Respiratory Physiology By: M.H.Dashti Lecture 2 mechanics of breathing, static Lung Volumes & capacities, Dynamic Lung Volumes

The mucociliary transport system in the airways: The sol phase or periciliary fluid, The gel phase or mucus layer & cilia

mechanics of breathing L ung & chest wall relationship Each lung is covered by one pleura a serous membrane lining the pleural cavity Parietal pleura- attaches to the walls of the pleural cavity Visceral pleura- adheres to the surface of the lungs

Pleural Pressure Lungs have a natural tendency to collapse –s–surface tension forces 2/3 –e–elastic fibers 1/3 Chest wall has a natural tendency to expand negative pleural pressure itself is produced by 2 opposite recoil tendencies of lung and chest wall and keeps these 2 Lungs Held against the chest wall by “suction” or negative pleural pressure

mechanics of breathing based on BOYL’S LAW of gasses ( PV=k )

According to Poiseuill’s law air flows in & out of the lungs by Alveolar Pressure Changes which is based on BOYL’S LAW P B =0 (P B – P alv ) Q or F = R

According to Boyl's Law, Pressure changes are related to volume changes which requires the contraction of ventilatory muscles Inspiratory muscles Sup. Serratus Levator Costarum Expiratory muscles Post Inf. Serratus Transverse Thoracis Pyramidal Deep Inspiratory muscles Tidal Inspiratory muscles

Changes in respiratory pressures & lung volume during a tidal respiratory cycle Spirometry – measurements of lung volumes

Static Lung Volumes & capacities

RESTRICTIVE lung disease reduces static lung volumes Volume (litres) Time (sec) Vital Capacity Total Lung Capacity Volume (litres) Time (sec) Residual Volume

Rest

Unknown Functional Residual Capacity (V2) in lungs (V2) Known Spirometer Volume (V1) (V1) (C1) = Initial conc. Helium dilution method for Determination Of RV, FRC, TLC add Helium (He) Lungs Spirometer At the Beginning Of normal inspiration

after 2-3 minuets rebreathing at the end Of normal expiration Known Spirometer Volume (V1) Unknown Functional Residual Capacity (V2) in lungs (V2) (V1) (C2) = Hel ium Conc. after rebreathing

At the beginning of test At the end of test Initial Amount of He=Final Amount of He Amount in Spirometer=Amount in Spirometer + Lungs (V1 x C1) = (V2 + V1) x C2 (V1 x C1) = (V2 x C2) + (V1 x C2) (V1 x C1) - (V1 x C2) = (V2 x C2) V1 x (C1 - C2) = V2 C2 V1 x (C1 - C2) / C2= V2 = FRC FRC – ERV = RV FRC + IC = TLC Helium dilution method for Determination Of RV, FRC & TLC

Pulmonary dynamic volumes Forced Rapid Expiration Fallowing a Deep Inspiration FVC =Forced Vital Capacity FEV1 =Forced Expiratory Volume in 1 st sec =%85 FEV3 =Forced Expiratory Volume in 3 rd sec =%97 F FEV 3 FVC CURVE

Maximal mid expiratory flow /FEF Maximal flow rate of expired air in the middle of forced expiration MMEF =MEV/MET - F X X X MEV MET

FEV 1 < 80% of FVC Forced Vital Capacity - FVC Forced Expiratory Volume in 1 sec - FEV 1 Volume (litres) Time (sec) Total Lung Capacity Residual Volume 1 sec OBSTRUCTIVE lung disease

Flow metery is one of the most convenient and widely used respiratory tests. Patient inspires to TLC and exhales forcibly through a flow meter Peak flow is: effort dependent dependent upon tissue recoil as well as airway calibre Flow volume curve- PEF Peak Expiratory Flow ( PEF ) flow (l/min) FVC (L) RVTLC FEF 25% FEF 50% FEF 75% Peak Expiratory Flow ( PEF ) flow (l/min) RVTLC

Lung volumes & capacities in different lung diseases