Surfactant & compliance, LAW OF LAPLACE, Work of Breathing (the guyton and hall physiology)

It is a lipoprotein mixture present in thin layer of fluid lining the alveoli at the air fluid interface.

COMPOSITION
It is composed of
Apoprotein
Calcium ions
Phospholipids i.e. dipalmitoyl lecithin
Surfactant is secreted by
1. Mainly type II alveolar cells in the lungs.
2. Clara cells, which are situated in the bronchioles.
It lowers the surface tension of fluid lining the alveoli.

Surface tension is inversely proportional to surfactant concentration.

During inspiration surfactant molecules move apart as lungs are expanded and during expiration surfactant molecules become concentrated as lungs shorten.

When there is no surfactant, Surface Tension is 50 dynes/cm. when surfactant is present it is 5-30 dynes/cm depending upon the concentration
Prevents collapse of lungs

Stabilize size of alveoli

Surfactant helps to keep lungs expanded. If there is deficiency of surfactant then the pressure of -20 to -30 mm of Hg will be required to keep the lungs expanded

Surfactant also helps to keep the alveoli dry and prevent development of pulmonary edema.

Surfactant is also helpful in lung expansion at birth. If there is deficiency then there is Respiratory Distress Syndrome.
LAW OF LAPLACE:

pressure required to keep a hollow viscous distended = 2 T/R
Where T is tension and R is radius.

During expiration, size of alveoli decreases so R is decreased and if T does not decrease, much higher pressure will be required to keep the alveoli distended.

When adequate amount of surfactant is there T also decreases so increased pressure is not required. This prevents the collapse of lungs and also stabilizes the equal size of alveoli
Definition:
“Compliance is the measure of expansibility or distensibility of the lungs. It indicates with how much ease lungs can be expanded”.
Work of Breathing
In certain diseases there is increased work of breathing and depending upon the nature of breath there will be specific increase in work of breathing.

In asthma there is increase in work of breathing to overcome airway resistance

In restrictive lung diseases there is increase work of breathing in both tissue resistance and elastic recoil.

1. SURFACTANT Source: The Guyton and Hall physiology Maryam Fida (o-1827)

2. SURFACTANT It is a lipoprotein mixture present in thin layer of fluid lining the alveoli at the air fluid interface. COMPOSITION It is composed of Apoprotein Calcium ions Phospholipids i.e. dipalmitoyl lecithin

3. SOURCE OF SECRETION OF SURFACTANT Surfactant is secreted by 1. Mainly type II alveolar cells in the lungs. 2. Clara cells, which are situated in the bronchioles.

4. RELATION WITH SURFACE TENSION It lowers the surface tension of fluid lining the alveoli. Surface tension is inversely proportional to surfactant concentration . During inspiration surfactant molecules move apart as lungs are expanded and during expiration surfactant molecules become concentrated as lungs shorten . When there is no surfactant, Surface Tension is 50 dynes/cm. when surfactant is present it is 5-30 dynes/cm depending upon the concentration

5. FUNCTIONS OF SURFACTANT Prevents collapse of lungs Stabilize size of alveoli Surfactant helps to keep lungs expanded. If there is deficiency of surfactant then the pressure of -20 to -30 mm of Hg will be required to keep the lungs expanded Surfactant also helps to keep the alveoli dry and prevent development of pulmonary edema . Surfactant is also helpful in lung expansion at birth. If there is deficiency then there is Respiratory Distress Syndrome.

6. LAW OF LAPLACE : pressure required to keep a hollow viscous distended = 2 T/R Where T is tension and R is radius . During expiration, size of alveoli decreases so R is decreased and if T does not decrease, much higher pressure will be required to keep the alveoli distended. When adequate amount of surfactant is there T also decreases so increased pressure is not required. This prevents the collapse of lungs and also stabilizes the equal size of alveoli

7. COMPLIANCE Definition: “ Compliance is the measure of expansibility or distensibility of the lungs. It indicates with how much ease lungs can be expanded”.

8. FORMULA Compliance is the change in lung volume per unit change of the transpulmunory pressure or pleural pressure. Compliance = ∆V/∆P Combined compliance of thorax and lungs is 110ml/cm of H2O C ompliance of the lungs alone is 200 ml/cm of H2O

9. Measurement of Compliance To measure compliance we ask the subject to inspire and expire in short steps of 50-100 ml. in this way we measure the transpulmunory pressure. Transpulmunory pressure = alveolar pressure – pleural pressure. When alveolar pressure becomes zero i.e. when the subject is not inspiring or expiring, alveolar pressure is zero. So transpulmunory pressure becomes equal to pleural pressure which we can measure by esophageal method. If we remove one lung, compliance becomes half

10. APPLIED PHYSIOLOGY Increase in Compliance Decrease in Compliance Physiological condition : Old age due to loss of elastic property of lung tissues. 2. Pathological condition : Emphysema only condition in which there is loss of membranes and loss of elastic tissue. Decreased compliance means lungs are difficult to expand. Decreased lung compliance occurs in fibrosis, atelectasis, COPD, effusion , Bony deformities kyphosis, scoliosis, surfactant deficiency, respiratory muscle weakness.

11. TYPES OF Compliance 1. STATIC COMPLIANCE : Recorded during breath holding. 2 . DYNAMIC COMPLIANCE : measured during regular breathing. 3. Specific Compliance: Specific compliance is the compliance per liter of lung volume. Specific compliance = Compliance of lungs Functional residual capacity Functional residual capacity is the volume of air present in lungs at the end of normal expiration. ELASTANCE : It is reciprocal of compliance. i.e. ∆P/∆V

12. Work of Breathing Definition : “Work of breathing is the work done by respiratory muscles during breathing to overcome the resistance in thorax and respiratory tract .”

13. WORK DONE BY RESPIRATORY MUSCLES During respiratory processes, inspiration is active process and the expiration is a passive process. So, during quiet breathing, respiratory muscles perform the work only during inspiration and not during expiration

14. Work of Breathing During quite inspiration : 65 % of work of breathing is to overcome elastic recoil tendency of the lungs and this is called the elastic work or compliance work. Lungs always tend to shorten back . 28% of work of breathing is to overcome the airway resistance. Medium and large sized airways offer most of the airway resistance not terminal bronchioles . 7 % of work of breathing is to overcome the tissue resistance

15. Work of Breathing In certain diseases there is increased work of breathing and depending upon the nature of breath there will be specific increase in work of breathing . In asthma there is increase in work of breathing to overcome airway resistance In restrictive lung diseases there is increase work of breathing in both tissue resistance and elastic recoil.