Hypoxia. Department of pathophysiology Basic Medical Science college. Air. Alveoli. Alveolar capillary. Gas transport. Tissue cells. Bound to haemoglobin. Internal respiration. Respiration and oxygen exchange. Ventilation. External respiration. Gas exchange. T ables of content.
Department of pathophysiology
Basic Medical Science college
Bound to haemoglobin
Respiration and oxygen exchange
Hypoxia is referred to a pathological process in which oxygen supply to tissues or organs is inadequate to meet the demand of cells, or there is adequate delivery to tissue but the tissue cells cannot make use of oxygen, leading to changes in functions, metabolisms and structures of cells and tissues of the body.
【 Partial pressure of oxygen, PO2 】
PO2 is the pressure or tension caused by oxygen physically dissolved in the blood.
PaO2: The partial pressure of oxygen in the plasma phase of arterial blood.
The PaO2 gives us valuable information about adequacy of gas exchange within the lungs, when it is subtracted from the calculated alveolar PO2.
PvO2: The partial pressure of oxygen in the plasma phase of venous blood.
The PvO2 is determined by whole body oxygen demand, and the capacity of the tissues to extract oxygen.
PaO2: 13.3kPa(100mmHg)；PvO2: 5.32kPa(40mmHg)。
CO2max Is the maximum amount of oxygen combined by Hb in 100ml blood under fully saturated condition in which the PO2 is 150mmHg, PCO2 40mmHg, and the temperature is 38℃.
CO2max: 8.92mmol/L (1.34ml/g×15gHb% =20ml%)。
The ability of Hb to carry O2.
The total amount of oxygen contained actually in 100 ml blood
sample, including the part combined with Hb and the part
physically dissolved in plasma.
CO2 = PaO2 + CO2max。
The difference value is between arterial and venous blood oxygen
A-VdO2 ≈ 2. 23～3.57mmol/L(5ml%～8ml%)。
A-VdO2 = volume of O2 tissue uptake = CaO2-CvO2
The percentage of hemoglobin present as oxyhemoglobin
SO2% = CO2 – O2 dissolved physically in plasma/ CO2max
The degree of connected Hb to oxygen
One measure of the position of the curve is the PO2 at the 50% SO2.
The P50 indicates affinity of hemoglobin for oxygen
H+, CO2, temperature,
Classification and Etiology
Hemic Hypoxia (Isotonic Hypoxia)
Circulatory Hypoxia(Hypokinetic Hypoxia)
Histogenous Hypoxia(Histotoxic Hypoxia)
oxygen tension in arterial blood is lower than normal,
which resulted in lack of oxygen from blood to tissues.
Causes : 1) Decreased PO2 of inspired air
2) External respiratory dysfunction
3) Venous-to-arterial shunt
Characteristics of blood oxygen
PaO2↓, SaO2↓, CaO2 ↓, CO2max N, CaO2-CvO2 ↓/N
The bluish color of skin, nails, lips and mucous membranes when the deoxyhemoglobin concentration of the blood in the capillaries is more than 5g/dl。
【Hemic hypoxia, isotonic hypoxia】
Hemic hypoxia refers to the altered affinity of Hb for oxygen or
decrease in amount of Hb in the blood
（2）Higher affinity of Hb to oxygen
（3）Carbon monoxide poisoning
High affinity of Hb for O2
CO can react with Hb to form carboxyhemoglobin which can not take up oxygen. So there is a deficiency of Hb that can carry oxygen.
CO can inhibit glycolysis in RBC, which reduces the production of 2,3-DPG and shifts the ODC to the left, decreasing the amount of oxygen released.
When a lot of pickled vegetables containing nitrate are taken, the reabsorbed nitrite reacts with HbFe2+ to form HbFe3+. The skin appears to coffee color. This phenomenon is called enterogenous cyanosis.
PaO2 N, SaO2 N, CaO2 ↓/N, CO2max ↓/N, CaO2-CvO2 ↓
Severe anemia : pallor
CO poisoning : cherry red
Methemoglobinemia: coffee color
【Circulatory hypoxia，hypokinetic hypoxia】
Circulatory hypoxia refers to inadequate blood flow leading to inadequate oxygenation of the tissues, which is also called hypokinetic hypoxia.
Etiology and mechanism
shock, left heart failure, thrombosis, arterial stenosis
right heart failure
Characteristics of blood oxygen：
PaO2 N, SaO2 N, CaO2 N, CO2max N, CaO2-CvO2 ↑
Histogenous hypoxia refers to the tissue cells can not make use of the oxygen supplied to them, though the amount of oxygen delivered to them is adequate.
Etiology and mechanism
Inhibition of oxidative phosphorylation - tissue intoxicity
cyanides, sulphuret, rotenone, ( cytochrome oxidase)
bacteriotoxin, radiation, free radical
Absence of Vitamin
Vit B1, Vit B2, Vit PP ，co-enzyme
Characteristics of blood oxygen：
PaO2 N, SaO2 N, CaO2 N, CO2max N, CaO2-CvO2 ↓
Changes of Blood Gas
Central nervous system
Tissues and cells
1. Compensatory response：
Low PaO2 stimulates the chemoreceptor in carotid and aortic body, which reflexly causes ventilation to increase.
PO2 → ventilation
2. Decompensatory effects:
1）High altitude pulmonary edema
2）Central respiratory failure
respiratory inhibition, irregular respiratory rhythm and frequency, hypoventilation, e.g. periodic breathing, Cheyne-Stoke respiration, Biot’s breathing
Hypoxic Pulmonary vasoconstriction (HPV)→PaO2 ↑
Humoral factors — AT、ET
Direct effect of O2 on SMC
Capillary proliferation --- VEGF
2,3-DPG binding site
blood flow resistance ↑,
afterload of heart ↑
When PO2 is low markedly, 2,3-DPG will cause CaO2 to decrease.
headache, agitation, poor faculty of memory, inability to make judgment, depress or loss of coordination
2. Chronic hypoxia:
impaired concentration, fatigue, drowsiness
3. Cerebral edema and neuron injury
1)Cell membrane injury
Na+ influx cell swelling
K+ efflux synthetic disorder
Ca2+-dependent protein kinase
2. Mitochondria injury severe hypoxia
3. Lysosome injury
【Pathophysiological basis of prevention and treatment】
Hyperbaric oxygen therapy