Basic situation of the survey subjects
Totally 218 and 510 participants were involved in the survey in 2019 and 2009, respectively. The average elevation was about 4200 m, and there was no significant difference between the two years. The subjects in 2019 lived longer on the plateau than those in 2009. The BP and HR of subjects in 2019 were significantly lower than those in 2009. There was no significant difference in Hb concentration between the two years, but the SO2 in 2019 subjects was significantly lower than those in 2009. (Table 1)
Prevalence of CMS
According to the Qinghai standard, among the 218 survey subjects in 2019, 184 of them (84.40%) had no CMS, 29 of them (13.30%) had mild CMS, 4 of them (1.83%) had moderate CMS, and only 1 of them (0.46%) had severe CMS, the total CMS prevalence rate was 15.60%. Among the 510 survey subjects in 2009, 351 of them (68.82%) had no CMS, 144 of them (28.24%) had mild CMS, 12 of them (2.35%) had moderate CMS and 3 of them (0.59%) had severe CMS, the total prevalence of CMS was 31.18% (See Additional file 1 for details). χ2 test analysis showed that the prevalence of CMS in 2019 was significantly lower than that in 2009 (χ2 = 19.028, P = 0.000).
The prevalence of symptoms
Among the survey subjects in 2019, 93 of them (42.66%) had dyspnea/palpitation, 87 of them (39.91%) had sleep disturbance, and 70 of them (32.11%) had headaches, the prevalence of the above three symptoms ranked in the top three among all the subjects surveyed. The prevalence of venous dilatation was the lowest, which was only 25 people (11.47%). 26 peoples’ (11.93%) Hb concentration reached 21g/dL or higher. Among the CMS patients (CMS ≥ 6), dyspnea/palpitation, sleep disturbance, and headache are still the main symptoms, but the prevalence of sleep disturbance became the highest. 32 out of 34 CMS patients (94.12%) had sleep disturbance problem in various degrees. And in these 32 people, 18 people suffered from the moderate or severe sleep disturbance, which became the severest symptom. 11 of the CMS patients had Hb concentration of 21g/dL or higher, accounting for 32.35%. (See Additional file 1 for details)
In 2009, dyspnea/palpitation (51.37%), cyanosis (48.63%) and sleep disturbance (47.45%) were the top three symptoms in prevalence, of which the number was 262, 248 and 242, respectively. The amount of people who suffered from headaches was 241 (47.25%), the prevalence of which was just 0.2% less than sleep disturbance. The number of people whose Hb concentration reached 21g/dL or higher was 121 (23.73%). Among the 159 CMS patients, sleep disturbance (84.91%), headache (83.02%) and cyanosis (82.39%) became the top three symptoms in prevalence, and the number of which was 135, 132 and 131, respectively. 43 people had Hb concentration of 21g/dL or higher, accounting for 27.04% of the number of CMS patients. (See Additional file 1 for details)
Symptom score comparison
Statistical analysis showed that the CMS score of the survey subjects in 2019 was significantly lower than that in 2009 (Table 1). For all subjects in the survey, there was no difference in the prevalence of sleep disturbance, but there was significant difference in the prevalence of dyspnea, cyanosis, venous dilatation, paresthesia, headache, and tinnitus. The ratio of Hb concentration 21g/dL or higher was lower in 2019 (See Additional file 1 for details). In addition, there was significant difference in the score of cyanosis (p=0.000), venous dilatation (p=0.006), paresthesia (p=0.000), and headache (p=0.000) between the two batches of data, and the scores of which were significantly lower in 2019 than that in 2009 (Figure 1 A-D), while no significant difference was found in the scores of dyspnea/palpitation, sleep disturbance and tinnitus (Figure 1 E-G).
Further analysis of the symptom scores of the CMS patients revealed that there was no significant difference in the prevalence of all symptoms between the two years. In terms of symptom scores, compared to the year 2009, the score of sleep disturbance (p=0.015) among the CMS patients surveyed in 2019 were significantly increased (Figure 1 H), while the score of cyanosis (p=0.016) were significantly decreased (Figure 1 I).
Correlations between Hb concentration and SO2
Analysis revealed that SO2 significant related with Hb concentration. Quadratic curve was identified to be the best fitting curve for the merged Hb and SO2 results from 2019 and 2009 survey (Table 2). Separate analysis of the Hb-SO2 correlation in 2019 (R2=0.057, p=0.002, other fitting parameters see additional file 2) or 2009 (R2=0.017, p=0.029, other fitting parameters see additional file 3) were also revealed that quadratic fitting was the best fitting method. (Figure 2)
Table 2 Parameters evaluation of Hb-SO2 correlation analysis
|
R square
|
F
|
Significance
|
Constant
|
b1
|
b2
|
b3
|
Linear
|
0.019
|
12.230
|
0.001
|
93.782
|
-0.215
|
|
|
Logarithmic
|
0.017
|
10.702
|
0.001
|
101.228
|
-3.924
|
|
|
Inverse
|
0.014
|
9.227
|
0.002
|
85.980
|
69.900
|
|
|
Quadratic
|
0.033
|
10.662
|
0.000
|
69.648
|
2.255
|
-0.063
|
|
Cubic*
|
0.033
|
10.755
|
0.000
|
84.399
|
0.000
|
0.051
|
-0.002
|
Compound
|
0.019
|
12.179
|
0.001
|
93.891
|
0.998
|
|
|
Power
|
0.017
|
10.656
|
0.001
|
102.127
|
-0.044
|
|
|
S
|
0.014
|
9.189
|
0.003
|
4.454
|
0.789
|
|
|
Growth
|
0.019
|
12.179
|
0.001
|
4.542
|
-0.002
|
|
|
Exponential
|
0.019
|
12.179
|
0.001
|
93.891
|
-0.002
|
|
|
Logistic
|
0.019
|
12.179
|
0.001
|
0.011
|
1.002
|
|
|
*The cubic model is not applicable due to the approximately liner coincidence