DISCUSSION
Current study investigated the role of spirometry and LCI in evaluation of long-term lung function in children with CLM after surgical intervention and revealed that children who underwent surgery for CLM have impairment in lung functions compared to healthy children.
Lung growth and development continues in childhood after birth15,16. Also lungs compansate the tissue loss by compensatory growth and remodeling which may result in improvement of clinical condition and respiratory functions after surgical intervention. Most reports showing normal lung functions with spirometry after surgery in the follow-up of CLM patients may suggest this mechanism11,12.
In our study, mean spirometric values were within normal range in patients with CLM. Similarly, normal spirometric results was reported by Keijer et al. in 14 post-operative CLM children11. Also Beres et al. showed that CLM patients mostly have normal spirometric results in the post-operative period12. Even though, lung function test parameters in spirometry were in normal range in both study groups, patients with CLM had significantly lower values than healthy control group. It may be speculated that, CLM patients may have a mild deterioration in lung function in the post-operative period.
Compensatory growth and remodeling after surgical resection of congenital abnormality may cause inhomogeneity in ventilation distribution. In such circumstances, LCI may be more accurate to detect early peripheric airway deterioration compared to spirometry. Therefore, LCI was used in addition to spirometry in this study and statistically significant differences were detected between the two groups. LCI assessment results, in long term follow-up, demonstrate that, impairment and incomplete recovery in peripheric small airways occur in CLM patients after surgery.
As mentioned before, LCI is more accurate and sensitive for early detection of lung diseases and evaluating lung function17-19. In a study conducted by 43 children with cystic fibrosis (CF) and 28 healthy controls, 23% of CF patients had reduced FEV1 and in contrast LCI was found to be abnormal in %63 of them20.
In the current study, although 11 patients out of 15 had abnormal LCI values, only 4 of them had lower spirometric results. So, LCI measurement enable to detect lung function impairement in 7 patients which had normal spirometric results. Also a strong inverse correlation between LCI and spirometry found in our study suggests the usage of LCI in the long-term follow-up of CLM patients
To our knowledge, there is only one previous study comparing LCI with spirometry for the assessment of lung function in post- operative. Mandaliya et al. found abnormal FEV1% and LCI values in CLM patients post-operatively compared to healthy controls similiar to our study21. In both studies, although FEV1 values were reported to be lower than the controls, they were over the 80% predicted which is accepted to be the cut-off point for normality. Mandaliya et al. reported lower BMI and height values which may result in a decrease in spirometry and LCI measurements21. In contrast to this study, BMI and height of all our patients were in normal range.
In the current study, LCI values of the healthy controls were higher than the previous studies. one of these studies, using the same technique, mean LCI value was found to be as 6.54 + 0.28 by Houltz B. et al. in 44 healthy children by nitrogen based LCI22. Mandaliya et. al. reported mean LCI value as 7.3+ 0.6 in the control group similiar to our study21. Differences in the mean LCI values in different countries requires to be investigated in the further studies. Somatic growth, gender, ethinicity and age can be potential factors explaining these discrepancy
Small sample size may be the major limitation of this study. Therefore, multicenter studies including larger number of patients with CLM are required. Also reference LCI values need to be defined in different groups in larger population studies.
In conclusion, patients operated due to CLM may have impairment in the peripheral airway function in the long term follow-up. Both spirometry and LCI enabled detection of such an impairment in our study. But LCI may be superior to detect changes earlier in the lung function