19. Hypoxia – definition, parameters. Pathogenetic classification of hypoxias. Characteristics of hypoxic hypoxias.

HYPOXIA – DEFINITIONS, PARAMETERS, HYPEROXIAS

• All cells in the body need O2 to make ATP
• The flow of O2 into the body is carried out by an integrated system including:

1. Respiratory system
2. Blood hemoglobin
3. Cardio-vascular system
4. Mitochondria

Functional stages of O2 regimen

1. a) O2 in alveoli transfers O2 to the blood
2. b) Binds to hemoglobin and transported by the blood
3. c) Distributed in the organism
4. d) Delivery of O2 + respiratory extraction of the tissues
5. e) O2 consumption + utilisation
6. f) O2/CO2 binding affinity to the Hb depends on the partial pressure

Hypoxia

• Has two definitions:

1. State of inadequacy between delivery and necessity of O2 for the cells, tissue, and organs

• An acute critical condition threatening the vital functions
• Decreased O2 delivery in case of normal necessity (e.g. due to obstruction of airways)
• Normal delivery but greater O2 requirements (e.g. athletes)

2. Decreased pO2 in arterial blood

Clinical signs of hypoxia

• Cyanosis
• Dyspnea
• Hypo/hyperkinetic circulation
• Hypoenergetic → fatigue, prostration, adynamia (lack of strength)

Parameters of hypoxia

• The assessment of oxygen regimen relies on 4 parameters

1) Intensity = O2 necessity

• Depends on:
• Body weight (total amount of body cells and corresponding structures)
• Functional status (amount of functionally active units)
• Body temperature and temperature gradient organism
• Metabolic status (substrates, active pathways, etc)
• Neurohormonal profile
• Presence (absence) of O2 debt

2) Adequacy = satisfied O2 necessity

• Recognised in:
• Cells (cell hypoxic markers; HIF-1, HIF-2)
• Organs (tonometric detection of arterial organs pH and pCO2 changes)
• Organism (metabolic markers for hyo- and anaerobiosis → concentration of blood lactate and the ratio of lactate to pyruvate)

3) Effectiveness = O2 utilisation

• Assessed in:

1. Cells, mitochondria and oxysomes

• By means of detecting the level of coupling of oxidative phosphorylation

2. Organism

• Determining the O2 consumption per unit body mass or body surface and/or percent change in a given function

4) Economy = O2 cost

• Information about the biological cost of O2 regimen is derived from the following equation:
• ★ O2 spent for maintaining O2 convection (breathing + circulation)

Total O2 consumption (total VO2)

• ★ ~ 15-16%