Lung Volumes and Capacities for Respiratory Health

Department of Anesthesia Techniques Title of Lect.2: Physiology of Respiratory System Assist.Prof.Dr. Aqeel Al Jothery Lecturer. Dr. Sajad A. Al-Ghazali Dr. Noor Kareem Dr.Amasee Falah

LUNG VOLUMES AND CAPACITIES Lung volumes and capacities: are fundamental measurements that describe the amounts of air the lungs can hold and how air moves in and out during breathing. They are important for assessing lung function and diagnosing respiratory conditions.

Lung Volumes: Lung volumes are also known as respiratory volumes. It refers to the volume of gas in the lungs at a given time during the respiratory cycle and measured in milliliters (mL) They include: 1. Tidal Volume (TV):The amount of air inhaled or exhaled during normal, resting breathing. Average: ~500 mL in a healthy adult 2-Inspiratory Reserve Volume (IRV): It is the amount of air that can be forcibly inhaled after a normal tidal volume. It is used during deep breathing. The normal adult value is 1900-3300ml. 3.Expiratory Reserve Volume (ERV): The additional air that can be exhaled forcibly after a normal tidal exhalation .Average: ~1,200 mL 4-Residual Volume (RV):The air remaining in the lungs after a maximal exhalation. Prevents lung collapse. Average: ~1,200 mL.

Lung Capacities Lung capacities are combinations of two or more lung volumes: 1.Inspiratory Capacity (IC):Maximum amount of air that can be inhaled after a normal exhalation. IC = TV + IRV . Average: ~3,500 mL. Air remaining in the lungs after a normal exhalation. 2. Functional Residual Capacity (FRC): FRC = ERV + RV, Average: ~2,400 mL. 3.Vital Capacity (VC): Maximum amount of air that can be exhaled after a maximal inhalation. VC = TV + IRV + ERV, Average: ~4,800 mL. 4.Total Lung Capacity (TLC):Total amount of air the lungs can hold. TLC = TV + IRV + ERV + RV

Clinical Relevance 1.Restrictive Lung Diseases (e.g., pulmonary fibrosis): Decrease in lung volumes (especially TLC, VC, and RV). Lungs are stiff or limited in expansion. 2.Obstructive Lung Diseases (e.g., COPD, asthma): Increase in RV and FRC due to air trapping. Decrease in expiratory flow rates Measurement Techniques 1-Spirometry: Measures TV, IRV, ERV, and VC. 2-Body Plethysmography: Measures RV, FRC, and TLC. 3-Gas Dilution Techniques: Used to calculate lung volumes like RV

Spirometry: is a common pulmonary function test used to measure lung functions and volumes. It helps diagnose and monitor conditions that affect breathing. During the test, a person breathes into a device called a spirometer, which records various parameters of lung function. Test : Spirometry. Device : Spirometer Gragh : Spirogram

Key Measurements in Spirometry Forced Vital Capacity (FVC): The total amount of air a person can exhale forcefully after taking the deepest breath possible. Forced Expiratory Volume in 1 Second (FEV ): The amount of air a person can forcefully exhale in the first second of the FVC test. It is a key indicator of lung function. FEV /FVC Ratio: The proportion of a person's vital capacity that can be exhaled in the first second. It helps differentiate between obstructive and restrictive lung diseases. Peak Expiratory Flow (PEF): The highest flow rate achieved during a forceful exhale.

Indications for Spirometry Diagnosis of respiratory conditions (e.g., asthma, chronic obstructive pulmonary disease [COPD]) Monitoring progression of lung diseases Assessing treatment efficacy Evaluating lung function prior to surgery Identifying occupational lung diseases

How the Test Is Performed 1.The patient inhales deeply and then exhales as forcefully and completely as possible into the spirometer. 2.The procedure may be repeated several times to ensure accuracy. 3.Results are compared to reference values based on age, sex, height, and ethnicity. Results Interpretation Obstructive Lung Disease: Reduced FEV and FEV /FVC ratio (e.g., asthma, COPD). Restrictive Lung Disease: Reduced FVC with a normal or high FEV /FVC ratio (e.g., pulmonary fibrosis, sarcoidosis). Normal Spirometry: Results within the predicted range.

Control of Ventilation: The regulation of ventilation in humans is a complicated process involving multiple systems that work together to maintain optimal gas exchange and homeostasis. 1. Respiratory Centers in the Brainstem: Medulla Oblongata: 1-Dorsal Respiratory Group (DRG): Primarily responsible for the rhythm of breathing, the DRG controls the basic rhythm of respiration by sending signals to the diaphragm and external intercostal muscles. 2-Ventral Respiratory Group (VRG): Involved in forced breathing, the VRG activates accessory muscles during vigorous respiratory efforts. Pons: 1-Pneumotaxic Center: Regulates the rate and pattern of breathing by inhibiting the DRG, thereby limiting the duration of inhalation. 2-Apneustic Center: Promotes inhalation by stimulating the DRG, leading to prolonged inspiratory phases.

2. Chemoreceptors: Central Chemoreceptors: -Located on the ventrolateral surface of the medulla, these receptors are sensitive to changes in the pH of cerebrospinal fluid, which reflects CO levels in the blood. An increase in CO leads to a decrease in pH, stimulating the respiratory centers to increase ventilation. Peripheral Chemoreceptors: -Found in the carotid and aortic bodies, they detect changes in blood oxygen (O ), CO , and pH levels. A significant drop in O levels (hypoxia) or an increase in CO levels (hypercapnia) prompts these chemoreceptors to send signals to the brainstem to adjust breathing accordingly.

3. Mechanoreceptors: Pulmonary Stretch Receptors: -Located in the smooth muscles of the airways, these receptors prevent overinflation of the lungs by initiating the Hering-Breuer reflex, which inhibits further inhalation when the lungs are stretched beyond a certain point. Other Mechanoreceptors: -Found in the airways and chest wall, they contribute to reflexes such as coughing and sneezing, which help clear the airways of irritants.

Reflexes Influencing Ventilation: 1-Hering-Breuer Reflex: -Triggered by the stretching of the lungs during deep inhalation, this reflex inhibits further inhalation to prevent overinflation. 2-Cough and Sneeze Reflexes: -Activated by irritants in the airways, these reflexes increase ventilation to expel the irritants and protect the respiratory tract. 3-Head's Paradoxical Reflex: -A sudden deep inhalation can lead to a brief period of apnea (cessation of breathing), followed by a rapid exhalation.

Factors Affecting Ventilation 1-Modulation by Higher Brain Centers: Emotional states, pain, and other factors can influence breathing patterns. For example, anxiety can lead to hyperventilation, while relaxation techniques can slow breathing. 2. Impact of External Factors: Exercise: During physical activity, increased metabolic demands lead to elevated CO production and decreased O levels, prompting an increase in ventilation to meet these demands. Disease States: Conditions such as asthma, COPD, and sleep apnea can alter normal ventilatory control mechanisms, leading to breathing difficulties.

: Non-respiratory lungs functions 1-Vocalization: The larynx, or voice box, houses the vocal cords (vocal folds). When air passes over these folds, they vibrate to produce sound, enabling speech and singing. 2.Olfaction (Sense of Smell): The nasal cavity contains olfactory receptors that detect airborne chemicals, allowing us to perceive odors. This sense is crucial for taste and environmental awareness. 3. Filtration of Blood: The lungs act as a filter for the blood, trapping and removing particles, such as thrombotic debris, fat globules, and other emboli, preventing them from entering the arterial circulation. 4. Immune Defense: The respiratory system plays a role in the body's defense mechanisms by trapping and removing pathogens and particles from the airways, contributing to the body's overall immune response.

5. Blood Reservoir: The lungs can act as a reservoir for blood, accommodating changes in blood volume and helping to maintain circulatory stability. 6. Metabolism: The lungs are involved in various metabolic processes, including the conversion of angiotensin I to angiotensin II, which is important for regulating blood pressure. 7. Drug Delivery: The respiratory system can be used for the delivery of inhalational anesthetics and other drugs, allowing for rapid absorption into the bloodstream. 8. Synthesis of Bioactive Molecules: The lungs synthesize various bioactive molecules, including certain hormones and enzymes, contributing to the body's endocrine functions.