Pulmonary Function Tests (PFT) PDF

Pulmonary Function Tests (PFT) Lung volume & capacities Exchange & transport of gases in the blood May/5th/2024 Pulmonary function tests are: - a se...

Pulmonary Function Tests (PFT) Lung volume & capacities Exchange & transport of gases in the blood May/5th/2024 Pulmonary function tests are: - a set of non-invasive, diagnostic tests that provide information about the function of the lungs. Understanding the lung volumes, capacities, and airflow parameters is ‎crucial for interpreting PFT results accurately and making ‎informed clinical decision , these tests help in assessing various aspects of lung function, including: - 1. Lung volumes 2. Capacities 3. Airflow. The Purposes of Pulmonary Function Testing:- I. Diagnosis: Helps diagnose respiratory conditions such as i- Asthma ii- Chronic obstructive pulmonary disease (COPD) iii- Restrictive lung diseases. II. Monitoring: Allows monitoring of disease progression and effectiveness of treatment. III. Preoperative Evaluation: Assesses pulmonary reserve before surgery. IV. Assessment of Disability: Evaluates impairment due to lung disease. 1. Lung Volumes involves the followings:- i. Tidal Volume (TV): The volume of air inspired or expired with each breath during quiet breathing. ii. Inspiratory Reserve Volume (IRV): The additional volume of air that can be inhaled after a normal inhalation.  iii. Expiratory Reserve Volume (ERV): The additional volume of air that can be exhaled after a normal exhalation. iv. Residual Volume (RV): The volume of air remaining in the lungs after maximum exhalation. It can be measured directly by using spirometry. II. Lung Capacities involves the followings: - 1. Inspiratory Capacity (IC): The maximum volume of air that can be inhaled after a normal exhalation. IC = TV + IRV. 2. Functional Residual Capacity (FRC): The volume of air remaining in the lungs at the end of normal expiration. FRC = ERV + RV. 3. Vital Capacity (VC): The maximum volume of air that can be exhaled after maximum inhalation. VC = TV + IRV + ERV. 4. Total Lung Capacity (TLC): The total volume of air in the lungs after maximum inhalation. TLC = VC + RV. PFT Techniques are the followings: - 1. Spirometry: Measures the volume of air inspired or expired as a function of time. Provides data on: - 1) lung volumes 2) capacities 3) Flow rates. Useful for diagnosing obstructive and restrictive lung diseases. 2. Body Plethysmography: Measures lung volumes by determining the pressure and volume changes in a closed chamber (body box); allows measurement of residual volume & useful for assessing air trapping in obstructive lung diseases. 3. Gas Diffusion Tests: Measures the ability of the lungs to transfer gases (e.g., oxygen and carbon dioxide) across the alveolar-capillary membrane & useful for detecting diffusion abnormalities seen in interstitial lung diseases.  4. Peak Expiratory Flow (PEF): Measures the maximum airflow during forced expiration after maximum inspiration & often used to monitor asthma and assess the severity of airflow obstruction. Interpretation of PFT Results: - Results are compared to predicted values based on: - 1. Age 2. Gender 3. Height, 4. Ethnicity. Patterns of abnormalities (e.g., obstructive vs. restrictive) help in diagnosing specific lung diseases, changes in lung function over time aid in monitoring disease progression and treatment response. Conclusion: - Pulmonary function tests are essential for: - 1. Assessing lung function 2. Diagnosing respiratory conditions 3. Monitoring disease progression. The exchange and transport of gases in the blood are essential processes for: - 1. Maintaining homeostasis 2. Ensuring the proper functioning of the body's cells. Gas Exchange in the Lungs: - Gas exchange occurs in the alveoli of the lungs. Oxygen diffuses from the alveolar air into the bloodstream across the alveolar-capillary membrane. Carbon dioxide diffuses from the bloodstream into the alveoli to be exhaled. Factors influencing gas exchange efficiency: -  i- surface area of alveoli iv - ventilation -perfusion matching ii- thickness of respiratory membrane iii- partial pressure gradients of gases Transport of Oxygen: Oxygen is transported in the blood in two forms: 1- Dissolved in plasma and 2- Bound to hemoglobin. Most oxygen (around 98.5%) is bound to hemoglobin within red blood cells, forming oxyhemoglobin. Hemoglobin has a high affinity for oxygen, which allows it to bind and release oxygen based on tissue oxygen demands. Factors affecting oxygen binding to hemoglobin: i- Partial pressure of oxygen ii- Temperature iii- PH (Bohr effect) iv- Concentration of 2,3-diphosphoglycerate (2,3-DPG) in red blood cells. Transport of Carbon Dioxide: Carbon dioxide is transported in the blood in three forms: i- Dissolved in plasma ii- As bicarbonate ions (HCO3-) formed via carbonic anhydrase reaction, iii- Bound to hemoglobin as carbaminohemoglobin. The majority of carbon dioxide (around 70%) is transported as bicarbonate ions. Carbon dioxide combines with water in the red blood cells to form carbonic acid, which dissociates into bicarbonate ions and hydrogen ions. Bicarbonate ions are transported out of red blood cells into plasma in exchange for chloride ions via the chloride shift mechanism.Carbon dioxide also binds to hemoglobin, although with lower affinity compared to oxygen, forming carbaminohemoglobin. Regulation of Respiration: Respiratory rate and depth are regulated by the respiratory center located in the brainstem, primarily influenced by feedback mechanisms based on: - 1-blood gas levels (partial pressures of oxygen and carbon dioxide) 3- pH. Chemoreceptors are sensitive to changes in blood gas levels and pH provide feedback signals to the respiratory center to adjust ventilation accordingly. 1. Peripheral chemoreceptors located in the carotid bodies and aortic arch monitor arterial blood oxygen and carbon dioxide levels. 2. Central chemoreceptors in the medulla oblongata primarily sense changes in cerebrospinal fluid pH, which will indirectly reflect only the arterial carbon dioxide levels.