observed in asthma. also decreases capillary leak and augments beta receptors response to beta - adrenergic agents
what does prednisolone do?
interferes with arachidonic acid metabolism and production of leukotrienes, reduced microvascular leakage, reduces cytokine production and prevents migration of inflammatory cells
what are some examples of SABAs?
salbutamol (ventolin)
terbutaline (bricanyl)
what are the side effects of SABAs?
tremor and tachycardia
what are long acting beta 2 agonists (LABA) used for?
nocturnal asthma symptoms, as natural cortisol decreases at night
what is an example of a LABA?
salmetrol (serevent)
what is an example of a SAMA?
ipratropium bromide (atrovent)
what is an example of a LAMA?
tiotropium bromide (spiriva)
which inhalers are used for asthma?
SABAs and LABAs
