What is hypoxia

  • Hypoxia is a condition where the body or a specific tissue is deprived of adequate oxygen supply.
  • It can result from a variety of factors, such as high altitude, lung diseases, heart failure, anemia, and carbon monoxide poisoning.
  • Symptoms of hypoxia can include shortness of breath, rapid heartbeat, confusion, and fatigue.
  • Severe or prolonged hypoxia can cause damage to vital organs, including the brain, heart, and lungs.

What is hypoxia? Explain the different types of hypoxia with examples. What types respond to oxygen therapy

Hypoxia is a condition characterized by a deficiency of oxygen supply to the tissues of the body. It can occur due to various reasons such as inadequate oxygen levels in the air, respiratory problems, circulatory problems, anemia, or carbon monoxide poisoning.

There are different types of hypoxia:

  1. Hypoxic hypoxia: This occurs due to a low level of oxygen in the arterial blood. For example, in high altitude areas where the air pressure is low, or in patients with lung diseases like pneumonia or emphysema.

    Characteristic feature 
    (1) low arterial pO2 
    (2) low arterial O2 content,
    (3) low arterial % O2-saturation of haemoglobin,
    (4) low A-V PO2 difference.

    1. Low pO2, in inspired air
    2. Decreased pulmonary ventilation
    3. Defect in exchange of gases
    4. Venous-arterial shunts

  2. Anemic hypoxia: This occurs due to a decrease in the amount of oxygen-carrying capacity of the blood. This can occur due to conditions like anemia, carbon monoxide poisoning, or any other condition that interferes with hemoglobin’s ability to carry oxygen.

     characteristic features 
    (1) normal arterial pO2
    (2) arterial O2 content, moderately reduced
    (3) arterial % O2-saturation of haemoglobin: decreases
    (4) A- V pO2 difference is normal.
    (5) A- V percentage O,-saturation of Hb difference : increases.


    1. Anaemia
    2. Haemorrhage
    3. Conversion of haemoglobin to some abnormal form.
    For example:
    (i) Methaemoglobin
    (ii) Carboxy (Carbonmonoxy) Haemoglobin


  3. Circulatory hypoxia: This occurs due to inadequate blood circulation to the tissues. This can occur due to a heart attack, heart failure, shock, or any other condition that impairs blood flow.

  4. Histotoxic hypoxia: This occurs when the tissues cannot use oxygen effectively. This can occur due to alcohol or drug abuse or exposure to cyanide.

    Hypoxic and anemic hypoxia can respond to oxygen therapy, while circulatory and histotoxic hypoxia may not respond to oxygen therapy alone.

What is Periodic breathing

Def- It is the repeated sequence of  apnoea followed by respiration
1. Cheyne – stokes respiration
2. Biot’s breathing

Cheyne – stokes respiration – the repeated sequence of gradual onset of apnoea followed by gradual restoration of respiration is called Cheyne – stokes respiration

Conditions: Premature infants, High altitude, voluntary hyperventilation, heart failure.

A. Physiological
(a) Voluntary hyperventilation
(b) High altitude
(c) During sleep in some normal individuals

B. Pathological
(a) Heart failure (left ventricular failure)
(b) Brain damage
(c) Uremia

Physiological basis:

Wash out of CO2 (respiratory alkalosis)
Inhibition of respiratory Center
Apnoea (cessation of breathing)
Build up of PCO2 & in PO2 (Hypoxia and hypercapnia)
Stimulation of respiratory center
Hyperopnea (The cycle continues till normal breathing is restored)


2. Biot’s Breathing

This is a type of periodic breathing in which there are 3-4 cycles of normal respiration followed by abrupt onset of apnoea and again abrupt onset of normal respiration. This cycle is repetitive
Seen in:
(i) meningitis, and
(ii) diseases affecting the medulla.


What do you mean by Cyanosis ?

Cyanosis is a diffused bluish colouration of the skin and mucous membranes
Cause: caused by increased amount of reduced hemoglobin (deoxyhemoglobin)
To produce cyanosis the reduced Hb should be more than 5 gms / 100 ml of blood


Cyanosis is commonly seen at sites where the skin is thin

1. Mucus membrane of under surface of tongue
2. Lips
3. Ear lobes
4. Nail beds
5. Tip of Nose.

Two Types
1) Peripheral cyanosis
2) Central cyanosis

Peripheral cyanosis
– Due to stagnant hypoxia
– Venous unsaturation is more
– only skin becomes bluish

Conditions which cause peripheral cyanosis
– cardiac failure
– shock
– exposure cold environment (Peripheral vasoconstriction)

Central cyanosis
– Due to hypoxic hypoxia
– Arterial unsaturation is more
– Skin & mucous membranes become bluish

Conditions which cause central cyanosis
– congenital heart disease
– AV admixture
– Lung diseases
– Presence of methaemoglobins and sulphaemoglobin

what are the causes of cyanosis

1. Hypoxic hypoxia: Since arterial pO2, is les than normal due to the defective oxygenation of blood, hence more of reduced haemoglobin will be there; when it exceeds 5 gm/dL, cyanosis develops.
2. Stagnant hypoxia: When blood flow through the capillaries becomes very low or nearly becomes stagnant, more oxygen is extracted from the blood causing increase in reduced haemoglobin producing cyanosis.
3. Polycythemia: There is increase in total haemoglobin content, therefore, polycythemia aggravates the cyanosis.
4. Local Factors
(i) Exposure to mild cold (i.e. at approx. 20°C) produces cyanosis. How?
Cold by producing cutaneous vasoconstriction (arteriolar as well as venous) decreases tissue blood flow (stagnant hypoxia). Therefore, more and more O, is extracted by the tissues; amount of reduced haemoglobin increases and cyanosis develops.
(ii) Exposure to severe cold (at approx. 10°C or below) produces no cyanosis. Why?
(a) Oxygen-haemoglobin dissociation curve shifts to left, thus, prevents release of O2 from the haemoglobin.
(b) O2 consumption of tissues decreases markedly.
Both the above factors decrease the amount of reduced haemoglobin, hence no cyanosis develops.

Write short note on acclimatization

Acclimatization refers to the process by which the body gradually adapts to a new environment over time. This process can occur in response to various environmental factors, including changes in altitude, temperature, humidity, and other factors.
At high altitudes, acclimatization can occur in response to the lower oxygen levels, which can cause hypoxia. The body adapts to this by increasing the number of red blood cells, which helps to transport more oxygen to the tissues. Additionally, the body increases its production of a hormone called erythropoietin, which stimulates the production of more red blood cells.

Acclimatization to high altitudes typically takes several days to weeks, and the degree of adaptation varies depending on factors such as age, physical fitness, and prior exposure to high altitudes.

1. Increase in Pulmonary Ventilation:
 There is more increase in pulmonary ventilation in acclimatized subjects at high altitude than  in an unacclimatized subjects. 

2. Alkaline Urine (for regulation of Blood pH):
Though with fall of arterial pCO2. there should be alkalosis maintained as but normal blood pH as kidneys actively excrete more HCO3- in urine producing alkaline urine.

3. Decrease affinity of the Hb for or under hypoxic condition:
 because of increase amount of 2,3 DPG in RBC.

4. Rise in Hb concentration:
because hypoxia is a powerful stimulus for erthropoiesis secretion thus activates the erythropoiesis and O2 carrying capacity of Hb increases.

5. Increase vasularity of hypoxic tissues:
“Hypoxia increases tissue capillary density ie. more capillaries open up and also vasodilate.

6. Increase diffusion capacity of lungs for O2:
due to increase no. of capillaries and pulmonary vasodilation.

7. Changes at tissue level to reduce the effect of hypoxia are-
(i) Increase in no. of mitochondria
(ii) increase in cytochrome oxidase
(iii) increase in synthesis of myoglobin

What is Asphyxia?

Definition:- Condition in which hypoxia (PO2) is associated with hypercapnia (PCO2) due to
obstruction in the air way.
Causes: Strangulation, drowning, tracheal obstruction (due to entry of food or choking) and paralysis of diaphragm



I stage- Stage of hyperopnea
II stage- Stage of central excitation
III stage- Stage of central depression

I-Stage of hyperopnea:- (lasts for 1 minute)

  • increase in rate & depth of respiration
  • Expiratory effort Dysponea, cyanosis
  • Prominence of eyeballs

(due to stimulation of respiratory centers by PCO2) 

II – stage of convulsions (lasts for a minute)


  • Violent expiration
  • increased HR & systolic BP
  • constriction of pupil
  • exaggeration of all reflexes
  • convulsions & loss of consciousness
    (due to stimulation of respiratory centers by PCO2 & O2)

 III- Stage of exhaustion & collapse (lasts for 2-3 minutes)
  • Convulsions disappear
  • Heart rate& systolic BP
  • Dilatation of pupil
  • Gasping (shallow & low frequency respiration)
  • Death

Explain why Cyanosis is not seen in anemic hypoxia ?

Cyanosis is a bluish discoloration of the skin and mucous membranes due to the presence of deoxygenated hemoglobin in the blood vessels near the surface of the skin. It is commonly seen in hypoxic individuals as a result of inadequate oxygen supply to the body tissues.

Anemic hypoxia is a type of hypoxia that occurs due to a decrease in the oxygen-carrying capacity of the blood, such as in cases of anemia. In anemic hypoxia, there may be a decreased amount of hemoglobin or decreased ability of hemoglobin to bind oxygen.

Since cyanosis is due to the presence of deoxygenated hemoglobin in the blood vessels, anemic hypoxia may not always result in cyanosis. In cases of anemia, the blood may have a normal oxygen saturation, but the total amount of hemoglobin is reduced, resulting in a decreased oxygen-carrying capacity of the blood. Therefore, individuals with anemic hypoxia may not show signs of cyanosis, even if they are hypoxic.

Caisson disease

When the diver is working in the deep sea for a long time he is exposed to high alveolar gas pressure (high barometric pressure le hyperbarism) to prevents the collapse of the lungs. The gas mixture administered to him contains O, CO, and N2 with high pressure. Because of these a large amount of N2 is dissolved in his body fluids and fats Sudden exposure of that diver to low barometric pressure at sea level causes the formation of N, bubbles in body fluids and faury tissues that may block capillaries, hearts and also affect nervous system badly. This results the development of some signs and symptoms which are collectively known as Decompression Sickness or Caisson disease or Dysbarism or Diver’s palsy. So this disease is basically due to effect of N2 with high pressure known as N2 narcosis.

 Signs and symptoms

  • Pain in joints, muscles of legs and arms.
  • Dizziness, paralysis, collapse, unconsciousness, temporary sensory and motor disturbances nervous system is affected
  • Bubbles formation in lung vessels results into chokes characterised by shortness of breathing and pulmonary oedema

  • Treatement immediate  recompression in a chamber and gradual decompression.
  • Prevention of decompression sickness: it can be prevented by:
  • Gradual ascent from sea
  •  Inhalation of O2 helium mixture before the ascent. However at high atmospheric pressure it  can produce high pressure nervous syndrome (NPNS) which is characterised by tremors, drowsiness and depression of a activity in EEG

  •  Mild N2 narcosis resembles alcohol intoxification and the person becomes very jovial careless and fails to understand the seriousness of the situation in severe cases the person develops lethargy drowsiness, rapid onset of fatigue and loss of conciousness.

Respiratory distress syndrome of new born

  • Hyaline membrane disease or infant respiratory distress syndrome (IRDS). It is a serious disease of newborn infants, due to deficiency of surfactant; or it develops in infants born before their surfactant system becomes functional. (Surfactant is always present by 25 weeks of gestation).
  • Normally after birth, the infant makes several strong inspiratory movements and the lungs expand. Surfactant keeps them from collapsing again. But due to prolonged immaturity of epithelial Na channels, Cl is secreted with the fluid within the alveoli, resulting in deficiency of surfactant.
  • Therefore, surface tension in the lungs of these infants is very high, and there are many areas in which alveoli are collapsed (atelectasis). These infants must use a tremendous amount of energy to expand their collapased lungs with each breath. Also pulmonary oedema occurs and infants die of pulmonary insufficiency.
  • Infants with “IRDS” show low thyroid hormone and cortisol levels in their plasma.
  • ‘IRDS’ is also called hyaline membrane disease due to formation of hyaline (a translucent) membrane from albuminous intrapulmonary fluid in the walls of the alveoli and respiratory bronchioles.

What is Herring – Breuer reflex

1)when the lungs become overly inflated, the stretch receptors activate and appropriate feedback response that “switches off the inspiration ramp and thus stops further inspiration. This mechanism is called the Herring -Brewer inflation reflex. This reflex also increases the rate of respiration, as is true for signals from the pneumotaxic center.

2). In humans, the Herring Brewer reflex probably is not activated until the tidal volume increases to more than three times normal (>=1.5L/ breath). Therefore, this reflex appears. to be mainly  protective mechanism for preventing excess lung inflation rather than an important ingredient in normal control of ventilation.

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