BDNF and depressive symptom measurement: It has been suggested that anxiety and depression may cause HVS through increased levels of stress hormones, which can lead to hyperventilation.[28] In addition, psychological factors may exacerbate HVS symptoms through increased awareness of breathing patterns and negative thoughts about the symptoms.[29] Therefore, in our study, we grouped all HVS patients according to HAMD scores and detected the levels of 2 depression-related serum markers, 5-HT and BDNF, in both patient groups.