Different Types Of Hypoxia

Hypoxia is one of the applied aspects of respiratory physiology. The term “hypoxia” refers to the decreased oxygen supply at the level of tissues. So, for any reason, if the tissue is getting less oxygen, it means hypoxia. Hypoxemia means a decrease in the partial pressure of oxygen at the level of Arterial blood. 

There are Different Types Of Hypoxia that can occur due to the decreased oxygen supply. It is highly recommended that the video on the same topic should be watched for a deeper understanding of the topic. This is a very important topic for competitive exams like NEET-PG, NExt, INICET, and FMGE. this blog will give you a gist of what can be expected in the exams. You can find related questions on this topic on the prepladder app. Let us start by discussing hypoxic hypoxia.

1. Hypoxic Hypoxia

• Hypoxic hypoxia is when due to any condition if the partial pressure of the oxygen in the arterial blood is less. Therefore, any cause of hypoxemia is hypoxic hypoxia. 
• Causes of hypoxic hypoxia: 
  • High altitude: The decrease of oxygen pressure at the level of arterial blood may be caused when the atmospheric air contains less oxygen.
  • Hypo ventilation:  In case of ventilation is not adequate, hypoxic hypoxia can occur.
  • Lung Fibrosis/ Oedema: Oxygen should be diffused through the membrane into the lungs. If this diffusion is problematic, the partial pressure of the oxygen will decrease. 
  • Right-to-left shunt: While the heart is pumping blood, if there is a gap between the interatrial septum and ventricular septum in the form of a defect and if there is any shunting at the heart's level, particularly from right to left, the partial pressure of oxygen will decrease.
• Impact of hypoxic hypoxia
  • The partial pressure of the oxygen is a determinant of the saturation of haemoglobin in the blood. So, whenever the partial pressure is low will lead to a proportional decrease in the saturation of haemoglobin as well. 
  • In the case of hypoxic hypoxia, both the dissolved oxygen and haemoglobin-bound oxygen will be low.
  • Since the partial pressure of oxygen is low, this results in low haemoglobin saturation, low dissolved Oxygen, and low haemoglobin-bound oxygen, which ultimately means the content of the arterial blood will also be low. This ultimately results in a low supply of oxygen to the tissue, resulting in hypoxia.
  • In hypoxic hypoxia, the tissue takes the normal amount of O2 from the already low O2-contained arterial blood, which decreases the O2 content of the venous blood. 
  • There is a proportionate decrease of O2 in arterial and venous blood 
  • Artery Venous oxygen difference ((A-V)O2 difference) will remain normal in case of hypoxic hypoxia

Also Read: Gastrointestinal Tract Hormones

2. Anaemic Hypoxia

• In anaemic hypoxia, haemoglobin decreases in quality or quantity. The partial pressure of oxygen in the arterial blood is normal. Since haemoglobin is the main source of transport of oxygen to the blood, when it is at fault, this type of hypoxia is called anaemic hypoxia.
• Causes of Anaemic Hypoxia
  • Anaemia: When there is low haemoglobin in the blood, it is called anaemia.
  • Carbon monoxide poisoning: Carbon monoxide has a 52% high affinity for haemoglobin, so it will not allow the haemoglobin to deliver oxygen at the tissue level. 
  • Methemoglobinemia: In methemoglobinemia, the ferric oxygen does not allow the ferrous oxygen to be delivered to the tissue level. 

3. Stagnant Hypoxia/ Ischemic Hypoxia

• In stagnant hypoxia, the flow of blood through the tissue is slow or sluggish. If the blood is not flowing, even though the oxygen content is normal, less oxygen will be delivered to the tissue. 
• Causes of Stagnant Hypoxia/ Ischemic Hypoxia:
  • Severe haemorrhage: Loss of a large amount of blood will result in less oxygen delivered to the tissue.
  • Heart failure: In a heart failure patient, the heart will not be able to pump an adequate amount of blood, and there will be no proper cardiac output.
  • Circulatory shock: In case of a shock there will be less amount of blood delivered. 
• The partial pressure of the oxygen (PaO2) at the arterial level is normal.
• The saturation of haemoglobin (Sao2) is also normal. 
• The dissolved Oxygen and the haemoglobin bound Oxygen will remain normal. 
• The content of Oxygen in the arterial blood will also remain normal. 
• The blood is not going adequately to the tissue, which requires 5 ml of oxygen from the blood. Because of the lack of an adequate blood supply, the tissue will keep extracting more and more oxygen from the same blood, leading to a low oxygen level in the venous blood. 
• The arterial and venous blood oxygen difference will increase.

4. Histotoxic Hypoxia 

• In histotoxic hypoxia the blood flow is normal till the level of tissue, but the tissue is unable to extract oxygen from the blood. So, in histotoxic hypoxia, the tissue is damaged.
•  Causes of Histotoxic Hypoxia :
  • Cyanide poisoning: Cytochrome c oxidase enzyme is damaged; this enzyme is responsible for the utilisation of oxygen at mitochondria. 
  • Beriberi: Multiple enzymes of the electron transport chain (ETC) will be affected due to the deficiency of Vitamin B1.
• In histotoxic hypoxia, the partial pressure of oxygen, the saturation of haemoglobin, dissolved oxygen, and haemoglobin-bound oxygen will remain normal. 
• The content of the blood at the arterial level will also remain normal. 
• Since the tissues are unable to extract oxygen from the blood the level of venous blood Oxygen will be higher than normal.
• So as a result, the artery venous oxygen difference will be low or decreased. 
• Hypoxia is a stimulator for peripheral chemoreceptors. Peripheral chemoreceptors are in the carotid (carotid sinus) and aortic bodies (aortic arch). Inside it is a glomus cell that senses hypoxia. The blood flow of this carotid body is huge, approximately 2000 ml / 100 gm of tissue /min. Due to the huge blood flow, the glomus cell can survive on dissolved oxygen. So, this glomus cell suffers from hypoxia only when there is a lack of dissolved oxygen in the blood. 
• In hypoxic hypoxia: the dissolved oxygen would be low, and the chemoreceptor will be stimulated. 
• In anaemic hypoxia: the dissolved Oxygen would be normal, and the chemoreceptor will not be stimulated.
• In stagnant hypoxia: the blood flow to glomus cells is low, and the chemoreceptor will be stimulated.
• In histotoxic hypoxia: the tissue is unable to extract oxygen from the blood, so the chemoreceptor will be strongly stimulated.
  • Therefore, Cyanide poisoning is the most potent stimulator for peripheral chemoreceptor.

Also Read: Hemostasis: Stages, Steps and Clinical Applications

Relationship Of Different Type Of Hypoxia With Cyanosis

• Cyanosis is the bluish discolouration of the skin and the mucus membrane due to the presence of a higher amount of reduced haemoglobin in the blood. So, if the deoxygenated haemoglobin amount is greater than a 4-gram percentage, then cyanosis will develop. 
• The Other form of pathological haemoglobin can also produce cyanosis-like
  • Met – Hb >> 1.5gm %
  • Sulf -Hb >> 0.5 gm%
• Cyanosis in areas with rich capillaries like the tip of the nose, inner oral mucus membrane, the tip of fingers, and ear lobules.
• This short table is all the information one needs to know for the purpose of competitive exams.

• Cyanosis never occurs in histotoxic hypoxia. 
• The most common hypoxia is hypoxic hypoxia because of ventilation-perfusion mismatch. 
• The most sensitive brain area in the case of hypoxia is
  • Hippocampus (CA1/Sommer’s area). 
  • The Purkinje cell of the cerebellum.
  • Striatal region of the basal ganglia. 
• The most resistant to hypoxia is the spinal cord. 

Also Read: Synapse: Components, Types and Function

Download the PrepLadder app now to access high-yield content with 24-hr Free Trial. Explore premium study resources like Video Lectures, digital notes, QBank, and Mock Tests for a seamless exam preparation. Time to begin your NEET PG coaching online with PrepLadder.