The reliability and validity of the Affinity Altitude hypoxic generators in acute and chronic conditions

This study investigated the reliability of the Affinity Altitude hypoxic generator within-day, between-day and between-generator under acute and chronic hypoxic conditions. An additional objective was to assess the validity of the fraction of inspired oxygen (FiO2) values in relation to the claimed manufacture’s reference values to ensure the accuracy and safety of the product. Three altitude generators (Affinity Altitude Ltd., Sussex, UK) were assessed across all available settings during a test–retest design for equivalent FiO2 and output volume. This consisted of two phases: 1) acute exposure (10 min per setting) and 2) chronic exposure (8 h per setting). FiO2 and volume data were calculated from 1 min collection samples using the Douglas bag method for acute and chronic exposures. There were low variations in FiO2 data across all settings within the acute exposure for within-day (coefficient of variation [CV] range: 0.0–2.6%), between-day (0.2–1.3%), and between-generator analysis (0.7–1.4%). This was similarly found for volume data within-day (0.1–3.7%), between-day (0.7–5.4%), and between-generator (1.2–3.0%). Equally, for chronic exposure trials, CV for FiO2 (< 4.0%) and volume (< 5.0%) across each of the generators presented low variations. The FiO2 values were similar to reference values, however, significant differences were found for settings 4 (−0.3% [17.6% vs. 17.9% reference value]) and 5 (−0.1% [15.8% vs. 15.9% reference value], both p < 0.05). A ‘good’ level of reliability (CV < 5%) and validity were found within and between the Affinity Altitude’s generators. However, a review of the reference values is warranted, and long-term experimental studies are required to determine the efficacy of this device for the purpose of physiological adaptations.