Mechanics of Respiration I PDF

Mechanics of Respiration I Dr. Sovan Bagchi Professor of Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Learning Objectives Describe the functions of muscles of inspiration and expiration...

Mechanics of Respiration I Dr. Sovan Bagchi Professor of Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Learning Objectives Describe the functions of muscles of inspiration and expiration Explain the process of inspiration and expiration Define the terms intra-alveolar, intra-pleural, trans-pulmonary pressure and describe their importance  Breathing Mechanical process that moves air in and out of the lungs. Repiratory Rate = 12-20/min Tachpnea ??? Bradypnea??? Apnea??? Inspiration: the act of taking air INTO the lungs, occurs when pressure inside the lungs is LOWER than pressure outside the lungs (i.e. atmospheric pressure) Expiration: the act of breathing OUT, occurs when pressure inside the lungs is GREATER than pressure outside the lungs.  Breathing Movements The body uses muscles to change the VOLUME of the thoracic cavity. This alters the PRESSURE inside the lungs An increase in volume = decrease in pressure (and vice versa) Basics of the Respiratory System Muscles & Membranes  Muscles of inspiration Diaphragm Principal muscle of inspiration. During inspiration, it contracts and increases the vertical diameter of thoracic cage. External Intercostals Responsible for movement of ribs. Contraction of these muscles increase both transverse and anteroposterior diameter of the chest. Inspiration is an active process  Muscles of Expiration Expiration is a passive process during quiet breathing. This is brought about by relaxation of inspiratory muscle. During forced expiration, (blowing, cough) muscles of expiration contract and help in reducing the volume of thoracic cage. Abdominal muscles (abdominal recti, internal and external oblique) Contraction of these muscles increases intra abdominal pressure which in turn pushes the diaphragm upwards and further reduces the size of the chest. Internal intercostals Contraction reduces the volume of thoracic cage by pulling the ribs downwards  Lung Pressures Intrapulmonary Pressure (intra-alveolar): Intra-alveolar pressure(pressure in the alveoli). (-1to +1) mmHg (0 mmHg =atmospheric pressure) Intrapleural Pressure: Pressure in the intrapleural space= (-6 to -3) mmHg Average -4 mmHg * Pressure is negative. Transpulmonary Pressure: Pressure difference across the wall of the lung. Intrapulmonary pressure – intrapleural pressure Always positive Importance of intrapleural pressure 1. Help lung inflation during inspiration 2. Prevents lung collapse 3. Decreases the work of breathing 4. Helps venous and lymphatic drainage  Learning Resources Textbook: Guyton and Hall Textbook of Medical Physiology, Chapter 38, 491-501. Fourteenth Edition. Link: https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3-s2.0- B9780323597128000382?indexOverride=GLOBAL Power-point presentation in the moodle www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Regulation of Respiration Sovan Bagchi Professor of Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Learning Objectives Explain the importance of breath control. Outline how the central nervous system controls breathing. List the anatomical locations of ventilation-controlling chemoreceptors sensitive to changes in arterial partial pressure of oxygen (PO2), partial pressure of carbon dioxide (PCO2), and pH. Describe the Hering-Breuer reflex and how chronic obstructive pulmonary disease (COPD) affects lung mechanoreceptors. Define Kussmaul, Cheyne-Stokes, and Biot breathing. Case presentation GB is brought to the emergency department with an altered mental status and a history of illicit drug use. She is lethargic, with a decreased respiratory rate characterized by irregular breathing with episodes of apnea (absent respirations). Given GB’s presentation, why is she breathing abnormally and deeply? Why Is Breath Control Important? Breathing is mostly an involuntary response Breathing occurs when the respiratory muscles (eg, diaphragm, intercostal, and abdominal wall muscles) receive signals that originate in the brainstem (pons and medulla). Although breathing is largely involuntary, there are also some voluntary controls. Breathing in activities such as swimming and singing, and in yoga How Does the Central Nervous System Control Breathing? Each brain region has groups of neurons with specific tasks related to respiration. The medulla and the pons control breathing by stimulating the respiratory muscles Medulla Dorsal Respiratory Group The dorsal respiratory group (DRG) controls inspiration and sets the respiratory rhythm during normal breathing. The efferent DRG sends impulses via the phrenic and intercostal nerves to stimulate inspiration by contracting the diaphragm and external intercostal muscles. Ventral Respiratory Group The ventral respiratory group (VRG) is largely inactive during normal, quiet breathing. It stimulates both forced inhalation and exhalation in states where breathing is more intense, such as in exercise or some illnesses. Pons The pneumotaxic center (PNC) Located in the upper pons. It acts to inhibit inspiration by lowering tidal volume and respiratory rate. The apneustic center (APC) Located in the lower pons. It stimulates inspiration and can cause deep, gasping inspirations with occasional expirations. What Chemical Sensors Control Breathing? Peripheral Chemoreceptors When the receptors detect Decreased PaO2, Increased PaCO2, Increased hydrogen ion concentration (acidemia, low blood pH) They send impulses to the cerebral medulla’s solitary nucleus. Decreased PaO2 is primary and most important Central Chemoreceptors Another group of chemoreceptors is located in the brain (specifically, the ventral medulla, the same region that receives the signals from the peripheral chemoreceptors). These central receptors are sensitive to decreased pH of the cerebrospinal fluid (CSF). This decreased (acidic) pH causes the central chemoreceptors to increase the respiratory rate and tidal volume. To summarize Peripheral chemoreceptors fire directly in response to low blood PaO2 (primary stimulus) as well as high PaCO2 and low blood pH. Central chemoreceptors fire indirectly in response to high PaCO2. What Mechanical Sensors Control Breathing? These are sensory receptors that detect mechanical pressure or distortion. The receptors include pulmonary stretch receptors, irritant receptors, and J receptors Pulmonary Stretch Receptors Stimulated by distention of the lungs during inspiration. Lung distension triggers the pulmonary stretch receptors to send impulses through the vagus nerve to the medulla, inhibiting inspiration and preventing lung overinflation. Hering-Breuer reflex. It typically does not occur at tidal volumes of less than 1 L It is clinically significant in patients with chronic obstructive pulmonary disease (COPD). Here, airflow blockage causes COPD by trapping air in the lungs. Because patients with COPD have chronic air trapping, their lungs are chronically distended (increased lung volumes). This diminishes the Hering-Breuer reflex, lowering the respiratory rate and prolonging inspiration. Irritant Receptors Found in the epithelium of the upper respiratory conduction airways (eg, trachea, bronchi). They respond to a variety of mechanical and chemical irritants. Chemicals, dust, pollens, and cold air. Afferent signals travel to the brain to initiate coughing and bronchoconstriction, which helps clear the trachea and bronchi of harmful substances. This is one of the reasons why coughing comes naturally after exposure to fumes or smoke. J Receptors Juxta-pulmonary capillary receptors (J receptors) are sensitive to increased pulmonary capillary pressure, which stimulates them to initiate rapid, shallow breathing. J receptors are located near the capillaries in the alveolar septa. Clinically, these are most important in patients with heart failure, where a failing left ventricle will cause blood to back up through the pulmonary veins into the pulmonary capillaries, resulting in increased pulmonary capillary pressure. J receptors also respond in conditions such as pulmonary edema and pulmonary emboli. Mechanical receptors that control breathing Receptor type What they sense Effect(s) Pulmonary stretch receptors Lung inflation Inflation terminates Noxious stimuli, eg, Coughing, Irritant receptors chemicals, dust, cold air bronchoconstriction Stretch (eg, pulmonary J receptors Shallow breathing edema) What Are Some Pathological Breathing Patterns?  Kussmaul respirations are deep, labored respirations associated with metabolic acidosis (low blood pH due to an abnormal circulating anion). It is most often associated with diabetic ketoacidosis, a complication of type 1 diabetes mellitus in which the blood pH falls to low levels due to the formation of ketoacids. Biot breathing (also called ataxic breathing) is an irregular breathing pattern with increasing episodes of apnea (absent respirations). It is most often associated with opioid intoxication or with injuries to the medulla. Cheyne-Stokes respirations are a characteristic pattern of alternating fast and slow breathing with periods of central apnea. In central apnea, the brain does not create the normal stimulation to breathe. It can be seen in patients with cardiac disease, neurologic disease, use of sedative drugs, acid-base disorders, and high-altitude exposure. Case connection GB’s history and Biot breathing pattern (inspiratory pauses) are suggestive of an opioid overdose. This represses the CNS respiratory centers, causing a low respiratory rate, and can also lead to the observed abnormal breathing pattern. Opioid intoxication can cause respiratory arrest and death, so it should be promptly reversed with an opioid receptor antagonist such as naloxone. This was done in the emergency department, and GB promptly became lucid, with normal breathing.  Learning Resources Text Book: Marieb EN. Human Anatomy and Physiology. 9th Edition, Pearson International Edition; 2014. ISBN-13: 978-1- 2920-2649-7. Power-point presentation in the moodle www.gmu.ac.ae COLLEGE OF MEDICINE