Talk:Hypoxia

Systematic definition of normoxia as a reference for hypoxia

For explaining normoxia and deviations from normoxia, we distinguish environmental, compartmental, and functional definitions of normoxia. These definitions provide a reference for distinguishing corresponding causes for deviations from normoxia or normoxic function.

Categories of normoxia

1. Environmental conditions

• Normoxia may be defined arbitrarily (like altitude relative to sealevel) as air-level p_O2 at sealevel in air or in the aqueous extra-organismic environment.

2. Compartmental respiratory cascade

• Normoxia may be defined arbitrarily as the p_O2 in any given compartment of a living organism (alveolar, arterial, venous, mixed-venous, intracellular) obtained under environmental normoxia in a steady state of physiological routine activity (here ‘routine’ is organismic physiological, whereas ‘ROUTINE’ is cellular physiological).

3. Biological response

• For any function, normoxic performance is defined as the biological response that does not deviate from the physiological function measured under environmental or compartmental normoxia.

Causes of deviations from normoxia

Based on definitions of the categories (1) environmental normoxia, (2) compartmental normoxia, and (3) normoxic function, the causes for deviations from normoxia are considered:

1. Environmental hypoxia and hyperoxia

• Hypobaric conditions: high altitude or low-pressure chamber with air
• Hyperbaric conditions: high-pressure chamber, diving with air
• Normobaric: O₂ deprivation in the environment (environmental normobaric hypoxia), O₂ supplementation (environmental normobaric hyperoxia)

2. Compartmental hypoxia and hyperoxia

• Environmentally induced hypoxia or hyperoxia on the compartmental level (living organism)
• Physiologically induced hypoxia on the compartmental level: tissue-work related; living organism at high workload of a tissue; ; (mal)adaptive responses of the respiratory cascade to (de)training and lifestyle
• O₂-transport related hypoxia (pathological: ischemia and stroke, anaemia, chronic heart disease, chronic obstructive pulmonary disease, severe COVID-19, obstructive sleep apnea, CO poisoning)
• Experimental for isolated organs, tissues, cells, and organelles: deviations of incubation O₂ levels of experimental preparations from compartmental or biological normoxia in the intact organism

3. Biological hypoxia and hyperoxia

• Compartmental: tissue-work related
• Compartmental: pathological
• Genetic: inhibition or acceleration of O₂-linked pathways (mutations, inherited diseases, knockout, knockin)
• Pharmacological-toxicological: inhibition or acceleration of O₂-linked pathways (cyanide, rotenone, NO, ..; doping, ..)

Extents of hypoxia

There is a continuous transition of hypoxia to anoxia, which is best represented on a logarithmic scale of p_O2. Only if the transition to anoxia is of interest, then further differentiation of microxia and anoxia is of technical and physiological interest taking into account the limit of detection of a method of determining p_O2 and different methods to detect functional responses to the presence (microxia) or absence (anoxia) of trace amounts of oxygen.