• Hypoxic Burden [ Time Frame: one month ]
  Desaturation area under curve × event frequency
• Arousal index [ Time Frame: one month ]
  Scored EEG arousals per hour (>3 s), % change from baseline
• Epworth Sleepiness Scale [ Time Frame: one month ]
  Self-reported sleepiness on scale of 0-24, higher being more sleepy
• Functional Outcomes of Sleep Questionnaire, Short Form [ Time Frame: one month ]
  Disease-specific quality of life
• Sleep Apnea Quality of Life Index, Short Form [ Time Frame: one month ]
  Disease-specific quality of life

• Hypoxic Burden [ Time Frame: one month ]
  Desaturation area under curve × event frequency
• Arousal index [ Time Frame: one month ]
  Scored EEG arousals per hour (>3 s), % change from baseline
• Epworth Sleepiness Scale [ Time Frame: one month ]
  Self-reported sleepiness
• Functional Outcomes of Sleep Questionnaire [ Time Frame: one month ]
  Disease-specific quality of life

Aim 1 - Effect of AtoOxy on sleep apnea severity. In a randomized controlled double-blind crossover study, 48 patients with moderate-to-severe OSA will take atomoxetine-plus-oxybutynin ("AtoOxy") versus placebo nightly for 1 month, with a 2-week washout in between. The investigators will test the hypothesis that AtoOxy reduces the Apnea-hypopnea index (primary outcome measure), and improves the following secondary outcomes:

• Nocturnal oxygenation, per "hypoxic burden of sleep apnea"
• Frequency of arousals from sleep (Arousal index)
• Self-reported sleepiness (Epworth Sleepiness Scale)
• Disease-specific quality of life (Functional Outcomes of Sleep Questionnaire, Short Form).
• Disease-specific quality of life (Sleep Apnea Quality of Life Index, Short Form)

Additional pre-specified exploratory outcome measures will be assessed, including Visual Analog Scales (Sleep Quality, Treatment Satisfaction) and additional polysomnographic measures of sleep (Stage 1 sleep, %total sleep time). Adherence and adverse events will also be carefully monitored to assess repeated-dose tolerance of the intervention.

Aim 2 - Determine which patient phenotypes respond best to AtoOxy. Patients will also take part in an additional night before initiating study medication to measure the key mechanisms causing OSA. The investigators will prospectively test the hypothesis that greater pharyngeal collapsibility determines a reduced response to therapy. They will also separately test the hypotheses that a reduced muscle responsiveness, reduced baseline muscle activation, a higher arousal threshold, and a lower loop gain will facilitate a greater response to therapy.

• Drug: Atomoxetine
  Atomoxetine 80 mg, per mouth, before bed
  Other Name: Strattera
• Drug: Oxybutynin
  Oxybutynin 5 mg, per mouth, before bed
  Other Name: Ditropan
• Drug: Placebo
  Placebo, per mouth, before bed

• Experimental: Atomoxetine and Oxybutynin
  Participants will take Atomoxetine and Oxybutynin nightly for one month. Half doses will be given on the first three nights.
  Interventions:

  • Drug: Atomoxetine
  • Drug: Oxybutynin
• Placebo Comparator: Placebo
  Participants will take Placebos nightly for one month. Half doses will be given on the first three nights.
  Intervention: Drug: Placebo

Inclusion criteria:

• Ages 21-70 years
• Diagnosed OSA or clinically-suspected OSA
• Not using CPAP (>1 month).

Exclusion criteria:

• Any uncontrolled medical condition
• Current use of the medications under investigation
• Use of medications expected to stimulate or depress respiration (including opioids, barbiturates, doxapram, almitrine, theophylline, 4-hydroxybutanoic acid).
• Current use of hypnotic medications (trazodone, eszopiclone, benzodiazepines).
• Current use of SNRIs/SSRIs or anticholinergic medications.
• Conditions likely to affect obstructive sleep apnea physiology: neuromuscular disease or other major neurological disorder, heart failure (also below), or any other unstable major medical condition.
• Respiratory disorders other than sleep disordered breathing:

chronic hypoventilation/hypoxemia (awake SaO2 < 92% by oximetry) due to chronic obstructive pulmonary disease or other respiratory conditions.

• Other sleep disorders: periodic limb movements (periodic limb movement arousal index > 10/hr), narcolepsy, or parasomnias.

• Contraindications for atomoxetine and oxybutynin, including:

  • hypersensitivity to study drugs (angioedema or urticaria)
  • pheochromocytoma
  • use of monoamine oxidase inhibitors
  • benign prostatic hypertrophy, urinary retention
  • untreated narrow angle glaucoma
  • bipolar disorder, mania, psychosis
  • history of major depressive disorder (age<24).
  • history of attempted suicide or suicidal ideation within one year prior to screening
  • clinically significant constipation, gastric retention
  • pre-existing seizure disorders
  • clinically-significant kidney disorders (eGFR<60 ml/min/1.73m2)
  • clinically-significant liver disorders
  • clinically-significant cardiovascular conditions
  • severe hypertension (SBP>180 mmHg or DBP>110 mmHg measured at baseline)
  • cardiomyopathy (LVEF<50%) or heart failure
  • advanced atherosclerosis
  • history of cerebrovascular events
  • history of cardiac arrhythmias e.g., atrial fibrillation, QT prolongation
  • other serious cardiac conditions that would raise the consequences of an increase in blood pressure or heart rate
  • myasthenia gravis
  • pregnancy/breast-feeding
• Allergy to lidocaine (Aim 2 only)
• Claustrophobia
• Pregnancy or nursing