Respiratory Physiology (Part 1).pdf

Pulmonary Function Test • Static Lung Volumes • 4 individual components • TV, IRV, ERV, RV • Static Lung Capacities • Sum of ≥ 2 Lung Vols • TLC, IC, FRC, VC K. Sam Fall 2023 5 Four Static Lung Volumes 1. 2. 3. 4. VT or TV (Tidal Vol.) IRV (Inspiratory Reserve Vol.) ERV (Expiratory Reserve Vol....

Pulmonary Function Test • Static Lung Volumes • 4 individual components • TV, IRV, ERV, RV • Static Lung Capacities • Sum of ≥ 2 Lung Vols • TLC, IC, FRC, VC K. Sam Fall 2023 5 Four Static Lung Volumes 1. 2. 3. 4. VT or TV (Tidal Vol.) IRV (Inspiratory Reserve Vol.) ERV (Expiratory Reserve Vol.) RV (Residual Vol.) Lung volumes are determined by the balance between the lung's elastic properties and the properties of the muscles of the chest wall. Pulmonary Function Test (3:44): https://westcoastuniversity.hosted.panopto.com/Panopto/Pag es/Viewer.aspx?id=e14cce3c-206c-440b-9985acbb014f9f85&start=2.353975 (Links to an external site.) Lung Function - Lung Volumes and Capacities (8:30): https://youtu.be/9VdHhD1vcDU 6 K. Sam Fall 2023 1. Tidal Volume (VT or TV) Take a normal breath, that’s Tidal Volume Tidal Volume (VT or TV) = (normal value: 0.5 L) the volume of air inhaled and exhaled with each normal breath during quiet breathing • includes: • Air in Alveoli with each breath, and • Air in (anatomical) Dead Space (VD) (0.15L) How much air participates in gas exchange? 7 K. Sam Fall 2023 2. & 3. Reserve Volumes Take a deep-deep breath in Then breathe out all the way Reserve volumes = maximal vol. of air that can be moved above or below a normal tidal volume 2. Inspiratory Reserve Vol (IRV) = Vol. of air that can be inhaled after a normal inspiration (3 L) 3. Expiratory Reserve Vol (ERV) = Maximal volume of air that can be exhaled from resting expiratory level (1 L) • With exercise, both reserve volumes decrease as tidal volume increases 8 K. Sam Fall 2023 4. Residual Volume (RV) Residual Volume is volume of air remaining in the lungs after a maximal exhalation (1.5 L). • This is the volume of air that stays in your lungs all the time …you don’t have any control over this… • Keep alveoli inflated between breaths • Mix with fresh air on next inspiration • RV - minimal vol. of air in the lung is controlled by expiratory muscle force. • ↓ lung volume → shortening of expiratory muscles → ↓ muscle force. • ↓ lung volume – ↑ outward recoil pressure of chest wall from chest wall. • RV occurs when expiratory muscle force is insufficient to further reduce chest wall volume. 9 K. Sam Fall 2023 Static Lung Capacities 1. IC (Inspiratory Capacity) 2. VC (Vital Capacity) 3. FRC (Functional Residual Capacity) 4. TLC (Total Lung Capacity) (Top:) https://www.google.com/imgres?imgurl=http%3A%2F%2Fd1j63owfs0b5j3.cloudfront.net%2Fterm%2Fimages%2F7001496070529120.png&imgrefurl=https%3A%2F%2Fwww.blendspace.com%2Flessons%2FXybRpOeTiGcl6Q%2Frespiratory-systempulmonary-volumes-and-capacities&tbnid=HitpUZEBlJxz5M&vet=10CBcQxiAoCGoXChMI-OjChOD9gIVAAAAAB0AAAAAEA4..i&docid=4mlUQn45B7HOoM&w=1968&h=1968&itg=1&q=lung%20volumes&ved=0CBcQxiAoCGoXChMI-OjChOD9gIVAAAAAB0AAAAAEA4 (Bottom:) https://www.coheadquarters.com/PennLibr/MyPhysiology/lect1p/lect1.01.htm K. Sam Fall 2023 10 Inspiratory Capacity (IC) It’s from the end of normal exhale – to the end of maximum inhale. • Maximal volume of air that can be inspired from the resting endexpiration level (3.5L) • IC = TV + IRV • It’s from the end of normal exhale – to the end of maximum inhale. Vital Capacity (VC) {Take A Deep-deep-deep breath in and blow all the way out until there is nothing more} • Maximal volume of air that can be expelled from the lungs after a maximal inspiration (4.5L) • VC = IRV + TV + ERV 11 K. Sam Fall 2023 Air left in lung after passive exhalation Functional Residual Capacity (FRC) • Is the Volume of air in the lungs at the end of normal expiration (2.5 L) • FRC = RV + ERV K. Sam Fall 2023 12 Total Lung Capacity (TLC) • Amount of air in the respiratory system after a maximal inspiration (6 L) • TLC = RV + ERV + TV + IRV • TLC - maximum vol. of air within the lung while chest wall is controlled by the muscles of inspiration. • With increasing lung volume, the chest wall muscles lengthen progressively. As these muscles lengthen, their ability to generate force decreases. • TLC occurs when the inspiratory chest wall muscles are unable to generate the additional force to further distend the lung and chest wall. K. Sam Fall 2023 13 (II) Pulmonary Ventilation • Process in which air is moved in and out of lungs • The amount of gas moves between the outside of the body and alveoli K. Sam Fall 2023 14 Respiratory Adjustment to Exercise • Minute Ventilation: • The amount of ventilation per minute • Minute Ventilation = Ventilatory Rate x Tidal Volume • Ve = RR x TV • Normal values = 5-10 L/min at rest • E.g., Ve = 15 x 500ml = ~ 7500 ml/min • Linear relationship between ventilation and increasing levels of activities • 15-20x during max exercise • Initial / lower level of activity = TV increases • Higher level of K.activity = RR increase Sam Fall 2023 15 Alveolar Ventilation (VA) • Amount of fresh air available for gas exchange • At each alveolus: O2 goes in, CO2 comes out • Hyperventilation = Increase in alveolar ventilation that exceeds the oxygen demand of metabolism. • The excessive release of carbon dioxide from the body via expired air decreases carbon dioxide levels below the normal limits (pCO2 = 40 mmHg), known as Hypocapnia • Hypoventilation: decrease in alveolar ventilation, which increases carbon dioxide beyond normal limits = Hypercapnia K. Sam Fall 2023 16 Mechanics of Breathing Ventilation (or airflow through conducting airway) is influenced by: • Directly proportional to pressure difference created between the two ends of airway • Inversely proportional to airway resistance • airway cross-sectional area ↑, airway resistance ↓ • More noticeable during expiration when lung volume is low, small airways may close completely • Affected by physical properties of lungs, including: • Compliance • Elasticity • Surface tension K. Sam Fall 2023 Excerpted from PT 731 Physiology Lecture by Dr. Burke-Doe • Surfactant 18 (Top) https://www.merckmanuals.com/home/lung-and-airwaydisorders/biology-of-the-lungs-and-airways/control-of-breathing What’s the term Therapy Ed use? At Rest After expiration ends and before inspiration begins. 1. With respiratory muscles at rest, elastic recoil of lung and of chest wall are equal but opposite (balanced). 2. Pleural (or intrapleural) pressure is subatmospheric (pleural relationship with chest wall maintains a stretch even at rest) 3. Pressure along the tracheobronchial tree and in the alveoli is equal to atmospheric pressure. There is no air flow. 4. Air will only flow only from an area of higher pressure to one of lower pressure. Since alveolar pressure equals atmospheric pressure there is no air flow. (0 cm of H2O) • Air volume is Forced Residual Capacity (FRC). Excerpted from PT 731 Physiology Lecture by Dr. Burke-Doe 19 During Inspiration During Inspiration: 1. Diaphragm and other respiratory muscles contract. 2. Because the diaphragm is curved, its contraction compresses the abdominal contents and decompresses the contents of the thorax, causing pleural (or intrapleural) pressure to fall. 3. pleural (or intrapleural) pressure falls, and alveolar pressure falls by an equal amount, becoming subatmospheric. 4. Air flows into the lungs down the pressure gradient from the mouth to the alveoli. 5. The lungs and chest expand in volume, and pressure changes until the thoracic cage stops expanding just before the end on inspiration. K. Sam Fall 2023 Excerpted from PT 731 Physiology Lecture by Dr. Burke-Doe 20 At End Inspiration End Inspiration: 1. An equilibrium exists after inspiration ends and before expiration begins. 2. Air flows down the pressure gradient until the lung reaches a new equilibrium volume at which alveolar pressure equals zero and the gradient for flow ceases to exist. 3. Lungs and chest are fully expanded. 4. You can demonstrate this by taking a deep breath and stopping the movement of your chest (no air is moving so pressures have to be equal) K. Sam Fall 2023 Excerpted from PT 731 Physiology Lecture by Dr. Burke-Doe 21 During Expiration: During Expiration: 1. The respiratory muscles relax, causing an abrupt increase in pleural pressure to a less negative value. 2. Recoil pressure of the lung causes a rise in pleural pressure causing the alveolar pressure to rise by the same amount (+1). 3. This establishes a pressure gradient from the alveoli to the mouth, down which air flows. 4. Lung and chest volume decrease as air flows out, causing lung recoil pressure to fall as well until a new equilibrium is reached. K. Sam Fall 2023 Excerpted from PT 731 Physiology Lecture by Dr. Burke-Doe 22 At End Expiration At the End of Expiration: 1. pleural cavity and alveoli return to the pressure relationship they had at the start of inspiration: • intrapleural pressure is -5 • alveolar pressure is 0 K. Sam Fall 2023 Excerpted from PT 731 Physiology Lecture by Dr. Burke-Doe 23 Generation of Pressure Changes necessary for Ventilation Alveolar pressure Transpulmonary pressure (across the organ) (Intra)pleural pressure Lung and Chest Wall Compliance | Breathing Mechanics | Respiratory Physiology (6:20) https://youtu.be/AWKTCwmXopY K. Sam Fall 2023 Key Factors affecting Alveolar Ventilation 1. 2. 3. 4. 5. 6. Pressure Compliance Mechanical Resistance Airway Resistance Diffusion Gradient Barriers 7. Control of Pressure • Innervation, nervous system, receptors. • Tissue • Blood • Pathology K. Sam Fall 2023 26 Factors affecting Alveolar Ventilation • Pressure • caused by elastic recoil of lungs and the chest wall; enable gas flow into alveoli • Compliance • ease at which the lungs inflate • Lungs stiffened by disease (low compliance) K. Sam Fall 2023 27 Factors affecting Alveolar Ventilation (cont.) Mechanical Resistance • During inhalation, alveoli expand, resulting in a drop of pressure in alveoli. • Bronchioles are tethered to alveoli/lung parenchyma – alveoli pull open the distal bronchioles, and these conducting airways are stretched and exposed to the drop in pressure as well. • On the contrary, at low lung volumes – there is less air flow –alveola does not open - small airways may close completely and can collapse. • E.g., Exhalation with pulm pathologies that has reduced lung volumes. • As a result, the airways increase in crosssectional area and decrease the resistance of airflow during inhalation. K. Sam Fall 2023 28 Factors affecting Alveolar Ventilation (cont.) Airway Resistance Upper airways Lower airways • At physiologic levels, airway resistance in the trachea is responsible for turbulent (irregular/chaotic) airflow • turbulent air leading to high resistance • while airway resistance in the bronchi and bronchioles allows for more laminar airflow, in which air smoothly flows to the distal segments of the lungs. • The smaller the airway, the higher the resistance • Increased airway resistance can limit airflow K. Sam Fall 2023 29 Factors affecting Alveolar Ventilation (cont.) Airway Resistance (cont.) • Lower airway • Individually, smaller airways have much high resistance than larger airways, such as the trachea. • However, the significant downstream branching of airways means that there are many smaller airways in parallel. This reduces total resistance to airflow. → Large number of small airways leading to lower resistance. • Therefore, resistance is greatest at the bronchi of intermediate size, in between the 4th and 8th bifurcation. K. Sam Fall 2023 From McArdle WD, Katch FI, Katch VL: Essentials of Exercise Physiology, 2nd Ed. Lippincott Williams & Wilkins, 2000 30 Gas Exchange • Respiratory gas exchange takes place in the alveoli, which have a very large surface area available for gas exchange • Capillary network covers the surface of alveoli, and gas exchange takes place by diffusion across the alveolar-capillary membrane, which is extremely thin (< 0.5 μm) to allow for easy gas exchange K. Sam Fall 2023 31 Blood Supply I. Pulmonary circulation • RV → pulmonary arteries → arterioles → meshwork of capillaries surrounding each alveolus • Delivers deoxygenated blood to the lungs; returns oxygenated blood to the heart K. Sam Fall 2023 32 Blood Supply II. Bronchial Circulation • Aorta → bronchial artery → arterioles → bronchial glands and walls of the bronchi to the level of the respiratory bronchioles • Delivers oxygenated blood supply to the bronchi and connective tissue of the lung • Does NOT participate in gas exchange K. Sam Fall 2023 (Top Left) https://memorang.com/flashcards/208 146/Horizontal+Fissure+and+more (Bottom Left) https://www.sciencedirect.com/scienc e/article/abs/pii/S1472029908001951 33 Diffusion • The movement of gases into and out of blood, occurs through the alveolar-capillary membrane • O2 from alveolar air into blood • CO2 from blood into alveolar air • From high to low concentration • Affected by: • • • • Concentration and solubility of gases Membrane thickness Surface area Pathology – fibrosis, fluid, edema, etc. K. Sam Fall 2023 34 Diffusion Gradient Key: A = Alveoli a = arterial blood Driving pressure v = venous blood • Oxygen: • goes from PAO2 100 mmHg in Alveoli → PVO2 40 mmHg in Veins • resulting in PaO2 100 mmHg in arterial blood • Carbon Dioxide: • goes from PVCO2 46 mmHg in Veins → PACO2 40 mmHg in Alveoli • resulting in PaCO2 40 mmHg in arterial blood • Normal transit time: < 1 second K. Sam Fall 2023 35 Fick’s Law • The net diffusion rate of a gas across a fluid membrane is: • proportional to the difference in partial pressure, • proportional to the area of the membrane, • and inversely proportional to the thickness of the membrane. • That means that the greater the partial pressure difference and the thinner the membrane, the faster diffusion happens, and vice versa. K. Sam Fall 2023 36 Diffusion of Respiratory Gases • Oxygen diffuses from alveolar air across the tissue barrier and plasma to the RBC, where it combines with hemoglobin • At the same time, carbon dioxide diffuses from the RBC across the plasma and tissue to the alveolus • Tissue barrier = surfactant, alveolar epithelium, interstitial tissue, capillary endothelium • Blood barrier = plasma, RBC membrane K. Sam Fall 2023 37 Pathology Affecting Diffusion 1. Alveolar collapse (e.g., atelectasis) 2. Alveolar wall thickening (e.g., alveolar fibrosis) 3. Alveolar consolidation (e.g., pneumonia) 4. Frothy secretions (e.g., pulmonary edema) 5. Interstitial edema 6. Alveolar-capillary destruction (e.g., emphysema) K. Sam Fall 2023 38 O2 Transport • From lungs to tissues • O2 attached to the hemoglobin (Hb), carried inside RBCs • Each Hb molecule is capable of combining with 4 O2 molecules • Normal Hb is 98% saturated with O2 • Small amount of O2 is dissolved in plasma • Plasma concentration of O2 is termed partial pressure of O2 in arterial blood (PaO2) K. Sam Fall 2023 40 CO2 Transport • From tissues to lungs • CO2 travels in the form of bicarbonate ions in RBCs • Smaller amounts of CO2 are dissolved in plasma or bound to Hb (carboxyhemoglobin) K. Sam Fall 2023 41 Control of Breathing • Primarily involuntary • Central chemoreceptors respond to changes in the acidity of the brain’s extracellular fluid • Increase in hydrogen ion concentration stimulates ventilation • Input from peripheral chemoreceptors – respond to changes in CO2, hydrogen ion, and partial pressure of O2 • Increase in arterial CO2 (and pH) or PaO2 < 60 mm Hg stimulates ventilation K. Sam Fall 2023 42 Other Sensors • Stretch receptors in alveoli • Proprioceptors in joints and muscles • Emotional input via the limbic system • Temperature, meds, anesthesia, and disease can alter breathing pattern K. Sam Fall 2023 43