PULMONARY VENTILATION DR AMNA TAHIR ASSISTANT PROFESSOR PHYSIOLOGY DEPARTMENT

PULMONARY VENTILATION It means the inflow and outflow of air between the atmosphere and the lung alveoli Movement of air in and out is brought by changes in size and volume of thoracic cavity which lungs passively following these changes ( so lungs have no active role to play in breathing mechanism)

PRESSURES IN PLEURAL CAVITY PLEURAL PRESSURE It is a negative pressure in pleural cavity which keeps the lungs expanded . During inspiration this pressure becomes more negative so lungs become more expanded .Normally it is -5 cm of water and become -7.5 cm of water during inspiration. During expiration the event essentially reversed

PRESSURES IN PLEURAL CAVITY Alveolar pressure It is the pressure of air inside the lung alveoli . When the glottis is open and no air is flowing into or out of lung ,the pressure in all parts of respiratory tree ,all the way to alveoli ,are equal to atmospheric pressure , which is considered to be zero reference in the airways… 0 cm of water

During inspiration the pressure in the alveoli falls below atmospheric pressure ( below zero ) to cause inward flow of air into the alveoli . So during inspiration it becomes - 1 cm of water and becomes + 1 cm of water in expiration .

TRANSPULMONARY PRESSURE DIFFERENCE BETWEEN Alveolar pressure AND PLEURAL PRESSURE DURING THERE PRESSURE CHANGE IN INSPIRATION THERE IS INCREASE IN LUNG VOLUME OF 0.5 LITER AND IN EXPIRATION THIS 0.5 LITER MOVES OUT S

Volume and Pressure Changes Figure 16.13 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

PULMONARY VENTILATION: MECHANISM During inspiration inspiratory muscles contract so size of thorasic cavity increases in all direction Pleural pressure becomes more negative( sub atmospheric) alveolar pressure also becomes below atmospheric pressure Air moves into the lungs .

PULMONARY VENTILATION: MECHANISM During quite expiration ,when inspiratory muscle relax , size of thoracic cavity decreases Pleural pressure becomes less negative , lungs are less expanded ,alveolar pressure rises above atmospheric preesure air moves out of lungs BASIC FACTOR IS THE CHANGE IN SIZE AND VOLUME OF THORACIC CAVITY

PULMONARY VENTILATION: MECHANISM 4/28/2017 Pressure gradients are established by changes in the size of the thoracic cavity that are produced by contraction and relaxation of muscles (Figures 24-4 and 24-5) Boyle’s law: the volume of gas varies inversely with pressure at a constant temperature Inspiration: contraction of the diaphragm and external intercostals produces inspiration; as they contract, the thoracic cavity becomes larger (Figures 24-6 and 24-7) Expansion of the thorax results in decreased intrapleural pressure, leading to decreased alveolar pressure Air moves into the lungs when alveolar pressure drops below atmospheric pressure Compliance: ability of pulmonary tissues to stretch, thus making inspiration possible

Chest Wall and Pleural Sac Figure 16.7 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Pulmonary Pressures Figure 16.8a–b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

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Minute Ventilation Total volume of air entering and leaving respiratory system each minute Minute ventilation = VT x RR Normal respiration rate = 12 breaths/min Normal VT = 500 mL Normal minute ventilation = 500 mL x 12 breaths/min = 6000 mL/min Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Dead Space and Ventilation Fresh air “Old air” Alveolus Conducting zone (anatomical dead space) Expiration Inspiration Exchange with blood CO2 O2 (a) (b) (c) Figure 16.17 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Respiratory Rate and Ventilation Table 16.1 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Alveolar Ventilation Volume of air reaching the gas exchange areas per minute Alveolar ventilation = RR X (VT- VD) Normal = 4200 mL/min 12 X( 500- 150) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

DEAD SPACE It is the portion of inspired air that does not take part in gaseous exchange with pulmonary capillary blood Tidal volume ; It is the volume of air inspired or expired with each normal breath .It is about is 500 ml in the adult male. Out of 500ml ,350 ml goes to alveoli 150ml remains in conducting airways.

Definitions of Dead Space Anatomic Dead Space Physiologic Dead Space Low Blood Flow Copyright © 2006 by Elsevier, Inc.

Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Respiratory Zone Figure 16.3 (3 of 3) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Anatomy of the Respiratory Zone Figure 16.5a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

TYPES OF DEAD SPACE ANATOMICAL DEAD SPCAE PHYSIOLOGICAL DEAD SPACE

Alveolar dead space ANATOMICAL DEAD SPCAE Consist of conducting airways= 150 ml Physiological dead space = anatomical dead space + alveolar dead space Alveolar dead space Consists of nonfunctional or partially functional alveoli or lack of perfusion Wastage ventilation

Physiological dead space = anatomical dead space as normally alveolar dead space is absent Dead space starts from nose to terminal bronchiole When we expire out first 150 ml comes from dead space expired out,then 350 ml from ventilation area is expired out s

Disadvantages of dead space

Measurement of ANATOMICAL DEAD SPCAE by Nitrogen Washout method Measurement of Physiological dead space by Bohr’s method s

Measurement of ANATOMICAL DEAD SPCAE by Nitrogen Washout method

Measurement of Physiological dead space by Bohr’s method

Factors that increase dead space Factors that decrease dead space