Alterations in autonomic nervous control of heart rate among tourists at 2700 and 3700m above sea level

Kanai, Masaki; Nishihara, Fumio; Shiga, Tatsuya; Shimada, Hitoshi; Saito, Shigeru

doi:10.1580/1080-6032(2001)012[0008:aianco]2.0.co;2

Cited by 66 publications

(51 citation statements)

References 26 publications

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“…During the hypoxic intervals, there was a substantial decrease in rMSSD, which supports the findings of other researchers (7,15,16,21). What was interesting, however, was the large variation in the individual HRV response to the IHE intervals (see Fig.…”

Section: Discussionsupporting

confidence: 90%

The effect of short-term intermittent hypoxic exposure on heart rate variability in a sedentary population

Lizamore¹,

Kathiravel²,

Elliott³

et al. 2016

Acta Physiologica Hungarica

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While the effects of instantaneous, single-bout exposure to hypoxia have been well researched, little is known about the autonomic response during, or as an adaptation to, repeated intermittent hypoxic exposure (IHE) in a sedentary population. Resting heart rate variability (HRV) and exercise capacity was assessed in 16 participants (8 receiving IHE, [Hyp] and 8 receiving a placebo treatment [C]) before and after a 4-week IHE intervention. Heart rate variability was also measured during an IHE session in the last week of the intervention. Post-intervention, the root mean squared successive difference (rMSSD) increased substantially in Hyp (71.6 ± 52.5%, mean change ± 90% confidence limits) compared to C suggesting an increase in vagal outflow. However, aside from a likely decrease in submaximal exercise heart rate in the Hyp group (-5.0 ± 6.4%) there was little evidence of improved exercise capacity. During the week 4 IHE measurement, HRV decreased during the hypoxic exposure (reduced R-R interval: -7.5 ± 3.2%; and rMSSD: -24.7 ± 17.3%) suggesting a decrease in the relative contribution of vagal activity. In summary, while 4 weeks of IHE is unlikely to improve maximal exercise capacity, it may be a useful means of increasing HRV in people unable to exercise.Keywords: autonomic nervous system, sedentary lifestyle, interval hypoxia, simulated altitude, physical fitness, health Heart rate variability (HRV) is the analysis of the variation in the beat to beat intervals in the heart rhythm, which reflects the autonomic nervous system (ANS) innervation on the sinus node (25). Heart rate variability is also responsive to the changes in the ANS associated with external stimuli such as real or simulated altitude (21). For example, an initially sharp increase in sympathetic activity is observed upon arrival at altitude (7, 28), which gradually declines through the acclimatization process (14, 23). The reduction in HRV is largely due to a reduction in the parasympathetic drive at the sinus node during hypoxia, the mechanism behind which has been well described by Roche et al. (20). The recovery of HRV to baseline levels upon return to normoxic ambient air depends on the length and severity of the initial exposure. That is, after 12 hours of continuous hypoxic exposure, a pronounced (dampened) effect on HRV is still evident an hour after returning to normoxic ambient air (7), but after a brief hypoxic exposure of 15 min, recovery is almost immediate (20).

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Section: Discussionsupporting

confidence: 90%

The effect of short-term intermittent hypoxic exposure on heart rate variability in a sedentary population

Lizamore¹,

Kathiravel²,

Elliott³

et al. 2016

Acta Physiologica Hungarica

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“…Increased sympathetic activity is a part of the integrated physiological response to a hypoxic stimulus (10,31). In the present study, we observed, in association with acute hypobaric hypoxia, an increase in heart rate, a reduction in R-R variability, and a relative increase of LF RR NU in asymptomatic subjects, consistent with a sympathetic predominance in the neural inputs to the heart and in agreement with previous studies conducted at high altitude (2,12,13). Little is known about the effect of AMS on the autonomic cardiovascular regulation.…”

Section: Cardiovascular Variability and Amssupporting

confidence: 93%

“…Although the HF rhythm primarily reflects the respirationdriven vagal modulation of sinus rhythm (32a), the nonrespiratory LF rhythm appears to have a widespread neural genesis (26) and, in normalized units (NU), apparently mainly reflects the sympathetic modulation of the heart (23, 26, 32a), as well as the baroreflex responsiveness to the beat-to-beat variations in arterial blood pressure (BP) (30). During exposure to high altitude, R-R variability is reduced with a relative increase in the LF component (2,12,13), suggesting an increased sympathetic modulation of the sinus node in response to hypobaric hypoxia. Little is known about whether this pattern is influenced and/or modified by AMS.…”

mentioning

confidence: 99%

Autonomic cardiovascular regulation in subjects with acute mountain sickness

Lanfranchi¹,

Colombo²,

Cremona³

et al. 2005

American Journal of Physiology-Heart and Circulatory Physiology

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The aims of this study were 1) to evaluate whether subjects suffering from acute mountain sickness (AMS) during exposure to high altitude have signs of autonomic dysfunction and 2) to verify whether autonomic variables at low altitude may identify subjects who are prone to develop AMS. Forty-one mountaineers were studied at 4,559-m altitude. AMS was diagnosed using the Lake Louise score, and autonomic cardiovascular function was explored using spectral analysis of R-R interval and blood pressure (BP) variability on 10-min resting recordings. Seventeen subjects (41%) had AMS. Subjects with AMS were older than those without AMS (P Ͻ 0.01). At high altitude, the lowfrequency (LF) component of systolic BP variability (LFSBP) was higher (P ϭ 0.02) and the LF component of R-R variability in normalized units (LFRRNU) was lower (P ϭ 0.001) in subjects with AMS. After 3 mo, 21 subjects (43% with AMS) repeated the evaluation at low altitude at rest and in response to a hypoxic gas mixture. LFRRNU was similar in the two groups at baseline and during hypoxia at low altitude but increased only in subjects without AMS at high altitude (P Ͻ 0.001) and did not change between low and high altitude in subjects with AMS. Conversely, LFSBP increased significantly during short-term hypoxia only in subjects with AMS, who also had higher resting BP (P Ͻ 0.05) than those without AMS. Autonomic cardiovascular dysfunction accompanies AMS. Marked LFSBP response to short-term hypoxia identifies AMS-prone subjects, supporting the potential role of an exaggerated individual chemoreflex vasoconstrictive response to hypoxia in the genesis of AMS.hypoxia; autonomic nervous system; heart rate; blood pressure ACUTE MOUNTAIN SICKNESS (AMS) is a complex syndrome characterized by headache, gastrointestinal symptoms, weakness, insomnia, and certain neurological signs, including ataxia and changes in mental status (1). It may occur in subjects ascending to Ͼ2,500 m and is reported in 53% of those at Ͼ4,000-m altitude (6,22).AMS is generally harmless and transient but may occasionally progress to the more serious life-threatening cerebral and pulmonary forms of mountain sickness, i.e., high-altitude cerebral and pulmonary edema (1, 6).The exact mechanism causing AMS is unknown, although the prevailing hypothesis points to a process within the central nervous system (1), possibly an altered adaptation to the neurohumoral and hemodynamic adjustments during hypoxia (8). A marked increase in peripheral sympathetic activity is a common feature of mountain sickness (4, 11) and has also been suggested to contribute to the genesis of high-altitude pulmonary edema (4). Whether autonomic hyperactivation may play a role in the genesis of AMS is not known.The autonomic nervous system plays a role in the modulation of the oscillatory behavior of the cardiovascular system (23, 32a). Spectral analysis of variability in the R-R interval is a recognized tool that allows quantification of the oscillatory components, which in short-term recordings appear mainly organized...

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“…1,2 Sympathetic overactivity with a relative reduction of parasympathetic activity has been found in untrained subjects. 3 Additionally, increased sympathetic activity occurs during exercise and much more so in untrained subjects. Furthermore, decreased baroreceptor activity has been demonstrated in healthy subjects at altitudes of approximately 4,500 m. 1 There is evidence that impaired autonomic function is associated with a significant risk for ventricular arrhythmias and sudden death in healthy subjects, 4 as well as in patients after myocardial infarction (MI).…”

mentioning

confidence: 99%

Autonomic and Cardiovascular Effects of Acute High Altitude Exposure After Myocardial Infarction and in Normal Volunteers

Messerli‐Bürgy

Meyer

Steptoe³

et al. 2009

Circ J

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Background: High sympathetic tone creates a significant risk for ventricular arrhythmias and sudden death, which can especially affect patients after a myocardial infarction (MI) when exercising in a hypoxic environment. Methods and Results: The 16 patients after MI and 10 normal volunteers (NV) underwent a 1-day trip from low altitude (540 m, Bern) to high altitude (3,564 m Jungfraujoch, Swiss Alps). Autonomic function under resting and mental stress conditions at low and high altitude was assessed. MI patients demonstrated a significantly lower stroke volume (P<0.05) at rest compared with the NV at low as well as high altitude. High altitude exposure was accompanied by higher low-frequency/high-frequency values in the MI patients compared with NV (P<0.01). Following mental stress, MI patients failed to show the normal return to resting values at high altitude, suggesting sustained sympathetic and diminished parasympathetic activation during post-stress recovery. Conclusions: Although all MI patients were either on β-blockers or AII inhibitors, they showed higher sympathetic activity during exposure to high altitude compared with NV. In addition, the respective parasympathetic tone was reduced, especially during recovery. This puts patients after MI at an increased risk for cardiac arrhythmias and they should be advised of this if going to high altitudes. (Circ J 2009; 73: 1485 -1491

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Alterations in autonomic nervous control of heart rate among tourists at 2700 and 3700m above sea level

Cited by 66 publications

References 26 publications

The effect of short-term intermittent hypoxic exposure on heart rate variability in a sedentary population

The effect of short-term intermittent hypoxic exposure on heart rate variability in a sedentary population

Autonomic cardiovascular regulation in subjects with acute mountain sickness

Autonomic and Cardiovascular Effects of Acute High Altitude Exposure After Myocardial Infarction and in Normal Volunteers

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