2022_Study material_lung function.pdf

LUNG FUNCTION TESTS OUTCOMES At the end of the practical the student should be able to: a. Name what spirometry can be used for. b. Know how to prepare a patient prior to lung function testing. c. Describe the different manoeuvers a patient needs to perform to obtain a spirogram and flow-volum...

LUNG FUNCTION TESTS OUTCOMES At the end of the practical the student should be able to: a. Name what spirometry can be used for. b. Know how to prepare a patient prior to lung function testing. c. Describe the different manoeuvers a patient needs to perform to obtain a spirogram and flow-volume curve. d. Name and describe the 4 lung volumes and 4 lung capacities that can be read off a spirogram. e. Read the different volumes and capacities from given spirograms. f. Name and describe the lung volumes, peak flow rates, FEV1 and FEV% found on a flow-volume curve. g. Read the different volumes, peak flow rates and FEV1 from given flow-volume curves. h. Calculate the FEV% from given flow-volume curves. i. Name and explain the different disorders associated with lung diseases/conditions. j. Know the influence different disorders have on a spirogram and flow-volume curve. k. Interpret given spirograms and flow volume curves. INTRODUCTION Numerous tests are available to investigate various aspects of the performance of the respiratory system. Spirometry is the measurement of lung volumes as well as the nature of airflow in and out of the lungs. Clinical spirometry can be used to distinguish between normal airflow and normal volumes as opposed to obstructive or restrictive lung disorders. Spirometry is often performed as a screening procedure. It may be the first test to indicate the presence of pulmonary disease. Spirometry alone, however, may not be sufficient to define the extent of the disease, response to therapy, preoperative risk, or the level of impairment. Spirometry can be used to: detect the presence or absence of lung disease quantify the extent of a known disease on lung function measure the effects of occupational or environmental exposure determine beneficial or side effects of therapy e.g. bronchodilators assess risk for surgical procedures evaluate disability or impairment 1 DIFFERENT LUNG FUNCTION TESTS The following table contains some of the tests available as well as the variables that it measures. NAME OF TEST TESTING FOR: 1 Spirogram Static lung volumes Static lung capacities 2 Flow-volume curve Dynamic lung volumes Flow rates 3 Volume-time curve Dynamic lung volumes Dynamic lung capacities 4 Helium equilibration technique Functional residual capacity Residual volume & total lung capacity 5 Whole body plethysmography Functional residual capacity Residual volume & total lung capacity 6 Single breath nitrogen washout Dead space volume 7 Lung compliance Elastic properties of the lung 8 Diffusion capacity Diffusion of gases across the alveolocapillary membrane In this practical we will only focus on test number 1 and 2 listed in the table above. To read more on test 4 and 5 please see p 11. SPIROMETRY (According to the information leaflet of SSEM Mthembu Medical equipment, supplies and logistics) Spirometry is the measurement of lung volumes and the flow of air into and out of the lungs. Instrument used: Spirometer INSTRUCTIONS TO PATIENT PRIOR TO TEST (WHEN MAKING THE APPOINTMENT): To achieve optimum results, it is necessary to inform the patient beforehand to avoid the following: wearing restrictive clothing smoking within one hour of testing alcohol within four hours of testing vigorous exercise within 30 minutes before testing a short-acting and long-acting bronchodilator, for 4 hours and 12 hours respectively, prior to testing a heavy meal within 2 hours of testing 2 ON TESTING DAY: 1. Do the daily calibration checks Always calibrate the spirometer before the first spirometry test of the day. Use a 3 litre calibration syringe. Remember to monitor the ambient conditions in the room with a hygrometer/barometer because room temperature, relative humidity, barometric pressure and altitude can influence the results. 3 litre calibration syringe firstaidwarehouse.co.uk 2. Introduce yourself to the patient and import various information into the program Various physical measurements are required for the software to estimate each patient’s expected level of lung function. The following information needs to be imported for each new patient: o date of birth (yyyy/mm/dd) o gender Number of cigarettes smoked per day x number of years smoking o height (cm) 20 o weight (kg) o ethnic origin o smoking history (pack years) 3. Describe and demonstrate the procedure to the patient 4. Preparation of the patient ensure that the patient is comfortable and relaxed ask the patient to sit in an upright position with his/her feet flat on the floor the patient’s chin should be upright with the neck slightly extended attach the nose clip, tightly sealing the nostrils 5. Obtain a spirogram: Instructions to patient: Place your teeth over the mouthpiece and seal it with your lips Perform the following slowly and completely o Breath normally for a few breaths o Inspire maximally o Exhale completely 3 Patient performs manoeuvre as explained by the technician Clip on Technician monitors nose and encourages patient during test Machine records the results of the nhlbi.nih.gov spirometry test 4 SPIROGRAM A spirogram is the registration obtained from a spirometer and is a graphic representation of the primary lung volumes and -capacities. The volume of air changes considerably during a respiratory cycle. Four static lung volumes and four static lung capacities are distinguished. Static volumes and capacities do not take into consideration the time necessary for volume change. Lung volumes vary considerably with age, sex, height and weight. Static Static capacities volumes 66 Inspiratory capacity (IC) 55 Total lung capacity (TLC) Vital capacity (VC) Inspiratory reserve volume (IRV) 44 Volume (l) 33 Tidal volume (VT) 22 Expiratory reserve volume (ERV) (FRC) 11 Residual volume (RV) 00 LUNG VOLUMES (STATIC): Tidal volume (VT) The volume of air that enters the lung during a single resting inspiration and is subsequently blown out by a calm expiration (~ 500 ml/0.5L). Inspiratory reserve volume (IRV) The additional volume of air that can be forced into the lung by maximal inspiration after inhalation of the tidal volume (~ 3000 ml/3L). Expiratory reserve volume (ERV) The maximum volume of air that can be forcibly exhaled after expiration of the tidal volume (~1000 ml - 1500 ml/1-1.5L). Residual volume (RV) The volume of air that remains in the lungs after maximal expiration (1000ml - 1500 ml/1-1.5L). This residual air prevents great oscillations in the PaO2 and PaCO2 and prevents collapse of the alveoli, thereby reducing the elastic resistance and the energy required for the next inspiration. LUNG CAPACITIES (STATIC): A lung capacity is the sum of two or more primary lung volumes. Vital capacity (VC) The maximum volume of air that can be in- or exhaled. VC = ERV + VT + IRV Inspiratory capacity (IC) The maximum volume of air that can be inspired after a restful expiration. IC = VT + IRV Total lung capacity (TLC) The volume of air in the respiratory system after maximal inspiration. TLC = IRV + VT + ERV + RV Functional residual capacity (FRC) The volume of air in the respiratory system after a normal expiration. FRC = RV + ERV (For more information on FRC, please see p 11) 5 6. Obtain a flow-volume curve: Instructions to patient: The manoeuvre the patient needs to perform depends on the software accompanying the spirometer. Option 1: 1. empty lungs (exhale) 2. place your teeth over the mouthpiece and seal it with your lips 3. take in a fast deep breath, filling the lungs (maximum inspiration) 4. blast out hard and fast until no more air can be expelled (maximum expiration) 5. as soon as the machine beeps, inhale as fast and deep as possible (maximum inspiration) Option 2: 1. place your teeth over the mouthpiece and seal it with your lips 2. breathe normal (x3) 3. take in a fast deep breath, filling the lungs (maximum inspiration) 4. blast out hard and fast until no more air can be expelled (maximum expiration) 5. Inhale as fast and deep as possible (maximum inspiration) Points to remember: To obtain valid data, patients must be instructed and coached continuously for each manoeuvre. During the actual test, vocal encouragement should be given so that the patient knows exactly what is expected for each part of the manoeuvre. A minimum of 3 acceptable manoeuvres must be performed with all acceptability and repeatability criteria having been met (Please see pages 13 and 14 for more information on acceptability and repeatability criteria). Avoid more than eight tests per patient session. FLOW-VOLUME CURVE Flow is defined as the change in volume per unit time. When a time factor is introduced the volumes obtained are called dynamic lung volumes. Dynamic lung volumes can be obtained with the use of a flow-volume curve. Dynamic lung volumes refer to the airflow, expressed as volume per unit time in or out of the respiratory apparatus. The most important factors you have to be able to read from this curve are the different lung volumes, peak flows, FEV1, FEV% and the flow pattern. 6  12 10 PEFR 8 6 Expiration 4 Flow (l/sec) IRV VT ERV 2 0 1 2 4 5 6 FEV1 4 -2 -4 FVC Inspiration -6 1 -8 PIFR -10 Volume (l) FVC = forced vital capacity VT = Tidal volume IRV = inspiratory reserve volume ERV = expiratory reserve volume PEFR = peak expiratory flow rate PIFR = peak inspiratory flow rate FEV% = FEV1 x 100 FEV1 = volume of air expired in 1 second FVC 1 Forced vital capacity (FVC) The forced vital capacity is the volume of air that can be expired as forcefully and rapidly as possible, preceded by a maximal inspiration. Forced expiratory volume in one second (FEV1) The fraction of the vital capacity that can be expired in the first second of expiration of the FVC (Thus it is the portion of the FVC expired in one second). Forced expiratory volume percentage (FEV%) The percentage of the total FVC volume that was exhaled within 1 second from the start of the manoeuvre. Peak expiratory flow rate (PEFR) The maximal flow rate achieved during a forced maximal expiratory effort following a maximal inspiration. Peak inspiratory flow rate (PIFR) The maximum flow rate achieved at any time point during the inspiratory part of the manoeuvre. Forced expiratory flow (FEF) 25-75% The average flow rate between 25% and 75% of the FVC, that is, in the middle of the curve, after 25% of the FVC is expired up to when 75% is expired. 7 DISORDERS Most pulmonary disorders can be described as either obstructive or restrictive processes. Spirometric measurements typically assess lung volumes and flows, and so are ideally suited to describe the effects of restriction and obstruction on lung functions. 1. OBSTRUCTIVE AIRWAY DISEASES An obstructive airway disease is one where air flow either into or out of the lungs is reduced. The site of airway obstruction might be in either the large airways or the small airways. The main result is a decrease in flow. 1.1 Large airway obstruction: Large airway obstruction is characterised by a reduced airflow in the upper airways, i.e., above the vocal cords, the trachea, main stem bronchi or segmental bronchi. These airways are characterized by having cartilage support and cross-sectional areas in which gas flow is turbulent. Maximal flow through large airways is dependent on the patency of these airways as well as the pressure that can be developed by the expiratory (abdominal) muscles. Examples of conditions that can cause large airway obstruction: vocal cord dysfunction or damage (caused by e.g. intubation of the trachea) tracheal lesions such as stenosis or malacia tumours foreign body aspirations goiters 1.2 Small airway obstruction: Small airway obstruction refers to flow limitation that occurs in airways less than 2 mm in diameter. These airways have no cartilage support in their walls. Support comes from interconnection with surrounding lung tissue and depends on the integrity of that tissue. The small airway walls contain smooth muscle and the tone of these muscles plays a major role in determining their patency. Flow through small airways is laminar. Examples of conditions that can cause small airway obstruction: asthma (see page 12 for more information) emphysema (see page 12 for more information) chronic bronchitis (see page 12 for more information) bronchiolitis cystic fibrosis (CF) 8  The effect of large and small airway obstructions on a flow-volume curve: Normal Small airway obstructions: Large airway obstructions: Chronic Variable Early small Fixed large obstructive extrathoracic airway airway pulmonary large airway obstruction obstruction disease (COPD) obstruction Flow rate (l/sec) Volume (l) 2. RESTRICTIVE LUNG DISEASE Any process that interferes with the expansion of the lungs, or chest wall, may be considered a restrictive disorder. The main result is a decrease in lung volume. Examples: Interstitial lung diseases: pulmonary fibrosis involves scarring of the lung at alveolar level which causes the lungs to become stiff. Causes of pulmonary fibroses include: environmental pollutants, smoking, radiation etc. pneumoconiosis is lung impairment caused by inhalation of dusts. Most pneumoconiosis are characterized by pulmonary fibrosis and chest x-ray abnormalities. Examples of pneumoconiosis include: silicosis, asbestosis, etc. sarcoidosis is a granulomatous disease that affects multiple organs including the lungs. Neuromuscular disorders e.g.: Myasthenia gravis (autoimmune disease which affect neuromuscular transmission) Guillain-Barre syndrome (body’s immune system attacks the peripheral nerves) Disorders that affect the chest wall or respiratory muscles also commonly result in restriction: pleural effusion (abnormal accumulation of fluid in the pleural space) pneumothorax (condition in which air enters the pleural space) Kyphoscoliosis (involves abnormal curvature of the spine) 9  pregnancy obesity tight bandages The effect of restriction on a flow volume curve. Restrictive Normal disease Flow rate (l/sec) Volume (l) 10 ENRICHMENT The Functional Residual Capacity (FRC) The volume of air in the respiratory system after a normal expiration FRC = RV + ERV It is also the volume of air present when the forces that incline the lung to collapse (elastic fibres = surface tension) are in equilibrium with the forces that tend to expand the chest outwards (EPP = equal pressure point). Theoretically this represents the "resting” volume of the respiratory apparatus and the arrested length of the respiratory muscles where opposite muscle forces are balanced. Considering that alveolar air has an important function in maintaining uniformity in gas pressures both in the alveoli and the alveolar blood, hence the emphasis on functional in FRC. The alveolar air (VA) refers to the volume of gas inside the lung able to exchange with gases in the blood. During relaxed breathing the pressures of oxygen (PAO2), carbon dioxide (PACO2), nitrogen, (PAN2), and aqueous vapour (PAH2O), remain remarkably constant. The alveoli serve as an air reservoir from which oxygen can diffuse to the pulmonary capillary blood and into which carbon dioxide can diffuse incessantly from the pulmonary capillary blood, regardless of whether the person is presently breathing in or out. If a person is breathing atmospheric air and his FRC is 3,0 litres, then ± 18% (0,54 litres) of this is oxygen. The function of the FRC can be summarised as follows: (i) it continually provides air for gas exchange with the blood (ii) It prevents alveoli from shrinking so much during expiration so as to encounter difficulty in opening again during inspiration: therefore it reduces the labour of inspiration. Helium-dilution technique for determination of FRC The residual volume and consequently the functional residual capacity cannot be determined by direct spirometry measurements. However the functional residual capacity can be determined by an indirect method known as the helium-dilution technique. The helium-dilution technique makes use of the following relationship; if the total amount of a substance dissolved in a volume is known and its concentration can be measured, the volume in which it is dissolved can be determined. In the helium-dilution technique helium is dissolved in the gas in the lungs and its concentration is determined with a helium meter, allowing calculation of the lung volume. Helium is used for this test because it is not taken up by the pulmonary capillary blood and because it does not diffuse out of the blood and so the total amount of helium does not change during the test. The subject breathes in and out of a spirometer filled with a mixture of helium and oxygen. The helium concentration is monitored continuously with a helium meter until its concentration in the inspired air equals its concentration in the subject’s expired air. At this point the concentration of helium is the same in the subject’s lungs as it is in the spirometer and the test is stopped at the end of a normal tidal expiration, i.e., at the functional residual capacity. The equation follows: FHeiVspi = FHef(Vspf + Vlf) That is the total amount of helium in the system initially is equal to its initial fractional concentration of helium (FHei) times the initial volume of the spirometer (Vspi). This must be equal to the amount of helium in the lungs and the spirometer at the end of the test, which is equal to the final fractional concentration of helium (FHef) times the final volume of the spirometer (Vspf) and the volume of the lungs at the end of the test (Vlf). Whole body plethysmography Another way of measuring the FRC is with a body plethysmograph. This is a large airtight box in which the subject sits. At the end of a normal expiration, a shutter closes the mouthpiece and the subject is asked to make respiratory efforts. As he tries to inhale the gas into his lungs, lung volume increases, and the box pressure rises since its gas volume decreases. Boyle’s law state that pressure x volume is constant (at constant temperature). Therefore, if the pressure in the box before and after the inspiratory effort are P1 and P2, respectively, V1 is the pre-inspiratory box volume, and delta V is the change in volume in the box (or lung), we can write P1V1 = P2(V1 - delta V). Thus delta V can be obtained. Next Boyle’s law is applied to the gas in the lung. Now P3V2 = P4(V2 + delta V), where P3 and P4 are the mouth pressures before and after the inspiratory effort, and V2 is the FRC. The body plethysmograph measures the total volume of gas in the lung, including any that is trapped behind closed airways and that therefore does not communicate with the mouth. By contrast, the helium dilution method measures only communicating gas, or ventilated lung volume. In young normal subjects these volumes are virtually the same, but in patients with lung diseases the ventilated volume may be considerably less than the total volume because of gas trapped behind obstructed airways. 11 Severe emphysema Flow in both the pressure- and volume dependent section of the flow-curve is reduced. The area of the inspiratory curve is much larger than that of the expiratory curve. This indicates minimal resistance to air flow during inspiration due to dilation of air passages. This phenomenon may be due to large air ducts being very plastic or collapsible. As soon as the patient starts to exhale forcibly, his flabby large air ducts are almost immediately occluded due to dynamic compression and this restricts further flow. This is a classic example of severe emphysema. Asthma and chronic bronchitis The pressure dependent section of the curve is normal, but at small lung volumes, the air flow is diminished. Diseases characterized by primary constriction of the medium or smaller bronchi, like asthma or chronic bronchitis, may cause this impairment. The primary bronchial constriction causes resistance to inspiratory flow, therefore the inspiratory curve is also curtailed. During expiration, the air flow is reduced by both bronchial constriction and dynamic compression. Characteristically, in asthma, the volume dependent flow restriction can be partly or totally reversed by administration of bronchodilators (i. e. 2 stimulants like Salbutamol, or phosphodiesterate inhibitors like Theophylli 12 13 14 15