Respiratory Physiology L3 (Blood Flow & Gas Exchange) Summer 2024 PDF

I Pulmonary circulation Receives the total cardiac output of the right ventricle. Considered as a single capillary bed, that holds ~10% to 20% of blood volume....

I Pulmonary circulation Receives the total cardiac output of the right ventricle. Considered as a single capillary bed, that holds ~10% to 20% of blood volume. Pulmonary arteries carry deoxygenated blood to the pulmonary capillaries, and oxygenated blood is returned in pulmonary veins. Pulmonary blood vessels can be classified as alveolar and extra-alveolar vessels pulmonaryarterybecomespulmonary capillaryasitnearsthe alveoli the pointthatthecapillarywallmeets andstructureofthealveoli It'satthis atHairI the reffing drefpffawtotnhemebmffahnif.es  Pulmonary circulation Alveolar vessels: Thin-walled capillaries that perfuse the alveolar septum Exposed almost directly to cyclic pressure changes https://teachmephysiology.com/cardiovascular-system/special-circulations/pulmonary-circulation/ that occur because of the alveoli Extra-alveolar vessels: foundin 3 aye Pulmonary arteries and veins Occur together with bronchi in a loose connective tissue sheath called bronchovascular bundle Exposed to pressures changes in the connective tissue space, approximate to the pleural pressure Cunningham's Textbook of Veterinary Physiology, 6th Edition  Pulmonary blood flow The pulmonary blood vessels offer low resistance to flow Pulmonary arterial pressures are much less than systemic pressures Systolic: 25 mmHg; diastolic: 10 mmHg; mean: 15 mmHg Left atrial: 4 mmHg Small difference between pulmonary artery mean and left atrium (pulmonary perfusion pressure =Add 9 mmHg) indicates the pulmonary circulation offers little resistance to blood flow For comparison - aortic systolic/diastolic/mean: 120 mmHg/80 mmHg/98 mmHg Vena cava: 3mmHg -> Systemic perfusion pressure = 95 mmHg Unlike the systemic circulation, small arteries in the pulmonary circulation neither provide large resistance nor dampen arterial pulsations – capillary blood flow is pulsatile  notreceivingappropriate alveolus amount ofairoxygen Hypoxic vasoconstriction of Hypoxemiaisone causes Hypoxia of Alveolar hypoxia is a potent constrictor of small pulmonary arteries The air in a poorly ventilated alveoli has a low partial pressure of oxygen -> limited benefit to keep sending blood to such alveoli. Alveolar hypoxia -> vasoconstriction of pulmonary arteries -> reduce blood flow to poorly ventilated area + redistributes blood flow to better-ventilated regions. Present in all species with varying intensity (depends on the amount of smooth muscle surrounding pulmonary arteries): More vigorous in cattle and pigs Less vigorous in horses Trivial in sheep and dogs  altitude high Ngatte generalised Measurement of pulmonary artery pressure Hypoxic vasoconstriction has allowed selection of breeding stock less susceptible to high altitude disease Hypoxic vasoconstriction can induce heart failure Hypoxic vasoconstriction is beneficial when there is localized alveolar hypoxia If hypoxia is generalized (high altitude or diffuse lung disease): generalized hypoxic vasoconstriction afterload increase pulmonary arterial pressure (pulmonary hypertension) increase right ventricle workload right-sided heart failure accumulation of edematous fluid in the briskets (“brisket disease”)  direct obstruction in Lung disease or Cor pulmonale pulmonary circulation chronic hypoventilation Cor pulmonale: an alteration in the structure and function of the right ventricle caused by a primary disorder of the respiratory system generalized CHRONIC BRONCHITIS pulmonary hypoxic HEARTWORM DISEASE vasoconstriction pulmonary hypertension right ventricular enlargement increased workload https://www.dog-nutrition-naturally.com/heartworms.html cor pulmonale of the right ventricle  Gas exchange Diffusion of O2 and CO2 in the lungs (external respiration) and in the peripheral tissues (internal respiration) https://quizlet.com/gb/271143185/human-gas-exchange-and-ventilation-diagram/  Gas exchange Diffusion of O2 and CO2 in the lungs (external respiration) and in the peripheral tissues (internal respiration) O2 is transferred from alveolar gas into pulmonary capillary blood, where it travels to the tissues and diffuses from systemic capillary blood into the cells CO2 is delivered from the tissues to the venous blood, to pulmonary capillary blood, and it is transferred to alveolar gas to be exhaled  Gas mixture The partial pressure is a measure of the concentration of the individual components in a mixture of gases. The composition of a gas mixture can be described by the fractional composition or PARTIAL PRESSURE wt atsealevel pressure Atmospheric air 21 atsealeveleverest all ofgases m ix nowgoto less oxygen still21 0 butoverallvolume Nitrogen ofairin Highlevelislower 78% Oxygen Other gases 21% gas 1% Nitrogen Oxygen Other gases http://www.pathwaymedicine.org/gas-partial-pressure  Mount Everest Gas mixture 8000 m (26000 feet) The composition of a gas mixture can be described by the fractional composition or PARTIAL PRESSURE (PO2) Barometric pressure (sea level) = 760 mmHg Fraction of oxygen in air (FO2) = 0.21 PO2 = barometric pressure x fraction of O2 PO2 = 760 mmHg x 0.21 = 160 mmHg At high altitude: same 21% of oxygen iii i no Barometric pressure (at 8000m) = 267 mmHg PO2 = 267 mmHg x 0.21 = 56 mmHg gmaies.teverestio.at warterialoxygeniscalledHypoxemia oxiaisreducedoxygenutilizationordeliverytotissues resultinHypoxemichypoxia Highaltitudecan  Alveolar gas composition The composition of alveolar air is determined by the balance between two basic processes: Alveolar Ventilation (renewal) Perfusion (gas exchange) http://www.pathwaymedicine.org/alveolar-air-composition  Gas partial pressures section rewatch sureofgasesonalveoli wehumidifyair remember then.PH ahf weaddwatervapor PiO2 = 150 mmHg PiCO2 = 0 mmHg air inspired air inspired dryinspiratoryairgetshumidifiedin Blood entering the alveolar passagesthewater capillaries from the travels theatmospheregets from respiratory watervaporpressure evaporates nspired theairinspiredgets creating pulmonary arteries is known humidifiedinrespiratorypassages thiswatervapordilutesthegasesand as mixed venous blood reducesthepartialpressure 102 760 4,2 0.21 isommits because it has returned off t.fi from oming R ifffhfiiniEffi heart PAO2 = 100 mmHg PACO2 = 40 mmHg watts from all parts of the systemic circulation Mixed venous blood Oxygenated blood PvO2 = 40 mmHg PvCO2 = 46 mmHg PaO2 = 100 mmHg PaCO2 = 40 mmHg alveoli bloodleaving YYff.TLntfo9tnkueYsehssthes thenproducedCO2 i mixedveno it ih.am blood  Alveolar partial pressure of CO2 PACO2 is directly proportional to CO2 production PACO2 = 40 mmHg knowthis PACO2 is inversely PACO2 = [PB – PH2O] x proportional to alveolar ventilation PACO2 = Alveolar partial pressure of CO2 PB = Barometric pressure PH2O = water vapor partial pressure If CO2 production increases, ventilation V CO2 = Metabolic rate of CO2 production must also increase to V A = Alveolar ventilation (ml/min) maintain a constant PACO2 = 40 mmHg http://www.pathwaymedicine.org/alveolar-air-composition  Alveolar partial pressure of O2 Respiratory exchange ratio CO2/O2 Glucose fuel: R = 1.0 Inhaled air oxygen partial pressure (discounting the Fatty acid fuel: R = 0.7 partial pressure of water) PAO2 = PiO2 – O2 consumption Typical mix glucose and PiO2 = [PB – PH2O] x FiO2 free fatty acids: R = 0.8 PAO2 = PiO2 - PiO2 = [760 – 50] x 0.21 PiO2 = 150 mmHg PAO2 = Alveolar partial pressure of O2 Indirectly includes into PiO2 = Inhaled air oxygen partial pressure consideration: PACO2 = Alveolar partial pressure of CO2 Alveolar ventilation R = respiratory exchange ratio Metabolic rate 𝟒𝟎 PAO2 = 150 - = 100 mmHg 𝟎.𝟖 http://www.pathwaymedicine.org/alveolar-air-composition  Example value: PACO2 = 46 mmHg Alveolar hyPOventilation PACO2 is inversely proportional to CAUSED BY: alveolar ventilation normal = 40 mmHg 1. Central nervous system depression by drugs or injury 2. Injury to nerve conduction pathways to the phrenic nerves 3. Neuromuscular junction disease 4. Damage to the thorax, pleural space or respiratory muscles 5. Substantial airway obstruction Cunningham's Textbook of Veterinary Physiology, 6th Edition 6. Decreased lung compliance  Example value: PACO2 = 30 mmHg Alveolar hyPERventilation PACO2 is inversely proportional to CAUSED BY: alveolar ventilation normal = 40 mmHg 1. Hypoxia 2. Acidosis 3. Increase in body temperature  Gas diffusion Exchange of O2 and CO2 between the alveolus and pulmonary capillary blood occurs by diffusion. Diffusion is the passive movement down a concentration (partial pressure) gradient The rate of gas movement between the alveolus and the blood is determined by: The physical properties of the gas (molecular weight and solubility) The surface area available for diffusion The thickness of the air-blood barrier (respiratory membrane) The driving pressure gradient of the gas between the alveolus and blood  Gas diffusion The air-blood barrier (respiratory membrane) – less than 1μm thick Components: Layer of surfactant lining alveolar surface Epithelial layer – pneumocyte type I Epithelial basement membrane Variable thickness interstitium Capillary basement membrane (could be fused with epithelial basement membrane) Capillary endothelium Cunningham's Textbook of Veterinary Physiology, 6th Edition  Afterdiffusionofgasinto bloodwillremaininoneof threeforms Gas diffusion 1 Dissolvedgas 2Boundform co Hb 3 chemicallymodifiede PiO2 = 150 mmHg gBica Driving pressure gradient for O2: PiCO2 = 0 mmHg HC 100 – 40 = 60 mmHg Driving pressure gradient for CO2: 46 – 40 = 6 mmHg PAO2 = 100 mmHg Despite this small driving pressure, PACO2 = 40 mmHg the amount of CO2 that diffuses per minute from the capillaries into the Mixed venous blood Oxygenated blood PvO2 = 40 mmHg PaO2 = 100 mmHg alveoli is similar to the amount of PvCO2 = 46 mmHg PaCO2 = 40 mmHg oxygen, because CO2 solubility is 20-fold greater.  Gas diffusion In resting animals, equilibrium between alveolar and capillary oxygen tensions occurs within 0.25 second – 1/3 of the time blood is in the pulmonary capillaries. Pearson Education  Systemic arterial blood The composition of the systemic arterial blood is determined by the composition of the capillary blood that drains each alveolus (each with slightly different levels of ventilation and perfusion)  Diseased lung Regions not ventilated form right-to-left shunts Cunningham's Textbook of Veterinary Physiology, 6th Edition  Diseased lung Inhaled air oxygen partial pressure (discounting the partial pressure of water) In a diseased lung, diffusion of oxygen may PiO2 = [PB – PH2O] x FiO2 be impeded as a result of inflammation PiO2 = [760 – 50] x 0.5 and edema PiO2 = 355 mmHg Thickening of the respiratory membrane Reduction of the surface area for gas exchange O2 administration can increase PAO2 and provide greater driving pressure to diffuse oxygen to the blood Gas partial pressures PiO2 = 150 mmHg PiCO2 = 0 mmHg Blood entering the alveolar capillaries from the pulmonary arteries is known as mixed venous blood because it has returned PAO2 = 100 mmHg PACO2 = 40 mmHg from all parts of the systemic circulation Mixed venous blood Oxygenated blood PvO2 = 40 mmHg PaO2 = 100 mmHg PvCO2 = 46 mmHg PaCO2 = 40 mmHg  Gas diffusion – internal respiration The exchange of gases between the tissues and blood: internal respiration Also occurs by diffusion, driven by the same forces Tissues with high oxygen demand have more capillaries per gram of tissue Larger surface area for diffusion Shorter distances between cells and nearest capillary  Gas exchange evaluation Arterial partial pressure of O2 (PaO2) and CO2 (PaCO2) are used to evaluate gas exchange -> blood gas analysis A systemic arterial blood sample is used to evaluate pulmonary gas exchange because this blood just passed through the lung Important to evaluate acid-base balance in the blood Hypoventilation: PaCO2 increase and PaO2 decrease Hyperventilation: PaCO2 decrease and PaO2 increase https://www.youtube.com/watch?v=LOQ6ADpx7Us