Studies on the action of bronchial muscle.

IT IS appropriate, in celebrating the great contribution which John McMichael has made to the physiological approach to medicine, to deal with a physiological subject. This paper gives a brief account of the investigations, still somewhat preliminary, which our group has been carrying out into the possible part played by bronchial muscle in airways obstruction. If increased tone of bronchial muscle contributed to airways obstruction in asthma or chronic bronchitis the tone might be either static, that is to say unaltered throughout the respiratory cycle, or dynamic, that is to say increasing on expiration. Classically, in the normal animal, there is said to be no increase of tone on expiration, but this might perhaps occur in disease. Our earlier investigations attempted to investigate whether the narrowing of bronchi on expiration was purely passive, reflecting the relaxation of negative intrathoracic pressure, or whether under some conditions there might be an active component in the bronchial muscle (dynamic increase in tone). At present we are carrying the investigation a step further and are attempting to record static increases in tone by measuring the elastance of the bronchial wall.