Cardiovascular disease (CVD) was ranked as the leading global cause of death in 1990 and 2010. The global death rate associated with CVD for individuals aged 15 to 49 was 10.7% in female patients and 12.8% in male patients in 2010 20. Fortunately, cardiovascular disease (CVD) is a relatively infrequent cause of sudden incapacitation in aircrew, but it accounts for 50% of all pilot licences declined or withdrawn for medical reasons in Western Europe 21–23. Aircrew is medically screened more intensively than many other professions; however, despite this, cardiovascular conditions such as acute coronary syndromes remain a causative factor in commercial aircraft accidents and fatalities 24, 25.
The metabolic syndrome is one of the major public health problems worldwide 29, the prevalence of MetS are continuously increasing and aircrews are not spared from this high prevalence. Military and civilian aircrew is held to stringent physical standards in order to be considered qualified for flight. While MetS itself can be a medical condition which causes flight disqualification if it’s associated with another cardiovascular disease like hypertension, diabetes, coronary disease or sleep apnea syndrome. The presence of the MetS is associated with a significant increase in cardiovascular mortality (12% vs. 2%) 30 and all-cause of mortality31. it’s also associated with a high risk of cardiovascular disease (CVD). In flight MetS can cause sudden or subtle incapacitation by the occurrence of acute myocardial infarction, stroke or by a sudden death32. These complications can be decompensated by altitude and flight conditions including altitude hypoxia, stress and + Gz acceleration in fighter pilot in a high-performance aircraft. Non-diabetic people with the MetS are at a very high risk for developing type 2 diabetes, the risk for diabetes is up to fivefold higher in patients with the syndrome31 In aircrew member, diabetes may have an impact on the flight safety through its complications (ocular, cardiovascular, stroke, etc.), and through the glycemic disorder which may cause hypoglycemia in flight33. Obesity is rising rapidly in many parts of the world34, and the high prevalence of the MetS is mainly related to the obesity epidemic35.
The aim of this study was to investigate the intima media thickness of the carotid artery and compare with the criteria of metabolic syndrome in pilots. The main results included a lack of association between increased carotid intima media thickness and metabolic syndrome and metabolic syndrome components, a higher carotid thickness in fighter pilots, and a correlation between carotid intima media thickness and age and flight time.
In our study, no significant statistical or clinical association was found between CIMT and metabolic syndrome and its components, perhaps most importantly due to the low number of people in the metabolic syndrome group and the consequent low prevalence of metabolic syndrome in the pilot population. In our study, the prevalence of metabolic syndrome was 8%, which is much lower than the reported global values, the Middle East region and the Iranian population in the general population. Currently, the global prevalence and prevalence in the Middle East is estimated at about 25%26. This rate is reported to be 29% for men in Iran27. Other studies show that the prevalence of metabolic syndrome in the group of pilots of the Jordanian Air Force is 18%, the Korean Air Force is 9.9%, the Taiwan Air Force is 5.32%, the German Air Force is 9.0%, the Serbian Air Force is 5.28% and the US Air Force Less than 1% 28, which shows a lower prevalence of the syndrome in countries that have stricter protocols in their pilots' health.
However, the results of this study showed that none of the known risk factors, despite having a relatively high prevalence in the subjects, were not significantly associated with the thickness of the carotid artery. This was confirmed both in intergroup analyzes using chi-square and t-test analyzes and in regression models. However, the findings of our study are different from the findings of a single study that was similar in design to our study.
In addition, due to the proven link between high blood pressure, dyslipidemia and high body mass index with coronary syndromes, cardiac arrhythmias, and heart attack, and the high prevalence of these risk factors, individually in the subjects studied, Precautions must be taken to ensure that pilots are closely monitored36. Although a person is not diagnosed with one or two positive criteria as metabolic syndrome, with age, the risk of metabolic syndrome, cardiovascular disease, and diabetes will be higher than in people without symptoms.
High blood pressure, diabetes mellitus, smoking, dyslipidemia, old age, as well as metabolic syndrome have been identified as common risk factors for atherosclerosis of the carotid and cardiac arteries. Although the possible underlying mechanisms of the causes of metabolic syndrome and carotid damage are not yet well understood and are not the subject of this study, some studies have shown that all metabolic components of the syndrome alone can accelerate vascular endothelial disorders and, as a result, progressive arterial damage, and increase the chances of developing carotid disorders as the number of metabolic syndrome components increases37.
Although the diagnosis of metabolic syndrome does not in itself cause the pilot to be disqualified, some of its components, such as hyperglycemia, hypertension, and fat profile disorder, can cause at least a temporary loss of a pilot's license. This is important in the sense that in our study, about 60% of pilots were overweight, more than 40% had triglyceride abnormalities, and about 20% smoked, once again demonstrates the importance of controlling and minimizing risk factors in order to reduce the risk of vascular disorders38.
The study was accompanied by limitations. This study was conducted cross-sectionally in one center, so there were all the limitations of cross-sectional studies, such as the inability to fully control distorting interventions in this study. Due to the time allotted for the project, it was not possible to examine more people, so it is recommended that the project be continued in a larger population of pilots and in multiple centers.