Title: The Effect of Oestrogen and Progesterone on Ventilation and Respiratory Muscle Recruitment during Exercise in Hypoxia
Supervisors: Dr. Bill Sheel
Committee members: Dr. Michael Koehle, Dr. Janice Leung
Abstract: The ovarian hormones oestrogen (E2) and progesterone influence ventilatory (V̇e) control. They fluctuate throughout the eumenorrheic menstrual cycle (MC) to create the early follicular (EF) and midluteal (ML) phase. Post menopause, these hormones remain chronically low. There is evidence to suggest increased resting hypoxic V̇e response during the ML phase of the MC when hormones are high. Whether this occurs during intense exercise, and how chronically low hormone level affect the exercise response post menopause, compared to pre menopause, is unknown. PURPOSE: The purpose of this thesis is three-fold. The first is to determine the effect of menstrual cycle (MC) hormones oestrogen and progesterone on ventilation and respiratory muscle recruitment in hypoxia during constant load cycling exercise in the early follicular and midluteal phase of the MC in young females. The second is to determine the effect of chronically low oestrogen and progesterone concentration (as seen post menopause) on ventilation and respiratory muscle recruitment in hypoxia during constant load cycling exercise, and to compare this to the response seen in the young females. A third purpose is to investigate the correlation between progesterone and ventilation. HYPOTHESIS: I hypothesize that higher levels of progesterone in the ML phase compared to lower levels of progesterone in the EF phase of the MC will increase ventilation in hypoxia. A secondary hypothesis is that there is an increase in respiratory muscle recruitment in the ML phase compared to the EF phase. Contrarily, post menopause, when progesterone is chronically downregulated, respiratory muscle recruitment and ventilation will be lower in the older compared to younger.
METHODS: Trained females (n=28) will complete two (post menopause) or three (pre menopause) testing days. Healthy young females between 19 and 35 years of age will be recruited for this study. In total, 14 participants per age group (A priori: Compute required sample size, ƿ = 0.5, α error of probability = 0.05, 1-ß error of probability = 0.95) will be recruited. An effect (f=1.10) and total sample (n=11) was determined using data on a transient hypoxic test completed during the follicular and luteal phase of the menstrual cycle from Takano et al., 1984. However, given that menstrual cycle hormone fluctuations are of interest, a larger sample is appropriate given the potential variability in ventilatory responses to hormone concentration, and the small changes seen between participants (G*Power Software). Additionally, 14 post-menopausal females between 50-65 years will be recruited to compare to young females. On day one, pulmonary function and maximal oxygen uptake, on a cycle ergometer, will be measured. On day two (and three) participants will be fitted with gastric and esophageal balloon catheters, before completing 5 minutes of exercise at 70% of peak power in normoxia and hypoxia (two bouts each). Opto-electronic plethysmography (OEP) will be used to determine ribcage and abdominal respiratory muscle recruitment during exercise. We will determine MC phase from the participant’s two previous periods and confirm phase retrospectively with serum progesterone and E2 measurements. These will be measured prior to starting exercise. Postmenopausal females will be a minimum of one full year without a period. ANALYSIS: We will analyze the last 30 seconds of exercise. A within subject ANOVA will be used to assess the effect of phase on ventilation and respiratory muscle recruitment. A within-subject and between-subject ANCOVA will covary for oestrogen and progesterone concentration and age. If significance is found a Tukey’s Post Hoc test will be used to a significance of p< 0.05. Finally, a linear regression will be used to compare young and older females to account for ageing effects. Ventilation and hormone concentration will be compared via Pearson’s r Correlation, where a p < 0.05 is considered significant.