Bronchi

Asthma

The most common cause of respiratory compromise at the bronchial level is asthma, which is the hyperreactivity of the bronchi to an inflammatory component, such as from allergens. Bronchi will constrict in response to inflammation and result in shortness of breath, difficulty breathing, and ultimately resulting in decreased amounts of oxygen available for cellular processes.

Some patients are often described as “pink puffers” due to their efforts required to breathe in enough air and devices known as “asthma puffers” (or more commonly, inhalers) can help alleviate asthma. These puffers contain a bronchodilator that will help soothe the constricted bronchi to allow them to expand the airways and allow more airflow again. Albuterol is a commonly used short acting β2-adrenergic receptor agonist that quickly allow for bronchodilation.

Aspiration

1. Standing/sitting position - Since the right main bronchus is wider, shorter, and more vertical, aspiration in adults whilst standing has higher chance of resulting in obstruction of right main bronchus instead of the left (which departs from the trachea at a more acute angle). And easy way to remember this is by using the mnemonic 'inhale a bite, goes down the right'. Patients who aspirate while standing can have bilateral lower lung lobe infiltrates. However, in children, this may not always be the case. In children, depending on age, the left mainstem bronchus may be closer in size to the right mainstem bronchus, and the left mainstem bronchus also will not branch at the same acute angle as in adults, so there may not be as much of an increased chance of aspiration into the right bronchus. In general, two-thirds of aspirated objects lodge in main stem bronchi rather than in the distal bronchi, and will aspirate into the right lower lobe area.
2. Supine position - When lying flat on the back, aspiration will often result in obstruction of the superior segment of the right lower lobe.
3. Lying on the right side - This position will result in obstruction of the right middle lobe or posterior segment of the right upper lobe
4. Endotracheal tube - If the endotracheal tube is inserted too far down the trachea, then it will lodge in the right main stem bronchus, which will allow ventilation of the right lung but not the left lung.

Bronchitis

Bronchitis is defined as inflammation of the bronchi, which can be an acute or chronic condition. Acute bronchitis is often caused by viral or bacterial infections. Patients with chronic bronchitis often also suffer from chronic obstructive pulmonary disease (COPD), with common associations with smoking or long-term exposure to irritants. In diseases such as emphysema that occurs in COPD, the alveoli are damaged or destroyed, which reduces the surface area available for effective gas exchange.

Surfactant production

Surfactant is a phospholipoprotein produced and distributed by type II alveolar cells, and absorbed by type I alveolar epithelial cells, with the main lipid component of the surfactant being dipalmitoylphosphatidylcholine (DPPC), which decreases surface tension of alveoli therefore making it easier for the lungs to expand.

Immature lungs of a preterm infant often fail to produce sufficient surfactant, which leads to respiratory problems. Commonly used is the lecithin-sphingomyelin ratio ("L/S ratio"), where a L/S ratio of less than 2:1 means that the fetal lungs may be surfactant deficient, which can result in infant respiratory distress syndrome (IRDS) and ultimately neonatal death. Another recent ratio used is the surfactant/albumin (S/A) ratio, where a S/A ratio of less than 35 indicates immature lungs, between 35-55 is indeterminate, and more than 55 indicates mature surfactant production (which correlates with a L/S ratio of 2.2 or greater).