The purpose of the present study is to determine whether there are sex differences in the reflex responses to hypoxia in humans.

Over 35% of the US population will develop sleep apnea at some point in their life. Sleep apnea is the most common form of sleep disordered breathing and patients with sleep apnea are at increased risk of developing high blood pressure. Intermittent, repeated exposures to low oxygen during sleep (intermittent hypoxia, IH) has been implicated as the primary stimulus for increases in sympathetic nervous system activity and blood pressure with sleep apnea. Interestingly there are some reports of a lower incidence of hypertension in women with sleep apnea when compared to men. Results from the present study will provide information important to the investigator's understanding of potential sex-differences in clinical outcomes for conditions related to acute/chronic hypoxia and may have important implications for treatments which may improve blood pressure control in patients with sleep apnea.

Inclusion Criteria:

• healthy adult men and women;
• BMI <30 kg/m2;
• non-pregnant;
• non-breastfeeding;
• non-smokers;
• premenopausal women with a normal menstrual cycle unaffected by hormonal contraceptive use;
• taking no medications known to affect autonomic or cardiovascular function (PI discretion).

Exclusion Criteria:

• taking any medications known to affect the cardiovascular or autonomic nervous system (e.g. alpha-blockers, beta-blockers, etc);
• a self-reported history of hepatic, renal, pulmonary, cardiovascular, or neurological diseases;
• stroke or neurovascular disease;
• bleeding/clotting disorder;
• sleep apnea or other sleep disorders;
• diabetes;
• smoking;
• history of alcoholism or substance abuse;
• hypertension.