Effect of a Single Session of Intermittent Hypoxia on Hematological Variables
Condition: Intermittent Hypoxia
MeSH terms: Hypoxia
Study type: Interventional

Summary: 
      The purpose of the study is to determine the effect of a single exposure of intermittent
      hypoxia on erythropoietin levels and hemoglobin mass in young adults, older adults and
      patients with type 2 diabetes.
    

Detailed description: 
      Cardiorespiratory fitness, assessed by measuring maximal oxygen consumption (VO2max), has a
      potential to predict cardiovascular disease and mortality risk to a greater extent than
      smoking, hypertension, type 2 diabetes or high cholesterol levels. Oxygen transport from the
      lungs to the exercising muscles is achieved through the binding of oxygen to hemoglobin, an
      iron-containing protein in the red blood cell. Therefore, hemoglobin mass represents the
      oxygen-carrying capacity of the blood and strongly correlates with VO2max. Patients with type
      2 diabetes have serious impairments in cardiorespiratory fitness, as observed through a 20%
      lower VO2max than individuals matched for age, weight and physical activity levels. The
      investigators previously showed that a lower hemoglobin mass limits oxygen-carrying capacity
      and contributes to the lower VO2max in patients with type 2 diabetes. Thus, interventions
      that can increase hemoglobin mass should result in improved oxygen-carrying capacity and
      VO2max in patients with type 2 diabetes. While the majority of patients with type 2 diabetes
      are aware of their need to perform exercise to improve their VO2max, less than 1/3 of
      patients meet recommended levels of physical activity. There is therefore an urgent need to
      develop alternative interventions that improve VO2max, as even minimal improvements in VO2max
      significantly decrease mortality risk in unfit individuals.

      Hypoxia deprives the body of adequate oxygen supply at the tissue level which stimulates the
      release of erythropoietin (EPO), the peptide hormone regulating red blood cell production, in
      order to restore oxygen supply to the tissues. Following a rise in EPO levels, it takes 5-6
      days for a newly created reticulocyte to mature into a red blood cell, and to observe an
      increased hemoglobin mass. Increases in EPO levels have been observed to reach maximum values
      approximately 2-3 h after continuous hypoxic exposure lasting between 90 minutes and 3 hours.
      It has consequently been suggested that intermittent hypoxia, consisting of alternating few
      minutes of breathing hypoxic air with few minutes of breathing normoxic air, would provide a
      stimulus sufficient to stimulate an increase in EPO levels and hematological variables. Only
      one study measured both EPO levels and hematological changes in responses to intermittent
      hypoxia. Elite distance runners completed 4 weeks of intermittent hypoxia consisting of
      5:5-minutes hypoxia-to-normoxia ratio for 70 min, 5 times/week. The fraction of inspired
      oxygen gradually declined from 0.12 to 0.10%. The authors did not observe any increase in EPO
      levels or hemoglobin concentration. However, there were several methodological limitations
      that could explain these findings. First, hemoglobin concentration is dependent on plasma
      volume and is therefore greatly influenced by hydration status, and correlates only to a
      modest extent with red blood cell mass. On the other hand, hemoglobin mass is reported in
      grams and is a more direct measure of oxygen-carrying capacity. Second, EPO measurements were
      performed at the same time of day to minimize any circadian variability in EPO levels, which
      likely prevented the detection of a rise in EPO within the first few hours following the
      exposure to intermittent hypoxia. Therefore, the purpose of the present study is to determine
      the effect of a single exposure of intermittent hypoxia on EPO levels and hemoglobin mass in
      healthy individuals. The cardiovascular and ventilatory responses to a single exposure of
      intermittent hypoxia will also be determined. If intermittent hypoxia improves
      oxygen-carrying capacity, the next step will be to apply this intervention to patients with
      type 2 diabetes.
    

Intervention name(s): Intermittent hypoxia; Intermittent normoxia
Intervention type(s): Behavioral; Behavioral
Intervention description(s): The intermittent hypoxia protocol will consist of eight 4-minute hypoxic cycles (arterial oxygen saturation of 80%) interspersed with normoxic cycles to resaturation.; The intermittent normoxia protocol will consist of eight 4-minute normoxic cycles (compressed air) interspersed with 1-minute normoxic cycles (room air)
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Treatment