Blunted cardiac autonomic responsiveness to hypoxemic stress in healthy older adults

[Improving parasympathetic functioning to contain the inflammatory response of COVID-19 infection]

COVID-19 infection results in an unrestrained inflammatory reaction in serious cases. The autonomic nervous system (ANS), in particular the parasympathetic branch, helps to regulate the inflammatory response. A dysfunction of this branch, frequent in people at risk of developing COVID-19, favours a pro-inflammatory effect. Reinforcing and stimulating the parasympathetic ANS is possible and accessible to paramedical and medical professionals.

Age-related reflex responses from peripheral and central chemoreceptors in healthy men

Objective

The study aimed: (i) to characterize reflex responses from peripheral and central chemoreceptors in different age groups of healthy men (<50 years old vs ≥50 years old) and, (ii) to assess, within these groups, whether there is any relationship between ventilatory and hemodynamic responses from chemoreceptors and indices of autonomic nervous system (ANS).

Methods

Peripheral chemoreflex sensitivity was assessed by the transient hypoxia method and respiratory, heart rate (HR) and blood pressure responses were calculated. Central chemoreflex sensitivity was assessed by the rebreathing method and respiratory response was calculated. ANS was assessed using heart rate variability indices and baroreflex sensitivity (BRS).

Results

Sixty-seven healthy men were divided into 2 groups: <50 years (n = 38, mean age: 32 ± 10 years) and ≥50 years (n = 29, mean age: 61 ± 8 years). There were no differences in respiratory response from central and peripheral chemoreceptors between the older and younger groups of healthy males. We found a significantly different pattern of hemodynamic responses from peripheral chemoreceptors between the older and the younger groups. The former expressed attenuated HR acceleration and exaggerated blood pressure increase in response to transient hypoxia. Blunted HR response was related to reduced BRS and sympathovagal imbalance characterized by reduced vagal tone. Blood pressure responses seemed to be independent of sympathovagal balance and BRS.

Interpretation

Ageing impacts hemodynamic rather than respiratory response from chemoreceptors. Impaired arterial baroreflex and sympathovagal imbalance related to ageing may contribute to decreased heart rate response, but not to increased blood pressure response from peripheral chemoreceptors.

Autonomic response to a visceral stressor is dysregulated in irritable bowel syndrome and correlates with duration of disease

BACKGROUND

Previous studies reported altered autonomic nervous system (ANS) responses in irritable bowel syndrome (IBS) at baseline and to colonic balloon distension. This study examined heart rate variability (HRV) and plasma catecholamines as an index of ANS responsiveness in IBS during flexible sigmoidoscopy (FS) and explored associations of HRV with clinical measures.

METHODS

Rome III-positive IBS patients and healthy controls completed questionnaires measuring gastrointestinal and psychological symptoms. Heart rate variability measures were calculated using electrocardiogram (ECG) data at rest and during FS. Plasma catecholamines were measured before and after the FS. Linear mixed effects models were used to compare HRV with IBS status and IBS duration across six time points. Significance was assessed at the 0.05 level.

KEY RESULTS

Thirty-six IBS patients (53% F, mean age 37.89) and 31 controls (58% F, mean age 37.26) participated. After adjusting for age, sex, body mass index, and current anxiety symptoms, IBS patients had a non-significant lower cardiovagal tone (P = 0.436) and higher cardiosympathetic balance (P = 0.316) at rest. During FS, controls showed a transient increase in cardiosympathetic balance and decrease in cardiovagal tone. However, IBS patients had significantly less cardiosympathetic and cardiovagal responsiveness both leading up to (P = 0.003, P = 0.005) and following (P = 0.001) this stimulus. Those with longer duration of disease had less cardiosympathetic (P = 0.014) and cardiovagal (P = 0.009) responsiveness than those with shorter duration. No differences in catecholamines between IBS and controls were found.

CONCLUSIONS & INFERENCES

Irritable bowel syndrome demonstrated dysregulated ANS responses to a visceral stressor which could be related to disease duration. Therefore, autonomic dysregulation is an objective physiologic correlate of IBS.

Fractal properties of human heart period variability: physiological and methodological implications

Fractal frequency scaling of heart period variability is used as a concise index of overall cardiac control. However, no prior study has assessed within-individual reproducibility of fractal indices of heart period, or reported how the estimated indices respond to autonomic blockade. Therefore, we examined fractal properties of the heart period from ten young, healthy individuals during three separate experimental sessions under control (saline) conditions and twice under combined autonomic blockade (atenolol and atropine sulfate) conditions. Under each condition, R-R intervals were recorded with the subject in the supine and the 40 deg upright tilt positions during 20 min of controlled breathing in each position. We calculated the fractal scaling exponent using detrended fluctuation analysis and estimated confidence intervals of the scaling exponents for each R-R interval time series within each individual. In the control condition, upright tilt significantly increased the scaling exponents (from 0.73 +/- 0.11 (+/-S.D., session 1), 0.72 +/- 0.10 (session 2) and 0.75 +/- 0.13 (session 3) to 0.82 +/- 0.12, 0.82 +/- 0.11 and 0.84 +/- 0.10; Student's paired t-test, t = 2.79, P = 0.02; t = 2.80, P = 0.02; and t = 2.07, P = 0.07). However, neither the absolute scaling exponents nor their change in response to upright tilt were reproducible (Lin's concordance coefficient less than 0.9, P > 0.1 for all comparisons). Following autonomic blockade, the scaling exponents were significantly increased (supine: 1.08 +/- 0.13 and 1.08 +/- 0.14; tilt: 1.07 +/- 0.21 and 1.08 +/- 0.14) for both experimental sessions (two-way repeated-measures ANOVA; F(17,1) = 40.89, P < 0.001 and F(17,1) = 42.72, P < 0.001) regardless of position. However, within individuals, the scaling exponents failed to distinguish between control and blockade for half of the subjects in at least one experimental session. Thus, fractal scaling exponents are not reproducible within individuals and do not reliably reflect the autonomic mechanisms responsible for heart period variability. In fact, data from combined blockade suggest that physiological effects of autonomic outflow may mask intrinsic fractal behaviour of the sinoatrial node.

Aging elevates basal adenosine monophosphate-activated protein kinase (AMPK) activity and eliminates hypoxic activation of AMPK in mouse liver

Despite the central role of adenosine monophosphate-activated protein kinase (AMPK) in the cellular stress response, it is unknown whether age-related changes in AMPK activity play a role in the diminished stress tolerance that is characteristic of aging. To address this question, we determined in the mouse liver how normal aging affects 1) basal AMPK activity, and 2) the degree to which AMPK activity is increased by in vivo hypoxia. We found that the basal activity of AMPK alpha1, but not alpha2, was higher in livers from 24-month-old mice compared to those from 5-month-old mice. Furthermore, while hypoxia elevated AMPK alpha1 and alpha2 activities in livers from 5-month-old mice, hypoxia failed to increase the activity of either isoform of AMPK in 24-month-old mice. These findings suggest that age-associated changes in hepatic AMPK activity may play a role in the physiological changes that occur in the liver with normal aging.