Spirometry What is a spirometer? Spirometer = an instrument for measuring air entering and leaving the lungs, used to assess pulmonary function. 1 The spirometer • It is simply a device used for quantifying lung volumes and capacities. •It measures volumes of air •In pulmonary function testing, we use standardized protocols A Collins Spirometer 2 How it works Advantages of Volume spirometers Cheap Simple Accurate Reliable Easy to maintain Permanent record of test 3 Disadvantages of Volume spirometers Difficult to clean Poor dynamic characteristics Common patient related problems with FVC measurements 1. Submaximal effort 2. Leaks between mouth and mouthpiece 3. Incomplete expiration 4. Hesitation of expiration 5. Cough 6. Obstruction of mouthpiece with tongue 7. Poor posture 8. Vocalization during the forced expiration 4 The mechanism of ventilation Spirogram of lung volume changes Values are for a young healthy male, values for females are somewhat lower 5 Lung volumes and capacities • Tidal volume (TV): •Inspiratory Reserve Volume (IRV): • Inspiration capacity (IC): •Expiratory Reserve volume (ERV): •Residual Volume (RV): Lung volumes and capacities •Functional Residual Capacity (FRC): •Vital Capacity (VC): •Total lung Capacity (TLC): •Peak Expiratory Flow (PEF): •Dead space: 6 Forced volumes • Forced vital capacity (FVC): •Forced expiratory volume (FEV1): •Forced expiratory Flow from 25-75% of exhalation (FEF25-75): Factors affecting forced volumes 1. Gender: males have a larger FEV1, FVC, FEF25-75 and PEF but lower FEV1/FVC% 2. Age: FEV1, FVC, FEF25-75 and PEF increase and FEV1/FVC% decrease with age until about 20-25 years after this the gradually fall. 3. Height: All indices other than FEV1/FVC% increase with standing height. 7 Typical lung volumes IRV . 3.1 L men; 1.9 L women TV . 0.5 L men; 0.5 L women ERV . 1.2 L men; 0.9 L women RV . 1.2 L men; 1.0 L women TLC . 6.0 L men; 4.2 L women Calculating FVC Volume FVC Time (seconds) 8 Calculating FEV1.0 Volume FVC 1 sec Time (seconds) Calculating FEF25-75 x0.25 Volume FVC x0.75 Time (seconds) 9 Components of IC, VC, FRC and TLC IC = IRV + TV . 3.6-3.8 L men; 2.4 L women VC = IRV + TV + ERV .4.8 L men; 3.1 L women FRC = ERV + RV .2.2 L men; 1.8 L women TLC = VC + RV . 6 L men; 4.2 L women Minute respiratory Volume Minute respiratory volume(MRV) MRV (ml/min) = TV (ml/breath) x f(breaths/min) During quiet breathing: MRV = 6-8 L/min (12-16 breaths/min x 0.5L/breath) During heavy breathing: MRV = 186-288 L/min (60 breaths/min x 3.1-4.8 L/breath 10 Ventilation rate • Minute ventilation = tidal volume x breaths/min • Minute ventilation = 0.5 L x 12 = 6.0 L •Alveolar ventilation = (tidal volume – dead space) x breath/min •Alveolar ventilation = (0.5 L – 0.05L) x 12 = 5.4 L/min Lung volumes and capacities during rest and exercise Tidal volume increases during exercise 11 Factors that change airways resistance • Contraction or relaxation of bronchial smooth muscle (change in radius of the airway). a) Irritants, asthma, parasympathetic stimulation – decrease the radius. b) Sympathetic stimulation – increase the radius •Lung volume •Viscosity, or density, of inspired gas •Sites of airways resistance – Aging effects on healthy pulmonary system • Loss of the elastic recoil of the lungs •Decreased surface area of the lungs •Increased dead space ventilation •Decreased rib cage compliance 12 The gas laws, and ATPS, BTPS and STPD conditions Review of the gas laws - Boyle’s law - Charles’s Law - Gay-Lussac’s Law and Avogadro’s Law - The ideal gas law ATPS, BTPS and STPD conditions Gas Standardization Environmental conditions have a significant effect on pulmonary gas volumes. The volume is dependent on • The temperature (T) and pressure (P) •The volume occupied by water vapor (pH2O) depends on the degree of saturation and temperature 13 The ideal gas laws • Boyle’s Law: V % 1/P (constant T, n) •Charles Law: V % T (constant P, n) •Avogadro’s Law: V % n If we combine these laws we get the Ideal Gas Law where: V % nT/P V= volume T = temperature P= pressure n= number of gas molecules Correlation with gas laws PV=nRT • P,V,n & T all affect each other. That is if one of them varies, then others will also. 14 STPD volume Standard Temperature and Pressure dry •Standard Temperature = 0°C •Standard Pressure = 760 mmHg = 1 atm •Dry = 0.0 mmHg H2O vapor pressure •Units are commonly expressed in L/min. ATPS volumes Ambient Temperature, Pressure, and Saturation •AT = Ambient Temperature in °C •P = Ambient pressure •S = Ambient PH2O (water vapor pressure) •Units are commonly expressed in L/min 15 BTPS Body Temperature, Pressure, and saturation • BT = body temperature • P = ambient pressure • S = saturated with H2O Converting From ATPS to BTPS •The values from the spirometer are ATPS units •In order for us to infer lung volumes from the data collected by the spirometer we must convert them to BTPS. 16 BTPS correction factor BTPSCF = TB(°C) + 273 TR(°C) + 273 x PB – (PH2O)RT PB – (PH2O)BT Where: TB = body temperature (37°C) TR = Room Temperature in °C 273 = factor to convert from °C to Kelvin PB = barometric pressure PH2O = water vapor pressure at body temperature (BT) or room temperature (RT) BTPS correction factor How to calculate BTPSCF 37 °C + 273 x 22°C + 273 756-19.8* 756- 47.1** = 1.091 *Water vapor pressure at 22 °C ** Water vapor pressure at 37°C When TVATPS = 1.12 L TVBTPS = 1.12 L x 1.091 = 1.22L When VCATPS = 6.16 L VCBTPS = 6.16 L x 1.091 = 6.72L 17 Measurement of residual volume Residual volume (RV) RV = VO2 x b 79.8 – b Where VO2 the volume of oxygen in the bag B= % nitrogen in the rebreathing bag Fictional example: RVATPS = 5L x 21.72 = 1.87L 79.8-21.72 RVBTPS = 1.87L x 1.091 = 2.04L Why spirometery •Results from different forced spirometric test (FVC, FEV etc) help to identify our state of pulmonary health. •Because tests are valid and reliable we can compare results with norms. 18