Ventilation and Compliance 3,4/ Surfactant, Compliance and lung function tests Flashcards
which cells produce surfactant?
Type 2 alveolar cells (pneumocytes)
what does surfactant do to surface tension?
reduces it, thus reducing tendency for alveoli to collapse
what is surface tension?
where there is an air-water interface, and refers to the attraction between water molecules
what does surfactant physically do to the lung?
increases lung compliance (distensibility), reduces lung’s tendency to recoil (makes breathing easier)
in which alveoli are surfactant molecules more effective ?
is small alveoli because it is more concentrated (larger alveoli don’t need to have their surface tension reduced by as much to prevent collapse because they have a bigger radius, and pressure is proportional to 2T/r with T= surface tension and r= radius)
when does surfactant production start and end?
starts at about 25 weeks gestation and ends at about 36 weeks gestation
which hormones stimulate surfactant production?
thyroid hormones and cortisol
how does the production of these hormones vary throughout pregnancy?
they increase at the end of pregnancy
what do premature babies therefore suffer from?
Infant Respiratory Distress Syndrome (IRDS)
why are lungs not inflated with air in utero?
to prevent an air-water interface (no surface tension), so the lung can inflate while requiring less pressure (no need to overcome surface tension)
what is compliance?
change in volume relative to change in pressure (how much does volume change for any given change in pressure), represents the stretchability (not elasticity, which refers to capability to return to original shape)
“the pressure required to inflate the lungs must overcome the airway resistance and expand the elastic elements of the chests as measured by compliance/ determined by elastic forces, surface tension at the alveolar air-liquid interface and by airway resistance”
what does a high compliance refer to in terms of variation of lung volume per variation in ip (intrapleural?) pressure
large increase in lung volume for small decrease in ip (intrapleural?) pressure
what does a low compliance refer to in terms of variation of lung volume per variation in ip (intrapleural?) pressure
small increase in lung volume for large decrease in ip (intrapleural?) pressure
what factors affect compliance?
disease states and age
which required greater change in pressure (= greater effort)? inspiration (reaching a particular lung volume) or expiration (maintaining that volume)
it requires a greater change in pressure (from FRC) to reach a particular lung volume during inspiration than to maintain that volume during expiration
expiration/ inspiration- which requires most effort in a healthy person?
effort (work) of inspiration is recovered as elastic recoil during expiration and in a healthy person, expiration is passive (no effort)
what do you call the loss of elastic tissue in ventilation mechanism? what is the consequence of this?
emphysema means expiration requires effort
what consequences does fibrosis have on fibrous tissue? on ventilation?
inert fibrous tissue means effort of inspiration increases (decreased compliance)
where is alveolar ventilation greatest? how does it vary throughout the lung?
alveolar ventilation declines with height from base to apex (greater at base)
where is compliance greatest? how does it vary throughout the lung?
compliance declines with height from base to apex (greater at base)
what does the anatomy of alveoli have to do with compliance at the base of the lung?
at the base the alveoli are compressed between the weight of the lung above and the diaphragm below and hence more compliant on inspiration
what does the anatomy of alveoli have to do with compliance at the apex of the lung?
at the apex, the alveoli are more inflated at FRC
what are the characteristics of an obstructive lung disorder?
obstruction of air flow, especially on expiration
what are the characteristics of a restrictive lung disorder?
restriction of lung expansion
is asthma an obstructive or restrictive lung disorder?
obstructed lung disorder, because increased airway resistance
are COPD obstructive or restrictive lung disorders?
COPD = chronic obstructive pulmonary disease (obstructive)
give examples of COPDs and their main characteristics
chronic bronchitis (inflammation of the bronchi), emphysema (destruction of the alveoli, loss of elasticity)
what is the prevalence for COPD? how does it vary with age?
80 000 000 people worldwide have moderate to severe COPD, its prevalence increases with age
is loss of lung compliance an obstructive or restrictive lung disorder?
restrictive lung disorder because associated with lung stiffness and incomplete lung expansion
is fibrosis an obstructive or restrictive lung disorder?
(fibrosis = formation or development of excess fibrous connective tissue) restrictive lung disorder
is fibrosis an obstructive or restrictive lung disorder?
restrictive
is oedema an obstructive or restrictive lung disorder?
restrictive
is pneumothorax an obstructive or restrictive lung disorder?
restrictive
what is taken into account in static measurements of lung function (static spirometry)?
only the volume exhaled
what is taken into account in dynamic measurements of lung function (dynamic spirometry)?
the time take to exhale a certain volume (so the volume and the time are taken into account)
which volumes can by measured by spirometry?
tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), inspiratory capacity (IC), vital capacity (VC) (NOTE: only residual volume cannot be measured, so functional residual capacity cannot be either)
what is the value of forced expiratory volume in 1 second (FEV1) in fit, healthy males?
4.0L
what is the forced vital capacity (FVC) in fit, healthy males?
5.0L
what is the value of FEV1/FVC in fit, healthy males?
80%
how does FEV1/FVC vary with an obstructive disorder?
both FEV and FVC fall but FEV more so, ratio is reduced
the rate at which air is exhaled is much slower, the FVC is also reduced (FRC may be increased), major effect is on the airways and so FEV is reduced to a greater extent than FVC, the ratio is also reduced)
how does FEV1/FVC vary with an restrictive disorder?
both FEV and FVC fall so ratio remains same
the absolute rate of airflow is reduced, total volume is reduced due to limitations to lung expansion, ratio remains constant or can increase as a large proportion of volume can be exhaled in the first second (no need to increase breathing rate)
is a normal FEV1/FVC ratio always indicative of health?
No, because constant FEV1/FVC in restrictive disorders despite sever compromise of function
what is the Forced Expiratory Flow (FEF25-75)
average expired flow over the middle of an FVC, correlates with FEV1 but changes are generally more striking
“normal” range is greater
(EN GROS: variations de la FEV1/FVC dans l’intervalle FVC)
