PROTON MAGNETIC-RESONANCE SPECTROSCOPY INVESTIGATION OF HYPERVENTILATION IN SUBJECTS WITH PANIC DISORDER AND COMPARISON SUBJECTS

Objective: The purpose of this study was to investigate differential e ffects of hyperventilation on brain lactate in patients with panic dis order and comparison subjects as a possible mechanism for explaining p revious observations of an excess rise in brain lactate among panic di sorder subjects during lactate infusion. Method: Seven treatment-respo nsive patients with panic disorder and seven healthy comparison subjec ts were studied with proton magnetic resonance spectroscopy to measure brain lactate during controlled voluntary hyperventilation over a per iod of 20 minutes. Hyperventilation was regulated with the use of capn ometry to maintain end-tidal PCO2 at approximately 20 mm Hg during the period of hyperventilation. Blood lactate was measured prior to and a t the end of hyperventilation. Results: At baseline the two groups had similar brain lactate levels. Panic disorder subjects exhibited signi ficantly greater rises in brain lactate than comparison subjects in re sponse to the same level of hyperventilation. Blood lactate levels bef ore and after 20 minutes of hyperventilation were not significantly di fferent between groups. Conclusions: Controlled hyperventilation incre ases brain lactate and does so disproportionately in subjects with pan ic disorder. This increase in brain lactate may result from decreased cerebral blood flow due to hypocapnia, and individuals with panic diso rder may have greater sensitivity to this regulatory mechanism.