Hypoxia (PDF)

Assoc. prof. Kameliya Bratoeva, M.D., PhD ES of pathophysiology, MU-Varna  HYPOXIA Hypoxia is a pathological condition of oxygen deficiency, when the partial pressure of oxygen in the mitochondria is under 0.1 - 1 mm Hg  HYPOXIA The term hypoxia refers to a p...

Assoc. prof. Kameliya Bratoeva, M.D., PhD ES of pathophysiology, MU-Varna  HYPOXIA Hypoxia is a pathological condition of oxygen deficiency, when the partial pressure of oxygen in the mitochondria is under 0.1 - 1 mm Hg  HYPOXIA The term hypoxia refers to a pathological process in which the tissues are not oxygenated adequately, usually due to an insufficient concentration of oxygen in the blood.  HYPOXIA The pathogenesis of hypoxia includes disorders in the systems that import, transport and use oxygen, as well as their regulatory mechanisms.  Hypoxia is the discordance between necessity and oxygen supply Normal supply / increased need Reduced supply / normal need Cellular metabolism and energy expenditure  Laboratory measurements of oxygen homeostasis Atmospheric air Arterial blood (a) Venous blood (v) РО2 – 158,8 мм Hg РaО2 – 80-100 мм Hg РvО2 – 35-40 мм Hg (kPa – 13.33) (kPa – 5.33) РCО2 – 0.23 мм Hg SaО2 - 95%-100% SvО2 > 60-80% (kPa – 0.03) CaО2 content 19-20 об. % CvО2 content 14-25 об. % (normoxemia) /a – v/ О2 - 5 - 6% /arterio - venous difference/ VО2 - 25- 30 % /oxygen utilization factor/  HYPOXIA, anoxia Hypoxia is a condition there is decreased oxygen supply to the tissue  Hypoxia in which there is complete deprivation of oxygen supply is referred to as anoxia  Classification of hypoxia  Fulminant (immediate)- several seconds І. According to the clinical course  Acute – several minute  Subacute – several hours or days  Chronic –months and years Hypoxic hypoxia ІІ. According to the pathogenetic principle (hypoxemic hypoxia) Circulatory (Stagnant) hypoxia Anemic hypoxia Histiotoxic hypoxia Mixed  HYPOXIA: CLASSIFICATION Hypoxemic Hypoxia: Arterial PO2 is less. Anemic Hypoxia: Decreased Hemoglobin causing decrease O2 carriage Stagnant Hypoxia: Due to slow & low blood flow.  Histotoxic Hypoxia: Tissue toxins refuse O2 to the cells  TYPES OF HYPOXIA 1. HYPOXIC HYPOXIA 2. ANEMIC HYPOXIA 3. STAGNANT HYPOXIA 4. HISTOTOXIC HYPOXIA  Hypoxic hypoxia Causes: 1. Decreased PaO2 in inhaled air - hypobaric Exogenous hypoxia hypoxia 2. Increased PaO2 in the inhaled air - hyperbaric hypoxia 3. Impaired gas exchange in the lungs- Endogenous Ventilation, perfusion, diffusion, respiratory /respiratory/ disorders during sleep hypoxia  Hypoxic hypoxia Hypobaric hypoxia– “Mountain disease” /a term that mean acute altitude sickness/ Acute:  Altitude-3300-3400 m (PaO2 is under 65 kPa)  Over 5200 m - breathing is with oxygen devices  Exogenous hypoxia Decreased atmospheric pressure and decreased partial oxygen pressure in the air Mountain sickness factors: low partial pressure of oxygen, low barometric pressure, physical loading, cooling  Hypoxic hypoxia- Exogenous hypoxia High altitudes > 3000 Alv. PO2 - 60mm Hg. First symptoms- irritability, euphoria and a carefree feeling. Oxygen starvation causes the brain and other vital organs to become impaired  Hypoxic hypoxia- endogenous hypoxia Alveolar hypoventilation reasons: Obstructive violations (lung edema, tumors or foreign bodies in the lumen of bronchi and bronchioles) Restrictive violation (chronic inflammatory or sclerotic processes in the lungs and in the chest)  Distrubances of respiratory regulation (toxic substances poisoning, brain trauma  Hypoxic hypoxia- endogenous hypoxia Disturbances of lungs blood supply- Heart failure, decreased ciculating blood volume (after blood loss) Disturbances of gases diffusion in lungs- chronic inflammatory diseases of the lungs, lungs edema. Blood indices: low oxigen, high CO2, low pH (acidosis)  Hypoxic hypoxia Ventilation/Perfusion imbalance:  Decreased Ventilation/perfusion in: -Bronchial Asthma -Emphysema - Sleep apnea –sleeping disorder in which person stop breathing during the night All these cause a decreased partial pressure of oxygen in arterial blood (paO2)- colled Hypoxemia  Hypoxic hypoxia- symptoms Cyanosis (blue finger nails and lips  Dyspnea (difficulty breathing)  Polycythemias (increase in RBC count  Hypoxic hypoxia- symptoms Early symptoms: Headache Speaking difficulty Restlessness Anxiety Tachycardia/Tachypnea  Hypoxic hypoxia- symptoms Late symptoms: Cyanosis (blue skin, finger, nails and lips  Dyspnea (difficulty breathing)  Polycythemias (increase in RBC count) Rapid breathing  TYPES OF HYPOXIA 1. HYPOXIC HYPOXIA 2. ANEMIC HYPOXIA 3. STAGNANT HYPOXIA 4. HISTOTOXIC HYPOXIA  Anemic Hypoxia In anemic hypoxia decrease in hemoglobin or RBC count causes decreased Oxygen carriage Indicators: Decreased oxygen capacity of the blood; Reduced oxygen content; Reduced oxygen delivery from inactivated hemoglobin molecules to tissues.  Anemic Hypoxia Causes: Severe blood loss Anemia;  Massive blood transfusions with preserved blood;  Chemical substances - CO2; H2S;  Congenital hemoglobin abnormalities;  Intoxication;  Severe infectious diseases - liver and kidney failure  Anemic Hypoxia Can also be due to CO Poisoning.  CO combines irreversibly with Hb. Abnormal Hemoglobins such as Sickle Hb can also cause Anemic Hypoxia.  Anemic Hypoxia Reduced number of erythrocytes occurs in heavy bleeding, some cancers, sickle cells anemia This condition leads to decreases the blood's capacity to carry the oxygen to the cells  Anemic Hypoxia- CO poisoning (carbon monoxide) Sources of carbon monoxide:  CO is a product of the incomplete combustion of organic substances such as petroleum products, firewood, etc. The haemoglobin picks up carbon monoxide over 200 times more readily than it picks up oxygen  Anemic Hypoxia- (carbon monoxide) - Sources of carbon monoxide: Common sources of carbon monoxide exposure are motor exhaust fumes, smoke from fires, fumes from malfunctioning heating systems and tobacco smoke.  TYPES OF HYPOXIA 1. HYPOXIC HYPOXIA 2. ANEMIC HYPOXIA 3. STAGNANT HYPOXIA 4. HISTOTOXIC HYPOXIA  Stagnant Hypoxic hypoxia hypoxia It is characterized by reduced or blocked oxygen transport to tissues due to cardiovascular pathology (decreased minute volume; decreased RR; impaired blood rheology) Also called “Ischemic” or “Hypo-perfusion Hypoxia”. The leading pathogenetic mechanism is tissue hypoperfusion with subsequent ischemia  Stagnant hypoxia In stagnant hypoxia, the oxygen-carrying capacity of the blood is adequate but, circulation is inadequate. Such decrease in blood flow results from the heart failing to pump effectively. Such conditions as heart failure, arterial problem, and blockage of a blood vessel predispose the individual to stagnant hypoxia. Stagnant hypoxia Main types: Ischemic type - ischemic heart disease Stagnant type - heart failure Ischemic-stagnant type - shock  Stagnant hypoxia Indicators: Utilization factor> 33% Venous hypoxemia PvO2; (a-v) O2> 5-6 vol.%  TYPES OF HYPOXIA 1. HYPOXIC HYPOXIA 2. ANEMIC HYPOXIA 3. STAGNANT HYPOXIA 4. HISTOTOXIC HYPOXIA  HISTOTOXIC HYPOXIA HISTOTOXIC HYPOXIA- impaired oxygen utilization by cells Types of histotoxic hypoxia : Reduced or blocked utilization of oxygen by cells; Reduced effect of utilized oxygen.  HISTOTOXIC HYPOXIA Etiology:  Infections  Intoxications Endogenous - uremic syndrome, hepatic coma Exogenous - cyanides, heavy metals, antibiotics, anticoagulants, drugs  Ionizing radiation  Hyperthermia  Hypothermia  Hypo and avitaminosis  Hormones - increased thyroxine and decreased insulin  Protein starvation  HISTOTOXIC HYPOXIA Cyanide inhibits the intracellular enzyme, “Cytochrome oxidase” which is the terminal enzyme of the mitochondrial respiratory chain, and stops its action and ATP production. Nervovus system and the heart are particulary affected.  HISTOTOXIC HYPOXIA Vitamin B deficiency or Beri Beri disease where also several important steps of O2 utilization are blocked. Blood indices: the pressure, saturation and content of O2 in blood are near normal, A- V difference is lower ((a-v) O2< 5-6 vol.%) and PvO2 is higher.  Adaptation to hypoxia The reactions of urgent adaptation (protective- adaptive) manifest in acute hypoxia. Permanent- adaptive Compensatory – during long-term or repeating hypoxic effects  Adaptation to hypoxia The reason of adaptation – lack of energy supply due to low ATP amount (lack of biological oxidation) Respiratory system – decreased blood oxigen and increased CO2 irritate chemoreceptors. This result in the increase of the alveolar ventilation.  Adaptation to hypoxia Heart – tachycardia, increased heart stroke volume and minute blood volume. Vessels – centralization of blood flow (dilation of the brain and heart arterioles with simultaneous constriction of the arterioles in others tissues and organs.)  Adaptation to hypoxia Blood – activation of RBC outflow from the bone marrow and blood depot (liver, spleen) Increased affinity of Hb to oxygen and the degree of oxyHb dissociation in the tissues. Tissues systems of biological oxidation – increased anaerobic glycolysis, the activation of respiratory enzymes.  Permanent adaptation to hypoxia Lungs – increased surface of alveoli, number of capillaries, rate of gases diffusion through alveoli to vessels. Respiratory muscles – hypertrophy and increased working capacity. Heart – the number of myocardial fibers, capillaries and nerves is increased. Increase of heart stroke volume and minute volume.  Permanent adaptation to hypoxia Number of the vessels in all organs and tissues is increased. Blood – increased blood cells number due to increased erythropoiesis. -Chronic lack of oxygen causes the activation of erythropoietin synthesis in kidneys. Metabolic processes: -decrease of metabolism intensiveness; -high efficiency of anaerobic glycolisis; -prevalence of anabolic processes in the cells.  Clinical application of hypoxia Adaptation to hypoxia provides resistance to other stress factors (cross-resistance) Adaptation to hypoxia is characterized with structural and functional changes in many organs and tissues. Body reistaance is increased to hypothermia, overheating, physical overstrain, infections. Thank you for your attention!