Respiratory Physiology PDF

RESPIRATORY PHYSIOLOGY Douglas Massey II, DNP, CRNA NURS 6413  1. Identify the functional anatomy relevant to understanding respiratory physiology 2. Describe the mechanics of breathing 3. Describe the principles of pulmonary b...

RESPIRATORY PHYSIOLOGY Douglas Massey II, DNP, CRNA NURS 6413  1. Identify the functional anatomy relevant to understanding respiratory physiology 2. Describe the mechanics of breathing 3. Describe the principles of pulmonary blood flow OBJECTIVE 4. Discuss the ventilation-perfusion relationship in the lung S 5. Distinguish the different mechanisms of breathing control 6. Compare the common features of gas exchange 7. Distinguish acid-base abnormalities OVERVIEW Functions of respiration: 1. Transport oxygen (O2) to tissues 2. Transport carbon dioxide (CO2) away from tissues Components of respiration: 1. Pulmonary ventilation 2. Diffusion of O2 and CO2 between alveoli and blood 3. Transport of in the O2 and CO2 blood 4. Regulation of ventilation FUNCTIONAL ANATOMY OF THE RESPIRATORY SYSTEM Airway Upper Nose/nasopharynx Mouth/oropharynx Larynx/hypopharynx Lower Trachea Main/lobar/segmental bronchi Conducting/terminal/ respiratory bronchioles Alveolar ducts Alveoli  Ala nasae (i.e., alar cartilage) forms the borders of the anterior nares Anterior nares lead into the nasal vestibules and eventually the nasal fossae, which are separated by the nasal septum The nasal septum consists of the vomer bones and the Nose - vomeronasal and nasal septal cartilages The three nasal conchae are scroll-shaped prominences along the Structures lateral walls that are involved in filtration The nasal fossae leads into the nasopharynx via the nasal choanae and also communicates with the paranasal air sinuses The paranasal air sinuses include the frontal, ethmoid, maxillary, and sphenoid sinuses  Arterial Perfusion Anterior and posterior branches of ophthalmic arteries Sphenopalatine artery, derived from internal maxillary artery Nose – Venous Drainage Neurovascu Ethmoid veins to superior sagittal sinus Nasal veins to the ophthalmic veins and the lar cavernous sinus Structures Lymphatic Drainage Deep cervical lymph nodes Innervation Afferent – olfactory nerve (CN I), ophthalmic nerve (CN V1), maxillary nerve (CN V2)  Heating Warmed by nasal conchae and nasal septum Humidification Humidified to nearly 100% relative Nose - humidity Filtration Functions Nasal hairs (large particles) Turbulent precipitation (small particles [>6 m]) Olfaction Pharynx Muscular tube that extends from skull base to the esophagus at vertebral level C6 Nasopharynx – extends from nasal choanae to soft palate Oropharynx – extends from soft palate to epiglottis Hypopharynx – extends from epiglottis to esophagus Tonsils – aggregations of lymphoid tissue Palatine (i.e., major tonsils) Lingual Tubal Pharyngeal (i.e., adenoids)  Protective structure to prevent aspiration during swallowing that extends from vertebral level C3 to C6 Supraglottic region – extends from epiglottis to false vocal cords (i.e., vestibular folds) Vestibular folds – bands of fibrous tissue covered by mucous membranes; superolateral to true vocal cords Larynx - Laryngeal ventricles (i.e., vestibule) – space between false vocal cords and true vocal cords True vocal cords – fibromembranous folds attach to thyroid cartilage and arytenoids Structures Infraglottic region – extends from true vocal cords to trachea Composed of one bone and nine cartilages, as well as ligaments, muscles, and membranes Hyoid bone Epiglottis, thyroid, cricoid, arytenoids, corniculates, cuneiforms Thyrohyoid membrane, cricothyroid membrane Larynx - Musculature Closure of laryngeal vestibule and Adduction of vestibular epiglottis – Abduction of vestibular folds – interarytenoid aryepiglottic muscle, folds – posterior muscles, lateral oblique arytenoid cricoarytenoid muscles cricoarytenoid muscles muscles, thyroepiglottic muscle Shortening of true Lengthening of true vocal cords – vocal cords – thyroarytenoid cricothyroid muscles muscles  Cormack-Lehane Classification Grade 1 – full view of laryngeal inlet Grade 2a – partial view of vocal cords Grade 2b – view of posterior aspect of vocal cords or arytenoids Grade 3 – view of epiglottis only Grade 4 – no visible laryngeal structures https://www.facebook.com/photo.php? fbid=2534801436572199&id=106706922715008&set=a.106797756039258  Arterial Perfusion Superior thyroid artery, derived from external carotid artery Inferior thyroid artery, derived from the thyrocervical trunk of subclavian artery Larynx – Innervation Ganglion nodosum of vagus nerve (CN X) Neurovascu Superior laryngeal nerve External branch of the superior laryngeal nerve – lar inferior constrictor muscle of pharynx, cricothyroid muscles Internal branch of the superior laryngeal nerve – Structures interarytenoid muscles, sensory innervation between inferior aspect of epiglottis and true vocal cords Inferior laryngeal nerve (i.e., recurrent laryngeal nerve [RLN]) – all intrinsic laryngeal muscles except cricothyroid muscles and part of interarytenoid muscles, sensory innervation between true vocal cords and trachea  Protective structure to prevent airway collapse consisting of incomplete rings of cartilage that extends from inferior larynx to carina Arterial Perfusion Inferior thyroid artery, derived from the thyrocervical trunk of subclavian artery Trachea Superior thyroid artery, bronchial artery, internal thoracic artery Venous Drainage Inferior thyroid veins Innervation Vagus nerve (CN X) – nociceptive, parasympathetic Bronchi Right and left mainstem bronchi derived from trachea at the carina Mainstem bronchi Right mainstem bronchus takes a less acute angle from the trachea Three right-sided lobar bronchi Lobar bronchi Two left-sided lobar bronchi Segmental Ventilate the ten bronchopulmonary segments of each lung bronchi Subsegmental bronchi … There are 20-25 generations (i.e., divisions of the airway) Terminal Final generation perfused by bronchial circulation bronchioles  Arterial Perfusion Bronchial arteries Venous Drainage Bronchial veins Bronchi – Innervation Sympathetic – Neurovascu epinephrine/norepinephrine from lar bronchial circulation Sympathetic stimulation produces Structures bronchodilation Parasympathetic - acetylcholine from Vagus nerve (CN X) Parasympathetic stimulation produces bronchoconstriction Histamine and slow reactive substance of anaphylaxis also induce bronchoconstriction Respiratory Zone Respiratory bronchioles Alveolar ducts Alveolar sacs Alveoli https://courses.lumenlearning.com/suny-ap2/chapter/organs-and-structures-of-the-respiratory-system/ Alveoli Area of respiratory zone which functions primarily in gas exchange Type I pneumocytes – structural cells Type II pneumocytes – surfactant-producing cells Type III pneumocytes – alveolar macrophages  Conduit to the lung Mainstem bronchus Pulmonary Pulmonary circulation Bronchial circulation Hilum Lymphatics/lymph nodes Pulmonary innervation (e.g., Vagus nerve, sympathetic nerves)  Consists of left pleural cavity, mediastinum, and right pleural cavity Mediastinum – area of thoracic cavity that contains heart, great vessels, trachea, esophagus, and thymus Thoracic Pleural cavity – space between parietal pleura and visceral pleura that Cavity contains pleural fluid; facilitates lung movement Pleura – serous membrane that separates the lungs from the mediastinum and thoracic cage Parietal – lines the chest wall, mediastinum, diaphragm Visceral – lines the lungs MECHANICS OF BREATHING Muscles of Ventilation  Primary muscle of inspiration; bilateral domes function independently Innervated by the phrenic nerve, which is derived from the third, fourth, and fifth cervical spinal nerve roots Diaphrag Separates thoracic cavity from m abdominal cavity Central tendon – conduit for inferior vena cava Aortic hiatus – conduit for aorta, azygous vein, thoracic duct Esophageal hiatus – conduit for esophagus Boyle’s Law Inspiration Contraction of inspiratory muscles increases the volume of the thoracic cavity, resulting in decreased alveolar pressure (i.e., negative pressure ventilation) Increased atmospheric pressure (i.e., positive pressure ventilation) can also drive air into the lungs Expiration Relaxation of the diaphragm causes the lungs to contract (i.e., increases pressure), driving air out of the lungs Pleural, Alveolar, and Transpulmonary Pressures Pleural pressure (Ppl) Continuous negative pressure favoring lung expansion Ppl during inspiration: - 7.5 cm H2O Ppl during expiration: -5 cm H2O Alveolar pressure (Palv) Fluctuates to drive movement of gas Palv at rest: 0 cm H2O Palv during inspiration: -1 cm H2O Palv during expiration: +1 cm H2O Transpulmonary pressure Under normal physiologic conditions, transpulmonary pressure is always positive and is a measure of elastic force Lung Compliance Compliance is the amount of force required to cause elastic deformation (i.e., expand) of the lung; measure of lung stiffness Compliance is determined by elastic forces Elastic forces of the lung tissue (e.g., collagen, elastin) Elastic forces caused by alveolar surface tension C - compliance V - volume P - pressure Compliance may also be described as the change in volume for a given change in transpulmonary pressure In a healthy lung, the compliance is 200 mL/1 cm H2O Surface Tension and Surfactant Interfaces between air and water normally cause water molecules to contract (i.e., create surface tension), resulting in collapse of the air space Surfactant, secreted by type II pneumocytes, contains phospholipids (e.g., dipalmitoyl phosphatidylcholine, surfactant apoproteins) that reduce surface tension Reduces surface tension (i.e., tendency of water molecules to contract) Increases lung compliance (i.e., alveoli remain open) Decreases work of breathing  Multiple factors oppose lung inflation (i.e., resistance to breathing) Elastic recoil of the lung Resistance Frictional resistance of lung tissues to Resistance to airflow (i.e., turbulent > laminar) Breathing Turbulent > laminar Autonomic Nervous System Sympathetic stimulation (e.g., epinephrine, norepinephrine) produces bronchodilation Parasympathetic stimulation (e.g., acetylcholine) produces bronchoconstriction Reynold’s Number Re – Reynold’s number (viscosity of fluid) = density of fluid Indicates whether flow is laminar or turbulent Turbulent – Re >2300 Laminar – Re < 2300  Poiseuille’s Law describes resistance to laminar Poiseuille’s flow According to Poiseuille’s Law, laminar flow is: Law directly proportional to the pressure gradient, directly proportional to the radius of the tube inversely proportional to the viscosity, and (Hagen-Poiseuille Equation) inversely proportional to the length of the tube Lung Elastic Recoil Lung elastic recoil refers to the forces responsible for emptying the lung during exhalation Lung elastic recoil is determined by elastic forces Elastic forces of the lung tissue (e.g., collagen, elastin) Elastic forces caused by alveolar surface tension According to the Law of Laplace, the force exerted by alveolar surface tension is inversely proportional to the radius of the alveolus Law of Laplace P – pressure T – surface tension r - radius Demonstrates relationship between radius and surface tension within a sphere However, alveoli are polyhedrons, not spheres Spirometry – measurement of the volume movement into and out of the lungs Lung Volumes Name Definition Volume Tidal Volume amount of air inspired or expired with 500 mL each normal breath Inspiratory Reserve Volume extra amount of air that can be inspired 3000 mL when the person inspires with full force Expiratory Reserve Volume extra amount of air that can be expired 1100 mL by forceful expiration after the end of a normal tidal expiration Residual Volume amount of air remaining in the lungs 1200 mL after the most forceful expiration Lung Capacities Name Definition Formula Volume Inspiratory Capacity amount of air that a person can IC = VT + IRV 3500 mL breathe in, beginning at the normal expiratory level and distending the lungs to the maximum amount Functional Residual amount of air that remains in FRC = ERV + RV 2300 mL Capacity the lungs at the end of normal expiration Vital Capacity maximum amount of air a VC = ERV + VT + IRV 4600 mL person can expel from the lungs after first filling the lungs to their maximum extent and then expiring them to the maximum extent Total Lung Capacity maximum amount of air that TLC = RV + ERV + VT 5800 mL the lungs can contain with the + IRV Helium Dilution Method Certain lung volumes/capacities cannot be measured directly (i.e., by spirometry) Functional Residual Capacity (FRC) Residual Volume (RV) Total Lung Capacity (TLC) Indirect measurement (i.e., helium dilution) may be used to determine these volumes Spirometer of known volume is filled with air/helium mixture of known concentration Person expires normally, then breathes in air/helium mixture Mixing of gas from spirometer and lungs (i.e., FRC) causes measurable dilution of helium  Minute Ventilation 𝑀𝑖𝑛𝑢𝑡𝑒𝑉 𝑛𝑡𝑖𝑙𝑎 𝑜𝑛=𝑇𝑖𝑑𝑎𝑙𝑉𝑜𝑙𝑢𝑚𝑒(𝑉𝑇)×𝑅𝑒𝑠𝑝𝑖𝑟𝑎𝑡𝑜𝑟𝑦𝑅𝑎𝑡𝑒(𝑅 )  Ventilated areas that do not receive adequate perfusion to participate in gas exchange Anatomic – volume of conducting airways; approximately 2 mL/kg Alveolar – alveoli that are well- Dead ventilated but poorly perfused Physiologic – sum of anatomic and Space alveolar dead space (i.e., approximates anatomic dead space under normal conditions) Alveolar ventilation – total volume of air each minute that is available for gas exchange Table 38-2 Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. 14th edition. Elsevier; 2021 PULMONARY BLOOD FLOW Pulmonary Circulation Bronchial Pulmonary circulation High-pressure (i.e., systemic), low-flow (i.e., 2% of CO) circulation Low-pressure (i.e., pulmonary), high-flow (i.e., all of CO) circulation circulation Supplies oxygenated blood to the conducting zone of Supplies deoxygenated blood to respiratory zone for the respiratory system gas exchange Thoracic aorta → bronchial arteries → … → bronchial Right ventricle → pulmonary arteries → … → pulmonary veins → azygos, hemiazygos, posterior intercostal, veins → left atrium pulmonary veins Vessels of the pulmonary arterial system are shorter, wider, and more distensible than systemic arteries, resulting in large compliance and low pulmonary vascular resistance (PVR) Pulmonary System Pressures Right Ventricular Pressure Systolic ~ 25 mm Hg Diastolic ~ 0-1 mm Hg Pulmonary Artery Pressure (PAP) Systolic ~ 25 mm Hg Diastolic ~ 8 mm Hg mean PAP ~ 15 mm Hg Pulmonary Capillary Pressure Mean ~ 7 mm Hg Pulmonary wedge pressure ~ 5 mm Hg Left Atrial/Pulmonary Venous Pressures Mean ~ 2 mm Hg  Systemic circulation Hypoxemia/hypercarbia/acidosis cause vasodilation Pulmonary circulation Hypoxia/hypercarbia/acidosis cause Hypoxic vasoconstriction (i.e., hypoxic Pulmonary pulmonary vasoconstriction) When the decreases (i.e., PA > portions of the cardiac cycle (i.e., shunt) PV Zone 2: PA > PALV > Intermittent blood flow PV Zone 3: Continuous P A > PV > blood flow (i.e., dead space) PALV Pulmonary Capillary Dynamics Interfaces between pulmonary capillaries, lymphatic vessels, and alveoli permit Like albumin movement of fluid; net forces favor slight movement from pulmonary capillaries to interstitial tissue Forces tending to favor movement of fluid from pulmonary capillary to interstital tissue Pc – 7 mm Hg  if – 14 mm Hg Pif – 8 mm Hg Forces tending to favor movement of fluid from interstitial tissue to pulmonary capillary p – 28 mm Hg The same concepts apply to peripheral capillaries; however, the forces are quantitatively different  Ventilation-Perfusion Ratio – VENTILATIO normally 0.8 Describes the distribution of N- ventilation (i.e., airflow) relative to PERFUSION perfusion (i.e., blood flow) V/Q varies in different regions of the lung RELATIONSH Ventilation > Perfusion (i.e., V/Q = ∞) IP IN THE Alveoli that are ventilated but not perfused result in dead space LUNG Ventilation < Perfusion (i.e., V/Q = 0) Alveoli that are perfused but not ventilated result in shunt GAS EXCHANGE Dalton’s Law of Partial Pressures Total pressure of a gas mixture is equal to the sum of the partial pressures of each constituent gas Atmospheric Air P = PO2 + PN2 P = (0.21 x 760 mm Hg) + (0.79 x 760 mm Hg) Inspired Air P = PO2 + PN2 + PH2O P = (0.21 x 713 mm Hg) + (0.79 x 713 mm Hg) + 47 mm Hg Alveolar Gas Equation PAO2 = PiO2 – (PACO2/RQ) PAO2 = (0.21 X [760 mm Hg – 47 mm Hg]) – (40 mm Hg/0.8) = 99 mm Hg Fick’s Law Describes the diffusion of gases across the alveolocapillary membrane Vgas=A×D(P1−P2) / T A – membrane surface area Directly proportional D – diffusion constant Directly proportional P1-P2 – partial pressure gradient Directly proportional T – membrane thickness Inversely proportional  Physical dissolution in plasma (0.3%) Solubility coeffieicnt of O2 in plasma is 0.003 0.003 mL of O2 is transported for every 1 mm Hg PO2 in 100 mL Oxygen Assuming a normal PaO2 of 100 mm Transport Hg, 0.3 mL of O2 is dissolved in blood Bound to hemoglobin (99.7%) 1 g Hgb can carry 1.36 mL of O2 Assuming a normal Hgb of 15 g/100 mL, 20.4 mL of O2 is bound to Hgb Oxyhemoglobin Dissociation Curve Rightward shift (i.e., enhances release of oxygen from hemoglobin) Increased H+ (i.e., decreased pH) Increased CO2 Increased temperature Increased 2,3-BPG Leftward shift (i.e., reduces release of oxygen from hemoglobin) Decreased H+ (i.e., increased pH) Decreased CO2 Decreased temperature Decreased 2,3-BPG Methemoglobin Carbon monoxide  Physical dissolution in plasma (5-10%) CO2 is approximately 20 times more soluble than O 2 Carbon Carbamino compounds (5-10%) Dioxide Bicarbonate (80-90%) CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3− Transport Catalyzed by carbonic anhydrase in RBCs HCO3- formed and diffuses out of the RBC CL- diffuses into the RBC maintaining equilibrium (i.e., Chloride shift) H+ buffered with the RBC binding to Hgb  Bohr Effect – CO2/H+ affect the affinity of Hgb for O2 Acidosis/hypercarbia facilitate release of O2 Bohr & at peripheral tissues Haldane Effect – O2 affects the affinity of Hgb Haldane for CO2/H+ Effects Deoxyhemoglobin has an increased affinity for CO2, thus facilitating transport to lungs Oxyhemoglobin has a decreased affinity for CO2, thus facilitating offloading of CO2 at alveoli CONTROL OF BREATHING Control of Breathing Function of respiration is to maintain homeostatic concentrations of O2, CO2, and H+ throughout the body CO2 and H+ may have direct effects on the respiratory center O2 has little effect on the respiratory center, but is detected by peripheral chemoreceptors Control of Pons Breathing Medullary respiratory center Nucleus of the tractus solitarius Contains afferent projections of the glossopharyngeal nerve (CN IX) and vagus nerve (CN X) Dorsal respiratory group Located in the nucleus of the tractus solitarius of the medulla oblongata “Pacemaker” of normal breathing Ventral respiratory group Located in the nucleus ambiguous and nucleus retroambiguus of the medulla oblongata Involved in both inspiration and expiration during periods of increased ventilation Pneumotaxic center Located in the nucleus parabrachialis of the upper pons Controls respiratory rate and depth (i.e., limits inspiration) Apneustic center Located caudad in the pons Unknown function  Central chemoreceptors are located in the medulla oblongata; exposed to cerebrospinal fluid Highly responsive to changes in cerebrospinal fluid pH (i.e., H+ Central concentration) Chemorecept Charged ions (e.g., H+ ) do not readily cross the blood-brain barrier ors Gases (e.g., CO2 ) readily diffuse across the blood-brain barrier In CSF, CO2 reacts with H2O to form carbonic acid, which then dissociates into HCO3- and H+ Minimally responsive to changes in  Peripheral chemoreceptors are located in the aortic bodies and carotid bodies; exposed to arterial blood Highly responsive to changes in Glomus cells contain O2-sensitive potassium channels that are inactivated by hypoxemia, Peripheral causing cellular depolarization Minimally responsive to changes in and pH Chemorecept Hypoxemia generates afferent impulses ors that are transmitted to the medulla oblongata Aortic bodies: afferent impulse transmitted via vagus nerve (CN X) Carotid bodies: afferent impulse transmitted via Hering’s nerve, a branch of the glossopharyngeal nerve (CN IX) Hering-Breuer Reflex Stretch receptors in the muscular walls of the bronchi and bronchioles transmit signals via the vagus nerve to the dorsal respiratory group These signals inhibit the dorsal respiratory group (i.e., inspiration) Serves to prevent overdistension of alveoli by inhibiting high tidal volumes (i.e., > 1500 mL) Cough and Sneeze Reflexes Stimulation of the nose, trachea, and bronchi may trigger reflex expulsion of irritants Irritation of epithelium generates afferent impulses that are transmitted to the medulla oblongata Sneeze: afferent impulse transmitted via trigeminal nerve (CN V) Cough: afferent impulse transmitted via vagus nerve (CN X) Rapid inspiration of air (i.e., approximately 2.5 L) Closure of epiglottis and true vocal cords Forceful contraction of abdominal muscles and other accessory muscles of ventilation Opening of epiglottis and vocal cords with forceful expulsion of irritants Nagelhout JJ, Elisha S, Heiner JS, eds. Nurse Table Anesthesia. 7th edition. Elsevier; 2023 29.6 ACID-BASE BALANCE Acid-Base Balance Acid-base balance is maintained by respiratory system, kidneys, and buffers (i.e., weak acid and conjugate base) Arterial Blood Gas Interpretation Acid-base disturbances Respiratory acidosis Metabolic acidosis Respiratory alkalosis Metabolic alkalosis Normal acid-base values pH: 7.35 – 7.45 : 35 – 45 mm Hg HCO3- : 22 – 26 mEq/L Nagelhout JJ, Elisha S, Heiner JS, eds. Nurse Table Anesthesia. 7th edition. Elsevier; 2023 29.5 Compensatory Mechanisms Respiratory system – fast Kidneys – slow acting acting Acidosis: hyperventilation Acidosis: increased excretion of Alkalosis: hypoventilation nonvolatile acid, increased retention of HCO3- Alkalosis: decreased excretion of H+ , decreased retention of HCO3-  Mechanical ventilation Adjust respiratory rate to achieve TREATMENT desired CO2 concentration OF BLOOD GAS NaHCO3 ABNORMALITIE Indicated in certain types of severe S metabolic acidosis (i.e., pH < 7.20) Initial administration of half the calculated deficit is recommended