Clinical Case Study
I Can't Stop Coughing: a Case Study on the Respiratory System

Clinical Case Study
I Can't Stop Coughing: A Case Study on the Respiratory System

Short Answer Questions

1. Describe the relationship between intrapulmonary pressure, atmospheric pressure, and air flow during normal inspiration and expiration, referring to Boyle's law.

According to Marieb & Hoehn, Boyle's law gives the relationship between pressure and volume of a gas: At constant temperature, Pressure (P) varies inversely with volume (V).

That is, P1V1 = P2V2, where P is the pressure of the gas, V is its volume, and subscripts 1 and 2 represent the initial and resulting conditions respectively. (Marieb & Hoehn, 2013, p. 817-819)

During normal inspiration

Inspiratory muscles contract (diaphragm descends; rib cage rises). Thoracic cavity volume increases → Intrapulmonary pressure drops (to -1 mm Hg).

 Lungs are stretched and intrapulmonary volume increases. 

Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is equal to atmospheric pressure. (Marieb & Hoehn, 2013, p. 817-819)

During normal expiration

Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages). Thoracic cavity volume decreases.

 Elastic lungs recoil and intrapulmonary volume decreases → pressure increases (Ppul rises to +1 mm Hg) →Air flows out of lungs down its pressure gradient until Ppul = 0. (Marieb & Hoehn, 2013, p. 817-819)

2. Resistance varies in Mike's conducting airways. Using your understanding of respiratory anatomy, explain where in his airway the resistance is highest and why.

In Mike’s case, airway resistance is highest in trachea, in middle-sized bronchi and bronchioles. The contraction of respiratory muscles causes airway resistance in and out of the lungs. The contraction occurs due to an excess concentration of ionic calcium within the cells. Narrow of conducting airways → increase airway resistance → Mike breathing problems. In addition, the mediators from mast cells trigger bronchospasm;...