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The effect of mountaineering on the association between blood pressure and physical activity: A new multi‐sensor ambulatory blood‐pressure monitoring device. The Mount Fuji Study

Abstract It has not been fully investigated whether the response of blood pressure (BP) to activity at high altitudes differs from that at low altitudes or how temperature is involved in these differences. The author compared BP response to accelerometer measurements during mountaineering and daily living. In 15 healthy people (mean age 33 ± 6 years), a new multi‐sensor ambulatory BP monitoring (ABPM) device equipped with barometer, thermometer, and accelerometer was used to measure BP responses to activity during a trip to Mt. Fuji and during daily living. Associations between physical activity (log‐transformed 5‐min average values of accelerometer just before each ambulatory BP) and the corresponding BP were obtained from 843 and 676 readings during the Mt. Fuji trip and daily living, respectively. All ambulatory systolic BP (SBP) parameters were significantly higher during the Mt. Fuji trip than during daily living (all p < .01). There were significant positive correlations between physical activity and corresponding BPs in both mountaineering and daily living (all p < .01), and there was an interaction between BPs and physical activity according to the two conditions (p < .01). On Mt. Fuji, multivariate regression analysis showed increased physical activity and lower temperature were associated with increased 24‐h SBP and diastolic BP (DBP) (all p < .05). The goodness‐of‐fit values of the association between activity and 24‐h SBP or DBP were improved by adding temperature to the model of both 24‐h SBP and DBP. However, these associations were not found in the daily living model. BP response to activity was more pronounced during mountaineering than daily living.


INTRODUCTION
Exercise is one of the non-pharmacological therapeutics for patients with cardiovascular diseases, hypertension, diabetes, and hyperlipidemia. 1,2 Aerobic exercise is recommended for all patients with cardiovascular disease. Although mountaineering is an aerobic exercise that can be performed at high altitude, there is limited evidence about its safety for patients with cardiovascular disease. 3 At high altitudes, both the temperature and barometric pressure are lower. These environmental changes contribute to an excessive blood pressure (BP) response to exercise. 4,5 As a result, the response of BP to exertion at high altitudes may differ from that during daily living at low altitudes, but these associations have not been fully investigated.
Physical activity is one of the important determinants of BP.
Ambulatory blood pressure monitoring (ABPM) is the only kind of BP measurement that can measure the response of BP to activity in daily life. However, there have been few devices that can simultaneously assess physical activity and BP in daily life, and research in this field has not progressed. We recently developed a multi-sensor ABPM system equipped with an accelerometer, a thermometer, and a barometer. 6 With the new capacity of this device to measure BP and physical activity simultaneously, we have proposed a new term to describe reactivity to physical activity: "actisensitivity". 7 We hypothesized the BP actisensitivity during mountaineering would be increased compared to that in daily living, and we conducted a comparison study using this novel ABPM device to measure BP and activity simultaneously during mountaineering and daily living.

METHODS
The present study was conducted in August of 2017-2019. We

Measurement by multi-sensor ABPM
Study participants wore the multi-sensor ABPM device (TM-2441; A&D, Tokyo, Japan), which has a barometer, a thermometer, and an accelerometer. BP (by the oscillometric method) and pulse rate (PR) were recorded every 30 min. The temperature and barometric pressure at the time of BP measurement were recorded. This device was validated previously. 6 During the Mt. Fuji trip, ABPM was worn continuously for 28 h (Figure 1), including the sleeping period at the Mt.
Fuji research station. Acute mountain sickness (AMS) score was also measured during mountaineering. 8 Concerning ABPM measurement during daily living, participants were instructed to follow their normal daily routine. The participants were doctors and office workers, and the altitudes of their workplaces were within 50-110 m above sea level.
Sleep BP was defined as the average of BP measurements during the time the participant was in bed, and awake BP was defined as the average of BP measurements recorded during the rest of the day.

RESULTS
Study participants, comprising 12 males and 3 females, had a mean age of 33 ± 6 years. Table 1 shows a comparison of BPs, activities, and some environmental data between mountaineering and daily living. SBP and PR in 24-h, awake, and sleep conditions were significantly higher on the mountaineering than those in daily living at low altitudes. Total activity was significantly higher in the mountains than at low altitudes. Mean temperature and mean barometric pressure were significantly lower in the mountains than in low altitudes. AMS defined by AMS score >3 was observed in 67% of study participants during their time in the mountains.
A total of 843 readings of BP and activity values during the mountaineering and 676 readings during daily living were obtained, and the association between BP and activity was investigated. We performed univariate analysis to investigate the factors affecting BP ( Abbreviations: AMS, acute mountain sickness; DBP, diastolic blood pressure; SBP, systolic blood pressure.

DISCUSSION
To our knowledge, this is the first study to show that the condition of activity, that is, mountaineering versus daily living, provided different interactions for the association between BP and activity level assessed by multi-sensor ABPM. Adding the measurements of temperature improved the goodness-of-fit of the association between SBP and activity in the high-altitude data.
The present study showed that both during mountaineering and during low-altitude daily living, activity was associated with BP, but the situation of the activity interacted with the relationship between BP and activity level. Simply put, the rate of increase in BP per the same amount of activity was higher during mountaineering than in daily living. Overall, the amount of activity during mountaineering was greater than that of daily living. Thus, it can be expected that average ambulatory BP levels would be higher during mountaineering than dur-TA B L E 4 Change in the goodness-of-fit of the linear relationship between blood pressure and activity induced by adding temperature and barometric pressure

CONCLUSIONS
The actisensitivity of BP during mountaineering was greater than that of daily living. Temperature was a factor more significantly associated with BP than barometric pressure and compounded the association between activity and BP increase during mountaineering. When people climb mountains, it is important to pay attention to temperature drop to prevent excessive BP variation.