Obesity and Respiratory Problems

Obesity is related to several respiratory problems including but not limited to:

• Obstructive sleep apnea
• Obesity hypoventilation syndrome
• Asthma

Obstructive sleep apnea

The muscles which control the tongue and soft palate (which ordinarily hold the airway open) relax too much, obstructing the upper airway and causing a temporary restricted breathing or cessation of breathing (despite continued contractions of the diaphragm). The continued cessation of breathing not only disturbs sleep and causes snoring disruptive for others, but is associated with increased risk of developing depression, chronic fatigue, cardiac arrythmia, pulmonary hypertension, congestive heart failure, stroke and impotence.

How obesity affects sleep apnea

Obesity is considered a major risk factor for both development and progression of obstructive sleep apnea, and the prevalence in people with obesity is approximately twice that of individuals within a healthy weight range¹⁹

The mechanisms are likely multifactorial, however, best understood are the mechanical factors:

• Excess fat deposition in the tissues surrounding the upper airway increases the collapsibility of the upper airway
• Fat deposition at the thorax also means that when an individual with obesity lies down, the added weight from adipose tissue on their abdomen opposes the outward recoil of the chest wall, reducing chest compliance, and the functional residual capacity of their lungs, in turn leading to an increased oxygen demand

Benefits of weight loss

Research shows that a 10% reduction in baseline body weight can improve the severity of obstructive sleep apnea by 20%¹⁹

Obesity hypoventilation syndrome (OHS)

This is a serious syndrome in which people with overweight or obesity fail to breathe quickly and deeply enough to satisfy their oxygen demands, resulting in too much carbon dioxide and too little oxygen in their bloodstream.

How obesity affects hypoventilation syndrome (OHS)

Again, fat deposition around the thorax makes the chest wall less compliant and restricts movement of the chest muscles, causing fatigue of the respiratory muscles and causing the individual with overweight or obesity to breathe less efficiently.

In addition, the compensatory mechanism in the brain which ordinarily responds to rising acidity in the blood (indicating too much carbon dioxide) by increasing breathing rate/depth is blunted in individuals with OHS²⁰

The benefits of weight loss

Weight loss is regarded as the most effective treatment for OHS²¹

Asthma

Asthma is a condition in which the airway becomes narrowed, inflamed and may produce extra mucus, all of which cause breathing to become more difficult. The severity varies from minor, to affecting or limiting daily activities, to potentially life-threatening attacks.

How obesity affects asthma

Obesity increases airway inflammation via several different systemic inflammatory pathways. These include the over-production of cytokines from excess adipose tissue, the knock on consequences of metabolic syndrome, and pathological responses to oxidative stress.

Mechanical mechanisms also contribute. Obesity reduces lung volumes through increased chest wall loading and reduces functional residual capacity. Increased airways resistance and excessive collapsibility of the bronchioles (small airways) is a feature of late onset asthma in people with obesity. This leads to symptoms such as shortness of breath, wheezing and cough²².

• Obesity doubles the risk of developing asthma
• There is a dose response between increasing BMI and the incidence of asthma²³
• Obesity is also associated with greater asthma morbidity²⁴

Benefits of weight loss

Research has shown that a 5-10% reduction in weight, achieved through either dietary or mixed dietary and physical activity interventions, is associated with clinically important improvements to asthma control (58%) and even greater improvements in quality of life (83%)²⁵