Pulmonary / Lung Function Tests (PFTs). SURFACTANT. Lipoprotein mixture present in thin layer of fluid lining the alveoli. Consist of surfactant apoprotein , a phospholipid which is dipalmityl lecithin & calcium ions . Secreted by type II alveolar cells. Present at fluid-air interface.
When lungs shorten, surfactant molecules move together and become concentrated surface tension is reduced
Presence of surfactant
Deficiency of surfactant
Fluid will move into the alveoli to cause pulmonary edema.
More surface tension due to less surfactant.
-3 mm Hg
increase in transpulmonary pressure (if enough time is
allowed to reach equilibrium).
are determined by:
Elastic forces of the lung tissue are determined mainly by elastin & collagen fibers in lung parenchyma.
In deflated lungs, these fibers are in an elastically contracted and kinked state;
when the lungs expand, the fibers become
stretched and unkinked, thus elongating and exerting even more elastic force.
When the lungs are filled with air, there is an interface between the alveolar fluid and air in alveoli.
In case of saline solution–filled lungs, there is no air-fluid interface; therefore, surface tension effect is not present—only tissue elastic forces are operative.
(Transpleural pr. required to expand air-filled lungs) is 3 x > (Transpleural pr. required to expand saline solution–filled lungs).
Tissue elastic forces tending to cause collapse of air-filled lung represent only 1/3 of total lung elasticity,
whereas fluid-air surface tension forces in alveoli represent 2/3 of total lung elasticity.
The fluid-air surface tension elastic forces of the lungs also increase tremendously when surfactant is not present.
Quiet inspiration is active, while quiet expiration is passive.
So at rest, energy expenditure is on inspiration.
3-5 % of total body energy at rest is used
in work of breathing.
There is increased rate of pulmonary ventilation & both inspiration & expiration become active.
So, energy used in work of breathing increases much.
But as total energy expenditure of body also increases very much, so %wise, it remains same, that is 3 – 5 %Work of breathing
fall in FEV-1 > fall in FVC.
fall in FEV-1 and FVC are usually proportional & so FEV-1% remains within normal limits.
If fall in FEV-1 is relatively less FEV-1% will be higher than normal.
Significance: Can differentiate between
reversible & irreversible
obstructive lung disease.
Reversible: Chronic bronchitis & bronchial
(Initial helium conc.) x (volume of spirometer) =
(final helium conc.) x (volume of spirometer + FRC)
Amount of gas transferred from alveoli to capillary blood per unit time as a function of mean partial pressure gradient.
D.C of a gas = amount of its uptake per min.
difference between its tension in alveolar air & capillary blood
SINGLE BREATH TECHNIQUE:
CO in a conc. of 0.3% is inspired in 1 single breath.
held in lungs for 10 sec & then forcefully expired.
Last portion of expired air is collected to determine its CO content.
Transfer factor for CO = ml CO transferred / min from alveolar gas to blood
(Mean alveolar PCO ) – (Mean capillary blood PCO )
1. Interstitial or alveolar pulmonary
Diffusion of O2 = 1.23 time that of CO.
So transfer factor for O2 =
Transfer factor for CO X 1.23
CO in a conc. of 0.3% is inspired in a single breath,
held in lungs for about 10 sec & then
Gives identical value to steady state method.
Steady state method:
CO in low conc. is breathed for several minutes.
Gives identical value to single breath method.Methods for measuring Diffusion Capacity of Gases:
Non respiratory air movement into respiratory tract:
2) Epiglottis closes.
3) Vocal cords shut tightly to entrap the air within the lungs.
5) While other expiratory muscles, like internal intercostals, also contract forcefully.
Hg or more.
7) The vocal cords & epiglottis suddenly
8) Air explodes outward (may be at 75 to
100 miles /hr) under this high pressure in
10) Exploding air passes through bronchial
& tracheal slits.
11) Rapidly moving air carries with it any
foreign matter present in bronchi or trachea.
Applies to nasal passages
Stimulus: irritation in nasal passages/ upper respiratory tract.
Afferents: cranial nerve V
Uvula: depressed, air passes through the nose as posterior nares are open.
Applies to lower respiratory passages.
Stimulus: irritation in lower respiratory passages.
Afferents: vagus nerve
Posterior nares: remain closed.SNEEZE REFLEX: