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Medicine | Respiratory

Respiratory

Presented below are some  pictures of the horse's respiratory tract. These images are something that we take for granted. Imagine what we would miss if we did not have this high tech equipment. 

Endoscopy examination for Respiratory Disease

Endoscopic examination by means of the flexible fibreoptic endoscope or videoscope allows the veterinarian to directly visualise a large proportion of the respiratory system of the horse.  Use of a video system allows live demonstration for owners and students directly via a monitor and recording for patient records and comparison for follow up examinations, if necessary.  The majority of endoscopic examinations will be performed in the patient standing and resting, usually restrained by means of a twitch.  Use of tranquillising agents may be contraindicated particularly when evaluating the upper respiratory tract for poor performance, as these agents may affect upper respiratory tract function to a small but significant degree.

GVEH has purchased a Dynamic Respiratory Scope (DRS) which can be used in teh horse, on the tract, while exercising at speed.  Dynamic changes in the upper respiratory tract, occurring only at exercise, can be diagnosed.  Since this modality has been available “new” upper airway disorders have been demonstrated. 

Endoscopic examination has enabled the veterinarian to make a definitive diagnosis in many conditions which in the past may not have been possible. In other conditions the endoscope may be used in conjunction with radiography, ultrasound examination, biopsy or cytology via the endoscope in order to reach a diagnosis. 

Clinical signs of respiratory disease, such as:

  • nasal discharge (mucus, pus, blood, food, milk),
  • respiratory noise ( at exercise or rest),
  • facial swelling,
  • coughing,
  • respiratory distress (dyspnoea),

 are indications for respiratory endoscopic examination.

The endoscopic examination of the respiratory tract of the horse begins by passage of the flexible endoscope through the externals nares or nostril, in a similar fashion to passing a stomach tube for drenching a horse. Past the nostril, the nasal cavity is entered which is partially divided by soft bones called turbinate bones.  Toward the back of the nasal cavity a slit like opening is visible which open into the sinus. This opening is adjacent to an intricate structure known as the ethmoturbinate bone.  On further passage of the endoscope the pharynx is entered. Up to entry into the pharynx the left and right nasal passages of the are separated by a bone / cartilage septum.  The pharynx is where the oral cavity and respiratory tract unite. The soft palate is a muscular membrane that channels airflow between the nostrils and larynxand combined with the epiglottis enables food material and water to be swallowed without risk of inhalation. The openings of the two guttural pouches are visualised within the pharynx. In some cases, direct visualisation within these pouches may be indicated.  Lymphoid tissue on the roof of the pharynx may be assessed. The arytenoid cartilages open to enable maximal airflow to the lung during exercise. Fluctuating pressures within the airway, generated by intense exercise may cause partial collapse of soft tissue structures in this area. Resulting turbulent air flow causes respiratory noises and in severe cases exercise tolerance may be affected.  Passage of the endoscope through the larynx into the trachea is well tolerated in the horse.  The trachea courses caudally along the neck to enter the chest. Within the chest, the trachea becomes almost horizontal for a portion creating a natural area for discharges (mucus, pus, blood) from the lung to accumulate.  A coughing horse may cause “splattering” of these secretions over the trachea or material may collect in a pool before being cleared by cilia. Secretions are then either removed from the respiratory tract by swallowing or as nasal discharge.  The endoscope may be passed to the carina where the trachea divides into the two major bronchi within the lung. Further entry to the lung is not usually performed because this area is very sensitive.  Secretions from the lung and trachea may be obtained using the biopsy channel of the endoscope. Broncho-alveolar lavage (BAL) or “lungwash” is a technique for sampling cells that line the very small bronchioles and alveoli.  This may be performed via the endoscope or more commonly via a special BAL tube.  Analysis of cells retrieved by this technique is very useful in detailed investigation of diffuse lung disease.  Broncho-alveolar lavage is performed in the standing sedated horse. 

Endoscopy

altThe hospital is equipped with two video-endoscopy units, which allow detailed examination and video-capture of footage. We have a narrow-bore smaller endoscope which is mostly used in foals, as well as a larger-bore, longer unit which we use in adults. These units are used to evaluate upper airway function.

 In selected cases, a horse may not have a lesion visible on standing endoscopy. With these so-called dynamic obstructions the horse may need to be examined on our 600-metre track, or treadmill-endoscopy unit.

Candidates for treadmill endoscopy must be in work, and will generally need to be admitted to the hospital for several days to allow for a few days of treadmill training and acclimatisation.

altThe hospital is also equipped with a 3-metre long gastroscope which allows evaluation of the stomach and the start of the duodenum, in horses where ulcers are suspected. Horses must be starved overnight, and have water withheld for several hours before gastroscopy is undertaken. If you require this procedure to be performed on your horse, please contact the hospital well in advance to allow coordination of events.