Fearful imagery induces hyperventilation and dyspnea in medically unexplained dyspnea

Background Medically unexplained dyspnea refers to a condition characterized by a sensation of dyspnea and istypically applied to patients presenting with anxiety and hyperventilation without underlying cardiopulmonary pathology.We were interested to know how anxiety triggers hyperventilation and elicits subjective symptoms in those patients.Using an imagery paradigm,we investigated the role of fearful imagery in provoking hyperventilation and in elicitingsymptoms,specifically dyspnea.Methods Forty patients with medically unexplained dyspnea and 40 normal subjects matched for age and gender wereexposed to scripts and asked to imagine both fearful and restful scenarios,while end-tidal PCO2（PetCO）and breathingfrequency were recorded and subjective symptoms evaluated.The subject who had PetCOfalling more than 5 mmHgfrom baseline and persisting at this low level for more than 15 seconds in the imagination was regarded as ahyperventilation responder.Results In patients with medically unexplained dyspnea,imagination of fearful scenarios,being blocked in an elevatorin particular,induced anxious feelings,and provoked a significant fall in PetCO（P<0.05）.Breathing frequency tended toincrease.Eighteen out of 40 patients were identified as hyperventilation responders compared to 5 out of 40 normalsubjects（P<0.01）.The patients reported symptoms of dyspnea,palpitation or fast heart beat in the same fearful scriptimagery.Additionally,PetCOfall was significantly correlated with the intensity of dyspnea and palpitation experiencedduring the mental imagery on one hand,and with anxiety symptoms on the other.Conclusions Fearful imagery provokes hyperventilation and induces subjective symptoms of dyspnea and palpitationin patients with medically unexplained dyspnea.