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Breathing difficu


									   Physiology of
breathing difficulties
   Dr. Dalia Abd-Elhalim
 Peoplewith pulmonary disorders frequently
 complain of dyspnea, a subjective feeling of
 shortness of breath.

 Dyspnea  may occur even when ventilation
 is normal, however, and may not occur
 even when total minute volume is very high,
 as in exercise
 Definition: It is difficult or labored breathing in
  which the subject is conscious of shortness of
  breath. A common synonym is air hunger
 Three factors enter into the development of
  the sensation of dyspnea:
1- Abnormality of respiratory gases in the body
  fluids, especially hypercapnia and, to a much
  less extent, hypoxia.
2- The amount of work that must be performed by
  the respiratory muscles to provide adequate
3- State of mind.
              Dyspneic index
   Breathing reserve = Maximum breathing capacity
    - Minute ventilation
   Significance:
                       Breathing reserve
Dyspneic index=                                  %
                    Maximum breathing capacity

Normally dyspneic index = 90%, when it decreases
to 60% or less, dyspnea occurs on slight effort
    Mechanisms of Dyspnea
Respiratory sensations are the consequence
of interactions between the efferent or motor
output from the brain to the ventilatory
muscles (feed-forward) and the afferent or
sensory input from receptors throughout the
body (feedback), as well as the integrative
processing of this information that we infer
must be occurring in the brain
    Mechanisms of Dyspnea (cont.)
Motor Efferents
   Disorders of the ventilatory pump are associated with
    increased work of breathing or a sense of an increased
    effort to breathe.

   When the muscles are weak or fatigued, greater effort is
    required, even though the mechanics of the system are

   The increased neural output from the motor cortex is
    thought to be sensed due to a corollary discharge that is
    sent to the sensory cortex at the same time that signals
    are sent to the ventilatory muscles.
    Mechanisms of Dyspnea (cont.)
Sensory Afferents
    Chemoreceptors are activated by hypoxemia, acute hypercapnia,
    and acidemia. Stimulation of these receptors, that lead to an
    increase in ventilation, produce a sensation of air hunger.

   Mechanoreceptors in the lungs, when stimulated by bronchospasm,
    lead to a sensation of chest tightness.

   J-receptors, sensitive to interstitial edema, and pulmonary vascular
    receptors, activated by acute changes in pulmonary artery pressure,
    appear to contribute to air hunger.

   Hyperinflation is associated with the sensation of an inability to get a
    deep breath or of an unsatisfying breath.

   Metaboreceptors, located in skeletal muscle, are believed to be
    activated by changes in the local biochemical milieu of the tissue
    active during exercise and, when stimulated, contribute to the
    breathing discomfort.
    Mechanisms of Dyspnea (cont.)
Integration: Efferent-Reafferent Mismatch
   A mismatch between the feed-forward message to the
    ventilatory muscles and the feedback from receptors that
    monitor the response of the ventilatory pump increases the
    intensity of dyspnea.

 This is particularly important when there is a mechanical
    derangement of the ventilatory pump, such as in asthma or
    chronic obstructive pulmonary disease (COPD).
 Mechanisms of Dyspnea (cont.)

Acute anxiety may increase the severity of
dyspnea either by altering the interpretation of
sensory data or by leading to patterns of breathing
that heighten physiologic abnormalities in the
respiratory system.
          Shortness of Breath:
           Common Causes
   Psychological
    e.g. anxiety and stress

   Pulmonary
    e.g. Asthma, bronchitis, emphysema, pulmonary fibrosis,
    pulmonary hypertension and pleurisy.

   Cardiac
    e.g. heart failure, cardiomyopathy and pericarditis

   Other Problems
    e.g. acute kidney failure, obesity and pregnancy
   Physiologic peculiarities of
specific pulmonary abnormalities
   The physiologic effects of chronic
1- An increase in airway resistance results in greatly
   increased work of breathing.
2- A decrease in the diffusing capacity of the lung
3- Abnormal ventilation-perfusion ratios, with a very low
   Va/Q in some parts (physiologic shunt), and very high
   Va/Q in other parts (physiologic dead space).
4- Pulmonary hypertension
   Physiologic peculiarities of
specific pulmonary abnormalities
   The physiologic effects of
1- Reduction in the total available surface area of the
   respiratory membrane
2- Decreased ventilation-perfusion ratio.
   Physiologic peculiarities of
specific pulmonary abnormalities
   Atelectasis

Airway Obstruction as a Cause of Lung Collapse
Lack of “Surfactant” as a Cause of Lung Collapse
   Physiologic peculiarities of
specific pulmonary abnormalities
 The physiologic effects of asthma
1- The functional residual capacity and residual volume of
   the lung become especially increased during the acute
   asthmatic attack because of the difficulty in expiring air
   from the lungs.

2- Over a period of years, the chest cage becomes
   permanently enlarged, causing a “barrel chest,” and both
   the functional residual capacity and lung residual volume
   become permanently increased.
   Physiologic peculiarities of
specific pulmonary abnormalities
 The    physiologic effects of Tuberculosis:
1- Increased “work” on the part of the respiratory muscles to
   cause pulmonary ventilation and reduced vital capacity.

2- Reduced total respiratory membrane surface area and
   increased thickness of the respiratory membrane,
   causing progressively diminished pulmonary diffusing

3- Abnormal ventilation-perfusion ratio in the lungs, further
   reducing overall pulmonary diffusion of oxygen and
   carbon dioxide.
Thank You

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