B_Ventilation_2023_notes.pdf

B. Ventilation Guyton chapters 37, 41 http://tabletopwhale.com/2014/10/24/3- different-ways-to-breathe.html Physiologic Description for Ventilation: The rhythmic movement of air between the environment and lungs Medical Description for Ventilation: Ventilation = body CO2 (PACO2 or PaCO2...

B. Ventilation Guyton chapters 37, 41 http://tabletopwhale.com/2014/10/24/3- different-ways-to-breathe.html Physiologic Description for Ventilation: The rhythmic movement of air between the environment and lungs Medical Description for Ventilation: Ventilation = body CO2 (PACO2 or PaCO2) Ventilation: Functional anatomy Nares Conducting airways Nasal cavity (anatomic dead space) Nasopharynx - Warming Larynx - humidifying Trachea - immune defense Bronchi Bronchioles Alveolar ducts Gas exchange Alveoli - VO2 & VCO2  Nares Nasal cavity Upper Airways Nasopharynx -extrathoracic Larynx Trachea Bronchi Bronchioles Lower Airways Alveolar ducts - intrathoracic Alveoli Ventilation: Functional anatomy Thoracic wall intercostal muscles external (inspiratory) internal (expiratory) Diaphragm (phrenic nerve) Mediastinum Pleural space What sensors or receptors control ventilation in the body? Ventilation: Respiratory volumes Guyton 37-6 Respiratory Volumes (L or ml) tidal volume (VT): volume normally inhaled or exhaled with each breath inspiratory reserve volume (IRV): additional volume of air that can be inhaled at the end of normal inspiration expiratory reserve volume (ERV): additional volume of air that can be exhaled at the end of normal exhalation residual volume (RV): air remaining in lungs after maximal exhalation (“trapped” air) Respiratory Capacities (L or ml) functional residual capacity (FRC): volume of the lungs at resting midposition (FRC = RV + ERV) vital capacity (VC): maximal volume of air that can be inhaled and exhaled inspiratory capacity (IC): maximal volume of air that can be inhaled (IC = TV + IRV) total lung capacity (TLC): total volume of air in lungs after maximal inhalation Respiratory volumes during exercise What sensors or receptors control ventilation in the body? Central and Peripheral Chemoreceptors PCO2 - PO2 - pH Alveolar ventilation (VA) TV (ml) X RR (/min) = minute ventilation (VE)(ml/min) Hypoventilation: PaCO2 > 45 mmHg Normoventilation: PaCO2 = 35-45 mmHg Hyperventilation: PaCO2 < 35 mmHg VCO2 PaCO2 = VA Alveolar vs. Dead Space Ventilation V E = VA + V D VE - minute ventilation (L/min) V A - alveolar ventilation (L/min) VD - dead space ventilation (L/min)  Nares VD Nasal cavity Nasopharynx Upper Airways Larynx VE Trachea Bronchi Bronchioles Alveolar ducts Lower Airways VA Alveoli  Terminal bronchiole Smooth muscle Bronchi Respiratory bronchioles Elastic Cartilage fibers Bronchioles Alveolus  Emphasis of Tidal Volume and Respiratory Rate for Minute Ventilation vs Dead Space consideration: TV (ml) X RR (/min) = minute ventilation (VE)(ml/min) – lets assume RR =1/min so that TV~VE VE = VA + VD Cunningham 45-3 Physiologic Dead Space = anatomic + alveolar (nonperfused) dead space  Effect of ventilation on PAO2 and PACO2 Guyton 39-4 Guyton 39-5  Hypoventilation (High CO2) Increase of PACO2 will occupy Alveoli the alveoli and decrease PAO2 Capillary CO2 RBC then decreasing PaO2 CO2 O2 Hb CO2 CO PaCO2 PaCO2 will remain high and in O2 2 equilibrium with the alveoli PaO2 PaCO2 PACO2 Hb-O2 PaCO2 PaO2 Capillary Normal A-a gradient Ventilation Pulmonary mechanics Definitions volume (V) - volume units (ml or L) flow (V) - volume / time pressure (P) - mm Hg or cm H2O compliance (C) - volume / pressure resistance (R) - pressure / flow  For effective ventilation to occur, the respiratory muscles must overcome the compliance (distensibility) of the lung and thorax, and the resistance to air flow. When the work needed to overcome these mechanical forces is excessive, hypoventilation and systemic decompensation can occur. Lung Compliance and Thoracic Compliance Lung Compliance or Pulmonary Compliance: Pulmonary compliance: pressure – volume relationship C C = ∆V / ∆P Volume C Pressure  Guyton 37-3 Pulmonary compliance characterized by hysteresis affected by lung volume Pulmonary compliance: lung vs thoracic wall Pleural pressure (Ppl) - 2 cmH2O at rest - 5 cmH2O inhalation FRC = lung volume at rest Pulmonary compliance Lung elastic recoil collagen & elastin surface tension Pleural pressure (Ppl) + Positive decreasing volume Pulmonary compliance during pneumothorax Open thorax loosing interpleural space tension and allowing lung to collapse Decrease FRC, atelectasis, hypoxemia  Questions Question: What is it about avian ventilation that allows them to fly at high altitude? B. Ventilation Question: What is it about avian ventilation that allows them to fly at high altitude?  Volume and pressure changes during normal breathing Guyton 37-2 Lung elastic recoil Collagen & elastin Alveolar Surface Tension acts to collapse lungs causes pressure-volume hysteresis Why is surfactant IMPORTANT? Concept of Resistance ∆ Pressure (P) Resistance (R) = Flow (V or Q) R≈1/r4 (r = radius of vessel or airway) Airway Resistance Upper Airways (60-80%) - nasal cavity, nasopharynx, larynx Lower Airways (20-40%) - total cross-sectional area increases - velocity of flow decreases - turbulent to laminar flow Cunningham 45-8 Lower Airways (R) Large (80%) - cross-sectional area - velocity Small (20%) - turbulent laminar flow - airflow resistance Lower airway resistance (active) - smooth muscle trachea to alveolar ducts Bronchoconstriction Bronchodilation - parasympathetic - sympathetic (vagus nn → acteylcholine → M3) - epinephrine (adrenal) - histamine - norepinephrine (nerves) - leukotrienes - nitric oxide (NO) Increased Upper Airway Resistance in a Horse Resistance from larynx and pneumonia Dynamic effect: extrathoracic airways 0 cm H2O -5 cm H2O -10 cm H2O Dynamic effect: intrathoracic airways -5 +30 0 0 +35 +30 Resting midposition Forced expiration Increased Expiratory Effort Work of Breathing (WB) The breathing force (energy) generated to overcome resistance, considering compliance to inhale and exhale WB ≈ elastic work (C) + resistance work (R) Increased WB is clinically described as “respiratory distress”  Resistance ≠ Compliance Resistance is a dynamic property that is only important when the lungs are in the process of changing volume (i.e. when air is flowing through airways) Compliance is measured in the static state, and reflects the volume of air that is inhaled into or exhaled out of the lungs in response to a given pressure change (at flow = 0)  A patient with restrictive lung disease has decreased lung compliance (i.e. elastic recoil is increased). Work is highest with slow, deep breathing (because increased lung volumes increase elastic recoil). Compensation occurs when patients breathe at smaller lung volumes more rapidly (reduce ∆V, increase C) A patient with obstructive lung disease (increased resistance) must overcome the increased resistance to air flow by hyperinflation via generation of increased negative pressure. Laryngeal collapse from severe Brachycephalic syndrome Clinical syndromes Neuromuscular-mediated hypoventilation injury to the neuromuscular apparatus of breathing trauma drugs toxins neuromuscular disease Bloat (mechanical effect) Pleural-coupling disorders disruption of coupling between lung and thoracic wall pleural effusion pneumothorax diaphragmatic hernia Canine pneumothorax and Equine pleura effusion Obstructive lung disease increased airway resistance possible hypoventilation 2o to WB upper airway obstruction laryngeal paralysis, brachycephalic syndrome lower airway obstruction COPD, asthma Laryngeal Paralysis in a Horse Restrictive lung disease decreased pulmonary compliance possible hypoventilation 2o to WB pulmonary fibrosis ( resistance and elastic recoil) alveolar collapse ( surface tension) surfactant deficiency ( surface tension) obesity ( thoracic wall compliance) Pulmonary Fibrosis (Pneumonia + Pyothorax) SAMPLE QUESTION: An animal presents with dyspnea and mild cyanosis. The following blood gas values are obtained (assume barometric pressure is 760 mm Hg). HOW WOULD YOU DESCRIBE WHAT IS WRONG WITH THIS PATIENT? What would you do help this patient? PaO2 48 mm Hg (normal = 96 mm Hg) PaCO2 80 mm Hg (normal = 40 mm Hg) SaO2 75% (normal = 98%) Hgb 9 gm/dl (normal = 15 gm/dl) SAMPLE QUESTION: PaO2 48 mm Hg (normal = 96 mm Hg) PaCO2 80 mm Hg (normal = 40 mm Hg) SaO2 75% (normal = 98%) Hgb 9 gm/dl (normal = 15 gm/dl) a) Hypoxemia b) Hypoventilation c) Anemia d) All of the above What would you do help this patient? Questions