Veterinary Clinical Medicine-I (General and Systemic)

EXAMINATION OF THE THORAX

• The thorax must be first examined by inspection to assess its form and shape. Unilateral narrowing of the thorax occurs in pleuritic diseases after absorption of exudate whereas bilateral narrowing occurs in tuberculosis, and in rickets.
• Bilateral enlargement (barrel shape) of the thorax is seen in bilateral alveolar emphysema, and bilateral exudative pleuritis. Unilateral enlargement of the thorax maybe seen in unilateral exudative pleuritis, pneumothorax and unilateral pneumonia.
• Palpation for assessing the sensitivity of the thorax and its temperature. Hotness and pain occurs in acute inflammatory conditions and pleuritis.
• Direct or indirect percussion is an important method of examination in small and large animals (dogs, cats, and ruminants, equines respectively). For percussion of thorax, the vet must first determine the area of percussion.
• On percussion of the thoracic wall, the area must be divided into upper, middle and lower thirds. The most intensive pulmonary sound is heard on percussion of the middle third where the thoracic wall is somewhat thin, curvature of the ribs is large and airwaves are deep. In the upper third, the heavy musculature hinders clear resonant sound of the lungs.

Changes in area of percussion

• Increased area of percussion is seen when the size of lung tissue increases, presence of large amount of air in the lungs as in alveolar emphysema, various forms of pneumonia and in cases of unilateral pneumonia and pneumothorax there is a unilateral increase in the area of lung percussion.
• Decreased area of lung percussion is seen in animals with acute gastric dilatation, tympany of the intestine, ruminal tympany and in cases of presence of fluids in the thoracic cavity.
• Normally in most animal species percussion over the lung area results in resonant sound; in very small animals it is more of a tympanic sound.

Abnormal percussive sounds

• Loud resonant sound (e.g. emphysema and pneumothorax).
• Tympanic sound; when a part of lung tissues are surrounded by solidified tissue or exudate, which isolates it from its environment. This occurs in the following conditions
  • In early and late stages of fibrinous pneumonia.
  • In catarrhal pneumonia.
  • In pulmonary oedema and atelectasis.
  • In presence of small or large tumors which surround lungs.
  • In prolapse of the bowel into the thoracic cavity in diaphragmatic hernia.
• Dull sound is heard when lung tissue becomes dense. This occurs in
  • Pneumonic hepatization.
  • Tuberculosis and metastatic pneumonia.
  • Tumors.

Notes of practical importance

• Changes in the character of the percussion sound is detectable only when a lesion is present in a considerable size and is superficially situated.
• A pain reaction maybe produced by percussion. This is indicated by the animal kicking or biting or even shying away from the examiner; vocalization in cases of dogs and cats.
• Percussion may also induce cough in cases of pneumonia, bronchitis and pleurisy.
• Differentiation between increased density of the lungs and that due to the presence of fluid in pleural sacs is determined as follows
  • Increased density of the lungs in pneumonia, the area of dullness has an irregular outline, the cardiac impulse is palpable, heart sounds are clearly audible outside the cardiac area, abnormal bronchial or other sounds are often heard during auscultation (rales or frictional sounds).
  • Presence of fluid in the pleural cavity (e.g. exudative pleurisy, hydrothorax) results in an area of dullness that has a horizontal delimitation, which changes when the posture of the animal is altered.
  • Auscultation is carried out to assess sounds produced during breathing when the air enters the lung. The sound normally heard on the healthy lung is termed vesicular murmur. This sounds like the soft pronunciation of the letter “V”. It begins with the inspiration, increasing as the inspiration continues, becomes fainter and shorter having the character of a softly aspirated “F” at expiration.
  • An exaggerated vesicular murmur occurs
  • If the respiration is intensified.
  • Physiological or pathological dyspnoea.
  • In bronchitis where the lumen of the bronchi are either swollen, or filled with exudate.

Adiminished vesicular murmur occurs in

• Thickened, swollen or neoplastic thoracic wall.
• In severe bronchitis.
• Complete absence of vesicular murmur occurs if plural exudate or tumours have replaced the lung tissue. Rarely occurs in severe vesicular pulmonary emphysema, or complete occlusion of a bronchus preventing access of air into a certain portion of the lung.

Rales

• These are abnormal respiratory sounds indicate presence of respiratory disease; if the bronchi or a cavern in the lung contain movable exudate.

Types of rales include

• Moist rales
  • If the bronchi contain light fluid (pus, liquid exudate or blood). Bronchitis with varying degrees result in moist rales.
• Crepitant rales
  • Fine cracking noises. They originate from a separation at respiration of the adhering walls of the bronchi and vesicles. They appear in bronchitis, pulmonary oedema and in early stages of fibrinous pneumonia.
• Dry rales
  • In cases of swelling of mucous membranes, or presence of tough bronchial secretion of small quantity. These result in rough mucous membranes, projecting irregularities, which vibrate during inspiration and expiration.
  • Sounds maybe humming, hissing or whistling in character. Dry rales are seen in chronic bronchitis, compression of the bronchi by nodules (tuberculosis, chronic pneumonia) and tumours.
  • Presence of peristaltic sounds in the thoracic cavity indicates ruptured diaphragm and protrusion of the intestine into the thoracic cavity. In contrast to the lung sounds, they are not synchronous with inspiration and expiration.
• Pleuritic frictional sounds
  • In cases of surface of pleura becomes rough and dry due to presence of inflammatory deposits, frictional sounds are heard. Pleuritic frictional sounds occur in dry or fibrinous pleuritis only. It is most frequently heard in contagious pleuro-pneumonia of horse and ox.
  • Summary of the differences between rales and frictional sounds.

    Rales	Frictional sounds
    More pronounced at inspiration than expiration	Heard at both inspiration and expiration regularly (i.e. associated with respiratory cycle).
    Removed or modified by cough	Cough does not affect its presence
    	Painful