Structure and Function of the Respiratory System
Case

Forty-five-year-old Brad has, ever since the age of 20, been working in the mines in the post of coal cutter. He is happy with his job as he earns a good wage and his father also worked in the very same mine. Akin to several co-workers of his, he suffers from chronic cough. However, Brad has neglected going for yearly health checks as is required for mine workers owing to his fear of being diagnosed with “black lung” (i.e., coal worker pneumoconiosis). This ailment results in fibrosis, lasting dilation of the small airways, and reduced diffusing capability. At more advanced stages of the disease, alveoli, airways and pulmonary capillaries get destroyed.

Chronic obstructive pulmonary disease (COPD)

COPD has been described as a persistent inflammatory lung ailment which obstructs flow of air from the patient’s lungs. Disease symptoms include difficulties in breathing, wheezing, coughing, and sputum (or mucus) secretion. COPD results from continuous exposure to particulate material or irritants in gaseous form such as cigarette smoke. Patients are highly vulnerable to contracting lung cancer, heart ailments, and various other health conditions. The biggest contributors to COPD contraction are chronic bronchitis and emphysema. The former is characterized by inflammation of bronchial tube linings (bronchial tubes are responsible for carrying air back and forth from the lungs’ alveoli (air sacs). Symptoms include coughing and sputum (mucus) generation on an everyday basis. Meanwhile, the latter condition entails destruction of the alveoli situated at the bronchioles’ (tiniest air passages’) end owing to exposure to harmful cigarette smoke as well as other particulate material and gaseous irritants (Mayo Clinic, 2019).

Accurate COPD diagnosis is vital as proper management may reduce symptoms (particularly dyspnea) and aggravation intensity and incidence, prolong life, and improve patients’ health status and exercise capacity. According to GOLD (Global Initiative for Chronic Obstructive Lung Disease), COPD has been defined as a widespread, typically-progressive, avoidable, and curable ailment marked by restricted airflow and linked to intensified chronic inflammatory reaction within the lungs and airways to poisonous gases or particles. Comorbidities and aggravations increase overall disease intensity among individual COPD-diagnosed persons (Angelis et al, 2014).

Mismatch between Ventilation and Perfusion

Hypoxemia’s key contributor among COPD-diagnosed persons is V/Q (ventilation/ perfusion) mismatch stemming from a progressive constriction of airflow and the pulmonary capillary bed’s emphysematous breakdown. Researches that employed multiple inert gas elimination method revealed COPD-diagnosed individuals exhibiting a chiefly...…the gases within both areas; carbon dioxide and oxygen within the lungs constantly enter and exit the alveoli; consequently, no such equilibrium occurs.

Oxygen enters the alveoli through bulk flow across conducting airways. During flow of air across conducting airways in the process of inspiration, the bulk flow’s linear velocity reduces upon approaching the alveoli owing to drastic increase in overall area of cross section in the tracheo-bronchial tree’s distal parts. The bulk flow’s linear velocity across a tube equals flow divided by area of cross section:

Linear velocity (cm/s) = Flow (cm3/s) ÷ Cross sectional area (cm2)

Bulk flow most likely stops when the air arrives at the alveoli, with further movement of gas taking place via diffusion. Subsequently, oxygen moves across the gaseous phase within the alveoli in accordance with its individual partial pressure gradient. Alveolar ducts are situated less than a millimeter from the alveoli-capillary interface. Alveolar gaseous phase diffusion is considered to be aided to a great extent by blood flow and heart pulsations that are communicated to the alveoli, increasing molecular motion. Later, oxygen diffuses through alveoli-capillary interface (Levitzky, 2013).

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