COMBAT Fellow Program Bios

John Hesling, MD is a graduate of the University of Colorado School of Medicine and fellow with the CU Anschutz Center for COmbat Medicine and BATtlefield (COMBAT) Research.

John served 11 years in the U.S. Navy as an F/A-18 Super Hornet pilot after graduating with distinction from the U.S. Naval Academy in 2008. He is a Navy Fighter Weapons School (TOPGUN) graduate and earned three Air Medals during combat operations in support of Operation Enduring Freedom in 2012 and Operation Inherent Resolve in 2017.

John's research characterizing Pediatric Supermassive Transfusion was published in the American Journal of Emergency Medicine. Additional research includes an assessment of Battlefield First Responders published in the U.S. Army Medical Department Journal and a F/A-18 tactical analysis published in the Naval Aviation Warfighting Development Center Journal.

John is completing his intern year in Internal Medicine at Saint Joseph’s Hospital in Denver and will complete his advanced residency training in Physical Medicine and Rehabilitation at the University of Colorado. He plans to pursue follow-on training in Interventional Pain or Interventional Spine.

Abhi is currently an Air Force civilian sponsored Emergency Medicine resident at the Denver Health Residency in Emergency Medicine. He graduated from the Icahn School of Mount Sinai with his MD and MPH focusing on global health. He initially commissioned into the United States Air Force through the Reserve Officer Training Corps (ROTC) at Boston University. His prior research has focused on global health (primarily in Uganda and Nepal), HIV Self-testing, and Neurotrauma outcomes. Following residency his goal is to continue to pursue global health program development, research, and operational medicine in his Air Force career.

Joe O'Brien, MD, MPH is a resident at the Denver Health Residency in Emergency Medicine and graduated from the Cleveland Clinic Lerner College of Medicine in 2025. Joe has 10 published peer-reviewed manuscripts and has delivered 12 research presentations at national conferences. As a COMBAT Fellow, he is interested in predictive modeling and prehospital medicine in austere settings.

Matt is a resident at the Denver Health Residency in Emergency Medicine and graduated from the University of Colorado’s Medical School in May 2023. Prior to medical school, Matt served as an Infantry Officer with the US Army’s 2nd Ranger Battalion and 10th Mountain Division. As a COMBAT Scholar and Fellow, his research interests focus on civilian and battlefield prehospital medicine. Matt has published 7 peer-reviewed manuscripts and has delivered 18 lectures and research presentations.

Matt founded a recurring Prehospital Trauma Lecture series which was featured in the Emergency Medical Minute podcast in 2023. He volunteers with the Three Rangers Foundation mentoring active duty Special Operations soldiers interested in transitioning to the world of civilian medicine.

Although born abroad in Ecuador, Daniel spent much of his childhood in Colorado Springs, Colorado. Growing up, he was influenced by several role models who were both military officers and physicians, which led him after high school to attend the college of his dreams, the U.S. Air Force Academy. While there, he enjoyed teaching younger cadets the basics of aviation as a soaring Instructor Pilot and studying Biology with the goal of attending medical school.

While at the University of Colorado for medical school, Daniel was quickly drawn to the world of surgery. He was impressed by the wide variety of anatomy and cutting-edge technology germane to vascular surgery after working closely with two attending vascular surgeons in Colorado Springs and San Antonio, Texas.

Daniel is deeply honored to have been selected through the military match for the University of Colorado’s Integrated Vascular Surgery Residency and looks forward to joining the long legacy of excellent military surgeons who have come before him. He is thrilled to join the CU Center for COMBAT Research, eager to learn from its outstanding mentors and contribute to high-impact military research, especially in the realm of vascular trauma, and hopes to continue the endeavor of surgical education throughout his active-duty career and beyond.

Outside of work, Daniel loves bodybuilding, skiing, enjoying various musical pursuits, watching Nuggets basketball, and spending time with his community of friends and family in Colorado.

Dr. Branson Taheri was born in Denver, Colorado and grew up in Casper, Wyoming. After completing high school, he attended the United States Air Force Academy in Colorado Springs, CO and completed a degree in computer science.

Branson proceeded from the U.S. Air Force Academy to medical school at the Uniformed Services University of the Health Sciences in Bethesda, Maryland. While in medical school, Dr. Taheri developed an interest in vascular surgery while working with a research group focused on investigating technology used to manage hemorrhagic and vascular trauma in both military and civilian settings. Dr. Taheri was selected through the military match process to join the University of Colorado’s integrated vascular surgery residency while continuing on active duty in the U.S. Air Force.

Outside of work, Branson enjoys playing and watching ice hockey, going to baseball games, and skiing. Dr. Taheri is excited for the opportunity to train at the University of Colorado and to gain the experience and skills needed to succeed in a career as an Air Force vascular surgeon.

Ricardo I. Villarreal is a current resident in the Department of Psychiatry and is a part of the Brain and Behavioral Innovation Center for novel mental health therapeutics research. He completed medical school at CU SOM as part of the CU MSTP program. He received his PhD from the Department of Microbiology and Immunology where he completed his thesis on neural inflammation.

Ricardo has published research findings in various biomedical fields and participated in clinical research investigating novel field devices for early medical intervention for the U.S. Army. As a previous COMBAT Scholar, his research focused on firearm safety in military and community members within the scope of suicide prevention.

Currently, Ricardo continues to engage in suicide prevention efforts with the hope of incorporating novel technological approaches in high-risk populations targeting common mental health conditions.

Coco Wham, MD, MS is a resident at the Denver Health Residency in Emergency Medicine and graduated from the University of Colorado Medical School in 2024. Dr. Wham is also a firefighter paramedic and has worked in EMS since 2012. She continues to be engaged on the frontlines as an EMS lieutenant and firefighter paramedic for a rural agency. She is also an instructor for the Counter Operations of Narcotics of Terrorism Operation Medical Support Unit and has spent time with a tactical medical unit associated with the Department of Health and Human Services. 

Dr. Wham also recently developed a prehospital research consortium that consisted of data from 85 EMS agencies across the state and over 40 receiving hospitals to link prehospital care and patient outcomes. As a COMBAT fellow, her research interests focus on the modeling of civilian prehospital medicine to help inform battlefield prehospital medicine.

She has been featured on several podcasts, including EMS Cast, discussing her most recent peer-reviewed publication that analyzed the ability of end-tidal capnography to predict morbidity and mortality in a cohort of injured patients.