Respiratory Distress in SA: Pathophysiology and clinical approach. JVECC. 2022

Question 1

List the main inspiratory muscles and the accessory muscles of inspiration

Answer 1

Main muscles of inspiration:
* diaphragm
* external intercostal muscles

Accessory muscles of inspiration:
* scalene muscles
* sternomastoids

Question 2

List 4 categories of conditions that can reduce the compliance during breathing

Answer 2

Pulmonary parenchymal disease
* edema
* alveolar infiltrates, e.g., pneumonia or contusions
* pulmonary fibrosis

Pleural space disease
* pneumothorax
* pleural effusion

Abdominal Distension

Inability to expand the rib cage
* pain
* thoracic wall injury
* constricting thoracic bandage

Question 3

Name and explain Poiseuille’s law

Answer 3

flow rate is proportional to the radius and pressure gradient and inversely proportional to the length and viscosity

Question 4

Where within the airways is most airway resistance?

Answer 4

upper airways - specifically nose

Question 5

What percentage of airway resistance do each contribute:

• nose
• larynx
• lower airways

Answer 5

Nose 68-82%
Larynx 6%
Lower airways 11-25%

Question 6

Is airflow in the trachea mostly turbulent or laminar?

Answer 6

Laminar

Flow becomes more turbulent when air wasses through airway divisiosn

Question 7

Name Fick’s law of diffusion

Answer 7

Diffusion is proportional to surface area, difference in the partial pressure of the diffusing gas, and diffusion constant
Diffusion is inversely proportional to thickness

Question 8

What determines the diffusion constant in Fick’s Law of diffusion?

Answer 8

Diffusion constant in dependent of the solubility and the molecular weight of the gas

e.g., CO2 higher solubility than O2 (20 times higher) –> diffuses more rapidly

Question 9

What are the 3 groups of receptors that control breathing? Name their locations and what they respond to

Answer 9

central chemoreceptors
* primarily in the medulla
* responds to changes in pH from CO2

peripheral chemoreceptors
* carotid and aortic bodies
* repsond to changes in pH, arterial O2 or arterial CO2

airway and pulmonary receptors
* Irritant receptors - respond to irritants, e.g., cold air, cigarette smoke –> bronchoconstriction, cough
* J receptors - located juxtacapillary - respond to fluid in the pulmonary interstitium or alveolar wall –> rapid shallow breathing
* C fibers - in airways and alveoli - respond to changes bronchiolar circulation –> rapid shallow breathing, bronchoconstriction, increased mucus secretion

Question 10

What constitutes the lower airways?

Answer 10

Bronchi and bronchioles

Question 11

What are the components of feline asthma versus chronic canine bronchitis?

Answer 11

Feline asthma –> smooth muscle constration and exessive mucus production

Chronic canine bronchitis –> neutrophilic and eosinophilic infiltrates in the mucose, thickening of the smooth muscle layer, fibrosis, increased amount of goblet and glandular cells

Question 12

List differentials for canine lower airway disease

Answer 12

• intrathoracic tracheal collapse
• chronic bronchitis
• infectious tracheobronchitis
• canine infectious bronchopneumonia
• lungworm
• eosinophilic bronchopneumopathy
• neoplasia

Question 13

List potential infectious etiologies of chronic canine bronchitis

Answer 13

• bordetella bronchiseptica
• canine parainfluenza virus
• canine adenovirus
• canine herpes virus
• Mycoplasma spp.
• Oslerus osleri

Question 14

List differentials for feline lower airway disease

Answer 14

• Feline asthma
• feline infectious bronchopneumonia
• Mycoplasma spp. infection
• neoplasia

Question 15

What is the normal amount of pleural fluid in a health dog or cat?

Answer 15

dog: 0.1 mL/kg
cat: 0.3 mL/kg

Question 16

What is the average pressure within the pleural space in health?

Answer 16

• 5 cm H2O

Question 17

If ultrasound is not available what are the landmarks for a thoracocentesis?

Answer 17

7-9th IC space

if pneumothorax suspected - dorsal 1/3
if fluid suspected - at costochrondral junction

Question 18

How do you confirm a chylothorax?

Answer 18

fluid triglyceride concentration higher than serum

Question 19

List differentials for pleural effusion with modified (protein-rich) transudate

Answer 19

• CHF
• Neoplasia
• lung lobe torsion
• diaphragmatic hernia
• cranial vena cava thrombus

Question 20

List differentials for chylothorax

Answer 20

• idiopathic
• CHF
• neoplasia
• thoracic duct trauma
• heartworm disease