Enlargement of the aorta: An occupational disease?

Abstract

BACKGROUND:

Aortic dilation may critically precede progression to thoracic aortic aneurysm (TAA). Prolonged or repetitive isometric-type heavier strenuous activities resulting from the nature of some professions may be an important causative factor for TAA.

METHOD:

The echocardiographic measurement data of middle-age subjects who were isometric-type daily strenuous activity trainers or ordinary activity trainers were retrospectively analyzed. Clinical features and echocardiographic parameters of the left ventricle and left atrium (LA), aortic root (AR) and ascending aorta (AA) were compared between the groups.

RESULTS:

AR (35.6±3.0 mm versus 33.5±1.9 mm), AA (36.8±3.0 mm versus 34.4±1.9 mm) and LA (37.4±2.2 mm versus 36.2±2.2 mm) diameters were significantly enlarged in the strenuous activity trainer group versus the ordinary activity group. Diastolic blood pressure was significantly lower (73.8±5.9 mmHg versus 78.3±6.0 mmHg) in this group. AR diameter was correlated with height (β=0.460; P=0.004) and LA diameter (β=0.280; P=0.008) while AA diameter was correlated with type of profession (β=0.309; P=0.003), left ventricular systolic diameter (β=0.500; P=0.001) and LA diameter (β=0.272; P=0.005) in regression analysis.

CONCLUSION:

Aortic dilation and, subsequently, TAA may be an occupational disease due to nature of some professions (eg, the military, security, weight lifters, athletes, heavy workers, etc). Echocardiography is a convenient method of imaging that could be easily applied either during preparticipation screening or during periodical examination of these subjects. Earlier detection of TAA and limitation of such strenuous activities in these individuals may be initial lifesaving measures for the prevention of future cases of aortic aneurysm and dissection.

Rupture or dissection of a thoracic aortic aneurysm is not an uncommon cause of mortality and morbidity among young or middle-age subjects who perform strenuous sports activities professionally (1). Enlargement or dilation of the proximal aorta or sinus of Valsalva is usually the initial anatomical deformation preceding further dissection (2). Etiologies of aortic disease are widely variable and include inherited, degenerative, atherosclerotic, inflammatory and traumatic causes (3). While inherited forms tend to cluster in a family, most forms are mainly related to individual characteristics.

However, environmental factors determined by an individual’s occupation may cause intensive hemodynamic insult to the aorta and may increase the probability of aortic aneurysm among subjects who are exposed to those occupational conditions; this may, therefore, deserve the definition of occupational disease. Subjects who participate in certain occupations, such as members of the military, security, heavy workers and weightlifters, may be repetitively exposed to extreme strenuous activity or isometric-type sports activity throughout the entire day. A few of them may have undergone an initial or periodical examination, while most may not have been examined by any means, even echocardiography, during the entire period of their employment (4). The physical conditioning process mainly includes isometric-type exercise and leads to increased muscularity and endurance (5). However, it may eventually lead to increased hemodynamic insult and mechanical stress on the great vascular structures and cardiac chambers (6).

In the present study, we aimed to evaluate and compare the characteristics of the aorta as well as echocardiographic parameters of the left ventricle and atrium among groups of individuals defined according to the type of sportive activity that they perform due to their occupation.

METHOD

Echocardiographic measurements obtained from the consecutive examination of personnel during January and February 2011 at Etimesgut Military Hospital, Ankara, Turkey, were retrospectively analyzed. The study was approved by the local ethics committee of Gulhane Military Medical Academy. The first group (the strenuous activity trainers [SAT] group) was defined as personnel who actively participated in routine daily exercise activity including isometric-type strenuous training, weight lifting, benching, jumping, squatting and hanging up, and necessitating at least a 4000 kcal/day energy consumption. The second group (the ordinary activity trainer [OAT] group) was defined as personnel who participated in exercise activity no more than twice per week. Exercise duration was limited to a period <2 h and mainly included aerobic exercise excluding the abovementioned activities performed by individuals in the SAT group. Participants’ exercise activities were derived from a detailed questionnaire about the exercise habits and a personnel data form about training performance completed by the subjects’ chiefs. Clinical features (age, height, weight, systolic and diastolic blood pressure), M-mode echocardiographic parameters of the left ventricle (left ventricular [LV] internal diameter at diastole and systole) and left atrial diameter (LAD) at diastole were recorded. A Vivid 7 Dimension (GE Healthcare, USA) echocardiography device was used to perform the echocardiographic examination.

LV mass was calculated according to the Devereux formula and indexed to the body surface area (BSA) calculated from the height and weight using Dubois’ formula (7,8):

$$\text{BSA}=0.20247\times \text{height}\hspace{0.17em}{(\text{m})}^{0.725}\times \text{weight}\hspace{0.17em}{(\text{kg})}^{0.425}$$

Aortic diameters were measured by an echocardiographer cardiologist as the distance between the outer contours of aortic wall at the levels of aortic root (AR) and sinotubular junction of ascending aorta (AA) at systole using a two-dimensional imaging modality which could provide exact dimensions of the aorta and prognostic information for aortic abnormalities (9). These measurements were confirmed by measurements on angiography of the aorta through multislice computed tomography with a mean (± SD) difference of 0.72±0.36 mm through 10 measurements in a previous study. In addition, aortic diameters (AR, AA and LAD) were indexed to BSA.

Subjects with abnormally enlarged aortic diameters (≥40 mm), bicuspid aortic valve (BAV), aortic valve stenosis or regurgitation, hypertension, dilated or hypertrophic cardiomyopathy, previously diagnosed coronary artery disease, and chest and sternum deformity were excluded from the study.

Statistical analysis was performed using SPSS 11.0 (IBM Corporation, USA) for Windows (Microsoft Corporation, USA). Numerical variables with normal distribution were analyzed using parametric tests (independent sample t tests). Categorized variables were analyzed using χ² tests. Correlation analyses of parametric and nonparametric data was performed using Pearson and Spearman’s correlation tests, respectively. These parameters were then tested in multiple regression analysis of the variables. P<0.05 was considered to be statistically significant.

RESULTS

When clinical features were compared, height (180.9±3.0 cm versus 178.8±2.2 cm; P=0.003) was significantly higher and diastolic blood pressure (73.8±5.9 mmHg versus 78.3±5.9 mmHg; P=0.001) was significantly lower in the SAT group, whereas age and systolic blood pressure were not significantly different between the groups. When the echocardiographic parameters, such as LV internal diameter at diastole and systole, thickness of interventricular septum at diastole, LV mass and mass index, were compared, LV ejection fraction and LAD index were not significantly different between groups; the exception was LAD (37.4±2.2 mm versus 36.2±2.2 mm; P=0.041), which was higher in the SAT group. In addition, AR diameter (35.6±3.0 mm versus 33.5±1.9 mm; P=0.001), AR index (17.6±1.5 versus 16.7±1.0; P=0.004), AA diameter (36.8±3.0 mm versus 34.4±1.9 mm, P=0.001) and AA index (18.2±1.5 versus 17.2±1.1; P=0.002) were significantly increased in the SAT group compared with the OAT group (Table 1).

TABLE 1.

Comparison of clinical features, echocardiographic parameters and aortic diameters among groups

	Ordinary activity trainers (n=30)	Strenuous activity trainers (n=30)	P
Clinical features
Age, years	38.0±3.7	37.4±3.5	0.578
Height, cm	178.8±2.2	180.9±3.0	0.003†
Weight, kg	81.3±2.9	82.2±3.7	0.324
SBP	126.6±7.3	125.3±7.7	0.497
DBP	78.3±5.9	73.8±5.9	0.001†
Echocardiographic parameteres
IVSD	9.20±0.40	9.26±0.44	0.549
LVIDD	48.2±2.8	48.8±3.8	0.446
LVIDS	32.2±2.7	31.8±3.2	0.613
LAD	36.2±2.2	37.4±2.2	0.041*
LAD index	18.1±1.3	18.4±1.2	0.221
LV mass	155.0±15.6	160.3±28.3	0.370
LV mass index	86.6±8.7	88.6±15.6	0.557
LVEF	68.2±5.1	69.5±5.0	0.334
Aortic diameters
Aortic root	33.5±1.9	35.6±3.0	0.001†
Aortic root index	16.7±1.0	17.6±1.5	0.004†
Ascending aorta (sinotubular junction)	34.4±1.9	36.8±3.0	0.001†
Ascending aorta index	17.2±1.1	18.2±1.5	0.002†

Data presented as mean ± SD unless otherwise indicated.

^*P<0.05;

^†P<0.01. DBP Diastolic blood pressure; IVSD Thickness of interventricular septum at diastole; LAD Left atrial diameter; LVIDD Internal diameter of left ventricle at diastole; LVIDS Internal diameter of left ventricle at systole; LV Left ventricle; LVEF LV ejection fraction; SBP Systolic blood pressure

In correlation analysis of all variables, AR diameter was significantly correlated with height (β=0.460; P=0.004) and LAD (β=0.280; P=0.008) whereas AA diameter was significantly correlated with the type of profession indirectly with the subjects’ group (β=0.309; P=0.003), LV internal diameter at systole (β=0.500; P=0.001) and LAD (β=0.272; P=0.005) in multiple regression analysis. The other variables found to be correlated in the Pearson’s correlation analysis were not significantly correlated in multiple regression analysis (Table 2).

TABLE 2.

Correlation analysis of aortic root and ascending aorta diameters, clinical features and echocardiographic parameters

	Aortic root		Ascending aorta
	R	P	R	P
Type of profession	0.196	0.070	0.309	0.003*
Height	0.460	0.004*	0.179	0.215
LVIDD	0.082	0.705	−0.031	0.878
LVIDS	0.238	0.089	0.500	0.001*
LAD	0.280	0.008*	0.272	0.005*
LV mass	−0.152	0.868	1.102	0.276
LV mass index	0.195	0.825	−0.944	0.252

^*Correlation is significant at P<0.01. LAD Left atrial diameter; LV Left ventricle; LVIDD Internal diameter of the LV at diastole; LVIDS Internal diameter of the LV at systole

DISCUSSION

AR dilation and aortic dissection are reported with a ratio varying from 3.1% to 5% among causes of sudden cardiac death in athletes (10). They are frequently observed in young subjects with Marfan syndrome, genetically inherited disease or Marfanoid body habitus (11). Weight lifters are also at an increased risk for aortic abnormalities such as dilation, aneurysm or dissection. It was reported that 65% of subjects had a moderately enlarged aortic diameter (<50 mm) at the time of dissection, and 30% occurred in a nonexercise setting. A total of 87.1% of subjects exhibited dissection of the proximal aorta or AA (type A) (12). Therefore, aortic aneurysm or dissection is not only confined to inherited collagen disorders, weight lifting, etc, but also may be observed in subjects with enlargement of aorta as a result of experiencing heavy, strenuous sport training programs due to their profession.

Normal ranges for AR diameter measured using computed tomography for male sex vary between 36.3 mm and 39.1 mm (13). Of the three layers of the aortic wall, the media is composed of mainly elastic fibres with interposed smooth muscle cells, and the adventitia is composed of mainly collagen and vasa vasorum (11). Medial degeneration may be one of the consequences of hemodynamic insult or increased shear stress. Hyperplastic cellular remodelling of the media and elongation of elastin fibres may be the initial adaptive responses to minimize increased wall stress resulting from vascular dilation (14). Okamoto et al (15) constituted a cylindrical model of the aorta from fresh aortic wall tissue and demonstrated that aging was one of the important determining factors in the reduction of elastic properties and extensibility of aortic tissue, especially in patients with BAV and degenerative aortic aneurysm. They also found that circumferential stress was intensified with increasing diameter of the aortic lumen and systolic blood pressure. This indicates that the greater the aortic diameter, the greater the circumferential stress. In our study, we found that aortic diameters were significantly increased at the level of the AA and also the AR in the SAT group compared with the OAT group. The two groups were matched according to age and sex. The higher aortic diameters in the SAT group may portend a vicious cycle of greater aortic diameter leading to a higher circumferential stress and vice versa. In the future, this will be associated with an exponentially increased risk of rapid progression and rupture or dissection, similar to patients with Marfan’s syndrome. Enlargement of the aorta is more predominant at the AA compared with the AR, and represents a conic deformation in the SAT group. The latter exhibits similarity with the poststenotic dilation observed in BAV even without a transvalvular gradient. However, in the exercise period, increased ejection velocity and eccentric deviation of the aortic jet from the axis directed toward the wall of ascending aorta likely lead to the aortic enlargement associated with BAV. Because similar hemodynamic changes, along with changes in the aortic valve and proximal aorta, are induced and developed during strenuous isometric exercise and training activities in the SAT group, medial degeneration (characterized by fragmentation and loss of elastic fibres) may have previously developed and preceded the initiation and progression of aortic aneurysm.

Elastin fibres have the capability to stretch up to three times their resting length. Their passive elastic recoil ability contributes to the propagation of blood flow anterogradely and also retrogradely within the aorta, and contributes to the formation of the diastolic blood pressure wave, in cooporation with collagen structures, following systole and aortic valve closure. Elastin fibres may function effectively within a half-life of 40 years and may lose elasticity under continuous low stresses (16). Aortic enlargement in BAV due to moderate or severe elastin fragmentation is a consequence of continuous hemodynamic stress, either at low grade during resting or high grade during exercise (17). This model of elastin fragmentation may be an appropriate model for our findings observed in SAT. Progression of aortic enlargement may be accelerated, likely due to the coexistence of increased aortic wall stress, loss of elastic properties and resistance of collagen, and increased diameter. This may only be counteracted by the avoidance of isometric-type activities by the subjects.

Cardiac output increases up to 30 L/min to 40 L/min with a positive linear relationship to intensity of activity during exercise in highly trained subjects (18). The mild and highest levels of aerobic exercise may induce modest (140 mmHg to 160 mmHg) and highest (180 mmHg to 220 mmHg) increases in arterial blood pressure, respectively. Weight lifting, bench pressing, extreme strength, etc, may induce acute rises in blood pressure to >300 mmHg (6). The Valsalva maneuvre (the struggle of forced expirium against a closed glottis) is one of the voluntary breathing maneuvres mostly used to increase the peak force produced by muscle contraction. Ikeda et al (19) reported that forced exhalation may have a significant impact on isometric muscle strength rather than the Valsalva maneuvre, which has unfavourable effects on cardiovascular system. In particular, an overshoot in blood pressure was observed during the initial 2 s to 3 s of phase I of the Valsalva maneuvre due to increased intrathoracic pressure and mechanical compression of the aorta. Following phase II and III, when the reduction in blood pressure and heart rate were observed, an overshoot of blood pressure develops again in phase IV, ie, the release of the Valsalva maneuvre, due to residual vasoconstriction and normalization of venous return and stroke volume (20). These relatively short but overt increases in blood pressure and heart rate may have been overlooked in routine daily practice. However, it is evident that sudden increases in blood pressure impose a mechanical force that drives the ascending aorta to expand during the systole period. Moreover, subjects participating in strenuous exercise may have been exposed to double periods of hemodynamic stress, similar to a ‘to and fro’ mechanism. Higher systolic blood pressure generates a tremendous expanding force anterogradely, perpendicular to the axis, and also both perpendicular and circumferential to the aortic walls during systole, whereas higher diastolic blood pressure will retrogradely force the proximal regions of the aorta (AA, AR and sinus of Valsalva) to expand against a closed aortic valve. Thus, the proximal aorta is exposed to mechanical insults both at systole and diastole (Figure 2A, 2B). AR diameter, AA diameter and their indexed measurements may have been significantly increased in the SAT group in our study as a result of the above-mentioned mechanisms. AR diameter was found to be significantly correlated with a constitutional feature (height; β=0.460; P=0.004), and nonsignificantly with the type of profession (β=0.196; P=0.070) whereas AA diameter was correlated with type of profession (β=0.309; P=0.003). The latter correlation may represent the influence of profession and also experiencing strenuous training and isometric-type exercise activities. The AA and the sinus of Valsalva may be the regions most influenced by expanding forces due to the absence of anatomical support, because the AR has constraining anatomical structures such as fibrous skeleton of cardiac valves and subvalvular structures.

Figure 2).

Representative drawing of aortic root and ascending aorta exposing to expanding force of high blood pressure both at systole (A) and diastole (B)

One of the significant findings to be discussed was the lower diastolic blood pressure in the SAT group. Chen et al (21) reported that systolic and diastolic blood pressure was significantly reduced in hypertensive patients, with a difference of 15 mmHg and 4 mmHg, respectively, after a 12-month period of regular sports training. But these reductions were not significant in normotensive subjects. In our study groups, mainly composed of normotensive subjects, diastolic blood pressure was significantly lower in the SAT group compared with the OAT group, with a difference of 4.8 mmHg. The higher conditioning levels or increased vagotonic activity frequently observed in subjects who train professionally may be accountable for this. However, reduced elastic recoil of the aortic wall due to elastic fragmentation and loss of resistance capacity of collagen accompanied by an increased aortic diameter may hypothetically cause the proximal aorta to inadequately and ineffectively initiate and propagate the diastolic component of blood pressure.

LAD was found to be significantly greater in the SAT group compared with the OAT group (37.4±2.2 mm versus 36.2±2.2 mm; P=0.041). That finding may be one of the echocardiographic results supporting that the SAT group professionally participated in sports training activities. Recently it was reported that left atrium diameters were increased as a left atrial remodelling response to prolonged duration of regular endurance sports (22,23). Although that physiological response was reported to be a risk factor for the development of atrial flutter, we did not observe atrial arrhythmia or palpitation in our study groups. The positive correlation between the AR and AA diameters and LAD (β=0.280, P=0.008; β=0.272, P=0.005, respectively) may support our suggestion that the enlargement of the diameters of the left atrium and aorta could have been developed as an abnormal response to the prolonged and higher levels of strenuous isometric training activities. Although LV internal diameter at diastole, LV internal diameter at systole, LV mass and LV mass index did not appear to be significantly different between groups, LV internal diameter at systole was slightly decreased and LV ejection fraction was slightly higher in the SAT group. Kaminski et al (24) evaluated the adaptive changes in the LV in response to static and dynamic efforts, and observed slightly increased thickness of LV walls with a smaller LV volume in the static effort group compared with the dynamic effort group. The authors also reported higher LV mass and LV mass index in the static effort group. These data overlap with our findings in the SAT group, who participated in intense and prolonged strenuous training, mainly composed of static effort rather than dynamic effort, due to their profession. All these findings are complementary to our findings and suggestions that the enlargement of diameters of AR and AA may have been unfavourable consequences of physical obligations induced by professional conditions. These changes may unfavourably precede irreversible changes, with potential for devastating events.

The importance of early diagnosis, prompt treatment and management of the patients with thoracic aortic aneurysms or enlargement by the physicians and health care professionals is critical (13). We suggest that subjects with certain professions and occupations, such as members of the military, security, Special Forces of the army, professional weight lifters, endurance athletes, etc, are at a risk for the development of aortic enlargement and, subsequently, aortic aneurysm, and should initially and periodically be examined using echocardiography. Individuals whose aortic diameters are increased or tended to rapidly enlarge during follow-up should be strictly prohibited from performing such strenuous activities, circumstances and occupations because delayed or missed cases could eventually result in catastrophic states of disease, such as aortic rupture or dissection, or sudden cardiac death. Furthermore, this issue is likely to have a greater medical-legal scrutiny in the future because specific cases from the public have been reported in increasing numbers and have been widely discussed (11). Also, detection of subjects with BAV with slightly enlarged aortas, or with Marfan syndrome and aortas with upper diameter of normal ranges, etc, may help the physician to guide the patients to take the measures to prevent further enlargement, rupture or dissecting of aortic aneurysm. Modification of lifestyle, avoidance of isometric exertion (eg, weight training, bench pressing, etc), effective therapy of hypertension, treatment with beta blocker drugs if not contraindicated, and avoidance of sports or military professions were all effective and life-saving measures that could prevent progression and fatal complications (4,25).

CONCLUSION

Aortic aneurysm and dilation may be one of the unfavourable consequences of certain occupations that involve prolonged and repetitive strenuous isometric training activities; therefore, it may be defined as an occupational disease when diagnosed in subjects with certain occupations. Echocardiography is a convenient method to identify subjects at risk for aortic dilation. It is easily performed either at preparticipation screening or during periodical examination of these subjects. Earlier detection of aortic aneurysm or tendency and avoidance of strenuous activities are initial lifesaving measures that may prevent progression and fatalities.

Figure 1).

Representative drawing of aortic root and ascending aorta in accordance with the mean diameters and differences of measurements among groups. OAT Ordinary activity trainers; SAT Strenuous activity trainers