Ventilation Lecture Notes PDF

(001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 OUTLINE I. VENTILATION A. Elements B. Minute Ventilation C. Goals of Ventilation II. L...

(001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 OUTLINE I. VENTILATION A. Elements B. Minute Ventilation C. Goals of Ventilation II. LUNG VOLUMES AND CAPACITIES III. PATTERNS OF VENTILATORY DYSFUNCTION A. Obstructive Defect B. Restrictive Defect IV. INGREDIENTS FOR PROPER VENTILATION V. VENTILATION AND DISORDERS IN VENTILATION VI. LABORATORY WORKSHEET & SAMPLE CASE I. VENTILATION Ventilation is the process by which atmospheric air moves Figure 1. Relationship between the frequency of breathing or into the lungs and out of the alveoli respiratory rate and the tidal volume More specifically, oxygen from the mixture of gases in the atmosphere enters the alveolar circulation and carbon Tidal volume affects the minute ventilation dioxide as a result of cellular metabolism gets removed More emphasis in CO2 elimination than Alveolar from the lungs in the same process. Oxygenation (more discussed in the process of gas Ventilation happens in two processes: INHALATION AND exchange). EXHALATION, a complex function that involves an Tidal volume, I:E Ratio and Exp time affects interplay of the ventilatory organs driven by pressure FREQUENCY. And the resultant changes affect the gradient. MINUTE VENTILATION. Disorders in ventilation results in the inability of the body Pressure gradient, Time constant, Compliance and to remove carbon dioxide thereby accumulating in the Resistance affects the TIDAL VOLUME. blood in a condition known as HYPERCARBIA. Any changes involving the Tidal volume and the Frequency will affect and alter the MINUTE A. ELEMENTS VENTILATION. 4 elements are needed for the respiration to commence If there is a decrease or ineffectivity of Minute Ventilation, o Atmospheric/ambient air then, CO2 Elimination will be affected. o Thoracic pump - Ventilatory organs/organs of respiration C. GOALS OF VENTILATION o Air conduit - Refers to process or passages of the respiratory tract that are responsible for air to go in and out the lungs (Nostrils down to the respiratory bronchioles). o Alveoli - Where the gas exchange occurs B. MINUTE VENTILATION Also known as alveolar equation Product of tidal volume (TV) and respiratory rate (RR) MV = TV x RR o Where: MV– minute ventilation Figure 2. Main goal of ventilation and the relationship of frequency TV– Tidal volume of breathing RR – Respiratory rate Alveolar oxygenation In a 60 kg man, NORMAL VOLUME (NV) is equivalent to CO2 elimination 6-8 liters per minute The relationship of frequency of breathing/respiratory rate and the tidal volume, affects the minute ventilation. Moreover, in ventilation, CO2 elimination is more emphasized rather than alveolar oxygenation, because alveolar oxygenation is more discussed in the process of gas exchange compared to ventilation. Page 1 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 II. LUNG VOLUMES AND CAPACITIES Diseased/ abnormal/ obstructed airway → OBSTRUCTIVE DEFECT → ↓AIRFLOW (volume/time) A. RESTRICTIVE DEFECTS If the removal of CO2 is due to an impediment in the normal expansion of the ventilatory organs. P Pleura* A Alveoli I Interstitium N Neuromuscular* T Thoracic Cage* Table 1. Thoracic pump* / lungs. Any disorder affecting the (THORACIC PUMP: PAINT) will present a ventilatory dysfunction Figure 3. Interpretation of lung volumes and capacities TOTAL LUNG CAPACITY (TLC) Affected thoracic pump → Inability to expand alveoli → o The entirety of gas in the lungs or air in the lungs at RESTRICTIVE DEFECT → ↓ LUNG VOLUME any given time o Subdivided into: *memorize structure Included/classified as the thoracic pump - VITAL CAPACITY (VC) (acronym: PAINT) - RESIDUAL VOLUME (RV) TIDAL VOLUME (TV) IV. INGREDIENTS FOR PROPER VENTILATION o Refers to the volume of air that goes in and out of the Thoracic pump must be efficient, effective in expanding lungs in a normal, relax/quiet breathing. the alveoli and that the airway should also be unobstructed INSPIRATORY RESERVE VOLUME (IRV) for the passage of air from the atmosphere down into the o Inhaling beyond the Tidal Volume. alveoli. EXPIRATORY RESERVE VOLUME (ERV) o Exhaling beyond the Tidal Volume. V. VENTILATION AND DISORDERS IN RESIDUAL VOLUME (RV) VENTILATION o Remaining air that stays in the alveoli after a forceful We look particularly in CO2 elimination rather than exhalation or expiration (remember that the lungs or oxygenation. alveolar sacs are not completely emptied after each We can determine that there are 2 patterns of ventilation exhalation). base on which ingredient is affected. o It is remaining amount of air to maintain alveolar inflatability. VI. LABORATORY WORKSHEET & CASE o It cannot be measured. 1. Fill up the table below based on your observations. Capacities are combination of volumes. INSPIRATORY CAPACITY (IC) – IRV and TV. Open Straw Tied Straw FUNCTIONAL RESIDUAL CAPACITY (FRC) – ERV and 1.Ease of Laminar airflow Turbulent airflow RV. airflow All the lung volumes and capacities can be measured directly or indirectly. 2.Movement Smooth, stable/ steady Unsteady/ unstable of balls The capacities or lung volumes that cannot be measured are those that are involved in RV. The RV can only be 3.Effort of Effortless Exerts greater effort surmised by inference. The FRC, VC and TLC are blowing measured by inferences. Comments The lower the The higher the pressure/ effort pressure/ effort III. PATTERNS OF VENTILATORY DYSFUNCTION needed to move air, needed to move air, A. OBSTRUCTIVE DEFECTS the lesser the airway the greater the airway When the removal of CO2 from the body is limited by resistance. resistance. narrowing of the airways by way of mechanical and 2. In a hypothetical situation, with regards to lung volumes, dynamic obstruction which portion of the total lung capacity contributed largely o AIRWAYS with the movement of ping pong balls when the straw is - nostrils → nasal passages → trachea → tracheal open? How about when the straw is tied? Explain your bronchi tree → bronchioles → alveoli answer briefly. - so, if there is an obstruction in any form, along these Movement of ping pong balls- Vital Capacity (IRV, TV, structures, then we expect a hindrance to free ERV) Tied straw- Increased Vital capacity (IRV, TV, ERV) passage of air. and Functional Residual volume (ERV, RV) because of increased effort in blowing air, thus maximizing expiration. Page 2 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 3. List the lung functions measured in a spirometry and 2. Expiratory Reserve Volume (ERV): their significance. A. is the maximal amount of air that can be exhaled from Forced vital capacity (FVC) the lungs after a normal expiration. - The total volume and largest amount of air that you B. is very small and unimportant in normal respiration. can forcefully exhale after breathing in as deeply as C. is kept at a low volume so that the vast bulk of the you can. alveolar gas can be replaced with fresh air during the next - A lower than normal FVC reading indicates restricted inspiration. breathing. 3. Residual Volume (RV): Forced expiratory volume (FEV) A. is mostly found in the anatomical dead space. - This is how much air you can force from your lungs in B. is the volume of gas left in the respiratory system after one second. exhaling maximally. - Lower FEV-1 readings indicate more significant C. makes no contribution to maintaining the patency of the obstruction. alveoli and terminal airways. 4. Vital Capacity (VC): SAMPLE CASE: A. is a measure of the maximum volume of gas in the A 26-year-old female came to the ER with cough and shortness of respiratory system that can be exchanged with each breath. She has been nursing a cold for the past 3 days and she breath. took nasal decongestants to relieve her symptoms. She had B. is a measure of the volume of gas normally exchanged childhood asthma and her last attack was during high school. She with each breath. is allergic to penicillin. On PE, she prefers to sit up on the bed. She C. is a measure of the amount of gas that it is vital to retain is speaking in phrases and is agitated. She has generalized in the respiratory system at the end of expiration. expiratory wheezing upon auscultation. 5. Total Lung Capacity (TLC): A. is a measure of the volume of gas in the respiratory 4. Explain why there is wheezing during exhalation. system at the end of a maximal inspiration. Airflow through a narrowed or compressed segment of a B. Increases as the frequency of breathing increases. small airway becomes turbulent, causing vibration of airway C. is constant in amount from person to person. walls; this vibration produces the sound of wheezing. 6. In the respiratory system, the major difference Wheezing is more common during expiration because between a volume and a capacity is that: increased intrathoracic pressure during this phase narrows A. a capacity is the sum of at least two volumes. the airways and airways narrow as lung volume decreases. B. a volume is the sum of at least two capacities. 5. Which type of ventilation dysfunction is exhibited by the C. Their units are different. patient? 7. Forced Expired Volume in one second (FEV1): Asthma causes severe airway obstruction. The patient A. has the units of liters per minute. has difficulty to expire than to inspire because the closing B. is the same whatever the starting volume in the airways. tendency of the airways is greatly increased by the extra C. Provides a measure of the resistance of the airways to positive pressure required in the chest to cause expiration. flow. 6. What is expected in the blood gas analysis of the patient? 8. During normal resting respiration, in the same breath: By observing the patient, the expected blood gas analysis A. The volume of the exhaled gas exceeds that of the of the patient is Respiratory alkalosis because hyperventilation inhaled gas. thru shortness of breath causes the patient to blow off extra B. The temperature of the exhaled gas is the same as that CO2. of the inhaled gas. Expected blood gas laboratory results are: C. The water content of the exhaled gas is that same as pH: >7.45 that of the inhaled gas. pO2: >80-100mmHg pCO2: 22-26 meq/L (may depend on 7. compensation status) If spirometry is performed at this state, what parameters REFERENCES will be affected and how? 1. Berne, R. M., Koeppen, B. M., & Stanton, B. A. In an obstructive disease, such as asthma, both forced (2010). Berne & Levy Physiology. Philadelphia, PA: expiratory volume (FEV1) and forced vital capacity (FVC) are Mosby/Elsevier. decreased, with the larger decrease occurring in FEV1. 2. Costanzo, L. S. (2014). Physiology (Fifth edition.). Therefore, the FEV1/FVC ratio is decreased. Poor ventilation Philadelphia, PA: Saunders/Elsevier. of the affected areas decreases the ventilation/perfusion (V/Q) 3. Guyton, A.C., Hall, J. E. Guyton and Hall Textbook ratio and causes hypoxemia. The patient’s residual volume of Medical Physiology. 13th ed., W B Saunders, 2015. (RV) will be increased because of breathing at a higher lung 4. https://www.msdmanuals.com/professional/pulmonary- volume to offset the increased resistance of his airways. disorders/symptoms-of-pulmonary-disorders/wheezing 5. https://oxfordmedicine.com/view/10.1093/med/97801996 00830.001.0001/med-9780199600830-chapter 114 TEST YOUR KNOWLEDGE 1. Tidal volume (VT): A. is the volume breathed in each minute. B. is the volume breathed in each breath. C. is unaffected by the frequency of breathing. Page 3 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 READING ASSIGNMENT (CHAPTER 22) Patterns Laminar Turbulent DYNAMIC LUNG AND CHEST WALL MECHANICS Flow Flow Gas Parallel to airway Parallel & OUTLINE movements walls perpendicular to the I. AIRFLOW IN AIRWAYS axis of tube A. 2 Major Patterns of Gas Flow in the Flow rates in Low and steady High which they flow rates flow rates Airways are present B. Reynolds Number Characteristic Streamlined Disorganize/Disordered II. AIRWAY RESISTANCE of Flow (from eddy currents) A. Factors that Contribute to Airway streams Resistance Airways in Smaller airways Larger airways which they (e.g. nose, mouth, B. Other Factors that Affects Airway flow glottis, bronchi, Resistance trachea) III. NUEROHUMORAL REGULATION OF AIRWAY Table 2. Difference between the 2 major patterns of gas flow in the RESISTANCE airways. A. Pathway The pressure-flow characteristics of laminar flow (applied B. Reflex Stimulation of the Vagus Nerve to both liquid and air): IV. MEASUREMENT OF EXPIRATORY FLOW o Flow Rate (V̇) – defined by the following equation: A. The Spirogram B. Flow-Volume Loop V. DETERMINANTS OF MAXIMAL FLOW VI. FLOW LIMITATION AND THE EQUAL o P = driving pressure PRESSURE POINT o r = radius of tube o η = viscosity of fluid VII. DYNAMIC COMPLIANCE o l = length of tube VIII. WORK OF BREATHING P is proportional to the V̇, thus the greater the pressure, the greater the flow I. AIRFLOW IN AIRWAYS Flow resistance (R) = change in driving pressure (ΔP) divided by the V̇ Air flows in & out when there is a pressure difference at the two ends of the airway Inspiration = diaphragm contracts > pleural pressure becomes more negative > gas flows into the lung gas exchange depends on the speed at which fresh gas is η increases with increasing gas density, therefore the brought to the alveoli and the rapidity with which the CO2 pressure drop will increase for a given flow (metabolic pact of respiration) are removed to meet the Higher P is needed to support a given Turbulent flow metabolic needs of body than to support a similar Laminar flow 2 major factors that determines speed of gas flows into the airways (with pressure changes): A. REYNOLDS NUMBER o Gas flow pattern A dimensionless value that expresses the ratio of two o Airway resistance to airflow dimensionally equivalent terms Whether flow through a tube is laminar or turbulent, A. 2 MAJOR PATTERNS OF GAS FLOW IN THE depends on the Re AIRWAYS LAMINAR FLOW– it is silent which makes small airway disease difficult to hear with a stethoscope TURBULENT FLOW– breath sounds heard with a stethoscope reflect this turbulent airflow o d = fluid density o v = average velocity o r = radius o η = viscosity In straight tubes, turbulence occurs when Re is >2000 From this relationship, turbulence is most likely to occur when the v of the GAS FLOW is HIGH and the RADIUS is LARGE In contrast, a LOW-DENSITY GAS (helium) is less likely to cause turbulent flow Page 4 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 clinically relevant in states of increased airway resistance B. OTHER FACTORS THAT AFFECTS AIRWAY where a DECREASE in gas DENSITY can improve airflow RESISTANCE (e.g., substituting helium for nitrogen in inspired air) INCREASES AIRWAY RESISTANCE o airway mucus II. AIWAY RESISTANCE o Edema is regulated by various neural and humoral agents o bronchial smooth muscle contraction 2nd major factor that determines rates of airflow in the -all of which ↓. the caliber of the airways airways o ↑ density and viscosity of the inspired gas Airflow resistance in the airways (Raw) differs in airways of -can exacerbate asthma and COPD different size DECREASES AIRWAY RESISTANCE o Trachea to Alveolus – individual airways become o Breathing a low-density gas (oxygen-helium mixture) smaller + number of airway branches increases -exploited in the treatment of Status dramatically Asthmaticus (a condition that ↑ airway o Raw is equal to the sum of the resistance of each of resistance due to bronchospasm, airway these airways (Raw = Rlarge + Rmedium + Rsmall) inflammation, and hypersecretion of mucus) The Major site of resistance along bronchial tree: o FIRST EIGHT GENERATIONS OF AIRWAYS III. NEUROHUMORAL REGULATION OF AIRWAY RESISTANCE A. PATHWAY Stimulation of efferent Vagal Fibers (either directly or reflexively) ↑ airway resistance and ↓ anatomic dead space (see Chapter 23) secondary to airway constriction (recall that the vagus nerve innervates airway smooth muscle). Stimulation of Sympathetic Nerves Release of the postganglionic neurotransmitter, NOREPINEPHRINE o Inhibits airway constriction = BRONCHODILATION Note: Vagus Nerve stimulation causes airway constriction (bronchoconstriction) while Norepinephrine causes airway dilation (bronchodilation) B. REFLEX STIMULATION OF THE VAGUS NERVE Results in AIRWAY CONSTRICTION AND COUGHING Trigger factors: o inhalation of smoke, dust, cold air, or other irritants o Agents (which act directly on airway smooth muscle to cause constriction) released by resident cells (e.g., Figure 4. Airway resistance as a function of the airway generation. mast cells, airway epithelial cells) and recruited cells In a normal lung, most of the resistance to airflow occurs in the first (e.g., neutrophils, eosinophils) eight airway generations. -Histamine -Acetylcholine The smallest airways (towards the respiratory zone) -thromboxane A2 contribute very little to the overall total resistance of the -prostaglandin F2 bronchial tree (Fig. 2). -leukotrienes (LTB4, LTC4, and LTD4) o Methacholine inhalation (acetylcholine derivative) A. FACTORS THAT CONTRIBUTE TO AIRWAY - used to diagnose airway hyperresponsiveness RESISTANCE in asthmatic patients Healthy individuals’ airway resistance o = approximately 1 cm H2O/L sec IV. MEASUREMENT OF EXPIRATORY FLOW LUNG VOLUME (LV) - one of the most important factors Measurement of Expiratory Flow Rates and Expiratory affecting resistance Volumes is an important clinical tool for evaluating and o Increasing LV increases caliber of the airways as it monitoring respiratory diseases. creates a positive trans airway pressure Commonly used clinical tests o Hence, RESISTANCE TO AIRFLOW ↓ (decrease) o the patient INHALE maximally to TLC WHILE LV ↑ (increase) o then EXHALE as rapidly and completely as possible o Or RESISTANCE TO AIRFLOW ↑ WHILE LV ↓. to RV Page 5 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 o test results are displayed either as a SPIROGRAM or A. THE SPIROGRAM as FLOW-VOLUME CURVE/ LOOP displays the volume of gas EXHALED as a function of time o Results from individuals with suspected lung disease it measures: are compared with results predicted from normal o forced vital capacity (FVC) healthy volunteers o forced expiratory volume in 1 second (FEV1) o Predicted or normal values vary with age, sex, o ratio of FEV1 to FVC (FEV1/ FVC) ethnicity, height, and to a lesser extent, weight o the average mid maximal expiratory flow (FEF25-75) o Abnormalities in values: o total volume of air that is exhaled during a maximal -Indicates abnormal pulmonary function forced exhalation from TLC to RV is called the FVC. -predict abnormalities in gas exchange o volume of air that is exhaled in the first -can detect the presence of abnormal lung second during the maneuver is called the function long before respiratory symptoms FEV1. develop In normal individuals, 70% to 85% (depending on age) of -used to determine disease severity and the the FVC can be exhaled in the first second. Thus, the response to therapy normal FEV1/FVC ratio is greater than 70% in healthy adults. A ratio < 70% suggests difficulty exhaling because of OBSTRUCTION (a hallmark of obstructive pulmonary disease) One expiratory flow rate—the average flow rate over the middle section of the VC—can be calculated from the spirogram. o This expiratory flow rate has several names: -MMEF (mid-maximal expiratory flow) -FEF25-75 (forced expiratory flow from 25%– 75% of VC) o Although it can be calculated from the spirogram, TODAY’S SPIROMETERS AUTOMATICALLY CALCULATE FEF25-75 B. FLOW-VOLUME LOOP Flow-volume curve or loop is another way of measuring lung function clinically It is created by displaying the instantaneous flow rate during a forced maneuver This instantaneous flow rate can be displayed both during: o Exhalation (expiratory flow-volume curve) o Inspiration (inspiratory flow-volume curve) (see Fig. 22.3B). The flow-volume loop measures: o FVC o Peak Expiratory Flow Rate (PEFR) – the greatest flow rate achieved during the expiratory maneuver, o multiple expiratory flow rates at various LV When the expiratory flow-volume curve is divided into quarters, the instantaneous flow rate at which 50% of the VC remains to be exhaled is called the FEF50 (also known as the V̇ max50) the instantaneous flow rate at which 75% of the VC has been exhaled is called the FEF75 (V̇ max75) the instantaneous flow rate at which 25% of the VC has been exhaled is called the FEF25 (V̇ max25). V. DETERMINANTS OF MAXIMAL FLOW shape of the flow-volume loop reveals important information about normal lung physiology that can be altered by disease Inspection of the flow-volume loop reveals that the Maximum Inspiratory Flow is the same or slightly greater than the Maximum Expiratory Flow Page 6 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 3 factors responsible for Maximum Inspiratory Flow Energy is expanded during breathing to overcome the o the force generated by the inspiratory muscles ↓ as inherent mechanical properties of the lung. lung volume ↑ above RV o recoil pressure of the lung ↑ as the lung volume ↑ VII. DYNAMIC COMPLIANCE above RV One additional measurement of dynamic lung mechanics o This opposes the force generated by the inspiratory A dynamic pressure-volume curve can be created by muscles and ↓ maximum inspiratory flow having an individual breathe over a normal LV range The combination of inspiratory muscle force, recoil of the (usually from FRC to FRC +1 L). lung, and changes in airway resistance causes Maximal The Mean Dynamic Compliance Of The Lung (dyn CL) Inspiratory Flow to occur about halfway between TLC and o calculated as the slope of the line that joins the end- RV. inspiratory and end-expiratory points of no flow (Fig. Expiratory Flow Limitation – demonstrated by asking an 22.7). individual to perform 3 forced expiratory maneuvers Dynamic compliance is always less than static with increasing effort. Fig. 22.4 shows the results of these compliance, and it increases during exercise. 3 maneuvers. During TIDAL VOLUME BREATHING, a SMALL change As effort increases, peak expiratory flow increases. in alveolar surface area is insufficient to bring additional Expiratory flow rates at lower lung volumes are said to be surfactant molecules to the surface = lung is LESS effort independent and flow limited because maximal COMPLIANT flow is achieved with modest effort, and no amount of During EXERCISE the opposite occurs; there are LARGE additional effort can increase the flow rate beyond this changes in tidal volume, and more surfactant material is limit. incorporated into the air-liquid interface = lung is MORE Events early in the expiratory maneuver are said to be COMPLIANT effort dependent; that is, increasing effort generates SIGHING and YAWNING increase dynamic compliance increasing flow rates. by increasing tidal volume and restoring the normal surfactant layer o both of these respiratory activities are important for maintaining normal lung compliance VI. FLOW LIMITATION AND THE EQUAL PRESSURE POINT Equal Pressure Point - point at which the pressure inside and surrounding the airway is the same. o Location: dynamic o Specifically, as lung volume and elastic recoil decrease, the equal pressure point moves toward the alveolus in normal individuals. In individuals with COPD, the equal pressure point at any lung volume is closer to the alveolus. Expiratory flow limitation occurs at the equal pressure point. Page 7 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 VIII. WORK OF BREATHING Breathing requires the use of respiratory muscles (diaphragm, intercostals, etc.), which expends energy. Work of breathing – required to overcome the inherent mechanical properties of the lung (i.e., elastic and flow- resistive forces) and to move both the lungs and the chest wall. FACTORS THAT INCREASE WORK OF BREATHING: o Changes in mechanical properties of lungs or chest wall (or both) o presence of disease Respiratory muscle fatigue is the most common cause of respiratory failure o A process in which gas exchange is inadequate to meet the metabolic needs of the body Work of breathing is calculated by: o multiplying the change in volume by the pressure exerted across the respiratory system: o Work of breathing (W) = Pressure (P) x Change in volume = (∆ V) Methods are not available to measure the total amount of work involved in breathing but it can be estimated by measuring the volume and pressure changes during a respiratory cycle. Analysis of pressure volume curves can be used to illustrate these points. Fig. 22.8A represents a respiratory cycle of a normal lung. The static inflation-deflation curve is represented by line ABC. The total mechanical workload is represented by the trapezoidal area OAECD. In restrictive lung diseases, such as pulmonary fibrosis, lung compliance is decreased, and the pressure- volume curve is shifted to the right. This results in a significant increase in the work of breathing (see Fig. 22.8B), as indicated by the increase in the trapezoidal area of OAECD. In obstructive lung diseases, such as asthma during an exacerbation or chronic bronchitis, airway resistance is elevated (see Fig. 22.8C) and greater negative pleural pressure is needed to maintain normal inspiratory flow rates. In addition to the increase in total inspiratory work (OAECD), individuals with obstructive lung disease have an increase in positive pleural pressure during exhalation because of the increase in resistance and the increased expiratory workload, which is visualized as area DFO. The stored elastic energy, represented by area ABCF of Fig. 22.8A, is not sufficient, and additional energy is needed for exhalation. Work of breathing is also increased when deeper breaths are taken (an increase in tidal volume requires more elastic work to overcome) People with or without lung disease adopt respiratory REFERENCE patterns that minimize the work of breathing. 1. Koeppen, B. M., Stanton, B.A. (2014). Berne and Levy Pulmonary fibrosis (increased elastic work) results in Physiology (Seventh edition). Philadelphia, 2018. more shallow and rapid breathing Obstructive Lung Disease (normal elastic work but increased resistive work) breathe more slowly and deeply. Page 8 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 READING ASSIGNMENT (CHAPTER 23) II. DEAD SPACE VENTILATION: ANATOMICAL VENTILATION, PERFUSION, AND AND PHYSIOLOGICAL VENTILATION/PERFUSION RELATIONSHIP Ventilation to airways that do not participate in gas OUTLINE exchange I. VENTILATION II. DEAD SPACE VENTILATION: ANATOMICAL A. ANATOMICAL DEAD SPACE AND PHYSIOLOGICAL Composed of volume of gas that fills the conducting airways. C. Anatomical Dead Space D. Physiological Dead Space VT = VD + VA III. ALVEOLAR VENTILATION o V refers to volume C. Composition of Air o Subscripts T, D, A refers to Tidal, Dead space, D. Alveolar Gas Composition Alveolar E. Arterial Gas Composition F. Distribution of Ventilation VT x n = (VD x n) + (VA x n) OR VE = VD = VA IV. PULMONARY VASCULAR RESISTANCE o “dot” above the V denotes volume per unit of time (n) V. DISTRIBUTION OF PULMONARY BLOOD o VE is the total volume of gas in liters expelled from FLOW the lungs per minute aka Exhaled per minute A. Gravity o VD is the dead space ventilation per minute B. Arterial and Venous Pressure o VA is the alveolar ventilation per minute In healthy adult, gas contained in conducting airways at C. Pulmonary Alveolar Pressure FRC or functional residual capacity is 100 to 200 mL D. Three Functional Zones of Lungs (compared to the 3L of gas in an entire lung). VI. ACTIVE REGULATION OF BLOOD FLOW VII. VENTILATION/PERFUSION RELATIONSHIPS VD = VD / VT x VE A. Regional Differences in o VD varies inversely with VT, the larger the VT, the Ventilation/Perfusion Ratios smaller the VD o Normally, VD/VT is 20% to 30% of exhaled minute B. Alveolar-Arterial Difference for ventilation or VE Oxygen Changes in dead space is important contributors to VIII. ARTERIAL BLOOD HYPOXEMIA, HYPOXIA breathing. AND HYPERCARBIA o If dead space is increased, individual must inspire IX. VENTILATION/PERFUSION ABNORMALITIES larger VT to maintain normal levels of blood gases AND SHUNTS (ex. Muscle fatigue, Respiratory failure) X. LOW VENTILATION/PERFUSION o If metabolic demands increase, people with lung disease cannot increase the VT XI. ALVEOLAR HYPOVENTILATION XII. DIFFUSION ABNORMALITIES B. PHYSIOLOGICAL DEAD SPACE XIII. MECHANISMS OF HYPERCAPNIA Total volume of gas in each breath that does not XIV. EFFECT OF 100% OXYGEN ON ARTERIAL participate in gas exchange. BLOOD GAS ABNORMALITIES In diseased lungs, some alveoli are perfused but not XV. REGIONAL DIFFERENCES ventilated. Large as anatomical dead space (larger in diseased lungs) I. VENTILATION III. ALVEOLAR VENTILATION Air that moves in composed of: o Volume that fills the conducting airways (dead space A. COMPOSITION OF AIR ventilation) Inspiration brings ambient/atmospheric air to the alveoli o Portion that fills the alveoli (alveolar ventilation) AMBIENT AIR o N2 and O2 plus minute quantities of carbon dioxide, VE = f x VT argon, and inert gases o because this is a gas mixture, GAS LAWS can be Minute/Total Ventilation (VE)- volume of air that enters or applied leave the lung per minute 2 PRINCIPLES OF GAS LAW: Frequency (f)- number of breaths per minute o When the components are viewed in terms of gas Tidal volume or volume of air inspired or expired per fractions (F), the sum of the individual gas fractions breath (VT) must equal one o varies with age, sex, body position, metabolic activity o average-sized adult at rest, VT= 500mL o children, VT= 3 to 5 mL/kg Page 9 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 o Partial pressure of a gas (Pgas) is equal to the D. DISTRIBUTION OF VENTILATION fraction of that gas in the gas mixture (Fgas) ▪ Upright position, at most lung volume, alveoli near apex multiplied by the atmospheric (barometric) pressure are most expanded than alveoli at base ▪ Gravity pulls lung downward and away from chest wall, as 3 IMPORTANT GAS LAWS that govern ambient air and a result pleural pressure is lower (more negative) at apex alveolar ventilation ▪ Ventilation of alveoli is not uniform because, variable o BOYLE’S LAW airway resistance (R) or compliance (C) is quantitatively -When TEMPERATURE is constant, PRESSURE (P) and VOLUME (V) are inversely related described by time constant (t) -Used to measure lung volume. t=RxC P1V1 = P2V2 ▪ Adult normal respiratory rate = 12 breaths per minute o Inspiratory time is 2 seconds o DALTON’S LAW o Expiratory time is 3 seconds -Partial pressure of a gas in a gas mixture is the pressure that gas would exert if it occupied the total IV. PULMONARY VASCULAR RESISTANCE volume of mixture in the ABSENCE of other Blood flow in pulmonary circulation is pulsative and components. influenced by: o HENRY’S LAW o Pulmonary vascular resistance (PVR) -The concentration of a gas dissolved in liquid is o Gravity proportional to its partial pressure -Ambient air = 21% oxygen and 79% N2 o Alveolar pressure Oxygen tension at the mouth is altered in 2 ways. o Atrial – to – venous pressure gradient Changing the fraction of O2 and FiO2; Changing the Pb PVR = PPA – PLA Ambient oxygen can increase with supplemental oxygen and decrease at high altitude. QT Inspired air becomes saturated with water vapor in glottis o PPA is the change in pulmonary artery pressure Water vapor exerts partial pressure and dilutes total (NORMAL = 14mmHg) pressure o PLA is the change in left atrium pressure (NORMAL= Water vapor pressure at body temperature is 47 mmHg 8mmHg) Water vapor pressure reduces partial pressure of O2 and o QT is the flow or cardiac output (NORMAL = 6L/min) N2 o PVR = 1.00 mmHg/minute (NORMAL) In calculation of partial pressure of ambient air, water Pulmonary circulation has 2 features that increase the vapor pressure is ignored because ambient air is dry blood flow without increased in pressure Conducting airways do not participate in gas exchange so o High demand (ex. In exercise), pulmonary vessels partial pressure of O2 and N2 are unchanged until it that are normally closed are recruited reaches alveoli o Blood vessels are distensible, and diameter increases B. ALVEOLAR GAS COMPOSITION At the end of the inspiration, air filled alveoli compresses At the end of inspiration (glottis is open), total pressure in alveolar capillaries and increased the PVR (except larger the alveolus is atmospheric vessels, their PVR is decreased) Composition of gas mixture is changed Capillary beds in lungs account for 40% PVR ALVEOLAR VENTILATION– process of elimination of In exhalation, deflated alveoli apply respiratory resistance carbon dioxide to capillaries and PVR decreases (larger vessels PVR ALVEOLAR CARBON DIOXIDE EQUATION– defines increases) the relationship between carbon dioxide production and TOTAL PVR IN THE LUNGS IS LOWEST AT FRC alveolar ventilation (FUNCTIONAL RESIDUAL CAPACITY C. ARTERIAL GAS COMPOSITION ▪ Acute increased in PACO2 = respiratory acidosis V. DISTRIBUTION OF PULMONARY BLOOD ▪ Acute decreased in PACO2 = respiratory alkalosis FLOW ▪ Hypercapnia = elevation in PACO2 Pulmonary circulation o when CO2 production exceeds alveolar ventilation o low-pressure/low resistance system, influenced by (hypoventilation) the following: Hypocapnia = decreased PACO2 A. GRAVITY o when alveolar ventilation exceeds CO2 production On leaving the pulmonary artery, blood must travel against gravity to the apex of the lung in upright people. Page 10 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 This gravitational effect contributes to an uneven VII. VENTILATION/PERFUSION RELATIONSHIPS distribution of blood flow in the lungs. Both ventilation (V̇) and lung perfusion (Q̇) are essential components of normal gas exchange, but a normal B. ARTERIAL AND VENOUS PRESSURE relationship between the two components is insufficient to The effect of gravity on blood flow affects arteries and ensure normal gas exchange. veins equally and results in wide variations in arterial (Pa) Ventilation/perfusion ratio and venous pressure (Pv) from the apex to the base of the o also referred to as the V̇/Q̇ ratio is the ratio of lung. ventilation to blood flow. These variations influence both flow and - this ratio can be defined for a single alveolus, ventilation/perfusion relationships. for a group of alveoli, or for the entire lung. In normal lungs: C. PULMONARY ALVEOLAR PRESSURE o Alveolar ventilation = 4.0 L/min Differences in pulmonary alveolar pressure (PA) also o Pulmonary blood flow = 5.0 L/min. influence blood flow in the lung. o Overall ventilation/perfusion ratio = 0.8 The range of V̇/Q̇ ratios varies widely in different lung THREE FUNCTIONAL ZONES OF LUNGS units. ZONE 1 When ventilation exceeds perfusion, the V/Q ratio is o represents the lung apex, where Pa is so low that it greater than 1 (V̇/Q̇ > 1), and when perfusion exceeds can be exceeded by PA. ventilation, the V/Q ratio is less than 1 (V̇/Q̇ < 1). -The capillaries collapse because of the greater Mismatching of pulmonary blood flow and ventilation external PA, and blood flow ceases. results in impaired O2 and CO2 transfer. -Under normal conditions, this zone does not In individuals with cardiopulmonary disease, mismatching exist; however, this state could be reached of pulmonary blood flow and alveolar ventilation is the during positive-pressure mechanical ventilation most frequent cause of systemic arterial hypoxemia or if Pa decreases sufficiently (such as might (reduced PaO2). occur with a marked decrease in blood volume). In general, V̇/Q̇ ratios greater than 1 are not associated ZONE 2 with hypoxemia. o The upper third of the lung, Pa is greater than PA, which is in turn is greater than Pv. A. REGIONAL DIFFERENCES IN -Because PA is greater than Pv, the greater external PA partially collapses the capillaries VENTILATION/PERFUSION RATIOS and causes a “damming” effect. This The ventilation/perfusion ratio varies in different areas of phenomenon is often referred to as the waterfall the lung. effect. In an upright individual, although both ventilation and ZONE 3 perfusion increase from the apex to the base of the lung, o Pa is greater than Pv, which is greater than PA, and the increase in ventilation is less than the increase in blood blood flows in this area in accordance with the flow. pressure gradients. Thus, pulmonary blood flow is greater in the base of the B. ALVEOLAR-ARTERIAL DIFFERENCE FOR OXYGEN lung because the increased transmural pressure distends The difference between PAO2 and PaO2 is called the the vessels and lowers the resistance. alveolar-arterial difference for oxygen (AaDO2). An increase in the AaDO2 is a hallmark of abnormal O2 VI. ACTIVE REGULATION OF BLOOD FLOW exchange. Oxygen levels have a major effect on blood flow. Abnormalities in PaO2 can occur with or without an elevation in AaDO2. Hypoxic vasoconstriction o occurs in arterioles in response to decreased PAO2. Hence, the relationship between PaO2 and AaDO2 is - the response is local, result to shifting of blood useful in determining the cause of an abnormal PaO2 and flow from hypoxic areas to well-perfused areas in predicting the response to therapy particularly to to enhance gas exchange. supplemental O2 administration. Isolated, local hypoxia does not alter pulmonary vascular resistance (PVR) unless 20% of the vessels is hypoxic. VIII. ARTERIAL BLOOD HYPOXEMIA, HYPOXIA, Low inspired O2 levels as a result of high altitude have a AND HYPERCARBIA greater effect on PVR because all vessels are affected. ARTERIAL HYPOXEMIA High levels of inspired O2 can dilate pulmonary vessels o PaO2 lower than 80 mm Hg in an adult who is and decrease PVR. breathing room air at sea level. Pulmonary Artery hypertension HYPOXIA o pulmonary artery pressures rise o insufficient O2 to carry out normal metabolic - consequence of chronic hypoxia or collagen functions hypoxia often occurs when the PaO2 is less vascular disease. than 60 mm Hg. 4 major categories of hypoxia. Page 11 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 o HYPOXIC HYPOXIA X. LOW VENTILATION/PERFUSION - most common and six main pulmonary When alveolar ventilation is distributed unevenly between conditions associated with hypoxic hypoxia are the two gas-exchange units and blood flow is equally anatomical shunt, physiological shunt, distributed, the unit with decreased ventilation has a V̇ /Q̇ decreased FiO2, V̇ /Q̇ mismatching, diffusion ratio of less than 1, whereas the unit with the increased abnormalities, and hypoventilation. ventilation has a V̇ /Q̇ of greater than 1. o ANEMIC HYPOXIA This causes the alveolar and end-capillary gas - caused by a decrease in the amount of compositions to vary. functioning hemoglobin as a result of too little hemoglobin, abnormal hemoglobin, or interference with the chemical combination of XI. ALVEOLAR HYPOVENTILATION oxygen and hemoglobin (e.g., carbon Determination of PAO2 - balance between the rate of O2 monoxide poisoning). uptake and the rate of O2 replenishment by ventilation. o HYPOPERFUSION HYPOXIA If ventilation decreases, PAO2 decreases. - results from low blood flow (e.g., decreased When ventilation is halved, the PACO2 and PaCO2 cardiac output) and reduced oxygen delivery to doubles. the tissues. HYPOVENTILATION o HISTOTOXIC HYPOXIA o ventilation insufficient to maintain normal levels of CO - occurs when the cellular machinery that uses o normal AaDO2 because gas exchange is normal; if oxygen to produce energy is poisoned, as in AaDO2 rises, atelectasis develops rapidly by creating cyanide poisoning. In this situation, arterial and regions with V/Q ratios of 0 venous PO2 are normal or increased because o decreases PaO2 and increases PaCO2. oxygen is not being utilized. XII. DIFFUSION ABNORMALITIES IX. VENTILATION/PERFUSION ABNORMALITIES Diffusion Disequilibrium AND SHUNTS o incomplete diffusion; increased AaDO2; observed in Anatomical Shunts normal exercising persons at high altitude o An anatomical shunt occurs when mixed venous Alveolar capillary block blood bypasses the gas-exchange unit and goes o thickening of the ai-blood barrier directly into the arterial circulation distribution of o uncommon cause of hypoxemia cardiac output is changed. o The blood that bypasses the gas-exchange unit is XIII. MECHANISMS OF HYPERCAPNIA thus shunted, and because the blood is Hypercapnia - elevated PCO2 deoxygenated, this type of bypass is called a right- 2 major mechanisms: to-left shunt. o HYPOVENTILATION o Most anatomical shunts develop within the heart, and - Hypoventilation always decreases PaO2 and the effect of this right-to-left shunt is to mix increases PaCO2 resulting to hypoxemia that deoxygenated blood with oxygenated blood, and it responds to an enriched source of O2. results in varying degrees of arterial hypoxemia. o WASTED OR INCREASED DEAD SPACE o An important feature of an anatomical shunt is that if VENTILATION an affected individual is given 100% O2 to breathe, - when pulmonary blood flow is interrupted in the the response is blunted severely. presence of normal ventilation. o The PaCO2 in an anatomical shunt is not usually -most often caused by a pulmonary embolus that increased even though the shunted blood has an obstructs blood flow. elevated level of CO2. - the embolus halts blood flow to pulmonary Physiological Shunts areas with normal ventilation (V/Q = ∞) o also known as venous admixture can develop when - fails to oxygenate any of the mixed venous ventilation to lung units is absent in the presence of blood. continuing perfusion. Compensation after embolus begins immediately by o The effect of a physiological shunt on oxygenation is o local bronchoconstriction like the effect of an anatomical shunt, deoxygenated o Distribution of ventilation shifts to the areas being blood bypasses a gas-exchanging unit and admixes perfused with arterial blood. If no compensation occur, PaCO2 increases and PaO2 o ATELECTASIS decreases. -obstruction to ventilation of a gas-exchanging unit with subsequent loss of volume XIV. EFFECT OF 100% OXYGEN ON ARTERIAL -is an example of a situation in which the lung BLOOD GAS ABNORMALITIES region has a V̇ /Q̇ of 0. Breath 100% O2 through a non-rebreathing face mask -Causes: mucous plugs, airway edema, foreign (15min) to distinguish a right-to-left shunt from other bodies, and tumors in the airway. causes of hypoxemia. Page 12 of 13 PREPARED BY: CMED 1C  (001) VENTILATION DR. DOMINETTA S. GONZALO | 11/30/20 When one breathes 100% O2, all N2 in the alveolus is replaced by O2; even areas with very low V/Q ratios develop high alveolar pressure as N2 is being replaced. PAO2 is calculated according to alveolar air equation: PAO2 = [1.0 X (Pb - PH2O)] - PaCO2/0.8 = [1.0 X (760 - 47)] - 40/0.8 = 663 mm Hg Presence of right-to-left shunt, oxygenation is not corrected because mixed venous blood continues to flow through the shunt and mix with blood that has perfused normal units. The poorly oxygenated blood from shunt lowers the arterial O2 content and maintains AaDO2. Elevated AaDO2 with 100% O2 = presence of shunt XV. REGIONAL DIFFERENCES The volume of the lung at the apex is less than the volume at the base. Ventilation and perfusion are less at the apex than at the base, but the differences in perfusion are greater than the differences in ventilation. V/Q ratio is high at the apex and low at the base. PAO2 is higher and PACO2 is lower in the apex than in the base. End-capillary PO2 is lower, and the O2 content becomes lower in end-capillary blood at the lung base than at the apex. During exercise, the difference between the content of gases in the apex and in the base of the lung diminishes due to increase of blood flow to the apex and becoming uniform in the lung. REFERENCE 2. Koeppen, B. M., Stanton, B.A. (2014). Berne and Levy Physiology (Seventh edition). Philadelphia, 2018. Page 13 of 13 PREPARED BY: CMED 1C