Cardiovascular autonomic modulation and activity of carotid baroreceptors at altitude

1.To assess the effects of acute exposure to high altitude on baroreceptor function in man we evaluated the effects of baroreceptor activation on R–R interval and blood pressure control at high altitude. We measured the low-frequency (LF) and high-frequency (HF) components in R–R, non-invasive blood pressure and skin blood flow, and the effect of baroreceptor modulation by 0.1-Hz sinusoidal neck suction. Ten healthy sea-level natives and three high-altitude native, long-term sea-level residents were evaluated at sea level, upon arrival at 4970 ;m and 1 week later. 2.Compared with sea level, acute high altitude decreased R–R and increased blood pressure in all subjects [sea-level natives: R–R from 1002±45 to 775±57 ;ms, systolic blood pressure from 130±3 to 150±8 ;mmHg; high-altitude natives: R–R from 809±116 to 749±47 ;ms, systolic blood pressure from 110±12 to 125±11 ;mmHg (P< 0.05 for all)]. One week later systolic blood pressure was similar to values at sea level in all subjects, whereas R–R remained elevated in sea-level natives. The low-frequency power in R–R and systolic blood pressure increased in sea-level natives [R–R-LF from 47±8 to 65±10% (P< 0.05), systolic blood pressure-LF from 1.7±0.3 to 2.6±0.4 ln-mmHg2 (P< 0.05)], but not in high-altitude natives (R–R-LF from 32±13 to 38±19%, systolic blood pressure-LF from 1.9±0.5 to 1.7±0.8 ln-mmHg2). The R–R-HF decreased in sea-level natives but not in high-altitude natives, and no changes occurred in systolic blood pressure-HF. These changes remained evident 1 week later. Skin blood flow variability and its spectral components decreased markedly at high altitude in sea-level natives but showed no changes in high-altitude natives. Neck suction significantly increased the R–R- and systolic blood pressure-LF in all subjects at both sea level and high altitude. 3.High altitude induces sympathetic activation in sea-level natives which is partially counteracted by active baroreflex. Despite long-term acclimatization at sea level, high-altitude natives also maintain active baroreflex at high altitude but with lower sympathetic activation, indicating a persisting high-altitude adaptation which may be genetic or due to baroreflex activity not completely lost by at least 1 year's sea-level residence.

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Synchronous and baroceptor-sensitive oscillations in skin microcirculation: evidence for central autonomic control

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1997.273.4.h1867 ◽

1997 ◽

Vol 273 (4) ◽

pp. H1867-H1878 ◽

Cited By ~ 30

Author(s):

Luciano Bernardi ◽

Daniel Hayoz ◽

René Wenzel ◽

Claudio Passino ◽

Alessandro Calciati ◽

...

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Skin Blood Flow ◽

Muscle Sympathetic Nerve Activity ◽

Low Frequency ◽

Doppler Flowmetry ◽

Sympathetic Modulation ◽

Baroreflex Stimulation ◽

The Relationship ◽

Spontaneous Fluctuations

To determine whether skin blood flow is local or takes part in general regulatory mechanisms, we recorded laser-Doppler flowmetry (LDF; left and right index fingers), blood pressure, muscle sympathetic nerve activity (MSNA), R-R interval, and respiration in 10 healthy volunteers and 3 subjects after sympathectomy. We evaluated 1) the synchronism of LDF fluctuations in two index fingers, 2) the relationship with autonomically mediated fluctuations in other signals, and 3) the LDF ability to respond to arterial baroreflex stimulation (by neck suction at frequencies from 0.02 to 0.20 Hz), using spectral analysis (autoregressive uni- and bivariate, time-variant algorithms). Synchronous LDF fluctuations were observed in the index fingers of healthy subjects but not in sympathectomized patients. LDF fluctuations were coherent with those obtained for blood pressure, MSNA, and R-R interval. LDF fluctuations were leading blood pressure in the low-frequency (LF; 0.1 Hz) band and lagging in the respiratory, high-frequency (HF; ∼0.25 Hz) band, suggesting passive “downstream” transmission only for HF and “upstream” transmission for LF from the microvessels. LDF fluctuations were responsive to sinusoidal neck suction up to 0.1 Hz, indicating response to sympathetic modulation. Skin blood flow thus reflects modifications determined by autonomic activity, detectable by frequency analysis of spontaneous fluctuations.

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Adenosine receptor-dependent signaling is not obligatory for normobaric and hypobaric hypoxia-induced cerebral vasodilation in humans

Journal of Applied Physiology ◽

10.1152/japplphysiol.00840.2016 ◽

2017 ◽

Vol 122 (4) ◽

pp. 795-808 ◽

Cited By ~ 13

Author(s):

Ryan L. Hoiland ◽

Anthony R. Bain ◽

Michael M. Tymko ◽

Mathew G. Rieger ◽

Connor A. Howe ◽

...

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Blood Flow ◽

Cerebral Blood Flow ◽

High Altitude ◽

Sea Level ◽

Adenosine Receptor ◽

Hypobaric Hypoxia ◽

End Tidal ◽

Double Blinded

Hypoxia increases cerebral blood flow (CBF) with the underlying signaling processes potentially including adenosine. A randomized, double-blinded, and placebo-controlled design, was implemented to determine if adenosine receptor antagonism (theophylline, 3.75 mg/Kg) would reduce the CBF response to normobaric and hypobaric hypoxia. In 12 participants the partial pressures of end-tidal oxygen ([Formula: see text]) and carbon dioxide ([Formula: see text]), ventilation (pneumotachography), blood pressure (finger photoplethysmography), heart rate (electrocardiogram), CBF (duplex ultrasound), and intracranial blood velocities (transcranial Doppler ultrasound) were measured during 5-min stages of isocapnic hypoxia at sea level (98, 90, 80, and 70% [Formula: see text]). Ventilation, [Formula: see text] and [Formula: see text], blood pressure, heart rate, and CBF were also measured upon exposure (128 ± 31 min following arrival) to high altitude (3,800 m) and 6 h following theophylline administration. At sea level, although the CBF response to hypoxia was unaltered pre- and postplacebo, it was reduced following theophylline ( P < 0.01), a finding explained by a lower [Formula: see text] ( P < 0.01). Upon mathematical correction for [Formula: see text], the CBF response to hypoxia was unaltered following theophylline. Cerebrovascular reactivity to hypoxia (i.e., response slope) was not different between trials, irrespective of [Formula: see text]. At high altitude, theophylline ( n = 6) had no effect on CBF compared with placebo ( n = 6) when end-tidal gases were comparable ( P > 0.05). We conclude that adenosine receptor-dependent signaling is not obligatory for cerebral hypoxic vasodilation in humans. NEW & NOTEWORTHY The signaling pathways that regulate human cerebral blood flow in hypoxia remain poorly understood. Using a randomized, double-blinded, and placebo-controlled study design, we determined that adenosine receptor-dependent signaling is not obligatory for the regulation of human cerebral blood flow at sea level; these findings also extend to high altitude.

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Alterations of Cardiovascular Complexity during Acute Exposure to High Altitude: A Multiscale Entropy Approach

Entropy ◽

10.3390/e21121224 ◽

2019 ◽

Vol 21 (12) ◽

pp. 1224 ◽

Cited By ~ 1

Author(s):

Andrea Faini ◽

Sergio Caravita ◽

Gianfranco Parati ◽

Paolo Castiglioni

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

High Altitude ◽

Sea Level ◽

Low Frequency ◽

Sample Entropy ◽

Significant Loss ◽

Multiscale Entropy ◽

Rehabilitation Protocols ◽

Chemoreflex Sensitivity

Stays at high altitude induce alterations in cardiovascular control and are a model of specific pathological cardiovascular derangements at sea level. However, high-altitude alterations of the complex cardiovascular dynamics remain an almost unexplored issue. Therefore, our aim is to describe the altered cardiovascular complexity at high altitude with a multiscale entropy (MSE) approach. We recorded the beat-by-beat series of systolic and diastolic blood pressure and heart rate in 20 participants for 15 min twice, at sea level and after arrival at 4554 m a.s.l. We estimated Sample Entropy and MSE at scales of up to 64 beats, deriving average MSE values over the scales corresponding to the high-frequency (MSEHF) and low-frequency (MSELF) bands of heart-rate variability. We found a significant loss of complexity at heart-rate and blood-pressure scales complementary to each other, with the decrease with high altitude being concentrated at Sample Entropy and at MSEHF for heart rate and at MSELF for blood pressure. These changes can be ascribed to the acutely increased chemoreflex sensitivity in hypoxia that causes sympathetic activation and hyperventilation. Considering high altitude as a model of pathological states like heart failure, our results suggest new ways for monitoring treatments and rehabilitation protocols.

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Effect of local cold provocation on systolic blood pressure and skin blood flow in the finger

Clinical Physiology ◽

10.1046/j.1365-2281.2001.00364.x ◽

2001 ◽

Vol 21 (5) ◽

pp. 570-575 ◽

Cited By ~ 17

Author(s):

S. Bornmyr ◽

J. Castenfors ◽

E. Evander ◽

G. Olsson ◽

U. Hjortsberg ◽

...

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Systolic Blood Pressure ◽

Skin Blood Flow ◽

Cold Provocation

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Long-term time-related predictivity of coronary events as a function of a single measurement of serum cholesterol and systolic blood pressure

Acta Cardiologica ◽

10.2143/ac.55.2.2005726 ◽

2000 ◽

Vol 55 (2) ◽

pp. 87-93 ◽

Cited By ~ 9

Author(s):

Alessandro MENOTTI ◽

Mariapaola LANTI ◽

Paolo Emilio PUDDU

Keyword(s):

Blood Pressure ◽

Systolic Blood Pressure ◽

Serum Cholesterol ◽

Single Measurement ◽

Coronary Events

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Intradialytic systolic blood pressure variation can predict long-term mortality in patients on maintenance hemodialysis

International Urology and Nephrology ◽

10.1007/s11255-020-02701-w ◽

2021 ◽

Author(s):

Jinbo Yu ◽

Xiaohong Chen ◽

Yaqiong Wang ◽

Zhonghua Liu ◽

Bo Shen ◽

...

Keyword(s):

Blood Pressure ◽

Systolic Blood Pressure ◽

Pressure Variation ◽

Maintenance Hemodialysis ◽

Blood Pressure Variation ◽

Long Term Mortality

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Long-term effects (>24 months) of multiple lifestyle intervention on major cardiovascular risk factors among high risk subjects: a meta-analysis

European Journal of Preventive Cardiology ◽

10.1093/eurjpc/zwab061.253 ◽

2021 ◽

Vol 28 (Supplement_1) ◽

Author(s):

H Bergum ◽

I Sandven ◽

TO Klemsdal

Keyword(s):

Risk Factors ◽

Blood Pressure ◽

Cardiovascular Risk ◽

Systolic Blood Pressure ◽

Total Cholesterol ◽

Cardiovascular Risk Factors ◽

Lifestyle Intervention ◽

Small Study ◽

Long Term Effects

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): The Norwegian health department Background The evidence of the long-term effects of multiple lifestyle intervention on cardiovascular risk is uncertain. We aimed to summarize the evidence from randomized clinical trials examining the efficacy of lifestyle intervention on major cardiovascular risk factors in subjects at high cardiovascular risk. Methods Eligible trials investigated the impact of lifestyle intervention versus usual care with minimum 24 months follow-up, reporting more than one major cardiovascular risk factor. A literature search updated April 15, 2020 identified 12 eligible studies. The results from individual trials were combined using fixed and random effect models, using the standardized mean difference (SMD) to estimate effect sizes. Small-study effect was evaluated, and heterogeneity between studies examined by subgroup and meta-regression analyses considering patient- and study-level variables. Results Small-study effect was not identified. Lifestyle intervention reduced systolic blood pressure modestly with an estimated SMD of -0.13, 95% confidence interval (CI): -0.21 to -0.04, with moderate heterogeneity (I² = 59%), corresponding to a mean difference of approximately 2 mmHg (MD = -1.86, 95% CI: -3.14 to -0.57, p = 0.0046). This effect disappeared in the subgroup of trials judged at low risk of bias (SMD = 0.02, 95% CI: -0.08 to 0.11). For the outcome total cholesterol SMD was -0.06, 95% CI: -0.13 to 0.00, with no heterogeneity (I² = 0%), indicating no effect of the intervention. Conclusion Lifestyle intervention resulted in only a modest effect on systolic blood pressure and no effect on total cholesterol after 24 months. Further lifestyle trials should consider the challenge of maintaining larger long-term benefits to ensure impact on cardiovascular outcomes.

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Long term habitual vigorous physical activity is associated with lower visit-to-visit systolic blood pressure variability

American Journal of Hypertension ◽

10.1093/ajh/hpaa198 ◽

2020 ◽

Author(s):

Xiaoyong Xu ◽

Xianghong Meng ◽

Shin-ichi Oka

Keyword(s):

Physical Activity ◽

Blood Pressure ◽

Standard Deviation ◽

Systolic Blood Pressure ◽

Blood Pressure Variability ◽

Vigorous Physical Activity ◽

Systolic Blood Pressure Variability ◽

Average Real Variability ◽

Post Hoc

Abstract Objective Our work aimed to investigate the association between vigorous physical activity and visit-to-visit systolic blood pressure variability (BPV). Methods We conducted a post hoc analysis of SPRINT (Systolic Blood Pressure Intervention Trial), a well-characterized cohort of participants randomized to intensive (<120 mmHg) or standard (<140 mmHg) SBP targets. We assessed whether patients with hypertension who habitually engage in vigorous physical activity would have lower visit-to-visit systolic BPV compared with those who do not engage in vigorous physical activity. Visit-to-visit systolic BPV was calculated by standard deviation (SD), average real variability (ARV), and standard deviation independent of the mean (SDIM) using measurements taken during the 1-, 2-, 3-, 6-, 9- and 12-month study visits. A medical history questionnaire assessed vigorous physical activity, which was divided into three categories according to the frequency of vigorous physical activity. Results A total of 7571 participants were eligible for analysis (34.8% female, mean age 67.9±9.3 years). During a follow-up of 1-year, vigorous physical activity could significantly reduce SD, ARV, and SDIM across increasing frequency of vigorous physical activity. There were negative linear trends between frequency of vigorous physical activity and visit-to-visit systolic BPV. Conclusions Long-term engagement in vigorous physical activity was associated with lower visit-to-visit systolic BPV.

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