During an attack, the respiratory tract becomes narrower, leading to gradual changes in the sound made during breathing. The intelligent computer program which Dr Oud developed while doing postdoctoral research at the University of Amsterdam, monitors these sound changes, something which the human ear cannot do. Previous research into respiratory sounds has focused mainly on being able to distinguish between patients who are breathing normally and those who are desperately short of breath.
Mireille Oud has found that respiratory sounds can provide enough information to precisely determine the level of shortness of breath. She is currently finishing off a concluding publication analysing the series of measurements she carried out. One potential use of the microphone system is to set off an alarm warning the patient of impending breathing problems while they are asleep. It can also help researchers to study a patient’s condition without him or her having to be made short of breath. Simply listening to their breathing is also a way of examining small children, who often find it difficult to blow hard several times in the course of a lung function test.
Before the computer could produce an accurate analysis of respiratory sounds, it first had to be fed with sound data and information on the state of the patient’s lungs. The medical physicist recorded the sounds produced during lung function tests. Directly after each recording, respiration measurements were also carried out. The test subject had to blow as hard as possible into a mouthpiece which measured the quantity of air passing through in the first second.
During lung function tests, histamine –produced by the body itself– is administered to the subject. Histamine causes obstruction of the respiratory tract, particularly in asthmatics. The researcher administered various different concentrations so that various gradations of breathlessness were produced. These could be recorded acoustically.
Mireille Oud intends to continue her work on respiratory sounds. One component of her research will be to use acoustic impedance measurements to determine levels of respiratory obstruction. Low-frequency sound waves will be projected into the subject’s mouth, setting the air in the lungs in motion. The level of the air flow will depend on the amount of obstruction.