Concurrent evaluation of cerebral oxygen metabolism and upper airway architecture via temporally resolved MRI.

Abstract

Obstructive sleep apnea (OSA) disrupts the oxygen supply during apneic and hypopneic events. To evaluate the feasibility of concurrently monitoring cerebral metabolic rate of oxygen (CMRO₂) and airway anatomy, a magnetic resonance imaging (MRI) pulse sequence was developed that interleaves measurements of CMRO₂ with anatomic imaging of the upper airway at a temporal resolution of 5 seconds. The sequence was first tested in healthy subjects during wakefulness to detect the effect of volitional breath-hold and swallowing apneas on neuro-metabolic parameters and airway morphology. Subsequently, select patients with diagnosed OSA and healthy reference subjects were scanned during 90 minutes of wakefulness and sleep with concurrent electroencephalographic (EEG) monitoring and airway plethysmography. During non-rapid eye movement sleep, changes in metabolic parameters caused by neurovascular-metabolic uncoupling were detected, resulting in sleep-stage dependent reductions in the CMRO₂. Spontaneous apneas were visible in airway images and confirmed plethysmographically. Recurrent apneas in patients during N1 and N2 sleep led to increased SvO₂ and CBF (hypercapnic-hypoxic response) and decreases in SaO₂ (hypoxemic response from airway closure) resulting in CMRO₂ reductions as large 60%. The results demonstrate the MRI potential of noninvasive assessment of the dynamic changes in airway anatomy and brain metabolism in OSA during sleep.