VENTILATION AND PERFUSION FOR NURSING ANATOMY

ANATOMY AND PHYSIOLOGY FOR NURSES RESPIRATORY

1. MUHIMBILI UNIVERSITY OF HEALTH AND ALLIED SCIENCIES SCHOOL OF NURSING COURSE : NA601-ANATOMY, PHYSIOLOGY AND HEALTH ASSESSMENT OF BODY SYSTEMS TOPIC : VENTILATION , PERFUSION AND DIFFUSION

2. PARTICIPANTS : GROUP 6 ITERITEKA GLORIA KASSIM KHEIR MAKAME SONGOMA JOHN

3. OBJECTIVES At the end of this presentation, one should be able to: Explain the concept of ventilation Describe the concept of perfusion Describe the concept of diffusion Describe the concept of ventilation /perfusion ratio

4. PULMONARY VENTILATION Is the inhalation (inflow) and exhalation (outflow) of air and involves the exchange of air between the atmosphere and the alveoli of the lungs In pulmonary ventilation, air flows between the atmosphere and the alveoli of the lungs because of pressure differences created by contraction and relaxation of respiratory muscles

5. MECHANISM OF PULMINARY VENTILATION Inhalation or inspiration Exhalation or expiration

6. INSPIRATION OR INHALATION Inspiration, or inhalation – a very active process that requires input of energy Air flows into the lungs when the thoracic pressure falls below atmospheric pressure. The diaphragm moves downward and flattens, when stimulated by phrenic nerves. External (inspiratory) intercostals muscles and thoracic muscles can be stimulated to contract and expand the thoracic cavity (chest cavity size increases)

7. EXPIRATION OR EXHALATION Expiration, or exhalation – a passive process that takes advantage of the recoil properties of elastic fibers . Air is forced out of the lungs when the thoracic pressure rises above atmospheric pressure. The diaphragm and expiratory muscles relax. The elasticity of the lungs and the thoracic cage allows them to return to their normal size and shape , volume decreases, intrapulmonic pressure increases, air rushes out (chest cavity size decreases)

8. FACTORS INFLUENCING PULMONARY VENTILATION Resistance to airflow-Diameter of bronchioles – controlled by smooth muscle Bronchoconstriction – reduce airflow Bronchodialation - increase airflow Pulmonary compliance – the ease at which lungs expand. Compliance can be reduced by degenerative lung disease, such as tuberculosis. Alveolar surface tension – surfactant reduces the surface tension in the alveoli and keep them from collapsing during expiration.

9. Compliance of the Lungs Compliance of the Lungs -Refers to how much effort is required to stretch the lungs and chest wall. High compliance means that the lungs and chest wall expand easily and vice versa Lungs, compliance is related to two principal factors Elastic fibers in lung tissue Surfactant

10. Compliance of the Lungs Decreased compliance is a common feature in pulmonary conditions: Scar lung tissue e.g. in tuberculosis Pulmonary edema Deficiency in surfactant. Paralysis of the intercostal muscles Emphysema

11. SURFACTANT Is a lipid surface tension lowering substance secreted by Alveolar Type II cells Is a mixture of lipids, and proteins Prevents oedema formation in the lungs Absence of surfactant in infants results in respiratory distress syndrome Maturation of surfactant is enhanced by glucocorticoids and lungs are rich in glucocorticoid receptors

12. PATTERNS OF BREATHING Apnea – temporary cessation of breathing (one or more skipped breaths) Dyspnea – labored , gasping breathing; shortness of breath Eupnea – Normal, relaxed, quiet breathing Hyperpnea – increased rate and depth of breathing in response to exercise, pain, or other conditions Hyperventilation – increased pulmonary ventilation Hypoventilation – reduced pulmonary ventilation Orthopnea – difficult in that occurs when a person is lying down flat Respiratory arrest – permanent cessation of breathing Tachypnea – accelerated respiration

13. MEASURES OF PULMONARY VENTILATION Respiratory Volumes– values determined by using a spirometer Tidal Volume (TV) – amount of air inhaled or exhaled with each breath under resting conditions (500 mL) Inspiratory Reserve Volume (IRV) – amount of air that can be inhaled during forced breathing in addition to resting tidal volume (3000 to 3300 mL) Expiratory Reserve Volume (ERV) – amount of air that can be exhaled during forced breathing in addition to tidal volume (1000 to 1200 mL)

14. MEASURES OF PULMONARY VENTILATION Residual Volume – (RV) - amount of air remaining in the lungs after a forced exhalation. (1200 mL) Force Vital Capacity (FVC) – maximal volume expired after maximal inspiration (TV+IRV+ERV= 5000 ml) Functional Residual Capacity (FRC) – Volume in lungs after tidal expiration (ERV + RV; 2500 ml) Total Lung Capacity (TLC) – volume in lungs after maximal inspiration (FVC + RV= 6000 ml)

15. Respiratory Capacities – values determined by adding two or more of the respiratory volumes Inspiratory Capacity (IC) – maximum volume of air that can be inhaled following exhalation of resting tidal volume IC = TV + IRV The minute ventilation (MV): Is the total volume of air inhaled and exhaled per minute. It is MV=RR ×VT MV= 12 breaths/min × 500 mL/breath = 6 liters /min Dead space -Refers to the space in which oxygen (O2) and carbon dioxide (CO2) gasses are not exchanged across the alveolar membrane in the respiratory tract. Dead space can be either anatomical or physiological dead space

16. DIFFUSION It is passive Movement of gases between the alveoli, plasma , and red blood cells Net movement of molecules from an area where the particular gas exerts a high partial pressure to an area where it exerts a lower partial pressure which is governed by the behavior of gases as described by two gas laws , Dalton’s law and Henry’s law . Dalton’s law explain how gases move down their pressure differences by diffusion. Henry’s law helps explain how the solubility of a gas relates to its diffusion

17. Cont ….. Dalton’s law: E ach gas in a mixture of gases exerts its own pressure as if no other gases were present. The pressure of a specific gas in a mixture is called its partial pressure (Px) Total atmospheric pressure (760 mmHg) = PN2 + PO2 + PAr + PH2O +PCO2 +Pother gases These partial pressures determine the movement of O2 and CO2 between atmosphere and lungs, between the lungs and blood, and between blood and body cells

18. Cont … Henry’s law: States that the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility In body fluids, the ability of a gas to stay in solution is greater when its partial pressure is higher and when it has a high solubility in water CO2 is dissolved in blood plasma because its solubility is 24 times greater than that of O2.

19. Cont …. Note Solubility of carbon dioxide is 20 times more soluble in water than oxygen As temperature of liquid rises, solubility decreases The concentration and partial pressure of both oxygen and carbon dioxide in alveoli are determined by a)Rates of absorption or excretion of two gases b) The amount of alveolar ventilation

20. Factors affecting the rate of gas diffusion through the membrane Thickness of membrane Surface area of the membrane The diffusion coefficient of the gas Partial pressure difference

21. PERFUSION Perfusion defined as the movement of blood into the lungs through the pulmonary capillaries bed. The blood is pumped into the lungs by the right ventricle through the pulmonary artery Right and Left Pulmonary artery supply both lungs

22. Pulmonary Circulation Pulmonary circulation supplies venous blood from all parts of the body to the alveolar capillaries where oxygen (O2)is added and carbon dioxide(CO2) is removed. Supplies deoxygenated blood to lungs to become oxygenated.

23. Cont … Starts at Rt atrium → Rt ventricle → Pulmonary artery →Capillaries → Pulmonary veins → Lt atrium. The pulmonary artery (which receives blood from the right ventricle) and its arterial branches carry blood to the alveolar capillaries for gas exchange, and the pulmonary veins then return the blood to the left atrium to be pumped by the left ventricle through the systemic circulation.

24. Ventilation-Perfusion Relationship Ventilation is the flow of gas in and out of the lungs. Perfusion is the filling of the pulmonary capillaries with blood. Adequate gas exchange depends on an adequate ventilation–perfusion ratio.

25. Ventilation /perfusion Ventilation perfusion ratio refers to the amount of air that reaches the alveoli per minute compared to the amount of blood that reaches the alveoli per minute . Is the ratio of alveolar ventilation and amount of blood perfuse the alveoli It is expressed as VA/Q. VA is alveolar ventilation and Q Is the blood flow (perfusion) VA =4.2 Q=5 There fore Normal VA/Q=4.2/5=0.84 Normal perfusion ventilation ratio is 0.8

26. NORMAL VALUE AND CALCULATION Ventilation perfusion ratio= Alveolar ventilation Pulmonary blood flow Alveolar ventilation = (Tidal volume –Dead space)x respiratory rate Under normal condition dead space =150ml Dead space is ventilation without perfusion Perfusion without ventilation =shunt

27. ventilation/perfusion mismatch The imbalance between alveolar ventilation and alveolar blood is called the ventilation/perfusion mismatch In quantitative terms, the ventilation-perfusion ratio is expressed as V/Q When V is normal for a given alveolus and Q is also normal for the same alveolus, V/Q ) is also said to be normal

28. Ventilation /perfusion ratio

29. Extremes that causes V/Q mismatch

30. Shunt This refers to blood that enters the arterial system without going through ventilated area Anatomical –right to left shunt mixture of blood occurs through the atrial and ventricular defect, also branching of pulmonary artery connecting directly to pulmonary vein Physiological –in bronchial circulation deoxygenated bronchial venous blood drains directly into oxygenated blood of pulmonary vein

31. Possible causes of shunt Pulmonary edema –alveoli with fluids Alveoli filling with cellular and micro organism debris eg in pneumonia Lung collapse eg in pneumothorax

32. EFFECT OF VENTILATION PERFUSION INEQUALITY ON OVERALL GASEOUS EXCHANGE V/Q=0 -Pulmonary shunt No vent but perfusion remain normal Causes: Alveolar flooding eg in pneumonia/ acute respiratory syndrome Complete obstruction of airway eg in chocking Extrinsic compression of alveoli present in compression, atelectasis eg in pneumothorax

33. INEQUALITY ON OVERALL GASEOUS EXCHANGE… 2. Low V/Q or V/Q Less than 1 Low vent. To perfusion eg in partial obstruction of airways Causes: Low compliance such in pulmonary fibrosis Lack surfactant or high airway resistance found in asthma and COPD

34. cont … 3. V/Q= INFINITY –dead space No perfusion but vent. Remains normal Causes: Embolism Emphysema bronchiectasis

35. cont … 4. High V/Q Low perfusion relative to vent. Causes: Hypotension Partial obstruction of pulmonary BV in pulmonary embolism

36. Regional gas exchange in the lung

37. Ventilation perfusion inequality V/Q ratio determines the gas exchange in any single lung unit Regional differences of V/Q in the upright human lung causes a pattern of regional gas exchange V/Q inequality impairs the uptake or elimination of all gases by the lung Although the elimination of carbon dioxide is impaired by V/Q mismatch this can be corrected by vent. To alveoli

38. Oxygen Transport Oxygen does not dissolve easily in water, only1.5% of inhaled O2 is dissolved in blood plasma, which is mostly water. About 98.5% of blood O2 is bound to hemoglobin in red blood cells Oxygen and hemoglobin bind in an easily reversible reaction to form oxyhemoglobin :

39. Cont.. The 98.5% of the O2 that is bound ( attached, liers ) to hemoglobin is trapped inside RBCs, so only the dissolved O2 (1.5%) can diffuse out of tissue capillaries into tissue cells.

40. The Relationship between Hemoglobin and Oxygen Partial Pressure The most important factor that determines how much O2 binds to hemoglobin is the PO2 The higher the PO2 , the more O2 combines with Hb . When reduced hemoglobin ( Hb ) is completely converted to oxyhemoglobin ( Hb —O2), the hemoglobin is said to be fully saturated When hemoglobin consists of a mixture of Hb and Hb - O2 , it is partially saturated.

41. Cont.. When the PO2 is high, hemoglobin binds with large amounts of O2 and is almost 100% saturated and vice versa. Therefore, in pulmonary capillaries, where PO2 is high, a lot of O2 binds to hemoglobin. In tissue capillaries, where the PO2 is lower, hemoglobin does not hold as much O2, and the dissolved O2 is unloaded via diffusion into tissue cells

42. Hemoglobin oxygen dissociation curve

43. Factors Affecting the Affinity of Hemoglobin for Oxygen Acidity (pH). ( Bohr effect) . As acidity increases (pH decreases), the affinity of hemoglobin for O2 decreases, and O2 dissociates more readily from hemoglobin. When pH decreases, the entire oxygen–hemoglobin dissociation curve shifts to the right; at any given PO2 Hb is less saturated with O2, a change termed the Bohr effect ( BOHR)

44. 2. Partial pressure of carbon dioxide CO2 also can bind to hemoglobin and the effect is similar to that of H (shifting the curve to the right). As PCO2 rises, hemoglobin releases O2 more readily PCO2 and pH are related factors because low blood pH (acidity) results from high PCO2 As CO2 enters the blood, much of it is temporarily converted to carbonic acid (H2CO3), a reaction catalyzed by an enzyme in red blood cells called carbonic anhydrase (CA).

45. Cont.. The carbonic acid thus formed in red blood cells dissociates into hydrogen ions and bicarbonate ions, pH decreases. Thus, an increased PCO2 produces a more acidic environment, which helps release O2 from hemoglobin Decreased PCO2 (and elevated pH) shifts the saturation curve to the left .

46. Temperature: Within limits, as temperature increases, so does the amount of O2 released from hemoglobin Heat is a by-product of the metabolic reactions of all cells, and the heat released by contracting muscle fibers tends to raise body temperature Metabolically active cells require more O2 and liberate more acids and heat. Hypothermia cellular metabolism slows, the need for O2 is reduced, and more O2 remains bound to hemoglobin (a shift to the left in the saturation curve)

47. 2,3-Bisphosphoglycerate ( BPG) A substance found in red blood cells Decreases the affinity of hemoglobin for O2 and thus helps unload O2 from hemoglobin Fetal hemoglobin ( Hb -F) differs from adult hemoglobin ( Hb -A) in structure and in its affinity for O2. Hb -F has a higher affinity for O2 because it binds BPG less strongly Thus, when PO2 is low, Hb -F can carry up to 30% more O2 than maternal Hb -A

48. CARBON DIOXIDE TRANSPORT Under normal resting conditions, each 100 mL of deoxygenated blood contains the equivalent of 53 mL of gaseous CO2, which is transported in the blood in three main forms Dissolved CO2 : 7% of CO2 is dissolved in blood plasma, it diffuses into alveolar air and is exhaled on reaching the lung. Carbamino compounds: 23%, combines with the amino groups of amino acids and proteins in blood to form carbamino compounds.

49. Carbon Dioxide Transport… The binding sites are the terminal amino acids in the two alpha and two beta globin chains. Hemoglobin that has bound CO2 is termed carbaminohemoglobin ( Hb —CO2) The formation of carbaminohemoglobin is greatly influenced by PCO2 Tissue capillaries PCO2 is relatively high, which promotes formation of carbaminohemoglobin Pulmonary capillaries, PCO2 is relatively low, and the CO2 readily splits apart from globin and enters the alveoli by diffusion

50. III. Bicarbonate ions. About 70% is transported in blood plasma as bicarbonate ions (HCO3- ). As CO2 diffuses into systemic capillaries and enters red blood cells, it reacts with water in the presence of the enzyme carbonic anhydrase (CA) to form carbonic acid, which dissociates into H+ and HCO3 –

51. Cont.. Bicarbonate ions. As blood picks up CO2, HCO3 - accumulates inside RBCs. Some HCO3 - moves out into the blood plasma, down its concentration gradient. In exchange, chloride ions (Cl-) move from plasma into the RBCs. This exchange of negative ions, which maintains the electrical balance between blood plasma and RBC cytosol, is known as the chloride shift

52. REFERENCES Guyton and Hall , text book of medical physiology, 12 edition Principles of ANATOMY & PHYSIOLOGY Gerard J. Tortora Bergen Community College. Bryan Derrickson Valencia Community College 13th Edition Fishman textbook of pulmonary disease and disorders Urden,DL., Stacy, MK., & Lough, EM,. (2014), Critical Care Nursing, Diagnosis and Management, 7 th ed : mosby , Inc.,an affiliate of Elsevier Inc.

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