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University of Toronto Scarborough
Biological Sciences
Stephen Reid

1Lecture 11 Pulmonary Function Tests and Alveolar Ventilation1 Lung Volumes and CapacitiesThe volume of a breath is referred to as tidal volume The average value for tidal volume is approximately 500 ml At a normal breathing frequency of 12 breaths per minute this translates into 6 000 ml of air taken into the lungs every minute However not all of this air enters the alveoli and is involved in gas exchange A portion of the inspired air remains in the anatomical dead space of the conducting zone where no gas transfer occurs see belowThe maximum amount of air exhaled following a maximal inspiration is called vital capacity However no matter how hard we expire there will always be approximately 12 L of air left in the lungs that cannot be exhaled residual volume Standard spirometry techniques which can measure breath volume cant be used to measure this residual volume of airbut there is another technique the inert gas technique that can measure this The residual volume plus our expiratory reserve volume is termed our functional residual capacity The entire air capacity of the respiratory system including the reserve volumes and residual volume is referred to as total lung capacity 2 Pulmonary Function TestsLung volumes are measured by pulmonary function tests which can also be used to diagnose various pathological conditions or lung disorders Generally these disorders can be classified as either restrictive or obstructive A restrictive pulmonary disease interferes with lung expansion and thus inspiration and may be caused by damage to the chest wall the lungs or the pleura There are several defining features of a restrictive lung disease including a decrease in vital capacity and total lung capacity more on this below Examples of restrictive pulmonary diseases include pulmonary edema where the expansion of the alveoli is inhibited by fluid in the lungs and pulmonary fibrosisThe other type of lung diseases assessed using these pulmonary function tests are classified as obstructive These conditions hinder expiration Since air does not leave the lungs efficiently the lungs overinflate and so one hallmark of an obstructive lung disease is an increase in functional residual capacity and an increase in total lung capacity Diseases that damage the alveoli such as asthma or emphysema are classic examples of obstructive disordersWhen we perform a lung function test we are often trying to measure forced vital capacity by breathing in as hard as one can and then exhaling as hard as one can This gives us then values for both our maximal inspiration and our maximal exhalation Forced vital capacity is determined by several factors including the strength of the chest and abdominal muscles airway resistance which can be altered by bronchitis or asthma lung size which can be altered by the size of the person or by diseases such as tuberculosis and the elasticity of the lung tissues also plays a factor this can be altered by diseases or simply by ageA second variable that is measured by lung function tests is forced expiratory volume which is the proportion of forced vital capacity that can be exhaled in a given time for example in one
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