3 RESULTS
3.1 Clinical characteristics
During the study period, 115 patients were screened, and 109 patients were enrolled, excluding 4 patients who had been using noninvasive ventilators and 2 patients treated with nusinersen. The age of the 109 patients were 4.2 (2.1, 7.6) years, ranged (0.2-15.8) years. Fifty-two patients were males. Twenty-three cases were type 1, 74 cases were type 2, and 12 cases were type 3. Thirty-four cases (31.2%) had RRTIs, 20 cases (18.3%) had ARF within one year, and 31 cases (28.4%) used MI-E regularly. The general characteristics, survival motor neuron 2 (SMN2) copies, MI-E usage, main parameters of PSG and lung function of different types of SMA are shown in Table 1.
3.2 Differences in sex, age, type, BMI and MI-E between the two groups
According to the group criteria, 109 patients were divided into the disease group with 39 cases and the control group with 70 cases. The proportion of type 1 was higher and the BMIz was lower in the disease group than in the control group (P < 0.05). There was no significant difference in sex, age or MI-E usage between the two groups. (Table 2)
3.3 Differences in lung function between the two groups
Spirometry was performed in 21 of the 39 patients in the disease group and 57 of the 70 patients in the control group. The percent predicted scores representing restrictive ventilation dysfunction, including forced vital capacity (FVC), inspiratory vital capacity (VC IN), expiratory vital capacity (VC EX), forced expiratory volume in one second (FEV1), peak expiratory flow (PEF), maximum expiratory flow at 75% vital capacity (MEF75), maximum expiratory flow at 50% vital capacity (MEF50) and maximum midexpiratory flow at 25% to 75% vital capacity (MMEF75/25) in the disease group were all lower than those in the control group (P < 0.05). There was no significant difference in the FEV1 to FVC ratio % predicted to represent obstructive ventilation dysfunction between the two groups (Table 2).
3.4 Differences in PSG between the two groups
End-tidal carbon dioxide (EtCO2) was measured in 9 patients in the disease group and 18 patients in the control group while PSG was performed. Nonrapid eye movement stage 2 (N2) was higher and N3 was lower in the disease group. In addition, the respiratory arousal index, AHI, ≥ 3% oxygen desaturation events and index were higher, and the average oxygen desaturation, MSpO2 and LSpO2 were lower (P < 0.05). Hypopnea was the main respiratory event in children with SMA. The events, index, mean time and longest time of hypopnea in the disease group were all higher than those in the control group (P < 0.05). There was no significant difference in apnea events between the two groups (Table 3).
3.5 Logistic regression analysis of risk factors for RRTIs and/or ARF in children with SMA
Type 1, BMI, AHI and MSpO2 with statistically significant differences between the two groups were entered as covariates into binary logistic regression, and all had statistical significance (P < 0.05), as shown in Table 4. The risk for the occurrence of RRTIs and/or ARF in SMA type 1 was approximately four times higher than that in types 2 and 3. Meanwhile, the risks were approximately 1.5, 1.1 and 1.5 times higher for every 1 decrease in BMIz, 1 events/h increase in AHI and 1% decrease in MSpO2, respectively.
3.6 ROC curve analysis of BMIz, AHI and MSpO2
ROC curves were drawn to analyze the prediction efficiency of BMI, AHI and MSpO2 for RRTIs and/or ARF. The best cutoff points of these three continuous variables were obtained by taking the maximum Jordan index, and the sensitivity and specificity are shown in Figure 1 and Table 5. The diagnostic value of MSpO2 was the best, with the highest area under the receiver operating characteristic curve (AUC). The sensitivity, specificity and accuracy of MSpO2 < 95.5% with the occurrence of RRTIs and/or ARF were 0.539, 0.886, and 0.761, respectively. To improve the specificity and accuracy, the indicators were used in combination. With the standard of MSpO2 < 96% and AHI > 10 events/h or BMI < -1, the specificity and accuracy were increased to 0.957 and 0.798, respectively, and the sensitivity was 0.513.