Much research supports the relation between respiration and mood, and more particularly, between hypocapnia and negative affect. A review of breathing trainings has demonstrated that traditional breathing trainings do not target CO2 directly, which maintains or worsens chronic hypocapnia. Capnometry-Assisted Respiratory Training (CART) was developed to directly target increasing CO2 with patients with panic disorder through the use of a biofeedback device. It is less known whether the positive effects of CART generalize to other negative mood states, such as non-panic anxiety, since hyperventilation is a well-known response to stress and anxiety. Further, the relation between CO2 and depression has been less extensively examined in therapeutic contexts, which would be of great importance given the high comorbidity rate of anxiety and depression. The current study aimed to examine the mediating role of CO2 in symptom change during CART using a transdiagnostic sample. Over the course of two study cycles (2015-2018; 2018-2021), participants (N = 175) were randomized to the Negative Affect Treatment (NAT; n = 94) and the Positive Affect Treatment (n = 81). As part of the intervention, participants in NAT completed one module of CART (n = 82). Results indicated that increases in baseline PCO2 fully mediated changes in anxiety and depression at the next session, but not in stress or negative affect. Our findings support previous research on the efficacy of CART in increasing PCO2, which demonstrates a mediating role in reducing anxiety symptoms, extending generalizability of past findings to transdiagnostic populations. Further, our study is the first to find a causal relation between CO2 and symptoms of depression, in that increases in baseline PCO2 led to increases in symptoms of depression. Clinical implications and future directions are discussed.

Degree Date

Spring 2023

Document Type


Degree Name





Alicia Meuret, Ph.D.

Second Advisor

Thomas Ritz, Ph.D.

Number of Pages




Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License