Brachycephalic Breathing

Question 1

Brachycephalic breed

Answer 1

-short head; short muzzle
-width:length ratio less than 0.81

Question 2

Cost of selected breeding (brachycephalic)

Answer 2

-reduced skull size but the soft tissue and teeth remain unchanged
-extra skin/tissue/teeth relative to skull size
-results in skin problems and massive under bite
-increased incidence and severity of respiratory disorders

Question 3

Brachycephalic obstructive airway syndrome (BOAS)

Answer 3

1.stenotic nares (primary symptom)
2. hypertrophic nasal turbinate (primary symptom)
3. elongated soft palate (primary symptom)
4.hypoplastic trachea (secondary symptom)
5. everted laryngeal saccules (secondary symptom)
**Overall very high airway resistance= inspiration and expiration both become an active process

Question 4

Stenotic nares

Answer 4

-obstructs nose breathing

Question 5

Hypertrophic nasal turbinate

Answer 5

-increase number of cells, extra folds, protrudes into nasopharynx

Question 6

Elongated soft palate

Answer 6

-narrows pharyngeal and nasopharyngeal path
-soft palate extends into larynx
**audible breath sounds
-can have surgery to remove extension and help with airflow/breathing

Question 7

Hypoplastic trachea

Answer 7

-less number of cells, thinner and narrower trachea, prone to collapse

Question 8

Everted laryngeal saccules

Answer 8

-pulled into airway due to excess negative pressure
-function may be to provide lubrication to vocal cords
**obstructs path of airflow resulting in increased airway resistance

Question 9

Airway resistance

Answer 9

-influences compliance (how easy/difficult it is for the air to go through tip of nose/mouth and distend the alveoli)
-normally air travels through resistance in airway but is easily overcome, reaches the alveoli and causes distention
-Air traveling in brachycephalics encounters much greater resistance (soft palate extension, stenotic nares, increased turbinate folds) resulting in less air reaching alveoli
*means only partial distension of alveoli
*Forced inspiration to generate more negative pressure to further expand alveoli

Question 10

Why do brachycephalics undergo more mouth breathing?

Answer 10

-more mouth breathing uses a path of reduced airway resistance
-results in air being less humidified and easier dehydration

Question 11

Inspiration and expiration effort of brachycephalics

Answer 11

-increased because need to overcome greater resistance to achieve sufficient ventilation
-they must work harder for every breath

Question 12

Increased airway resistance in brachycephalics

Answer 12

-more negative pleural pressure is required to meet compliance/extend alveoli
-more positive pressure needed to overcome resistance for expiration
-increased inspiration and expiration effort to overcome resistance to achieve sufficient ventilation
**work harder for every breath

Question 13

Compliance curve shift

Answer 13

-more pressure is required to reach total lung capacity

Question 14

Consequences of increased pressure requirements

Answer 14

1. increased respiration effort
2. audible breathing sounds caused by high velocity turbulent airflow
3. poor thermoregulation
4. exercise intolerant

Question 15

Increased respiration effort and effect on tissues

Answer 15

-generates high negative pressure that sucks soft tissues into the airway. Tissues become hyperplastic (stretched and expands; eg. Laryngeal saccules) and laryngeal cartilage can collapse and exacerbate obstruction

Question 16

Audible breathing sounds

Answer 16

-caused by high velocity turbulent airflow

Question 17

Poor thermoregulation

Answer 17

-overheating
-panting allows heat to escape as moisture that evaporate in air
-BOAS causes exhalation to be a forceful process which requires energy and generates more heat

Question 18

Exercise intolerant

Answer 18

-leads to obesity
-excess fatty tissues impedes thoracic cage expansion during respiration
-increased risk for metabolic disorders

Question 19

Stertor

Answer 19

-caused by elongated and thick soft palate that extends into larynx
-extra effort needed to move soft palate out of larynx to allow air to pass which triggers the vibration

Question 20

Sleep disordered breathing

Answer 20

-normally metabolism decreases in sleep and slower respiratory activity occurs

-brachycephalic animals sleep breathing:
1. use normal ribcage and diaphragm breathing, but they also use abdominal muscles to help increase pressure and breath out air
2. Apnea- paused breathing in sleep that can lead to hypoxia (can lead to hypertension, heart failure, heart disease in humans). 50% reduction in breath movement and reduction of oxyhemoglobin 97% to 89% leading to period of hypoxemia
3. Leads to gasp in breath to forcefully reopen airways

Question 21

Treatment options

Answer 21

-surgical corrections (soft palate resection, resection of stenotic nares)
-management- (kept in thin body condition to avoid obesity through diet and exercise, minimize extreme activity/exertion and heat climate, use harness rather than neck collar)
-prognosis- (surgical corrections earlier in life have improved prognosis BUT once animals develop secondary issues such as hyperplastic tissues, infection, airway disease, then they have diminished prognosis)

Question 22

Brachycephalic anesthetic risks

Answer 22

-anesthesia relaxes the muscles of respiration impacting ability to generate forceful inhalation or exhalation. Extra pressure is needed to pull air through the excessive tissue, and passive recoil is insufficient to exhale air

• these breeds need to be intubated with endotracheal tube under anesthesia (to bypass elongated soft palate; endotracheal tube overcomes hypoplastic trachea)