Discussion
The most objective method to measure exercise capacity is cardiopulmonary exercise test which measures peak oxygen consumption14. Non-invasive examination methods without exposure to radiation exposure are the preferred options in assessing the health status of pediatric patients 15. PE is the most common deformity of the child’s chest, which can have a major impact on the quality of life of the child not only by reducing physical condition but also by the psychological effect that hinders the full development of the child. Current therapeutic options are based on a quality functional assessment of the health condition of a patient with PE, on the basis of which surgeons decide on the suitability of a surgical or conservative procedure in the treatment of chest deformity. Static examination methods (imaging and functional) have long been used in the monitoring of patients with PE, which by their nature do not directly tell about the functional capacities of the child’s body, as their results correspond to resting capacities and do not reflect functional changes during exercise (both normal daily and peak)9. It is the effort of clinical workplaces to obtain clinically relevant data on patients related to the functional capacity of the organism using examination methodologies that do not evaluate the affected organ systems independently, but comprehensively, in the context of real clinical burden.
By analysing the exhaled air using continuous monitoring of the cardiovascular system under load, it is possible to evaluate the functional capacity of the cardiovascular, pulmonary and musculoskeletal systems in one session 16. For such an assessment, it is necessary to know the physiology of these systems under load and the pathophysiological mechanisms that are the essence of clinical difficulties.
The relationship between deformity severity and performance parameters in patients with PE has so far been evaluated in published works most often on the basis of the Haller index, which, however, carries with it the need for radiation exposure (computed tomography) or high cost and low availability (magnetic resonance imaging). In order to non-invasively monitor patients with PE who are not indicated for surgery, a proposal was submitted to assess the severity of pectus excavatum, the so-called anthropometric index (AI) 5. The use of an anthropometric index in the context of evaluating the functional capacity of an organism with PE has not yet been published. In our work, we evaluate the correlation of individual monitored parameters with the severity of chest deformity using the Pearson index.
It is assumed that increased respiratory work arising from the partial restriction of chest movements in PE appears to play a role in limiting physical activity 2. This assumption should be supported by the finding of an increased maximum respiratory rate, a decreased tidal volume at peak load, and a high respiratory reserve. We did not show a dependence of the severity of the deformity on the maximum respiratory rate (r = 0.05). According to Malek et al. sternal compression results in a reduced sternum volume, leading to a reduction in maximal oxygen consumption during exercise, a reduction in exercise tolerance, a reduction in tidal volume, vital capacity, which reduces body endurance and causes dyspnoea and compensatory tachypnoea during exercise 9. Comparison of tidal volume alone at the peak of load between individual groups is not possible due to the dependence of VT on anthropometric parameters of the patient. The ratio of tidal volume to FVC (Max VT/FVC) is comparable to each other. In this parameter, the severity of the deformity did not have a statistically demonstrable effect on Max VT/FVC, but the linear prognosis (taking into account all data) shows a declining trend and a direct dependence of the severity of the deformity on the maximum tidal volume Respiratory reserve (BR) expressed as a percentage of peak ventilation to maximum voluntary ventilation (VE/MVV) is a parameter evaluating the total respiratory reserve of the organism at the peak of exercise and in practice is used to discriminate patients with respiratory load limitation 9. In our study, we did not demonstrate a relationship between deformity severity and BR (r = - 0.08).
Reduced oxygen supply to the working muscle as a consequence of reduced venous return to the right atrium also contributes to reduced physical fitness of patients with PE 1. In patients whose right side of the heart is in contact with the sternum, a decrease in maximal O2Pulse is expected as a result of limited right ventricular filling at maximal load 2. The relationship of the chest deformity to the position of the heart leads to a reduction in the ejection volume of the heart and in severe deformities to a decrease in cardiac output, which results in compensatory tachycardia and consequently accelerated fatigue 17. We did not demonstrate the relationship of O2Pulse to chest deformity (r = -0.26; p> 0.05), but the graph of linear dependence using the forecast shows a decreasing trend (graph 4). Maximum peak heart rate (HRpeak) did not correlate with the severity of the deformity (r = 0.04, p> 0.05) and thus we did not confirm the presence of compensatory tachycardia, which should compensate for insufficient cardiac output during exercise.
Oxygen consumption values ​​(VO2Max, VO2Peak) may be significantly lower in patients with PE than the predicted values ​​for patient height and weight 7. However, other studies have provided conflicting information because in the study by Quigley et al. patients with PE had higher VO2peak scores than controls 18 but in a study by Wynn et al. these results were reversed19. Due to the discrepancy of these data, a meta-analysis of CPET data was performed in 2006, where cardiovascular and respiratory parameters before and after surgical correction of PE were evaluated. The finding of this study was that after the operation itself, in the period from 9 to 12 months after its operation, there was no significant increase in VO2 in the monitored patients9. As an explanation for this condition, it is stated that deformity alone would not lead to reduced aerobic capacity of the body and physical deconditioning of patients after surgery had a greater effect on VO2 than the limitations resulting from deformity9,10. By correlating the measured values ​​of oxygen consumption, we did not show that the severity of the deformity correlates with the measured oxygen consumption (r = -0.09; p> 0.05) or with exercise tolerance (r = -0.07, p> 0.05). The VO2/WR assessment can express the efficiency with which the person’s muscles use the supplied oxygen20. In studies evaluating this efficacy in patients with PE before and after surgery, they did not show that correction of deformity would lead to an improvement (increase) in this efficacy10. By correlating the severity of the deformity with VO2/WR, we did not demonstrate the dependence of VO2/WR on AI (r = 0.20; p> 0.05). The VE/VCO2 parameter (the steepness of its rise) is a parameter determining the efficiency of pulmonary perfusion, respiration and ventilation pairing and thus the efficiency of the whole act of ventilation 21. In patients with PE there has not been hypotheses of the effect of deformity on this parameter postulated. In our study, we observed a lower VE/VCO2 (slope) value in patients with less severe deformity compared to patients with more severe deformity (27.29 vs 29.78; p> 0.05).
A rather novel parameter that has not yet been evaluated in patients with PE is the oxygen uptake efficacy slope. Its use to evaluate the effectiveness of a patient’s use of oxygen under increasing load was suggested in an electronic commentary on the evaluation of cardiorespiratory parameters before and after surgery in adult patients with PE 22.23. The advantage of using this parameter is that it is independent of effort and motivation, easily reproducible and is obtained without the need for a maximum stress test (even without meeting the criteria for maximum test). The disadvantage is lack of standardized reference data both for children and in general for patients with non-cardiovascular diseases. In our work, we obtained the parameter by automatic recalculation of all submaximal data in the Bluecherry software (Geratherm Respiratory, Germany). In patients, we demonstrated a slight dependence of OUES on the severity of the deformity (r = - 0.33; p = 0.05). Linear regression and the created trend line indicate a negative correlation of OUES with the severity of the deformity, which is an interesting observation, given that it may be a suitable parameter that indicates the body’s overall ability to efficiently obtain and use oxygen from the atmosphere (Graph 3). Since the parameter is independent of the effort, it can be used in less cooperative or motivated patients.
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