Respiration Volumes & Lung Function PDF

Respiratory system D/Suzan Mustafa Hazzaa Professor of clinical physiology Physiology department Menoufia University Surfactant  surfactant Is a substance produced in the lungs that plays a critical role in maintaining proper lung function by reducing surface tens...

Respiratory system D/Suzan Mustafa Hazzaa Professor of clinical physiology Physiology department Menoufia University Surfactant  surfactant Is a substance produced in the lungs that plays a critical role in maintaining proper lung function by reducing surface tension within the alveoli. It is essential for efficient breathing, especially in preventing collapsing of the alveoli during expiration. Composition of Surfactant: Phospholipids: The main component that helps reducing the surface tension. Proteins: These proteins stabilize the surfactant layer, it is a vital component and the surfactant become inactive in absence of proteins. Functions of Surfactant: 1. Reduces Surface Tension. 2. Prevent lung collapse (atelectasis). 3. Improve lung compliance. 4. Help in immune defense.  Production of Surfactant: Surfactant is produced by type II alveolar cells within the alveoli. Production begins during the later stages of fetal development, typically around week 24-28 of gestation, but it only reaches sufficient levels around 34-36 weeks, making it especially critical for premature infants. Clinical Importance of Surfactant: Respiratory Distress Syndrome (RDS) in Infants: Premature babies often lack adequate surfactant.Without enough surfactant, their alveoli tend to collapse, making breathing extremely difficult. Treatment: administering exogenous surfactant (artificial surfactant) and providing respiratory support.  1- Tidal volume 2- Inspiratory reserve volume 1-Lung volumes 3- Expiratory reserve volume 4- Residual volume  Lung volumes 1. Tidal volume (VT ) The volume of air inspired or expired with each normal breath; it amounts to about 500 milliliters in the adult male. 2. Inspiratory reserve volume (IRV) The extra volume of air that can be inspired over and above the normal tidal volume when the person inspires with full force; it is usually equal to about 3000 milliliters. 3. Expiratory reserve volume (ERV) The maximum volume of air that can be expired by forceful expiration after the end of a normal tidal expiration; this is about 1200 milliliters. 4. Residual volume (RV) The volume of air remaining in the lungs after the most maximal expiration; this volume averages about 1200 milliliters.  Residual volume (RV) Can be expelled from the lung only when the chest wall is opened, and the lungs are collapsed completely. However, the lung still contains small amount of air (minimal air). Significance of R.V.: 1. Prevents Lung Collapse: Residual volume helps keep the alveoli open at the end of expiration, 2. Maintains Continuous Gas Exchange: Even between breaths, 3. Buffers Changes in Blood Gas Concentration: The presence of RV helps buffer fluctuations in the levels of oxygen (O₂) and carbon dioxide (CO₂) in the blood. 4. Prevents Sudden Pressure Changes: RV helps maintain airway pressure and prevents drastic changes in thoracic pressure during the respiratory cycle. Clinical Relevance of Residual Volume: Increased RV: Conditions like chronic obstructive pulmonary disease (COPD), emphysema, or asthma may cause an increase in RV because of air trapping, where the lungs cannot fully expel air due to obstruction or loss of elastic recoil. Decreased RV: Certain restrictive lung diseases (e.g., pulmonary fibrosis) may reduce RV because the lungs become stiff and lose their ability to expand and hold air. Minimal air Definition: is the small volume of air that remains in the lungs even after they have collapsed, such as after a chest injury or when removed from the chest cavity. It is the air that cannot be expelled even when the lungs are collapsed because it remains in the smallest airways and alveoli. Physiological Relevance: a. Associated with Lung Collapse: Minimal air is usually a concept studied after the lung has collapsed due to conditions like pneumothorax (air in the pleural cavity), trauma, or artificial collapse during surgery. In such cases, the lungs are deflated, but a small volume of air remains. b. Used in Postmortem Testing: Minimal volume is important in forensic science. In cases involving stillbirths or infant deaths, the presence of minimal air is tested by floating a section of the lung in water. If the lung floats, it means that the infant took a breath, suggesting the baby was alive at birth. If it sinks, it suggests the lungs never inflated, indicating that the infant did not take a breath. c. Different from Residual Volume: Residual Volume (RV) is the amount of air that remains in the lungs after maximal exhalation during normal lung function. Minimal air, on the other hand, refers to the air left in the lungs after a collapse or during extreme conditions.  Pulmonary Capacities Two or more of these volumes make up a capacity. 1.Inspiratory capacity tidal volume + inspiratory reserve volume. IC = TV + IR = 500 + 3000 = 3500ml This is the amount of air (about 3500 milliliters) a person can breathe in, beginning at the normal expiratory level and distending the lungs to the maximum amount. 2. Functional residual capacity This is the amount of air that remains in the lungs at the end of normal expiration Expiratory reserve volume + The residual volume. FRC = ERV + RV = 1200 + 1200 = 2400 m (about 2300 milliliters). 3. Total lung capacity The volume of air contained in the lung at the end of maximal inspiration (about 5900 milliliters). Vital capacity + the residual volume IRV + TV + ERV + RV = TLC 3000 + 500+ 1200 + 1200 = 5900 ≈ 6000 ml 4. Vital capacity This is the maximum amount of air can be expelled from the lungs by maximal expiration after maximal inspiration (4700 milliliters). Inspiratory reserve volume+ tidal volume + expiratory reserve volume. IRV + TV + ERV = VC 3000 +500 +1200 = 4700 It is a good index for pulmonary efficiency Factors Influencing Vital Capacity: i. Age – VC tends to decrease with age due to reduced lung elasticity. ii. Gender – Males generally have larger lung capacities than females. iii.Body Size – Taller individuals usually have a larger vital capacity. iv.Physical Fitness – Athletes and those who engage in regular exercise often have a higher VC. v. Lung Health – Diseases like COPD or restrictive lung diseases can lower VC. Physiological significance of vital capacity: 1. Indicator of Lung Health: VC provides a good measure of the lungs to hold and move air. Reduced vital capacity can be an early sign of respiratory diseases such as COPD, asthma, or restrictive lung conditions like pulmonary fibrosis. 2. Assessment of Respiratory Muscle Strength: A lower VC may indicate weakness in respiratory muscles, which is crucial in conditions like muscular dystrophy, or after spinal cord injuries. 3. Diagnosis of Pulmonary Diseases: VC is used to distinguish between obstructive and restrictive lung diseases. In obstructive diseases (e.g., COPD, asthma), airflow is reduced but lung volumes may not decrease as much. In restrictive diseases (e.g., pulmonary fibrosis), lung volumes, including VC, are significantly reduced. 4. Monitoring Progression of a Disease: Regular measurement of VC can help monitor the progression of chronic lung diseases or assess the effectiveness of treatment in conditions like COPD or asthma. 5. Exercise Performance: A good vital capacity reflects efficient oxygen delivery and usage during exercise. Athletes often have higher VC due to better lung function and stronger respiratory muscles.  Forced expiratory volume (timed vital capacity) It is the volume of air that can be expired by fastest and deepest expiration after maximal inspiration in 1st, 2nd and 3rd seconds. FEV1: the volume of air expired forcefully in 1 second (normally 83% of total VC). FEV2: the volume of air expired forcefully in 2 second (normally 94% of total VC). FEV3: the volume of air expired forcefully in 3 second (normally 97% of total VC). Clinical Importance of FVC: 1. Diagnosis of Lung Diseases: FVC is a key test in diagnosing both obstructive and restrictive lung diseases. Obstructive diseases (e.g., COPD, asthma) result in a reduced FEV1 but often a relatively normal or mildly reduced total FVC. Restrictive diseases (e.g., pulmonary fibrosis, interstitial lung diseases) show a decrease in FVC and the FEV1, remains about 83% of the reduced VC. 2. Early Detection: A decrease in FVC can signal early stages of diseases like COPD, asthma, or restrictive lung disorders, even before symptoms become prominent. 3. Assessing Disease Severity: In conditions like asthma or COPD, the degree of reduction in FVC can help assess the severity of the disease and guide treatment decisions. 4. Evaluating Treatment Efficacy: Regular FVC testing is used to monitor response to treatments, such as bronchodilators, steroids, or pulmonary rehabilitation. Improvement in FVC can indicate better lung function.  Obstructive vs. Restrictive Lung Diseases in FVC: In obstructive lung diseases (e.g., asthma, COPD): FVC is often reduced due to airway narrowing. The FEV1/FVC ratio is decreased because airflow is impeded, especially in the first second of expiration. In restrictive lung diseases (e.g., pulmonary fibrosis): Both FVC and FEV1 are reduced, but the FEV1/FVC ratio may remain normal because lung volume is reduced without significant obstruction to airflow.