Current Research

CO2 Tolerance and Anxiety Study

CO2 Tolerance and Anxiety Study

Firefighter Performance Program

Firefighter Performance Program

Microbiome Study

Microbiome Study


CO2 Tolerance And Anxiety Study

HHPF has been helping researchers at California State University, Fullerton evaluate use of a timed exhale CO2 tolerance test (CO2TT) as an index of anxiety in healthy adults.

The study was a 2-visit, single-arm pilot evaluating the feasibility and effectiveness of a timed exhale test — the CO2TT — as a quick, easy-to-use, equipment-free tool for diagnosing short-term (“state”) and long-term (“trait”) anxiety among healthy adults.

Performance on the CO2TT was found negatively correlated with state anxiety. In other words, people with higher CO2TT results had lower in-the-moment anxiety, while those with lower CO2TT had higher in-the-moment anxiety.

This line of research aims to 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.

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

Collaborator: California State University, Fullerton


Firefighter Performance PROGRAM

HHPF has designed a program to help improve the health, performance, and experiences of firefighters. The program involves a simple breathing exercise to be done 3 times/week for 6 weeks, and a firefighting activity simulation to be done at the beginning and end of the 6-week period.

HHPF has partnered with the Henderson Fire Department to implement this program and, after its completion, to evaluate its effectiveness on firefighter stress, performance, & work-related burnout.

Findings from this program will be used to determine if it should be implemented on a broader scale at this and/or other fire departments, and to guide the design of a clinical trial of breath practices among the firefighter population.

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

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