L28 - Respiratory System PDF

L28- RESPIRATORY SYSTEM Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua LEARNING OUTCOMES Describe the Lung function tests and their significance Describe the Physiological changes in pressures of the respirat...

L28- RESPIRATORY SYSTEM Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua LEARNING OUTCOMES Describe the Lung function tests and their significance Describe the Physiological changes in pressures of the respiratory system and lung expansions.  Question A person who is born and lives at sea level will develop a slightly smaller lung capacity than a person who spends their life at a high altitude. Lung Function Tests Also called pulmonary function tests (PFTs) Evaluate how well your lungs work. The tests determine how much air your lungs can hold, how quickly you can move air in and out of your lungs, and how well your lungs add oxygen and remove carbon dioxide from your blood. The tests can diagnose lung diseases and measure the severity of lung problems INDICATIONS FOR PFTs Evaluation of patients presenting with dyspnea Evaluating disease severity and monitoring response to treatment Determine fitness for surgery *thoracic surgery/lung resection Clinical Significances: Lung function tests are valuable because they give some measure of Lung compliance or elasticity Airway resistance Respiratory muscle strength These three factors determine how much air a person can move into lungs per unit of time and this is what the pulmonary function tests measure. PFTS: AVAILABLE MEASURES Spirometry - Airflow (how much air, how fast) (Static) Lung volumes - Volume (how much air) Diffusing Capacity - Gas exchange (how effective) Other testing: Airway responsiveness Respiratory muscle strength testing Compliance of the lung Spirometry Is the first lung function test done. It measures how much and how quickly you can move air out of your lungs. For this test, you breath into a mouthpiece attached to a recording device (spirometer). Spirometer There are tow types of spirometer: 1- Mechanical devices: (Incentive spirometer) 2- Electronic devices  Respiratory Volumes The total capacity of the lungs is divided into various volumes and capacities according to the function of these in the intake or exhalation of air. The average total lung capacity of an adult human male is about 6 liters of air, but only a small amount of this capacity is used during normal breathing. The average human respiratory rate is 30-60 breaths per minute at birth, decreasing to 12-20 breaths per minute in adults. The total amount of air one’s lung can possibly hold can be subdivided into four Volumes defined as follow:  The Tidal Volume (TV): Is the volume of air inspired or expired with each normal breath and it is about 500 ml in average young adult man.  The inspiratory reserve volume (IRV): Is the extra volume of air that can be inspired over and beyond tidal volume and it is about 3000 ml.  The expiratory reserve volume (ERV): Is the amount of air that can be expired after the normal tidal expiration, which is about 1100 ml  The residual volume (RV): Is the volume of air still remaining in the lungs after the most forceful expiration, which is about 1200 ml. This volume can not be measured directly by spirometer. Therefore, an indirect method must be used usually the helium dilution method.  Lung Capacities In addition to four volumes, which don’t overlap, there are four capacities, which are combined of two or more volumes: The inspiratory capacity (IC) = TV +IRV = 500 +3000 = 3500 ml. This is the amount of air that a person can breathe beginning at the normal expiratory level and distending the lungs to the maximum amount.  The functional residual capacity (FRC) = ERV + RV = 1100 + 1200 = 2300 ml. This is the amount of air remaining in the lungs at the end of normal expiration.  The vital capacity (VC) = IRV + TV + ERV = 3000 + 500 + 1100 = 4600 ml. This is the maximum amount of air that a person can expel from the lungs after filling the lungs first to their maximum extent, and then expiring to the maximum extent.  The total lung capacity (TLC) = VC + RV = 4600 + 1200 = 5800 ml. This is the maximum volume to which the lungs can be expanded with the greatest possible inspiratory effort.  Peak expiratory flow (PEF): Is the maximum or peak rate (or velocity), in liters per minute, with which air is expelled with maximum force after a deep inspiration. It can be measured by wright peak flow meter. The maximum expiratory flow is much greater when the lungs are filled with a large volume of air than when they are almost empty Is spirometry the same as peak flow readings? No. A peak flow meter is a small device that measures the fastest rate of air that you can blow out of your lungs. Like spirometry, it can detect airways narrowing. It is more convenient than spirometry and is commonly used to help diagnose asthma.  Factors affecting lung volume Several factors affect lung volumes, some that can be controlled and some that can not. These factors include: Larger volumes Smaller volumes Males females Taller people shorter people Non-smokers heavy smokers Professional athletes non-athletes People living at high altitudes people living at low altitudes Restrictive and obstructive Pulmonary disease Pulmonary function testing primarily detects two abnormal patterns: 1- Obstructive ventilatory defects such as asthma and COPD. There is obstruction to the outflow of air The main feature is a decrease in expiratory flow rate throughout expiration 2- Restrictive (constricted) ventilatory defects such as interstitial fibrosis and chest wall deformities. That reduce the air in the lungs. There is no obstruction to the outflow of air. The main feature is reduced lung volume (mainly TLC and RV). Is there any risk in having spirometry?  Spirometry is a very low risk test.  However, blowing out hard can increase the pressure in your chest, abdomen and eye.  So, you may be advised not to have spirometry if you have: 1- Unstable angina. 2- Had a recent pneumothorax (air trapped beneath the chest wall). 3- Had a recent heart attack or stroke. 4- Had recent eye or abdominal surgery. 5- Coughed up blood recently and the cause is not known. OBSTRUCTIVE v/s RESTRICTIVE Obstructive Disorders Restrictive Disorders Characterized by a Characterized by reduced limitation of expiratory lung volumes/decreased airflow so that airways lung compliance cannot empty as rapidly Examples: compared to normal (such Interstitial Fibrosis as through narrowed Scoliosis airways from Obesity bronchospasm, Lung Resection inflammation, etc.) Neuromuscular diseases Examples: Asthma Emphysema Cystic Fibrosis  In restrictive diseases, the maximum flow rate is reduced, as is the total volume exhaled. The flow rate is often abnormally high during the latter part of expiration because of the increased lung recoil. By contrast, in obstructive diseases, the flow rate is very low in relation to lung volume, and a scooped-out appearance is seen. Answer In response to higher altitude, the body's oxygen diffusing capacity increases in order to process more air.  REFERENCES Drake R.L., Gray’s Anatomy for Students, 2nd Edition, 2009, Churchill Livingstone Moore, Clinically Oriented Anatomy, 6th Edition, 2009, Lippincott Williams & Wilkins Textbook of Medical Physiology – Guyton & Hall Medical Physiology – R.K Marya 9-Oct-24 27