Smoking's Impact on Chronic Respiratory Disease

Introduction

Chronic respiratory diseases and risks factors

Chronic respiratory diseases (CRD’s) is a term used to describe diseases of the airway and other lung structures, some examples of CRD’s are: Chronic Obstructive Pulmonary Disease (COPD), Chronic Bronchitis, Emphysema and the most common one being Asthma [3]. There are many risk factors which can contribute to the risk of getting a CRD or worsening it. The main risk factors are: smoking, air pollution, dust, occupational chemicals etc. The inhalation of tobacco smoke can have detrimental effects on a person’s health (their respiratory system in particular) [7]. Tobacco smoke contains approximately 7,000 chemicals, out of these 7,000 at least 250 are known to be extremely dangerous for human health, these chemicals do harm by damaging important lung tissues such as the alveoli, ciliated epithelium and many more, this leaves the lungs vulnerable to getting CRD’s and other respiratory system complications [12].

Main body

Smoke induced Lung damage as a risk factor for Asthma and Chronic Bronchitis

Lung damage is one of the most severe effects that tobacco smoking has on the human body. Asthma and Chronic Bronchitis are two major CRDs which are closely related to lung damage and therefore to tobacco smoking as a risk factor. Asthma is the most common CRD affecting 235 million people worldwide [11]. It is a condition which causes the so-called asthma attacks which consist of swelling and inflammation of the airway linings and reduces the organism respiratory capacity. The typical symptoms presented by a person suffering from an asthma attack may include tight-chested sensations, coughing, shortness of breathing and wheezing On the other hand, Chronic Bronchitis is another common CRD, especially in long term smokers. Chronic Bronchitis is characterised by a shortness of breath or a productive cough (a cough which produces mucus) for at least 3 months out of a year or more each year for 2 or more years in a row [25].

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Smoking has been shown to be the main risk factor of acquiring Chronic Bronchitis [18] and rather an increased risk of contracting or worsening an asthmatic condition. Since the damage that the toxic compounds in cigarette smoke cause to the respiratory system of a smoker are permanent, former smokers have also been proven to be at a higher risk than people who have never smoked in their lifetime [24].

Both conditions, Asthma and Chronic Bronchitis, can be triggered and worsened by the toxic components of tobacco smoke which damage the structures and tissues in a person’s lungs in a very progressive way and are only perceptible when the damage is very severe. Two of the most dangerous compounds present in tobacco smoke are HCN (Hydrogen Cyanide) and Tar. HCN inhibits the mitochondrial respiration leading to a quick cellular death. Tar is a complex mix of genotoxic substances leading to DNA damage, this is dangerous because DNA is essential for cell reproduction and repairing. As the person inhales the tobacco smoke, chemical compounds such as HCN and Tar cause injuries to the ciliated epithelium (Cilia cells tissue) (Fig. 2) which lines the trachea and bronchi. This tissue is composed of specialised cells with fine hair which are used for propelling dust and microbes out of the airways (Fig. 1) [26]. This means that dangerous compounds or pathogens are accumulated in the lungs, bronchi and bronchioles. The Goblet cells (Fig. 2), which at normal conditions secrete protective mucus, start to produce it excessively leading to frequent coughing. To make the lungs less vulnerable the body tries to replace the damaged ciliated epithelium in the trachea and bronchi with scar tissue, causing the airways to become thicker, meaning less air can be inhaled and exhaled. The Respiratory system therefore is more exposed to infections leading to inflammation of bronchi, trachea and bronchioles [9, 14, 15].

When exposed to tobacco smoke a person may begin experiencing symptoms of respiratory system damage- which can later develop into Asthma. People who already suffer from Asthma find that tobacco smoke can act as a trigger to their Asthma attacks. Although asthma can be developed before starting smoking because of hereditary predisposition, asthma developed after starting smoking is strongly associated with a decreased respiratory capacity [7].

The slow decline in the lung function can lead to Chronic Bronchitis if the person smokes regularly. Regular smokers are at a very high risk of getting Chronic Bronchitis due to the frequent exposure to the toxic chemicals in tobacco smoke. This is not only damaging to the lungs but also to the rest of the body, as the airways become inflamed lower volumes of Oxygen can be inhaled, so less Oxygen is transported around the body to vital organs such as the heart. In addition to this the Carbon Monoxide from cigarette smoke binds to haemoglobin in red blood cells instead of Oxygen, this means even less Oxygen is transported around the body which puts strain on the heart as it would have to pump faster and harder to make up for the lower volumes of Oxygen around the body [23].

Smoking is not only dangerous for the active smoker but also for the bystanders that maybe inhaling the tobacco smoke passively, breathing in secondary tobacco smoke is proven to be just as hazardous to a person’s health as if the person would be smoking a cigarette themselves. This is because the toxic compounds in tobacco smoke are released into the air as the smoker exhales, these toxic compounds are then breathed in by bystanders [7, 9] this also causes damage to their respiratory systems which increases their chance of getting Asthma or worsening it if they already have it by making their respiratory systems more sensitive to other Asthma inducing triggers such as pollen [12, 13].

Chronic Obstructive Pulmonary Diseases

After a person gets Chronic Bronchitis it becomes very easy to get Emphysema too, when a person has both Chronic Bronchitis and Emphysema their condition becomes classed as a Chronic Obstructive Pulmonary Disease (COPD) [22]. Emphysema is a condition which causes the terminal part of the respiratory tree (bronchioles) to abnormally dilate and even cause the airways to collapse if the bronchiole tissues are damaged enough. When they collapse the air inside the lungs is unable to be exhaled, this causes excess gas to be trapped in the lungs, leading to hyperinflation [22]. Trapped air pushes down on the diaphragm (one of the main muscles responsible for inhalation and exhalation) and prevents efficient exhalation and inhalation from occurring. Emphysema is also caused when the alveoli (tiny air sacs that allow gas exchange to occur) begin to break down. Smoking is the main cause of Emphysema because the tobacco smoke causes abnormal inflammatory responses in the lungs. The enzyme elastase is released by inflammatory cells and begins to break down the elastin (an important cell structure protein) which lines the alveoli walls. Without this protein the alveoli cannot perform adequate gas exchange of Oxygen and Carbon Dioxide as their walls are more rigid and unable to hold maximum gas volumes. Furthermore, when cigarette smoke is inhaled the oxidants that are released into the lungs inactivate the enzyme alpha-1-antitrypsin, this enzyme is responsible for the regulation of elastase which remains continuously active and destroys the alveoli until the tissue collapses [20]. Therefore, the low gas exchange capacity is yet more reduced. Alveoli damage causes people who are suffering from Emphysema to have less Oxygen transported around the body, the body tries to compensate low oxygen levels by deeper and more frequent breathing. Low oxygen levels in the blood for a long time can also cause Pulmonary Hypertension, which is defined as a high blood pressure in the arteries of the lungs caused by a higher requirement of flowing blood in this area for attenuating the decreased Oxygen levels [23]. Some symptoms of emphysema include: shortness of breath while doing simple activities such as climbing the stairs, wheezing, fatigue, blue-tinged fingernail beds or lips, frequent headaches (due to the lack of oxygen) etc. Although quitting smoking will not cure/treat the condition it is heavily advised for smokers who suffer from emphysema to stop smoking as it can prevent the disease progression [19, 21].

Conclusion

Evidently, smoking tobacco is a serious health hazard, impacting not only the smoker themselves but also the people around them, who are also breathing in the polluted air. It is clear that smoking cigarettes is one of the main risk factors (if not the main one) to getting a Chronic Respiratory Disease and worsening it if a person already has one, as mentioned above continuing to smoke whilst having a Chronic Respiratory Disease can have critical effects on a person’s overall health, especially their respiratory system, leading to additional conditions such as pathogenic infections. Currently there are no known cures to the CRD’s mentioned above, however there are many available treatments and medications that can minimise the symptoms and improve the life quality of the patients. Finally, it is also very important for society to be conscious of the relationship of these diseases and smoking habits.