Respiratory Toxicology

What are the functions of the oronasal zone?

• Olfaction and chemosensation

• Humidifies and warms air

• Filters air

• Slows airflow – 50-70% of resistance here.

• CYP 450s in nasal epithelium. 

What are the functions of the conducting zone?

• Filters air – mucociliary apparatus.

• Further slows air – remainder of resistance here.

• Some biotransformation.

What are the functions of the respiratory zone?

• Gas exchange (O 2, CO 2)

• CYP 450s and phase II enzymes in alveoli.

What are the layers of the respiratory membrane that a toxicant must traverse?

1. Fluid layer with surfactant

2. Alveolar epithelium

3. Epithelial basement membrane

4. Narrow interstitial space

5. Capillary basement membrane

6. Capillary endothelial membrane.

How do the pulmonary and systemic circuits differ in regards to O 2 and CO 2 content?

• Pulmonary capillary beds: highest O2, lowest CO 2 levels.

• Systemic capillary beds: highest CO 2, lowest O2 levels.

Describe signs of upper respiratory irritants (aka rapid-acting)

• Coughing, sneezing

• Drooling

• Runny nose and edema/swelling of nasal passages, oral cavity

• Lacrimation and redness of eyes

• Nasal, oropharyngeal, ocular pain.

*coughing similar to lower resp. irritants

Describe signs of lower respiratory irritants (aka slow-acting)

• Coughing, wheezing

• Bronchospasm → shortened but more frequent breathing

• Tightness of chest

• Pulmonary edema

• Mucous secretions, watery foam

What are decontamination steps to consider for exposure to respiratory irritants?

• Go to highest ground possible (resp. irritants are dense)

• Remove exposed clothes

• Wash with soap and water

• Rinse eyes with water 10-15 mins

What is the concentration-related progression of signs from H 2S exposure?

• Odor threshold 0.01-0.03 ppm

• Strong, intense rotten-egg odor 20-30 ppm

• Olfactory nerve paralysis 100-150 ppm

• Rapid knockdown > 500 ppm

• Breathing ceases after 1-2 breaths > 1000 ppm.

Define hypoxemia

• ↓ O 2 levels in blood

  • Partial pressure arterial O 2 (PaO2)

• Often due to pulmonary problems

Define hypoxia

↓ oxygenation of tissues or poor utilization of O2 by tissues.