title: The biphasic pattern of end-expiratory carbon dioxide pressure: a method for identification of the fertile phase of the menstrual cycle.
abstract: OBJECTIVE
  To examine the changes of end-tidal carbon dioxide pressure (P(ET)CO(2)) during the menstrual cycle.
  
  
  METHODS
  Controlled clinical study.
  
  
  METHODS
  Department of Gynecologic Endocrinology and Reproductive Medicine, Medical University of Innsbruck, Austria.
  
  
  METHODS
  One hundred sixty women with a history of regular menstrual cycles were studied.
  
  
  METHODS
  The P(ET)CO(2) was determined once daily. Monitoring of the cycles was performed by ultrasonography and determination of E(2), P, and LH in blood or LH in urine samples.
  
  
  METHODS
  The changes in P(ET)CO(2) during the ovulatory and anovulatory cycles were analyzed.
  
  
  RESULTS
  The time course of P(ET)CO(2) followed a biphasic pattern with luteal phase values being on average 6.5 +/- 2.5 mm Hg lower than during the follicular phase. The decrease of P(ET)CO(2) started, coincident with the increase of E(2), 1-8 days (median: 4.5 days) before onset of the LH surge. No such changes in P(ET)CO(2) could be observed during the anovulatory cycles. These changes could be mimicked by administration of E(2) or P. The P(ET)CO(2) did not exhibit a circadian rhythm and was not influenced by normal physical activity.
  
  
  CONCLUSIONS
  The P(ET)CO(2) changes in a characteristic way during the menstrual cycle. Determination of P(ET)CO(2) appears to be a promising method for the detection of the fertile phase of the menstrual cycle in the context of natural family planning.
authors.affiliation: Department of Gynecologic Endocrinology and Reproductive Medicine, Medical University of Innsbruck, Innsbruck, Austria.
authors.forename: Dijana
authors.initials: D
authors.lastname: Hadziomerović
authors.forename: Kay Thomas
authors.initials: KT
authors.lastname: Moeller
authors.forename: Peter
authors.initials: P
authors.lastname: Licht
authors.forename: Achim
authors.initials: A
authors.lastname: Hein
authors.forename: Stephan
authors.initials: S
authors.lastname: Veitenhansel
authors.forename: Martina
authors.initials: M
authors.lastname: Kusmitsch
authors.forename: Ludwig
authors.initials: L
authors.lastname: Wildt
mesh_terms: D000293:Adolescent; D000328:Adult; D001944:Breath Tests / Q000379:methods*; D002245:Carbon Dioxide / Q000032:analysis*; D045853:Exhalation / Q000502:physiology*; D005260:Female; D046910:Fertile Period / Q000502:physiology*; D006801:Humans; D010061:Ovulation Detection / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D002245:Carbon Dioxide