DYSPNEIC INDEX
Dyspneic index is the index
between breathing reserve and maximum breathing capacity (MBC). Breathing reserve is the
balance (difference) between MBC and respiratory minute
volume (RMV).
For example, in a normal subject, MBC
is 116 L and RMV is 6 L.
MBC – RMV
Dyspneic index = × 100 MBC
116 – 6 = × 100
116
= 94.8%.
Dyspnea develops when the dyspneic
index decreases below 60%.
PERIODIC BREATHING
Periodic breathing is
the abnormal or uneven respiratory rhythm. It is of two types:
1. Cheyne-Stokes
breathing
2. Biot breathing.
CHEYNE-STOKES
BREATHING
Features of
Cheyne-Stokes Breathing
Cheyne-Stokes breathing
is the periodic breathing characterized by rhythmic hyperpnea and apnea. It is
the most common type
of periodic breathing. It is marked by two alternate patterns of respiration:
i. Hyperpneic period
ii. Apneic period.
Hyperpneic period –
waxing and waning of breathing To begin with, the breathing
is shallow. Force of
respiration increases
gradually and reaches the maximum (hyperpnea). Then, it decreases gradually
and reaches minimum and is followed by
apnea. Gradual increase followed by gradual decrease in force
of respiration is called waxing and waning of
breathing.
Apneic period
When, the force of breathing
is reduced to minimum, cessation of breathing occurs for a short period. It is
again followed by hyperpneic
period and the cycle is
repeated. Duration of one cycle is about 1 minute.
Sometimes, waxing and
waning of breathing occurs without apnea.
Causes for Waxing and
Waning
Initially, during forced
breathing, large quantity of carbon dioxide is washed out from blood. When partial
pressure of carbon dioxide decreases,
respiratory centers become inactive. It causes apnea. During
apnea, there is accumulation of carbon
dioxide (hypercapnea)
and reduction in oxygen tension
(hypoxia). Now, the respiratory
centers are activated, resulting in gradual increase in the force of
breathing.
When the force of breathing reaches maximum, the cycle
is repeated.
Conditions when
Cheyne-Stokes Breathing Occurs
Cheyne-Stokes
breathing occurs in both physiological and pathological conditions.
Physiological
conditions when Cheyne-Stokes breathing occurs
i. During deep sleep
ii. In high altitude
iii. After prolonged
voluntary hyperventilation
iv. During hibernation
in animals
v. In newborn babies
vi. After severe muscular exercise.
Pathological
conditions when Cheyne-Stokes breathing occurs
i. During increased
intracranial pressure
ii. During advanced
cardiac diseases, leading to cardiac failure
iii. During advanced
renal diseases, leading to uremia
iv. Poisoning by
narcotics
v. In premature infants.
BIOT BREATHING
Features of Biot
Breathing
Biot breathing is another
form of periodic breathing characterized by period of apnea and hyperpnea.
Waxing and waning of
breathing do not occur.
After apneic period, hyperpnea occurs abruptly.
Causes of Abrupt
Apnea and Hyperpnea
Due to apnea, carbon dioxide
accumulates and it stimulates the respiratory centers, leading to
hyperventilation.
During hyperventilation, lot of carbon dioxide is washed out.
So, the respiratory centers are not stimulated and apnea occurs.
Conditions when Biot
Breathing Occurs
Biot breathing does
not occur in physiological conditions. It occurs only in pathological
conditions. It occurs in conditions involving nervous disorders due to lesions or injuries to brain.
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