Biomarkers in aneurysmal subarachnoid hemorrhage: A short review

Poor outcomes of aneurysmal subarachnoid hemorrhage (aSAH) can be the result of the initial catastrophic event or the many acute or delayed neurological complications. Recent evidence suggests that some molecules play a critical role in both events, through some unknown pathways involved. Understanding the role of these molecules in these events could allow to improve diagnostic accuracy, guide management, and prevent long-term disability in aSAH. Here we present the studies on aSAH biomarkers present in current medical literature, highlighting their roles and main results.

Immunological Profile of Vasospasm after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) carries high mortality and disability rates, which are substantially driven by complications. Early brain injury and vasospasm can happen after SAH and are crucial events to prevent and treat to improve prognosis. In recent decades, immunological mechanisms have been implicated in SAH complications, with both innate and adaptive immunity involved in mechanisms of damage after SAH. The purpose of this review is to summarize the immunological profile of vasospasm, highlighting the potential implementation of biomarkers for its prediction and management. Overall, the kinetics of central nervous system (CNS) immune invasion and soluble factors' production critically differs between patients developing vasospasm compared to those not experiencing this complication. In particular, in people developing vasospasm, a neutrophil increase develops in the first minutes to days and pairs with a mild depletion of CD45+ lymphocytes. Cytokine production is boosted early on after SAH, and a steep increase in interleukin-6, metalloproteinase-9 and vascular endothelial growth factor (VEGF) anticipates the development of vasospasm after SAH. We also highlight the role of microglia and the potential influence of genetic polymorphism in the development of vasospasm and SAH-related complications.

A Review of Genetic Polymorphisms and Susceptibilities to Complications after Aneurysmal Subarachnoid Hemorrhage

Delayed cerebral ischemia (DCI) and vasospasm are two complications of subarachnoid hemorrhages (SAHs) which entail high risks of morbidity and mortality. However, it is unknown why only some patients who suffer SAHs will experience DCI and vasospasm. The purpose of this review is to describe the main genetic single nucleotide polymorphisms (SNPs) that have demonstrated a relationship with these complications. The SNP of the nitric oxide endothelial synthase (eNOS) has been related to the size and rupture of an aneurysm, as well as to DCI, vasospasm, and poor neurological outcome. The SNPs responsible for the asymmetric dimetilarginine and the high-mobility group box 1 have also been associated with DCI. An association between vasospasm and the SNPs of the eNOS, the haptoglobin, and the endothelin-1 receptor has been found. The SNPs of the angiotensin-converting enzyme have been related to DCI and poor neurological outcome. Studies on the SNPs of the Ryanodine Receptor yielded varying results regarding their association with vasospasm.

Brain Oxygen-Directed Management of Aneurysmal Subarachnoid Hemorrhage. Temporal Patterns of Cerebral Ischemia During Acute Brain Attack, Early Brain Injury, and Territorial Sonographic Vasospasm

BACKGROUND

Neurocritical management of aneurysmal subarachnoid hemorrhage focuses on delayed cerebral ischemia (DCI) after aneurysm repair.

METHODS

This study conceptualizes the pathophysiology of cerebral ischemia and its management using a brain oxygen-directed protocol (intracranial pressure [ICP] control, eubaric hyperoxia, hemodynamic therapy, arterial vasodilation, and neuroprotection) in patients with subarachnoid hemorrhage, undergoing aneurysm clipping (n = 40).

RESULTS

The brain oxygen-directed protocol reduced Lbo₂ (Pbto₂ [partial pressure of brain tissue oxygen] <20 mm Hg) from 67% to 15% during acute brain attack (<24 hours of ictus), by increasing Pbto₂ from 11.31 ± 9.34 to 27.85 ± 6.76 (P < 0.0001) and then to 29.09 ± 17.88 within 72 hours. Day-after-bleed, Fio₂ change, ICP, hemoglobin, and oxygen saturation were predictors for Pbto₂ during early brain injury. Transcranial Doppler ultrasonography velocities (>20 cm/second) increased at day 2. During DCI caused by territorial sonographic vasospasm (TSV), middle cerebral artery mean velocity (V_m) increased from 45.00 ± 15.12 to 80.37 ± 38.33/second by day 4 with concomitant Pbto₂ reduction from 29.09 ± 17.88 to 22.66 ± 8.19. Peak TSV (days 7-12) coincided with decline in Pbto₂. Nicardipine mitigated Lbo₂ during peak TSV, in contrast to nimodipine, with survival benefit (P < 0.01). Intravenous and cisternal nicardipine combination had survival benefit (Cramer Φ = 0.43 and 0.327; G² = 28.32; P < 0.001). This study identifies 4 zones of Lbo₂ during survival benefit (Cramer Φ = 0.43 and 0.3) TSV, uncompensated; global cerebral ischemia, compensated, and normal Pbto₂. Admission Glasgow Coma Scale score (not increased ICP) was predictive of low Pbto₂ (β = 0.812, R² = 0.661, F_1,30 = 58.41; P < 0.0001) during early brain injury. Coma was the only credible predictor for mortality (odds ratio, 7.33/>4.8∗; χ² = 7.556; confidence interval, 1.70-31.54; P < 0.01) followed by basilar aneurysm, poor grade, high ICP and Lbo₂ during TSV. Global cerebral ischemia occurs immediately after the ictus, persisting in 30% of patients despite the high therapeutic intensity level, superimposed by DCI during TSV.

CONCLUSIONS

We propose implications for clinical practice and patient management to minimize cerebral ischemia.

The role of L-arginine metabolism in neurocritical care patients

Nitric oxide is an important mediator of vascular autoregulation and is involved in pathophysiological changes after acute neurological disorders. Nitric oxide is generated by nitric oxide synthases from the amino acid L-arginine. L-arginine can also serve as a substrate for arginases or lead to the generation of dimethylarginines, asymmetric dimethylarginine, and symmetric dimethylarginine, by methylation. Asymmetric dimethylarginine is an endogenous inhibitor of nitric oxide synthase and can lead to endothelial dysfunction. This review discusses the role of L-arginine metabolism in patients suffering from acute and critical neurological disorders often requiring neuro-intensive care treatment. Conditions addressed in this review include intracerebral hemorrhage, aneurysmal subarachnoid hemorrhage, and traumatic brain injury. Recent therapeutic advances in the field are described including current randomized controlled trials for traumatic brain injuries and hemorrhagic stroke.

Peripheral arterial tonometry as a method of measuring reactive hyperaemia correlates with organ dysfunction and prognosis in the critically ill patient: a prospective observational study

Predictions of mortality may help in the selection of patients who benefit from intensive care. Endothelial dysfunction is partially responsible for many of the organic dysfunctions in critical illness. Reactive hyperaemia is a vascular response of the endothelium that can be measured by peripheral arterial tonometry (RH-PAT). We aimed to assess if reactive hyperaemia is affected by critical illness and if it correlates with outcomes. Prospective study with a cohort of consecutive patients admitted to an Intensive Care Unit. RH-PAT was accessed on admission and on the 7th day after admission. Early and late survivors were compared to non-survivors. The effect of RH-PAT variation on late mortality was studied by a logistic regression model. The association between RH-PAT and severity scores and biomarkers of organic dysfunction was investigated by multivariate analysis. 86 patients were enrolled. Mean ln(RHI) on admission was 0.580 and was significantly lower in patients with higher severity scores (p < 0.01) and early non-survivors (0.388; p = 0.027). The model for prediction of early-mortality estimated that each 0.1 decrease in ln(RHI) increased the odds for mortality by 13%. In 39 patients, a 2nd RH-PAT measurement was performed on the 7th day. The variation of ln(RHI) was significantly different between non-survivors and survivors (− 24.2% vs. 63.9%, p = 0.026). Ln(RHI) was significantly lower in patients with renal and cardiovascular dysfunction (p < 0.01). RH-PAT is correlated with disease severity and seems to be an independent marker of early mortality, cardiovascular and renal dysfunctions. RH-PAT variation predicts late mortality. There appears to be an RH-PAT impairment in the acute phase of severe diseases that may be reversible and associated with better outcomes.

Measurement of peripheral arterial tonometry in patients with diabetic foot ulcers during courses of hyperbaric oxygen treatment

INTRODUCTION

Treatment of diabetic foot ulcers is complex and often protracted. Hyperbaric oxygen treatment (HBOT) improves wound healing in diabetic ulcers and serves as an important adjunct to regular diabetic wound care. Endothelial dysfunction plays a central role in diabetes-related vascular complications and may be evaluated by a non-invasive technique called peripheral arterial tonometry which measures a reactive hyperaemia index (RHI). We hypothesized that endothelial function measured by peripheral arterial tonometry is impaired in diabetic foot ulcer patients and that HBOT might improve endothelial function.

METHODS

Endothelial function was prospectively assessed by peripheral arterial tonometry in 22 subjects with diabetic foot ulcers and 17 subjects without diabetes during courses of HBOT. Endothelial function was evaluated before first (baseline) and 30th treatments, and at 90-day follow-up. Serum insulin growth factor-I (IGF-I) concentrations were determined by immunoassay. Results were compared to 23 healthy subjects.

RESULTS

No baseline differences were found in endothelial function between subjects with diabetes, HBOT patients without-diabetes and healthy control subjects (RHI; 1.26, 1.61 and 1.81, respectively). No significant changes in RHI were found in patients with (P = 0.17) or without (P = 0.30) diabetes during courses of HBOT. At 90-day follow-up IGF-I was significantly reduced in the subjects with diabetes (P = 0.001) and unchanged in the group without diabetes (P = 0.99).

CONCLUSIONS

We found no significant differences in RHI between subjects with diabetic foot ulcers and patients without diabetes, nor improvement in endothelial function assessed by peripheral arterial tonometry during courses of HBOT.

Endothelial dysfunction and myocardial injury after major emergency abdominal surgery: a prospective cohort study

Background

Preoperative endothelial dysfunction is a predictor of myocardial injury and major adverse cardiac events. Non-cardiac surgery is known to induce acute endothelial changes. The aim of this explorative cohort study was to assess the extent of systemic endothelial dysfunction after major emergency abdominal surgery and the potential association with postoperative myocardial injury.

Methods

Patients undergoing major emergency abdominal surgery were included in this prospective cohort study. The primary outcome was the change in endothelial function expressed as the reactive hyperemia index from 4-24 h after surgery until postoperative day 3–5. The reactive hyperemia index was assessed by non-invasive digital pulse tonometry. Secondary outcomes included changes in biomarkers of nitric oxide metabolism and bioavailability. All assessments were performed at the two separate time points in the postoperative period. Clinical outcomes included myocardial injury within the third postoperative day and major adverse cardiovascular events within 30 days of surgery.

Results

Between October 2016 and June 2017, 83 patients were included. The first assessment of the endothelial function, 4–24 h, was performed 15.8 (SD 6.9) hours after surgery and the second assessment, postoperative day 3–5, was performed 83.7 (SD 19.8) hours after surgery. The reactive hyperemia index was suppressed early after surgery and did not increase significantly; 1.64 (95% CI 1.52–177) at 4–24 h after surgery vs. 1.75 (95% CI 1.63–1.89) at postoperative day 3–5, p = 0.34. The L-arginine/ADMA ratio, expressing the nitric oxide production, was reduced in the perioperative period and correlated significantly with the reactive hyperemia index. A total of 16 patients (19.3%) had a major adverse cardiovascular event, of which 11 patients (13.3%) had myocardial injury. The L-arginine/ADMA ratio was significantly decreased at 4–24 h after surgery in patients suffering myocardial injury.

Conclusion

This explorative pathophysiological study showed that acute systemic endothelial dysfunction was present early after major emergency abdominal surgery and remained unchanged until day 3–5 after the procedure. Early postoperative disturbances in the nitric oxide bioavailability might add to the pathogenesis of myocardial injury. This pathophysiological link should be confirmed in larger studies.

Trial registration

clinicaltrials.gov no. NCT03010969.

Comparison of Three Sample Preparation Procedures for the Quantification of L-Arginine, Asymmetric Dimethylarginine, and Symmetric Dimethylarginine in Human Plasma Using HPLC-FLD

Increased asymmetric dimethylarginine (ADMA) in human plasma has been associated with reduced generation of nitric oxide, leading to atherosclerotic diseases. ADMA may therefore be an important biomarker for cardiovascular disease. In the present study, three sample preparation techniques were compared regarding the quantification of L-arginine and ADMA in human plasma: (A) protein precipitation (PP) based on aqueous trichloroacetic acid (TCA), (B) PP using a mixture of ammonia and acetonitrile, and (C) solid-phase extraction (SPE). The samples were analysed by using high-performance liquid chromatography with fluorescence detection (HPLC-FLD). The analytical performance of (A) was comparable with that of (C), demonstrating recoveries of >90%, coefficient of variations (CVs, %) of <8, and a resolution (R_s ) between ADMA and symmetric dimethylarginine (SDMA) of 1.2. (B) was disregarded due to recoveries below 75%. (A) was validated with good results regarding linearity (>0.994), precision (<5%), and sensitivity (lower limit of quantification (LLOQ)) of 0.14 µM and 12 nM for L-arginine and ADMA, respectively. Due to the simplicity and speed of procedure (A), this approach may serve as preferred sample preparation of human plasma samples before HPLC-FLD in providing important information regarding elevated ADMA concentrations.

Cerebral artery myogenic reactivity: The next frontier in developing effective interventions for subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating cerebral event that kills or debilitates the majority of those afflicted. The blood that spills into the subarachnoid space stimulates profound cerebral artery vasoconstriction and consequently, cerebral ischemia. Thus, once the initial bleeding in SAH is appropriately managed, the clinical focus shifts to maintaining/improving cerebral perfusion. However, current therapeutic interventions largely fail to improve clinical outcome, because they do not effectively restore normal cerebral artery function. This review discusses emerging evidence that perturbed cerebrovascular "myogenic reactivity," a crucial microvascular process that potently dictates cerebral perfusion, is the critical element underlying cerebral ischemia in SAH. In fact, the myogenic mechanism could be the reason why many therapeutic interventions, including "Triple H" therapy, fail to deliver benefit to patients. Understanding the molecular basis for myogenic reactivity changes in SAH holds the key to develop more effective therapeutic interventions; indeed, promising recent advancements fuel optimism that vascular dysfunction in SAH can be corrected to improve outcome.

Progressive DNA and RNA damage from oxidation after aneurysmal subarachnoid haemorrhage in humans

Free radical toxicity is considered as a key mechanism in the neuronal damage occurring after aneurysmal subarachnoid haemorrhage (SAH). We measured markers of DNA and RNA damage from oxidation (8-oxodG and 8-oxoGuo, respectively) in cerebrospinal fluid from 45 patients with SAH on day 1-14 after ictus and 45 age-matched healthy control subjects. At baseline, both markers were significantly increased in patients compared to controls (p values < .001), and exhibited a progressive further increase (to >20-fold above control levels) from day 5-14. None of the markers predicted the occurrence of vasospasms or mortality, although there was a trend that the 8-oxoGuo marker was more strongly associated with mortality than the 8-oxodG marker. We conclude that SAH leads to a massive increase in damage to nucleic acids from oxidative stress, which is likely to play a role in neuronal dysfunction and death. As only patients in need of a ventriculostomy catheter were included in the study, the findings cannot necessarily be extrapolated to all patients with SAH.

Serum asymmetric dimethylarginine and arginine levels predict microvascular and macrovascular complications in type 2 diabetes mellitus

BACKGROUND

Increased oxidative stress in diabetes increases nitric oxide (NO) oxidation and low l-arginine (Arg) could further reduce NO and impair vascular function, thereby accelerating, in the long run, vascular complications. We therefore measured Arg and asymmetric dimethylarginine (ADMA) levels in patients with type 2 diabetes mellitus (T2DM) and healthy controls. Additionally, we observed the diabetic individuals over time to see if Arg and asymmetric dimethylarginine predicted T2DM complications.

METHODS

We examined baseline serum Arg and ADMA levels in a cohort of 105 participants with type 2 diabetes and compared them with an age- and weight-matched nondiabetic group of 137 individuals who served as a reference population. Additionally, we assessed whether Arg and/or ADMA predicted macrovascular and microvascular complications over 6 years of follow-up.

RESULTS

Serum Arg was lower in individuals with T2DM than in controls (64 ± 28 vs 75 ± 31 μmol/L; P = .009) and inversely related to hemoglobin A1c (r = -0.2; P = .002). Over follow-up, we observed that participants with T2DM in the lowest quartile of Arg had increased risk for the subsequent evolution of nephropathy, peripheral neuropathy, and composite microvascular complications (odds ratio [OR] = 5.5; 95% confidence interval [CI] -1.9 to 16; P = .002). The highest ADMA quartile was associated with increased risk for both microvascular (OR = 4.5; 95% CI -1.4 to 14.1; P = .009) and 6.5-year incident macrovascular complications (OR = 8.3; 95% CI 1.9-35.5; P = .004).

CONCLUSION

l-Arginine levels are lower in individuals with T2DM than in matched controls. Both low Arg and high ADMA, independent of each other and adjusted for classical risk factors, predict the incidence of microvascular complications.

Insular and Sylvian Fissure Dermoid Cyst with Giant Cell Reactivity: Case Report and Review of Literature

BACKGROUND

Dermoid cysts are rare intracranial tumors that are most commonly found infratentorially and along the midline. Characterized by slow growth and often found incidentally, these lesions can nonetheless have severe complications, notably rupture leading to chemical meningitis. They infrequently present as a supratentorial and lateralized mass. As such, sylvian fissure dermoid cysts are exquisitely rare. We present a rare case of a dermoid cyst with giant cell reactivity suggestive of focal rupture and chronic inflammation.

CASE DESCRIPTION

A 61-year-old female presented with new-onset seizures. Magnetic resonance imaging revealed a right insular mass measuring 4.3 × 4.5 cm with compression of the ipsilateral frontal and temporal lobes. The mass was nonenhancing; however, it was bright on diffusion-weighted imaging, suggesting a dermoid cyst. She underwent craniotomy for tumor resection. Histologic analysis revealed keratinizing squamous epithelium, sebaceous glands, and hair follicles associated with giant cell reaction involving the capsule of the cyst consisted with dermoid cyst. At 2.5 years post operation, she is seizure free and without evidence of recurrence.

CONCLUSION

The dermoid cyst in our patient was not grossly ruptured, but histopathologic analysis revealed giant cell reactivity, which may indicate focal rupture or chronic inflammation. The relationship between rupture of dermoid cysts and inflammation is not well elucidated. It is not known whether symptoms occur immediately after rupture or as an acute manifestation of a chronic process following rupture. As these lesions are quite rare and rupture is even rarer, more diligence on our part regarding details of histopathology for dermoid cysts is necessary.

Asymmetric dimethylarginine in somatically healthy schizophrenia patients treated with atypical antipsychotics: a case-control study

BACKGROUND

Schizophrenia is associated with increased cardiovascular morbidity and mortality. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of the nitric oxide synthase, and the L-arginine:ADMA ratio are markers of endothelial dysfunction that predict mortality and adverse outcome in a range of cardiovascular disorders. Increased ADMA levels may also lead to increased oxidative stress. We hypothesized that ADMA and the L-arginine:ADMA ratio are increased in somatically healthy schizophrenia patients treated with atypical antipsychotics (AAP), and that the ADMA and the L-arginine: ADMA ratio are positively correlated to measures of oxidative stress.

METHODS

We included 40 schizophrenia patients treated with AAP, but without somatic disease or drug abuse, and 40 healthy controls. Plasma concentrations of ADMA and L-arginine were determined by high-performance liquid chromatography. Data were related to markers of systemic oxidative stress on DNA, RNA and lipids, as well as measures of medication load, duration of disease and current symptomatology.

RESULTS

Plasma ADMA and the L-arginine:ADMA ratio did not differ between schizophrenia patients and controls. Furthermore, ADMA and the L-arginine:ADMA ratio showed no correlations with oxidative stress markers, medication load, or Positive and Negative Syndrome Scale scores.

CONCLUSIONS

Schizophrenia and treatment with AAP was not associated with increased levels of plasma ADMA or the L-arginine:ADMA ratio. Furthermore, plasma levels of ADMA were not associated with levels of systemic oxidative stress in vivo.

Endothelial dysfunction in acute brain injury and the development of cerebral ischemia

Cerebral ischemia (CeI) is a major complicating event after acute brain injury (ABI) in which endothelial dysfunction is a key player. This study evaluates cellular markers of endothelial function and in vivo reactive hyperemia in patients with ABI and their relationship to the development of cerebral ischemia. We studied cellular markers of endothelial dysfunction and the peripheral reactive hyperemia index (RHI) in 26 patients with ABI at admission and after 6 and 12 days, and compared these with those of healthy volunteers (n = 15). CeI was determined clinically or by computer tomography. In patients with ABI, RHI at admission was significantly reduced compared with healthy subjects (P = 0.003), coinciding with a decrease in circulating endothelial progenitor cells (EPC; P = 0.002). The RHI recovered in eight patients without development of CeI, but failed to fully recover by day 12 in three of four patients who developed CeI. Despite recovery of the RHI within 12 days in these patients (P = 0.003), EPC count remained significantly lower after 12 days in patients with ABI (P = 0.022). CD31(+) T cells and endothelial microparticles were not different between controls and patients. No differences were noted in cellular markers of endothelial dysfunction in patients developing CeI and those not. In conclusion, patients with ABI exhibit impaired microvascular endothelial function measured as RHI and a decreased circulating level of EPC.

Effects of sapropterin on endothelium-dependent vasodilation in patients with CADASIL: a randomized controlled trial

BACKGROUND AND PURPOSE

Cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a rare autosomal dominant disorder caused by NOTCH3 mutations, is characterized by vascular smooth muscle and endothelial cells abnormalities, altered vasoreactivity, and recurrent lacunar infarcts. Vasomotor function may represent a key factor for disease progression. Tetrahydrobiopterin, essential cofactor for nitric oxide synthesis in endothelial cells, ameliorates endothelial function. We assessed whether supplementation with sapropterin, a synthetic tetrahydrobiopterin analog, improves endothelium-dependent vasodilation in CADASIL patients.

METHODS

In a 24-month, multicenter randomized, double-blind, placebo-controlled trial, CADASIL patients aged 30 to 65 years were randomly assigned to receive placebo or sapropterin 200 to 400 mg BID. The primary end point was change in the reactive hyperemia index by peripheral arterial tonometry at 24 months. We also assessed the safety and tolerability of sapropterin. Analysis was done by intention-to-treat.

RESULTS

The intention-to-treat population included 61 patients. We found no significant difference between sapropterin (n=32) and placebo (n=29) in the primary end point (mean difference in reactive hyperemia index by peripheral arterial tonometry changes 0.19 [95% confidence interval, -0.18, 0.56]). Reactive hyperemia index by peripheral arterial tonometry increased after 24 months in 37% of patients on sapropterin and in 28% on placebo; however, after adjustment for age, sex, and clinical characteristics, improvement was not associated with treatment arm. The proportion of patients with adverse events was similar on sapropterin and on placebo (50% versus 48.3%); serious adverse events occurred in 6.3% versus 13.8%, respectively.

CONCLUSIONS

Sapropterin was safe and well-tolerated at the average dose of 5 mg/kg/day, but did not affect endothelium-dependent vasodilation in CADASIL patients.

CLINICAL TRIAL REGISTRATION URL

https://www.clinicaltrialsregister.eu. Unique identifier: 2007-004370-55.

Postoperative ICU management of patients after subarachnoid hemorrhage

PURPOSE OF REVIEW

This article reviews recent advances in the postoperative ICU management of patients after subarachnoid hemorrhage (SAH), especially with regards to hemodynamic management, methods of improving neurological outcomes, and management of cardiac and pulmonary complications.

RECENT FINDINGS

Several hemodynamic monitors and parameters may be useful for guiding volume therapy, including cardiac output, stroke volume variation monitoring, and global end-diastolic volume index. Early goal-directed hemodynamic therapy after SAH has recently been shown to improve clinical outcomes in patients with a poor clinical grade or coexisting cardiopulmonary complications. Recent laboratory and imaging modalities are being developed to identify patients at risk for developing vasospasm after SAH. Evidence for the use of various prophylactic adjuvant therapies to prevent vasospasm, including magnesium, phosphodiesterase 3 inhibitors, and therapeutic hypothermia, is emerging. Intrathecal administration of vasodilators or fibrinolytics may have offered advantages over systemic drug administration in the treatment of vasospasm. Pulmonary and cardiac complications are common after SAH, and are associated with an increased risk of mortality.

SUMMARY

The postoperative ICU period after SAH is associated with a significant morbidity and mortality risk, and recent studies have greatly contributed to our understanding of how to optimally manage these patients.

Evaluation of endothelial function by peripheral arterial tonometry and relation with the nitric oxide pathway

Endothelial dysfunction is an important component in the development of cardiovascular diseases. Endothelial function may be evaluated by peripheral arterial tonometry (PAT) which measures the vasodilator function in the microvasculature of the fingertip during reactive hyperaemia. The reactive hyperaemia index (RHI) is decreased in the presence of cardiovascular risk factors and thus far several studies have shown that PAT-RHI may provide reliable prediction of outcome. The technique is operator independent and easy to perform. Abnormalities measured by PAT follow the same trend as those measured by flow-mediated dilation in the brachial artery, but the two methods are not interchangeable. We have reviewed the recent literature in an effort to evaluate peripheral arterial tonometry as a method to assess the function of the endothelium and additionally suggest directions for future research. Special attention will be directed to the nitric oxide dependency of the reactive hyperaemia index obtained by peripheral arterial tonometry.