Neuro-autonomic changes induced by remote ischemic preconditioning (RIPC) in healthy young adults: Implications for stress

Acute sleep deprivation (ASD) and cardioprotection: Impact of ASD on oxytocin-mediated sympathetic nervous activation preceding myocardial infarction

INTRODUCTION

This study explored how acute sleep deprivation (ASD) before myocardial ischemia influences oxytocin release from paraventricular (PVN) neurons and its correlation with sympathetic nervous system (SNS) activity post-acute sleep loss, impacting subsequent left ventricular (LV) remodeling following myocardial infarction (MI).

METHODS

The study was conducted in two phases: induction of ASD, inducing MI, blood sampling, euthanizing animals and collecting their heart and brain for histological and gene expression evaluations. The animals in first and second phase were euthanized 24 h and 14 days after MI, respectively.

RESULTS

Pre-MI ASD, accompanied by increased serum epinephrine levels within 24 h of MI, upregulated oxytocin and cFos expression in the PVN. Also, pre-MI ASD resulted in decreased serum PAB levels 14 days post-MI (P < 0.001). While notable echocardiographic changes were seen in MI versus sham groups, ASD demonstrated protective effects. This was evidenced by reduced infarct size, elevated TIMP1, MMP2, and MMP9 in the LV of SD + MI animals versus MI alone (P < 0.05). Additionally, histological analysis showed reduced LV fibrosis in pre-MI ASD subjects (P < 0.05).

CONCLUSION

Our study supports the notion that activation of oxytocin neurons within the PVN subsequent to ASD interacts with autonomic centers in the central nervous system. This enhanced sympathetic outflow to the heart prior to MI triggers a preconditioning response, thereby mediating cardioprotection through decreased oxidative stress biomarkers and regulated extracellular matrix (ECM) turnover.

Immediate Increase in the Root Mean Square of Successive Differences after Three Bouts of Remote Ischemic Preconditioning: A Randomized Controlled Trial

(1) Background: Remote ischemic preconditioning (RIPC) is an intervention involving the application of brief episodes of ischemia and reperfusion to distant tissues to activate protective pathways in the heart. There is evidence suggesting the involvement of the autonomic nervous system (ANS) in RIPC-induced cardioprotection. This study aimed to investigate the immediate effects of RIPC on the ANS using a randomized controlled trial. (2) Methods: From March 2018 to November 2018, we conducted a single-blinded randomized controlled study involving 51 healthy volunteers (29 female, 24.9 [23.8, 26.4] years). Participants were placed in a supine position and heart rate variability was measured over 260 consecutive beats before they were randomized into either the intervention or the SHAM group. The intervention group underwent an RIPC protocol (3 cycles of 5 min of 200 mmHg ischemia followed by 5 min reperfusion) at the upper thigh. The SHAM group followed the same protocol but on the right upper arm, with just 40 mmHg of pressure inflation, resulting in no ischemic stimulus. Heart rate variability measures were reassessed afterward. (3) Results: The intervention group showed a significant increase in RMSSD, the possible marker of the parasympathetic nervous system (IG: 14.5 [5.4, 27.5] ms vs. CG: 7.0 [-4.3, 23.1 ms], p = 0.027), as well as a significant improvement in Alpha 1 levels compared to the control group (IG: -0.1 [-0.2, 0.1] vs. CG: 0.0 [-0.1, 0.2], p = 0.001). (4) Conclusions: Our results hint that RIPC increases the RMSSD and Alpha 1 parameters showing possible immediate parasympathetic modulations. RIPC could be favorable in promoting cardioprotective or/and cardiovascular effects by ameliorating ANS modulations.

Acute Microcirculatory Effects of Remote Ischemic Conditioning in Superficial Partial Thickness Burn Wounds

Microcirculation is a critical factor in burn wound healing. Remote ischemic conditioning (RIC) has been shown to improve microcirculation in healthy skin and demonstrated ischemic protective effects on heart, kidney, and liver cells. Therefore, we examined microcirculatory effects of RIC in partial thickness burn wounds. The hypothesis of this study is that RIC improves cutaneous microcirculation in partial thickness burn wounds. Twenty patients with partial thickness burn wounds within 48 hours after trauma were included in this study. RIC was performed with an upper arm blood pressure cuff on a healthy upper arm using three ischemia cycles (5 min inflation to 200 mm Hg) followed by 10-minute reperfusion phases. The third and final reperfusion phase lasted 20 minutes. Microcirculation of the remote (lower/upper extremities or torso) burn wound was continuously quantified, using a combined Laser Doppler and white light spectrometry. The capillary blood flow in the burn wounds increased by a maximum of 9.6% after RIC (percentage change from baseline; P < .01). Relative hemoglobin was increased by a maximum of 2.8% (vs. baseline; P < .01), while cutaneous tissue oxygen saturation remained constant (P > .05). RIC improves microcirculation in partial thickness burn wounds by improving blood flow and elevating relative hemoglobin.

Potential physiological responses contributing to the ergogenic effects of acute ischemic preconditioning during exercise: A narrative review

Ischemic preconditioning (IPC) has been reported to augment exercise performance, but there is considerable heterogeneity in the magnitude and frequency of performance improvements. Despite a burgeoning interest in IPC as an ergogenic aid, much is still unknown about the physiological mechanisms that mediate the observed performance enhancing effects. This narrative review collates those physiological responses to IPC reported in the IPC literature and discusses how these responses may contribute to the ergogenic effects of IPC. Specifically, this review discusses documented central and peripheral cardiovascular responses, as well as selected metabolic, neurological, and perceptual effects of IPC that have been reported in the literature.

Effect of ischemic preconditioning on maximum accumulated oxygen deficit in 400-meter runners

The main aim of this study was to examine the influence of ischemic preconditioning (IPC) on maximal accumulated oxygen deficit (MAOD). We conducted a three-arm and assessor-blinded randomized, controlled crossover study. Sixteen 400-meter running male athletes (19.9±1.3 years; 1.78±0.05 m; 67.9±5.5 kg) completed three supramaximal intensity tests separated with Control, Local (legs), and Remote (arms) IPC interventions. IPC was induced on the limbs on both sides (4×5 min alternating unilateral occlusion 220 mmHg and reperfusion; arms or thighs; right side first) before participants performed the supramaximal intensity test on a treadmill at 110% VO_2max intensity to exhaustion. During each test, indices of respiratory gas exchange, blood lactate, and heart rate were determined. The MAOD was calculated as the difference between the theoretical VO₂ demand and the actual VO₂ during the supramaximal intensity test. Differences from three trials were analyzed using ANOVA with repeated measures. IPC increased MAOD (RIPC, 59±17 ml/kg/min, p=0.018; LIPC, 57±15 ml/kg/min, p=0.037; p<0.05) compared with Control (49±9 ml/kg/min). Time to exhaustion was enhanced after IPC (Control: 257.2±69.5 s, RIPC, 292.3±66.6 s, p= 0.048; LIPC, 291.6±79.2 s, p=0.042; p<0.05). In contrast, the enhancements of RIPC and LIPC trials were similar (p=1.000). Blood lactate concentrations were similar across the three intervention conditions (p>0.05). Acute IPC improved MAOD and supramaximal intensity exercise capacity in 400-meter running athletes. The increased MAOD indicated greater anaerobic capacity, which can be the potential mediator for improvement in exhaustion time.

Chronic Limb Remote Ischemic Conditioning may have an Antihypertensive Effect in Patients with Hypertension

Hypertension is the leading preventable risk factor for all-cause morbidity and mortality worldwide. Despite antihypertensive medications have been available for decades, a big challenge we are facing is to increase the blood pressure (BP) control rate among the population. Therefore, it is necessary to search for new antihypertensive means to reduce the burden of disease caused by hypertension. Limb remote ischemic conditioning (LRIC) can trigger endogenous protective effects through transient and repeated ischemia on the limb to protect specific organs and tissues including the brain, heart, and kidney. The mechanisms of LRIC involve the regulation of the autonomic nervous system, releasing humoral factors, improvement of vascular endothelial function, and modulation of immune/inflammatory responses. These underlying mechanisms of LRIC may restrain the pathogenesis of hypertension through multiple pathways theoretically, leading to a potential decline in BP. Several existing studies have explored the impact of LRIC on BP, however, controversial findings were reported. To explore the potential antihypertensive effect of LRIC and the underlying mechanisms, we systematically reviewed the relevant articles to provide an insight into the novel therapy of hypertension.

Remote but not Distant: a Review on Experimental Models and Clinical Trials in Remote Ischemic Conditioning as Potential Therapy in Ischemic Stroke

Stroke is one of the main causes of neurological disability worldwide and the second cause of death in people over 65 years old, resulting in great economic and social burden. Ischemic stroke accounts for 85% of total cases, and the approved therapies are based on re-establishment of blood flow, and do not directly target brain parenchyma. Thus, novel therapies are urgently needed. In this review, limb remote ischemic conditioning (RIC) is revised and discussed as a potential therapy against ischemic stroke. The review targets both (i) fundamental research based on experimental models and (ii) clinical research based on clinical trials and human interventional studies with healthy volunteers. Moreover, it also presents two approaches concerning RIC mechanisms in stroke: (i) description of the underlying cerebral cellular and molecular mechanisms triggered by limb RIC that promote neuroprotection against stroke induced damage and (ii) the identification of signaling factors involved in inter-organ communication following RIC procedure. Limb to brain remote signaling can occur via circulating biochemical factors, immune cells, and/or stimulation of autonomic nervous system. In this review, these three hypotheses are explored in both humans and experimental models. Finally, the challenges involved in translating experimentally generated scientific knowledge to a clinical setting are also discussed.

Remote Ischemic Preconditioning to Prevent Acute Kidney Injury After Cardiac Surgery: A Meta-Analysis of Randomized Controlled Trials

Objective: Randomized controlled trials (RCTs) evaluating the influence of remote ischemic preconditioning (RIPC) on acute kidney injury (AKI) after cardiac surgery showed inconsistent results. We performed a meta-analysis to evaluate the efficacy of RIPC on AKI after cardiac surgery.

Methods: Relevant studies were obtained by search of PubMed, Embase, and Cochrane's Library databases. A random-effect model was used to pool the results. Meta-regression and subgroup analyses were used to determine the source of heterogeneity.

Results: Twenty-two RCTs with 5,389 patients who received cardiac surgery −2,702 patients in the RIPC group and 2,687 patients in the control group—were included. Moderate heterogeneity was detected (p for Cochrane's Q test = 0.03, I² = 40%). Pooled results showed that RIPC significantly reduced the incidence of AKI compared with control [odds ratio (OR): 0.76, 95% confidence intervals (CI): 0.61–0.94, p = 0.01]. Results limited to on-pump surgery (OR: 0.78, 95% CI: 0.64–0.95, p = 0.01) or studies with acute RIPC (OR: 0.78, 95% CI: 0.63–0.97, p = 0.03) showed consistent results. Meta-regression and subgroup analyses indicated that study characteristics, including study design, country, age, gender, diabetic status, surgery type, use of propofol or volatile anesthetics, cross-clamp time, RIPC protocol, definition of AKI, and sample size did not significantly affect the outcome of AKI. Results of stratified analysis showed that RIPC significantly reduced the risk of mild-to-moderate AKI that did not require renal replacement therapy (RRT, OR: 0.76, 95% CI: 0.60–0.96, p = 0.02) but did not significantly reduce the risk of severe AKI that required RRT in patients after cardiac surgery (OR: 0.73, 95% CI: 0.50–1.07, p = 0.11).

Conclusions: Current evidence supports RIPC as an effective strategy to prevent AKI after cardiac surgery, which seems to be mainly driven by the reduced mild-to-moderate AKI events that did not require RRT. Efforts are needed to determine the influences of patient characteristics, procedure, perioperative drugs, and RIPC protocol on the outcome.

The Impact of Remote Ischaemic Conditioning on Beat-to-Beat Heart Rate Variability Circadian Rhythm in Healthy Adults

BACKGROUND

Remote ischaemic conditioning (RIC) is an intervention that may exert a protective effect over multiple tissues or organs by regulating neuronal signal transduction. Heart rate variability (HRV) can assess the state of the autonomic nervous system. However, whether RIC can also regulate HRV in humans remains unknown.

METHOD

This was a self-controlled interventional study in which serial beat-to-beat monitoring was performed at the same seven time points (7, 9, and 11 AM; 2, 5, and 8 PM; and 8 AM on the next day) with or without RIC in 50 healthy adults. The seven time points on the RIC day were defined as baseline, 1 hour, 3 hours, 6 hours, 9 hours, 12 hours, and 24 hours after RIC. The RIC protocol consisted of 4×5-minute inflation/deflation in one arm and one thigh cuff at 200 mmHg pressure from 7:20 to 8 AM. This study is registered on ClinicalTrials.gov (NCT02965547).

RESULTS

We included 50 healthy adult volunteers (aged 34.54±12.01 years, 22 men [44%], all Asian). The variables analysed in frequency-domain measures performed as power of low-frequency in normalised units (0.04-0.15 Hz), high-frequency in normalised units (0.15-0.40 Hz), and ratio of low frequency to high frequency. The time-domain parameters standard deviation (SD) of all normal to normal (NN) intervals (SDNN), mean of the 5-minute SD of the NN intervals, SD of the consecutive 5-minute averages of NN intervals, and the root mean square of successive differences of NN intervals, and time-domain parameters calculated from Poincaré plots, SD of the short diagonal axis in Poincaré plot (SD1), SD of the long diagonal axis in Poincaré plot (SD2), and SD1/SD2 were also obtained. The SDNN and SD2 significantly increased 1 hour after RIC (p=0.029 and p=0.045, respectively). Additionally, the SD2 increased a second time 12 hours after RIC (p=0.041), which represented inhibited sympathetic activity.

CONCLUSIONS

Heart rate variability increase and sympathetic inhibition induced by RIC appeared both on the early and delayed protective window of RIC, which may indicate some of the underlying mechanisms by which RIC may offer protection.

Two weeks of remote ischaemic preconditioning alters sympathovagal balance in healthy humans

NEW FINDINGS

What is the central question of this study? Delayed cardiovascular responses occur following a single bout of remote ischaemic preconditioning (RIPC). Is heart rate variability (HRV), a surrogate marker of cardiac vagal control, able to detect a delayed effect after a single bout of RIPC? Do repeated bouts of RIPC further alter HRV? What is the main finding and its importance? Indices of HRV indicated a shift in sympathovagal balance toward greater parasympathetic activity following 2 weeks of RIPC but not after a single bout of RIPC. Thus, repeated bouts of RIPC were necessary to elicit changes in autonomic function.

ABSTRACT

Remote ischaemic preconditioning (RIPC), induced by brief periods of ischaemia followed by reperfusion, protects against ischaemia-reperfusion injury and improves microvascular function. However, the effect of RIPC on autonomic function remains unclear. We hypothesized that RIPC, administered as a single bout or repeated over a 2-week period, will increase markers of cardiac vagal control measured by heart rate variability (HRV). Thirty-two young adults performed a single bout (n = 13), repeated bouts (n = 11), or served as a time control (n = 8). RIPC sessions consisted of four repetitions of 5 min unilateral brachial artery occlusion interspersed by 5 min of reperfusion. For the single bout protocol, resting lead II electrocardiogram (ECG) was collected before and 24, 48, 72 and 168 h post-RIPC. The repeated bout protocol consisted of three 4-day periods of RIPC training, each interspersed by a 1-day break. Similar to time controls, ECG was collected before and 24 h after the last RIPC bout. HRV was analysed by power spectral density and symbolic dynamics using 350-beat ECG segments. After a single bout of RIPC, no changes in HRV were observed at any time point (P > 0.05). After 2 weeks of repeated RIPC, the percentage of zero-variation fragments (baseline = 13.1 ± 1.9%, post-RIPC = 6.9 ± 1.5%, P < 0.05) and the LF/HF ratio decreased (baseline = 1.1 ± 0.2, post-RIPC = 0.7 ± 0.1, P < 0.01), whereas the percentage of two-variation fragments increased (baseline = 42.9 ± 3.6%, post-RIPC = 52.5 ± 3.0%, P < 0.01). These data indicate that repeated RIPC is necessary to elicit changes in sympathovagal balance, specifically resulting in increased vagal and decreased sympathetic activity.