Thorax: Respiratory and Cardiac Evaluation

The thoracic cage is observed and respiratory rate & effort noted. The thoracic cavity is palpated to evaluate for any anatomic abnormalities, and palpation of the precordial area can be performed prior to auscultation.

Cardiovascular System

The animal should be standing for cardiac auscultation. Begin the exam by palpating over the cranioventral thoracic cavity to locate the heart beat (left of sternum). Place your stethoscope over this area to begin your cardiac auscultation. Move your stethoscope around this region and note when the heart beat changes in intensity. Carefully auscultate both sides of the thoracic wall over the heart; calculate a heart rate.

Normal heart sounds (note the 2 separate/distinct sounds – “lub dub”):

Palpate the femoral pulse while auscultating the heart to ensure that the heart and pulse rate match – if pulses are nor present for some heart beats, this is consistent with an arrhythmia.

Muffled heart sounds may be due to pericardial effusion or pleural space disease (as outlined above).

Further details will be given in the Cardiac Auscultation laboratory of this course on specific cardiac valve location & auscultation techniques.

Respiratory System

Evaluate the breathing pattern and rate prior to auscultation. The pattern is a description of the relationship between inspiration and expiration plus the depth of respiration (shallow vs. deep). Examples of pathological respiratory signs:

• Inspiratory dyspnea, or difficulty breathing,  usually indicates a problem above the carina.
• Expiratory dyspnea can be detected by observing an expiratory phase > inspiratory phase.This usually indicates a problem in the lower airways.
• Significant pleural space disease (pneumothorax, effusions, masses, hernias) usually causes a rapid, shallow breathing pattern, with shortened inspiratory and expiratory phases.
• Open mouthed breathing and expiratory dyspnea can be detected by observing an expiratory phase > inspiratory phase. This usually indicates a problem in the lower airways.

• Upper airway sounds can be reflected to the lower airway (always listen to the trachea to differentiate this).
  • Stertor: low-pitched upper respiratory sound similar to a snore, caused by vibration of pharyngeal flaccid soft tissues. For example: brachycephalic dogs with elongated soft palates.
  • Stridor: high-pitched upper respiratory sound, caused by vibrations of rigid tissue (laryngeal cartridges, trachea). For example: laryngeal paralysis, tracheal collapse.

The lung fields are ausculted in a systemic method – use a grid system with your stethoscope to cover the entire lung field on each side (usually 4-6 spots over the thorax per each side depending on body size). It may be normal to hear very quiet or undetectable breath sounds while ausculting the cat chest.

Abnormal lung sounds can be described as continuous (wheezes) or discontinuous (crackles). If abnormal sounds are detected, note if they exist in specific region(s) or diffusely.

Normal lung sound:

Lung sound in a dog with bronchitis (note high pitched wheeze sound):

The absence of lung sounds may be indicative of pleural space disease (pneumothorax, pleural effusion, masses, diaphragmatic hernia) or lung lobe consolidation.

Percussion of the thoracic wall is not routinely done in small animals.