[Clinical application of portable spirometry in asthma]

To investigate the clinical applications of portable spirometry in asthma.

Twenty patients with asthma were recruited from Peking Union Medical College Hospital. Flow-volume loop, simultaneous asthma symptoms, and mood were monitored three times a day for consecutive 14 days.

In patients with a normal daytime spirometry, marked decline of forced expiratory volume in one second (FEV1) and peak expiratory flow (PEF) were observed at night and/or in the early morning. A within subject correlation analysis between FEV1, PEF, and asthma symptoms showed that the correlation between symptoms and airway obstruction was found only in seven out of twenty patients (35%). Four patients (20%) reported many symptoms with nearly normal portable spirometry. Accordingly, their symptoms were not correlated with FEV1 and PEF. This group of patients was defined as over-perceivers. On the contrary, another two patients (10%) did not report any symptoms while obvious airways obstruction was recorded by a portable spirometry. These patients were defined as under-perceivers.

Dynamic monitoring of flow-volume loop with a portable spirometry is more accurate than routine lung function test in assessment of asthma severity. In addition, combined with simultaneous monitoring of symptoms, it would be of particularly helpful in identifying two specific types of asthma patients, e.g. over-perceivers and under-perceivers.