Human cardiac autonomic responses to head-up tilting during 72-h starvation

Brown, Stephen; Bryant, Marsha; Mündel, Toby; Stannard, Stephen R.

doi:10.1007/s00421-011-2207-6

Cited by 4 publications

(2 citation statements)

References 30 publications

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“…The only purported sympathetic HRV marker that showed a statistically significant increase in response to both stressors was the LF spectral component when expressed as LF (nu). Statistically significant increases in LF power, when expressed in normalized units, have been reported in many previous studies for both the Stroop test [68] and head-up tilt [60-65, 76, 81, 82]. With regard to the absolute units of LF, a small number of studies have reported a significant increase in LF (ms 2 ) in response to orthostatic stress [62, 66, 76].…”

Section: Discussionmentioning

confidence: 99%

Validity of Commonly Used Heart Rate Variability Markers of Autonomic Nervous System Function

et al. 2019

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Background: Despite strong reservations regarding the validity of a number of heart rate variability (HRV) measures, these are still being used in recent studies. Aims: We aimed to compare the reactivity of ostensible sympathetic HRV markers (low and very low frequency [LF and VLF]) to that of electrodermal activity (EDA), an exclusively sympathetic marker, in response to cognitive and orthostatic stress, investigate the possibility of LF as a vagal-mediated marker of baroreflex modulation, and compare the ability of HRV markers of parasympathetic function (root mean square of successive differences [RMSSD] and high frequency [HF]) to quantify vagal reactivity to cognitive and orthostatic stress. Results: None of the purported sympathetic HRV markers displayed a reactivity that correlated with electrodermal reactivity. LF (ms²) reactivity correlated with the reactivity of both RMSSD and HF during baroreflex modulation. RMSSD and HF indexed the reactivity of the parasympathetic nervous system under conditions of normal breathing; however, RMSSD performed better as a marker of vagal activity when the task required breathing changes. Conclusions: Neither LF (in ms² or normalized units [nu]) nor VLF represent cardiac sympathetic modulation of the heart. LF (ms²) may reflect vagally mediated baroreflex cardiac effects. HRV linear analysis therefore appears to be restricted to the determination of vagal influences on heart rate. With regard to HRV parasympathetic markers, this study supports the suggestion that HRV frequency domain analyses, such as HF, should not be used as an index of vagal activity in study tasks where verbal responses are required, as these responses may induce respiratory changes great enough to distort HF power.

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Section: Discussionmentioning

confidence: 99%

Validity of Commonly Used Heart Rate Variability Markers of Autonomic Nervous System Function

et al. 2019

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“…Moreover, a 3‐month weight reduction treatment, comprised of 1,000‐Kcal hypocaloric diet with exercise, did not alter the frequency of positive results of HUT in obese patients, while reduced DBP at 1 min of HUT, suggesting an impaired vasoconstriction during orthostatic stress . Furthermore, increased OI, as indicated by greater HR response during HUT, was shown in two studies, after water‐only fast for 72 h and after 4 weeks of Ramadan fasting respectively . An important limitation of the studies evaluating the effects of hypocaloric diet on orthostatic tolerance was that they did not mention whether daily sodium intake decreased during hypocaloric diet.…”

Section: The Effects Of Body Weight Status On Orthostatic Intolerancementioning

confidence: 99%

The effects of body weight status on orthostatic intolerance and predisposition to noncardiac syncope

Christou

Kiortsis

2017

Obesity Reviews

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Orthostatic intolerance (OI) is frequently the mechanism underlying the occurrence of noncardiac syncope (NCS) and is associated with substantial risk for injury. Body weight status appears to be a modifier of orthostatic responses and possibly influences the propensity to NCS. The majority of cross-sectional studies have found that the lower the body mass index (BMI) the greater the predisposition to OI is, accompanied with both down-regulation of sympathetic nervous system activity and up-regulation of parasympathetic nervous system activity. These changes appear to occur across the whole spectrum of BMI values from underweight to obesity, while they may be associated more strongly with central body fat than total body fat. Weight loss following bariatric surgery has been consistently found to increase OI, attributed first to the effects of weight loss per se, second to the specific type of surgical procedure and third to the potential postoperative autonomic neuropathy due to vitamin deficiency. The increased OI following bariatric surgery renders this intervention not easily tolerable for the affected individuals, mandating increased fluid and salt intake, pharmacological measures or surgical adjustments to attenuate OI. All future studies investigating orthostatic responses and NCS should implement a matching of the population arms for BMI and ideally for body fat.

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Acute fasting reduces tolerance to progressive central hypovolemia in humans

Gonzalez,

Cooke

2024

Journal of Applied Physiology

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Potential health benefits of an acute fast include reductions in blood pressure and increases in vagal cardiac control. These purported health benefits could put fasted humans at risk for cardiovascular collapse when exposed to central hypovolemia. The purpose of this study was to test the hypothesis that an acute 24-hour fast (vs 3-hours postprandial) would reduce tolerance to central hypovolemia induced via lower body negative pressure (LBNP). We measured blood ketones (β-OHB) to confirm a successful fast (N=18). We recorded the ECG, beat-to-beat arterial pressure, muscle sympathetic nerve activity (MSNA; N=7), middle cerebral artery blood velocity (MCAv), and forearm blood flow. Following a 5-min baseline, LBNP was increased by 15 mmHg until -60 mmHg and then increased by 10 mmHg every 5-min in a stepwise manner until onset of presyncope. Data are expressed as means ± SE. P-values ≤ 0.05 were considered statistically significant. β-OHB increased (β-OHB; 0.12±.04 fed vs. 0.47±.11, p<0.01 mmol/L fast). Tolerance to central hypovolemia was decreased by ~10% in the fasted condition measured via total duration of negative pressure (1370 89 fed vs. 1229±94 s fast, p=0.04), and was negatively associated with fasting blood ketones (R =-0.542, P = 0.02). During LBNP, heart rate and MSNA increased similarly, but in the fasted condition forearm vascular resistance was significantly reduced. Our results suggest that acute fasting reduces tolerance to central hypovolemia by blunting increases in peripheral resistance, indicating that prolonged fasting may hinder an individual's ability to compensate to a loss of blood volume.

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Human cardiac autonomic responses to head-up tilting during 72-h starvation

Cited by 4 publications

References 30 publications

Validity of Commonly Used Heart Rate Variability Markers of Autonomic Nervous System Function

Validity of Commonly Used Heart Rate Variability Markers of Autonomic Nervous System Function

The effects of body weight status on orthostatic intolerance and predisposition to noncardiac syncope

Acute fasting reduces tolerance to progressive central hypovolemia in humans

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