external respiration

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					      Expiratory dyspnea is characterized by increased expiratory movements.
Etiology: bronchial asthma and emphysema, the second phase of axphyxia.
      Pathogenesis. Expiratory airflow obstruction may result either from
anatomic airway narrowing, such as is classically obserued in asthma, or from loss
of elastic recoil of the lung, which occurs in emphysema
      Attacks of bronchial asthma arise as a result of sudden spasm of the bronchi,
especially of the bronchioles, and are due to increased excitability of the efferent
fibres of the vagus nerve. It occurs in exhalation. That becomes particularly
laboured. Expiratory dyspnea in asthmatics is due to the resistance which has to be
overcome by the air leaving the alveoli. (Expiration is prolonged). During
exhalation the air is retained in the alveoli, the pressure in them rises and they
dilate, the dilation affects the capillary network of the lung. This in its turn
influences the blood flow and pressure in the pulmonary circulation and
,consequenty, the work of the right heart.
      Periodic respiration includes Biot"s and Cheyne-Stokes types of
respiration.
      Cheyne-Stokes respiration is characterized by increasingly greater
respiratory movements wich reach their maximum lend then gradually decrease.
The respiration unnoticeably becoming shallow and ending in a pause wich lasts
up to 30 seconds. After the pause the same phenomena recur.
      This form of periodic respiration is sometimes observed in deep sleep
(especially in old people). It is strongly pronounced in extreme cases of oxygen
deficiency (for example in severe pulmonary insufficiency), chronic nephritis,
decompensated heart diseases, cerebral lesions (sclerosis, hemorrhages, embolisms
tumours), increased intracranial pressure. Biot"s respiration is characterized by
pauses in ordinary respiration, i.e. a series of respiratory movements are followed
by a long pause, after wich there is a new series of respiratory-movements also
followed by a pause, etc. This form of respiration is seen in meningitides,
encephalitides, some cases of poisoning ,and heat stroke.
      Phatogenesis.
      Two hypothesis explaining the mechanisms of periodic respiration is named
the medullary hypothesis. According to this periodic respiration. Cheyne-Stokes
respiration in particular, is based on reduced excitubility of the respiratory centre
wich reacts weackly to the usial carbon dioxide concentration in the blood. During
apnea carbon dioxide accumulates in the blood wich the result that respiration is
resumed , the excess of carbon dioxide is eliminated from the blood and espiration
is suspended again.
      It is now held that the impaired excitability of the respiratory centre is due to
oxygen deficiency,
				
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Description: disorders in external respiration
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