Hypoventilation Therapy Alleviates Panic by Repeated Induction of Dyspnea

BACKGROUND: Previous research has shown that hypoventilation therapy reduces panic symptoms in part by increasing basal partial pressure of carbon dioxide (PCO2) levels. We tested an additional pathway by which hypoventilation therapy could exert its therapeutic effects: through repeated interoceptive exposure to sensations of dyspnea. METHODS: A total of 35 patients with panic disorder were trained to perform exercises to raise their end-tidal PCO2 levels using a portable capnometry device. Anxiety, dyspnea, end-tidal PCO2, and respiratory rate were assessed during each exercise across 4 weeks of training. Mixed-model analysis examined whether within-exercise levels of dyspnea were predictive of reduction of panicogenic cognitions. RESULTS: As expected, within-exercise anxiety and respiratory rate decreased over time. Unexpectedly, PCO2 dropped significantly from the beginning to the end of exercise, with these drops becoming progressively smaller across weeks. Dyspnea increased and remained consistently above basal levels across weeks. As hypothesized, greater dyspnea was related to significantly lower panicogenic cognitions over time even after controlling for anxiety and PCO2. Additional exploratory analyses showed that within-exercise increases in dyspnea were related to within-exercise increases in anxiety but were not related to within-exercise increases in PCO2. CONCLUSIONS: In support of the interoceptive exposure model, we found that greater dyspnea during hypoventilation exercises resulted in lower panicogenic cognitions even after the effect of PCO2 was taken into account. The findings offer an additional important target in panic treatment.