Concentration Gradients of Gases 22 1 Ambient Pressure and Concentration Gradients 22 2 Factors Affecting Gas Exchange Membrane thickness respiratory membrane is very thin Left ventricular failure causes pulmonary edema Due to BP backs up into the lungs and causes the resp membranes to fill with up fluid and thicken gases have farther to travel between blood and air greater diffusion distance not enough time for gases to reach equilibrium between lungs and blood Membrane surface area Healthy lung has a lot of respiratory membrane surface area Several pul diseases decrease the alveolar surface lung cancer tuberculosis emphysema 22 3 Lung Disease Affects Gas Exchange 22 4 Ventilation Perfusion Coupling Ventilation perfusion coupling is the ability to match ventilation and perfusion to each other Poor ventilation of some alveoli Because of tissue destruction or airway blockage causes reduced PO2 in blood vessels in lungs causes local vasoconstriction of the pulmonary arteries in response redirecting blood to better ventilated alveoli perfusion adjustment Opposite from the systemic arteries where local hypoxia causes local vasodilation Poor ventilation Cause local increase in arterial CO2 levels stimulates local bronchodilation and improves airflow ventilation adjustment 22 5 Ventilation Perfusion Coupling Good ventilation of some alveoli Increased PO2 in blood vessels in lungs causes local vasodilation of the pulmonary arteries in response increasing perfusion by directing blood towards the better ventilated alveoli perfusion adjustment Good ventilation Cause local decrease in arterial CO2 levels stimulates local bronchoconstriction and decreases airflow ventilation adjustment 22 6 Perfusion Adjustments 22 7 Ventilation Perfusion Coupling Poor perfusion of capillary bed of some alveoli means reduced blood flow to those alveoli lead to decreased PCO2 in those alveoli less CO2 rich blood entering those alveoli It causes local bronchoconstriction and decreased air flow ventilation adjustment Good perfusion of capillary bed of some alveoli means increased blood flow to those alveoli Lead to increase PCO2 in those alveoli more CO2 rich blood entering those alveoli It causes local bronchodilation and increased air flow ventilation adjustment 22 8 Ventilation Adjustments 22 9 Ventilation Perfusion Coupling In sum if local blood flow is low then local air flow is low while if local air flow is low then local blood flow is low And vice versa 22 10 Respiratory System Alveolar Ventilation Respiratory Disorders Read on your own Measurements of Ventilation Read on your own Gas Transport Systemic Gas Exchange Alveolar Gas Exchange Finished 22 11 Alveolar Ventilation Tidal volume is the amount of air inhaled or exhaled in one breath during relaxed quiet breathing Dead air Not all the air that is inhaled goes as far as the alveoli About 150 mL of the 500 mL of atmospheric air never reaches the respiratory division during each inspiration This 150 mL of dead air merely moves into the conducting airways Anatomic dead space cannot exchange gases in this space After each expiration 150 mL of the 500 mL of alveolar air remains in the conducting division having pushed out the 150 mL of atmospheric air which means only 350 mL of alveolar is exhaled during each expiration 22 12 Alveolar Ventilation Physiologic total dead space sum of anatomic dead space and any pathological alveolar dead space In healthy people the anatomical and physiological dead spaces are equal i e they have zero alveolar dead space In pul diseases some alveoli may be unable to exchange gases because of reduced blood flow or thickened pul membrane dead space is the structural feature where gas is not exchanged It is NOT a function of how hard once can inspire or expire air 22 13 Alveolar Ventilation Alveolar ventilation rate air that ventilates alveoli X respiratory rate If 500 mL of inhaled air then 150 mL stays in the dead space which leaves 350 mL to ventilate the alveoli If the rate of respiration is 12 breaths per minute then AVR 350 mL per breath x 12 breaths per min 4 200 mL min Increased depth of breathing is more effective in elevating AVR than increase in breathing rate 22 14 Respiratory Disorders Restrictive disorders those that reduce pulmonary compliance limit the amount to which the lungs can be inflated examples are diseases that cause pulmonary fibrosis such as black lung disease and tuberculosis Obstructive disorders those that interfere with airflow by narrowing or blocking the airway make it harder to inhale or exhale a given amount of air examples are asthma and chronic bronchitis excess mucus like a chest cold blocks or reduces airflow Emphysema combines elements of restrictive and obstructive disorders lung tissue damage interferes with expiration less compliant too 22 15 Measurements of Ventilation Spirometer measurements of ventilation are commonly made using a spirometer which recaptures expired breath and records rate and depth of breathing speed of expiration and rate of oxygen consumption Respiratory volumes tidal volume TV volume of air in one quiet breath inspiratory reserve volume IRV air in excess of tidal inspiration that can be inhaled with maximum effort expiratory reserve volume ERV air in excess of tidal expiration that can be exhaled with maximum effort residual volume RV air remaining in lungs after maximum voluntary expiration 22 16 Residual Volume The alveoli will never completely empty after maximal active expiration The remaining air in lungs which cannot be exhaled after maximum effort is the residual volume The left behind air is mostly a function of physical breathing capacity or physical ability to breath It does help keep alveoli inflated between breaths and mixes with fresh air on next inspiration 22 17 Respiratory Capacities Vital capacity ERV TV IRV total amount of air that can be exhaled with effort after maximum inspiration Maximum ability to ventilate the lungs in one breath assesses strength of thoracic muscles and pulmonary function Inspiratory capacity TV IRV maximum amount of air that can be inhaled after a normal tidal expiration Total lung capacity VC RV maximum amount of air lungs can hold Minute respiratory volume air inhaled per min TV x respiratory rate at rest 500 ml x 12 min 6 L min 22 18 Lung Volumes and Capacities 22 19 Oxygen Transport Gas transport in blood is the process of moving gases from the alveoli to the systemic tissues and vice versa Oxygen concentration