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.
Learning points:
- Patients with pectus excavatum showed no signs of direct
cardiopulmonary impairment.
- Severity of the chest deformity expressed with anthropometric index
does not statistically correlate well with cardiopulmonary exercise
data (such as VO2, O2Pulse or VO2/WR) but graphically expressed
relations show dependence and correlation.
- OUES is new perspective parameter showing negative correlation with
deformity severity.