Respiratory Examination – Dyspnea

Definition: Breathlessness inappropriate to the level of physical exertion or even occurring at rest (subjective and not a sign)

Mechanisms:

Chemoreceptors:

Peripheral: Carotid and aortic bodies (to pO2, pCO2 and H+)
Central: Medulla (to pCO2, not pO2, change in pH of CSF)

a. Increased work of breathing:

  • Airflow obstruction: Bronchial asthma, COPD, Tracheal obstruction
  • Decreased pulmonary compliance: Pulmonary edema, fibrosis, allergic alveolitis
  • Restricted chest expansion: Ankylosing spondylitis, Respiratory paralysis, Kyphoscoliosis

b. Increased ventilatory drive:

  • Increased physiological deadspace (V/Q mismatch): Consolidation, Collapse, PE, Pulmonary edema
  • Hyperventilation due to receptor stimulation:
    • Chemoreceptors: Acidosis, Hypoxia (Shock, Pneumonia), Hypercapnia
    • J receptors at alveolo-capillary junction: Pulmonary edema, Pulmonary embolism, Pulmonary congestion (Activates Hering-Breur reflex which terminates inspiratory effort before full inspiration is achieved – rapid and shallow)
    • Muscle spindles in intercostal muscles: Tension-length disparity
  • Central: Exertion, anxiety, thyrotoxicosis, pheochromocytoma

c. Impaired respiratory muscle function: Polio, GBS, Myasthenia

Corollary discharge: When the CNS voluntarily sends a signal to the respiratory muscles to increase the work of breathing, it also sends a copy to the sensory cortex telling it there is an increased work of breathing.

Orthopnea:

  1. Pulmonary congestion during recumbency (cannot be pumped out of LV) seen in CHF, COPD and Asthma
  2. Increased venous return
  3. Diaphragm elevation leading to decreased vital capacity

orthopnea

Dyspnea in COPD:

  1. Hypoxia and hypercapnia: Chemoreceptors
  2. Increased airway resistance and hyperinflation
  3. Deconditioning: Reduced threshold at which respiratory muscles produce lactic acidosis

Basics: A normal 70 kg person breathes 12-15/min with a tidal volume of 600 ml. A normal individual is not aware of respiratory effort until ventilation is doubled, and dyspnea is not experienced until ventilation is tripled.

Paraoxysmal nocturnal dyspnea: Decreased responsiveness of respiratory center in brain and decreased adrenergic activity in myocardium during sleep and pulmonary congestion 2-5 hours after onset of sleep

  • Takes 10-30 min for recovery after upright posture

orthopnea vs pnd

Trepopnea: Dyspnea worse when lying on one side and relieved by lying on opposite side

Causes:

  1. Unilateral lung disease: Good lung receives more blood supply due to gravity
  2. CHF: Lying on right side enhances venous return and sympathetic activity
  3. Lung tumor: Gravity induced compression of blood vessels or lung

Platypnea: Dyspnea on sitting or standing and relieved by supine position

Causes:

  1. Venous to arterial shunting (Lung bases)
  2. Intra-cardiac shunts (ASD, Pneumonectomy)
  3. Intrapulmonary Rt to Lt shunt (Hepatopulmonary syndrome, PE, COPD)
  4. ARDS

Platypnea in Hepatopulmonary syndrome:

  1. Diffuse intrapulmonary shunts
  2. Impaired hypoxic vasoconstriction (V/Q mismatch)
  3. Pleural effusion and diaphragmatic dysfunction
  4. Hyperdynamic circulation and low pulmonary resistance

Features:

a. Onset and Duration: Can ask when able to run upstairs?

  • Minutes to hours (Rapid onset): Pneumothorax, Acute asthma, PE, Pulmonary edema, Foreign Body
  • Hours to days (Gradual onset): Pneumonia, Pleural effusion, Anemia, GBS
  • Months to years (Slow onset): PTB, COPD, Carcinoma, Fibrosing alveolitis

b. Severity: How far before stopping? How any flights of stairs? At rest? Sleep? Talking? Dressing?

MRC grading:

  • I – On sternous exertion
  • II – Hurrying on level ground or Walking up slight hill
  • III – Walks slower than people of same age or Stops when walking at own pace on level
  • IV – Stops after 100 yards (90 m) or after few minutes in level
  • V – Breathless to leave house, dress or undress

NYHA classification of severity of heart failure:

  • I – No limitation with ordinary physical activity
  • II – Mild limitation of ordinary physical activity
  • III – Marked limitation of activity, symptoms with exertion
  • IV – Symptoms at rest

c. Aggravating and relieving factors:

  • Improves on weekend/holidays: Occupational asthma, extrinsic allergic alveolitis
  • Recumbency/Sleep: Orthopnea/PND

d. Associated symptoms:

  • Pleuritic chest pain: Pneumonia, Pulmonary infarction, Rib fracture, Pneumothorax
  • Central non-pleuritic chest pain: MI, Massive PE
  • Cough or wheeze: Asthma, PE, Pneumothorax

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