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Effects of altitude in high-rise building on the autonomic nervous modulation in healthy subjects
Autonomic Neuroscience: Basic and Clinical 161 (2011) 126–131
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Autonomic Neuroscience: Basic and Clinical j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / a u t n e u
Effects of altitude in high-rise building on the autonomic nervous modulation in healthy subjects Pao-Chen Lin a,1, Wei-Lung Chen b,c,1, Wei-Fong Kao d, Yi-Hsuan Yang a, Cheng-Deng Kuo a,⁎ a
Laboratory of Biophysics, Department of Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan Department of Emergency Medicine, Cathay General Hospital, Taipei, Taiwan School of Medicine, Fu Jen Catholic University, Taipei, Taiwan d Department of Emergency Medicine, Taipei Veterans General Hospital, Taipei, Taiwan b c
a r t i c l e
i n f o
Article history: Received 18 August 2010 Received in revised form 11 December 2010 Accepted 29 December 2010 Keywords: Altitude Heart rate variability Autonomic nervous modulation Vagal activity
a b s t r a c t This study intended to study the effects of altitude in the high-rise building on the automatic nervous modulation in healthy subjects. Heart rate variability (HRV) analysis was performed to assess the automatic nervous modulation of the subjects at three different altitudes in the air-conditioned high-rise building, i.e., the first basement (4 m beneath sea level), the 31st floor (133 m above sea level), and the 46th floor (200 m above sea level). We found that the heart rate was significantly decreased, whereas the standard deviation of RR intervals (SDRR), total power and high frequency power were significantly increased when the subject was elevated to a higher altitude. The normalized low frequency power and low-/high-frequency power ratio on the 31st and 46th floors were significantly different between genders; however, no such difference was found on the first basement. The age correlated significantly and positively with the percentage change in the SDRR and coefficient of variation of RR intervals when the subjects were elevated from the first basement to the 46th floor. In conclusion, higher altitude in an air-conditioned high-rise building can lead to an increase in HRV/vagal modulation. The stay at a higher altitude in a high-rise building may lead to increased overall HRV and vagal modulation of a subject, especially for the elder people and the people who had a small HRV at ground level. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Because of increasing population density in the cities, more and more high-rise buildings are being built to accommodate the increasing number of people living and working in the cities nowadays. Some studies have investigated the illness caused by the environmental condition in the buildings, such as the air, temperature, humidity, and pollution in the environment (Bachmann and Myers, 1995; Niven et al., 2000; Park et al., 2004; Woods, 1991). The frequently reported illness in the buildings is the sick building syndrome which is most probably caused by indoor air problem (Reijula and Sundman-Digert, 2004; Salem and Bartsch, 2001). Sharshenova et al. (2006) found in apparently healthy children residents of moderate altitudes that increase in altitude levels is accompanied by higher overall variability and parasympathetic modulation of the sinus node and lower sympathetic response to posture, and that the heart rate variability in children residents of moderate altitudes is also dependent on gender, resembling similar
⁎ Corresponding author. Tel.: + 886 2 28757745; fax: + 886 2 28710773. E-mail address: [email protected] (C.-D. Kuo). 1 The first two authors contribute equally. 1566-0702/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.autneu.2010.12.005
relationship in inhabitants of sea level. Thus, altitude probably is one of the most important factors associated with the health status of the subjects in a high-rise building, yet not many studies have investigated the effects of altitude within the high-rise buildings on the physiology of the people in those buildings. Heart rate variability (HRV) analysis is a noninvasive monitoring method frequently used to assess the autonomic nervous modulation of the subject (Task force, 1996). It has been employed to evaluate the changes in autonomic nervous modulation in humans on high mountains (Bernardi et al., 1998; Farinelli et al., 1994; Kanai et al., 2001; Lanfranchi et al., 2005; Perini et al., 1996). However, the knowledge obtained on the high mountains may not be directly applicable to the high-rise buildings because the temperature, humidity and oxygen concentration on the mountain as well as the physical efforts exhausted to reach the high altitude are different from those in the high-rise buildings. Since more and more people live or work in high-rise buildings, it is worthwhile to investigate the effect of altitude on the autonomic nervous modulation of the subjects in the high-rise buildings by using HRV analysis. Thus, the aim of this study was to compare the effects of different altitudes in the high-rise buildings on the autonomic nervous modulation of the subjects.
P.-C. Lin et al. / Autonomic Neuroscience: Basic and Clinical 161 (2011) 126–131
2. Methods 2.1. Participants The subjects included in this study were healthy volunteers recruited from the community who have no cardiopulmonary or other major diseases that may influence HRV, such as diabetes mellitus, hypertension, or autonomic neuropathy. 2.2. Study protocol The high-rise building chosen in this study was the Shin Kong Life Tower that has been the tallest building in Taiwan from 1993 to 1997, and is the third highest building in Taiwan now. The height of the Shin Kong Life Tower is 245 m above sea level, and the number of floors is 51. Three floors in this building were chosen for study, i.e., the first basement (B1F, 4 m beneath sea level), the 31st floor (31F, 133 m above sea level), and the 46th floor (46F, 200 m above sea level). The B1F and 46F were chosen because there were the lowest and the highest floor levels in the high-rise building, respectively. Between these two floors, the intermediate 31F was chosen because it was the most convenient floor to the visitors that could be used for study. To investigate if there was any dose–response effect of altitude on HRV measures, three kinds of altitude change were defined: (1) short-distance altitude change (from 31F to 46F, an ascent of 15 F or 67 m); (2) mid-distance altitude change (From B1F to 31F, an ascent of 31 F or 137 m); and (3) longdistance altitude change (from B1F to 46F, an ascent of 46 F or 204 m). The recording of ECG signals was performed in a quiet, air-conditioned room with constant temperature and suitable humidity on each floor. The Institutional Review Board of the hospital has approved this research. Informed written consent was obtained from each subject before the study. All participants were asked not to have any drink that may influence HRV, such as coffee, alcohol, or tea 24 h before the study. All subjects reached 31F and 46F by the elevator to avoid unnecessary confounding factors to this study, such as physical exertion, oxygen consumption, profuse sweating. 2.3. Equipments and measurements On arrival at each floor, the subjects were requested to take a rest for at least 10 min on the chair. After that, preliminary physical check-up, including measurement of forehead temperature and blood pressures, was done on each subject. A trend of electrocardiographic (ECG) signals was picked up by a physiological signal acquisition apparatus (Biopac MP35, Biopac Systems, Inc., USA) and transmitted to a notebook computer for recording. The ECG signals were recorded for 12 min with a sampling frequency of 500 Hz. The subjects were asked to sit on the chair and close their eyes during the recording period. The ambient temperature and relative humidity were measured by a portable temperature humidity indicator (HygroPalm 0, Rotronic Ag, Switzerland) at the same time. 2.4. HRV analysis The recorded ECG signals were retrieved afterwards to detect the consecutive RR intervals by using the software developed on Matlab 6.5 (The MathWorks Inc., Natick, MA). The last 512 stationary RR intervals were picked up for HRV analysis. The time domain HRV measures used were the heart rate (HR), and standard deviation (SDRR) and coefficient of variation (CVRR) of RR intervals. The frequency domain HRV measures were obtained by transforming the RR intervals into power spectrum using Fast Fourier transformation. The area under spectral peaks in the HRV spectrum within the range of 0.01–0.04, 0.04–0.15, 0.15–0.4, and 0.01–0.4 Hz was defined as the very low-frequency power (VLFP), lowfrequency power (LFP), high frequency power (HFP), and total power (TP), respectively. The normalized LFP (nLFP = LFP/TP) was used as the index of combined vagal and sympathetic modulations, the normalized
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HFP (nHFP = HFP/TP) as the index of vagal modulation, the low-/highfrequency power ratio (LFP/HFP) as the index of sympathovagal balance (Saul et al., 1988), and the normalized very low-frequency power (nVLFP = VLFP/TP) as the index of renin-angiotensin-aldosterone system and vagal withdrawal of the subject (Taylor et al., 1998). 2.5. Data analysis The values are presented as median (25th to 75th interquartile range) because nearly all the parameters are not normally distributed. Friedman repeated-measures analysis of variance on ranks with Student–Newman–Keuls test for post hoc comparisons was employed to compare the clinical data and HRV measures among three different altitudes, and the percentage change in HRV measures among three kinds of altitude change. The Mann–Whitney rank sum test was used to compare the HRV measures between different genders. The percentage changes in HRV measures between different altitudes which were calculated by using the following formulae: Short−distance ascent = %X31F−46F = 100%⋅ðX46F −X31F Þ = X31F Mid−distance ascent = %XB1F−31F = 100%⋅ðX31F −XB1F Þ = XB1F Long−distance ascent = %XB1F−46F = 100%⋅ðX46F −XB1F Þ = XB1F ; where ‘X’ stands for the HRV measure to be analyzed. Spearman rank order correlation and linear regression analysis were used to evaluate the relationship between subjects' basic characteristics as well as environmental factors and the percentage change in HRV measures. All statistical tests were performed using SigmaStat version 3.0 statistical software (SPSS Inc., Chicago, IL, USA). A p b 0.05 was considered statistically significant. 3. Results 3.1. General characteristics of participants Thirty-five normal subjects (M/F = 10/25, aged 21–65 years old) were included in this study. All measured data are presented as median and inter-quartile range (25th to 75th percentiles). Table 1 shows the general characteristics of the participants. All parameters measured on B1F, 31F and 4F were within normal ranges. However, the forehead temperature measured on 46F was significantly increased, as compared to that on B1F and 31F. 3.2. HRV at different altitudes Table 2 compares the HRV measures of the study subjects at different floors. In the time domain, the HR on 31F and 46F was significantly lower than that on B1F (p b 0.001). In contrast, the SDRR on 31F and 46F was significantly increased, as compared to that on B1F. (p = 0.008). In the frequency domain, the TP and HFP on 31 F and 46 F were also significantly increased, as compared to those on B1F (p = 0.003 for TP and p b 0.001 for HFP, respectively). 3.3. Percentage change in HRV measures between different altitudes The percentage decrease in HR, and the percentage increase in TP and HFP caused by mid-distance (from B1F to 31F) and long-distance (from B1F to 46F) ascent were significantly larger than those caused by a short-distance ascent (from 31F to 46F). The information obtained from comparing the percentage changes in HRV measures due to the change in altitude are similar to those presented in Table 2, hence the data of the percentage changes in HRV measures due to the change in altitude are not shown here.
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Table 1 General characteristics of the subjects (n = 35).
Gender (M/F) Age (year) Height (cm) Weight (kg) BMI SBP (mmHg) DBP (mmHg) PP (mmHg) Forehead temperature (oC)
B1F
31F
46F
P
10/25 33.0 (25.0–49.8) 163.0 (157.3–170.8) 57.0 (51.0–62.3) 21.1 (19.9–22.9) 111 (99–128) 71 (63–76) 42 (36–45) 36.4 (36.1–36.6)
113 (104–123) 72 (66–78) 41 (33–49) 36.3 (36.1–36.4)
110 (100–121) 72 (65–80) 40 (34–44) 36.5 (36.1–36.7)†
0.221 0.678 0.627 0.015
Values are expressed as medians (IQR, 25–75%). Friedman repeated-measures analysis of variance on ranks with Student–Newman–Keuls test for pairwise comparisons (post hoc). BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; PP, pulse pressure. † p b 0.05 vs. 31F.
3.4. Correlations between age and percentage change in HRV measures Linear regression analysis showed that both SDRR and CVRR at B1F correlate negatively with age (Fig. 1 A and B). That is, both SDRR and CVRR at B1F decreased with increasing age. This result suggested that older subjects had smaller SDRR and CVRR at the ground level. Linear regression analysis also showed that the percentage changes in SDRR and CVRR when the subjects moved from B1F to 46F correlated positively with the age of the subjects (Fig. 1C and D). That is, the %SDRR 31F–46F and %CVRR 31F–46F increased with increasing age. This result suggested that the older the subject was, the larger the increase in SDRR and CVRR the subject had when the subject moved from B1F to 46F. Further analysis showed that %SDRR_B1F-46F correlated negatively with SDRR_B1F, and that %CVRR_B1F-46F correlated negatively with CVRR_B1F (Fig. 1E and F). This result indicated that the subject who had a smaller SDRR and CVRR at B1F had a larger increase in SDRR and CVRR when the subject moved from B1F to 46F. 3.5. Gender-related differences Table 3 shows that there was no significant difference in HRV measures between different genders on B1F. However, on 31F and 46F, both nLFP and LFP/HFP of male subjects were significantly higher than those of female subjects. 3.6. Environmental effects Table 4 shows the environmental conditions on the three floors. The ambient temperature and relative humidity on those three floors were significantly different (p b 0.001). Table 2 HRV measures of the subjects at different altitudes.
Heart rate (bpm) SDRR (ms) CVRR (%) TP (ms2) VLFP (ms2) LFP (ms2) HFP (ms2) nVLF (nu) nLFP (nu) nHFP (nu) LFP/HFP
B1F
31F
46F
P
78 (71–86) 35 (31–53) 5.2 (3.8–6.6) 523 (352–806) 196 (121–308) 158 (87–275) 151 (63–261) 37.7 (28.3–54.1) 26.2 (19.6–35.4) 24.4 (16.2–43.3) 0.8 (0.5–2.2)
72 (66–80)⁎ 43 (34–55)⁎ 5.5 (4.3–6.5) 807 (416–1212)⁎
71 (66–78)⁎ 46 (32–58)⁎ 5.4 (4.3–6.8) 855 (362–1124)⁎
222 (159–381) 249 (108–365) 217 (98–466)⁎ 32.4 (23.7–42.3) 29.9 (17.5–39.2) 34.0 (20.7–41.7) 1.0 (0.5–1.5)
217 (122–407) 211 (102–340) 231 (99–465)⁎ 35.5 (24.5–48.3) 26.4 (20.5–38.7) 31.4 (20.5–45.3) 1.1 (0.6–1.8)
b 0.001 0.008 0.347 0.003 0.247 0.074 b 0.001 0.581 0.449 0.449 0.293
Values are expressed as medians (IQR, 25–75%). Friedman repeated measures analysis of variance on ranks with Student–Newman–Keuls tests for post hoc comparisons between floors. bpm, beats per minute; nu, normalized unit; SDRR, standard deviation of RR intervals; CVRR, coefficient of variation of RR intervals; TP, total power; VLFP, very low frequency power; LFP, low frequency power; HFP, high frequency power; nVLFP, normalized VLFP; nLFP, normalized LFP; LFP/HFP, low-/high-frequency power ratio. ⁎ p b 0.05 vs. B1F.
The percent change in ambient temperature correlated significantly and positively with the percentage change in nLFP (r=0.445, p=0.0074), and nearly significantly and positively with the percentage change in LFP/ HFP (r=0.304, p=0.0757) between 31F to 46F. No significant correlations existed between the percent change in relative humidity and the percent changes in all HRV measures between 31F and 46F. The percent change in relative humidity correlated significantly and positively with the percentage change in nLFP between B1F to 46 F (r = 0.375, p = 0.0266). 4. Discussion 4.1. Effects of altitude on HRV This study examined how the autonomic nervous modulation of healthy subjects was affected by altitudes in the high-rise building. Our research was different from those studies performed on the mountain because the interference from confounding factors such as physical exertion, oxygen consumption, and environmental temperature, were minimized or mostly excluded. Thus, most of the changes in HRV or autonomic nervous modulation observed in this study were mainly caused by the change in altitude. In this study, it was demonstrated that the altitude within a high-rise building of 245 m above sea level could affect the autonomic nervous modulation of the subjects. By increasing the altitude, the heart rate was decreased, and the overall HRV (SDRR and TP) and vagal modulation (HFP) were increased. Our results are in accordance with the study of Sharshenova et al. (2006), which showed that the effect of altitude between 1650 m and 2030 m in the high mountain on HRV was significant increase in SDRR, TP, and HFP. We further found that the percentage increase in TP and HFP caused by mid-distance (from B1F to 31F) and long-distance (from B1F to 46F) ascent were significantly larger than those caused by a short-distance ascent (from 31F to 46F), which suggested that there might be a dose–response effect on these measures with altitude. Both SDRR and TP are the variance of the entire series of RR intervals (Sharshenova et al., 2006), and the increase in SDRR, TP and HFP was presumably caused by increased vagal tone. Studies have also suggested that the status of the autonomic nervous system is a major determinant of cardiovascular health and prognosis (Curtis and O'keefe, 2002). Any therapy that can activate the sympathetic nervous system and/or diminish the parasympathetic tone may increase the risk of cardiovascular events. In contrast, therapies that tip the autonomic balance toward parasympathetic dominance and decreased sympathetic tone may improve the prognosis. Since a greater change in HRV measures was observed after a long-distance ascent in this study, altitude is probably a means that can be employed to increase the overall HRV and vagal modulation of the subject. However, it should be noted that a high HRV that correlates with good health may not necessarily be a cause of good health. Thus, altitude may be used to increase the HRV and vagal modulation of a subject, but the health of the subject may not necessarily be improved by adopting a higher altitude.
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Fig. 1. (A) positive correlation (r = 0.395, p b 0.05) between age and the percentage change in SDRR (from B1F to 46F). (B) positive correlation (r = 0.416, p b 0.05) between age and the percentage change in CVRR (from B1F to 46F).
Many studies have reported that HRV correlated negatively with age (Antelmi et al., 2004; Korkushkio et al., 1991; O'Brien et al., 1986). Low HRV is considered a significant finding of aging, disease conditions, and even a risk factor of mortality (Task force, 1996; Bigger et al., 1992). In a 24-hour time domain HRV analysis, Umetani et al. concluded that normal aging is associated with low HRV, that the significant indicators of aging were SDRR index, RMSSD and pNN50 (Umetani et al., 1998). It is generally agreed that the HRV were decreased in patients with cardiovascular disease such as hypertension, myocardial infarction, and diabetic autonomic neuropathy (Bernardi et al., 1998). In this study, we found that age correlated positively with the percentage change in SDRR and CVRR due to altitude change. The older the subject was, the
greater the increase in SDRR and CVRR due to the increase in altitude. In addition, we found that the subject who had a smaller SDRR or CVRR on B1F could have a greater increase in SDRR and CVRR when the subject was moved to a higher altitude. Therefore, our results suggested that people, especially the older people and the people who had a small HRV, might benefit from staying at a higher altitude in a high-rise building in term of HRV. 4.2. Gender-related difference in the effect of altitude on HRV Gender-related difference in HRV has been reported by many researchers. For instance, Huikuri et al. (Huikuri et al., 1996) reported
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Table 3 HRV measures on the three floors in the high-rise building for different genders. Male (n = 10) Heart rate (bpm) B1F 75 (65–81) 31F 69 (62–80) 46F 68 (60–80) SDRR (ms) B1F 36 (31–54) 31F 47 (35–56) 46F 53 (32–69) CVRR (%) B1F 5.0 (3.7–7.0) 31F 5.5 (4.2–6.1) 46F 5.8 (4.6–8.1) 2 TP (ms ) B1F 538 (386–1073) 31F 924 (475–1440) 46F 1065 (465–2106) VLFP (ms2) B1F 164 (121.5–271.9) 31F 225 (184–589) 46F 249 (191–659) 2 LFP (ms ) B1F 205 (97–367) 31F 341 (142–719) 46F 398 (153–696) HFP (ms2) B1F 138 (79–205) 31F 189 (118–239) 46F 233 (110–355) nVLFP (nu) B1F 35.2 (23.2–47.6) 31F 34.5 (23.3–51.0) 46F 38.3 (24.4–54.8) nLFP (nu) B1F 32.3 (21.0–53.0) 31F 40.4 (29.8–52.0) 46F 32.7 (28.1–47.0) nHFP (nu) B1F 24.0 (14.7–35.9) 31F 23.8 (17.8–34.4) 46F 21.0 (15.3–32.5) LFP/HFP B1F 1.5 (0.8–2.2) 31F 1.5 (1.4–1.9) 46F 1.8 (1.3–2.6)
Female (n = 25)
P
78 (74–86) 73 (67–78) 72 (68–76)
0.333 0.547 0.476
35 (31–52) 46 (33–54) 46 (32–55)
0.869 0.869 0.352
5.2 (3.8–6.5) 5.3 (4.3–6.7) 5.4 (4.2–6.8)
0.927 0.985 0.476
523 (342–788) 807 (398–1158) 751 (351–932)
0.648 0.596 0.208
214.3 (120.7–326.2) 222 (151–379) 190.0 (114–363)
0.596 0.812 0.221
158 (68–205) 234 (99–334) 171 (97–267)
0.265 0.139 0.071
152 (62–263) 258 (80–496) 231 (89–505)
0.784 0.675 0.927
39.3 (31.4–57.0) 32.0 (24.2–47.2) 35.5 (24.3–46.5)
0.411 0.784 0.784
26.1 (17.0–31.1) 28.1 (15.6–35.2) 25.0 (18.8–37.2)
0.139 0.043⁎ 0.043⁎
28.8 (17.3–44.5) 36.1 (23.1–43.2) 32.5 (21.4–48.3)
0.499 0.051 0.104
0.7 (0.5–2.2) 0.7 (0.5–1.2) 0.9 (0.5–1.4)
0.298 0.014⁎ 0.030⁎
Values are expressed as medians (IQR, 25–75%). SDRR, standard deviation of RR intervals; CVRR, coefficient of variation of RR intervals; TP, total power; VLFP, very low frequency power; LFP, low frequency power; HFP, high frequency power; nVLFP, normalized VLFP; nLFP, normalized LFP; LFP/HFP, low-/highfrequency power ratio. ⁎ p b 0.05.
that the nLFP and LFP/HFP of male subjects were larger than those of female subjects. Antelmi et al. (2004) reported that women had higher HFP, RMSSD, and pNN50, while men had higher VLFP, LFP, and SDRR. Ettinger et al. (1996) reported that higher sympathetic nerve activities were found in men compared with women during static exercise. In contrast, Bigger et al. (1995) reported that HRV did not differ by gender because men and women have similar autonomic
nerve modulation not only in healthy subjects but also in the coronary heart disease (CAD) and the acute myocardial infarction (AMI) patients. In this study, the differences in HRV between different genders at sea level were not observed; however, both nLFP and LFP/ HFP of male subjects were significantly higher than those of female subjects at altitude higher than 31F in the high-rise building. Our results suggested that different genders reacted somewhat differently to altitude in terms of autonomic nerve modulation. The sympathetic modulation of male subjects seems to be more easily aroused by ascent to a high altitude than the female subjects. 4.3. Environmental factors The environment within the high-rise building might be a factor that could affect the autonomic nerve modulation of the subject in the building. Although the ambient temperature and the relative humidity were steady and within the standard housing range of 21– 28 °C and 45–62%, respectively, they were still statistically different between floors. The ambient temperature might influence the HRV of the subject because the VLF component was considered to be related to thermoregulation (K'Itney, 1974). The cardiovascular response to the change in ambient temperature has been reported. For instance, Sollers et al. (2002) found that VLFP and diastolic blood pressure were increased in a cold room (13 °C); and that the heart rate and nLFP were increased whereas nHFP and systolic blood pressure were decreased in a hot room (35 °C). Kinugasa and Hirayanagi (1999) found that HFP declined steadily with skin surface heating, whereas LFP/HFP increased, in a chamber (18–60 °C). In this study, the change in ambient temperature between different floors correlated positively with the change in nLFP, and the change in humidity correlated positively with LFP. These results suggested that temperature and humidity in the high-rise building might affect the vagal and sympathetic modulations of the subjects staying in that building. The forehead temperature of the study subjects on 46F was found to be significantly higher than that on B1F and 31F. This small rise in forehead temperature might be caused by the small rise in ambient temperature on 46F due to poor air-conditioning on that floor, since the 46F of the building was not in use at the time of study. Some studies have suggested that body temperature change due to heat-stress may influence the baroreflex modulation of sympathetic nerve activity. For instance, Crandall et al. (2000) reported that sublingual temperature increased in parallel with increasing heart rate, reducing HFP of HRV and LFP of systolic blood pressure variability by whole body heating. However, the change in HRV in this study might not be caused mainly by the change in body temperature, since the HFP was increased and the heart rate was decreased significantly on the 46F, and since there was no statistical correlation between the change in forehead temperature and the change in HRV measures in the subjects ascending to 46F. 4.4. Limitations The strength of this study lies in its relevance to the daily life experience in a modern city. The results of this study may provide clue to the answer of the common question on why people feel relaxed and calm when they are up in a high-rise building. However, this study has
Table 4 Environmental conditions on the three floors in the high-rise building.
Ambient temperature (°C) Relative humidity (%)
B1F
31F
46F
P
23.0 (22.8–23.5) 58.8 (56.6–60.3)
22.6 (22.3–23.0)⁎ 62.4 (59.6–65.1)⁎
24.8 (23.8–25.6)⁎† 54.5 (52.7–57.7)⁎†
b0.001 b0.001
Values are expressed as medians (IQR, 25–75%). Friedman repeated measures analysis of variance on ranks with Student–Newman–Keuls tests for post hoc comparisons between floors. ⁎ p b 0.05 vs. B1F. † p b 0.05 vs. 31F.
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some limitations. Firstly, the study subjects stayed at each floor for about 30 min. It may not be appropriate to draw conclusions from the results obtained from so short a stay at each floor. Secondly, the case number was not large enough, and the age range of the study subjects was not wide enough. Thirdly, the air condition of the 46th floor was not turned on at the time of study because that floor was not in use at that time. The difference in room temperature caused by the use or no use of air-conditioning and its possible effect on the autonomic nervous modulation made the interpretation of the results a little difficult. Finally, this study used only HRV analysis to assess the autonomic nervous modulation of the subjects at different floors for several minutes. Without other studies and analysis, the result of this study was only a preliminary one. 4.5. Clinical implications and conclusions The ascent to a higher altitude in a high-rise building can lead to an increase in overall HRV and vagal modulation because the heart rate was decreased while the SDRR, TP and HFP were increased. The older the subject was or the smaller SDRR and CVRR the subject had, the greater increase in SDRR and CVRR the subject has when he/she was elevated to a higher altitude. Male subjects had a higher sympathetic modulation than female ones when they were elevated to a higher altitude. Thus, high altitude in a high-rise building may be used to increase the overall HRV and vagal modulation of a subject, especially for elder people and for people who have a small HRV at ground level. Whether a longer stay at a high altitude in a high-rise building is really good for health remains to be explored by further studies. Acknowledgements This study was supported by the grant VGHUST96-P1-06 of the Joint Research Program of Taipei Veterans General Hospital and University System of Taiwan, Taiwan. We are grateful to the staff of Shin Kong Life Tower, who provided us with important assistance so that this study could be completed. References Antelmi, I., de Paula, R.S., Shinzato, A.R., Peres, C.A., Mansur, A.J., Grupi, C.J., 2004. Influence of age, gender, body mass index, and functional capacity on heart rate variability in a cohort of subjects without heart disease. Am. J. Cardiol. 93, 381–385. Bachmann, M.O., Myers, J.E., 1995. Influences on sick building syndrome symptoms in three buildings. Soc. Sci. Med. 40, 245–251. Bernardi, L., Passino, C., Spadacini, G., Calclati, A., Robergs, R., Greene, R., Martignonie, E., Anand, I., Appenzeller, O., 1998. Cardiovascular autonomic modulation and activity of carotid baroreceptors at altitude. Clin. Sci. (Lond.) 95, 565–573. Bigger Jr., J.T., Fleiss, J.L., Steinman, R.C., Rolnitzky, L.M., Kleiger, R.E., Rottman, J.N., 1992. Frequency domain measures of heart period variability and mortality after myocardial infarction. Circulation 85, 164–171. Bigger Jr., J.T., Fleiss, J.L., Steinman, R.C., Rolnitzky, L.M., Schneider, W.J., Stein, P.K., 1995. RR variability in healthy, middle-aged persons compared with patients with chronic coronary heart disease or recent acute myocardial infarction. Circulation 91, 1936–1943.
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Autonomic Neuroscience: Basic and Clinical j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / a u t n e u
Effects of altitude in high-rise building on the autonomic nervous modulation in healthy subjects Pao-Chen Lin a,1, Wei-Lung Chen b,c,1, Wei-Fong Kao d, Yi-Hsuan Yang a, Cheng-Deng Kuo a,⁎ a
Laboratory of Biophysics, Department of Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan Department of Emergency Medicine, Cathay General Hospital, Taipei, Taiwan School of Medicine, Fu Jen Catholic University, Taipei, Taiwan d Department of Emergency Medicine, Taipei Veterans General Hospital, Taipei, Taiwan b c
a r t i c l e
i n f o
Article history: Received 18 August 2010 Received in revised form 11 December 2010 Accepted 29 December 2010 Keywords: Altitude Heart rate variability Autonomic nervous modulation Vagal activity
a b s t r a c t This study intended to study the effects of altitude in the high-rise building on the automatic nervous modulation in healthy subjects. Heart rate variability (HRV) analysis was performed to assess the automatic nervous modulation of the subjects at three different altitudes in the air-conditioned high-rise building, i.e., the first basement (4 m beneath sea level), the 31st floor (133 m above sea level), and the 46th floor (200 m above sea level). We found that the heart rate was significantly decreased, whereas the standard deviation of RR intervals (SDRR), total power and high frequency power were significantly increased when the subject was elevated to a higher altitude. The normalized low frequency power and low-/high-frequency power ratio on the 31st and 46th floors were significantly different between genders; however, no such difference was found on the first basement. The age correlated significantly and positively with the percentage change in the SDRR and coefficient of variation of RR intervals when the subjects were elevated from the first basement to the 46th floor. In conclusion, higher altitude in an air-conditioned high-rise building can lead to an increase in HRV/vagal modulation. The stay at a higher altitude in a high-rise building may lead to increased overall HRV and vagal modulation of a subject, especially for the elder people and the people who had a small HRV at ground level. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Because of increasing population density in the cities, more and more high-rise buildings are being built to accommodate the increasing number of people living and working in the cities nowadays. Some studies have investigated the illness caused by the environmental condition in the buildings, such as the air, temperature, humidity, and pollution in the environment (Bachmann and Myers, 1995; Niven et al., 2000; Park et al., 2004; Woods, 1991). The frequently reported illness in the buildings is the sick building syndrome which is most probably caused by indoor air problem (Reijula and Sundman-Digert, 2004; Salem and Bartsch, 2001). Sharshenova et al. (2006) found in apparently healthy children residents of moderate altitudes that increase in altitude levels is accompanied by higher overall variability and parasympathetic modulation of the sinus node and lower sympathetic response to posture, and that the heart rate variability in children residents of moderate altitudes is also dependent on gender, resembling similar
⁎ Corresponding author. Tel.: + 886 2 28757745; fax: + 886 2 28710773. E-mail address: [email protected] (C.-D. Kuo). 1 The first two authors contribute equally. 1566-0702/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.autneu.2010.12.005
relationship in inhabitants of sea level. Thus, altitude probably is one of the most important factors associated with the health status of the subjects in a high-rise building, yet not many studies have investigated the effects of altitude within the high-rise buildings on the physiology of the people in those buildings. Heart rate variability (HRV) analysis is a noninvasive monitoring method frequently used to assess the autonomic nervous modulation of the subject (Task force, 1996). It has been employed to evaluate the changes in autonomic nervous modulation in humans on high mountains (Bernardi et al., 1998; Farinelli et al., 1994; Kanai et al., 2001; Lanfranchi et al., 2005; Perini et al., 1996). However, the knowledge obtained on the high mountains may not be directly applicable to the high-rise buildings because the temperature, humidity and oxygen concentration on the mountain as well as the physical efforts exhausted to reach the high altitude are different from those in the high-rise buildings. Since more and more people live or work in high-rise buildings, it is worthwhile to investigate the effect of altitude on the autonomic nervous modulation of the subjects in the high-rise buildings by using HRV analysis. Thus, the aim of this study was to compare the effects of different altitudes in the high-rise buildings on the autonomic nervous modulation of the subjects.
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2. Methods 2.1. Participants The subjects included in this study were healthy volunteers recruited from the community who have no cardiopulmonary or other major diseases that may influence HRV, such as diabetes mellitus, hypertension, or autonomic neuropathy. 2.2. Study protocol The high-rise building chosen in this study was the Shin Kong Life Tower that has been the tallest building in Taiwan from 1993 to 1997, and is the third highest building in Taiwan now. The height of the Shin Kong Life Tower is 245 m above sea level, and the number of floors is 51. Three floors in this building were chosen for study, i.e., the first basement (B1F, 4 m beneath sea level), the 31st floor (31F, 133 m above sea level), and the 46th floor (46F, 200 m above sea level). The B1F and 46F were chosen because there were the lowest and the highest floor levels in the high-rise building, respectively. Between these two floors, the intermediate 31F was chosen because it was the most convenient floor to the visitors that could be used for study. To investigate if there was any dose–response effect of altitude on HRV measures, three kinds of altitude change were defined: (1) short-distance altitude change (from 31F to 46F, an ascent of 15 F or 67 m); (2) mid-distance altitude change (From B1F to 31F, an ascent of 31 F or 137 m); and (3) longdistance altitude change (from B1F to 46F, an ascent of 46 F or 204 m). The recording of ECG signals was performed in a quiet, air-conditioned room with constant temperature and suitable humidity on each floor. The Institutional Review Board of the hospital has approved this research. Informed written consent was obtained from each subject before the study. All participants were asked not to have any drink that may influence HRV, such as coffee, alcohol, or tea 24 h before the study. All subjects reached 31F and 46F by the elevator to avoid unnecessary confounding factors to this study, such as physical exertion, oxygen consumption, profuse sweating. 2.3. Equipments and measurements On arrival at each floor, the subjects were requested to take a rest for at least 10 min on the chair. After that, preliminary physical check-up, including measurement of forehead temperature and blood pressures, was done on each subject. A trend of electrocardiographic (ECG) signals was picked up by a physiological signal acquisition apparatus (Biopac MP35, Biopac Systems, Inc., USA) and transmitted to a notebook computer for recording. The ECG signals were recorded for 12 min with a sampling frequency of 500 Hz. The subjects were asked to sit on the chair and close their eyes during the recording period. The ambient temperature and relative humidity were measured by a portable temperature humidity indicator (HygroPalm 0, Rotronic Ag, Switzerland) at the same time. 2.4. HRV analysis The recorded ECG signals were retrieved afterwards to detect the consecutive RR intervals by using the software developed on Matlab 6.5 (The MathWorks Inc., Natick, MA). The last 512 stationary RR intervals were picked up for HRV analysis. The time domain HRV measures used were the heart rate (HR), and standard deviation (SDRR) and coefficient of variation (CVRR) of RR intervals. The frequency domain HRV measures were obtained by transforming the RR intervals into power spectrum using Fast Fourier transformation. The area under spectral peaks in the HRV spectrum within the range of 0.01–0.04, 0.04–0.15, 0.15–0.4, and 0.01–0.4 Hz was defined as the very low-frequency power (VLFP), lowfrequency power (LFP), high frequency power (HFP), and total power (TP), respectively. The normalized LFP (nLFP = LFP/TP) was used as the index of combined vagal and sympathetic modulations, the normalized
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HFP (nHFP = HFP/TP) as the index of vagal modulation, the low-/highfrequency power ratio (LFP/HFP) as the index of sympathovagal balance (Saul et al., 1988), and the normalized very low-frequency power (nVLFP = VLFP/TP) as the index of renin-angiotensin-aldosterone system and vagal withdrawal of the subject (Taylor et al., 1998). 2.5. Data analysis The values are presented as median (25th to 75th interquartile range) because nearly all the parameters are not normally distributed. Friedman repeated-measures analysis of variance on ranks with Student–Newman–Keuls test for post hoc comparisons was employed to compare the clinical data and HRV measures among three different altitudes, and the percentage change in HRV measures among three kinds of altitude change. The Mann–Whitney rank sum test was used to compare the HRV measures between different genders. The percentage changes in HRV measures between different altitudes which were calculated by using the following formulae: Short−distance ascent = %X31F−46F = 100%⋅ðX46F −X31F Þ = X31F Mid−distance ascent = %XB1F−31F = 100%⋅ðX31F −XB1F Þ = XB1F Long−distance ascent = %XB1F−46F = 100%⋅ðX46F −XB1F Þ = XB1F ; where ‘X’ stands for the HRV measure to be analyzed. Spearman rank order correlation and linear regression analysis were used to evaluate the relationship between subjects' basic characteristics as well as environmental factors and the percentage change in HRV measures. All statistical tests were performed using SigmaStat version 3.0 statistical software (SPSS Inc., Chicago, IL, USA). A p b 0.05 was considered statistically significant. 3. Results 3.1. General characteristics of participants Thirty-five normal subjects (M/F = 10/25, aged 21–65 years old) were included in this study. All measured data are presented as median and inter-quartile range (25th to 75th percentiles). Table 1 shows the general characteristics of the participants. All parameters measured on B1F, 31F and 4F were within normal ranges. However, the forehead temperature measured on 46F was significantly increased, as compared to that on B1F and 31F. 3.2. HRV at different altitudes Table 2 compares the HRV measures of the study subjects at different floors. In the time domain, the HR on 31F and 46F was significantly lower than that on B1F (p b 0.001). In contrast, the SDRR on 31F and 46F was significantly increased, as compared to that on B1F. (p = 0.008). In the frequency domain, the TP and HFP on 31 F and 46 F were also significantly increased, as compared to those on B1F (p = 0.003 for TP and p b 0.001 for HFP, respectively). 3.3. Percentage change in HRV measures between different altitudes The percentage decrease in HR, and the percentage increase in TP and HFP caused by mid-distance (from B1F to 31F) and long-distance (from B1F to 46F) ascent were significantly larger than those caused by a short-distance ascent (from 31F to 46F). The information obtained from comparing the percentage changes in HRV measures due to the change in altitude are similar to those presented in Table 2, hence the data of the percentage changes in HRV measures due to the change in altitude are not shown here.
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Table 1 General characteristics of the subjects (n = 35).
Gender (M/F) Age (year) Height (cm) Weight (kg) BMI SBP (mmHg) DBP (mmHg) PP (mmHg) Forehead temperature (oC)
B1F
31F
46F
P
10/25 33.0 (25.0–49.8) 163.0 (157.3–170.8) 57.0 (51.0–62.3) 21.1 (19.9–22.9) 111 (99–128) 71 (63–76) 42 (36–45) 36.4 (36.1–36.6)
113 (104–123) 72 (66–78) 41 (33–49) 36.3 (36.1–36.4)
110 (100–121) 72 (65–80) 40 (34–44) 36.5 (36.1–36.7)†
0.221 0.678 0.627 0.015
Values are expressed as medians (IQR, 25–75%). Friedman repeated-measures analysis of variance on ranks with Student–Newman–Keuls test for pairwise comparisons (post hoc). BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; PP, pulse pressure. † p b 0.05 vs. 31F.
3.4. Correlations between age and percentage change in HRV measures Linear regression analysis showed that both SDRR and CVRR at B1F correlate negatively with age (Fig. 1 A and B). That is, both SDRR and CVRR at B1F decreased with increasing age. This result suggested that older subjects had smaller SDRR and CVRR at the ground level. Linear regression analysis also showed that the percentage changes in SDRR and CVRR when the subjects moved from B1F to 46F correlated positively with the age of the subjects (Fig. 1C and D). That is, the %SDRR 31F–46F and %CVRR 31F–46F increased with increasing age. This result suggested that the older the subject was, the larger the increase in SDRR and CVRR the subject had when the subject moved from B1F to 46F. Further analysis showed that %SDRR_B1F-46F correlated negatively with SDRR_B1F, and that %CVRR_B1F-46F correlated negatively with CVRR_B1F (Fig. 1E and F). This result indicated that the subject who had a smaller SDRR and CVRR at B1F had a larger increase in SDRR and CVRR when the subject moved from B1F to 46F. 3.5. Gender-related differences Table 3 shows that there was no significant difference in HRV measures between different genders on B1F. However, on 31F and 46F, both nLFP and LFP/HFP of male subjects were significantly higher than those of female subjects. 3.6. Environmental effects Table 4 shows the environmental conditions on the three floors. The ambient temperature and relative humidity on those three floors were significantly different (p b 0.001). Table 2 HRV measures of the subjects at different altitudes.
Heart rate (bpm) SDRR (ms) CVRR (%) TP (ms2) VLFP (ms2) LFP (ms2) HFP (ms2) nVLF (nu) nLFP (nu) nHFP (nu) LFP/HFP
B1F
31F
46F
P
78 (71–86) 35 (31–53) 5.2 (3.8–6.6) 523 (352–806) 196 (121–308) 158 (87–275) 151 (63–261) 37.7 (28.3–54.1) 26.2 (19.6–35.4) 24.4 (16.2–43.3) 0.8 (0.5–2.2)
72 (66–80)⁎ 43 (34–55)⁎ 5.5 (4.3–6.5) 807 (416–1212)⁎
71 (66–78)⁎ 46 (32–58)⁎ 5.4 (4.3–6.8) 855 (362–1124)⁎
222 (159–381) 249 (108–365) 217 (98–466)⁎ 32.4 (23.7–42.3) 29.9 (17.5–39.2) 34.0 (20.7–41.7) 1.0 (0.5–1.5)
217 (122–407) 211 (102–340) 231 (99–465)⁎ 35.5 (24.5–48.3) 26.4 (20.5–38.7) 31.4 (20.5–45.3) 1.1 (0.6–1.8)
b 0.001 0.008 0.347 0.003 0.247 0.074 b 0.001 0.581 0.449 0.449 0.293
Values are expressed as medians (IQR, 25–75%). Friedman repeated measures analysis of variance on ranks with Student–Newman–Keuls tests for post hoc comparisons between floors. bpm, beats per minute; nu, normalized unit; SDRR, standard deviation of RR intervals; CVRR, coefficient of variation of RR intervals; TP, total power; VLFP, very low frequency power; LFP, low frequency power; HFP, high frequency power; nVLFP, normalized VLFP; nLFP, normalized LFP; LFP/HFP, low-/high-frequency power ratio. ⁎ p b 0.05 vs. B1F.
The percent change in ambient temperature correlated significantly and positively with the percentage change in nLFP (r=0.445, p=0.0074), and nearly significantly and positively with the percentage change in LFP/ HFP (r=0.304, p=0.0757) between 31F to 46F. No significant correlations existed between the percent change in relative humidity and the percent changes in all HRV measures between 31F and 46F. The percent change in relative humidity correlated significantly and positively with the percentage change in nLFP between B1F to 46 F (r = 0.375, p = 0.0266). 4. Discussion 4.1. Effects of altitude on HRV This study examined how the autonomic nervous modulation of healthy subjects was affected by altitudes in the high-rise building. Our research was different from those studies performed on the mountain because the interference from confounding factors such as physical exertion, oxygen consumption, and environmental temperature, were minimized or mostly excluded. Thus, most of the changes in HRV or autonomic nervous modulation observed in this study were mainly caused by the change in altitude. In this study, it was demonstrated that the altitude within a high-rise building of 245 m above sea level could affect the autonomic nervous modulation of the subjects. By increasing the altitude, the heart rate was decreased, and the overall HRV (SDRR and TP) and vagal modulation (HFP) were increased. Our results are in accordance with the study of Sharshenova et al. (2006), which showed that the effect of altitude between 1650 m and 2030 m in the high mountain on HRV was significant increase in SDRR, TP, and HFP. We further found that the percentage increase in TP and HFP caused by mid-distance (from B1F to 31F) and long-distance (from B1F to 46F) ascent were significantly larger than those caused by a short-distance ascent (from 31F to 46F), which suggested that there might be a dose–response effect on these measures with altitude. Both SDRR and TP are the variance of the entire series of RR intervals (Sharshenova et al., 2006), and the increase in SDRR, TP and HFP was presumably caused by increased vagal tone. Studies have also suggested that the status of the autonomic nervous system is a major determinant of cardiovascular health and prognosis (Curtis and O'keefe, 2002). Any therapy that can activate the sympathetic nervous system and/or diminish the parasympathetic tone may increase the risk of cardiovascular events. In contrast, therapies that tip the autonomic balance toward parasympathetic dominance and decreased sympathetic tone may improve the prognosis. Since a greater change in HRV measures was observed after a long-distance ascent in this study, altitude is probably a means that can be employed to increase the overall HRV and vagal modulation of the subject. However, it should be noted that a high HRV that correlates with good health may not necessarily be a cause of good health. Thus, altitude may be used to increase the HRV and vagal modulation of a subject, but the health of the subject may not necessarily be improved by adopting a higher altitude.
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Fig. 1. (A) positive correlation (r = 0.395, p b 0.05) between age and the percentage change in SDRR (from B1F to 46F). (B) positive correlation (r = 0.416, p b 0.05) between age and the percentage change in CVRR (from B1F to 46F).
Many studies have reported that HRV correlated negatively with age (Antelmi et al., 2004; Korkushkio et al., 1991; O'Brien et al., 1986). Low HRV is considered a significant finding of aging, disease conditions, and even a risk factor of mortality (Task force, 1996; Bigger et al., 1992). In a 24-hour time domain HRV analysis, Umetani et al. concluded that normal aging is associated with low HRV, that the significant indicators of aging were SDRR index, RMSSD and pNN50 (Umetani et al., 1998). It is generally agreed that the HRV were decreased in patients with cardiovascular disease such as hypertension, myocardial infarction, and diabetic autonomic neuropathy (Bernardi et al., 1998). In this study, we found that age correlated positively with the percentage change in SDRR and CVRR due to altitude change. The older the subject was, the
greater the increase in SDRR and CVRR due to the increase in altitude. In addition, we found that the subject who had a smaller SDRR or CVRR on B1F could have a greater increase in SDRR and CVRR when the subject was moved to a higher altitude. Therefore, our results suggested that people, especially the older people and the people who had a small HRV, might benefit from staying at a higher altitude in a high-rise building in term of HRV. 4.2. Gender-related difference in the effect of altitude on HRV Gender-related difference in HRV has been reported by many researchers. For instance, Huikuri et al. (Huikuri et al., 1996) reported
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Table 3 HRV measures on the three floors in the high-rise building for different genders. Male (n = 10) Heart rate (bpm) B1F 75 (65–81) 31F 69 (62–80) 46F 68 (60–80) SDRR (ms) B1F 36 (31–54) 31F 47 (35–56) 46F 53 (32–69) CVRR (%) B1F 5.0 (3.7–7.0) 31F 5.5 (4.2–6.1) 46F 5.8 (4.6–8.1) 2 TP (ms ) B1F 538 (386–1073) 31F 924 (475–1440) 46F 1065 (465–2106) VLFP (ms2) B1F 164 (121.5–271.9) 31F 225 (184–589) 46F 249 (191–659) 2 LFP (ms ) B1F 205 (97–367) 31F 341 (142–719) 46F 398 (153–696) HFP (ms2) B1F 138 (79–205) 31F 189 (118–239) 46F 233 (110–355) nVLFP (nu) B1F 35.2 (23.2–47.6) 31F 34.5 (23.3–51.0) 46F 38.3 (24.4–54.8) nLFP (nu) B1F 32.3 (21.0–53.0) 31F 40.4 (29.8–52.0) 46F 32.7 (28.1–47.0) nHFP (nu) B1F 24.0 (14.7–35.9) 31F 23.8 (17.8–34.4) 46F 21.0 (15.3–32.5) LFP/HFP B1F 1.5 (0.8–2.2) 31F 1.5 (1.4–1.9) 46F 1.8 (1.3–2.6)
Female (n = 25)
P
78 (74–86) 73 (67–78) 72 (68–76)
0.333 0.547 0.476
35 (31–52) 46 (33–54) 46 (32–55)
0.869 0.869 0.352
5.2 (3.8–6.5) 5.3 (4.3–6.7) 5.4 (4.2–6.8)
0.927 0.985 0.476
523 (342–788) 807 (398–1158) 751 (351–932)
0.648 0.596 0.208
214.3 (120.7–326.2) 222 (151–379) 190.0 (114–363)
0.596 0.812 0.221
158 (68–205) 234 (99–334) 171 (97–267)
0.265 0.139 0.071
152 (62–263) 258 (80–496) 231 (89–505)
0.784 0.675 0.927
39.3 (31.4–57.0) 32.0 (24.2–47.2) 35.5 (24.3–46.5)
0.411 0.784 0.784
26.1 (17.0–31.1) 28.1 (15.6–35.2) 25.0 (18.8–37.2)
0.139 0.043⁎ 0.043⁎
28.8 (17.3–44.5) 36.1 (23.1–43.2) 32.5 (21.4–48.3)
0.499 0.051 0.104
0.7 (0.5–2.2) 0.7 (0.5–1.2) 0.9 (0.5–1.4)
0.298 0.014⁎ 0.030⁎
Values are expressed as medians (IQR, 25–75%). SDRR, standard deviation of RR intervals; CVRR, coefficient of variation of RR intervals; TP, total power; VLFP, very low frequency power; LFP, low frequency power; HFP, high frequency power; nVLFP, normalized VLFP; nLFP, normalized LFP; LFP/HFP, low-/highfrequency power ratio. ⁎ p b 0.05.
that the nLFP and LFP/HFP of male subjects were larger than those of female subjects. Antelmi et al. (2004) reported that women had higher HFP, RMSSD, and pNN50, while men had higher VLFP, LFP, and SDRR. Ettinger et al. (1996) reported that higher sympathetic nerve activities were found in men compared with women during static exercise. In contrast, Bigger et al. (1995) reported that HRV did not differ by gender because men and women have similar autonomic
nerve modulation not only in healthy subjects but also in the coronary heart disease (CAD) and the acute myocardial infarction (AMI) patients. In this study, the differences in HRV between different genders at sea level were not observed; however, both nLFP and LFP/ HFP of male subjects were significantly higher than those of female subjects at altitude higher than 31F in the high-rise building. Our results suggested that different genders reacted somewhat differently to altitude in terms of autonomic nerve modulation. The sympathetic modulation of male subjects seems to be more easily aroused by ascent to a high altitude than the female subjects. 4.3. Environmental factors The environment within the high-rise building might be a factor that could affect the autonomic nerve modulation of the subject in the building. Although the ambient temperature and the relative humidity were steady and within the standard housing range of 21– 28 °C and 45–62%, respectively, they were still statistically different between floors. The ambient temperature might influence the HRV of the subject because the VLF component was considered to be related to thermoregulation (K'Itney, 1974). The cardiovascular response to the change in ambient temperature has been reported. For instance, Sollers et al. (2002) found that VLFP and diastolic blood pressure were increased in a cold room (13 °C); and that the heart rate and nLFP were increased whereas nHFP and systolic blood pressure were decreased in a hot room (35 °C). Kinugasa and Hirayanagi (1999) found that HFP declined steadily with skin surface heating, whereas LFP/HFP increased, in a chamber (18–60 °C). In this study, the change in ambient temperature between different floors correlated positively with the change in nLFP, and the change in humidity correlated positively with LFP. These results suggested that temperature and humidity in the high-rise building might affect the vagal and sympathetic modulations of the subjects staying in that building. The forehead temperature of the study subjects on 46F was found to be significantly higher than that on B1F and 31F. This small rise in forehead temperature might be caused by the small rise in ambient temperature on 46F due to poor air-conditioning on that floor, since the 46F of the building was not in use at the time of study. Some studies have suggested that body temperature change due to heat-stress may influence the baroreflex modulation of sympathetic nerve activity. For instance, Crandall et al. (2000) reported that sublingual temperature increased in parallel with increasing heart rate, reducing HFP of HRV and LFP of systolic blood pressure variability by whole body heating. However, the change in HRV in this study might not be caused mainly by the change in body temperature, since the HFP was increased and the heart rate was decreased significantly on the 46F, and since there was no statistical correlation between the change in forehead temperature and the change in HRV measures in the subjects ascending to 46F. 4.4. Limitations The strength of this study lies in its relevance to the daily life experience in a modern city. The results of this study may provide clue to the answer of the common question on why people feel relaxed and calm when they are up in a high-rise building. However, this study has
Table 4 Environmental conditions on the three floors in the high-rise building.
Ambient temperature (°C) Relative humidity (%)
B1F
31F
46F
P
23.0 (22.8–23.5) 58.8 (56.6–60.3)
22.6 (22.3–23.0)⁎ 62.4 (59.6–65.1)⁎
24.8 (23.8–25.6)⁎† 54.5 (52.7–57.7)⁎†
b0.001 b0.001
Values are expressed as medians (IQR, 25–75%). Friedman repeated measures analysis of variance on ranks with Student–Newman–Keuls tests for post hoc comparisons between floors. ⁎ p b 0.05 vs. B1F. † p b 0.05 vs. 31F.
P.-C. Lin et al. / Autonomic Neuroscience: Basic and Clinical 161 (2011) 126–131
some limitations. Firstly, the study subjects stayed at each floor for about 30 min. It may not be appropriate to draw conclusions from the results obtained from so short a stay at each floor. Secondly, the case number was not large enough, and the age range of the study subjects was not wide enough. Thirdly, the air condition of the 46th floor was not turned on at the time of study because that floor was not in use at that time. The difference in room temperature caused by the use or no use of air-conditioning and its possible effect on the autonomic nervous modulation made the interpretation of the results a little difficult. Finally, this study used only HRV analysis to assess the autonomic nervous modulation of the subjects at different floors for several minutes. Without other studies and analysis, the result of this study was only a preliminary one. 4.5. Clinical implications and conclusions The ascent to a higher altitude in a high-rise building can lead to an increase in overall HRV and vagal modulation because the heart rate was decreased while the SDRR, TP and HFP were increased. The older the subject was or the smaller SDRR and CVRR the subject had, the greater increase in SDRR and CVRR the subject has when he/she was elevated to a higher altitude. Male subjects had a higher sympathetic modulation than female ones when they were elevated to a higher altitude. Thus, high altitude in a high-rise building may be used to increase the overall HRV and vagal modulation of a subject, especially for elder people and for people who have a small HRV at ground level. Whether a longer stay at a high altitude in a high-rise building is really good for health remains to be explored by further studies. Acknowledgements This study was supported by the grant VGHUST96-P1-06 of the Joint Research Program of Taipei Veterans General Hospital and University System of Taiwan, Taiwan. We are grateful to the staff of Shin Kong Life Tower, who provided us with important assistance so that this study could be completed. References Antelmi, I., de Paula, R.S., Shinzato, A.R., Peres, C.A., Mansur, A.J., Grupi, C.J., 2004. Influence of age, gender, body mass index, and functional capacity on heart rate variability in a cohort of subjects without heart disease. Am. J. Cardiol. 93, 381–385. Bachmann, M.O., Myers, J.E., 1995. Influences on sick building syndrome symptoms in three buildings. Soc. Sci. Med. 40, 245–251. Bernardi, L., Passino, C., Spadacini, G., Calclati, A., Robergs, R., Greene, R., Martignonie, E., Anand, I., Appenzeller, O., 1998. Cardiovascular autonomic modulation and activity of carotid baroreceptors at altitude. Clin. Sci. (Lond.) 95, 565–573. Bigger Jr., J.T., Fleiss, J.L., Steinman, R.C., Rolnitzky, L.M., Kleiger, R.E., Rottman, J.N., 1992. Frequency domain measures of heart period variability and mortality after myocardial infarction. Circulation 85, 164–171. Bigger Jr., J.T., Fleiss, J.L., Steinman, R.C., Rolnitzky, L.M., Schneider, W.J., Stein, P.K., 1995. RR variability in healthy, middle-aged persons compared with patients with chronic coronary heart disease or recent acute myocardial infarction. Circulation 91, 1936–1943.
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