CHANGES IN REGIONAL VENTILATION DURING HISTAMINE BRONCHIAL CHALLENGE IN STABLE ASTHMA

Our objective was to examine the changes in regional ventilation durin g histamine-induced bronchoconstriction in stable asthma. We measured regional ventilation by a new method which measures regional distribut ion of inhaled Xe-127 during tidal breathing by a gated method and, by simultaneously measuring Tc-99m counts from labelled macroaggregates, allowed for changes in lung shape during the breathing cycle. We stud ied 10 asthmatic patients [forced expiratory volume in 1 s (FEV(1) 2.0 4-4.37 litres)] and measured, in addition to the regional ventilation, oxygen saturation (SaO(2)), minute ventilation (V-E) and tidal volume (V-t) before and after inhaling enough histamine to lower FEV(1) by > 20% and/or SaO(2) by >4%. Histamine inhalation reduced FEV(1) by 0.44- 1.15 liters and SaO(2) by 0-4%. It increased V-E and functional residu al capacity (FRC) in 8 of the 10 patients. The FEV(1) fall did not cor relate with the SaO(2) fall, V-E or FRC changes. Histamine inhalation increased apical ventilation in most patients, but the changes in regi onal ventilation in the left and right lungs were asymmetrical in 17 o ut of the 30 lung regions studied (upper, middle and lower paired regi ons in 10 patients). These results demonstrate that histamine bronchia l challenge causes uneven regional ventilation. OAny resultant change in ventilation-perfusion balance may be the underlying mechanism of ox ygen desaturation seen in this procedure and in spontaneous attacks of asthma.