The normal breathing is known as eupnoea. Sometimes breathing occurs at a faster rate, then is known as tachypnoea and sometimes breathing occurs at a slower rate is called bradypnoea. The normal breathing is often disturbed by certain environmental and physiological conditions. The most important disorders are Asphyxia, Hypoxia, Carbon monoxide poisoning and High altitude problems.
i) Asphyxia: The failure of delivery of oxygen to the tissues is known as asphyxia or breathlessness. It may occur due to drowning, chocking etc. These prevent the entry of air into the lungs. When breathing is obstructed, there occurs cough and violent respiratory efforts. This results in a dyspnoea (difficulty in breathing).
ii) Hypoxia: The oxygen deficiency at the tissue level is known as hypoxia or anoxia. It may be classified into the following types.
a) Arterial hypoxia: It is due to the low level oxygen in the blood. It occurs when the atmosphere does not contain sufficient oxygen or when there is an obstruction in the respiratory passage.
b) Anaemic hypoxia: It is due to the low level of haemoglobin in the blood.
c) Stagnant hypoxia: In this, the blood flow is adequate to deliver oxygen to the tissues.
d) Histoxic hypoxia: In this, the tissues cannot make use of oxygen delivered to them because of the presence of toxic substances. Cyanide poisoning causes histoxic hypoxia
 iii) High altitude problems (Mountain sickness):
If a man is going to high altitude about 8000 feet from the sea level, he develops certain symptoms such as breathlessness, headache, dizziness, nausea, vomiting, fatigue and bluish tinge on the skin, nails and lips in 8-24 hours. This is known as Mountain sickness. This is due to fall of PO2 level at high altitude. This lowers alveolar PO2 and consequently reduces the diffusion of oxygen from the alveolar air to the blood. So oxygenation of blood is decreased progressively. The fall in oxygen level in the blood causes the symptoms.
RBC count in the blood is increased by the stimulation of bone marrow. The haemoglobin level and oxygen carrying capacity are also increased. As a result each ml of blood takes more oxygen than the normal level.
 iv) Carbon monoxide poisoning: Carbon monoxide is a toxic gas that binds hemoglobin and forms a stable compound known as carboxy hemoglobin. The affinity of Hb for carbon monoxide is 250 times greater than oxygen. Thus the amount of hemoglobin available for oxygen transport is reduced. The resulting deficiency of oxygen causes headache, dizziness, nausea and even death. This is known as carbon monoxide poisoning. The treatment of carbon monoxide poisoning is the administration of oxygen with 6% carbon dioxide. CO2 stimulates the respiratory centre of the brain.
