Rationale:Static apnoeas performed after an overnight fast as opposed to postprandially have been evinced to improve apnoeic performance. However, no study has explored the effect of dietary intake on apnoeic performance, cardiovascular nor splenic responses over a series of repeated apnoeas. Method:Ten healthy adults attended the laboratory on three separate occasions (≥48-h apart) after: a 14-h fast (F14), 1-h post consumption of a high-calory-high-carbohydrate (HCHC) or a low-calory-low-carbohydrate (LCLC) based-meal. During each visit the subjects performed a hyperoxic rebreathing trial and a series of three repeated maximal static apnoeas. Heart rate, peripheral oxyhaemoglobin saturation (SpO2) and gas exchange were monitored continuously whereas splenic volume (SV) and haematology were assessed after the rebreathing and apnoeas. Results:At rest, after HCHC the respiratory exchange ratio (0.87±0.17,p≤0.043), expired minute volume of carbon dioxide (CO2) (HCHC,0.35±0.09L/min,p≤0.014) and SV (227±45mL,p≤0.031) were higher compared to F14 (0.71±0.08;0.23±0.04L/min;204±49mL) and LCLC (0.72±0.07;0.25±0.03L/min;199±49mL). A faster CO2 accumulation was recorded during the HCHC (96±35s) rebreathing trial (F14,162±42s,p=0.001;LCLC,151±23s,p=0.002). Longer apnoeas were reported in F14 compared with HCHC (apnoeas 1-3,p≤0.046) and LCLC (apnoeas 2-3,p≤0.006). After the first apnoea SV was lower in F14 (141±43mL,p=0.015) compared with HCHC (180±34mL). Moreover, following the third apnoea end-tidal partial pressure of oxygen and nadir SpO2 were lower in F14 (8.6±2.2kPa,p=0.028;77±13%,p=0.009) compared with HCHC (10.1±1.7kPa;84±9%). No differences were measured in end-apnoeic end-tidal partial pressure of CO2, heart rate nor haematology across diets. Conclusion:Fasting improved apnoeic performance with apnoeas being terminated at lower oxygen levels through altering the rate of CO2 accumulation but without affecting the cardiovascular responses.

Introduction For tactical reasons, the foot-borne soldiers sometimes undertake nighttime operations. However, the metabolic demand during walking in complete darkness may be markedly increased. The purpose of this study was to investigate if metabolic demand and kinematics would change while walking on a gravel road and a slightly hilly trail in darkness with or without visual aid. Materials and Methods Fourteen cadets (11 men and 3 women, age: 25 ± 7 years, height: 178 ± 8 cm, and weight: 78 ± 13 kg) walked at 4 km/h on a straight gravel road and on a slightly hilly forest trail (n = 9). Both trials were performed at nighttime under four different conditions, wearing a headlamp (Light), blindfold (Dark), monocular (Mono), or binocular (Bino) night vision goggles. During the 10-minute walks, oxygen uptake, heart rate, and kinematic data were assessed. Ratings of perceived exertion, discomfort, and mental stress were evaluated after each condition using a category ratio scale. Physiologic and kinematic variables were evaluated using repeated-measures analysis of variance, whereas ratings were evaluated using non-parametric Friedman analysis of variance. Results Oxygen uptake was higher in all three conditions with no or limited vision (Dark, Mono, and Bino) than in the Light condition (P ≤ 0.02) when walking on both the gravel road (+5–8%) and the forest trail (+6–14%). Heart rate was higher during the Dark than during the Light condition when walking on the forest trail, whereas there was no difference between conditions on the gravel road. During both trials, gait frequency was higher during the Dark than during the Light, Mono, and Bino conditions. Ratings were generally low during all conditions. Conclusions Walking on a gravel road or a forest trail wearing a blindfold or visual aid increased the metabolic demand. Thus, it appears that the metabolic demand is higher during overground walking with night vision goggles than with full vision, which may influence the performance of nighttime operations.

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