4. Respiratory Physiology.pdf

RESPIRATORY PHYSIOLOGY * Respiration is the process by which one exchange gases with the environment. Its purpose is to trade CO2 for O and to help maintain body temperature and acid-base balance. * The cardiopulmonary system provides the mechanism. It is designed to work efficiently at sea level....

RESPIRATORY PHYSIOLOGY * Respiration is the process by which one exchange gases with the environment. Its purpose is to trade CO2 for O and to help maintain body temperature and acid-base balance. * The cardiopulmonary system provides the mechanism. It is designed to work efficiently at sea level. However, this can be achieved in wide range of environment from deep undersea to the lunar surface by combining – life support systems – training – and human adaptation. Purpose of Reviewing the Respiratory Physiology In order to understand the physiological disturbances caused by exposure to high altitude, one must have a good idea about the physiology of respiration under both normal and abnormal environmental conditions The Respiratory Process 2 Processes 1. External Respiratory -Ventilation of lungs -Transfer of gases through the pulmonary membrane (alveolar & capillary) into the blood 2. Internal Respiratory -Transporting gases to and from the tissues -Exchanging gases in the tissues Phases of Gas Exchange 1. Ventilation – a cyclic process by which inhaled air is drawn into the alveoli and an equal volume of pulmonary gas is exhaled. 2. Diffusion (lung)– the process by which O2 and CO2 pass through the alveolar membrane and capillary walls 3. Transportation – the transfer of gases by the blood between the lungs and the tissues. 4. Diffusion (tissues) – the process by which gases are exchanged between the blood and tissues 5. Utilization – the chemical reaction within the cells that use O2 to produce the energy needed to sustain life. A. Tissue Respiration For all tissue’s biological process, energy is required. The source of energy is held in energy-rich bonds of Adenosine Triphosphate (ATP). Hydrolysis of ATP to produce Adenosine Diphosphate (ADP) will produce the energy for the biological process. The source of ATP is from oxidation of complex molecules (glucose) to CO2 and water. *One molecule of glucose, when completely oxidized, yields 38 molecules of ATP. Breakdown of glucose molecule without O2 (anaerobic metabolism) will yield only 2 molecules of ATP. This process occurs in the mitochondria of the cytoplasm and CO2 + H2O with generator of molecules of ATP will be the product of it (oxidative phosphorylation). The oxidative phosphorylation requires a certain minimum molecular concentration (tension) of O2 (from 0.53.0mmHg to 240mmHg). If PO2 is less than the minimum required → No oxidative phosphorylation i.e. Less than 0.5-3.0 mmHg (Hypoxia) → No oxygen consumption … If PO2 is very high tension → No oxidative phosphorylation i.e. More than 240 mmHg (oxygen toxicity) → No oxygen consumption … The major products of the complete oxidation of food stuff are CO2 and water. The ratio of the volume of CO2 produced to the volume of O2 consumed by the tissue is termed Respiratory Quotient (RQ). Rise in the molecular concentration of CO2 → increase Acidity B. Blood-Tissue Gas Exchange The O2 required for oxidation brought to a tissue by the capillaries. The same flow of blood removes the CO2 produces as product of oxidation process. The exchange occurs by simple diffusion through the capillary wall and the cell wall as per the concentration gradient in accordance with Fick’s Law of Diffusion. “Fick’s Law of Diffusion.” ”The rate of diffusion of a gas between 2 points in a fluid is proportional to the difference of concentration (partial pressure) of the gas at the 2 points and inversely proportional to the distance between them.” “The rate of diffusion is also proportional to the solubility of the gas in the fluid and inversely proportional to the sequence root of the molecular weight of the gas.” B. Blood-Tissue Gas Exchange * CO2 diffuses 20 times more rapidly than O2 * Transfer of CO2 to the blood is easier than delivery of O2 to the tissues. * In the tissues consumption of O2 by the cells → PO2 to fall C. Carriage of Gases by the Blood O2 is carried by the blood in physical solution and in chemical combination. Only 1.5% of the carried O2 is dissolved and the rest is combined with Hb (Oxyhaemoglobin- the easily reversible). The maximum amount of O2 which can be combined with one gram of Hb is 1.39ml. So 1.39mx15gm/dl=20.8ml/dl blood. This is expressed as the O2 saturation of Hb. • The relationship between O2 saturation of Hb and O2 tension in blood is described by the O2 Dissociation Curve. • The O2 Dissociation Curve is sigmoid in shape. * The O2 saturation of the Hb is about 97.5% at D2 tension of 100mmHg (PH of blood is 7.4 and Temp. 37° C). * The Hb become fully saturated (100%) when O2 tension is>200mmHg. * At higher O2 tension (60-100mmHg), The curve is much flatter. * At lower O2 tension (<60mmHg), the saturation increases rapidly. * Increase the O2 tension (10mmHg) from 90-100mmHg will increase the saturation by 1% only * Whereas, similar change in O2 tension from 35-45mmHg will ↑’’ ‘’ by 14% Hb is half saturated (50%) is at O2 tension of 26mmHg. Significance of the Sigmoid Shape * The flat upper portion means moderate variation in O2 → small effect on saturation. * The steep part means (O2 tension 40-55) ensures that during passage of blood through pulmonary capillaries. * The O2 tension does not rise until much of O2 has been transferred to the blood, i.e. maintain the tension at which O2 is delivered to the tissue when the arterial O2 tension is lowered by hypoxia. * Fall in PH, rise in PCO2, and rise of temperature, will shift the curve to right, i.e. when tissue working → increase the amount of O2 given up by blood (improving O2 delivery) * Bohr effect (the affinity of O2 for Hb increases → O2 dissociation curve to left) D. Gas Exchange in the Lungs * Primary function of the lung is the exchange of O2 and CO2 between the venous blood and the air. * Other functions: • Filtering toxic materials (blood thrombi) • Metabolism of certain active agents (heparin, histamine) • Acts as reservoir of blood Functional Anatomy of the lungs * Contains 300 000 000 air sacs (alveoli). * Gases are exchange across the alveolar capillary membrane (total area of exchange gases = 50-100m²) * Surfactant lowers the surface tension of the alveolar lining fluid. • Respiratory passages (bronchial tree) • Upper conducting airways → The nose, Mouth, pharynx, trachea, & the main, lobar, segmental, & terminal bronchi. They are functioning to carry inspired air down to the gas exchange regions (Dead space). • The terminal bronchioles divides into Respiratory bronchioles, which have Alveoli attached their walls. The final division of the airways constitutes the alveolar ducts, which are lined completely with alveoli (Respiratory zones of the lungs). • The respiratory zone volume = 2500 ml. • In the Resp. zone, ventilation occurs mainly by diffusion (no movement of gas). Capillary Bed & The pulmonary arterial/Capillary beds surround the alveoli The networks of capillaries around the alveoli are very dense & the capillary segments are so narrow & short that there is a continuous sheet of blood over the alveolar wall. Lung Measurements For both physiologic & clinical purposes, the ventilatory function of the lung has been divided into functional volume measurements, These lung Volumes are defined as follows: Tidal Volume: The Volume of air inspired or expired with each Normal breath → 500 ml. Inspiratory reverse Volume: The extra Volume of air that can be inspired above the Normal Tidal Volume by Conscious Forceful Inspiration → 3100 ml Expiratory reverse Volume: The Volume of air that can be expired by a forceful expiration after the end of Normal Tidal Volume expiration → 1200 ml. Residual Volume: The Volume of air in the lungs that can not be expired → 1200 ml Lung Capacities Inspiratory Capacity: The Tidal Volume + Inspiratory Reverse Volume → 3600 ml Functional Residual Capacity: The Residual Volume + Expiratory Reverse Volume → 2400 ml Vital Capacity: The Sum of Exp. Res. Volume + Tidal Volume +Ins. Res. Volume → 4800 ml Total Lung Capacity: The Sum of the 4 Lung Volumes → 6000 ml E. Pulmonary Ventilation Ventilation is the cyclic process of Inspiration & Expiration in which fresh air is drawn into the respiratory tract & pulmonary gas is expelled from it. The total volume of gas expired from the lungs per unit of time is termed the pulmonary ventilation (Volume expired / minute) often called the “minute Volume”. Respiratory minute Volume = 500 x 16 = 8 Liters/min * Since pulmonary ventilation is the product of the Tidal Volume & respiration frequency, either or both components can contributes to an increase in pulmonary ventilation. Thank you