Effect of acute hypoxia on inspiratory muscle oxygenation during incremental inspiratory loading in healthy adults
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To non-invasively examine the effect of acute hypoxia and inspiratory threshold loading (ITL) on inspiratory muscles [sternocleidomastoid (SCM), scalene (SA) and parasternal (PS)] oxygenation in healthy adults using near-infrared spectroscopy (NIRS).
Twenty healthy adults (12 M/8 F) were randomly assigned to perform two ITL tests while breathing a normoxic or hypoxic (FIO2 = 15 %) gas mixture. NIRS devices were placed over the SCM, PS, SA, and a control muscle, tibialis anterior (TA), to monitor oxygenated (O2Hb), deoxygenated (HHb), total hemoglobin (tHb) and tissue saturation index (TSI). With the nose occluded, subjects breathed normally for 4 min through a mouthpiece that was connected to a weighted threshold loading device. ITL began by adding a 100-g weight to the ITL device. Then, every 2 min 50-g was added until task failure. Vital signs, ECG and ventilatory measures were monitored throughout the protocol.
Participants were 31 ± 12 year and had normal spirometry. At task failure, the maximum load and ventilatory parameters did not differ between the hypoxic and normoxic ITL. At hypoxic ITL task failure, SpO2 was significantly lower, and ∆HHb increased more so in SA, SCM and PS than normoxic values. SCM ∆TSI decreased more so during hypoxic compared to normoxic ITL. ∆tHb in the inspiratory muscles (SCM, PS and SA) increased significantly compared to the decrease in TA during both hypoxic and normoxic ITL.
The SCM, an accessory inspiratory muscle was the most vulnerable to deoxygenation during incremental loading and this response was accentuated by acute hypoxia.
KeywordsInspiratory muscle Respiratory muscle Near-infrared spectroscopy NIRS Acute hypoxia Inspiratory load
Forced expiratory volume in 1 s
- FEV1/FVC ratio
Ratio of the forced expiratory volume in the first 1 s to the forced vital capacity of the lungs
Fraction of inspired oxygen
Forced vital capacity
Inspiratory threshold loading
End tidal carbon dioxide partial pressure
Peak mouth pressure
Saturation of hemoglobin with oxygen as measured by pulse oximetry
Tissue saturation index
We thank all subjects for their participation. We are also very appreciative of the valuable assistance given by Carmen Ma during data collection and Dr. Salem Bahubeshi for ECG monitoring. This study was supported by a grant and scholarship funding from Princess Nora bint Abdul Rahman University.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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