The effects of hormonal status on upper airway patency in normal female subjects during propofol anesthesia

Study Objective: To 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. Design: Prospective, randomized study. Setting: University-affiliated hospital. Subjects: 12 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). Measurements: The 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 Results: Passive P _CRIT was significantly higher in the mid-late luteal phase (-4.7 cm H ₂O) than in the follicular phase (-6.2 cmH ₂O; P < 0.05). Active P _CRIT significantly decreased compared with passive P _CRIT in the follicular phase (-10.1 cm H ₂O) and in the mid-late luteal phase (-7.7 cm H ₂O) and (P < 0.05). No significant difference was noted in ΔP _CRIT between the follicular (3.9 ± 2.9 cm H ₂O) and mid-late luteal phases (3.0 ± 2.6 cm H ₂O). No differences were seen in R _US between the menstrual phases for either the passive (P = 0.8) or active (P = 0.75) states. Conclusions: Menstrual phase has an effect on anatomical alterations (mechanical properties) in the hypotonic upper airway during propofol anesthesia.