Comment regarding “Five-year blood pressure trajectories of survivors of the tsunami following the Great East Japan Earthquake in Iwate,” by Takahashi et al. Hypertens Res 2021

Immediately after a natural or man-made disaster, the sympathetic nervous system of individuals affected by the disaster is abnormally activated; in addition, their blood pressure (BP) may rise due to this sympathetic hyperactivity and the mental and physiological stress, insomnia, lack of exercise, increased salt intake, and changes in the living environment that occur when evacuees are moved from their homes to shelters [1,2,3]. The rate of cardiovascular events has also been reported to increase immediately after disasters [1,2,3].

Few studies have reported the relationship between disasters and changes in BP values. Takahashi et al. prospectively observed BP trajectories from 2010 to 2015 in Rikuzentakata City, Iwate Prefecture, which is one of the areas that was affected by the 2011 Great East Japan Earthquake and tsunami, and they focused on areas that were heavily damaged by the tsunami that followed the earthquake [4]. The study’s BP data were drawn from the annual health checkups of the participants, who were divided into two groups: the participants whose lives were severely disrupted by the tsunami and who were forced to move away from their homes and the participants whose lives were relatively mildly disrupted by the tsunami and who did not leave their homes. The results of the data analysis demonstrated that in the entire population, the BP values tended to decrease both before and after the earthquake [4]. Table 1 summarizes the previous and current evidence regarding BP changes during disasters (i.e., earthquakes, a hurricane, and the September 11, 2001 attack). Earlier studies reported that the subjects’ BP values were elevated when measured 1–2 weeks after the disaster and that 3–6 weeks later, the BP values peaked and gradually returned to baseline (i.e., the values recorded before the disaster). Other studies that followed subjects for several years before and after a disaster have also reported that their BP values were not elevated at time points >1 year after the disaster [1, 3]. These results are similar to those of the recent Takahashi et al. study. Moreover, in the Takahashi et al. investigation, the tendency for a reduction in BP was more pronounced in the participants who obliged to move to temporary housing after the tsunami than in the participants who did not move. Takahashi et al. speculated that this finding was affected by the enormous investment of medical resources in Iwate Prefecture, especially in the areas in which the tsunami damage was severe after the earthquake.

Table 1 Evidence of blood pressure regarding disasters
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Disaster hypertension, which specifically refers to the condition of elevated BP levels (>140/90 mmHg) after a disaster, occurs immediately after a disaster and continues until both the residents’ living environment and their lifestyle habits have improved and stabilized [2, 3]. Systolic blood pressure has been reported to increase by an average of 5–25 mmHg in the 2–4 weeks after an earthquake [2, 3]. In addition, disaster hypertension is likely to persist for a long period in elderly patients; in patients with increased salt sensitivity, such as those with metabolic syndrome; and in individuals with chronic kidney disease, microalbuminuria, or obesity [1, 3, 5]. The mechanism underlying the onset of disaster hypertension includes physical and mental stress due to the disaster and changes in the living environment. Disruptions of circadian rhythms due to decreased daytime activity and sleep disorders each promote sympathetic hyperactivity and increase the levels of stress-induced hormones, such as glucocorticoids [3]. It has been reported that even some children who were exposed to psychiatric trauma showed prolonged elevations of BP during a period of several years after a disaster [6].

In the management of disaster hypertension, although no clear evidence is available regarding the target BP level during a disaster, we recommend that the primary target BP level should be an office BP level <140/90 mmHg in the acute phase of the disaster because the diagnostic criteria for disaster hypertension is a BP level ≥140/90 mmHg [2, 3]. After the improvement of an individual’s living environment after the disaster, the target BP level should be an office BP level <130/80 mmHg, based on most international guidelines.

Although medical interventions for controlling BP in the medium to long term after a disaster can be important, it is also known that the incidence of disaster-related cardiovascular diseases (CVDs) increases immediately and from several hours to several months after a disaster [1,2,3]. Figure 1 shows the time course of BP variation and the incidence of disaster-related CVDs after the occurrence of disasters. The incidences of sudden cardiac death, fatal arrhythmia, and Takotsubo cardiomyopathy have been reported to increase immediately after a disaster [2]. It was also demonstrated that the incidences of sudden cardiac death and fatal arrhythmia increased immediately after the 2011 Great East Japan Earthquake; in addition, pulmonary embolism (PE) was observed to be likely to occur several days after that disaster [7, 8].

Fig. 1: Time course of BP changes and disaster-related CVDs during disasters.
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BP blood pressure, CVD cardiovascular disease, DCAP disaster cardiovascular prevention, DVT deep venous thrombosis, ICT information communication technology, PE pulmonary embolism

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Long-term residence in a car or shelter, inadequate water intake, and postdisaster stress promote thrombus formation, potentially resulting in deep vein thrombosis (DVT) or PE. The risk factors for DVT include female sex, age >40 years, living in a car, trauma, and poor toileting conditions [1, 2, 8]. Sato et al. reported that 178 (10.6%) of 1673 individuals who were screened for DVT with a portable echo device 1 month after the 2016 Kumamoto earthquake had experienced DVT [8]. The measurement of the D-dimer level and portable echo measurements are suggested to be useful for DVT screening.

During the period from several days to several months after disasters, the incidences of myocardial infarction, stroke, and heart failure reportedly increase [1, 2, 9]. An increase in the incidence of heart failure during disasters was first reported during the Great East Japan Earthquake [9]. The causes were considered to be sympathetic hyperactivity, elevated BP, arrhythmias (including atrial fibrillation) during the disaster, medication procurement delays, excessive salt intake due to stored food consumption, exposure to cold due to difficulty in controlling room temperatures, and pneumonia, and other infectious diseases [1,2,3]. In light of these findings, disaster-related CVDs may be most common immediately or several hours to several weeks or months after disasters. Moreover, myocardial infarction, stroke, and heart failure, which are likely to be triggered by an acute elevation of BP, are thought to coincide with the timing of the elevation of BP levels after disasters [1, 3]. To achieve the goal of preventing disaster-related CVDs, it is thus important to intervene as quickly as possible after a disaster.

Immediately after the 2011 Great East Japan Earthquake, our group distributed the “Disaster Cardiovascular Prevention (DCAP) risk/prevention score” on a website to contribute to the prevention of disaster-related CVDs. Individuals with a risk score of more than four points were categorized into the high-risk group, and such high-risk patients were advised to attempt to improve their living environment and lifestyle to achieve a prevention score of greater than six points [3, 10, 11]. We recommend that medical teams use the DCAP score in evacuation facilities during a disaster [10, 11].

We also used information and communication technology (ICT) to perform BP monitoring and risk management. In cooperation with healthcare practitioners in Minamisanriku Town, which was severely damaged by the earthquake and tsunami, we introduced an ICT-based BP monitoring device at evacuation centers and shared patients’ BP values in the database to support BP management with remote monitoring [10, 11]. Consequently, we succeeded in improving the evacuees’ BP control and suppressing the seasonal variation in their BP (i.e., an increase in BP from summer to winter) during the acute to chronic phase after the disaster [11, 12]. We thus propose that ICT can be useful for anticipating the interventions needed due to BP elevation after a disaster and can contribute to the prevention of disaster-related CVDs. ICT-based devices are now available for home BP monitoring, and these devices could be used to evaluate home BP levels during disasters. By using ICT to closely manage high-risk patients, we can reduce the burden on medical institutions in disaster areas and support efficient risk management [13].

The results of the Takahashi et al. study of BP trajectories from 2010 to 2015 (which covers a period before and after the 2011 Great East Japan Earthquake) suggested that mid- to long-term medical interventions after multiple disasters in 2011 (earthquake, tsunami, and nuclear power plant disaster) may have contributed to the improvement of BP control. In addition to these mid- to long-term interventions in a disaster-affected area, early interventions that consider the timing of the onset of disaster-related CVDs could be useful to suppress the incidence of disaster-related CVDs.