OXYGEN TOXICITY (POISONING)
Oxygen toxicity is the increased oxygen content in tissues, beyond certain critical level. It is also called oxygen poisoning. It occurs because of breathing pure oxygen with a high pressure of 2 to 3 atmosphere (hyperbaric oxygen). In this condition, an excess amount of oxygen is transported in plasma as dissolved form because oxygen carrying capacity of hemoglobin is limited to 1.34 mL/g.
EFFECTS OF OXYGEN
TOXICITY
1. Lung tissues are
affected first with tracheobronchial irritation and pulmonary edema
2. Metabolic rate increases in all the
body tissues andthe tissues are burnt out by excess heat. Heat also
destroys cytochrome system, leading
to damage of tissues.
3. When brain is
affected, first hyperirritability occurs. Later, it is followed by increased
muscular twitching,
ringing in ears and
dizziness.
4. Finally, the toxicity results in
convulsions, coma and death.
HYPERCAPNEA
Hypercapnea is the increased carbon
dioxide content of blood.
CONDITIONS WHEN HYPERCAPNEA
OCCURS
Hypercapnea occurs in conditions,
which leads to blockage of respiratory pathway, as in case of
asphyxia.
It also occurs while breathing the air containing excess carbon dioxide
content.
EFFECTS OF
HYPERCAPNEA
1. Effects on
Respiration
During hypercapnea,
the respiratory centers are stimulated excessively. It leads to dyspnea.
2. Effects on
Blood
The pH of blood reduces and blood
becomes acidic.
3. Effects on
Cardiovascular System
Hypercapnea is associated with
tachycardia and increased blood pressure. There is flushing of
skin due
to peripheral vasodilatation.
4. Effects on
Central Nervous System
During hypercapnea,
the nervous system is also affected, resulting in headache, depression and
laziness. These symptoms are followed by muscular rigidity, fine tremors and
generalized convulsions. Finally, giddiness and loss of consciousness occur.
HYPOCAPNEA
Hypocapnea is the decreased carbon
dioxide content in blood.
CONDITIONS WHEN HYPOCAPNEA
OCCURS
Hypocapnea occurs in conditions associated
with hypoventilation. It also occurs after prolonged hyperventilation, because
of washing out of excess carbon dioxide.
EFFECTS OF HYPOCAPNEA
1. Effects on
Respiration
Respiratory centers
are depressed, leading to decreased rate and force of respiration.
2. Effects on Blood
The pH of blood
increases, leading to respiratory alkalosis. Calcium concentration decreases. It
causes
tetany, which is characterized by neuromuscular
hyperexcitability and
carpopedal
spasm.
3. Effects on
Central Nervous System
Dizziness, mental confusion,
muscular twitching and loss
of consciousness are the common features of
hypocapnea.
ASPHYXIA
Asphyxia is the condition
characterized by combination of hypoxia and hypercapnea, due to obstruction of
air passage.
CONDITIONS WHEN
ASPHYXIA OCCURS
Axphyxia develops in conditions
characterized by
acute obstruction of
air passage such as:
1. Strangulation
2. Hanging
3. Drowning, etc.
EFFECTS OF ASPHYXIA
Effects of asphyxia
develop in three stages:
1. Stage of hyperpnea
2. Stage of
convulsions
3. Stage of collapse.
1. Stage of
Hyperpnea
Hyperpnea is the first
stage of asphyxia. It extends for about 1 minute. In this stage, breathing
becomes
deep and rapid. It is due to the
powerful stimulation of respiratory centers by excess of carbon dioxide.
Hyperpnea is followed by dyspnea and cyanosis. Eyes become more
prominent.
2. Stage of
Convulsions
Stage of convulsions
is characterized mainly by convulsions (uncontrolled involuntary muscular
contractions). Duration of this stage is less than 1 minute.
Hypercapnea
acts on brain and produces the following effects:
i. Violent expiratory efforts
ii. Generalized convulsions
iii. Increase in heart rate
iv. Increase in arterial blood
pressure
v. Loss of consciousness.
3. Stage of
Collapse
Stage of collapse lasts
for about 3 minutes. Severe hypoxia produces the following effects during this
stage:
i. Depression of centers in brain and
disappearance of convulsions
ii. Development of
respiratory gasping occurs.During respiratory gasping, there is stretching of
the body with opening of mouth, as if gasping for breath.
iii. Dilatation of pupils
iv. Decrease in heart rate
v. Loss of all
reflexes.
Duration between the
gasps is gradually increased and finally death occurs.
All together, asphyxia
extends only for 5 minutes. The person can survive only by timely help such as
relieving the
respiratory obstruction, good aeration, etc.
DYSPNEA
Dyspnea means
difficulty in breathing. It is otherwise called the air hunger. Normally, the
breathing goes on without consciousness. When breathing enters the consciousness and
produces discomfort, it is called
dyspnea. Dyspnea is
also defined ‘as a consciousness of necessity for increased respiratory effort’.
DYSPNEA POINT
Dyspnea point is the level at which
there is increased ventilation with severe breathing discomfort. The
normal person
is not aware of any increase in breathing until the pulmonary
ventilation is doubled. The real discomfort develops when ventilation increases
by 4 or 5 times.
CONDITIONS WHEN
DYSPNEA OCCURS
Physiologically,
dyspnea occurs during severe muscular exercise. The pathological conditions
when
dyspnea occurs are:
1. Respiratory
Disorders
Dyspnea occurs in the respiratory
disorders, characterized by mechanical or nervous hindrance to respiratory movements
and obstruction in any part of respiratory tract. Thus, dyspnea occurs in:
i. Pneumonia
ii. Pulmonary edema
iii. Pulmonary
effusion
iv. Poliomyelitis
v. Pneumothorax
vi. Severe asthma, etc.
2. Cardiac
Disorders
Dyspnea is common in left ventricular
failure and decompensated mitral stenosis.
3. Metabolic
Disorders
Metabolic disorders, which cause
dyspnea are diabetic acidosis, uremia and increased hydrogen
ion
concentration.
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