The evaluation of the cerebral blood flow with SPECT imaging during panic attack induced by CO2 inhalation in patients with panic disorder

Introduction: The investigations concerning patophysiology of panic disorder are still going on. The studies evaluating the cerebral hemodynamic features are being used to put forward the etiopathogenesis of panic disorder.Purpose: The aim of the present study was to evaluate whether there would be a difference in the regional cerebral blood flow (rCBF) of parahippocampal, hippocampal, temporal regions and basal ganglia between the patients with panic disorder and healthy volunteers, measured by Tc-99m-HMPAO (Technetium- Hexamethylpropylenamine) SPECT in resting baseline condition and after 5 % CO2 inhalation. Additionally, rCBF changes in the patients who had panic attack, who did not have panic attack and healthy volunteers who did not have panic attack were compared after 5 % CO2 inhalation as well.Method: Fourteen unmedicated panic disorder patients without any additional psychiatric and medical ilness and 11 healthy volunteers were included in the study. In the first visit the subjects were evaluated by HAM-D, HAM-A, PDSS, PAS and ASI scales. Before the resting baseline condition, the subjects were given Visual Analog Sale (VAS) and Acute Panic Inventory (API) and then Tc-99m-HMPAO SPECT measurements were performed. At least two days after the initial SPECT measurements, the second SPECT measurements were performed to the subjects (12 Panic patients and 11 healthy volunteers) after 5 % CO2 inhalation by 20 minute steady ? state method. The subjects were evaluated again by VAS and API scales both after the CO2 inhalation (before SPECT measurement) and after the SPECT measurement. Patients who had panic attack were identified according to patients? feedback, clinical observation, and VAS and API scores. SPECT imaging was performed at (?) 35 seconds and 128 frames with 128x128 matrix, using double head (?) gamma camera (FORTE, PHILIPS) and LEHR collimator.Findings: No difference was found in rCBF measurements between patients with panic disorder and healthy volunteers in the resting baseline condition. Additionally, no significant difference was found in rCBF measurements after 5 % CO2 inhalation between the patients who had a panic attack (n = 5) and who did not have panic attack (n = 7) and healthy volunteers who had not panic attack (n = 10) either. The changes in rCBF during resting baseline condition and after CO2 inhalation were not statistically significant between these three groups. However, statistically significant difference (p = 0.04) was found in rCBF of right parahippocampal gyrus between patients who had panic attack and those who did not have.Result: In our study, no significant difference was found between patients with panic disorder and healthy volunteers in rCBF of parahippocampal, hippocampal and temporal regions which were proposed to be important neuroanatomic structures in the pathophysiology of panic disorder and in which contradictory results were detected in previous studies. In addition, no significant difference was detected in the rCBF changes after 5 % CO2 inhalation with respect to the resting baseline condition in patients having panic attack, patients not having panic attack and healthy volunteers. We might not detect this probable change, since we did not predict to which degree 5 % CO2 inhalation affect blood pCO2 levels due to methodologic limitations. However, after 5 % CO2 inhalation a significant difference (p = 0.04) was detected in rCBF between the patients having panic attack and the patients not having panic attack. This difference might result from minimal decrease detected in rCBF in the patients having panic attack due to severe anxiety and from minimal increase detected in rCBF in the patients not having panic attack who had mild anxiety due to habituation in the experimental setting.