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Pulmonary Function TestsLungTissuesINOutPulmonary VentilationGas exchangeRBCsPa O2 & Pa CO2

Pulmonary Function Tests They are physiological tests that assess the capacity of the respiratory system to meet the requirements of different levels of exertion, working ability and endurance. They are classified into:Lung volumes and capacities

Lung volumes and capacities Tidal volume (TV): Is the volume of air inspired or expired with each normal quite breath (eupnoea). It equals 500 ml in the normal young adult male.Inspiratory reserve volume (IRV):It is the maximum extra volume of air that can be inspired by forced inspiration after normal inspiration. It equals 3000 ml.Expiratory reserve volume (ERV):It is the maximum volume of air that can be expired by forced expiration after the end of normal expiration. It equals 1000 ml.Residual volume (RV): It is the volume of air that remains in the lung after forced expiration. It is about 1200 ml.Minimal air: It is the volume of air remaining in the lungs after opening the chest and expelling the residual volume. It is the air that enter the lung with the first breath of the new birth. It has a medicolegal importance to determine whether the newborn was born live or dead. If a piece of lung floats, minimal air is present indicating that the infant respire then died. If it does not float, it means that he was born dead.Lung capacities 1. Inspiratory capacity (IC):It is the maximal volume of air which can be inspired by forced inspiration after normal expiration. It equals TV + IRV = 500 + 3000 = 3500 ml.2. Functional residual capacity (FRC): It is the volume of air remaining in lung after normal expiration. It equals ERV + RV = 1000 + 1200 = 2200 ml. 4. Total lung capacity: It is the maximum volume of air contained in the lung after forced inspiration. It equals RV + VC = 1200 + 4500 = 5700ml.3. Vital capacity: It is the maximum volume of air that can be expired by forced expiration after forced inspiration. It equals IRV + TV + ERV = 500 + 3000 + 1000 = 4500 ml.

The various lung volumes and capacities are measured by means of a technique known as spirometry, except the residual volume and the capacities that include this volume which are functional Residual capacity (FRC) and Total Lung Capacity (TLC).spirometry: A subject breathes in a closed system in which air is trapped within a light plastic bell floating on water. The bell moves up when the subject exhales and down when the subject inhales. The movements of the bell cause corresponding movements of a pen, which traces a record of the breathing on a rotating drum recorder.

Residual volumeDefinition: It is the volume of air that remains in the lung after forced expiration. It is about 1200 ml. in young adult male. It has a higher values in females due to weaker respiratory muscles. This residual air leaves the lung only after opening the chest (as in pneumothorax) causing lung collapse. Clinically: The ratio of RV/TLC normally ranges from 25-30%. It increases in conditions associated with difficult expiration. e.g., bronchial asthma and decreased lung elasticity as emphysema. Significance: Physiologically: It keeps air in alveoli to aerate blood between breathes. This prevents marked changes in blood concentration of O2 and CO2 with each respiration. Vital capacityDefinition: It is the volume of air that can be expired by forced expiration after forced inspiration. It varies with the body size, so, it is usually related to body surface area. Normally, it is about 2500 ml/m2 in male and 2000 ml/m2 in female. It is one of the best pulmonary function tests as it is an efficient measure of the pulmonary capacity. Posture:VC is greater in the standing and sitting position than in the recumbent position. This is because in the standing position: a) The diaphragm descends freely. b) about 400 ml blood are shifted to the lower limbs by the effect of gravity ----> decrease of the blood content in the pulmonary vessels which permits greater alveolar expansion.

2) Condition of the respiratory muscles: Stronger respiratory muscles gives greater VC and vice versa. This is because the lungs can distend more efficiently with stronger respiratory muscles (as in athletes). If the respiratory muscles are affected by disease such as poliomyelitis, myasthenia gravis, VC is decreased. 3) Expansibility of the thoracic wall:The greater the expansibility of the chest wall, the greater VC and vice versa.So, VC decreases in conditions which decrease the expansion of the thoracic wall e.g. tumors in the chest wall and deformities of the vertebral column. e.g. kyphosis & scoliosis.4) Resistance to air flow:VC decreases when the resistance increases and vice versa So, VC decreases in bronchial asthma.5) Lung elasticity:Decrease in lung elasticity causes a decrease in VC.So, VC decreases in condition of emphysema, pneumonia, and pulmonary fibrosis.7) Abdominal content:Increased abdominal contents decreases VC as it hinders the descend of diaphragm. This occurs in abdominal distension, ascites, late pregnancy, and tumors. 6) Pulmonary blood volume:Increased blood volume in the pulmonary circulation (as left sided heart failure) will decrease VC because the excess blood decreases lung distensibility and takes the space for air.Forced (Timed) vital capacity (FVC) & Forced Expiratory volumes (FEV)Definition: It is a measurement of vital capacity in unit time. Procedure: The person inspires maximally to the total lung capacity, then exhales into the spirometer with maximal expiratory effort as fast and as strong as possible. Normal values: Normally, the whole value of FVC is expelled in 4 seconds. The % volume of air expired after one second (FEV1 / FVC %) is 83%, after two second (FEV2 / FVC %) is 93%, and after 3 second (FEV3 / FVC %) is 97%.

FEV2FEV3Significance:It is a useful clinical pulmonary test that measure the rate of expiration. Its values is reduced in obstructive lung diseases as bronchial asthma and emphysema. i.e., less volumes of air are expelled in longer duration.

A- normalB-obstructiveC-restrictiveD-obstruction of upper airwayPulmonary Ventilation (Minute Respiratory Volume) (MRV)Definition: It is the total amount of air inspired per minute. It equals the respiratory rate per minute x the tidal volume. MRV = RR x TV = 12 x 500 = 6 L / min.Alveolar Ventilation (Effective Pulmonary Ventilation) (EPV)Definition: The volume of air that enters the alveoli per minute and hence can undergo gas exchange with blood in the pulmonary capillaries. So, Alveolar ventilation (EPV) = Respiratory rate x (MRV Dead space ventilation) = 12 x (500 150 ) = 4.2 L / min. Significance: Alveolar ventilation is sensitive to changes in the respiratory rate and depth rather than pulmonary ventilation. - During quite normal inspiration, only the first 350 ml of the 500 ml inspired with each breath that enters the alveoli and mixes with alveolar air. The remaining 150 ml occupies the conducting zone (anatomical dead space).Example: In pulmonary congestion: There is shallow (decreased depth) rapid (increased rate) breathing. The respiratory rate may increase to 30/ minute while TV is reduced to 200 ml. In such case, MRV is normal 6 L/min. while the alveolar ventilation is markedly decreased (200 - 150 x 30) = 1.5 L/min.Dead space (DS) airDefinition: It is the volume of air which dose not undergoes gas exchange with blood in pulmonary capillaries. Types of Dead space:Anatomical dead space: It is the volume of air in the conducting zone of the respiratory system whose wall is thick and hence interferes with the gas exchangeDuring quite normal inspiration, only the first 350 ml of the 500 ml inspired with each breath that enters the alveoli and the remaining 150 ml occupies the conducting zone (anatomical dead space). With the next expiration, air in DS is expired first to atmosphere followed by alveolar air. So, DS is filled with atmospheric air at end of inspiration and with alveolar air at end of expiration.Alveolar dead space: In disease states, some of the alveoli have poor or absent blood flow through pulmonary capillaries (under- or non-perfused). Some others are hyperventilated. In both conditions, some air in those alveoli does not undergo gas exchange with the blood in the pulmonary capillaries. From functional point of view, this air should be considered dead space. Physiological DS = Anatomical DS + nonfunctioning alveoliIn the normal person, the anatomical and physiologic dead spaces are equal because all the alveoli are functional (ventilated and perfused with blood).Maximal breathing capacity (MBC) = Maximal voluntary ventilation (MVV)Definition: It is the maximal volume of air that can breathed / minute (moves in and out) using the fastest and deepest respiratory effort possible.Measurement:The subject breathes as fast and as deep as possible for 15 seconds in a spirometer. Then the volume recorded is multiplied by 4 to get the volume in one minute. The person breath only for 15 seconds to avoid fatigue of the respiratory musclesNormally, MBC = 80 160 L / min. for male & 60 - 120 L/min. for female.MBC is the best pulmonary function test.Breathing Reserve (BR): Definition: It is the difference between MBC and pulmonary ventilation. BR = MBC MRV = 100 6 = 94 L/min.Dyspnea index (DI): Definition: It is the ratio between BR& MBC.Significance:Dyspnea index is usually 90%. If it decreases less than 60% dyspnea (difficulty in breathing) occurs. Maximal (peak) expiratory flow rate (PEFR)Definition: It is the maximal velocity of air flow that can be produced during a forced expiration. Measurement: After a maximal inspiration, the subject expires as forcefully as he can, and the maximum flow rate is measured by an apparatus called peak flow meter. Significance: This test is an alternative to FEV. Low value are obtained when there is an obstruction to air flow (as in asthma & other diseases associated with bronchoconstriction).