Neuromodulation of innate immunity by remote ischaemic conditioning in humans: Experimental cross-over study.

Experimental animal studies on the mechanisms of remote ischaemic conditioning (RIC)-induced cardioprotection against ischaemia/reperfusion injury demonstrate involvement of both neuronal and humoral pathways. Autonomic parasympathetic (vagal) pathways confer organ protection through both direct innervation and/or immunomodulation, but evidence in humans is lacking. During acute inflammation, vagal release of acetylcholine suppresses CD11b expression, a critical ß2-integrin regulating neutrophil adhesion to the endothelium and transmigration to sites of injury. Here, we tested the hypothesis that RIC recruits vagal activity in humans and has an anti-inflammatory effect by reducing neutrophil CD11b expression. Participants (age:50 â€‹± â€‹19 years; 53% female) underwent ultrasound-guided injection of local anaesthetic within the brachial plexus before applying 3 â€‹× â€‹8 min cycles of brachial artery occlusion using a blood pressure cuff (RICblock). RIC was repeated 6 weeks later without brachial plexus block. Masked analysers quantified vagal activity (heart rate, heart rate variability (HRV)) before, and 10 â€‹min after, the last cycle of RIC. RR-interval increased after RIC (reduced heart rate) by 40 â€‹ms (95% confidence intervals (95%CI):13-66; n â€‹= â€‹17 subjects; P â€‹= â€‹0.003). RR-interval did not change after brachial plexus blockade (mean difference: 20 â€‹ms (95%CI:-11 to 50); P â€‹= â€‹0.19). The high-frequency component of HRV was reduced after RICblock, but remained unchanged after RIC (P â€‹< â€‹0.001), indicating that RIC preserved vagal activity. LPS-induced CD16+CD11b+ expression in whole blood (measured by flow cytometry) was reduced by RIC (3615 median fluorescence units (95%CI:475-6754); P = 0.026), compared with 2331 units (95%CI:-3921 to 8582); P = 0.726) after RICblock. These data suggest that in humans RIC recruits vagal cardiac and anti-inflammatory mechanisms via ischaemia/reperfusion-induced activation of sensory nerve fibres that innervate the organ undergoing RIC.

MicroRNA signatures of perioperative myocardial injury after elective noncardiac surgery: a prospective observational mechanistic cohort study.

BACKGROUND: Elevated plasma or serum troponin, indicating perioperative myocardial injury (PMI), is common after noncardiac surgery. However, underlying mechanisms remain unclear. Acute coronary syndrome (ACS) is associated with the early appearance of circulating microRNAs, which regulate post-translational gene expression. We hypothesised that if PMI and ACS share pathophysiological mechanisms, common microRNA signatures should be evident. METHODS: We performed a nested case control study of samples obtained before and after noncardiac surgery from patients enrolled in two prospective observational studies of PMI (postoperative troponin I/T>99th centile). In cohort one, serum microRNAs were compared between patients with or without PMI, matched for age, gender, and comorbidity. Real-time polymerase chain reaction quantified (qRT-PCR) relative microRNA expression (cycle quantification [Cq] threshold <37) before and after surgery for microRNA signatures associated with ACS, blinded to PMI. In cohort two, we analysed (EdgeR) microRNA from plasma extracellular vesicles using next-generation sequencing (Illumina HiSeq 500). microRNA-messenger RNA-function pathway analysis was performed (DIANA miRPath v3.0/TopGO). RESULTS: MicroRNAs were detectable in all 59 patients (median age 67 yr [61-75]; 42% male), who had similar clinical characteristics independent of developing PMI. In cohort one, serum microRNA expression increased after surgery (mean fold-change) hsa-miR-1-3p: 3.99 (95% confidence interval [CI: 1.95-8.19]; hsa-miR-133-3p: 5.67 [95% CI: 2.94-10.91]; P<0.001). These changes were not associated with PMI. Bioinformatic analysis of differentially expressed microRNAs from cohorts one (n=48) and two (n=11) identified pathways associated with adrenergic stress and calcium dysregulation, rather than ischaemia. CONCLUSIONS: Circulating microRNAs associated with cardiac ischaemia were universally elevated in patients after surgery, independent of development of myocardial injury.

Acquired loss of cardiac vagal activity is associated with myocardial injury in patients undergoing noncardiac surgery: prospective observational mechanistic cohort study.

BACKGROUND: Myocardial injury is more frequent after noncardiac surgery in patients with preoperative cardiac vagal dysfunction, as quantified by delayed heart rate (HR) recovery after cessation of cardiopulmonary exercise testing. We hypothesised that serial and dynamic measures of cardiac vagal activity are also associated with myocardial injury after noncardiac surgery. METHODS: Serial autonomic measurements were made before and after surgery in patients undergoing elective noncardiac surgery. Cardiac vagal activity was quantified by HR variability and HR recovery after orthostatic challenge (supine to sitting). Revised cardiac risk index (RCRI) was calculated for each patient. The primary outcome was myocardial injury (high-sensitivity troponin ≥15 ng L-1) within 48 h of surgery, masked to investigators. The exposure of interest was cardiac vagal activity (high-frequency power spectral analysis [HFLn]) and HR recovery 90 s from peak HR after the orthostatic challenge. RESULTS: Myocardial injury occurred in 48/189 (25%) patients, in whom 41/48 (85%) RCRI was <2. In patients with myocardial injury, vagal activity (HFLn) declined from 5.15 (95% confidence interval [CI]: 4.58-5.72) before surgery to 4.33 (95% CI: 3.76-4.90; P<0.001) 24 h after surgery. In patients who remained free of myocardial injury, HFLn did not change (4.95 [95% CI: 4.64-5.26] before surgery vs 4.76 [95% CI: 4.44-5.08] after surgery). Before and after surgery, the orthostatic HR recovery was slower in patients with myocardial injury (5 beats min-1 [95% CI: 3-7]), compared with HR recovery in patients who remained free of myocardial injury (10 beats min-1 [95% CI: 7-12]; P=0.02). CONCLUSIONS: Serial HR measures indicating loss of cardiac vagal activity are associated with perioperative myocardial injury in lower-risk patients undergoing noncardiac surgery.