Deployed Veterans exhibit distinct respiratory patterns and greater dyspnea during maximal cardiopulmonary exercise: A case-control study

• Published in: PloS one Vol. 18; no. 5; p. e0286015
• Main Authors: Alexander, Thomas, Watson, Matthew A, Klein-Adams, Jacquelyn C, Ndirangu, Duncan S, Serrador, Jorge M, Falvo, Michael J, Lindheimer, Jacob B
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 24-05-2023; Public Library of Science (PLoS)
• Subjects: Anaerobic threshold; Analysis of Variance; Biology and Life Sciences; Calorimetry; Carbon dioxide; Care and treatment; Case-Control Studies; Contraindications; Diagnosis; Dyspnea; Exercise; Health aspects; Heart rate; Humans; Hypotheses; Intolerance; Mechanical ventilation; Medical screening; Medicine and Health Sciences; Metabolism; Military deployment; Military personnel; Outdoor air quality; Oxygen; Oxygen consumption; Physical fitness; Physical training; Pilot projects; Psychological aspects; Questionnaires; Ratings; Research and Analysis Methods; Respiration; Shortness of breath; Social Sciences; Spirometry; Variance analysis; Ventilation; Veterans; United States; Italy; Rome Italy; United States > US; New Jersey
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0286015

Exertional dyspnea and exercise intolerance are frequently endorsed in Veterans of post 9/11 conflicts in Southwest Asia (SWA). Studying the dynamic behavior of ventilation during exercise may provide mechanistic insight into these symptoms. Using maximal cardiopulmonary exercise testing (CPET) to experimentally induce exertional symptoms, we aimed to identify potential physiological differences between deployed Veterans and non-deployed controls.
Deployed (n = 31) and non-deployed (n = 17) participants performed a maximal effort CPET via the Bruce treadmill protocol. Indirect calorimetry and perceptual rating scales were used to measure rate of oxygen consumption ([Formula: see text]), rate of carbon dioxide production ([Formula: see text]), respiratory frequency (f R), tidal volume (VT), minute ventilation ([Formula: see text]), heart rate (HR), perceived exertion (RPE; 6-20 scale), and dyspnea (Borg Breathlessness Scale; 0-10 scale). A repeated measures analysis of variance (RM-ANOVA) model (2 groups: deployed vs non-deployed X 6 timepoints: 0%, 20%, 40%, 60%, 80%, and 100% [Formula: see text]) was conducted for participants meeting valid effort criteria (deployed = 25; non-deployed = 11).
Significant group (η2partial = 0.26) and interaction (η2partial = 0.10) effects were observed such that deployed Veterans exhibited reduced f R and a greater change over time relative to non-deployed controls. There was also a significant group effect for dyspnea ratings (η2partial = 0.18) showing higher values in deployed participants. Exploratory correlational analyses revealed significant associations between dyspnea ratings and fR at 80% (R2 = 0.34) and 100% (R2 = 0.17) of [Formula: see text], but only in deployed Veterans.
Relative to non-deployed controls, Veterans deployed to SWA exhibited reduced fR and greater dyspnea during maximal exercise. Further, associations between these parameters occurred only in deployed Veterans. These findings support an association between SWA deployment and affected respiratory health, and also highlight the utility of CPET in the clinical evaluation of deployment-related dyspnea in Veterans.