Introduction to Test of Pulmonary Function PDF

INTRODUCTION TO TEST OF volumes, and to prevent air from PULMONARY FUNCTION escaping or entering from the nose.  In 1793 John Abernathy developed a met...

INTRODUCTION TO TEST OF volumes, and to prevent air from PULMONARY FUNCTION escaping or entering from the nose.  In 1793 John Abernathy developed a method of collecting expired gas over Basic Lung Physiology mercury and attempted to determine  Primary function of the respiratory how much those gases had been system is the continuous absorption used up by the body- VITAL of oxygen and the excretion of CAPACITY carbon dioxide.  1800 Sir Humphrey Davey (1778-  This exchange between the gas of 1829), assistant to Beddoes, used the atmosphere and blood is termed the gasometer of Watt to measure external respiration. various lung volumes (Tidal Volume and Residual Volume)  Internal respiration which is the exchange of gases between blood  1846 John Hutchinson invented the and tissues Spirometer The ability of the lungs to perform gas SPIROMETER exchange depends on the following PULMONARY FUNCTION TESTS FOUR general physiologic functions:  Disorders of the pulmonary system 1. The diaphragm and thoracic muscles can affect its function in many ways. must be capable of expanding the thorax and lungs to produce a sub atmospheric - reduced ability to move air into pressure. and out of the lungs because of airway resistance problems. 2. The airways must be unobstructed to allow gas to flow into the lungs and reach - Conversely, the difficulty may the alveoli. relate to poor compliance of the pulmonary or thoracic structures. 3. O2 and CO2 must be able to diffuse through the alveolar capillary membrane. - Disorders of gas exchange withim the lung can be another 4. The cardiovascular system must source of dysfunction. circulate blood through the lungs and ventilated alveoli.  Regardless of the source of dysfunction, pulmonary function testing is a key method used for Brief History of PFT evaluating and managing pulmonary disorders  The first known recorded spirometry test was performed by Greco-Roman  Many different tests are used to physician Claudius Galen way back evaluate lung function. in the period of 129-200 A.D.  Divided into categories based on the  Alfonso Borelli (1608-1679) had a aspect of lung function they measure. volunteer plug his nose to assure an accurate measurement of lung  Tests can be performed individually, 1. Vital Capacity (VC)- The total volume they are often performed in of air that can be exhaled after a combination. maximum inhalation: TV + IRV + ERV 2. Inspiratory Capacity (IC)- maximum volume of air that can be inhaled following a resting state: IRV +TV 3. Functional Residual Capacity (FRC)- amount of air remaining in the lungs at the end of a normal exhalation: RV + ERV 4. Total Lung Capacity (TLC)- maximum volume of air the lungs can accommodate or sum of all volume compartments or volume of air in Lung Volumes and Capacities lungs after maximum inspiration. 4- 6Liters LUNG VOLUMES 1. Tidal Volume (TV/Vt)- volume of air breathed in and out without CATEGORIES OF PULMONARY conscious effort - 300-500ml (6‐8 FUNCTION TESTS ml/kg) 2. Inspiratory Reserve Volume (IRV)- I. AIRWAY FUNCTION TEST The additional volume of air that can be inhaled with maximum effort after  VITAL CAPACITY (VC)- most basic a normal inspiration- 1900-3300ml test of pulmonary function; measures the largest volume of air that can be 3. Expiratory Reserve Volume (ERV)- moved into or out of the lungs. The additional volume of air that can be forcibly exhaled after normal exhalation- 700-1200ml.  FORCED VITAL CAPACITY (FVC) - 4. Residual Volume (RV)- volume of air is an enhancement of the simple VC remaining in the lungs after test; volume of an expiratory vital maximum exhalation (the lungs can capacity maneuver exhaled as never be completely emptied)- rapidly and forcefully as possible. 1200ml(20‐25 ml/kg)  FORCED EXPIRATORY FLOW 25%- 75% (FEF25%-75%)- previously called maximal midexpiratory flow rate (MMFR); The average expiratory LUNG CAPACITIES: flow rate over the middle 50% of the FVC volume. Made up of 2 or more Lung volumes  FORCED EXPIRATORY VOLUME and deeply for 12 to 15 seconds. The (FEV)T (time)- The percent of the volume of air exchanged is total FVC volume that was exhaled expressed in liters per minute. The within a specified time from the start MVV gives an estimate of the peak of the maneuver-specifically, within ventilation available to meet the first 0.5, 1, 2, 3 second(s). physiologic demands.  PEAK EXPIRATORY FLOW-  Measurement of respiratory muscle measured using either a flow-sensing strength is accomplished by spirometer or a peak flow meter. The assessing maximal inspiratory maximum expiratory flow rate pressure (MIP) and maximal achieved at any point during the FVC expiratory pressure (MEP) using maneuver. either a pressure transducer or a simple aneroid manometer. - Pediatric PEFR meter measurements typically range from 60 l/mh to 100 l/min (no  MIP and MEP are important adjuncts less than 60 l/min) to spirometry for monitoring. - Adult PEFR meter Respiratory muscle function in a measurements typically range variety of pulmonary and from 100 llmin to 850 l/rnin (no nonpulmonary diseases less than 100 I/min),  Airway resistance (Raw) and  FVC, FEV1, and other flows, along Compliance (Cl) measurements with flow volume loops, are all used  The patient sits in an airtight box to measure response to called a plethysmograph; bronchodilator medications  The plethysmographic method allows the calculation of the pressure drop  Tests are performed before and after across the airways related to flow at inhalation of a bronchodilator, and the mouth the percentage of change is  This is significant because it allows calculated. for measurement of Raw and subject's lung volume at the same time.  Bronchial challenge or bronchial provocation tests- used to assess airway response after a challenge to II. LUNG VOLUME and ventilation the airways; The challenge may be in tests the form of a nonspecific inhaled agent (e.g., methacholine) or a  Various techniques have been used physical agent (e.g., exercise) to estimate the volume of gas remaining in the lung after a  Maximal voluntary ventilation complete exhalation. (MVV)- the patient breathes rapidly  The collection and analysis of the  Most of these techniques allowed volume of exhaled N2 allowed the patients to breathe normally, rather functional residual capacity (FRC) to than hold their breath. These be estimated. methods are called steady-state techniques.  Using simple spirometry combined with FRC determinations allows total lung capacity (TLC) and residual volume (RV) to be calculated.  Other commonly used method for measuring lung volumes uses the body plethysmograph to measure VTG (Volume of Thoracic Gas) or FRC.  Closed-circuit (He dilution) and open- circuit (N2 washout) techniques are both widely used to measure FRC.  Measurement of resting ventilation requires only a simple gas-metering device and a means of collecting expired air.  Portable computerized spirometers allow minute ventilation, tidal volume (VT), and breathing rate to be readily measured in almost any setting.  Determination of alveolar ventilation or dead space (wasted ventilation) requires measurement of arterial partial pressure of carbon dioxide (Paco2) in addition to total ventilation. IV. Blood Gases and Gas Exchange Tests III. Diffusing Capacity Tests  These three electrodes (pH, Pco2, and partial pressure of oxygen [Po2])  The basis for the modern single- were the basic measurement device breath diffusing capacity (Dlco) test in blood gas analyzers for many was initially described when it was years. shown that small but measurable differences existed between inspired  Various fractions of Hb, such as and expired gas containing carbon O2Hb and COHb and measure monoxide (CO). electrolytes (K++, Na++, Cl-) are also included in many blood gas analyzer  A tool to measure the gas exchange systems. capacity of the lung. Transfer of gas from alveoli to pulmonary capillaries  Pulse oximetry was developed in the 1970s as a result of efforts to  monitor cardiac rate by using a light beam to sense pulsatile blood flow- changes in light absorption could also be used to estimate arterial oxygen saturation  Capnography, or monitoring of exhaled carbon dioxide, was developed in conjunction with the infrared gas analyzer.  Most critical care units, operating rooms, and emergency departments use some combination of blood gas analysis, pulse oximetry, and capnography for patient monitoring. V. Cardiopulmonary Exercise Tests  Exercise tests commonly use a treadmill or cycle ergometer to impose an external workload that stresses the cardiovascular and musculoskeletal systems.  The simplest types of exercise tests are those in which the patient performs work and only noninvasive measurements are made. Such measurements include heart rate and rhythm monitoring using an electrocardiogram (ECG).  Analysis of exhaled gas is noninvasive, but the patient does have to breathe through a mouthpiece or mask.  Ventilation and tidal volume (VT) can be estimated by collecting the exhaled air. Analysis of expired gases permits oxygen consumption and CO2 production to be measured.  Simple exercise tests, such as the 6- Minute Walk Test (6MWT)