HUBS192 Lecture 17: The Work of Breathing (2024) Lecture Notes PDF

HUBS192 Lecture Material This pre-lecture material is to help you prepare for the lecture and to assist your note-taking within the lecture, it is NOT a substitute for the lecture ! Please note that although every effort is made to ensure this pre-lecture material...

HUBS192 Lecture Material This pre-lecture material is to help you prepare for the lecture and to assist your note-taking within the lecture, it is NOT a substitute for the lecture ! Please note that although every effort is made to ensure this pre-lecture material corresponds to the live-lecture there may be differences / additions.  HUBS 192 Jeff Erickson – Department of Physiology Lecture 17 The Work of Breathing  GET IT IN KEEP IT GOING GET IT ACROSS GET IT AROUND Patton & Thibodeau, Anatomy and Physiology (8th ed), Figure 27-1, pg 825. 2  Objectives and Study Guide After this lecture you should be able to: Use Boyle’s Law to describe how we are able to inhale and exhale. Describe the two opposing forces that must be overcome to take a breath. Identify the volumes and capacities on a spirometry trace. Related reading: Martini et al. Modules 21.9-21.11 (p. 854-859) 3  Quantifying liquids vs. gases Liquids are usually quantified Gases are usually quantified in terms of volume in terms of pressure Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.9, pg 854. 4  Boyle’s Law The pressure of a gas is inversely related to it’s volume Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.9, pg 854. 5  Creating a pressure gradient Gas will move from high pressure to low pressure Right before a breath, the pressure outside the body and inside the lungs are equal, so no air is moving Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.9, pg 854. 6  Creating a pressure gradient As you inhale, your diaphragm drops while your rib cage expands This increases the volume in your chest, which lowers the pressure Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.9, pg 854. 7  Creating a pressure gradient Inhalation Exhalation Volume is increasing Volume is decreasing Pressure inside the lungs is Pressure inside the lungs is decreasing increasing Pressure outside is now greater Pressure outside is now lower than inside, so air rushes in than inside, so air rushes out Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.9, pg 855. 8  The Work of Breathing Two opposing forces that must be overcome to take a breath: 1. Stiffness of the lungs Lungs must expand to take in air How compliant are the lungs? Surface tension holds lungs in place 2. Resistance of the airways to the lungs Need to move the air from outside to the alveoli How much resistance is the respiratory tract putting on the movement of air? 9  Lung stiffness is related to Compliance Compliance = V/P Lung Volume (L) 10  Lung stiffness is related to Compliance Pulmonary Fibrosis Thickening and scarring of the alveolar membranes Can arise from chronic inflammation or exposure to industrial chemicals 11  Lung stiffness is related to Compliance Compliance = V/P Lung Volume (L) 12  Fluids surrounding the lungs exert surface tension Alveoli are lined with fluid that exert surface tension Walls of alveoli are very thin, enhancing this effect Must overcome surface tension to expand the lungs 13  Alveoli produce surfactant to disrupt surface tension Relieves surface tension and allows the alveoli to expand during a breath Failure to produce adequate surfactant results in difficulty in expanding the lungs and reduced oxygen intake Premature infants don’t produce surfactant, resulting in respiratory distress syndrome (RDS) 14  Example exam question Which of the following statements about the work of breathing is NOT CORRECT? A. The chest and lungs expand during inhalation. B. The alveoli release surfactant to overcome surface tension from the surrounding fluid. C. Low compliance of the lungs allows them to more easily fill with air. D. Thickening and scarring of the alveolar membranes can lead to a reduction in lung compliance. 15  The Work of Breathing Two opposing forces that must be overcome to take a breath: 1. Stiffness of the lungs Lungs must expand to take in air How compliant are the lungs? Surface tension holds lungs in place 2. Resistance of the airways to the lungs Need to move the air from outside to the alveoli How much resistance is the respiratory tract putting on the movement of air? 16  Airway resistance through the respiratory tract Need to move air from outside to the alveoli Air is conducted through the bronchi and bronchioles Exert force (friction) on the air that must be overcome 17 18  Resistance to blood flow and vessel radius Luminal radius 1 1 R = r = (0.5d) 4 4 d r r d Martini et al., Visual Anatomy and Physiology (3rd ed), Module 19.6, pg 748. 19  Resistance to air flow and bronchial radius Luminal radius 1 1 R = r = (0.5d) 4 4 d r r d Martini et al., Visual Anatomy and Physiology (3rd ed), Module 19.6, pg 748. 20 Obstructive versus restrictive issues with breathing Reduced lung compliance (e.g. fibrosis) Insufficient surfactant release REDUCED LUNG CAPACITY Obstructive vs. Restrictive RESISTANCE TO AIRFLOW Asthma Chronic bronchitis 21 21  Spirometry: The Pulmonary Function Test A spirometer measures volume inspired / exhaled Common, simple test Can measure how much and how fast you breathe Test response to therapy 22  Spirometry Trace Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.10, pg 857. 23  Spirometry Trace Volumes Tidal volume (VT) Volume of air moved in and out during normal quiet breath Inspiratory reserve volume (IRV) Extra volume that can be inspired with maximal inhalation Expiratory reserve volume (ERV) Extra volume that can be exhaled with maximal effort Residual volume Volume remaining in lungs after maximal exhalation Minimal volume Volume remaining in lungs if they collapsed 24  Spirometry Trace Inspiratory Reserve Volume (IRV) Tidal volume (VT) Expiratory Reserve Volume (ERV) Residual Minimal Volume Volume Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.10, pg 857. 25  Spirometry Trace Capacities Vital capacity Inspiratory reserve + Expiratory reserve + Tidal volume Volume of air you can shift in and out of your lungs Total lung capacity Vital capacity + Residual volume Total volume in lungs when you’ve filled them to max Inspiratory capacity Inspiratory reserve + Tidal volume Total volume of air you can inspire from rest Functional residual capacity Expiratory reserve + Residual volume Volume remaining in lungs after normal exhalation 26  Spirometry Trace Inspiratory Capacity Inspiratory Reserve Volume (IRV) Vital Tidal volume Capacity (VT) Expiratory Reserve Volume Functional (ERV) residual capacity Residual Minimal Volume Total Lung Volume Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.10, pg 857. Capacity 27  Spirometry Trace – Both volume and rate matter! Forced expiratory volume in one second FEV1 i.e How much of the vital capacity (VC) comes out in first second Reduced with diseases causing resistance to airflow (ex. asthma) FEV1/VC ratio Normal ~ 80% < 0.70 indicates airways obstruction 28 28  Spirometry Trace Worksheet – Match the term on the left to the definition on the right Volume remaining in lungs if they Tidal volume collapsed Extra volume that can be exhaled with Inspiratory reserve volume maximal effort Volume of air you can shift in and out of Expiratory reserve volume your lungs Residual volume Volume of air moved in and out during normal quiet breath Minimal volume Total volume of air you can inspire from rest Inspiratory capacity Volume remaining in lungs after normal exhalation Total lung capacity Extra volume that can be inspired with maximal inhalation Vital capacity Total volume in lungs when you’ve filled them to max Functional residual capacity Volume remaining in lungs after maximal exhalation 29 Spirometry Trace Worksheet – Fill in the Leaders with the correct Volume or Capacity Martini et al., Visual Anatomy and Physiology (3rd ed), Module 21.10, pg 857. 30  Summary Changes in chest volume create a pressure differential that drives air in and out of the lungs during breathing. The stiffness of the lungs and the resistance of the airways must be overcome to breathe. Spirometry is a test to measure pulmonary function and yields a complex trace with a number of volumes and capacities. Because spirometry measures both volume and rate of inhalation/exhalation, it can discern between obstructive and restrictive issues. 31  Example exam question Which of the following best describes the vital capacity? A. Volume remaining in lungs if they collapsed B. Volume of air moved in and out during normal quiet breath C. Total volume in lungs when you’ve filled them to max D. Volume of air you can shift in and out of your lungs 32  HUBS192 Copyright Warning Notice This coursepack may be used only for the University’s educational purposes. It includes extracts of copyright works copied under copyright licences. You may not copy or distribute any part of this coursepack to any other person. Where this coursepack is provided to you in electronic format you may only print from it for your own use. You may not make a further copy for any other purpose. Failure to comply with the terms of this warning may expose you to legal action for copyright infringement and/or disciplinary action by the University