When Spirometry or Whole Body Plethysmography and Lung Compliance Test Is Indicated?

Український пульмонологічний журнал. 2005, No 3 (додаток) 1.0 INTRODUCTION The detection of lung function disturbances has a great value in health and disease. We use the lung function tests in the diag nosis and monitoring procedures in different lung diseases and in general medicine. These methods are also very useful in qualifica tion of patients before thoracic surgery interventions, to deter mine the grade of respiratory impairment in patients and in epide miological studies evaluating the negative influences of outdoors or indoors environment factors in workers and in inhabitants of different regions. The analysis of lung ventilation disturbances concerns the degree of impairment and especially the mechanisms, which are responsible for respiratory insufficiency. The identification of lung function disturbances helps us very often in the diagnostic proce dure and in the decision about therapy. Analysis of lung mechanic impairment is the first important step of diagnostic procedures in lung diseases. According to guidelines of the European Respiratory Society 1993 [2] the diagnostic procedures of lung mechanics distur bances include spirometry (VC, FEV1), the registration of maximal expiratory flow volume loop and the calculation of maximal expira tory flow rates (PEF, MEF50, MEF25), and the measurement of functional residual capacity (FRC) and airway resistance (Raw) with whole body plethysmography. Estimation of static lung com pliance (Cst) especially in the interstitial lung diseases is needed. In the Lung Function Department of the Institute of Tuber culosis and Lung Diseases in Warsaw the annual number of spirom etry measurements is about 7000, bodyplethysmography analysis about 2000, lung compliance tests about 1000 and lung diffusion tests about 1000 pro year. 2.0 SPIROMETRY From theoretical point of view the ventilation disturbances of the lung is a result of impairment of elastic and/or non elastic resistances of respiratory system. For these reason two important methods as spirometry and bodyplethysmography are very often used. We understand spi rometry as a first step in the analysis of lung mechanic distur bances but this must be very often supplemented and verified by bodyplethysmography. These two methods are complementary and no one can be replaced through the another. The advantage of spirometry is the relative exact measurement of bronchial obstruc tion with relatively inexpensive equipment. Negative sign is the necessity of very good cooperation of the proband during testing of maximal forced expiration. The spirometric equipments for ventilation measurement are divided in two groups. To the first group of spirometers belongs the volumeter for direct estimation of lung volumes. This type of spirometer is very frequently used in hospitals and in outpatient's clinics. With this apparatus we can measure the static and dynamic spirometric parameters. The static values are vital capacity (VC) and their com ponents (TV, IRV, ERV) and the dynamic values, which contain the volumes in relation to time like FEV1, FEV1 %VC ratio (Tiffeneau Index). (Fig. 1a). In the second group there are so called computerized spiro meters, which today substitute volumetric devices. The modern spirometer consists of two important compounds: the pneumota chograph to appropriate measuring of flow in the airways and a computer device for mathematical calculation (integration) of the volume (VC). So the volume measurement with this device is a indi rect procedure. The recording of classical spirometry is in fact an examination of relation between volume and time (V/t). The recording of the lung mechanics parameters with the use of electronic spirometer is an analysis of volume/flow measurement (V/V°) (Fig. 1b). Today the recording of the maximal expiratory flow volume loop and estimation of the maximal expiratory flow rates (MEF50, MEF25) and the FVC are the most frequent tests used in the diag nosis of airflow obstruction and in the analysis of FVC diminishing (restrictive defect). With the use of FVC or VC measurement we can speculate only roughly about the restrictive ventilatory defect. According to the statements of the European Respiratory Society [2] the restrictive ventilatory defect is better described by reduction of TLC than by VC measurement. The decrease of VC permit only a suspicion of restrictive defect which must be very often verified by the TLC detecting during plethysmography testing. STATIC LUNG VOLUMES: VC, FRC, RV, TLC. Vital capacity (VC) is equal the volume change at the mouth between of full inspiration and complete expiration. The measure ment may be made in one of the following manner: Inspiratory vital capacity (IVC) — the measurement is performed in a relaxed manner, from a position of full expiration to full inspira$ tion. This technique gives the best information about the value of VC. Expiratory vital capacity (EVC) — the measurement is per formed from a position of full inspiration to full expiration. This technique is very often used but sometime the results are unsatis factory, especially in obstructive patients. The forced vital capacity (FVC) is very often obtained dur ing the registration of maximal expiratory flow volume loop. The FVC represents the volume of gas, which is maximal exhaled dur ing a forced expiration, starting from a position of full inspiration. It is important to note that in healthy subjects differences between IVC and FVC or EVC are minimal. But in patients with airflow limi tation the relaxed or slow expiratory vital capacity (EVC or SVC) and particularly the forced vital capacity (FVC) can be considerable less than IVC. As a consequence the evaluation of restrictive defect on the basis of FVC is limited. On the other side the calcu lation of FEV1 %VC ratio can be overestimated. DIAGNOSIS OF THE RESTRICTIVE VENTILATORY DEFECT As it was pointed out above the decrease of VC or FVC is only first sign about a restrictive ventilatory defect. Confirmation of this type of ventilatory defect is necessary. It is important to know if the decrease of vital capacity is reversible or not. In this aim we have to perform bronchodilatatory test — a second spirometry about 15 min after the inhalation. An increase of 15 % FVC (in relation to the first spirometry) after a bron chodilator inhalation is a sing that the reduction of FVC has a func tional mechanisms connected with airway obstruction. This func tional type of FVC decrease we can often seen in patients with bronchial asthma or sometimes in patients with COPD. Second procedure is measuring of FRC in body plethysmo graph. Especially in emphysema the reduction of FVC is often a secondary effect of over inflation of the lung, which cause an increase of FRC and RV. In patients with emphysema the decrease of VC in spite of increase of TLC is a result of increased FRC. Only in interstitial lung diseases especially in lung fibrosis the FRC is often reduced as a consequence of reduction of lung paren chyma. Classification of VC restriction : small — between 75 % and 60 % of pred. VC ; medium — between 60 % and 50 % of pred. and advanced between 50 and 30 % of pred. VC [1]. FUNCTIONAL RESIDUAL CAPACITY (FRC) It is important to underline that the analysis of FRC (TGV) or RV and total lung capacity (TLC) are very important in the diagno © Kowalski J., 2005 J. Kowalski WHEN SPIROMETRY OR WHOLE BODY PLETHYSMOGRAPHY AND LUNG COMPLIANCE TEST IS INDICATED?