Development and evaluation of new blood pressure and heart rate signal analysis techniques to assess orthostatic hypotension and its subtypes

Prefrontally modulated vagal neuroimmunomodulation is associated with telomere length

Background

Accumulated senescent cells are proposed to be one of the main drivers of age-related pathology such as dementia and cancer through disruption of tissue structure and function. We recently proposed the Neuro-Immuno-Senescence Integrative Model (NISIM), which relates prefrontally modulated vagal tone and subsequent balance between vagal and sympathetic input to the spleen to inflammatory responses leading to generation of reactive oxygen species and oxidative telomere damage.

Aim

In this study, we assess inflammation as a mediator in the relationship between prefrontally modulated vagal tone and leukocyte telomere length (LTL). We also assess the relationship between a recently proposed index of vagal neuroimmunomodulation (vagal tone/inflammation ratio; NIM index) and telomere length.

Methods

This study uses participant data from a large nationally representative longitudinal study since 1974 with a total of 45,000 Norwegian residents so far. A sub-sample of 131 participants from which ultrashort recordings (30 s) of vagal tone, c reactive protein, and LTL could be obtained were included in the study. Relationships were analyzed with Pearson's correlations and hierarchical multiple linear regression using either vagal tone and CRP or the NIM index to predict telomere length.

Results

Vagal tone was a significant positive predictor of telomere length but this was not mediated by c reactive protein, even after controlling for confounders. The NIM index was a significant positive predictor of telomere length, also when controlling for confounders. In a follow-up analysis simultaneously comparing telomere length between groups with high and low values of vagal tone, and between groups with high and low NIM index values, telomere length was only significantly different between NIM index groups.

Conclusion

This is the first study suggesting that prefrontally modulated vagal neuroimmunomodulation is associated with telomere length thus supporting the NISIM. Results indicate that the NIM index is a more sensitive indicator of vagal neuroimmunomodulation than vagal tone and CRP in isolation.

Mechanism of neuronal activity and synaptic transmission in rostral ventrolateral medulla

Rostral ventrolateral medulla (RVLM) plays an essential role in blood pressure homeostasis. This study was aimed to investigate the mechanism of neuronal activity and synaptic transmission in the RVLM. Medulla oblongata slices were carefully obtained from brainstem of rats. With continues perfusion of artificial cerebrospinal fluid (ACSF), the spontaneous firing of slices and amplitudes were assayed by conventional whole cell patch-clamp recording after addition of gamma-aminobutyric acid (GABA), α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and N-methyl d-aspartate (NMDA). Furthermore, the effects of agonist or antagonist targeted Type-A GABA (GABAA) or glutamate receptors on spontaneous excitatory postsynaptic potential (sEPSP) and spontaneous inhibitory postsynaptic potential (sIPSP) of neurons in RVLM were determined. The spontaneous firing of neurons in RVLM were inhibited by GABA (P<0.001) while were promoted by NMDA or AMPA (P<0.01 or P<0.001). In terms of sEPSP and sIPSP, the numbers of firing neurons in RVLM were both improved by GABAA receptor antagonist (P<0.01 or P<0.001) while were both decreased by GABAA receptor agonist or glutamate receptor antagonist (P<0.05, P<0.01 or P<0.001). The corresponding effects of agonist and antagonist on amplitudes were the same as the effects on number of firing neurons in RVLM. The spontaneous firing, sEPSP and sIPSP of neurons in RVLM were all activated by GABAA receptor antagonist while were all suppressed by GABAA receptor agonist or glutamate receptor antagonist.

The prevalence and pathological correlates of orthostatic hypotension and its subtypes when measured using beat-to-beat technology in a sample of older adults living in the community

BACKGROUND

beat-to-beat technology is increasingly used for investigating orthostatic intolerance (OI) but the prevalence of orthostatic hypotension (OH) diagnosed with this technology is unclear.

OBJECTIVES

(i) to use beat-to-beat technology to define the prevalence of OH, (ii) to investigate the pathological correlates of OH, (iii) to report the diversity of postural BP responses.

METHODS

cross-sectional study of adults ≥ 65 years. BP responses to a 3-min head-up tilt were analysed.

RESULTS

of 326 participants, 203(62.3%) were females. The median (IQR) age was 73 (70-78). One hundred and ninety-one (58.6%) met standard (20 mmHg systolic/10 mmHg diastolic) criteria for OH. The prevalence was higher in females (60.1% F versus 56.1% M); 47% were arteriolar subtype, 33% were venular, 9% were mixed and 11.0% could not be classified. Morphological analysis identified 102 subjects with 'small drop, overshoot', 131 with 'medium drop, slow recovery' and 31 with 'large drop, nonrecovery'. Those with OH had a lower BMI (P = 0.02), a higher resting heart rate (P = 0.005), were more likely to take a psychotropic (P = 0.02), have vertigo (P = 0.004) and report OI (P = 0.02). The 95th centile for the duration of systolic BP (SYSBP) decay >20 mmHg was 175 s and the slope of systolic BP decay was 4.75 mmHg/s. The 5th centile for percentage recovery of SYSBP was 81.4%.

CONCLUSION

(i) beat-to-beat methods identify a higher prevalence of OH than sphygmomanometry, (ii) the pathological correlates of OH diagnosed in this manner are similar to those described for sphygmomanometry, (iii) there is a diverse pattern of orthostatic BP decay that could be used in future research to predict adverse outcomes in OH.

Gender related differences in cerebral autoregulation in older healthy subjects

Cerebral autoregulation is an intrinsic mechanism of the cerebrovasculature that maintains cerebral blood flow relatively constant over a wide range of blood pressures. Recent studies have shown sex differences in cerebral autoregulation in adolescents and young adults. We evaluated cerebral auturegulation in 419 (186 male) subjects over the age of 70 recruited as part of the MOBILIZE Boston study. CO(2) reactivity, transfer function gain and autoregulatory index (ARI) during sit to stand tests were assessed. Female subjects had significantly higher CO(2) reactivity (p < 0.001) and vasomotor range (p<0.001) as well as ARI indices (p<0.001) and lower transfer function gain in the autoregulatory band (p=0.001), implying better cerebral autoregulation, than male subjects. The mechanisms of sex based differences in cerebral autoregulation remain unclear, but the results of this study highlight the need for future work to better understand these underlying autoregulatory differences.