Gas Exchange & Perfusion II 2024-2025 Lecture Notes PDF

Block 1.2 lectures 2024-2025 lecture Highlighter key Writer Reviewer...

Block 1.2 lectures 2024-2025 lecture Highlighter key Writer Reviewer Doctor explanation Abbreviation Key information Book >> >> Zainab Adel Alali Zahraa Albarraqi Zahraa Albarraqi Zainab Adel Alali Student explaintion 221-222-223 notes References Deleted  COLLEGE OF MEDICINE ACADEMIC YEAR: 2022-2023 TITLE: GASEOUS EXCHANGE AND PERFUSION II CRN NO. 15571 (MALES) 15583 ( FEMALES) BLOCK: 1.3 SUBJECT / DISCIPLINE: PHYSIOLOGY EXPERT: DR ARIF MOHYUDIN BLOCK COORDINATOR: DR SHAHINA KHAN  Vision num< >ber To become a model in the community engagement through excellence and international recognition in medical education, research and health care. 12/24/24  MISSION num< >ber To promote higher standards in medical education, health care, research and community health services. 12/24/24  VALUES num< >ber Islamic values Excellence Creativity Compassion Leadership Responsiveness to Community 12/24/24  Gas Exchange & Perfusion II Dr. Arif Mohyuddin Associate Professor Department of Biomedical sciences Physiology Section College of Medicine, in Al Hassa King Faisal University, KSA < nu 12/24/24 >mber  Theme: 4 < Learning Question nu >mber 2. Define right-to-left shunt & physiological dead space (wasted ventilation). What effect does either have on pulmonary gas exchange? 12/24/24  Effect of the Ventilation-Perfusion Ratio on < Alveolar Gas Concentration nu >mber Two factors determine the PO₂ and the PCO₂ in the alveoli: (1) Rate of alveolar ventilation & (2) Rate of transfer of oxygen and carbon dioxide through the respiratory other names : Blood-air barrie or Alveolar- capillary membrane. membrane. Ventilation: The act of air movement into and out of the lungs. Perfusion: The circulation of blood through the tissues and organs of the body. Factors that affect the rate of gas diffusion through the respiratory membrane: 1- Thickness of the membrane 3. The di fusion coeficient of the gas in the substance of the membrane 4- The partial pressure difference of the gas between two sides of the membrane. 12/24/24  Effect of the Ventilation-Perfusion Ratio on < Alveolar Gas Concentration nu >mber However, even normally to some extent, and especially in many lung diseases, some areas of the lungs are well ventilated but have almost no blood flow, whereas other areas may have excellent blood flow but little or no ventilation. Normal function depends on : 1- proper ventilation 2- adequate perfusion. Abnormal function occurs in the following cases: 1. Air gets in, but no blood flows. 1. Good ventilation but no perfusion. 2. Blood flows, but little or no air gets in. 2. Minimal or no ventilation and well perfusion 12/24/24  Effect of the Ventilation-Perfusion Ratio on < Alveolar Gas Concentration nu >mber Therefore, a highly quantitative concept has been developed to help us understand respiratory exchange when there is imbalance between alveolar ventilation and alveolar blood flow. This concept is called the ventilation- perfusion ratio. Aeffective balanced ventilation/perfusion (V/Q) ratio is crucial for gas exchange, allowing oxygen to enter the blood and carbon dioxide to be removed from the body. 12/24/24  Effect of the Ventilation-Perfusion Ratio on < Alveolar Gas Concentration nu >mber In quantitative terms, the ventilation- VA = Alveolar Ventilation perfusion ratio is expressed as VA/Q. Q= Blood flow When VA (alveolar ventilation) is normal for a given alveolus and Q (blood flow) is also normal for the same alveolus, the ventilation- perfusion ratio (VA/Q) is also said to be normal. 12/24/24  Effect of the Ventilation-Perfusion Ratio on < Alveolar Gas Concentration nu >mber When the ventilation (VA) is zero, yet there is still perfusion (Q) of the alveolus, the VA/Q is zero. VA/Q= 0/1 = 0 1. Ventilation stops when the airway is blocked (e.g., trachea or bronchi). 2. The blockage can be caused by factors like stuck mucus. 3. Air can no longer flow in or out of the alveolus. 4. There is no renewal or exchange of air in the alveolus. 12/24/24  Effect of the Ventilation-Perfusion Ratio on < Alveolar Gas Concentration nu >mber Or, at the other extreme, when there is adequate ventilation (VA) but zero perfusion (Q), the ratio VA/Q is infinity. VA/Q= 1/0 = 1. A pulmonary embolism occurs when a blood clot, fat, or air blocks a pulmonary artery or one of its branches. 2. Blood flow (perfusion) to the affected lung area is stopped. 3. Ventilation continues, but there is no blood flow to exchange gases. 4. This causes the ventilation-perfusion (V/Q) ratio in the blocked area to approach infinity. 12/24/24  Effect of the Ventilation-Perfusion Ratio on < Alveolar Gas Concentration nu >mber At a ratio of either zero or infinity, there is no exchange of gases through the respiratory membrane of the affected alveoli, which explains the importance of this concept. Therefore, let us explain the respiratory consequences of these two extremes. 12/24/24  < nu >mber Concept of "Physiologic Shunt" (When VA/Q Is Below Normal) Normal PO₂-PCO₂, VA/Q diagram. 12/24/24.Normal Po2-Pco2, VA/Q diagram Downloaded from: StudentConsult (on 6 January 2013 08:44 AM) Elsevier 2005 © This curve illustrates the range of possible gas values in different conditions of ventilation and perfusion. 1 3 1. Point V (Venous Blood): Represents when the ventilation-perfusion (V/Q) ratio is zero. PO₂: 40 mmHg (oxygen in venous blood). PCO₂: 45 mmHg (carbon dioxide in venous blood). 2. Point ∞ (Inspired Air): Represents when the V/Q ratio is infinity. 2 PO₂: 149 mmHg (oxygen in inspired air). PCO₂: 0 mmHg (no carbon dioxide in inspired air). 3. Normal Alveolar Air: Represents the values in the alveoli when the V/Q ratio is normal. PO₂: 104 mmHg. PCO₂: 40 mmHg..Normal Po2-Pco2, VA/Q diagram Downloaded from: StudentConsult (on 6 January 2013 08:44 AM) Elsevier 2005 ©  1 3 1. V/Q Ratio = 0 (No Ventilation): Fresh air does not enter the alveoli. The gas levels in the alveoli match those of venous blood: PO₂: 40 mmHg. PCO₂: 45 mmHg 2. V/Q Ratio = ∞ (No Perfusion): 2 Blood flow to the alveoli is absent. The gas levels in the alveoli are the same as inspired air: PO₂: 149 mmHg. PCO₂: 0 mmHg..Normal Po2-Pco2, VA/Q diagram Downloaded from: StudentConsult (on 6 January 2013 08:44 AM) Elsevier 2005 ©  "Physiologic Shunt" Va = alveolar ventilation Q = blood flow < nu >mber Whenever VA/Q is below normal, there is inadequate ventilation to provide the oxygen needed to fully oxygenate the blood flowing through the alveolar capillaries. Therefore, a certain fraction of the venous blood passing through the pulmonary capillaries does not become oxygenated. This fraction is called shunted blood. It’s when there is less oxygen in the alveolus, shunted blood : is the fraction “amount” of venous Blood comes within the alveolar capillaries blood that pass through the pulmonary capillaries but doesn’t get oxygenated duo to the low without being oxygenated, the result will be less amount of oxygen in the alveolus oxygen in blood ( hypoxia ) This is called : shunted blood 12/24/24  "Physiologic Shunt" < nu >mber Also, some additional blood flows through bronchial vessels rather than through alveolar capillaries, normally about 2 percent of the cardiac output; this, too, is unoxygenated, shunted blood. Cardiac output = 5 L of blood/min There is some shunted blood normally existing in the body In pulmonary circulation, 98% of the cardiac output flows to the alveolar capillaries for oxygen exchange in the lungs The remaining 2% can enter and mix up with the arterial Not all the blood entering the lungs goes only to the capillaries of blood. the alveoli, some of the blood ( the remaining 2% ) goes to the This is normal shunting, bronchial vessels to supply the lung tissues, and doesn’t participate in therefore, a further slight fall in the gas exchanging process, This 2% of blood is called shunted PO2, the alveoli are 104, but blood ( normally exist in the body ) the artery is 100  "Physiologic Shunt" < nu >mber The total quantitative amount of shunted blood per minute is called the physiologic shunt. The greater the physiologic shunt, the greater the amount of blood that fails to be oxygenated as it passes through the lungs. These two cases of blood being shunted ( blood not being oxygenated because of blocked alveolus Or the normally 2% of blood supplying lung tissues by the bronchial vessels ) are called physiological shunted blood The PO2 in the arterial blood will be less than the normal value and that will lead to potential issues with oxygen delivery to the body’s tissues and organs 12/24/24  < "Physiologic Dead Space" nu >mber Concept of the "Physiologic Dead Space" (When VA/Q Is Greater Than Normal) When ventilation of some of the alveoli is great but alveolar blood flow is low, there is far more available oxygen in the alveoli than can be transported away from the alveoli by the flowing blood. Thus, the ventilation of these alveoli is said to be wasted. The exchange of gases occurs in the The physiological dead space is when : alveoli of the lungs, so, the air in the Va ( alveolar ventilation ) = 1 other areas cannot be exchanged with and, Q ( blood flow ) = 0, so : Va/Q = 1/0 ‎=♾️ the blood, these areas are known as dead Which means that there is air ready to be exchanged with space the blood but there is no enough amount of blood to carry this oxygen We inhale 500 ml of air normally, onle That’s why Va/Q is said to be “Greater than normal” 2/3 of the 500 ( 350 ml ) can reach the alveoli and go through the exchange Why the air in the dead space is described as “wasted” ? process, while the other 1/3 of the 500 Because we have a good amount of air “ oxygen” but we ml ( 150 ml ) are wasted in the don’t have enough blood to carry it anatomical dead space  "Physiologic Dead Space" Dead space : Trachea / all of the Conducting passage < nu >mber The ventilation of the anatomical dead space areas of the respiratory passageways is also wasted. The sum of these two types of wasted ventilation is called the physiologic dead space. Anatomical dead space : the area where the air is not oxygenated like trachea Physiological dead space : wasted ventilation of alveoli + anatomical dead space 12/24/24  "Physiologic Dead Space" < nu >mber When the physiologic dead space is great, much of the work of ventilation is wasted effort because so much of the ventilating air never reaches the blood. 12/24/24  Abnormal VA/Q in Chronic Obstructive Lung < Disease nu >mber Most people who smoke for many years develop various degrees of bronchial obstruction; in a large share of these persons, this condition eventually becomes so severe that they develop serious alveolar air trapping and resultant emphysema. The emphysema in turn causes many of the alveolar walls to be destroyed. The wall between two alveoli is destroyed, resulting in the enlargement of the individual alveoli, however, this destruction means that there is no longer an intact exchange membrane  Abnormal VA/Q in Chronic Obstructive Lung < Disease nu >mber Thus, two abnormalities occur in smokers to cause abnormal VA/Q. First, because many of the small bronchioles are obstructed & thus are unventilated, causing a VA/Q that approaches zero. Second, in those areas of the lung where the alveolar walls have been mainly destroyed but there is still alveolar ventilation, most of the ventilation is wasted. if Va ( alveolar ventilation ) = 0 and, Q ( blood flow ) = 1, then : Va/Q = 0/1 ‎= 0 as we know smokers will develop COPD then they will have inadequate ventilation which means the Va/Q will be zero. Also, in areas that have a destroyed wall of alveoli, the ventilation will be wasted 12/24/24  Abnormal VA/Q in Chronic Obstructive Lung < Disease nu >mber Thus, in chronic obstructive lung disease, some areas of the lung exhibit serious physiologic shunt, and other areas exhibit serious physiologic dead space. Both conditions tremendously decrease the effectiveness of the lungs as gas exchange organs, sometimes reducing their effectiveness to as little as one-tenth normal. both of the two pathological conditions ( pathological shunt & physiological dead space ) affect the lungs and decrease their function ( PaO2 will be reduced and PaCO2 will increase ) 12/24/24  Theme: 4 < Learning Question nu >mber 3. Describe the relationship between alveolar gas exchange and the arterial blood gas values PCO2 and PO2. 12/24/24  Normal Values < >number Mixed Arterial Alveoli Venous Blood Blood A = Alveolar a = arterial PA O2 (mmHg) PaO2 PvO2 oxygen saturation : is how many SAO2 molecules of oxygen are carried by SaO2 97% SvO2 75% haemoglobin PA CO2 PaCO2 PvCO2 (mmHg) HCO3 mE/L HCO3 HCO3 12/24/24 pH pH pH  Normal Values < number Mixed Arterial Alveoli Venous Blood Blood PA O2 (mmHg) 104 PaO2 100 PvO2 40 SAO2 SaO2 97% SvO2 75% PA CO2 40 PaCO2 40 PvCO2 46 (mmHg) 22-28 22-28 HCO3 mE/L HCO3 mEq/L HCO3 mEq/L pH pH 7.45 pH 12/24/24 7.35 Average resting Normal PO2 at PO2 at systemic pulmonary capillaries capillaries Explanation in the next slides This diagram is called : oxyhemoglobin dissociation curve ( S-shaped curve ) In the blood, oxygen is transported by hemoglobin, there are several reactions ( reversible reactions ) : when the hemoglobin takes the O2 it’s called “association” when the haemoglobin breaks down in the tissues it’s called “dissociation” How to read the curve ? The red part : is called the association part, the oxygen is loaded on the hemoglobin The blue part : is called the dissociation part, the hemoglobin is dissociated from the hemoglobin saturation of 50: means that out of 100, 50 hemoglobin are oxyhemoglobin and the other 50 are without oxygen Saturation of 97% means out of 100 hemoglobin, 97 are oxyhemoglobin and the other 3 are without oxygen and so on … for example, if we take 10 test tubes, in each test tube there are 100 hemoglobin, in the first tube we put PO2 equals to 10, and in the second tube we put PO2 equals to 20, and the third tube we put PO2 equals to 30 and kept doing this until we reach the last tube with a 100 PO2, the amount of oxyhemoglobin in each tube will equal to its PO2; so in the first tube there will be 10 oxyhemoglobin, in the second tube there will be 20 oxyhemoglobin … etc In such a case, the curve will be Linear curve If the person is in a hypoxic situation, the partial pressure that was normally 100 now will fall to 90 What is the benefit of this curve ? The benefit : is that it shows the oxygen will be loaded on the hemoglobin even at very low partial pressure, even it the partial pressure falls from 100 to 90 still 60% of the hemoglobin will be saturated 100 ml of blood have 15 gram of hemoglobin, 1 gram of hemoglobin transport 1.34 ml of oxygen; So 15x1.34 ‎= 20.1 ml of oxygen is transported in 100 ml of blood In venous blood, the partial pressure is 40 and the saturation is 70 and in venous blood there are 15 ml of oxygen In arterial blood there are 20 ml of oxygen in each 100 ml of blood During exercising, the body needs more oxygen, so one of the ways the body can get oxygen is by extracting more oxygen from the mixed venous blood In resting person, one deciliter of blood gives 5 ml And in person who is exercising, one deciliter of blood can deliver 6-10 ml to the tissue The partial pressure of the maternal blood coming to the fetus is 30-40, but if there was a slight change in the curve, there will be low amount of hemoglobin loading oxygen to enter the circulation of the blood The fetal has HbF ( fetal hemoglobin ) Adults have HbA ( adult hemoglobin )  Further Reading < nu >mber References. Guyton & Hall, Textbook of Medical Physiology, 14th Edition, Saunders Elsevier, Philadelphia PA, 2021 Chapter 40. Page: 515-520. 12/24/24  < nu >mber 12/24/24  Quiz 1. The amount of blood that has failed to be oxygenated A. Dead space B. Shunted air ventilation C. Shunted blood 2. If there is normal ventilation (Va) but there is no perfusion (Q) in the alveolus A. Ventilation / perfusion ratio is normal B. Ventilation / perfusion ratio is zero C. Ventilation / perfusion ratio is infinity. 3. Which type of chronic obstructive pulmonary disease is characterised by a breakdown of alveolar walls and collapse of the smaller airways ? A. Emphysema B. Chronic bronchitis C. Asthma Answers: 1-C 2-C 3-A  team Wishes you the best