Work of ventilation 1 Flashcards
work required to move the lung and chest wall
P X /_\ V
what muscles do all the work in normal breathing and why
inspiratory muscles
expiration is passive
minute volume and units
respiratory rate per minute x tidal volume
how can any given ventilation be achieved
a high tidal volume & lower rate
a lower tidal volume but higher rate
optimum value of respiratory rate to minimise to work
15/min
optimum value of rtidal volume to minimise to work
500ml
compliance
measure of the ease with which the lungs can be stretched or inflated.
CL = ΔV / ΔP
ΔV : change in lung volume
ΔP: change in transmural pressure
transmural pressure
difference in pressure in alveoli and pressure in pleural cavity
how does the increased elastic resistance change optimal respiratory rate and tidal volume
increased work needed for total volume
increased respiratory frequency
how does the increased airway resistance change optimal respiratory rate and tidal volume
even more work needed for total volume
decreased respiratory frequency
name the 2 types of works of breathing
Compliance (Elastic) Work:
1. Force to expand lung against its elastic properties
Frictional/Resistive Work:
2. Force to overcome air-flow resistance
name the 3 types of compliance
Static compliance
Dynamic compliance
Specific compliance
static compliance
is measured when there is no airflow (airway resistance does not contribute)
dynamic compliance
is measured during airflow (Hysteresis loop)
specific compliance
measures elastic properties (corrects for lung volume)
relationship between volume change (ΔV) and pressure change (ΔP) during quiet breathing
Hysteresis
increased compliance is caused by … and is a symptom of ..
Loss of elastin fibres/elastic tissue in early emphysema or ageing
decreased compliance is caused by … and is a symptom of ..
Chest wall compliance: scoliosis, ankylosing spondylitis
Pulmonary fibrosis
how is elastance related to compliance
inversely
measure of snap back or elastic recoil
how is emphysema related to compliance and elastance
increased compliance - loss of elastin fibres
decreased elastance
how is fibrosis related to compliance and elastance
decreased compliance, increased elastance
tissue elasticity
Energy (ATP) is required to deform elastic tissues (stretch elastin fibers and overcome surface tension)
how is the work of tissue elasticity stored
as potential energy
surface tension
Water molecules are more attracted to each other than to air, creating a surface tension.
Surface tension contributes to minimising the surface area of alveoli
what alleviates surface tension
surfactant
what can surface tension lead to
alveolar and lung collapse
high surface tension leads to
low compliance
surfactant consists of
10% surfactant specific proteins (SPA, SPB, SPC, SPD)
90% lipids - phospholipids mainly DPPC (Disaturated palmitoyl phosphatidylcholine)
surfactant is synthesised by and when
type II pneumocytes (alveolar cells) between 22-32 weeks gestation
where is surfactant stored
Stored in cytoplasmic lamellar bodies until released to surface of alveolus and made available at air-liquid interface
function of surfactant
Reduces surface tension by interfering with water molecule interactions
increases compliance of the lung
Important role also in stabilising alveoli of different sizes
what does laplaces relate to
pressure to surface tension and radius
small radius = high pressure
law of laplace
pressure = 2 x surface tension/radius of alveolus
how does surfactant change surface tension and pressure
surface tension is no longer constant
alveoli of different radius and pressures can now have the same pressure
where do the surfactant molecules position themselves?
position at air-liquid interface with hydrophobic fatty acid chains projecting into alveolar air and hydrophyllic end into the fluid lining of the alveolus.
when is surface tension lowering effect at its greatast
as alveoli become smaller in expiration as concentration of surfactant increases at air-liquid interface.
how does surfactant change surface tension and when
differentially reduces surface tension in alveoli, more at lower volumes and less at higher volumes leading to alveolar stability and co-existence of large and small alveoli
newborn respiratory distress syndrome
Developing foetal lungs do not normally synthesise surfactant until late in pregnancy.
Therefore, premature infants may not have enough pulmonary surfactant and struggle to breathe.
treatment of newborn respiratory distress syndrome
Stimulated by corticosteroids given to mother prior to delivery of premature infant
Oxygen through continuous positive airway pressure
Survanta (surfactant)
surface tension definition and its importance in the lungs
the force exerted by water molecules on the surface of the lung tissue as those water molecules pull together.
.As the air inside the lungs is moist, there is considerable surface tension within the tissue of the lungs.
