Reliability of Spirometric Tests during the Different Menstrual Cycle Phases in Healthy Women

Several studies have suggested that respiratory function is influenced by female sexual hormones. Considering a normal 28-day menstrual cycle, three phases can be distinguished: menstrual, follicular and luteal. Respiratory function is influenced by female sexual hormones, which could increase ventilatory response during the luteal phase (1). In contrast, no changes for pulmonary capacities, flows and volumes evaluated by spirometry were found in other investigations (2). These conflicting results may be due to that those studies have not evaluated either, the test reliability or the smallest real difference (SRD) during the menstrual cycle phases. Reliability and SRD are important prerequisites for the correct interpretation of spirometric data, which indicate to the clinician whether or not a genuine and real change has occurred. Therefore, the aim of this study has been to check the reliability of spirometric tests during the menstrual cycle phases and to investigate if spirometric variables are modified across the menstrual cycle. Twenty-three healthy non-smoker women, aged 18 to 35 yr, performed several spirometric tests in three different phases of the menstrual cycle (menstrual, follicular and luteal). In this way, basal body temperature was taken daily upon waking in order to estimate the date of ovulation and to define menstrual cycle phases. Technician provided proper instructions and demonstrated the appropriate techniques before starting the tests. Values of forced expiratory volume at 1 s (FEV1), forced vital capacity (FVC), peak expiratory flow (PEF) and maximum voluntary ventilation (MVV) were tested. Spirometric values were verified in accordance with the standard of acceptability and criterion of reproducibility recommended by American Thoracic Society and European Respiratory Society (3). In connection with statistical analysis, the sample size was calculated to achieve a power of 0.95. Data indicated that a minimum of 23 participants were required. Reliability was determined according to the intraclass correlation coefficient (ICC) with 95% confidence intervals across the 3 test sessions. However, more information was needed to analyze how much difference must exist to detect a real variation in a spirometric variable, and therefore standard error of measurement (SEM) and smallest real difference (SRD) were studied as well. No significant change for flows and volumes were observed during the menstrual cycle (Table 1). All measurements had an intraclass correlation coefficient greater than 0.90. In addition, measurement errors were assessed. Values of SEM (SEM%) ranged from 2.2 % to 3.0 % and values of SRD (SRD%) ranged from 6.5 % to 8.3 …