Discuss the effect of obesity on respiratory function and respiratory

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Obesity can be more specifically explained by the National Institutes of Health (NIH) as an individual having a body mass index (BMI) of or over 30, (over one billion people fit within this statistic. Essay info4) The BMI links a persons' weight (kg) to their height (m2) and is calculated by dividing the weight (kg) by the height (m2). Although the BMI refers to the weight related to height, a person with a muscular build could have a very high BMI with no health threats. (1)

The incidence of obesity is on the rise in several countries across the world. Therefore it is expected that it will add to ill health and cause of death. (2). In 2000, obesity accounted for around 400,000 deaths in the USA. (3)

Obesity has been proved to stimulate respiratory mechanical damage possibly along with gas exchange irregularities, therefore causing changes in the balance of the system. In obese individuals, a decreased Functional Residual Capacity (FRC) is achieved; this is because the diaphragm sits in a higher position. Chest wall resistance could be increased and also the upper airways may be restricted due to fat deposition or decreased tone of the pharynx. (4)

Obesity, more specifically of abdominal origin, poses a great threat for cardiovascular disease, type 2 diabetes, rheumatoid arthritis and cancer. Of late, it has been uncovered that there is an association between obesity and chronic respiratory diseases. Diseases such as chronic obstructive pulmonary disease (COPD), asthma or obstructive sleep apnoea are on the rise. Professionals are faced with obese individuals frequently displaying some sort of chronic respiratory disease. In specific situations, the respiratory disease is caused by the obesity, for example; in obstructive sleep apnoea and obesity hypoventilation syndrome. Obesity is frequently linked to COPD and asthma, but it is not known fully how this relationship is formed. (3)

Obesity Itself

The BMI is known as the most functional tool for evaluating the threat to an individuals' health that may be over/under weight. The BMI does not however give any indication about the fat percentage in the body. The health dangers associated with obesity, also its influence of respiratory function, are related to the degree of obesity, but also the incidence of abdominal fat. Waist circumference can be used along with BMI to help measure an individuals' likeliness of suffering cardiovascular damage linked to obesity. For women, a waist circumference of 35 inches or above is thought to be unhealthy and for males, a circumference of 40 inches or higher is unhealthy. There is no ideal way to measure obesity, but these two are the most frequently used by professionals. (5)

Besides the risk of development of a respiratory disorder, an obese individual is susceptible to acquiring one or more of over 30 medical conditions. The most frequent diseases related to obesity comprise: Hypertension, Hypercholesterolaemia, Diabetes, Heart Disease, Stroke, Gallbladder disease, Osteoarthritis and some cancers. (5)

Obesity can be caused by direct or indirect factors. It is thought that behaviour, the environment and genetics are the 3 main contributing factors to the obesity epidemic. Behavioural causes refers to the choices made by the individual, for example, the food they eat or the level of activity the person undergoes, portion sizes are also important. Exercise is a crucial part of changing behaviour patterns. Environmental factors encompasses the fact that people now have a less active life, for example taking the car instead of walking and also healthy balanced diets have been taken over by the fact that you can 'pop to Greggs for a pie on lunch hour' instead of your usual packed lunch. Genetics have been proved to have a link to obesity as genes can lead to some disorders that cause obesity. Although this is true, not all people in this case progress to an obese state. Investigations are in progress to help us understand specific genes adding most frequently to obesity. (5)

With regard to treatments, there are many ways in which an obese individual can tackle their problem. This is most commonly through behaviour strategies. For example, modifying eating habits, upping exercise, getting to know what a healthy balanced diet is, joining a support group and making sensible weight loss targets. People may find it easier to incorporate their family or friends to help them, for example keeping their motivation up and reassuring them of the positive outcome and helping them reach their targets. Doctor managed weight loss programmes usually incorporate nutrition education, pharmacotherapy, physical activity and behavioural therapy. (5)

Obesity's Effect on Respiratory Function

Normal breathing includes movement of gasses in and out of the lungs via use of the strength of the thorax and modulations between intrathroacic and atmospheric pressures. For inhalation the atmospheric pressure must be more than the pressure in the lungs and thorax. The diaphragm and intercostal muscles enlarge the thorax, the pressure reduces less than that of the atmosphere and inspiration occurs. For expiration these muscles relax, elastic recoil of lung tissue alongside increases in pressure means air exits the lungs. The diaphragm is the most important muscle involved in breathing and the phrenic nerve controls the diaphragm. In some disorders, respiration may require help from other muscles called secondary or accessory muscles. (6)

The build-up of fat tissue influences respiratory function in adults and children. An individual with an ascending BMI is generally linked with a decrease in forced expiratory volume in one second (FEV1), forced vital capacity (FVC), total lung capacity, functional residual capacity and expiratory reserve volume. Constraint to the thorax linked to obesity is normally slight and is accredited to the physical pressure caused to the diaphragm and chest wall by the fat accumulation. A total lung capacity of below 85% is normally obtained in morbid obesity. Abdominal fat accumulation can also cause a restrictive disorder, this occurs in individuals with a waist to hip circumference fraction of 0.95 or above. In obesity at a lower degree however, a restrictive disorder should not be accredited to fat build-up until interstitial lung disease or neuromuscular disease (which also leads to restrictive damage) have been explored and ruled out. (3)

It is thought that respiratory muscle power could be weakened in obesity; this was found via a decreased maximal inspiratory pressure in obese individuals when paralleled with individuals with a normal weight. This lack of muscle power has been accredited to muscle inadequacy, due to decreased chest wall compliance or decreased functioning lung volumes. The ability of obese individuals to exercise is rather obviously diminished. (3)

Difficulty in breathing or a shortness of breath is evidently linked to obesity. Obesity makes it harder to breath due to decreases in the chest wall compliance and respiratory muscle strength. Disproportion between the requirement of the muscles to work and their ability to work results from this; therefore causing an elevated struggle to breath. Also, this difficulty in breathing or shortness of breath could reveal other linked disorders, for example respiratory and heart diseases. Individuals with obesity often complain of shortness of breath and/or wheeziness and are treated for asthma, whilst testing for pulmonary function is overlooked. It is vital that a definite and sure diagnosis is given as shortness of breath can be implicated in many disorders and also could need a different treatment altogether. (3)

Respiratory Disorders Related to Obesity


Chronic obstructive Pulmonary Disorder (COPD) and Asthma should be investigated in any individual with symptoms such as a chronic cough, mucus over production, difficulty breathing or shortness of breath, this is particularly important in smokers for example. (3)

Regardless of obesity's adverse effects, it is surprisingly linked with increased survival rate in patients with COPD. You would however assume that a person with COPD would suffer from increased shortness of breath compared to those of a normal weight. (info 8) This is Mainly due to the fact that individuals with COPD frequently show a decreased FEV1 and FVC and that airflow obstruction is persistent in COPD sufferers. (3) However, Guenette et al (2010) indicate that overweight COPD individuals may have an alike or improved dyspnea score whilst undergoing exercise when compared to normal subjects. This may be because obese COPD individuals have a decreased operating lung volumes and increased inspiratory capacity to total lung capacity ratios. This suggests that obesity could be linked to increased survival in COPD, however the particular means for this is not yet fully understood. (7)


Asthma is symbolised for its varying obstruction of airflow either impulsively or with treatment. Asthma sufferers often have a normal lung function on testing after suitable treatment. Methacholine challenges are used to determine airway over-reaction and to validate asthma if a spirometry test has proved normal. (3)

In very overweight individuals, the function of the respiratory system is greatly altered. A decreased tidal lung capacity endangers the widening forces that uphold the diameter of the airways; this may cause an excess contraction response by the smooth muscle or a rise of airway reaction. (3)

Surplus inflammatory mediators are produced by adipose tissue, this proposes an immunologic association between obesity and asthma; this is supported by the higher incidence of C-reactive protein, tumour necrosis factor α and interleukin-6 in obese individuals. It is thought that rising leptin emission in obesity could be linked to the progression of asthma through modifying airway inflammation. Also, a decrease in the emission of adiponectin (anti-inflammatory cytokine) is an additional possible link between obesity and asthma. (3)

The link between BMI and asthma is greater in women than in men, therefore it has been proposed that higher concentrations of the female sex hormones could be involved in the higher incidence of asthma seen in obese women. (3)

It is possible that oestrogens can modify the immune response and cause a rise of the likelihood of the individual developing asthma. Nevertheless, the link between oestrogens and inflammation of the airway in asthma is not yet fully understood. (3)

There are genetic factors to take in to account also. It is possible that obesity genes could have an effect on an individuals' predisposition to asthma. Many genes have been associated with asthma and obesity. These genes are located near to chromosomal areas that are linked to asthma, also these genes may code for inflammatory mediators that may be clearly concerned with the progression of asthma. (3)

Obstructive sleep apnoea

Obstructive sleep apnoea (OSA) incidence varies greatly within the population. It varies from 25%-58% in men and from 10% to 37% in women, this is reliant on their ethnicity and the particular area investigated. OSA is symbolised by recurrent upper airway obstruction caused by dysfunction of the musculature to uphold opening of the airways in respect to change in the shape and diameter of the airway. Consequently a decrease in arterial oxygen and increased carbon dioxide levels are observed. This causes distressed breathing for the individual and sudden awakening due to the person fighting for breathe. The person therefore has an extremely unstable sleep pattern. (3)

Obesity causes a rise in fat accumulation in the pharyngeal area and decreased functioning lung volumes. These act alongside one another to decrease the upper airway diameter, alter airway configuration and therefore cause increased risk of their downfall. This means the airways are subjected to persistent collapse whilst the individual is asleep. It is thought that up to 70% of individuals with OSA are overweight. OSA is linked to increased number of deaths caused by daytime tiredness and also a large correlation to cardiovascular diseases seen in the disorder. Thus, OSA is said to be a life-threatening consequence of obesity. (3)

Obesity Hypoventilation syndrome

Respiratory failure associated with increased carbon dioxide concentration in the blood and increased workload of the right side of the heart is often seen in obesity. It is referred to as obesity hypoventilation syndrome if there is a lack of any known sources of the respiratory failure. The main symptoms of this syndrome are: respiratory failure, extreme deficiency of oxygen in the blood, increased carbon dioxide levels and pulmonary hypertension. The majority of individuals with this syndrome also suffer from OSA. However, a few patients with obesity hypoventilation syndrome in absence of OSA proposes that obesity individually could cause prolonged hypoventilation. (3)


For overweight individuals with a respiratory condition, the most obvious solution for many of their health problems would be to lose weight. However, many obese subjects with a respiratory condition lead sedentary lives, it is not recommended they suddenly heighten their exercise levels. Pulling pulmonary rehabilitation and exercise training methods together could support these subjects to exercise initially. (3)

Loss of weight has proved beneficial to lung function and certain symptoms in asthma patients, for example every 10% relative reduction in weight benefitted the FVC by 92mL and FEV1 by 73mL. (3)

Reduction of weight also helps some of the signs of OSA and also decreases the number of disturbances whilst the subject is asleep. Nasal continuous positive airway pressure (CPAP) is the gold standard for over-weight individuals with OSA, as many of these patients cannot keep most of the lost weight off. (3)

Weight loss back to a healthy weight is the only treatment for obesity hypoventilation syndrome. Weight loss in this cohort helps recover blood gases, breathing disorders linked to sleep and hypertension. Bariatric surgery is an option if the level of weight loss is un-achievable through the diet. (3)


To conclude, obesity is on the rise worldwide. Many obese patients suffer from respiratory disorders as well as other complications such as hypertension and diabetes. Some of these respiratory disorders include: COPD, Asthma, Obstructive Sleep Apnoea and Obesity Hypoventilation syndrome. Both adults and children can be affected by obesity related respiratory conditions. Obese patients generally have decreased FEV1, FVC, total lung capacity, functional residual capacity and expiratory reserve volume. The best overall outcome would be for the patient to lose weight in a managed fashion, usually increase exercise is not recommended in patients with respiratory disorders, however bariatric surgery is possible if the patient cannot lose the weight plainly through the diet alone.