Do asthmatic patients correctly record home spirometry measurements?

BMJ 1994; 309 doi: (Published 17 December 1994) Cite this as: BMJ 1994;309:1618
  1. P J Chowienczyk,
  2. D H Parkin,
  3. C P Lawson,
  4. G M Cochrane
  1. Department of Clinical Pharmacology, St Thomas's Hospital, London SE1 7EH, lecturer, research nurse. Micro Medical, Chatham, Kent, electronics engineer. Department of Thoracic Medicine, Guy's Hospital, London SE1 9RT, consultant physician.
  1. Correspondence to: Dr Chowienczyk.
  • Accepted 19 October 1994

Asthma diary cards for entering measurements of peak expiratory flow and subjective symptom scores are widely used in clinical trials1 and have been recommended for guiding management.2 We compared the record keeping of peak expiratory flow and spirometry measurements of two groups of patients with asthma, with only one group knowing that all data, including time and date, were being electronically recorded and stored by the spirometers.

Patients, methods, and results

We recruited 33 adults with asthma (16 men; mean age 52 (range 19-78); mean peak expiratory flow before use of bronchodilator 58% predicted (35 to 117%)) from the chest clinic of Guy's Hospital. All patients were receiving inhaled steroids and ß2 sympathomimetic agents.

Patients randomly received either a hand held spirometer (with, unknown to the patient, electronic recording and storage) plus conventional diary card or a combined electronic spirometer and diary card.3 Patients were asked to record peak expiratory flow, forced expiratory volume in one second, and forced vital capacity twice daily at prearranged times for eight weeks. The electronic diary card spirometers incororated an alarm, which reminded patients to take the measurements; we suggested to the patients with conventional diary cards that they could use an alarm clock as a prompt. Patients with conventional diary cards copied the results displayed on their spirometers into their diaries by hand. Patients with electronic diary card spirometers were told that their data were being recorded electronically and did not keep a written record of results. Six of the 16 patients with conventional diary cards and one of the 17 patients with electronic diaries withdrew from the study in the first week (six because of lack of time, one because of admission to hospital). The remaining 26 patients completed the study. We compared entries on the conventional diary cards with the data held electronically to identify incorrect manual entries.

The table shows the proportion of entries for which no corresponding data were recorded with the spirometer (invented entries) and the proportion of entries made more than six hours after or before the correct time (mistimed entries). Completed entries (as a proportion of the expected total) and the accuracy of timing were significantly greater in the patients with electronic diary cards than in those with conventional cards (P<0.05 and P<0.001 respectively; MannWhitney U test).

Incorrect entries on conventional asthma diary cards and accuracy of timing in recording peak expiratory flow and spirometry in 26 subjects with conventional or electronic diary cards

View this table:


Previous studies on the accuracy of diaries have been hampered by the lack of an objective measurement of time and date of entries and by the investigators not knowing whether measurements such as peak expiratory flow had been really measured or just invented by the patient.4 5 Using a spirometer with hidden memory allowed us to show the frequency of invented entries. In patients with conventional diary cards about a quarter of entries were either invented or mistimed, a proportion similar to that which we obtained in a preliminary study lasting one week.3 The rationale behind inventing data or entering data retrospectively may be patients' reluctance to admit poor record keeping. The most striking example to support this is the patient who performed 54 forced expirations in three hours on one day and entered these data retrospectively for the previous six days. Patients' awareness that their results are being recorded electronically might be expected to discourage them from entering data retrospectively, and we found a significantly greater proportion of completed entries and greater accuracy of timing of recordings in patients with electronic diary cards.

In conclusion, conventional asthma diary cards contain a high number of invented and retrospective entries. Electronic recording with a combined spirometer and diary prevents invented entries and identifies mistimed entries. Furthermore, a higher proportion of measurements are completed, and accuracy of the timing of measurements is improved. Cost may initially prevent widespread use of electronic recording in routine therapeutic monitoring but in clinical trials is likely to be offset by more accurate data.1

DHP was supported by a grant from Micro Medical, who also supplied the spirometers and diary cards.


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