The biphasic pattern of end-expiratory carbon dioxide pressure: a method for identification of the fertile phase of the menstrual cycle  Dijana Hadžiomerović, M.D., Kay Thomas Moeller, M.D., Peter Licht, M.D., Achim Hein, M.D., Stephan Veitenhansel, M.D., Martina Kusmitsch, M.D., Ludwig Wildt, M.D.  Fertility and Sterility  Volume 90, Issue 3, Pages 731-736 (September 2008) DOI: 10.1016/j.fertnstert.2007.06.078 Copyright © 2008 American Society for Reproductive Medicine Terms and Conditions

Figure 1 Time course of end-tidal carbon dioxide pressure (PETCO2), basal body temperature (BBT), LH, E2, and P during a menstrual cycle of a 25-year-old female volunteer. The data are normalized to the day of the LH surge as day 0. The decrease of PETCO2 starts 4 days before the LH peak and 5 days before the increase in BBT. A follicle with 12 mm in diameter could be identified by ultrasonography on day −4. Fertility and Sterility 2008 90, 731-736DOI: (10.1016/j.fertnstert.2007.06.078) Copyright © 2008 American Society for Reproductive Medicine Terms and Conditions

Figure 2 Time course of end-tidal carbon dioxide pressure (PETCO2) during 150 ovulatory menstrual cycles normalized to the day of the onset of the LH surge as day 0. Values are expressed as percentage of the baseline PETCO2. The arrow indicates the day when PETCO2 was for the first time significantly lower than baseline, as determined by CUSUM method. Data represent mean ± SD of at least 120 observations per day. Fertility and Sterility 2008 90, 731-736DOI: (10.1016/j.fertnstert.2007.06.078) Copyright © 2008 American Society for Reproductive Medicine Terms and Conditions

Figure 3 Temporal relationship between the start of the preovulatory E2 increase and the decrease of end-tidal carbon dioxide pressure (PETCO2) in 150 ovulatory cycles (solid lines). The PETCO2 decreases when E2 is increasing. The data for anovulatory cycles (n = 5, dotted lines) are given for comparison. Data are expressed as percentage of baseline values, calculated from the first 5–7 days of the cycle and represent mean ± SD. Open circles, E2; solid circles, PETCO2. The error bars for the data points representing anovulatory cycles show + SD for E2 and − SD for PETCO2. Day 0 represents the last day with E2 at baseline levels in ovulatory cycles; days 10–12 were designated arbitrarily as day 0 in anovulatory cycles. Fertility and Sterility 2008 90, 731-736DOI: (10.1016/j.fertnstert.2007.06.078) Copyright © 2008 American Society for Reproductive Medicine Terms and Conditions

Figure 4 Left panel: Effect of P, administered as vaginal suppository containing 600 mg of P in six women in whom ovarian function had been temporarily suppressed by treatment with a GnRH analogue, on end-tidal carbon dioxide pressure (PETCO2). Note the decrease of PETCO2 (closed circles) as soon as P increasing to more than 1–2 ng/mL. The figure shows mean ± SD of data from six women. Middle panel: Effect of E2 on PETCO2 in four women treated with a GnRH analogue 3 weeks earlier. The E2 was administered transdermally. The serum concentrations of E2 did increase abruptly in four women to preovulatory levels. In these women, PETCO2 decreased, whereas in two women, shown on the right panel, in whom E2 did not increase substantially during the observation period, no change of PETCO2 was observed. The E2 levels are depicted with open circles, the values for PETCO2 are represented by solid circles. Data points represent means and SD. Fertility and Sterility 2008 90, 731-736DOI: (10.1016/j.fertnstert.2007.06.078) Copyright © 2008 American Society for Reproductive Medicine Terms and Conditions