• Masato Kobayashi, Takao Ayuse, Yuko Hoshino, Shinji Kurata, Hartmut Schneider, Jason P Kirkness, Alan R Schwartz, Kumiko Oi, Mari Kawai, and Susheel P Patil.
• Department of Clinical Physiology, Nagasaki University Graduate School of Biomedical Science, Nagasaki, 852-8588, Japan.
• J Clin Anesth. 2011 Nov 1;23(7):527-33.

Study ObjectiveTo determine the mechanical upper airway properties and compensatory neuromuscular responses to obstruction during propofol anesthesia in the follicular and luteal phases of the menstrual cycle.DesignProspective, randomized study.SettingUniversity-affiliated hospital.Subjects12 premenopausal female volunteers for studies of upper airway collapse throughout their menstrual cycle during the follicular phase (6 -10 days) and mid-late luteal phase (20 - 24 days).MeasurementsThe level of propofol anesthesia (1.5 - 2.0 μg/mL) required to suppress arousal responses was determined by Observer's Assessment of Alertness/Sedation scoring (level 2) and confirmed by bispectral index monitoring. Pressure-flow relationships were constructed to evaluate collapsibility (P(CRIT)) and up-stream resistance (R(US)) during acute [Passive; hypotonic electromyography (EMG)] and sustained (Active; elevated EMG) changes in nasal mask pressure. The difference between passive P(CRIT) and active P(CRIT) (ΔP(CRIT A-P)) represented the magnitude of the compensatory response to obstruction.Main ResultsPassive P(CRIT) was significantly higher in the mid-late luteal phase (-4.7 cm H(2)O) than in the follicular phase (-6.2 cmH(2)O; P < 0.05). Active P(CRIT) significantly decreased compared with passive P(CRIT) in the follicular phase (-10.1 cm H(2)O) and in the mid-late luteal phase (-7.7 cm H(2)O) and (P < 0.05). No significant difference was noted in ΔP(CRIT) between the follicular (3.9 ± 2.9 cm H(2)O) and mid-late luteal phases (3.0 ± 2.6 cm H(2)O). No differences were seen in R(US) between the menstrual phases for either the passive (P = 0.8) or active (P = 0.75) states.ConclusionsMenstrual phase has an effect on anatomical alterations (mechanical properties) in the hypotonic upper airway during propofol anesthesia.Copyright © 2011 Elsevier Inc. All rights reserved.

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