Of them.the helium dilution technic which probably is the most popular method,

hod. Of them.the helium dilution technic which probably is the most popular method, is described below. The subject breathes in and out from a spirometer containing a known concentration of helium . Let the volume of the spiro meter (including the tube leading from the spirometer to the patient) be VS. Further, let the volume of the lungs during quiet breathing, at the end ef an ordinary expiration, (i. e. FRC of the subject), be VL In the beginning (before start of the experiment), the volume of the helium was C1 x Vs where C1 was the concentiation of hetium in the spirometer. Now the subject breathes through the spirometer and after sometime, concentration of helium is same throughout the spirometer. the tube (connecting the spirometer and the subject) and the lungs (to be understood is, thaithese three, now make a continuous chamber). After this new equilibrium, the concentration of helium falls Now, let C2 be the new concentration of helium in the spirometer after the equilibrium is reached; then, the volume of helium is The value of Vs, C1 and C2 being known, the value of VL can be found out N.B. It should be remembered that the gas helium is insoluble in blood Helium therefore does not escape From the alveoli to enter capillary blood of the lungs. The FRC and RV are increased in emphysema Flow volume curve (loop) Flow volume curve can demonstrate whether or not there is obstruction in the smaller bronchioles Recall, small bronchial obstruction (and therefore its consequence of increased 'airway resistance') occurs classically in emphysema and bronchial asthma (during paroxysm). The flow volume loop, FVL, has a characteristic shape in normal persons (fig. 4. 2.5) The hollowed out shape in the phase of exptration (line a' b' in fig. 4. 2.5, B) is characteristic of emphysema (the hollowed our shape is because of excess time required to breathe out fully in the face of increased airway obstruction). Conclusion and Summary. There are many items in lung function Tests (LUFT) However, one electronically operated computerised spt-romeler can look after most of the LUFTs required in ordinary clinical units Such a spirometer will determine. VC (FVC) , FEVI., FEV1 : FVC , PVV., PEFR. and also give a FVL (flow volume foop) However, such spirometers will not give, RV , FRC or TL values. Such spirometers are only moderately expensive and are manufactured in India. Closing Volume Towards the basal region, the intrapleural pressure is less negative than that in the apical region. Therefore, at the basal region, the traction on the bronchial walls are less and the fine bronchial tubes, (the respiratory bronchioles, to be specific) have a tendency Lo collapse (obliterate) particularly during a forcible enpiration. The lung volume at which this closure actually occurs is called the closing capacity Closing volume is closing capacity minus the residual volume. Closing capacity is high in emphysema. In advanced cases of emphysema The closing capacity may encroach the tidal air volume and at this stage the subject suffers from dyspnea even at rest