CAUSES OF NEGATIVE OF INTRAPLEURAL PRESSUREIPP 1 Lack

CAUSES OF NEGATIVE OF INTRAPLEURAL PRESSURE(IPP) 1 -Lack of air in pleural cavity. 2 -Elastic recoil of the lung which continuously pulls against the continuous tendency of relatively rigid chest wall to expand creates a continuous negative pressure. This negative pressure antagonizes the elastic recoil.

THE ELASTIC RECOIL OF THE LUNG IS DUE TO: • 1 -The fibers of the lung tissue which are continuously stretched , always tend to recoil(=1/3 of the recoil) • 2 -The surface tension of the fluid lining the alveoli causes intermolecular attraction between the surface molecules of the fluid, so the alveoli always tend to collapse (2/3 of the recoil)

IMPORTANCE OF NEGATIVITY OF IPP • 1 -It helps expansion of the lungs. • 2 -It is responsible for the negative intrathoracic pressure which also helps • -Venous return to the heart. • -Lymphatic flow in thoracic duct.

Alveolar pressure(Intrapulmonary P): • Alveolar pressure is the pressure inside the lung alveoli(is connected with the atmosphere. (which is considered to be 0 cm H 2 O)to cause inward flow of air during inspiration, the pressure in the alveoli must fall to a value slightly below atmospheric P (-2 cm. H 2 O)this slight negative P is enough to move about 500 m. L of air into the lungs in the 2 seconds required for inspiration

Alveolar pressure(Intrapulmonary P): • During expiration , opposite changes occur, the alveolar pressure rises to about (+2 cm. H 2 O)this forces the 500 ml of inspired air out of the lungs during 2 -3 seconds of expiration • Transpulmonary Pressure: It is the pressure difference between IPP&intra-alveolar pressure, it is the P difference between the alveoli and outer surfaces of the lungs (measure of elastic forces in the lungs that tend to collapse)

COMPLIANCE • Compliance of the lungs: The change in lung volume per unit change in air way pressure(strechibility)the normal compliance of both lungs together in adult human =200 ml/cm. H 2 O pressure. • Compliance depends on: • 1 -The elastic forces of the lung tissue itself. • 2 -The elastic forces caused by surface tension of the fluid that lines the inside walls of the alveoli and other lung air spaces. • Causes of decreased compliance • 1 -Deformity of spine and bone diseases. • 2 -Skeletal muscle disease. • 3 -Interstitial pulmonary fibrosis(increased stiffness). • 4 -Collection of air or fluid in intrapleural space.

SURFACTANT • Surfactant is a surface active agent, which means that when it spreads over the surface of a fluid, it greatly reduces the surface tension. It secreted by type II alveolar epithelial cells. • Surfactant is a complex mixture of several phospholipids, proteins and ions. The most important components are the phospholipid dipalmitoil phosphatidylcholine

FUNCTIONS OF SURFACTANT • 1 -Stability and fluid balance of the pulmonary alveoli. • 2 -Is very important in maintaining the equality of size of the alveoli. The large alveoli develop greater surface tension and therefore contract tending to empty their contents while the small alveoli develop less surface tension and therefore and to enlarge. • 3 -It helps to keep alveoli dry. • 4 -It prevents collapse of the lungs after expiration

LUNG VOLUMES AND CAPACITIES • PULMONARY VOLUMES • 1 -Tidal volume: (VT) It is the volume of air inspired or expired each cycle during normal quiet breathing , it is about 500. • 2 -Inspiratory reserve volume: (IRV) It is the maximal volume of air which can be inspired after a normal inspiration. It is about 3000 ml. • 3 -Expiratory reserve volume: (ERV)IT Is the maximal volume of air which can be expired after a normal expiration. It is about 1100 ml. • 4 -Residual volume: (RV)It is the volume of air remaining in the lungs after maximal expiration it is about 1200 ml.

PULMONARY CAPACITIES • 1 -Inspiratory capacity: (IC)It is the maximal volume of air that can be inspired from the resting expiratory level. • IC=TV+IRV=about 3500 ml. • 2 -Functional residual capacity: FRC. It is the volume of air remaining in the lung at the resting expiratory level(i. e. after normal expiration) • FRC=RV+ERV=about 2300 ml. • 3 -Vital capacity: VC. It is the maximal volume of air that can be expelled from the lung by a maximal expiration following a maximal inspiration • VC=IRV+ERV+TV=about 4600 ml. • 4 -Total lung capacity: TLC. It is the volume of air contained in the lungs at the end of maximal inspiration • TLC=IRV+TV+ERV+RV=about 5800 ml • Clinical importance of spirometric measurements:

Vital capacity: • It is a good index of pulmonary deficiency and it is affected by the following factors: • 1 -Posture • 2 -Respiratory muscles • 3 -lung elasticity.

TIMED VITAL CAPACITY • The forced vital capacity (FVC) is used to evaluate resistance properties of the airways and the strength of the expiratory muscles. The FVC is obtained by having the subject inspire as deeply as possible then expire as rapidly as possible into a spirometer, that measures not only volumes but also the time to expire. • Normally the FVC on forced expiratory volume(FEV)takes place in 4 seconds