Introduction to Pulmonary Pathology

Dyspnea or shortness of breath is a normal manifestation of heavy exertion, but it can also be caused by different underlying diseases, therefore understanding the etiology, pathophysiology and differential diagnosis of dyspnea is important in the diagnosis of serious underlying clinical conditions. In this article, the etiology, pathophysiology and differential diagnosis of dyspnea will be discussed in detail.

A cough is one of the common presenting symptoms in the clinic and is associated with a number of respiratory and non-respiratory diseases. It can have a number of distinguishing characteristics such as quality, sputum production, timing, onset, duration and associated symptoms. The physiological mechanisms underlying cough involve a reflex arc with a command center in the medulla. Common non-respiratory causes include gastroesophageal reflux disease and postnasal drip, whereas, the most common respiratory etiologies are infectious diseases, chronic obstructive pulmonary disease, asthma and interstitial lung disease. Wheezes are high-pitched, loud sounds that usually accompany asthma, while stridor is most prominent with upper respiratory obstruction. In this article, physiology, different causes of cough and wheezing will be discussed in detail.

Without oxygen, the human organism is not capable of living. It gains a major part of its energy from oxidative degradation of nutrients. The processes involved in this are called pulmonary respiration or external respiration. The carbon dioxide that is formed in the process of combustion has to be released. The gas exchange between air and blood takes place in the lung. When nutrients are degraded in order to gain energy, oxygen is consumed – a process that takes place in every individual cell of the body and is therefore called cell respiration or internal respiration. The detailed processes of cell respiration are the subject of biochemistry and will not be discussed here.

Hemoptysis can be defined as the expectoration of blood during coughing that originates from the lower respiratory tract. Per this definition, coughing of blood from an upper respiratory tract illness can be excluded. While coughing blood can be alarming to the patient, it is usually a self-limiting symptom. In clinical practice, only 5% of the patients who present with hemoptysis are found to have a serious medical condition that needs further treatment.