Current Research

CO2 Tolerance and Anxiety Study

CO2 Tolerance and Anxiety Study

Firefighter Performance Study

Firefighter Performance Study

Microbiome Study

Microbiome Study


CO2 Tolerance And Anxiety Study

HHPF is helping researchers at California State University, Fullerton evaluate use of a timed exhale CO2 tolerance test as an index of anxiety in healthy adults.

The study is a 2-visit, single-arm pilot evaluating the feasibility and effectiveness of a timed exhale test as a quick, easy-to-use, equipment-free tool for diagnosing short-term (“state”) and long-term (“trait”) anxiety among healthy adults.

The study also examines the connections between breathing and anxiety, particularly at nonclinical levels.

Insights gained from this pilot will be used to design a longer-term, randomized trial.

This line of research will identify and test simple ways to measure the impact of stress on respiratory physiology, so we can ultimately evaluate the effectiveness of breath-related interventions in measuring and addressing physiological (CO2 “tolerance”) and psychological (measures of anxiety) responses to stress.

Collaborator: California State University, Fullerton


Firefighter Performance STUDY

A Pilot Study of Interventions for Improving Firefighter Health & Performance

HHPF is collaborating with Dartmouth College and the Henderson, KY fire department to conduct a 6-week, single-arm pilot (N=20) evaluating the feasibility and effectiveness of a 12-minute, 3x/week diaphragmatic breathing intervention on firefighter performance during a simulated firefighting activity.

The study also assesses the effectiveness of this practice on firefighter stress & work-related burnout.

Findings from this pilot will be used to design a larger randomized and controlled followup study.

Our goal is to find and test simple ways to keep firefights healthy, performing well and staying on-the-job.

The study is currently under IRB review and will begin after IRB approval has been granted.

Collaborators: Dartmouth College and Henderson, Kentucky Fire Department



HHPF is helping researchers at San Francisco State University (SFSU) conduct an investigation of the gut-muscle-brain axis in a 2-week aerobic exercise training study.

The study is 3-arm randomized trial evaluating changes in gut microbiota composition associated with a 2-week training program comprising either:

  • Aerobic exercise only

  • Nasal breathing training only

  • Aerobic exercise + nasal breathing

The study will also assess associations between changes in gut microbiota and aerobic fitness and vagal modulation.

Findings will help us more thoroughly understand the complex and multi-dimensional relationship between gut microbiota, fitness, and our nervous system.

The study is currently under IRB review and will begin after IRB approval has been granted.

Collaborator: San Francisco State University


Related Publications

Gregory J. Grosicki, Roger A. Fielding, Michael S. Lustgarten, Gut Microbiota Contribute to Age-Related Changes in Skeletal Muscle Size, Composition, and Function: Biological Basis
for a Gut-Muscle Axis

P. Durk, Ryan & Castillo, Esperanza & Márquez-Magaña, Leticia & Grosicki, Greg & Bolter, Nicole & Matthew Lee, C & Bagley, James. (2018). Gut Microbiota Composition Is Related to Cardiorespiratory Fitness in Healthy Young Adults. International Journal of Sport Nutrition and Exercise Metabolism. 1-15. 10.1123/ijsnem.2018-0024.


Breath and Stress Systematic Literature Review

HHPF is conducting a systematic review of peer-reviewed, published literature examining effectiveness of intentional breathing practices on anxiety and stress outcomes.

  • We will disseminate findings to identify gaps in the literature and recommend directions for future research.

Collaborator: University of Southern California, California State University, Fullerton