Brain pH response to hyperventilation in panic disorder: preliminary evidence for altered acid-base regulation.
OBJECTIVE
Previous findings of excess brain lactate and delayed end-tidal CO(2) (pCO(2)) recovery in subjects with panic disorder during hyperventilation suggested altered acid-base regulation. Two models were posited to explain these results: 1) subjects with panic disorder demonstrate greater alkalosis to hyperventilation, implicating increased lactate as directly compensatory, or 2) subjects with panic disorder demonstrate reduced or blunted alkalosis, implicating increased lactate as overly compensatory to a normal pH response. In both models, delayed pCO(2) recovery in subjects with panic disorder could reflect slower pH normalization in the recovery phase.


METHODS
Asymptomatic medicated patients with panic disorder were studied during regulated hyperventilation. Phosphorous spectroscopy was used to measure brain pH every 2 minutes. Nine subjects with panic disorder were compared to 11 healthy subjects at baseline (five scans), during regulated hyperventilation (five scans), and across recovery (10 scans). Anxiety symptoms were assessed with standard ratings.


RESULTS
No subject had a panic attack before hyperventilation. Subjects with panic disorder had lower pCO(2) during hyperventilation and slower pCO(2) recovery across the posthyperventilation interval. Despite this different respiratory response in the panic disorder group, brain pH increases were not significantly greater during hyperventilation, nor was pH return to baseline slowed during posthyperventilation. A linear regression model derived from data of healthy subjects showed pH blunting in the panic disorder group.


CONCLUSIONS
Although subjects with panic disorder had greater hypocapnea during hyperventilation, their observed pH response, not altered from comparison levels, implicated exaggerated buffering. It is suggested that increased lactate could account for these findings.
Department of Radiology, 1100 N.E. 45th St., Suite 555, Seattle, WA 98105, USA. sethf@u.washington.edu
Seth D
SD
Friedman
C Mark
CM
Mathis
Cecil
C
Hayes
Perry
P
Renshaw
Stephen R
SR
Dager
D000137:Acid-Base Imbalance / Q000378:metabolism*; D000471:Alkalosis / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006985:Hyperventilation / Q000097:blood / Q000378:metabolism*; D007773:Lactates / Q000097:blood / Q000378:metabolism; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data; D009682:Magnetic Resonance Spectroscopy / Q000706:statistics & numerical data; D008297:Male; D016584:Panic Disorder / Q000097:blood / Q000175:diagnosis* / Q000378:metabolism*; D010313:Partial Pressure; D010758:Phosphorus
D007773:Lactates; D002245:Carbon Dioxide; D010758:Phosphorus