fMRI responses to cold pressor challenges in control and obstructive sleep apnea subjects.
Obstructive sleep apnea (OSA) patients exhibit altered sympathetic outflow, which may reveal mechanisms underlying the syndrome. We used functional MRI (fMRI) in 16 control and 10 OSA subjects who were free of cardiovascular or mood-altering drugs to examine neural responses to a forehead cold pressor challenge, which elicits respiratory slowing, bradycardia, and enhanced sympathetic outflow. The magnitude of cold-induced bradycardia was smaller, and respiratory slowing showed greater intersubject variability and reached a nadir later in OSA patients. Both groups showed similar signal changes to cold stimulation in multiple brain sites. However, signal increases emerged in OSA over controls in anterior and posterior cingulate and cerebellar and frontal cortex, whereas signals markedly declined in the ventral thalamus, hippocampus, and insula rather than rising as in controls. Anomalous responses often paralleled changes in breathing and heart rate. Medullary, midbrain areas and lentiform and cerebellar dentate nuclei also showed lower signals in OSA cases. Cold pressor physiological responses are modified in OSA and may result from both diminished and exaggerated responses in multiple brain structures.
Harper
Ronald M
RM
Departments of Neurobiology, Radiology, and Neurology, School of Nursing, and Brain Research Institute, University of California at Los Angeles, Los Angeles, California 90095, USA. rharper@ucla.edu
Macey
Paul M
PM
Henderson
Luke A
LA
Woo
Mary A
MA
Macey
Katherine E
KE
Frysinger
Robert C
RC
Alger
Jeffry R
JR
Nguyen
Khanh P
KP
Yan-Go
Frisca L
FL
D000328:Adult; D001794:Blood Pressure; D001921:Brain / Q000503:physiopathology*; D016022:Case-Control Studies; D016000:Cluster Analysis; D003080:Cold Temperature; D006339:Heart Rate; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015656:Respiratory Mechanics; D012891:Sleep Apnea Syndromes / Q000175:diagnosis* / Q000503:physiopathology*