Obesity Cardiovascular and Respiratory Complications
Clinical background
Obesity is associated with a number of
complications and comorbidities. Cardiovascular disease is the major cause of
death in obese patients and there is a direct link between the degree of
obesity and the degree of hypertension. Other risk factors for coronary heart
disease, such as smoking and hyper- lipidaemia, should be addressed. There is
also a higher risk of thromboembolism and stroke in the obese population. Other
complications include osteoarthritis, back pain, ligament and tendon injury,
gallstones and an increased risk of certain cancers, in particular those of the
colon, rectum, breast, endometrium and prostate (Fig. 47a). Sleep apnoea
syndrome is more common in the obese, particularly men.
Cardiovascular complications of
obesity
Obesity not only relates to but also
predicts coronary atherosclerosis in both men and women, even with minimal
increases in BMI (Fig. 47b). Disordered lipid metabolism occurs partly through
decreased levels of the enzyme lipoprotein lipase, an insulin-sensitive enzyme
that breaks down fat. This results in elevated serum triglycerides and reduced
HDL cholesterol. Hyperglycaemia results
in the glycation of more LDL, which increases the affinity of LDL for the
modified LDL receptors on macrophages. This in turn promotes endothelial cell
cyto- toxicity, foam cell production and smooth muscle proliferation.
Plasminogen activator inhibitor (PAI-1) is raised (Fig. 47b), and this
prothrombic state is a further risk factor for coronary artery disease.
Elevated circulating levels of C-reactive protein, a systemic marker of
inflammation, also occur as increased visceral fat appears to enhance the
inflammatory pathway response that involves phospholipase A2, intracellular
adhesion molecule and C-reactive protein.
Congestive cardiac failure. Left ventricular hypertrophy is a common feature
of obesity. In the absence of hypertension, increases in cardiac output and
stroke volume with diastolic dysfunction and have been related to sudden death
in obese patients. Changes in the right heart are also seen in obese patients.
These changes may occur as a consequence of sleep apnoea and the obesity
hypoventilation syndrome, and result in right ventricular hypertrophy and
pulmonary hypertension, and eventual failure. Right ventricular dysfunction may
also occur as a result of left ventricular dysfunction, with subsequent
biventricular failure.
Hypertension is often a consequence of obesity, particularly in
patients who have also developed hyperinsulinaemia and hypertriglyceridaemia.
These patients will be predisposed to myocardial infarction, stroke and renal
failure. Obesity-related hypertension is of complex aetiology. Free fatty
acids, leptin and insulin may all be raised in the patient’s blood and may act
together to activate the renin–angiotensin system and promote sympathetic
activity with consequent vasoconstriction and sodium retention.
It has been found, using animal models
of obesity, that obesity causes inflammatory changes in small blood vessel
walls with adverse consequences for perfusion of vascular beds.
Respiratory complications of
obesity Sleep apnoea describes
the cessation of breathing during sleep. This syndrome is characterized by
snoring and apnoeic episodes culminating in sudden waking associated with a
rise in arterial Pa CO2. Patients may experience many apnoeic
episodes in a single night, resulting in severe sleep disturbance and daytime
somnolence. Fat deposition in the neck may externally compress the upper
airways and infiltration of adipose tissue into muscle may decrease upper
airway size, render the pharynx more susceptible to collapse and decrease chest
wall compli- ance. Furthermore, abdominal fat may impede diaphragmatic
movement, especially in the supine position. In obesity hypoventilation
syndrome, there may also be a reduced central respiratory drive.
Detailed sleep studies should be
performed as, untreated, sleep apnoea syndrome may lead to the development of
pulmonary hypertension and right heart failure. Machines exerting continuous
positive airway pressure (CPAP; Fig. 47c) are available which effectively
‘splint’ the upper airways preventing their collapse. These provide relief for
sufferers of sleep apnoea,and also for their partners.
