Discussion
PE and PC continue to be widely considered primarily as an aesthetic issue even though evidence of CPF impact is accumulating, also for the older population.23 Previous work mainly reported results in relatively small patient samples where cardiac and pulmonary impact had been considered independently from each other.3 8 9 To our knowledge, there is no published data coupling cardiac and pulmonary function evaluation for the same cohort of paediatric subjects presenting PE or PC. In addition, most of the studies reported small series of patients with only little detailed data on CPF.
In our study, the prevalence of a positive family history as well as spinal deformity is concordant with previous publications. Our results show a clear tendency towards lower CPF values in both PE and PC patients. For pulmonary function, PE patients were more affected than PC patients, whereas cardiac functional values were equally impacted among both groups.
Regarding pulmonary results, we observed that even if symptoms were reported at rest, they had little effect on clinical evaluation, with mild functional anomalies. Indeed, only PE patients presented decreased lung flow measured by spirometry, but both pectus subtypes had a tendency to decreased lung volumes.
Lung function in PE patients was associated with mean Z scores for FVC, FEV1 and FEF25-75 within the normal range, although scores were lower than in the general population. This confirms previous studies on adult subjects in which obstructive patterns have been observed.24 Nonetheless, the FEV1/FVC ratio in PE patients was similar to the general population. Decreased mid expiratory flows (FEF25-75) suggests obstruction on small airways and is also associated with asthma symptoms. We reported values under the LLN for FVC (30%), FEV1 (27%) and FEF 25–75 (13.3%) of PE patients corresponding to previous studies where 5.6% to 41% of obstructive syndrome was reported.3 7 Lung volumes were associated with a restrictive syndrome in 23% of PE patients, consistent with previous studies.3 7 These results can be explained by a deformed thoracic cage in PE and PC that decreases mechanical compliance and certainly impacts respiratory muscle efficiency. As abnormal development of the sternocostal cartilage is thought to be a determinant in pectus formation, increased thoracic wall stiffness is also possibly present. However, in PC patients, only VC was significantly decreased, as previously described.3 25 Considering the scarcity of lung function data in PC paediatric patients, this represents an important learning that differs clearly from PE data.
A proportion of PE patients complained of dyspnoea on exertion (13.3%) and chest pain at rest (20%), although rates were lower compared with previously published data. A large multicentric study reported a prevalence 62% for shortness of breath, and 32% for chest pain at rest.26 Casar Berazaluce et al recently published a similar prevalence of 41% of shortness of breath and 62% for chest pain at rest in 345 patients with PE.27 Even if the precise prevalence of thoracic symptoms in PC patients is not well documented, progressive symptoms of dyspnoea or reduced endurance improving after surgical repair were described in moderate to severe thoracic deformity.28 Our results confirm these tendencies, with 29% of PC patients reporting thoracic symptoms at rest or during physical activity without correlation with pectus severity. Unfortunately, we lacked a prospective quantifiable value to evaluate pain level and duration.
For both pectus types, these symptoms could have been partially associated with a relative exercise deconditioning secondary to embarrassment to undress in public.29 30 In addition, asthmatic patients were excluded, which could also have decreased the number of patients with pulmonary symptoms.
As for pulmonary function, cardiac function was also close to normal range. A set of reference values for cardiac function evaluated by MRI in children exists and has Z scores with ULN and LLN defined as mean ±2 SD.12 It is worth noting that these values are only normalised for sex and total body surface and can therefore not be used as strict normative values. To date, percentage of EF remains the main tool to evaluate cardiac function, with abnormal values below 55%. Applying these values to our PE and PC patients, around 50% and 25% had an RVEF under the LLN, respectively. Nonetheless, no RVEF value was recorded below 50% either for PE or PC, highlighting the absence of an argument for significant cardiac functional impairment at rest in these patients.
Consistent with these observations, the mean values for LVCI, LVEF and RVCI in PE and PC patients were significantly lower than expected, but within normal range. Here again, despite no clearly defined pathological patterns, observations confirmed a shift towards lower normal values for the major indicators of cardiac function at rest in pectus patients consistent with previously published data.8 31 However, no correlation was found between EF and HI severity.
Our results confirm a tendency toward lower RVEF in PE and attest the possibility of a same effect on LVEF. Our data also show elevated ventricular end-diastolic and end-systolic volumes in both types of pectus. This reinforces the probability of an anatomically driven bilateral relative impairment of myocardial contractility due to thoracic and sternal cardiac compression. Such a mechanism was previously assumed in the presence of lower RVEF and decreased RV circumferential strain magnitude in PE compared with controls.32
Both pectus groups showed pulmonary and cardiac functions within the normal range, with a tendency toward statistically significant lower values. We did not find any association between cardiac and pulmonary function. Even though symptoms were present at rest, these functional anomalies are not a proper reflection of clinical impairment, which depends, among other factors, on physiological adaptation to exercise and training. Previous studies evaluating the relation between PE and CPF during physical effort using treadmill or cycle ergometer exercise testing showed improved maximal oxygen consumption after surgical repair.9 11 CPF parameters have yet to be precisely and directly observed during exercise, in particular using functional cardiac MRI during or directly after physical effort.
Finally, previous publications report a possible association between severity of HI and reduction of pulmonary function in PE.33 In our cohort, we did not find any statistically significant association between HI and STA with pulmonary or cardiac functional parameters in PE and PC patients, reinforcing the need of an accurate cardiopulmonary evaluation of these patients.
According to previously published work, even though CPF impairment is more likely to be observed both at rest and during exercise in PE patients with increased thoracic deformity, modest pectus can also be accompanied by thoracic symptoms or functional limitations. Conversely, some patients more severely affected according to standard morphological evaluation tools, such as HI, display no major impairment of pulmonary function. It is worth noting that a significant 47% of overlapping HI values between PE patients and controls in a previous paediatric population.34
Full cardiopulmonary pathophysiology of pectus patients is not yet fully understood, and a more refined evaluation is needed to properly assess each situation, especially in the case of mixed deformities combining morphological measurements, such as HI and STA, with functional imaging and tests. The external three-dimensional scanner is a promising tool and has shown a certain degree of correlation with HI in PE.35
Although our study examined pectus malformation in a paediatric cohort in great detail and, to the best of our knowledge, is the first to precisely analyse the impact of PC on CPF, it does present several limitations. Indeed, the limited number of patients might have contributed toward the lack of correlation between severity of thorax deformity and diminished functional parameters. No control group was enrolled, but all parameters were normalised using published Z-score data. In addition, PE patients did not present severe HI, with a relatively dense distribution of mean values around 4.6. Regarding the relatively high frequency of associated symptoms in our cohort, the psychological aspect of chest deformities could play a significant role. Finally, our evaluation was performed before treatment and at rest. We, therefore, cannot exclude an impact of PE or PC during exercise in patients with values at the LLN. This could have explained an absence of correlation between HI and impaired functional values.