Page 615 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

590 CHAPTER 3

VetBooks.ir Lymph nodes • Induction of cough: squeezing the larynx to
• Submandibular lymph nodes are located
induce a cough may provide some indication of
between the horizontal rami of the mandible
and are palpable in normal horses as a group laryngeal sensitivity, but this is a highly subjective
procedure that has limited clinical value.
of small, loosely associated lymphoid nodules. • Auscultation of the larynx may provide some
These lymph nodes receive drainage from the information about the larynx and is worthwhile
rostral nasal cavity and nasopharynx and thus because laryngeal noise will be audible in the
become enlarged in most URT infection cases lung field and can confuse thoracic auscultation.
and in some cases of dental disease.
• Retropharyngeal lymph nodes are located Trachea
immediately dorsal to the oesophageal pharynx Palpation of the trachea can help detect physical
and immediately ventral to the floor of the deformity, and squeezing the trachea to induce a
medial pouch of the guttural pouch (the nodes cough is carried out by some clinicians. This, as for
are clearly visible through the guttural pouch the larynx, is a highly subjective measure of tracheal
floor). They are not palpable in normal horses. sensitivity and has limited value.
All lymph flow from the head passes through Auscultation of the trachea is worthwhile because
these nodes; they become enlarged in response tracheal noise radiates to the lung field and airway
to infection, but need to be grossly enlarged discharges pool at the thoracic inlet and it provides
before they become palpable. a valuable estimate of events in the distal airway
• The parotid lymph node drains the orbit and lung.
and ear region, but does sometimes become
abscessed in Streptococcus equi infection. Lung field auscultation
The auscultation area of the lung field is triangular
Guttural pouches in shape. Its cranial boundary is the vertical line of
• Palpate retropharyngeal area for swelling or the caudal edge of the triceps muscle between the
pain (not a sensitive indicator of guttural pouch caudal border of the scapula and the olecranon. Its
disease). dorsal boundary is a horizontal line from the caudal
• Obvious distension usually indicates tympany, border of the scapula to the tuber coxae. The caudal
although it may also occur in severe cases of border of the lung field slopes cranioventrally from
empyema. the 16th or 17th intercostal space to the olecranon.
In normal adult horses there is little audible noise
Larynx in any part of the lung field. Foals and thin adults
• Palpate the dorsal surface of the larynx have much more obvious noise on auscultation. The
for symmetry of the left and right dorsal hilar region, immediately dorsal to the heart base,
cricoarytenoid muscles and laryngeal cartilages. contains the major divisions of the bronchial tree
• Slap test: a slap just caudal to the withers and there is air movement noise (bronchial sounds)
induces a brief contralateral adduction of the in this region on inspiration, with quiet bronchial
arytenoid cartilage that can be palpated as a sounds on expiration. The peripheral lung field is
flick of the cricoarytenoid muscle or visualised quiet, with barely perceptible air movement sounds
endoscopically. The reflex requires intact on inspiration or expiration.
spinal cord ascending white matter pathways The audible area of the lung field may be expanded
(cuneate and gracile pathways in the dorsal in horses with severe recurrent airway obstruction
funiculus) as well as intact motor pathways in or decreased ventrally if there is pleural effusion or
the recurrent laryngeal nerve and functional pulmonary consolidation.
cricoarytenoid muscles. Recent research has Auscultation at rest is not a sensitive means of
cast doubt on its relevance to the respiratory assessing the lung fields because of the slow breath-
examination. ing rate and small tidal volume compared with when