The descriptive statistics of air pollutants, meteorological factors, hypertension, CHD, HD from November 2013 to October 2018 were shown in Table 1. During the five-year study period, 1,153,045 patients with hypertension, 180,777 patients with CHD, and 202,683 patients with HD were included in our analysis. The average daily hospital visits for hypertension, CHD, HD were 631, 98, and 110, respectively. There were more hospital visits for patients with hypertension in men than women, but the opposite is true for CHD. Hospital visits for hypertension, CHD, HD were higher in the elderly (≥ 65 years old) and blue-collar workers. The daily mean concentrations of SO2, NO2, O3, PM10, and PM2.5 were 17.50 µg/m3, 47.60 µg/m3, 55.47 µg/m3, 96.32 µg/m3, and 63.31 µg/m3, respectively. The average ambient temperature and relative humidity were 17.28℃ and 78.25% in the 1,827 days of observation during 2013–2018. The distribution of air pollutant concentrations, meteorological factors, and hospital visits for hypertension, CHD, and HD is presented in Fig. S1.
Table 1
The summary statistics of air pollutants, meteorological factors, and hospital visits for hypertension, coronary heart disease (CHD), and heart disease (HD) in Wuhan, China from November 1st, 2013 to October 31st, 2018.
Daily data
|
N
|
Mean
|
SD
|
Min
|
P25
|
Median
|
P75
|
Max
|
SO2 (µg/m3)
|
1817
|
17.50
|
16.23
|
2
|
7
|
13
|
22
|
112
|
NO2 (µg/m3)
|
1817
|
47.60
|
20.98
|
11
|
31
|
43
|
60
|
132
|
O3 (µg/m3)
|
1817
|
55.47
|
28.51
|
3
|
32
|
53
|
76
|
190
|
PM10 (µg/m3)
|
1817
|
96.32
|
56.35
|
0
|
55
|
86
|
123
|
406
|
PM2.5 (µg/m3)
|
1817
|
63.31
|
45.13
|
5
|
32
|
51
|
80
|
298
|
Ambient temperature (°C)
|
1827
|
17.28
|
8.98
|
-3
|
9.5
|
18.4
|
24.9
|
34
|
Relative humidity (%)
|
1827
|
78.25
|
9.81
|
46
|
71.2
|
78.8
|
85.9
|
99
|
Hypertension (counts/day)
|
Gender
|
Female
|
560,919
|
307.02
|
309.52
|
18
|
129
|
200
|
313
|
1624
|
Male
|
592,119
|
324.09
|
380.99
|
13
|
115
|
176
|
299
|
2004
|
Age
|
< 65
|
509,960
|
279.12
|
271.84
|
20
|
118
|
181
|
291
|
1429
|
≥ 65
|
643,081
|
351.99
|
419.56
|
13
|
124
|
199
|
325
|
2215
|
Socioeconomic factors
|
Blue-collar worker
|
592,771
|
324.45
|
325.45
|
24
|
138
|
214
|
335
|
1756
|
White-collar worker
|
206,644
|
113.11
|
115.43
|
6
|
44
|
76
|
124
|
574
|
Total
|
1153,045
|
631.11
|
689.42
|
37
|
245
|
377
|
613
|
3628
|
CHD (counts/day)
|
Gender
|
Female
|
91,622
|
50.15
|
30.88
|
6
|
29
|
44
|
59
|
199
|
Male
|
89,154
|
48.80
|
34.80
|
2
|
26
|
422
|
55
|
226
|
Age
|
<65
|
59,955
|
32.82
|
21.82
|
2
|
18
|
28
|
39
|
134
|
≥65
|
120,821
|
66.13
|
43.91
|
3
|
38
|
57
|
75
|
291
|
Socioeconomic factors
|
Blue-collar worker
|
99,918
|
54.69
|
33.62
|
5
|
31
|
48
|
65
|
231
|
White-collar worker
|
31,050
|
17
|
10.88
|
0
|
9
|
15
|
22
|
69
|
Total
|
180,777
|
98.95
|
64.74
|
8
|
56
|
86
|
111
|
425
|
HD (counts/day)
|
Gender
|
Female
|
89,883
|
49.20
|
47.47
|
1
|
18
|
33
|
58
|
280
|
Male
|
112,798
|
61.74
|
72.59
|
2
|
18
|
36
|
64
|
469
|
Age
|
<65
|
78,739
|
43.10
|
45.40
|
1
|
12
|
28
|
52
|
249
|
≥65
|
123,942
|
67.84
|
74.61
|
2
|
24
|
41
|
70
|
483
|
Socioeconomic factors
|
Blue-collar worker
|
106,540
|
58.31
|
61.87
|
2
|
20
|
36
|
66
|
450
|
White-collar worker
|
35,673
|
19.53
|
19.86
|
0
|
6
|
13
|
24
|
118
|
Total
|
202,683
|
110.94
|
119.12
|
4
|
37
|
68
|
121
|
732
|
CHD: Coronary heart disease; HD: Heart disease; SD: Standard deviation; Min: Minimum; |
Table S1 shows the Pearson’s correlation coefficients of air pollutants, ambient temperature, and relative humidity, which range from 0.007 (ambient temperature and relative humidity) to 0.740 (PM2.5 and PM10). SO2, NO2, PM10, and PM2.5 were all positively correlated with each other and were negatively correlated with ambient temperature and relative humidity. O3 was positively correlated with ambient temperature (r = 0.659), while it was negatively correlated with the remaining four air pollutants and relative humidity.
Figure 2 shows the RRs and 95% CIs of hospital visits for hypertension, CHD, and HD associated with a 10 µg/m3 increase in pollutant concentrations at lag 0, 1, 2, 3, 0–3 in the single pollutant model. The complete results regarding the single-day lag model and the cumulative day lag model were shown in Fig. S2. The effects of exposure to air pollution on hypertension, CHD, and HD have similar trends. SO2, NO2, PM10, and PM2.5 were significantly associated with daily hospital visits for CVDs. In the single-day lag model, the effects of the four air pollutants on daily hospital visits for CVDs is highest at lag 0 and then shows a downward trend. For each 10 µg/m3 increase in SO2, NO2, PM10, and PM2.5 concentrations, the RRs of daily hospital visits for hypertension increased by 3.8% (95%CI: 1.8%, 5.9%), 2.5% (95%CI: 1.9%, 3.2%), 0.5% (95%CI: 0.2%, 0.7%), and 0.7% (95%CI: 0.3%, 1.1%) at lag 0, respectively; the RRs of daily hospital visits for CHD increased by 3.6% (95%CI: 1.8%, 5.5%), 2.6% (95%CI: 1.9%, 3.4%), 0.4% (95%CI: 0.1%, 0.7%), and 0.5% (95%CI: 0.1%, 0.9%) at lag 0, respectively; the RRs of daily hospital visits for HD increased by 3.6% (95%CI: 1.4%, 5.8%), 2.1% (95%CI: 1.4%, 2.7%), 0.3% (95%CI: 0.1%, 0.6%), and 0.4% (95%CI: 0, 0.8%) at lag 0, respectively. In the multi-day lag model, the effects of SO2 and NO2 on hypertension, CHD, and HD remain significantly at lag 0–3.
The seasonal analysis shows the RRs and 95% CIs of hospital visits for hypertension, CHD, and HD associated with a 10 µg/m3 increase in pollutant concentrations at different lag days during the cold and warm seasons (Fig. 3). In both the single-day lag model and the multi-day lag model, SO2, NO2, PM10, and PM2.5 have a stronger effect on hypertension, CHD, and HD in the cold season than in the hot season. On the contrary, O3 has a stronger effect in the warm season than in the cold season.
The results of RR and 95% CIs of hospital visits for hypertension, CHD, and HD based on the single- and two-pollutant models were shown in Table 2. The results of multi-pollutant models were presented at Table S2. Considering the collinearity between pollutants, the correlation coefficient between the two pollutants has to be less than 0.7 in order to include them in the two-pollutant model, otherwise would be excluded from the analysis. The effect of PM10 and PM2.5 on CHD and HD decreased after the adjustment for SO2 in the two-pollutant model. Meanwhile, after adjusting for NO2, the effects of SO2 and PM2.5 on hypertension, CHD, and HD become statistically insignificant. In addition, NO2 can strengthen the effect of O3 on CHD and HD.
Table 2
Estimated relative risks (RRs) and 95% confidence intervals (CIs) of hospital visits for a 10 µg/m3 increase of pollutant concentrations based on the single- and two-pollutant models.
Pollutant
|
|
|
RR (95%CI)
|
|
|
|
Hypertension
|
CHD
|
HD
|
SO2
|
|
1.038 (1.018–1.059)
|
1.036 (1.018–1.055)
|
1.036 (1.014–1.058)
|
|
+NO2
|
0.989 (0.966–1.014)
|
1.002 (0.980–1.023)
|
0.991 (0.965–1.018)
|
|
+O3
|
1.038 (1.018–1.058)
|
1.036 (1.018–1.055)
|
1.035 (1.013–1.058)
|
|
+PM10
|
1.027 (1.005–1.049)
|
1.030 (1.010–1.051)
|
1.028 (1.004–1.053)
|
|
+PM2.5
|
1.030 (1.009–1.052)
|
1.033 (1.014–1.052)
|
1.032 (1.009–1.055)
|
NO2
|
|
1.025 (1.019–1.032)
|
1.026 (1.019–1.034)
|
1.021 (1.014–1.027)
|
|
+ SO2
|
1.027 (1.019–1.036)
|
1.026 (1.017–1.035)
|
1.023 (1.014–1.031)
|
|
+O3
|
1.025 (1.019–1.032)
|
1.026 (1.019–1.034)
|
1.021 (1.014–1.028)
|
|
+PM2.5
|
1.026 (1.018–1.033)
|
1.028 (1.019–1.037)
|
1.023 (1.015–1.030)
|
O3
|
|
1.028 (0.982–1.077)
|
1.051 (0.993–1.112)
|
1.040 (0.994–1.089)
|
|
+ SO2
|
1.028 (0.981–1.076)
|
1.050 (0.993–1.112)
|
1.040 (0.993–1.088)
|
|
+NO2
|
1.038 (0.991–1.086)
|
1.059 (1.001–1.121)
|
1.048 (1.001–1.096)
|
|
+PM10
|
1.025 (0.979–1.074)
|
1.048 (0.990–1.109)
|
1.038 (0.991–1.087)
|
|
+PM2.5
|
1.027 (0.981–1.075)
|
1.050 (0.992–1.111)
|
1.039 (0.992–1.088)
|
PM10
|
|
1.005 (1.002–1.007)
|
1.004 (1.001–1.007)
|
1.003 (1.001–1.006)
|
|
+SO2
|
1.003 (1.000-1.006)
|
1.002 (0.999–1.005)
|
1.002 (0.999–1.005)
|
|
+O3
|
1.005 (1.002–1.007)
|
1.004 (1.001–1.007)
|
1.003 (1.001–1.006)
|
PM2.5
|
|
1.007 (1.003–1.011)
|
1.005 (1.001–1.009)
|
1.004 (1.000-1.008)
|
|
+SO2
|
1.005 (1.001–1.009)
|
1.002 (0.998–1.007)
|
1.002 (0.998–1.007)
|
|
+NO2
|
1.000 (0.995–1.004)
|
0.998 (0.994–1.003)
|
0.998 (0.993–1.002)
|
|
+O3
|
1.007 (1.003–1.011)
|
1.005 (1.001–1.009)
|
1.004 (1.000-1.008)
|
Table 3 shows the results of the stratified analysis by gender (male and female), age (<65 and ≥ 65 years old), and socioeconomic status (blue-collar worker and white-collar worker) at lag 0. We have not observed considerable differences in the effects of air pollution on CVDs in terms of age, gender, and socioeconomic status. All results regarding the stratified analysis are presented in Fig. S3 (gender), Fig. S4 (age), and Fig. S5 (socioeconomic status). Since the number of CVDs in late 2017 to the most of 2018 was significantly higher than the previous year (see Fig. S1), we compared the differences in the effects of air pollution on CVD in the months when the number of visits was high and the effects in the previous year (the months when the number of visits was low). The results show that similar trends were observed in both periods (Fig. S6).
Table 3. Estimated relative risks (RRs) and 95% confidence intervals (CIs) of hospital visits for a 10 μg/m3 increase of pollutant concentrations by gender, age, and socioeconomic factors among patients had hypertension, coronary heart disease (CHD), and heart disease (HD).
Variables
|
Gender
|
Age
|
Socioeconomic factors
|
Female
|
Male
|
<65
|
≥65
|
Blue-collar worker
|
White-collar worker
|
Hypertension
|
|
|
|
|
|
|
SO2
|
1.044 (1.024-1.064)
|
1.032 (1.011-1.054)
|
1.036 (1.018-1.055)
|
1.040 (1.017-1.063)
|
1.036 (1.015-1.057)
|
1.028 (1.004-1.052)
|
NO2
|
1.027 (1.021-1.034)
|
1.023 (1.017-1.030)
|
1.023 (1.017-1.029)
|
1.027 (1.020-1.034)
|
1.026 (1.019-1.033)
|
1.026 (1.018-1.034)
|
O3
|
1.025 (0.977-1.075)
|
1.031 (0.984-1.081)
|
1.021 (0.977-1.066)
|
1.033 (0.982-1.087)
|
1.048 (0.996-1.103)
|
1.057 (0.999-1.119)
|
PM10
|
1.005 (1.003-1.008)
|
1.004 (1.002-1.007)
|
1.004 (1.002-1.006)
|
1.005 (1.002-1.008)
|
1.005 (1.002-1.007)
|
1.005 (1.002-1.008)
|
PM2.5
|
1.008 (1.004-1.012)
|
1.006 (1.002-1.011)
|
1.006 (1.003-1.010)
|
1.008 (1.003-1.012)
|
1.007 (1.003-1.011)
|
1.006 (1.002-1.011)
|
CHD
|
|
|
|
|
|
|
SO2
|
1.043 (1.024-1.062)
|
1.029 (1.009-1.049)
|
1.042 (1.021-1.063)
|
1.034 (1.015-1.053)
|
1.036 (1.017-1.056)
|
1.022 (0.997-1.048)
|
NO2
|
1.027 (1.018-1.035)
|
1.026 (1.018-1.035)
|
1.023 (1.014-1.032)
|
1.028 (1.020-1.036)
|
1.026 (1.018-1.035)
|
1.022 (1.011-1.033)
|
O3
|
1.046 (0.985-1.111)
|
1.056 (0.992-1.124)
|
1.077 (1.009-1.149)
|
1.038 (0.978-1.103)
|
1.051 (0.985-1.121)
|
1.059 (0.975-1.149)
|
PM10
|
1.004 (1.001-1.007)
|
1.004 (1.001-1.007)
|
1.003 (0.999-1.006)
|
1.005 (1.002-1.008)
|
1.004 (1.001-1.008)
|
1.003 (0.999-1.008)
|
PM2.5
|
1.005 (1.000-1.009)
|
1.005 (1.000-1.009)
|
1.003 (0.998-1.008)
|
1.006 (1.001-1.010)
|
1.005 (1.000-1.009)
|
1.005 (0.999-1.010)
|
HD
|
|
|
|
|
|
|
SO2
|
1.049 (1.025-1.074)
|
1.024 (0.999-1.049)
|
1.013 (0.998-1.040)
|
1.048 (1.025-1.072)
|
1.039 (1.015-1.065)
|
1.042 (1.010-1.074)
|
NO2
|
1.023 (1.016-1.031)
|
1.019 (1.012-1.026)
|
1.016 (1.008-1.023)
|
1.024 (1.017-1.031)
|
1.024 (1.016-1.031)
|
1.021 (1.011-1.030)
|
O3
|
1.034 (0.982-1.089)
|
1.046 (0.994-1.101)
|
1.047 (0.992-1.104)
|
1.036 (0.986-1.090)
|
1.051 (0.997-1.108)
|
1.078 (1.008-1.153)
|
PM10
|
1.005 (1.002-1.007)
|
1.002 (1.000-1.005)
|
1.002 (0.999-1.005)
|
1.004 (1.002-1.007)
|
1.004 (1.002-1.007)
|
1.003 (0.999-1.007)
|
PM2.5
|
1.005 (1.000-1.009)
|
1.004 (0.999-1.009)
|
1.003 (0.998-1.008)
|
1.005 (1.000-1.009)
|
1.006 (1.001-1.010)
|
1.007 (1.001-1.013)
|