**3. Results**

There were 17,114 emergency calls for EABP during the 911 days of the study: 26% of the calls were received in the morning until the early afternoon (8:00–13:59), 44.5%—in the afternoon (14:00–21:59) and 29.5%—at night (22:00–7:59); 60.2% of the patients were older than 65 years. The mean number of EACs during the whole day was 18.8, during the time period of 8:00–13:59 it was 4.9, during the period of 14:00–21:59—8.4 and during the period of 22:00–7:59—5.5 [15]. The mean daily number of EACs for elderly was 11.3 and for younger patients it was 7.5. No significant difference was observed in the distribution of NAOI categories during the colder and the warmer periods. During the colder period, more days of NAOI < −0.5 were observed in December and more days of NAOI > 0.5 in March (48.7%). During the warmer period, about 30% of days of NAOI < −1 was in June and 58.4% of days of NAOI > 0.5 during the period of April–May (Figure 1).

**Figure 1.** The monthly distribution in the categories of the NAO index during the colder period and the warmer period.

A non-linear impact of the NAOI on the risk of EACs was observed (Figure 2). During the whole day, an increase in the risk of EACs was associated both with NAOI < −0.5 on the day of the call and on two previous days and NAOI > 0.5 with a lag of 2 days (Table 1). A protective impact of the NAOI between −0.5 and 0 was seen especially on the same and on the previous day (Figure 2). A negative impact of NAOI < −1 or NAOI > 0.5 on the same day was stronger during the period of November–March (Figure 2). No any significant associations between the NAOI and daily EACs were found during the period of April–October).

**Figure 2.** *Cont.*

**Figure 2.** Rate ratios of emergency ambulance calls for elevated arterial blood pressure in the categories of the NAO index (reference category the NAO index between −0.5 and 0), adjusting for years, month, the day of the week, day length, weather and space weather variables.


**Table 1.** Significant associations between the NAO index and daily emergency calls for elevated arterial blood pressure in rate ratios (RR), adjusting for day length, month, years, the day of the week, space weather variable, weather variables and exposure to CO, PM10 and ozone.

<sup>a</sup> RR per increase 1.

No significant associations were found between the NAO index and EACs for EABP during the period of 8:00–13:59. In the afternoon-evening, a significant impact of a lower and a higher NAOI was observed only on the day of the call. The stronger impact was observed during the colder months (Figure 2, Table 1). At night until early morning, only the negative NAO (NAOI < −0.5) was associated with an increased number of EACs; the stronger impact was observed during the period of April–October (Figure 2).

For subjects, aged ≤65 years, during the period of April–October, a higher NAOI (>0.5) was associated with an increased risk of EACs. Also, a positive association between the daily NAOI and the daily EACs was found (Table 1). During the colder period, the risk of EACs was associated both with a lower and a higher NAOI (Table 1). For the elderly subjects, during the period of April–October, an increased risk of EACs was associated with a negative NAO (NAOI < −0.5). Also, the association between the NAOI and the risk of EACs tended to be negative (RR = 0.97, *p* = 0.065 on the same day) (Table 1).

For sensitivity analysis, we randomly divided the sample into five similar size parts and assessed regression coefficients *β* and its standard deviations for NAOI > 0.5 and NAOI < −0.5 with a lag of 2 days. After, we calculated the mean values of *β* and it confidence interval. For the daily number of EACs, the correspondence values for RRs (exp(*β*)) were, respectively, 1.052 (1.0005, 1.1061) and 1.068 (1.022, 1.115).
