Respiratory Physiology L2 (Ventilation) - Summer 2024 PDF

Pulmonary ventilation Ventilation is the process of exchanging the gas in the airways and alveoli with gas from the environment Air flows into the lungs during inspiration, and out during expiration. Replenish O2 and remove CO2  Respiratory cycle A RESPIRATORY CYCLE consists...

Pulmonary ventilation Ventilation is the process of exchanging the gas in the airways and alveoli with gas from the environment Air flows into the lungs during inspiration, and out during expiration. Replenish O2 and remove CO2  Respiratory cycle A RESPIRATORY CYCLE consists of an inspiratory phase and an expiratory phase Inspiration – active process that involves an enlargement of the thorax and lungs with an accompanying inflow of air Diaphragm – contracts and enlarges the thorax caudally fibers caudoventral External intercostal muscles – contract and enlarge the thorax cranially and outward  Respiratory cycle lungs elastic have properties Expiration Normally a passive process, where diaphragm and external intercostal muscles relax, and thorax comes back to “normal” volume. Can become an active process, with the contraction of the internal intercostal muscles and abdominal muscles, during times of accelerated breathing or when there are impediments to the outflow of the air.  I IEii netnisvennanin Mechanics of ventilation 1. The pressure of a gas increases as its volume decreases – and decreases as its volume increases. 2. Gases tend to flow from a high-pressure area to a low-pressure area, until balance is established. https://sciencenotes.org/boyles-law-definition-formula-example/  Mechanics of ventilation P int et 1. The pressure of a gas increases as its volume decreases – and decreases as its volume increases. 2. Gases tend to flow from a high-pressure area to a impotonotetranspum a lways needsb to e Both intra can't punpleural bethesame low-pressure area, until balance is established. 3. The lungs are elastic, and tend to collapse 4. The intrapleural pressure is slightly lower than atmospheric pressure – keeps the lung inflated win the within iiiiii pressure wanna  Mechanics of ventilation - pressures Atmospheric pressure (or barometric pressure) – sum of the partial pressures of all gases in the air mixture – 760 mmHg at sea level. Intrapleural pressure (or pleural pressure) – pressure exerted outside the lungs within the pleural cavity. Slightly negative from atmospheric pressure. Intrapulmonary pressure (or alveolar pressure) – pressure within the alveoli that increases and decreases with each breath: volume increase  pressure decrease  air inflow volume decrease  pressure increase  air outflow Transpulmonary pressure – difference between alveolar pressure and pleural caseis the pressure. theorganthis across pressure lungs  Mechanics of ventilation - pressures Transpulmonary pressure Equal and opposite to the elastic recoil pressure of the lung (max distention = max transpulmonary pressure) Always positive What if it equals zero? collapse Cunningham's Textbook of Veterinary Physiology, 6th Edition  Mechanics of ventilation - pressures Transpulmonary pressure Equal and opposite to the elastic recoil pressure of the lung (max distention = max transpulmonary pressure) Always positive What if it equals zero? - Lung collapses  tissuedoesn'twant rememberelastic tobestretched itwantstoresistthe tobestretched desire back recoil Elastic recoil Elastic recoil pressure of the lungs due to: 1. Stretching of elastin and collagen fibers during inflation 2. Surface tension (attractive forces) of water molecules in the liquid film lining each alveolus eoliwanttogoback sizepossible smallest Seshadri and Ramamurthi, Frontiers in Pharmacology, 2018, 9:759 Pearson Education  Surfactant Surface-active substance for which water molecules have lesser attraction Lipoprotein (30% protein, 70% lipids) Produced by Type II pneumocytes Accumulate on the surface of the alveoli Displace water molecules  decrease surface tension Prevent collapse of the lungs Increase pulmonary compliance (reduces elastic recoil, making it easier to inflate the lungs) Fathi-Azarbayjani and Jouyban, BioImpacts, 2015, 5:1 no surfactant  alveoli would collapse Surfactants LAW OF LAPLACE P = 2xT/r Pressure is directly proportional to surface tension, and inversely proportional to radius P = 2x P=x P=x P=x https://simplemed.co.uk/subjects/respiratory/ventilation-and-lung-mechanics  compliance Compliance x Elasticity i i c hanges once remember stretch lungs torecoil itwants back itasmallervolumeneedsahigherpressurethat it's means lowcompliance In order to EXPIRATION to occur, lungs must get smaller when stretching force is released - ELASTICITY Elastic fibers Surface tension anairfluidinterface In order to INSPIRATION to occur, lungs must be able to expand when stretched – COMPLIANCE Factors that reduce compliance (turning breathing more difficult): Destruction/fibrosis of lung tissue Lack of surfactant  atrestalveolarpressureisatzero Compliance x Elasticity Seshadri and Ramamurthi, Frontiers in Pharmacology, 2018, 9:759  basically Prnventalationdon't under inspire max expire air Lung volumes 1. Tidal volume (VT) volume of air moved into or out of the lungs during quiet resting breathing. VT can increase or decrease on demand. 0 Time  canhold maxvolumeyourlungs basically Lung volumes isthecombinationofTWOORMORE respiratorycapacity theamoun bes ofa InYESaffinity 2. Total lung capacity (TLC) TLC volume of air in the lungs after maximum inspiration. VT c sumofatthelungvolumes TVERVIRV RV 0 Time  Lung volumes 3. Residual volume (RV) TLC volume of air that remains after maximal forced expiration. VT willnotexpelallair Forcedexpiration RV 0 Time  Lung volumes 4. Inspiratory reserve volume IRV TLC (IRV) amount of air that can still be inspired after inhaling VT tidal volume. RV 0 Time  Lung volumes 5. Inspiratory capacity (IC) IRV IC TLC total amount of air that can be inspired after normal exhalation. VT IC = VT + IRV tithume RV 0 Time  Lung volumes 6. Expiratory reserve volume IRV IC TLC (ERV) amount of air the can still be expired after exhaling VT tidal volume. ERV RV 0 Time  Lung volumes 7. Functional residual capacity IRV IC TLC (FRC) air that remains in the lungs after normal exhalation. VT FRC = ERV + RV ERV FRC RV 0 Time  Lung volumes 8. Vital capacity (VC) IRV IC TLC VC maximum amount of air that can be moved (forced inspiration and forced VT expiration) VC = IRV + VT + ERV ERV amountofairaperson can move ofhisherlungs intoorout FRC RV 0 Time  Lung volumes 1. Tidal volume (VT) – volume of air moved into or out of the lungs during quiet resting breathing; can increase or decrease on demand. 2. Total lung capacity (TLC) – volume of air in the lungs after maximum inspiration. 3. Residual volume (RV) – volume of air that remains after maximal forced expiration. 4. Inspiratory reserve volume (IRV) – amount of air that can still be inspired after inhaling tidal volume. 5. Inspiratory capacity (IC) – total amount of air that can be inspired after normal exhalation. IC = VT + IRV 6. Expiratory reserve volume (ERV) – amount of air that can still be expired after exhaling tidal volume. 7. Functional residual capacity (FRC) – air that remains in the lungs after normal exhalation. FRC = ERV + RV 8. Vital capacity (VC) – maximum amount of air that can be moved (forced inspiration and forced expiration). VC = IRV + VT + ERV  ̇ ) Minute-ventilation (𝐕E Total volume of air breathed per minute tidal volume ̇ = VT x f 𝐕E rate respiratory ̇ (increasing O2 offer) Increase in 𝐕E can be brought through an increase in VT, f, or both  Physiological dead space Ventilated parts of the respiratory system where gas exchange does not occur. Anatomic dead space: airways Alveolar dead space: nonperfused alveoli dead space volume (anatomic + alveolar) Cunningham's Textbook of Veterinary Physiology, 6th Edition VT = VD + VA ̇ = VT x f 𝐕E ̇ = (VD + VA) x f 𝐕E alveolar volume (not dead space) ̇ = (VA x f) + (VD x f) 𝐕𝑬 ̇ = 𝐕A 𝐕𝑬 ̇ + 𝐕Ḋ ̇ = alveolar ventilation (𝐕A) Minute-ventilation (𝐕E) ̇ + dead space ventilation (𝐕D) ̇  despite panting thelevelsofo coarethesame Dead space Dead space ventilation is not totally wasted, it is part of the process Assists tempering and humidifying inhaled air Helps cooling of the body under certain conditions – panting respiratory rate is increased, and the tidal volume is decreased so that minute-ventilation remains relatively constant during heat stress, hyperventilation can occur and lead to respiratory alkalosis ̇ = VT x f 𝐕E ̇ = alveolar ventilation + dead space ventilation Minute-ventilation (𝐕E)  Airway resistance Airflow is opposed by frictional resistance in the airways Resistance to airflow is determined by the radius and length of the airways Length does not change much, but radius can be altered by passive and active forces As the lung inflates, airways dilate passively and airway resistance decreases POISEUILLE’S R - resistance Airway smooth muscle can actively EQUATION n – viscosity contract reducing radius, and airway 𝟖𝒏𝒍 l – length 𝑹= resistance increases 𝝅𝒓𝟒 r - radius Airway resistance As lung volume increases, airways dilate, and resistance is reduced Cunningham's Textbook of Veterinary Physiology, 6th Edition  Airway resistance In the resting animal, nasal cavity, pharynx and larynx provide ~60% of the airway resistance Areas that humidify and warm the air Nasal resistance can be decreased during exercise by dilation of the external nares and by vasoconstriction of the vascular tissue (decrease mucosal thickness) Or can bypassed by mouth breathing (dogs, cats, cows etc) Horses are obligate nose breathers Cunningham's Textbook of Veterinary Physiology, 6th Edition  Velocity of airflow The velocity of airway flow diminishes progressively from the trachea toward the bronchioles. Branching pattern of the tracheobronchial tree  total cross- sectional area increases towards the periphery of the lungs. High velocity turbulent airflow in trachea and bronchi  lung sounds. Low velocity airflow in the bronchioles produces no sound. Cunningham's Textbook of Veterinary Physiology, 6th Edition