Introduction. Sleep-disordered breathing is frequent in children and adolescents. Patients with obstructive sleep apnea (OSA) have repetitive airway obstructions and breathing pauses associated with desaturations, arousals and poor sleep quality. In children with neuromuscular or lung disease hypoxemia or even hypercapnia can be present without obstructive events during sleep. These patients often require night time respiratory support. The influence of altered gas exchange on sleep quality has not been extensively studied in such children. Polysomnography (PSG) is considered the gold standard for the assessment of sleep but its complexity often limits its availability in clinical practice. Several alternative approaches have been used to bridge these restrictions. Actigraphy has been shown to produce acceptable estimates for several sleep quality parameters. Continuous measurement of oxygen hemoglobin saturation by pulse oximetry (SpO2) and transcutaneous measurement of carbon dioxide partial pressure (PtcCO2) can be performed noninvasively at the earlobe. Simultaneously collected data on pulse rate variability can contribute to the assessment of cardiovascular stress and its impact on sleep quality.
Aims and hypothesis. The purposes of the study was to analyze associations between objective indicators of sleep quality and nocturnal gas exchange alterations with pulse rate variability in children with various chronic respiratory health conditions. We aimed to determine whether associations exist between sleep efficiency (EFF) and sleep fragmentation (FI) measured by actigraphy and nocturnal hypoxemia, hypercapnia and pulse rate variability noninvasively assessed by a combined SpO2/ PtcCO2 monitor. Findings in patients with nocturnal hypoventilation would be compared to those with partially corrected and normal nocturnal gas exchange. The two study hypotheses were: (1) low sleep quality is associated with nocturnal hypoxemia in children and adolescents and (2) low sleep quality is associated with nocturnal hypercapnia in children and adolescents.
Subjects and methods. Children and adolescents with various conditions leading to sleep-disordered breathing were included into the study. The majority was affected by large airway pathology, lung disease and chest wall abnormalities. Consecutive patients were prospectively recruited and categorized a priori into three groups. The first group contained 38 subjects with nocturnal hypoventilation defined by coexisting nocturnal hypoxemia and hypercapnia (NH group). Nocturnal hypoventilation was defined by a minimal SpO2 < 90 % for at least 5 consecutive minutes and/or for > 10 % of night time, and a PtcCO2 > 50 mm Hg for at least 5 consecutive minutes and/or > 10 % of night time. Criteria for noninvasive respiratory support were nocturnal hypoxemia with SpO2 < 90 % for > 10 % of night time and/or nocturnal hypercapnia with a PtcCO2 > 50 mm Hg for > 10% of night time. The second group included 25 other subjects with partially corrected nocturnal hypoventilation (PC-NH group). Subjects evaluated during the first days of adaptation to noninvasive respiratory support, when an incomplete correction of nocturnal hypoxemia and hypercapnia was present. The third group contained patients without nocturnal hypoventilation, defined as nocturnal SpO2 > 90% and PtcCO2 < 50 mm Hg (no-NH group). This group included 11 subjects, 7 subjects well controlled by noninvasive respiratory support, and 4 subjects with cured nocturnal alveolar hypoventilation. Exclusion criteria were: treatment with any medication that would influence sleep, abnormal daytime blood gases and/or need for supplemental oxygen. Also, subjects with impaired upper limbs mobility (actigraphy requirement) and those younger than one year of age or with dark skin (technical limitation of the combined SpO2/PtcCO2 monitor) were excluded. Actigraphy measurements were performed by a wrist actimeter (Actiwatch, Cambridge Neurotechnlogy). Overnight gas exchange recordings were performed noninvasively by a combined SpO2/PtcCO2 monitor (SenTec Digital Monitor).
Results. A total of 74 subjects were included. Subject’s mean age and body mass index (BMI) did not differ significantly between the groups. Comparison of sleep indicators in no-NH group and NH group reviled significantly longer mean actual sleep time (418 min ± 60 vs. 369 min ± 98, p = 0,001), higher EFF (92 % ± 5 vs. 78 % ± 11, p < 0,001) and lower FI (21 ± 9 vs. 34 ± 16, p = 0,001) in no-NH group. Likewise, comparison of sleep indicators in no-NH group and PC-NH group showed significantly longer mean actual sleep time (418 min ± 60 vs. 390 min ± 95, p = 0,002), higher EFF (92 % ± 5 vs. 81 % ± 8, p < 0,001) and lower FI (21 ± 9 vs. 32 ± 16, p = 0,006) in no-NH group. Also, subjects in PC-NH group had significantly longer mean actual sleep time (390 min ± 95 vs. 369 min ± 98, p = 0,004) and higher EFF (81 % ± 8 vs. 78 % ± 11, p = 0,004) compared to those in the NH group. Evaluation of gas exchange and pulse rate parameters in the no-NH group and NH group showed significantly higher mean value of minimal night time SpO2 (90 % ± 4 vs. 85 % ± 7, p = 0,03) and lower mean percent of time spent with a PtcCO2 > 50 mm Hg (0 % vs. 20 % ± 31, p = 0,006) in the no-NH group. The no-NH group recorded lower mean values of the percent of time spent with SpO2 < 90%, <92%, desaturation index and maximal PtcCO2 that other two groups, but the differences did not reach statistical significance. Pulse frequency results did not differ among groups except for pulse rate rise index by > 6 / min (PRRI-6). Mean recorded value in group no-NH was significantly higher than in group NH (38 ± 22 vs. 17 ± 4, p = 0,01) and in group PC-NH (38 ± 22 vs. 19 ± 6, p = 0,03). In NH group, analysis showed association of actigraphy parameters EFF and FI with minimal SpO2 (r2 = 0,21, p = 0,004 and r2 = - 0,10, p = 0,050, respectively) and with the time spent with SpO2 < 90 % (r2 = - 0,33, p < 0,001 and r2 = 0,13, p = 0,028, respectively). EFF and FI were also associated with standard deviation of the pulse rate (r2 = - 0,42, p < 0,001 and r2 = 0,37, p < 0,001, respectively), PRRI-6 (r2 = - 0,33, p < 0,001 and r2 = 0,13, p < 0,028, respectively), PRRI-10 (r2 = - 0,33, p < 0,001 and r2 = 0,15, p = 0,034, respectively) and PRRI-15 (r2 = - 0,33, p < 0,001 and r2 = 0,33, p = 0,07, respectively). We found no association between EFF nor FI and PtcCO2 parameters. Subjects in PC-NH group recorded only mild abnormalities in night time SpO2 and PtcCO2 measurements. No association was observed between EFF, FI, gas exchange parameters and pulse rate values. In no-NH group, the observed parameters of sleep quality, SpO2, PtcCO2, and pulse rate were within normal range. No association was determined among them.
Conclusions. Objective evaluation of the interplay between sleep and breathing is challenging in children. Respect for the nature of pediatric sleep precludes specific approach to research. Our study managed to get insight on sleep quality and gas exchange by actigraphy and noninvasive SpO2/PtcCO2 monitoring. Objective assessment showed that poor sleep quality was associated with nocturnal hypoxemia and pulse rate variability, whereas such an association was not confirmed for hypercapnia. These observations require further validation in larger patient groups. Sleep evaluation by PSG and delineation of respiratory support interactions could allow for additional insight. The importance of timely recognition and treatment of sleep-disordered breathing has been well acknowledged in children. Therefore, deleterious consequences of seep related breathing disturbances should become only a rare exception in pediatric and adolescent age.
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