The Suitability of the Hypoxico Hyp123 Altitude Generator as a Low Oxygen Delivery Method for Therapeutic Acute Intermittent Hypoxia Research Trials
Author List
Nicole L Sheers,1,2 Talia Clohessy,2,3 David J Berlowitz.1,2,3
1. School of Health Sciences, The University of Melbourne, Victoria, Australia
2. Institute for Breathing and Sleep, Heidelberg, Victoria, Australia
3. Department of Physiotherapy, Austin Health, Heidelberg, Victoria, Australia
Introduction
Therapeutic acute intermittent hypoxia (tAIH) is a novel treatment which may improve motor function for people with spinal cord injury (SCI). Pre-clinical and preliminary clinical studies in SCI suggest that breathing short periods of low oxygen concentration (%O2) air stimulates hypoxia-induced neuroplasticity, strengthens motor neuron output, and improves clinical outcomes. Commercially available “altitude generators” have been used as a source of low %O2 air, however variable %O2 and flow rates have been noted. Study aims were to test the suitability of the altitude generator we planned to use in a clinical trial of tAIH, specifically the step-change response time (Experiment 1), %O2 variability (Experiment 2) and flow characteristics (Experiment 3).
Methods
Three bench-tests using a Hyp123 Altitude Generator with high altitude adapter (Hypoxico Altitude Training Systems), with air output sampled using a digital optical oxygen sensor (FDO2, PyroScience GmbH) connected to a data acquisition system (Spike2 version7, Micro 1401, Cambridge Electronic Design Ltd). Experiment 1: The generator was set to deliver room air (21%O2), turned on and manually adjusted to deliver 9%O2. Five, six-minute trials were conducted and the T90 response time of the 21 to 9%O2 step change was calculated. Experiment 2: From a steady-state 9%O2 output, the %O2 variability (coefficient of variation (CV)) was measured over ten, two-minute trials. Experiment 3: Five, two-minute trials as per Experiment 2 were conducted with a pneumotachograph (Model 3700A, Hans Rudolph Inc) added to the circuit to record airflow.
Results
The altitude generator’s mean response time (T90) was 81.7 ± 3.8 seconds. Minimal variability (CV = 0.01) was observed at steady-state 9%O2 target (9.0 ± 0.1%O2 [range 8.2 – 9.3%]). Airflow at 9%O2 was generated as a sinusoidal wave (2.5 second period) with trough and peak flow rates of 2.0 to 70.9 L/min (mean 34.9 ± 17.8 L/min).
Conclusion
The Hypoxico Hyp123 Altitude Generator can generate low oxygen concentration air with minimal variability in %O2 once at a target steady-state of 9%O2. However, the device has a response time exceeding the commonly used tAIH protocol of 15, 60-second hypoxic episodes with 1-2 minute intervals of room air. Moreover, the generator does not output 9%O2 air at a steady flow rate, and trough values may be insufficient to meet an adult’s inspiratory flow rate during tidal breathing. Commercially available altitude generators may not be suitable for generating low oxygen concentration air required for tAIH research and translation to clinical environments. Alternative systems for delivering tAIH should be investigated.
Nicole L Sheers,1,2 Talia Clohessy,2,3 David J Berlowitz.1,2,3
1. School of Health Sciences, The University of Melbourne, Victoria, Australia
2. Institute for Breathing and Sleep, Heidelberg, Victoria, Australia
3. Department of Physiotherapy, Austin Health, Heidelberg, Victoria, Australia
Introduction
Therapeutic acute intermittent hypoxia (tAIH) is a novel treatment which may improve motor function for people with spinal cord injury (SCI). Pre-clinical and preliminary clinical studies in SCI suggest that breathing short periods of low oxygen concentration (%O2) air stimulates hypoxia-induced neuroplasticity, strengthens motor neuron output, and improves clinical outcomes. Commercially available “altitude generators” have been used as a source of low %O2 air, however variable %O2 and flow rates have been noted. Study aims were to test the suitability of the altitude generator we planned to use in a clinical trial of tAIH, specifically the step-change response time (Experiment 1), %O2 variability (Experiment 2) and flow characteristics (Experiment 3).
Methods
Three bench-tests using a Hyp123 Altitude Generator with high altitude adapter (Hypoxico Altitude Training Systems), with air output sampled using a digital optical oxygen sensor (FDO2, PyroScience GmbH) connected to a data acquisition system (Spike2 version7, Micro 1401, Cambridge Electronic Design Ltd). Experiment 1: The generator was set to deliver room air (21%O2), turned on and manually adjusted to deliver 9%O2. Five, six-minute trials were conducted and the T90 response time of the 21 to 9%O2 step change was calculated. Experiment 2: From a steady-state 9%O2 output, the %O2 variability (coefficient of variation (CV)) was measured over ten, two-minute trials. Experiment 3: Five, two-minute trials as per Experiment 2 were conducted with a pneumotachograph (Model 3700A, Hans Rudolph Inc) added to the circuit to record airflow.
Results
The altitude generator’s mean response time (T90) was 81.7 ± 3.8 seconds. Minimal variability (CV = 0.01) was observed at steady-state 9%O2 target (9.0 ± 0.1%O2 [range 8.2 – 9.3%]). Airflow at 9%O2 was generated as a sinusoidal wave (2.5 second period) with trough and peak flow rates of 2.0 to 70.9 L/min (mean 34.9 ± 17.8 L/min).
Conclusion
The Hypoxico Hyp123 Altitude Generator can generate low oxygen concentration air with minimal variability in %O2 once at a target steady-state of 9%O2. However, the device has a response time exceeding the commonly used tAIH protocol of 15, 60-second hypoxic episodes with 1-2 minute intervals of room air. Moreover, the generator does not output 9%O2 air at a steady flow rate, and trough values may be insufficient to meet an adult’s inspiratory flow rate during tidal breathing. Commercially available altitude generators may not be suitable for generating low oxygen concentration air required for tAIH research and translation to clinical environments. Alternative systems for delivering tAIH should be investigated.
