Respiration 2 movement of air Flashcards
Semester 1 year 1
What does the distensibility of the lungs mean (measure of elasticity)?
The ease with which the lungs and thorax expand during pressure changes
How do you measure distensibility?
Change in volume / change in pressure
What is the effect on inspiration and expiration when there’s a high or low compliance?
- low compliance = more work required to inspire
- high compliance = often involves more difficulty expiring (loss of elastic recoil)
What is transpulmonary pressure?
The pressure gradient between the intrapleural space + the alveoli
What is the ‘anatomical’ component of elastic recoil in the lungs?
Elastic nature of the cells + extracellular matrix
What is the elastic recoil in the lung due to?
Surface tension generated at the air-fluid interface
What results in surface tension?
Differences in forces on water molecules at air/water interfaces
How are the forces balanced in a gas bubble?
Balance between the pressure exerted by the gas + the surface tension at the gas/water border
What is the equation that describes the balance of forces in a gas bubble?
- Laplace’s equation
- P = 2T / r
Is surface tension constant or not?
Constant
How does the volume of the air sacs in the lungs differ?
Pressure in larger sacs < smaller sacs
How does air flow between the alveoli?
- from smaller to larger alveoli
- leads to their collapse
How do smaller alveoli overcome collapsing?
Production of surfactant
What produces surfactant?
- type II pneumocytes
- composed of a number of lipids + proteins
What are the functions of surfactant and how does it do it?
-prevent alveolar collapse - decrease surface tension
-alveolar size regulation - spread of surfactant slows rate of inflation
-increases compliance - lungs can inflate more easily
-prevents oedema - reduces fluid entering alveoli
What is anatomical dead space?
Volume of conducting airways
What is physiological dead space?
Volume of lungs not participating in gas exchange
What is vital capacity?
-fullest inhale followed by fullest exhale, then it’s the volume remaining in the lungs
-from highest peak to next trough
What is FEV1?
-forced expiratory volume in 1 second
-amount that’s forcibly exhaled in 1 second
What is inspiratory reserve volume?
-breathe in normally, then breath in without breathing out
-from peak of regular breathing to peak of max inhale (highest peak)
What is expiratory reserve volume?
-breathe out normally, then breathe out again without breathing in
-from trough of regular breathing to trough of max exhale
What is tidal volume on a graph?
From peak to trough of regular breathing
What is residual volume on a graph?
From trough of max exhale to 0
What is total lung capacity on a graph?
From 0 to peak of max inhale
What is inspiratory capacity on a graph?
From trough of regular exhale to peak of max inhale
What is functional residual capacity on a graph?
From 0 to trough of regular exhale
What is the flow of air into or out of the lungs proportional and inversely proportional to?
-proportional to pressure gradient
-inversely proportional to resistance
How do you calculate the flow of air into or out of the lungs?
change in pressure / resistance
What law determines the impact of resistance on flow?
Poiseuille’s law
What is airway resistance proportional or inversely proportional to?
-proportional to gas viscosity + tube length
-inversely proportional to the 4th power of the radius
How do you calculate the airway resistance?
(8 / pi) x [(gas viscosity x length) / r^4]
What do small changes in airway diameter have a big impact on?
Resistance + so flow rate
How do you calculate total resistance when resistance is in series + parallel?
-in series: Rt = R1 + R2 + R3 + …
-in parallel: 1/Rt = 1/R1 + 1/R2 + 1/R3 + …
What factors impact on airway resistance?
-airway diameter
-increased mucus secretion - reduce airway diameter
- oedema - increased fluid retention in lung tissue causes swelling + narrowing of airways
-airway collapse - narrows airway
What controls bronchial smooth muscle?
-autonomic nervous system
-humoral factors
How does the autonomic nervous system control the bronchial smooth muscle?
-parasympathetic - ACh released from vagus, acts on muscarinic receptors leading to constriction
-sympathetic - release of norepinephrine from nerves - weak agonist leads to dilation
How do humoral factors control the bronchial smooth muscle?
-epinephrine circulating in blood - better agonist leads to dilation
-histamine - released during inflammatory processes + leads to constriction
