VENTILATORY RESPONSES TO LOAD CARRIAGE IN NORMOXIA AND HYPOXIA
Beverley K. Buchanan, Abaigeal G. Doody, Miles J. Ortiz, Katherine G. Baur, Daniel A. Baur. Virginia Military Institute, Lexington, VA.
BACKGROUND: Soldiers are required to operate in high altitude environments while carrying heavy loads. This study investigates how load carriage affects the ventilatory response in normoxic and hypoxic environments (simulated altitude of ~3,650 m) in order to improve military training and preparedness. METHODS: Healthy male subjects (n=10) performed 3 exercise tests on a treadmill consisting of the following conditions: 1) unloaded normoxic (UL: FiO2=20.93%), 2) loaded (~30 kg) normoxic (LN), and 3) loaded hypoxic simulating 3,650 m (LH: FiO2=~13%). Exercise consisted of 2 x 10 min walking (separated by 5 min rest) with stages matched with the UL condition for absolute VO2 (1.7 L/min), and walking velocity (1.45±0.15 m/s). Breath-by-breath analysis via an automated metabolic system was used to determine ventilatory responses including ventilation (VE), tidal volume (VT), and breathing frequency (fB). Data were analyzed via two-way repeated measures ANOVA with post hoc one-way ANOVA tests to identify differences in the case of significant interactions (α=0.05). RESULTS:At rest, VE increased with LH (11.4 ± 2.4 L/min) versus UL (9.8 ± 1.5 L/min; p = 0.015) and LN (10.2 ± 1.6 L/min; p = 0.008). At the same absolute intensity, there was an increase in VT with LH (1.7 ± 0.4 L) versus LN (1.5 ± 0.3 L; p = 0.007), and a trend for an increase with UL (1.9 ± 0.6 L) relative to LN (p = 0.065). Also, VE was higher with LH (58.1 ± 6.5 L/min) versus UL (43.7 ± 3.3; p < 0.001), and LN (44.9 ± 2.9 L/min; p < 0.001). Finally, there were differences in fB across all conditions (UL: 25.5 ± 6.5; LN: 30.0 ± 5.1; LH: 35.8 ± 9.6; p < 0.05). At matched velocity, there were stepwise increases in VE (UL: 44.3 ± 3.4 L/min; LN: 71.5 ± 17.9 L/min; LH: 98.8 ± 22.9 L/min; p < 0.01) and fB (UL: 26.4 ± 7.2 b/min; LN: 38.2 ± 9.8 b/min; LH: 46.4 ± 13.3 b/min; p < 0.01) across conditions, and VT was increased with LH (2.2 ± 0.3 L) versus LN (1.9 ± 0.3 L; p < 0.001). CONCLUSIONS: Load carriage seems to result in shallower breathing patterns in normoxia and hypoxia. This likely compensatory breathing mechanism may increase the respiratory muscle load and impair a soldier’s capacity to march for prolonged periods of time.Grant or funding information: This study was funded by the Jackson Hope New Directions in Research grant.
Buchanan, BK; Doody, AG; Ortiz, MJ; Baur, KG; and Baur, DA
"VENTILATORY RESPONSES TO LOAD CARRIAGE IN NORMOXIA AND HYPOXIA,"
International Journal of Exercise Science: Conference Proceedings: Vol. 16:
2, Article 65.
Available at: https://digitalcommons.wku.edu/ijesab/vol16/iss2/65