Study objectives: To characterize intrasubject, intersubject, and diurnal variability in peak expiratory flow rates (PEFR) of healthy nonasthmatic women over at least one complete menstrual cycle; to determine whether a relationship exists between PEFR and premenstrual symptoms in these women; and to provide a forum to educate women pharmacy students by interactive study participation.
Design: Longitudinal, investigator-blinded study.
Setting: University of British Columbia and Children's and Women's Health Centre.
Patients: Forty healthy nonasthmatic female pharmacy students were enrolled, and 31 (aged 22.1+/-1.5 yrs) completed the study.
Intervention: Women were followed for at least one menstrual cycle during which they recorded premenstrual symptom questionnaire scores daily (15 mood and physical symptoms, graded 0-3 in severity). They also measured and recorded PEFR (3 consecutive attempts) every morning and every evening. A feedback survey was later administered by electronic mail.
Measurements and main results: Thirty-one women, 28 of whom were of Asian descent, completed the study. Over half of them (58.1%) showed classic patterns of premenstrual symptoms, whereas PEFR fluctuated randomly over the course of the cycle. Average coefficients of variation (CVs) were 4.17+/-2.09% for morning PEFR, 3.97+/-2.25% for evening PEFR, and 3.72+/-2.55% for mean daily PEFR. Average absolute diurnal variation was 17.13+/-12.46 L/minute, and relative diurnal variation was 3.98+/-2.52%. Intersubject variability for morning, evening, and mean daily PEFRs yielded low CVs of 13.7%, 14.3%, and 13.9%, respectively Only 14 (11.3%) of 124 correlations between PEFR and premenstrual symptoms were significant (p<0.05). Most participants responded positively (mean score 3.87 on a 5-point scale) to the survey on the impact of this study.
Conclusion: Intrasubject and diurnal variability in PEFR are minimal in nonasthmatic women; similarly, intersubject variability is relatively low. The menstrual cycle appears to have little effect on PEFR in healthy nonasthmatic Asian women. Pharmacy students who take part in serial PEFR monitoring gain new appreciation for asthma and asthmatic patients.