Improvement of vagal tone by ACE inhibition: a mechanism of cardioprotection in patients with mild-to-moderate heart failure

Hypotension as a marker or mediator of perioperative organ injury: a narrative review

Perioperative hypotension has been repeatedly associated with organ injury and worse outcome, yet many interventions to reduce morbidity by attempting to avoid or reverse hypotension have floundered. In part, this reflects uncertainty as to what threshold of hypotension is relevant in the perioperative setting. Shifting population-based definitions for hypertension, plus uncertainty regarding individualised norms before surgery, both present major challenges in constructing useful clinical guidelines that may help improve clinical outcomes. Aside from these major pragmatic challenges, a wealth of biological mechanisms that underpin the development of higher blood pressure, particularly with increasing age, suggest that hypotension (however defined) or lower blood pressure per se does not account solely for developing organ injury after major surgery. The mosaic theory of hypertension, first proposed more than 60 yr ago, incorporates multiple, complementary mechanistic pathways through which clinical (macrovascular) attempts to minimise perioperative organ injury may unintentionally subvert protective or adaptive pathways that are fundamental in shaping the integrative host response to injury and inflammation. Consideration of the mosaic framework is critical for a more complete understanding of the perioperative response to acute sterile and infectious inflammation. The largely arbitrary treatment of perioperative blood pressure remains rudimentary in the context of multiple complex adaptive hypertensive endotypes, defined by distinct functional or pathobiological mechanisms, including the regulation of reactive oxygen species, autonomic dysfunction, and inflammation. Developing coherent strategies for the management of perioperative hypotension requires smarter, mechanistically solid interventions delivered by RCTs where observer bias is minimised.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Burnout Is Associated with Reduced Parasympathetic Activity and Reduced HPA Axis Responsiveness, Predominantly in Males

There is mounting evidence that burnout is a risk factor for cardiovascular disease (CVD). Stress-related dysregulation of the sympathetic and parasympathetic system and the hypothalamic pituitary adrenal (HPA) axis may explain the enhanced risk for CVD. To test this hypothesis, 55 patients (34 males and 21 females) with burnout on sickness absence and 40 healthy participants (16 males and 24 females) were exposed to a psychosocial stressor consisting of mental arithmetic and public speech. Physiological variables (i.e., blood pressure, heart rate, cardiac output, vascular resistance, cortisol, and alpha-amylase) were measured. Basal levels, reactivity, and recovery were compared between groups. In male patients, baseline systolic blood pressure was higher, whereas basal alpha-amylase and cortisol reactivity were lower than in healthy males. In female patients, a tendency for lower basal cortisol was found as compared to healthy females. Furthermore, reduced basal heart rate variability and a trend for elevated basal cardiac output were observed in both male and female patients. Burnout is characterised by dysregulation of the sympathetic and parasympathetic system and the HPA axis, which was more pronounced in males than in females. This study further supports burnout as being a risk factor for CVD through dysregulation of the sympathetic and parasympathetic system and the HPA axis.

Heart failure-induced changes of voltage-gated Ca2+ channels and cell excitability in rat cardiac postganglionic neurons

Chronic heart failure (CHF) is characterized by decreased cardiac parasympathetic and increased cardiac sympathetic nerve activity. This autonomic imbalance increases the risk of arrhythmias and sudden death in patients with CHF. We hypothesized that the molecular and cellular alterations of cardiac postganglionic parasympathetic (CPP) neurons located in the intracardiac ganglia and sympathetic (CPS) neurons located in the stellate ganglia (SG) possibly link to the cardiac autonomic imbalance in CHF. Rat CHF was induced by left coronary artery ligation. Single-cell real-time PCR and immunofluorescent data showed that L (Ca(v)1.2 and Ca(v)1.3), P/Q (Ca(v)2.1), N (Ca(v)2.2), and R (Ca(v)2.3) types of Ca2+ channels were expressed in CPP and CPS neurons, but CHF decreased the mRNA and protein expression of only the N-type Ca2+ channels in CPP neurons, and it did not affect mRNA and protein expression of all Ca2+ channel subtypes in the CPS neurons. Patch-clamp recording confirmed that CHF reduced N-type Ca2+ currents and cell excitability in the CPP neurons and enhanced N-type Ca2+ currents and cell excitability in the CPS neurons. N-type Ca2+ channel blocker (1 μM ω-conotoxin GVIA) lowered Ca2+ currents and cell excitability in the CPP and CPS neurons from sham-operated and CHF rats. These results suggest that CHF reduces the N-type Ca2+ channel currents and cell excitability in the CPP neurons and enhances the N-type Ca2+ currents and cell excitability in the CPS neurons, which may contribute to the cardiac autonomic imbalance in CHF.

Very low frequency oscillations in the power spectra of heart rate variability during dry supine immersion and exposure to non-hypoxic hypobaria

The origin of very low frequency (VLF) oscillations in the power spectra of heart rate variability (HRV) is controversial with possible mechanisms involving thermoregulation and/or renin-angiotensin-aldosterone system. Recently, a major contribution from vagal influences has been suggested. The present study investigated the behaviour of VLF (0.004-0.040 Hz) components of HRV power spectra in a group of healthy male volunteers during their exposure to (1) dry, supine, immersion in thermo-neutral water for 6 h (n = 7) and (2) non-hypoxic hypobaria (breathing 40-60% oxygen at 15,000' simulated in a decompression chamber) for 5 h (n = 15). The two manoeuvres are established to increase vagal outflow. During both the manoeuvres, all the frequency domain indices of HRV exhibited a significant increase. Increase in HRV was much more than that in the R-R interval. At 6 h of immersion, the R-R interval increased by ∼ 15% but the total power increased ∼ fourfold. Similarly, at 5 h of exposure to hypobaria, total power increased ∼ twofold with a very modest increase in an R-R of ∼ 9%. Increase in spectral power was appreciable even after normalization with mean R-R(2). Increase in VLF during immersion was more than reported during enalaprilat blockade of angiotensin convertase enzyme. Plasma renin activity did not vary during hypobaria. There was a significant increase in pNN50, an established marker of cardiac vagal activity. Centre frequencies of the spectra and slope (β) of the relation between log(PSD) and log(frequency) did not change. Results were supportive of the notion that the parasympathetic system is pre-potent to influence slower (than respiratory) frequency components in HRV spectrum. Additionally, such an effect was without a change in the time constant of effector responses or pacemaker frequencies of VLF and LF periodicities and HRV was not a simple linear surrogate for cardiac vagal effects. An invariance of spectral exponent (β) ruled out contamination of VLF and LF spectra from fractal power as an alternate explanation.

Nocturnal home hemodialysis improves baroreflex effectiveness index of end-stage renal disease patients

BACKGROUND

In patients with end-stage renal disease receiving conventional hemodialysis, both the frequency with which brief rises or falls in systolic blood pressure initiate concordant changes in pulse interval (arterial baroreflex effectiveness index), and the gain of reflex heart rate responses to these stimuli (arterial baroreflex sensitivity) are diminished. In chronic renal failure, low baroreflex effectiveness index and baroreflex sensitivity are associated with increased rates of all-cause mortality and sudden death, respectively. Conversion to home nocturnal hemodialysis augments baroreflex sensitivity but its effects on baroreflex effectiveness index have not been reported.

METHODS

In 20 consecutive hypertensive conventional hemodialysis patients training to transition to nocturnal hemodialysis (age 41 +/- 2 years; mean +/- standard error), baroreflex effectiveness index, baroreflex sensitivity (sequence method) and total arterial compliance (stroke volume/pulse pressure) were determined during quiet rest before and 2 months after conversion.

RESULTS

With nocturnal hemodialysis, dialysis frequency doubled, the dose per session increased by 70% and antihypertensive medications were withdrawn (from 2.5 +/- 0.3 to 0.2 +/- 0.1 drugs/patient, P < 0.01) because systolic blood pressure fell (from 139 +/- 5 to 119 +/- 4 mmHg, P < 0.05). Baroreflex effectiveness index increased from (0.33 +/- 0.03 to 0.42 +/- 0.03, P = 0.01). Baroreflex sensitivity increased from 5.60 +/- 0.88 to 8.48 +/- 1.60 ms/mmHg (P < 0.05). Changes in total arterial compliance correlated with changes in baroreflex sensitivity (r = 0.63, P = 0.004) but not baroreflex effectiveness index (r = 0.05, P = 0.95), suggesting independent mechanisms for their attenuation and recovery in end-stage renal disease.

CONCLUSION

Nocturnal hemodialysis increases baroreflex effectiveness index in addition to baroreflex sensitivity. The hypothesis that such changes might reduce cardiovascular event rates in this high-risk population merits prospective evaluation. More frequent engagement of the arterial baroreflex after conversion to nocturnal hemodialysis may improve short-term cardiovascular regulation.

Deficiency in angiotensin AT1a receptors prevents diabetes-induced hypertension

The renin-angiotensin system has been implicated in the etiology of the cardiovascular complications of diabetes. Our studies extend these findings to show a specific role for angiotensin AT1a receptors in mediating diabetes-induced hypertension. Male angiotensin AT1a knockout (AT1aKO) and wild-type (AT1aWT) mice with arterial telemetric catheters were injected with streptozotocin (STZ; 150 mg/kg ip). The STZ dose was selected on the basis of a dose-response experiment in C57/BL mice. Blood glucose, water intake, body weight, blood pressure (BP), and heart rate (HR) were measured over a 2-wk period. Estimates of BP and HR variance (BPV and HRV) and their low- and high-frequency domains were also determined. STZ induced similar levels of hyperglycemia and polydypsia in the groups. Mean arterial pressure (MAP) was increased from 100 ± 6 to 124 ± 6 mmHg in diabetic AT1aWT. MAP was unchanged in AT1aKO (80 ± 4 vs. 85 ± 5 mmHg, basal vs. STZ). Treatment with an ACE inhibitor, captopril, produced a greater reduction in MAP (−18%) in diabetic AT1aWT than in AT1aKO (−3.4%). BPV was lower in AT1aKO (19 ± 0.5 vs. 9 ± 2 mmHg2, AT1aWT vs. AT1aKO). Diabetes reduced BPV but only in AT1aWT (19 ± 0.5 vs. 8 ± 1 mmHg2, basal vs. STZ). There were no changes in HR in either group. In AT1aKO, STZ increased HRV and its high-frequency domain with no changes seen in AT1aWT. Results document that ANG AT1a receptors are critical in diabetes-induced hypertension and in cardiac autonomic responses.

Blunted heart rate response to vagal withdrawal in persons with tetraplegia

Cardiovascular autonomic mechanisms control heart rate (HR) and determination of heart rate variability (HRV) permits the quantitative assessment of relative shifts in autonomic cardiac control during head-up tilt (HUT). The study herein used HRV techniques to determine the vagal and sympathetic contribution to the change in HR during HUT in persons with tetraplegia (T; n = 7) paraplegia (P; n = 7) and a non-spinal cord injured (non-SCI; n = 8) control group. Heart rate (HR) was continuously monitored and cardiovascular autonomic responses were assessed for 5-minutes at supine and at 45 degrees HUT. Change associated with tilt from supine to 45 degrees HUT was calculated for HR (deltaHR), high & low frequency HRV (HF & LF) and the LF/HF ratio. HR and LF power were lower in the T compared to the P and non-SCI groups at 45 degrees HUT, whereas there were no group differences for HF at 45 degrees HUT. The LF/HF ratio was lower in the T compared to the non-SCI group at 45 degrees HUT. The relationship between delta HR and delta HF response differed between groups (significant group x delta HF interaction) such that the slope of this relationship was reduced in the T (-1.026: 95% CI: -2.623 to 0.571) compared with the non-SCI (-6.985: 95% CI: -11.25 to 2.72) and P (-5.218: 95% CI: -8.197 to -2.239) groups. There was no significant interaction effect for the relationships between deltaHR and deltaLF or deltaLF/HF. In summary, although the magnitude of vagal withdrawal was comparable among the groups, the increase in HR was attenuated in the group with tetraplegia, which may reflect reduced sympathetic cardiac modulation or altered SA node responsiveness to vagal withdrawal.

Respiratory sinus arrhythmia and diseases of aging: obesity, diabetes mellitus, and hypertension

Associations between respiratory sinus arrhythmia (RSA) and several chronic diseases, including obesity, diabetes mellitus, and hypertension, have been documented in recent years. Although most evidence suggests reduced RSA is the result of chronic disease rather than the cause, some studies have documented reduced RSA among at-risk individuals prior to disease onset. These results raise the possibility that decreased vagal tone may play a role in the pathogenesis of certain chronic diseases. Presented here is a brief overview of studies which examine the relationship between vagal tone, as measured by RSA and baroreflex gain, and diseases of aging, including obesity, diabetes mellitus, and hypertension. Mechanisms by which vagal tone may be related to disease processes are discussed. In addition, we present results from a population-based study of RSA and hypertension in older adults. Consistent with previous studies, we found an inverse relationship between RSA and age, cigarette use, and diabetes. In logistic regression models which control for age, cigarette use, and diabetes, we found RSA was a significant negative predictor of hypertension. We conclude that the relationship between RSA and hypertension is somewhat independent of the age-related decline in parasympathetic activity.

Mechanisms of Cardiovascular Protection by Resveratrol

The phytoantitoxin resveratrol is a plant-derived polyphenol with phytoestrogenic properties. Resveratrol protects the cardiovascular system by mechanisms that include defense against ischemic-reperfusion injury, promotion of vasorelaxation, protection and maintenance of intact endothelium, anti-atherosclerotic properties, inhibition of low-density lipoprotein oxidation, suppression of platelet aggregation, and estrogen-like actions. The purpose of this article is to review the mechanisms of these effects.

Diarrhoea, vomiting and ACE inhibitors:--an important cause of acute renal failure

The occurrence of severe acute renal failure in 3 patients who developed diarrhoea while taking angiotensin converting enzyme (ACE) inhibitors led us to undertake a retrospective cohort survey to determine the frequency with which diarrhoea and vomiting are associated with acute renal failure in patients taking this class of drug. Serum creatinine was measured as part of the diagnostic workup of 2398 consecutive admissions to an acute medical receiving unit in a district general hospital. Outcome measures were the presence of diarrhoea and/or vomiting, and whether taking an ACE inhibitor, NSAID or diuretic at the time of admission, also previous, initial and follow up serum creatinine concentrations. Peak serum creatinine in the 3 cases was 1159, 989 and 765 micromol/l. None of the 3 required dialysis and all recovered renal function completely after receiving large volumes of intravenous fluid. In the cohort study, 89 of 2398(3.7%) admissions had serum creatinine >/=200 micromol/l. Nine were regular dialysis patients. Of the remaining patients, 30 (37.5%) were taking an ACE inhibitor. Six of 30 (20%) gave a history of diarrhoea and/or vomiting. Median creatinine concentration in this group was 135 (range 111-209) micromol/l before admission, 292 (216-724) micromol/l when first seen in hospital, and 134 (94-219) micromol/l following the withdrawal of drug therapy and fluid replacement. In conclusion, volume depletion causing acute renal failure in patients taking ACE inhibitors is not uncommon. Such patients and their general practitioners should be aware that reversible renal impairment may occur during intercurrent illnesses, particularly if characterised by diarrhoea and/or vomiting.

Autonomic function in elderly patients with chronic heart failure

AIMS

Autonomic function (AF) is attenuated by heart failure (HF). Reports have been based on studies of young patients with systolic heart failure (SHF). However, HF is a disease of older patients who are more likely to have diastolic heart failure (DHF). We investigated whether age alters AF in elderly HF patients and whether the haemodynamic type of HF influences AF.

METHOD AND RESULTS

Thirty-six elderly HF (Framingham criteria) patients (11 with SHF, 25 with DHF) and 21 matched healthy subjects underwent simple bedside AF tests. Compared with the reference values for healthy adults, the mean E:I ratios and the median 30:15 ratios standing were all essentially normal. The median 30:15 ratios tilt and the mean Valsalva ratios were all significantly below the reference value (P for all cases <<0.050). Comparing three groups, there were no significant differences for mean E:I ratio (P=0.111), 30:15 tilt (P=0.619) and 30:15 standing (P=0.167), whereas there were significant differences for the mean Valsalva ratios (P=0.001). The mean Valsalva ratio of the SHF patients was significantly lower than that for the DHF patients (P<0.001) which in turn was significantly lower than the result of the healthy subjects (P<0.001).

CONCLUSION

There is an age-related impairment in AF with further impairment occurring in patients with HF. However, the severity of autonomic dysfunction is less in patients with DHF compared with patients with SHF.

Circadian variation in the effects of aldosterone blockade on heart rate variability and QT dispersion in congestive heart failure

OBJECTIVES

The study was designed to comprehensively evaluate the circadian effects of aldosterone blockade on autonomic tone and QT dispersion in chronic heart failure (CHF).

BACKGROUND

Spironolactone therapy given in addition to angiotensin-converting enzyme inhibitors improved survival in CHF, but the mechanism of its benefit is uncertain. Experimental evidence suggests that aldosterone may have detrimental effects on the autonomic nervous system, especially during the morning hours.

METHODS

Twenty-eight patients with New York Heart Association class II to IV CHF received spironolactone 50 mg daily and placebo for four weeks each in a double-blind crossover fashion. After each treatment phase, a full circadian assessment was undertaken of spironolactone's autonomic effects. The assessment included monitoring heart rate, QT dispersion, continuous Holter recordings, heart rate variability (HRV) and norepinephrine kinetics.

RESULTS

Spironolactone significantly reduced all indices of QT dispersion. The reductions in QTcmax, QTd and QTcd were greatest at 6 AM. In addition, spironolactone had favorable autonomic effects, which were limited to the morning (6-10 AM), including heart rate reduction and an improvement in HRV.

CONCLUSIONS

Spironolactone reduced heart rate and improved HRV and QT dispersion in CHF. Its effects were particularly prominent during the morning hours.

Heart rate variability at rest and during mental stress in patients with coronary artery disease: differences in patients with high and low depression scores

This study tested the hypothesis that coronary artery disease (CAD) patients with high depressed mood scores differ in sympatho-vagal balance during mental stress compared to patients with low depressed mood scores. Using electrocardiographic monitoring, heart variability data from spectral analysis and hemodynamic parameters were obtained prior to and during mental stress from 34 men and 7 women. A public speaking task was used as the mental stressor. Patients were grouped by a median split of their Minnesota Multiphasic Personality Inventory-Depression score. During mental stress, patients with higher depression scores had greater changes in peak heart rate (p < .05) and low frequency to high frequency power ratio (p < 0.05) than patients with lower scores suggesting a shift toward more sympathetic activity during mental stress. These findings may be related to the reported relation between depression and survival risk in patients with CAD.