Role of Nitric Oxide in Buffering Short-Term Blood Pressure Fluctuations

Transcranial Doppler Ultrasound and Concussion-Supplemental Symptoms with Physiology: A Systematic Review

Sport-related concussion (SRC) can impair the cerebrovasculature both acutely and chronically. Transcranial Doppler (TCD) ultrasound assessment has the potential to illuminate the mechanisms of impairment and provide an objective evaluation of SRC. The current systematic review investigated studies employing TCD ultrasound assessment of intracranial arteries across three broad categories of cerebrovascular regulation: neurovascular coupling (NVC), cerebrovascular reactivity (CVR), and dynamic cerebral autoregulation (dCA). The current review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (CRD42021275627). The search strategy was applied to PubMed, as this database indexes all biomedical journals. Original articles on TCD for athletes with medically diagnosed SRC were included. Title/abstract and full-text screening were completed by three authors. Two authors completed data extraction and risk of bias using the Methodological Index for Non-Randomized Studies and Scottish Intercollegiate Guideline Network checklists. Of the 141 articles identified, 14 met the eligibility criteria. One article used an NVC challenge, eight assessed CVR, and six investigated dCA. Methodologies varied widely among studies, and results were heterogeneous. There was evidence of cerebrovascular impairment in all three domains roughly 2 days post-SRC, but the magnitude and recovery of these impairments were not clear. There was evidence that clinical symptom resolution occurred before cerebrovascular function, indicating that physiological deficits may persist despite clinical recovery and return to play. Collectively, this emphasizes an opportunity for the use of TCD to illuminate the cerebrovascular deficits caused by SRC. It also highlights that there is need for consistent methodological rigor when employing TCD in a SRC population.

Association of enterolactone with blood pressure and hypertension risk in NHANES

The gut microbiome may affect overall cardiometabolic health. Enterolactone is an enterolignan reflective of dietary lignan intake and gut microbiota composition and diversity that can be measured in the urine. The purpose of this study was to examine the association between urinary enterolactone concentration as a reflection of gut health and blood pressure/risk of hypertension in a large representative sample from the US population. This analysis was conducted using data from the National Health and Nutrition Examination Survey (NHANES) collected from January 1999 through December 2010. Variables of interest included participant characteristics (including demographic, anthropometric and social/environmental factors), resting blood pressure and hypertension history, and urinary enterolactone concentration. 10,637 participants (45 years (SE = 0.3), 51.7% (SE = 0.6%) were female) were included in analyses. In multivariable models adjusted for demographic, socioeconomic and behavioral/environmental covariates, each one-unit change in log-transformed increase in enterolactone was associated with a 0.738 point (95% CI: -0.946, -0.529; p<0.001) decrease in systolic blood pressure and a 0.407 point (95% CI: -0.575, -0.239; p<0.001) decrease in diastolic blood pressure. Moreover, in fully adjusted models, each one-unit change in log-transformed enterolactone was associated with 8.2% lower odds of hypertension (OR = 0.918; 95% CI: 0.892, 0.944; p<0.001). Urinary enterolactone, an indicator of gut microbiome health, is inversely associated with blood pressure and hypertension risk in a nationally representative sample of U.S. adults.

Dietary nitrate supplementation reduces low frequency blood pressure fluctuations in rats following distal middle cerebral artery occlusion

It is known that high blood pressure variability (BPV) in acute ischemic stroke is associated with adverse outcomes, yet there are no therapeutic treatments to reduce BPV. Studies have found increasing nitric oxide (NO) bioavailability improves neurological function following stroke, but whether dietary nitrate supplementation could reduce BPV remains unknown. We investigated the effects of dietary nitrate supplementation on heart rate (HR), blood pressure (BP), and beat-to-beat BPV using wireless telemetry in a rat model of distal middle cerebral artery occlusion. Blood pressure variability was characterized by spectral power analysis in the low frequency (LF; 0.2–0.6 Hz) range prestroke and during the 7 days poststroke in a control group ( n = 8) and a treatment group ( n = 8, 183 mg/l sodium nitrate in drinking water). Dietary nitrate supplementation moderately reduced systolic BPV in the LF range by ~11% compared with the control group ( P = 0.03), while resting BP and HR were not different between the two groups ( P = 0.28 and 0.33, respectively). Despite systolic BPV being reduced with dietary nitrate, we found no difference in infarct volumes between the treatment and the control groups (1.59 vs. 1.62 mm3, P = 0.86). These findings indicate that dietary nitrate supplementation is effective in reducing systolic BPV following stroke without affecting absolute BP. In light of mounting evidence linking increased BPV with poor stroke patient outcome, our data support the role of dietary nitrate as an adjunct treatment following ischemic stroke.

NEW & NOTEWORTHY Using a rat model of stroke, we found that dietary nitrate supplementation reduced low frequency blood pressure fluctuations following stroke without affecting absolute blood pressure values. Since blood pressure fluctuations are associated with poor clinical outcome in stroke patients, our findings indicate that dietary nitrate could be an effective strategy for reducing blood pressure fluctuations, which could help reduce stroke severity and improve patient recovery.

The physiological effects of slow breathing in the healthy human

Slow breathing practices have been adopted in the modern world across the globe due to their claimed health benefits. This has piqued the interest of researchers and clinicians who have initiated investigations into the physiological (and psychological) effects of slow breathing techniques and attempted to uncover the underlying mechanisms. The aim of this article is to provide a comprehensive overview of normal respiratory physiology and the documented physiological effects of slow breathing techniques according to research in healthy humans. The review focuses on the physiological implications to the respiratory, cardiovascular, cardiorespiratory and autonomic nervous systems, with particular focus on diaphragm activity, ventilation efficiency, haemodynamics, heart rate variability, cardiorespiratory coupling, respiratory sinus arrhythmia and sympathovagal balance. The review ends with a brief discussion of the potential clinical implications of slow breathing techniques. This is a topic that warrants further research, understanding and discussion.

Slow breathing techniques have been used in asthma but are there effects in healthy individuals?http://ow.ly/gCPO30eQOPZ

Effect of age and gender on the progression of adult vascular dysfunction in a mouse model of fetal programming lacking endothelial nitric oxide synthase

The objective of this study was to investigate vascular function at different ages in a transgenic murine model of fetal vascular programming using a model of uteroplacental insufficiency induced by lack of endothelial nitric oxide synthase. Homozygous NOS3 knockout (KO) and wild-type (WT) mice were cross bred to produce WT, KO, and heterozygous that developed in WT (KOP) or KO (KOM) mothers. Male/female offspring from the four groups were killed at 7, 14, and 21 wk of age (n = 5-10/group), and carotid arteries were used for in vitro vascular studies. Responses to phenylephrine (PE), with/without N(G)-nitro-L-arginine methyl ester (L-NAME), angiotensin (ANG), acetylcholine (ACh), sodium nitroprusside, and isoproterenol (ISO) were studied. At 7 wk, only KO offspring showed higher contractile response to PE, whereas, at 14 and 21 wk, both KO and KOM had a higher response. Incubation with L-NAME abolished these differences. ANG contraction was higher in male KO in all age groups and in 21-wk-old females. Relaxation to ACh and ISO was absent in KO, and significantly decreased in KOM offspring in all age groups compared with KOP and WT, independent of gender. Sodium nitroprusside was not different between groups. The effect of the altered intrauterine environment on the development of abnormal vascular function was limited at 7 wk of age and most evident at 14 wk; further deterioration was limited to ANG-mediated vascular contractility in KO offspring. Our findings provide some hope that at least the first seven postnatal weeks may be an appropriate therapeutic window to prevent cardiovascular disease later in life.

Increased nitric oxide and attenuated diastolic blood pressure variability in african americans with mildly impaired renal function

We investigated the relationship between renal function, blood pressure variability (BPV), and nitric oxide (NO) in a group of African Americans with normal or mildly impaired renal function. 24-hour ambulatory blood pressure monitoring was performed, NO measured, and glomerular filtration rate (GFR) calculated in 38 African Americans. Participants were categorized as having normal (GFR > 90 mL/min per 1.73 m²) or mildly impaired (GFR 60–89 mL/min per 1.73 m²) renal function. Diastolic BPV was significantly lower in the mildly impaired renal function group. Regression analyses revealed a significant positive association between GFR and diastolic BPV for the entire study group. Plasma NO levels were significantly higher in the mildly impaired renal function group and negatively correlated with diastolic BPV. In conclusion, diastolic BPV was reduced in African Americans with mildly impaired renal function, which may be the result of increased NO production. These results conflict with previous findings in diseased and nonblack populations and could provide rationale for studying BPV early in the disease state when BP-buffering mechanisms are still preserved.

Association of eNOS gene polymorphisms T-786C and G894T with blood pressure variability in man

The aim of this study was to evaluate the association of single nucleotide polymorphisms (SNPs) T-786C and G894T in the gene encoding eNOS with blood pressure variability (BPV) in man. Blood pressure was recorded beat-to-beat at rest three times in periods of one week (5 min, Finapres, breathing at 0.33 Hz) in 152 subjects (19-24 years). Systolic (SBPV(0.1r)/SBPV(0.1a)) and diastolic (DBPV(0.1r)/DBPV(0.1a)) blood pressure variabilities in relative (r.u.) and absolute (mm Hg(2)/Hz) units were determined by the spectral method as spectral power at the frequency of 0.1 Hz. Genotypes of both polymorphisms were detected using polymerase chain reaction and restriction analysis using enzymes Msp I and Ban II. Significant differences were observed in BPV among genotypes of T-786C SNP (p<0.05; Kruskal-Wallis), and among haplotypes of both SNPs (p<0.05; Kruskal-Wallis) as well. In T-786C SNP, carriers of less frequent allele (CC homozygotes and TC heterozygotes) showed significantly greater SBPV(0.1r) and SBPV(0.1a) compared to TT homozygotes (Mann-Whitney; p<0.05). The G894T variant showed no significant differences, but, both SNPs were in linkage disequilibrium (D'=0.37; p<0.01). Carriers of haplotype CT/CT (CC homozygotes of -786C/T and TT homozygotes of G894T) displayed significantly greater SBPV(0.1r), SBPV(0.1a) and DBPV(0.1a) compared to carriers of other haplotype combinations (Kruskal-Wallis; p=0.015, p=0.048, and p=0.026, respectively). In conclusion, the haplotype formed by less frequent alleles of both eNOS variants was associated with increased systolic and diastolic BPV in this study.

Effect of intrauterine fetal programming on response to postnatal shaker stress in endothelial nitric oxide knockout mouse model

OBJECTIVE

To determine whether the intrauterine environment affects the postnatal vascular response to stress in a model of fetal programming induced by endothelial nitric oxide synthase deficiency.

STUDY DESIGN

Homozygous nitric oxide synthase knockout and wild-type controls were crossbred to obtain maternally and paternally derived heterozygous offspring. At 14 weeks of age, in vivo blood pressure measurements by telemetry, and in vitro carotid arteries vascular reactivity studies were performed in male offspring after subjecting them to shaker stress.

RESULTS

Maternally derived heterozygous offspring, compared with paternally derived heterozygous offspring, had significantly higher systolic blood pressure, mean arterial blood pressure, and pulse pressure before, as well as after introduction of the shaker stress. The difference in the latter between maternally and paternally derived heterozygous offspring was accentuated after stress. Maternally derived heterozygous offspring also had significantly higher contractile responses to phenylephrine when compared with paternally derived heterozygous offspring, and this was abolished after incubation with L-NAME.

CONCLUSION

The adverse uterine environment affects the postnatal vascular response to stress.

Inhibition of nitric oxide synthase does not alter dynamic cerebral autoregulation in humans

The aim of this study was to determine whether inhibition of nitric oxide synthase (NOS) alters dynamic cerebral autoregulation in humans. Beat-to-beat blood pressure (BP) and cerebral blood flow (CBF) velocity (transcranial Doppler) were measured in eight healthy subjects in the supine position and during 60 degrees head-up tilt (HUT). NOS was inhibited by intravenous NG-monomethyl-L-arginine (L-NMMA) infusion. Dynamic cerebral autoregulation was quantified by transfer function analysis of beat-to-beat changes in BP and CBF velocity. Pressor effects of L-NMMA on cerebral hemodynamics were compared with those of phenylephrine infusion. In the supine position, L-NMMA increased mean BP from 83+/-3 to 94+/-3 mmHg (P < 0.01). However, CBF velocity remained unchanged. Consequently, cerebrovascular resistance index (CVRI) increased by 15% (P < 0.05). BP and CBF velocity variability and transfer function gain at the low frequencies of 0.07-0.20 Hz did not change with L-NMMA infusion. Similar changes in mean BP, CBF velocity, and CVRI were observed after phenylephrine infusion, suggesting that increase in CVRI after L-NMMA was mediated myogenically by increase in arterial pressure rather than a direct effect of cerebrovascular NOS inhibition. During baseline tilt without L-NMMA, steady-state BP increased and CBF velocity decreased. BP and CBF velocity variability at low frequencies increased in parallel by 277% and 217%, respectively (P < 0.05). However, transfer function gain remained unchanged. During tilt with L-NMMA, changes in steady-state hemodynamics and BP and CBF velocity variability as well as transfer gain and phase were similar to those without L-NMMA. These data suggest that inhibition of tonic production of NO does not appear to alter dynamic cerebral autoregulation in humans.

Enhanced heart rate variability and baroreflex index after stress and cholinesterase inhibition in mice

Experiments tested the effect of stress coupled with cholinesterase inhibition on blood pressure, heart rate, baroreflex index, and variability in time and frequency domain in conscious mice. The objective was to determine whether cholinergic systems interact with stress to alter cardiovascular responses. Male C57BL/6J mice with arterial catheters were exposed to 3-day treatments: 1) intermittent shaker stress, 2) pyridostigmine (10 mg.kg(-1).day(-1)); or 3) combined pyridostigmine and stress. Pyridostigmine reduced blood cholinesterase (-33%) with no added effects of stress. Twenty-four-hour blood pressure recordings showed that there were no differences in blood pressure and heart rate with the treatments. Pulse interval standard deviation was greatly increased in the pyridostigmine/stress group compared with stress or pyridostigmine groups (11.0 +/- 1.4, 5.0 +/- 0.9, and 7.5 +/- 0.9 ms, respectively). Spectral analysis showed two distinct components for pulse interval variability (low and high frequency). Variability in the low-frequency range was greatly enhanced in the pyridostigmine/stress group, seen as a doubling of the power (9.5 +/- 1.7, 3.3 +/- 0.9, and 5.0 +/- 0.6 ms for pyridostigmine/stress, stress and pyridostigmine groups, respectively). Baroreflex sensitivity was also increased in the pyridostigmine/stress group (3.6 +/- 0.5 compared with 1.8 +/- 0.3 and 1.7 +/- 0.5 ms/mmHg in the stress and pyridostigmine groups, respectively). There was no difference in blood pressure variability or its spectral components. Results demonstrate that there are potent interactions between a mild stressor and cholinesterase inhibition seen as an accentuation of low-frequency variability in pulse interval time series, probably associated with baroreflex input and autonomic drive.