Relationship between Physical Activity and the Very Low-Frequency Component of Heart Rate Variability after Stroke Harunobu Usui, MS, RPT and Yuusuke Nishida, PhD, RPT
Background: The present study aimed to clarify the relationship between high physical activity (PA) and function of the autonomic nervous system, which is important in the prognosis after stroke. We hypothesized a positive association between PA and the very low-frequency (VLF) component of heart rate variability (HRV). Methods: Eight patients participated in this study. PA was measured using an accelerometer, and HRV was measured using a heart rate monitor. Results: A significant and positive relationship was observed between the VLF component of HRV and PA. A significant negative relationship was observed between the VLF component of HRV and the duration of inactivity. No significant relationship was identified between the low-to-high frequency ratio of HRV and between the highfrequency component of HRV and PA. Conclusions: A positive correlation was observed between the VLF component of HRV and PA in stroke patients. Therefore, the VLF component of HRV links PA to cardiovascular prognosis. Key Words: Physical activity—autonomic nervous system—heart rate variability—very low frequency—stroke. Ó 2015 by National Stroke Association
Physical activity (PA) can facilitate the performance of activities of daily living, increase walking speed, improve exercise tolerance, and reduce the risk of cardiovascular disease after stroke.1 Chronic PA reduces resting proinflammatory cytokines such as high-sensitivity C-reactive protein and interleukin-62,3 and arrests the progression of atherosclerosis.3 In community-dwelling individuals with stroke, low PA may contribute to the progression of arterial stiffness.4 Increased proinflammatory cytokine levels have been identified as a risk factor for adverse cardiovascular events5 and associated with poor outcome and mortality after stroke.6,7 The autonomic nervous
From the Department of Rehabilitation Science, Seirei Christopher University, Hamamatsu, Shizuoka, Japan. Received November 14, 2014; accepted November 24, 2014. Address correspondence to Harunobu Usui, MS, RPT, Rehabilitation Science, Seirei Christopher University, 3453 Mikatabarachou, Kitaku, Hamamatsu, Shizuoka 433-8558, Japan. E-mail: 13dr01@g. seirei.ac.jp. 1052-3057/$ - see front matter Ó 2015 by National Stroke Association http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2014.11.026
840
system (ANS) plays an important role in the regulation of proinflammatory responses via the inflammatory reflex.8,9 Night-time and 24-hour heart rate variability (HRV) is associated with the metabolic status.10 Increased proinflammatory cytokine levels have been associated with the very low-frequency (VLF) component of HRV,11-13 which in turn has been associated with metabolic syndrome and recovery after adverse coronary events.10,14 In addition, the VLF component of HRV has been identified as a powerful predictor of clinical prognosis in patients with cardiovascular disease.15,16 In recent research, decreased VLF component of HRV was reported as an independent predictor of mortality and morbidity in hemodynamically stable trauma patients.17 Moreover, the night-time VLF component of HRV may be a predictor of infection after acute stroke18 and of mortality after stroke.19 To clarify the mechanism that PA affects cardiovascular prognosis, in this study, the association between PA and ANS activity was investigated in stroke patients. We hypothesized that high PA is related to higher levels of ANS activity, which is important in the prognosis after
Journal of Stroke and Cerebrovascular Diseases, Vol. 24, No. 4 (April), 2015: pp 840-843
PHYSICAL ACTIVITY AND HEART RATE VARIABILITY
stroke and that high PA is associated with increased VLF component of HRV.
Methods All patients provided informed consent for participation in this study. Ethical approval was obtained from the Ethics Committee of Seirei Christopher University and Omaezaki Municipal Hospital.
Participants The participants of the present study included 8 patients who suffered from ischemic stroke 2-4 months back. All patients were admitted to the comprehensive rehabilitation unit of Omaezaki Municipal Hospital between April and August 2012. The patients were included in this study if they were able to independently walk with or without assistance (e.g., a cane). The exclusion criteria included concomitant cardiovascular disorders affecting the ANS activity, cardiac arrhythmia, medical instability, and insufficient electrocardiographic or PA recording. The participants were volunteers interested in recruitment.
Physical Activity The duration and intensity of PA were measured using a portable accelerometer, which recorded the metabolic equivalents (METs) every 10 seconds. The efficacy of this accelerometer in the assessment of PA levels in stroke patients has been previously demonstrated.20,21 All patients were asked to wear the accelerometer on the nonparetic hip for 24 hours. A physical therapist attached and detached these accelerometers. The resulting data were downloaded to a personal computer for calculation of PA during specified time intervals. PA was defined according to the following equation: METs 3 number of minutes. Values for PA were grouped as follows: 1.1-2.9 METs (light), 3.0-5.9 METs (moderate), and $6.0 METs (vigorous).22 Furthermore, inactive time was calculated as 1440 2 (time spent in light PA 1 moderate PA 1 vigorous PA).23
Heart Rate Variability HRV was measured using a heart rate monitor and analyzed using a software program. Heart rate recording was performed over a period of 24 hours (from 17:00 hours on 1 day to 17:00 hours the next day). The R wave to R wave interval was calculated using a heart rate monitor. Abnormal R wave to R wave signals were automatically retrieved from the program for analysis. Spectral power was calculated within each frequency interval using the following parameters: VLF power 5 .003-.04 Hz, low-frequency (LF) power 5 .04.15 Hz, high-frequency (HF) power 5 .15-.40 Hz, and the ratio of LF-to-HF (LF/HF). VLF, HF, and the LF/HF
841
ratio were transformed by the natural logarithm (ln). These respective HRV components were analyzed over the entire 24 hours of recorded data and all the nighttime recordings (21:00-05:00 hours).
Statistics Pearson correlation coefficients were calculated to evaluate the relationships between PA and HRV. The results are expressed as mean 6 standard deviation. SPSS software (version 19.0; SPSS, Inc, Chicago, IL) was used for statistical analysis.
Results Fourteen stroke patients were enrolled in this study. Two patients were excluded because of inadequate HRV data, and eventually, data for 12 patients were included in this study (age, 67.7 6 14.8 years; 7 males).
Physical Activity Average values for PA are presented in Table 1. Only 3 patients engaged in vigorous PA; therefore, data for vigorous PA were excluded from the analysis. All patients spent the longest time for light activities in their active time. However, all patients spent longer inactivity time than active time.
Heart Rate Variability Average values over 24-hour and night-time values for HRV are summarized in Table 2. LnHF and lnLF/HF of 24-hour values were bigger than night-time values. In contrast, lnVLF of night-time values were bigger than 24-hour values.
Association between Physical Activity and Heart Rate Variability Table 3 presents the correlations between PA and HRV in the study patients. A significant positive relationship was observed between the lnVLF component of HRV and PA (P , .05). Furthermore, a significant negative relationship was observed between the lnVLF component of HRV and inactivity time (P , .05). The relationships of the night-time lnVLF and PA are stronger correlation Table 1. Average levels of physical activity in stroke patients Physical activity levels
Data
Inactivity (min) Light PA (min 3 METs) Moderate PA (min 3 METs) Vigorous PA (min 3 METs)
1059.1 6 144.3 569.1 6 226.5 89.4 6 56.5 1.3 6 2.6
Abbreviations: METs, metabolic equivalents; PA, physical activity. Values are averages 6 standard deviations.
H. USUI AND Y. NISHIDA
842
Table 2. Average of 24-hour and night-time HRV HRV component
24 h
Night time
lnHF lnLF/HF lnVLF
5.38 6 1.21 1.20 6 .68 6.70 6 .73
5.23 6 1.43 1.10 6 .90 6.89 6 .80
Abbreviations: HF, high-frequency component; HRV, heart rate variability; ln, natural logarithm; LF, low-frequency component; VLF, very low-frequency component. Values are averages 6 standard deviations.
than the relationships of the 24-hour VLF and PA. The lnLF/HF ratio and the lnHF component of HRV were not significantly related to PA.
Discussion In the present study, the lnVLF component of HRV was significantly related to PA; however, no significant relationship was observed between the lnLF/HF ratio and the lnHF component of HRV and PA. In general, the HF component of HRV indicates vagal activity, and the LF/ HF ratio indicates sympathetic activity.24 However, it is yet to be clarified what the VLF component of HRV indicates. A few reports have indicated that the VLF component of HRV is a powerful predictor of clinical prognosis in cardiovascular diseases13,16 and that it is associated with chronic inflammation.11-13 Our data support the hypothesis that an association exists between PA and the VLF component of HRV. In this study, high PA was related to higher levels of ANS activity, which is important in the prognosis after stroke. PA can inhibit the progression of arterial stiffness4 and reduce the risk of cardiovascular disease after stroke.2 The results of the present study may indicate that the VLF component of HRV links PA to cardiovascular prognosis. In this study, a stronger relationship was observed between the night-time lnVLF component of HRV and PA compared with that between the 24-hour lnVLF component of HRV and PA. This result was similar to that of a previous report.10 Data collected during the night may
be more stable compared with those collected at other times because the influence of mental stress, exercise, diet, and other factors is eliminated. PA levels are reportedly low in hospitalized stroke patients.25 PAs after stroke were impaired various factors, including cognitive dysfunction.26 Low level of PA was associated with mobility, quality of life, and fall-related self-efficacy.27 Similar to other reports,2-4 PA contributed to health improvement in stroke patients in the present study as well. Therefore, this study provides further evidence that stroke patients should be advised to increase their PA levels.
Study Strength To our knowledge, this is the first study to provide data regarding the VLF component of HRV and to report a positive correlation between this component and PA in stroke patients. The VLF component of HRV is reportedly a powerful predictor of clinical prognosis in patients with cardiovascular diseases.15,16 Thus, the results of this study may encourage stroke patients to increase their PA levels. In future, evaluation of the effects of increasing PA levels may be accomplished using the VLF component of HRV.
Study Limitations This study has some limitations. First, walking speed is often variable in stroke patients. In a previous study, accelerometers were not recommended for use in stroke patients walking at speeds ,.5 m/second.28 In the present study, walking speed exceeded .5 m/second in all patients. Second, inflammatory cytokine levels were not measured in this study. Therefore, the association between PA and inflammation could not be assessed. Finally, the significance of the VLF component of HRV is unknown. In a separate study, we intend to explore the significance of the VLF component of HRV.
Conclusion In this study, a positive correlation was observed between the VLF component of HRV and PA in stroke
Table 3. Correlation between physical activity and heart rate variability lnHF
lnLF/HF
lnVLF
Physical activity level
24 h
Night time
24 h
Night time
24 h
Night time
Inactivity Light PA Moderate PA
2.21 .19 .13
2.40 .38 .22
.01 .01 .23
2.09 .09 .39
2.68* .67* .80*
2.74* .71* .85*
Abbreviations: HF, high-frequency component; ln, natural logarithm; LF, low-frequency component; PA, physical activity; VLF, very lowfrequency component. Values are Pearson correlation. *Correlation significant at the .05 level.
PHYSICAL ACTIVITY AND HEART RATE VARIABILITY
patients. This finding may indicate that the VLF component of HRV links PA to cardiovascular prognosis. Nevertheless, further research is necessary to evaluate the effects of increasing PA levels on the VLF component of HRV.
843
14.
15.
References 1. Gordon NF, Gulanick M, Costa F, et al. Physical activity and exercise recommendations for stroke survivors: an American Heart Association scientific statement from the Council on Clinical Cardiology, Subcommittee on Exercise, Cardiac Rehabilitation, and Prevention; the Council on Cardiovascular Nursing; the Council on Nutrition, Physical Activity, and Metabolism; and the Stroke Council. Stroke 2004;35:1230-1240. 2. Kasapis C, Thompson PD. The effects of physical activity on serum C-reactive protein and inflammatory markers. J Am Coll Cardiol 2005;45:1563-1569. 3. Kokkinos P, Myers J. Exercise and physical activity: clinical outcomes and applications. Circulation 2010;122: 1637-1648. 4. Ada T, Janice JE, Penelope MB, , et alTeresa SMT. Physical activity correlates with arterial stiffness in communitydwelling individuals with stroke. J Stroke Cerebrovasc Dis 2014;23:259-266. 5. Wannamethee SG, Whincup PH, Rumley A, et al. Interrelationship of interleukin-6, cardiovascular risk factors and the metabolic syndrome among older men. J Thromb Haemost 2007;5:1637-1643. 6. Basic Kes V, Simundic AM, Nikolac N, et al. Pro-inflammatory and anti-inflammatory cytokines in acute ischemic stroke and their relation to early neurological deficit and stroke outcome. Clin Biochem 2008;41:1330-1334. 7. Whiteley W, Jackson C, Lewis S, et al. Association of circulating inflammatory markers with recurrent vascular events after stroke. A prospective cohort study. Stroke 2011;42:10-16. 8. Pavlov VA, Tracey KJ. The vagus nerve and the inflammatory reflex-linking immunity and metabolism. Nat Rev Endocrinol 2012;8:743-754. 9. Thayer JF, Sternberg EM. Neural aspects of immunomodulation: focus on the vagus nerve. Brain Behav Immun 2010;24:1223-1228. 10. Assoumou HG, Pichot V, Barthelemy JC, et al. Metabolic syndrome and short-term and long-term heart rate variability in elderly free of clinical cardiovascular disease: the PROOF study. Rejuvenation Res 2010;13:653-663. 11. Stein PK, Barzilay JI, Chaves PH, et al. Higher levels of inflammatory factors and greater insulin resistance are independently associated with higher heart rate and lower heart rate variability in normoglycemic older individuals: the Cardiovascular Health Study. J Am Geriatr Soc 2008;56:315-321. 12. Janszky I, Ericson M, Lekander M, et al. Inflammatory markers and heart rate variability in women with coronary heart disease. J Intern Med 2004;256:421-428. 13. Lampert R, Bremner JD, Su S, et al. Decreased heart rate variability is associated with higher levels of inflamma-
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
tion in middle-aged men. Am Heart J 2008; 156:759.e1-759.e7. Kanel RV, Orth-Gomer K. Autonomic function and prothrombotic activity in women after an acute coronary event. J Women’s Health 2007;17:1331-1337. Guzzetti S, La Rovere MT, Pinna GD, et al. Different spectral components of 24 h heart rate variability are related to different modes of death in chronic heart failure. Euro Heart J 2005;26:357-362. Hadase M, Azuma A, Zen K, et al. Very low frequency power of heart rate variability is a powerful predictor of clinical prognosis in patients with congestive heart failure. Circ J 2004;68:343-347. Ryan ML, Ogilvie MP, Pereira BM, et al. Heart rate variability is an independent predictor of morbidity and mortality in hemodynamically stable trauma patients. J Trauma 2011;70:1371-1380. G€ unther A, Salzmann I, Nowack S, et al. Heart rate variability-a potential early marker of sub-acute post-stroke infections. Acta Neurol Scand 2012; 126:189-196. Gujjar AR, Sathyaprabha TN, Nagaraja D, et al. Heart rate variability and outcome in acute severe stroke role of power spectral analysis. Neurocrit Care 2004; 1:347-354. Rand D, Eng JJ, Tang PF, et al. How active are people with stroke? Use of accelerometers to assess physical activity. Stroke 2009;40:163-168. Gebruers N, Vanroy C, Truijen S, et al. Monitoring of physical activity after stroke: a systematic review of accelerometry-based measures. Arch Phys Med Rehabil 2010;91:288-297. Haskell WL, Lee IM, Pate RR, et al. Physical activity and public health: updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Circulation 2007; 116:1081-1093. Gando Y, Yamamoto K, Murakami H, et al. Longer time spent in light physical activity is associated with reduced arterial stiffness in older adults. Hypertension 2010; 56:540-546. Task Force. Heart rate variability: standards of measurement, physiological interpretation, and clinical use. Euro Heart J 1996;17:354-381. Tanya W, Julie B. Physical activity in hospitalized stroke patients. Stroke Research and Treatment 2012;13 http://dx.doi.org/10.1155/2012/813765. Ulrika P, Marianne S, Elisabeth T. Cognitive dysfunction and physical activity after stroke: the Gothenburg Cognitive Stroke Study in the elderly. J Stroke Cerebrovasc Dis 2012;21:652-658. Birgit V, Tommy C, Birgitta L, et al. Factors related to performance-based mobility and self-reported physical activity in individuals 1-3 years after stroke: a crosssectional cohort study. J Stroke Cerebrovasc Dis 2013; 22:e426-e434. Carroll SL, Greig CA, Lewis SJ, et al. The use of pedometers in stroke survivors: are they feasible and how well do they detect steps? Arch Phys Med Rehabil 2012; 93:466-470.
Background: The present study aimed to clarify the relationship between high physical activity (PA) and function of the autonomic nervous system, which is important in the prognosis after stroke. We hypothesized a positive association between PA and the very low-frequency (VLF) component of heart rate variability (HRV). Methods: Eight patients participated in this study. PA was measured using an accelerometer, and HRV was measured using a heart rate monitor. Results: A significant and positive relationship was observed between the VLF component of HRV and PA. A significant negative relationship was observed between the VLF component of HRV and the duration of inactivity. No significant relationship was identified between the low-to-high frequency ratio of HRV and between the highfrequency component of HRV and PA. Conclusions: A positive correlation was observed between the VLF component of HRV and PA in stroke patients. Therefore, the VLF component of HRV links PA to cardiovascular prognosis. Key Words: Physical activity—autonomic nervous system—heart rate variability—very low frequency—stroke. Ó 2015 by National Stroke Association
Physical activity (PA) can facilitate the performance of activities of daily living, increase walking speed, improve exercise tolerance, and reduce the risk of cardiovascular disease after stroke.1 Chronic PA reduces resting proinflammatory cytokines such as high-sensitivity C-reactive protein and interleukin-62,3 and arrests the progression of atherosclerosis.3 In community-dwelling individuals with stroke, low PA may contribute to the progression of arterial stiffness.4 Increased proinflammatory cytokine levels have been identified as a risk factor for adverse cardiovascular events5 and associated with poor outcome and mortality after stroke.6,7 The autonomic nervous
From the Department of Rehabilitation Science, Seirei Christopher University, Hamamatsu, Shizuoka, Japan. Received November 14, 2014; accepted November 24, 2014. Address correspondence to Harunobu Usui, MS, RPT, Rehabilitation Science, Seirei Christopher University, 3453 Mikatabarachou, Kitaku, Hamamatsu, Shizuoka 433-8558, Japan. E-mail: 13dr01@g. seirei.ac.jp. 1052-3057/$ - see front matter Ó 2015 by National Stroke Association http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2014.11.026
840
system (ANS) plays an important role in the regulation of proinflammatory responses via the inflammatory reflex.8,9 Night-time and 24-hour heart rate variability (HRV) is associated with the metabolic status.10 Increased proinflammatory cytokine levels have been associated with the very low-frequency (VLF) component of HRV,11-13 which in turn has been associated with metabolic syndrome and recovery after adverse coronary events.10,14 In addition, the VLF component of HRV has been identified as a powerful predictor of clinical prognosis in patients with cardiovascular disease.15,16 In recent research, decreased VLF component of HRV was reported as an independent predictor of mortality and morbidity in hemodynamically stable trauma patients.17 Moreover, the night-time VLF component of HRV may be a predictor of infection after acute stroke18 and of mortality after stroke.19 To clarify the mechanism that PA affects cardiovascular prognosis, in this study, the association between PA and ANS activity was investigated in stroke patients. We hypothesized that high PA is related to higher levels of ANS activity, which is important in the prognosis after
Journal of Stroke and Cerebrovascular Diseases, Vol. 24, No. 4 (April), 2015: pp 840-843
PHYSICAL ACTIVITY AND HEART RATE VARIABILITY
stroke and that high PA is associated with increased VLF component of HRV.
Methods All patients provided informed consent for participation in this study. Ethical approval was obtained from the Ethics Committee of Seirei Christopher University and Omaezaki Municipal Hospital.
Participants The participants of the present study included 8 patients who suffered from ischemic stroke 2-4 months back. All patients were admitted to the comprehensive rehabilitation unit of Omaezaki Municipal Hospital between April and August 2012. The patients were included in this study if they were able to independently walk with or without assistance (e.g., a cane). The exclusion criteria included concomitant cardiovascular disorders affecting the ANS activity, cardiac arrhythmia, medical instability, and insufficient electrocardiographic or PA recording. The participants were volunteers interested in recruitment.
Physical Activity The duration and intensity of PA were measured using a portable accelerometer, which recorded the metabolic equivalents (METs) every 10 seconds. The efficacy of this accelerometer in the assessment of PA levels in stroke patients has been previously demonstrated.20,21 All patients were asked to wear the accelerometer on the nonparetic hip for 24 hours. A physical therapist attached and detached these accelerometers. The resulting data were downloaded to a personal computer for calculation of PA during specified time intervals. PA was defined according to the following equation: METs 3 number of minutes. Values for PA were grouped as follows: 1.1-2.9 METs (light), 3.0-5.9 METs (moderate), and $6.0 METs (vigorous).22 Furthermore, inactive time was calculated as 1440 2 (time spent in light PA 1 moderate PA 1 vigorous PA).23
Heart Rate Variability HRV was measured using a heart rate monitor and analyzed using a software program. Heart rate recording was performed over a period of 24 hours (from 17:00 hours on 1 day to 17:00 hours the next day). The R wave to R wave interval was calculated using a heart rate monitor. Abnormal R wave to R wave signals were automatically retrieved from the program for analysis. Spectral power was calculated within each frequency interval using the following parameters: VLF power 5 .003-.04 Hz, low-frequency (LF) power 5 .04.15 Hz, high-frequency (HF) power 5 .15-.40 Hz, and the ratio of LF-to-HF (LF/HF). VLF, HF, and the LF/HF
841
ratio were transformed by the natural logarithm (ln). These respective HRV components were analyzed over the entire 24 hours of recorded data and all the nighttime recordings (21:00-05:00 hours).
Statistics Pearson correlation coefficients were calculated to evaluate the relationships between PA and HRV. The results are expressed as mean 6 standard deviation. SPSS software (version 19.0; SPSS, Inc, Chicago, IL) was used for statistical analysis.
Results Fourteen stroke patients were enrolled in this study. Two patients were excluded because of inadequate HRV data, and eventually, data for 12 patients were included in this study (age, 67.7 6 14.8 years; 7 males).
Physical Activity Average values for PA are presented in Table 1. Only 3 patients engaged in vigorous PA; therefore, data for vigorous PA were excluded from the analysis. All patients spent the longest time for light activities in their active time. However, all patients spent longer inactivity time than active time.
Heart Rate Variability Average values over 24-hour and night-time values for HRV are summarized in Table 2. LnHF and lnLF/HF of 24-hour values were bigger than night-time values. In contrast, lnVLF of night-time values were bigger than 24-hour values.
Association between Physical Activity and Heart Rate Variability Table 3 presents the correlations between PA and HRV in the study patients. A significant positive relationship was observed between the lnVLF component of HRV and PA (P , .05). Furthermore, a significant negative relationship was observed between the lnVLF component of HRV and inactivity time (P , .05). The relationships of the night-time lnVLF and PA are stronger correlation Table 1. Average levels of physical activity in stroke patients Physical activity levels
Data
Inactivity (min) Light PA (min 3 METs) Moderate PA (min 3 METs) Vigorous PA (min 3 METs)
1059.1 6 144.3 569.1 6 226.5 89.4 6 56.5 1.3 6 2.6
Abbreviations: METs, metabolic equivalents; PA, physical activity. Values are averages 6 standard deviations.
H. USUI AND Y. NISHIDA
842
Table 2. Average of 24-hour and night-time HRV HRV component
24 h
Night time
lnHF lnLF/HF lnVLF
5.38 6 1.21 1.20 6 .68 6.70 6 .73
5.23 6 1.43 1.10 6 .90 6.89 6 .80
Abbreviations: HF, high-frequency component; HRV, heart rate variability; ln, natural logarithm; LF, low-frequency component; VLF, very low-frequency component. Values are averages 6 standard deviations.
than the relationships of the 24-hour VLF and PA. The lnLF/HF ratio and the lnHF component of HRV were not significantly related to PA.
Discussion In the present study, the lnVLF component of HRV was significantly related to PA; however, no significant relationship was observed between the lnLF/HF ratio and the lnHF component of HRV and PA. In general, the HF component of HRV indicates vagal activity, and the LF/ HF ratio indicates sympathetic activity.24 However, it is yet to be clarified what the VLF component of HRV indicates. A few reports have indicated that the VLF component of HRV is a powerful predictor of clinical prognosis in cardiovascular diseases13,16 and that it is associated with chronic inflammation.11-13 Our data support the hypothesis that an association exists between PA and the VLF component of HRV. In this study, high PA was related to higher levels of ANS activity, which is important in the prognosis after stroke. PA can inhibit the progression of arterial stiffness4 and reduce the risk of cardiovascular disease after stroke.2 The results of the present study may indicate that the VLF component of HRV links PA to cardiovascular prognosis. In this study, a stronger relationship was observed between the night-time lnVLF component of HRV and PA compared with that between the 24-hour lnVLF component of HRV and PA. This result was similar to that of a previous report.10 Data collected during the night may
be more stable compared with those collected at other times because the influence of mental stress, exercise, diet, and other factors is eliminated. PA levels are reportedly low in hospitalized stroke patients.25 PAs after stroke were impaired various factors, including cognitive dysfunction.26 Low level of PA was associated with mobility, quality of life, and fall-related self-efficacy.27 Similar to other reports,2-4 PA contributed to health improvement in stroke patients in the present study as well. Therefore, this study provides further evidence that stroke patients should be advised to increase their PA levels.
Study Strength To our knowledge, this is the first study to provide data regarding the VLF component of HRV and to report a positive correlation between this component and PA in stroke patients. The VLF component of HRV is reportedly a powerful predictor of clinical prognosis in patients with cardiovascular diseases.15,16 Thus, the results of this study may encourage stroke patients to increase their PA levels. In future, evaluation of the effects of increasing PA levels may be accomplished using the VLF component of HRV.
Study Limitations This study has some limitations. First, walking speed is often variable in stroke patients. In a previous study, accelerometers were not recommended for use in stroke patients walking at speeds ,.5 m/second.28 In the present study, walking speed exceeded .5 m/second in all patients. Second, inflammatory cytokine levels were not measured in this study. Therefore, the association between PA and inflammation could not be assessed. Finally, the significance of the VLF component of HRV is unknown. In a separate study, we intend to explore the significance of the VLF component of HRV.
Conclusion In this study, a positive correlation was observed between the VLF component of HRV and PA in stroke
Table 3. Correlation between physical activity and heart rate variability lnHF
lnLF/HF
lnVLF
Physical activity level
24 h
Night time
24 h
Night time
24 h
Night time
Inactivity Light PA Moderate PA
2.21 .19 .13
2.40 .38 .22
.01 .01 .23
2.09 .09 .39
2.68* .67* .80*
2.74* .71* .85*
Abbreviations: HF, high-frequency component; ln, natural logarithm; LF, low-frequency component; PA, physical activity; VLF, very lowfrequency component. Values are Pearson correlation. *Correlation significant at the .05 level.
PHYSICAL ACTIVITY AND HEART RATE VARIABILITY
patients. This finding may indicate that the VLF component of HRV links PA to cardiovascular prognosis. Nevertheless, further research is necessary to evaluate the effects of increasing PA levels on the VLF component of HRV.
843
14.
15.
References 1. Gordon NF, Gulanick M, Costa F, et al. Physical activity and exercise recommendations for stroke survivors: an American Heart Association scientific statement from the Council on Clinical Cardiology, Subcommittee on Exercise, Cardiac Rehabilitation, and Prevention; the Council on Cardiovascular Nursing; the Council on Nutrition, Physical Activity, and Metabolism; and the Stroke Council. Stroke 2004;35:1230-1240. 2. Kasapis C, Thompson PD. The effects of physical activity on serum C-reactive protein and inflammatory markers. J Am Coll Cardiol 2005;45:1563-1569. 3. Kokkinos P, Myers J. Exercise and physical activity: clinical outcomes and applications. Circulation 2010;122: 1637-1648. 4. Ada T, Janice JE, Penelope MB, , et alTeresa SMT. Physical activity correlates with arterial stiffness in communitydwelling individuals with stroke. J Stroke Cerebrovasc Dis 2014;23:259-266. 5. Wannamethee SG, Whincup PH, Rumley A, et al. Interrelationship of interleukin-6, cardiovascular risk factors and the metabolic syndrome among older men. J Thromb Haemost 2007;5:1637-1643. 6. Basic Kes V, Simundic AM, Nikolac N, et al. Pro-inflammatory and anti-inflammatory cytokines in acute ischemic stroke and their relation to early neurological deficit and stroke outcome. Clin Biochem 2008;41:1330-1334. 7. Whiteley W, Jackson C, Lewis S, et al. Association of circulating inflammatory markers with recurrent vascular events after stroke. A prospective cohort study. Stroke 2011;42:10-16. 8. Pavlov VA, Tracey KJ. The vagus nerve and the inflammatory reflex-linking immunity and metabolism. Nat Rev Endocrinol 2012;8:743-754. 9. Thayer JF, Sternberg EM. Neural aspects of immunomodulation: focus on the vagus nerve. Brain Behav Immun 2010;24:1223-1228. 10. Assoumou HG, Pichot V, Barthelemy JC, et al. Metabolic syndrome and short-term and long-term heart rate variability in elderly free of clinical cardiovascular disease: the PROOF study. Rejuvenation Res 2010;13:653-663. 11. Stein PK, Barzilay JI, Chaves PH, et al. Higher levels of inflammatory factors and greater insulin resistance are independently associated with higher heart rate and lower heart rate variability in normoglycemic older individuals: the Cardiovascular Health Study. J Am Geriatr Soc 2008;56:315-321. 12. Janszky I, Ericson M, Lekander M, et al. Inflammatory markers and heart rate variability in women with coronary heart disease. J Intern Med 2004;256:421-428. 13. Lampert R, Bremner JD, Su S, et al. Decreased heart rate variability is associated with higher levels of inflamma-
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
tion in middle-aged men. Am Heart J 2008; 156:759.e1-759.e7. Kanel RV, Orth-Gomer K. Autonomic function and prothrombotic activity in women after an acute coronary event. J Women’s Health 2007;17:1331-1337. Guzzetti S, La Rovere MT, Pinna GD, et al. Different spectral components of 24 h heart rate variability are related to different modes of death in chronic heart failure. Euro Heart J 2005;26:357-362. Hadase M, Azuma A, Zen K, et al. Very low frequency power of heart rate variability is a powerful predictor of clinical prognosis in patients with congestive heart failure. Circ J 2004;68:343-347. Ryan ML, Ogilvie MP, Pereira BM, et al. Heart rate variability is an independent predictor of morbidity and mortality in hemodynamically stable trauma patients. J Trauma 2011;70:1371-1380. G€ unther A, Salzmann I, Nowack S, et al. Heart rate variability-a potential early marker of sub-acute post-stroke infections. Acta Neurol Scand 2012; 126:189-196. Gujjar AR, Sathyaprabha TN, Nagaraja D, et al. Heart rate variability and outcome in acute severe stroke role of power spectral analysis. Neurocrit Care 2004; 1:347-354. Rand D, Eng JJ, Tang PF, et al. How active are people with stroke? Use of accelerometers to assess physical activity. Stroke 2009;40:163-168. Gebruers N, Vanroy C, Truijen S, et al. Monitoring of physical activity after stroke: a systematic review of accelerometry-based measures. Arch Phys Med Rehabil 2010;91:288-297. Haskell WL, Lee IM, Pate RR, et al. Physical activity and public health: updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Circulation 2007; 116:1081-1093. Gando Y, Yamamoto K, Murakami H, et al. Longer time spent in light physical activity is associated with reduced arterial stiffness in older adults. Hypertension 2010; 56:540-546. Task Force. Heart rate variability: standards of measurement, physiological interpretation, and clinical use. Euro Heart J 1996;17:354-381. Tanya W, Julie B. Physical activity in hospitalized stroke patients. Stroke Research and Treatment 2012;13 http://dx.doi.org/10.1155/2012/813765. Ulrika P, Marianne S, Elisabeth T. Cognitive dysfunction and physical activity after stroke: the Gothenburg Cognitive Stroke Study in the elderly. J Stroke Cerebrovasc Dis 2012;21:652-658. Birgit V, Tommy C, Birgitta L, et al. Factors related to performance-based mobility and self-reported physical activity in individuals 1-3 years after stroke: a crosssectional cohort study. J Stroke Cerebrovasc Dis 2013; 22:e426-e434. Carroll SL, Greig CA, Lewis SJ, et al. The use of pedometers in stroke survivors: are they feasible and how well do they detect steps? Arch Phys Med Rehabil 2012; 93:466-470.
