Changes in subendocardial viability ratio with acute high-altitude exposure and protective role of acetazolamide

Research Progress and Clinical Value of Subendocardial Viability Ratio

Cardiovascular disease remains the leading cause of morbidity and mortality worldwide, with ischemic heart disease being a major contributor, either through coronary atherosclerotic plaque-related major vascular disease or coronary microvascular dysfunction. Obstruction of coronary blood flow impairs myocardial perfusion, which may lead to acute myocardial infarction in severe cases. The subendocardial viability ratio, also known as the Buckberg index, is a valuable tool for evaluation of myocardial perfusion because it reflects the balance between myocardial oxygen supply and oxygen demand. The subendocardial viability ratio can effectively evaluate the function of the coronary microcirculation and is associated with arterial stiffness. This ratio also has potential value in predicting adverse cardiovascular events and mortality in various populations. Moreover, the subendocardial viability ratio has demonstrated clinical significance in a range of diseases, including hypertension, aortic stenosis, peripheral arterial disease, chronic kidney disease, diabetes, and rheumatoid arthritis. This review summarizes the applications of the subendocardial viability ratio, its particular progress in the relevant research, and its clinical significance in cardiovascular diseases.

Cardiovascular physiology and pathophysiology at high altitude

Oxygen is vital for cellular metabolism; therefore, the hypoxic conditions encountered at high altitude affect all physiological functions. Acute hypoxia activates the adrenergic system and induces tachycardia, whereas hypoxic pulmonary vasoconstriction increases pulmonary artery pressure. After a few days of exposure to low oxygen concentrations, the autonomic nervous system adapts and tachycardia decreases, thereby protecting the myocardium against high energy consumption. Permanent exposure to high altitude induces erythropoiesis, which if excessive can be deleterious and lead to chronic mountain sickness, often associated with pulmonary hypertension and heart failure. Genetic factors might account for the variable prevalence of chronic mountain sickness, depending on the population and geographical region. Cardiovascular adaptations to hypoxia provide a remarkable model of the regulation of oxygen availability at the cellular and systemic levels. Rapid exposure to high altitude can have adverse effects in patients with cardiovascular diseases. However, intermittent, moderate hypoxia might be useful in the management of some cardiovascular disorders, such as coronary heart disease and heart failure. The aim of this Review is to help physicians to understand the cardiovascular responses to hypoxia and to outline some recommendations that they can give to patients with cardiovascular disease who wish to travel to high-altitude destinations.

Exercise in hypoxia: a model from laboratory to on-field studies

Clinical outcome and quality of life of patients with chronic heart failure (HF) have greatly improved over the last two decades. These results and the availability of modern lifts allow many cardiac patients to spend leisure time at altitude. Heart failure per se does not impede a safe stay at altitude, but exercise at both simulated and real altitudes is associated with a reduction in performance, which is inversely proportional to HF severity. For example, in normal subjects, the reduction in functional capacity is ∼2% every 1000 m altitude increase, whereas it is 4 and 10% in HF patients with normal or slightly diminished exercise capacity and in HF patients with markedly diminished exercise capacity, respectively. Also, the on-field experience with HF patients at altitude confirms safety and shows overall similar data to that reported at simulated altitude. Even 'optimal' HF treatment in patients spending time at altitude or at hypoxic conditions is likely different from optimal treatment at sea level, particularly with regard to the selectivity of β-blockers. Furthermore, high altitude, both simulated and on-field, represents a stimulating model of hypoxia in HF patients and healthy subjects. Our data suggest that spending time at altitude (<3500 m) can be safe even for HF patients, provided that subjects are free from comorbidities that may directly interfere with the adaptation to altitude and are stable. However, HF patients experience a reduction of exercise capacity directly proportional to HF severity and altitude. Finally, HF patients should be tested for functional capacity and must undergo a specific 'hypoxic-tailored treatment' to avoid pharmacological interference with altitude adaptation mechanisms, particularly with regard to the selectivity of β-blockers.

Markers of early vascular aging are not associated with cryptogenic ischemic stroke in the young: A case-control study

BACKGROUND AND PURPOSE

We aimed to assess the association between covert atherosclerosis, arterial stiffness, and early-onset cryptogenic ischemic stroke (CIS) in a prospective case-control study.

METHODS

We enrolled 123 young CIS patients (median age 41 years; 42% women) and 123 age- and sex-matched controls. Carotid intima-media thickness (CIMT), Augmentation Index (AIx), central pulse wave velocity (PWV), and subendocardial viability ratio (SEVR) were compared between patients and controls. Conditional logistic regression was used adjusting for age, systolic blood pressure, diastolic blood pressure, current smoking, total cholesterol/high-density lipoprotein cholesterol (Total-C/HDL-C) ratio, and glycated albumin to assess the independent association between CIMT, arterial stiffness and CIS.

RESULTS

Patients with higher CIMT and PWV were older, more often men and they had more frequently well-documented risk factors, lower HDL and higher Total-C/HDL-C ratio compared to other tertiles. In univariate comparisons, we found no differences between patients and controls regarding CIMT, AIx, or PWV. In the entire cohort, patients had a significantly lower SEVR compared to controls (146.3%, interquartile range [IQR] 125.7-170.3 vs. 158.0%, IQR 141.3-181.0, P=0.010). SEVR was lower also in women compared to their controls (132.0%, IQR 119.4-156.1 vs. 158.7%, IQR 142.0-182.8, P=0.001) but no significant difference appeared between male patients and male controls. However, after adjusting for comorbidities and laboratory values these significant differences were lost (odds ratio [OR] 1.52, 95% confidence interval [CI] 0.47-4.91) in the entire cohort and OR 3.89, 95% CI 0.30-50.80 in women).

CONCLUSIONS

Higher CIMT and PWV were associated to higher age, male sex, and several well-documented cardiovascular risk factors. However, in this study we could not prove that either covert atherosclerosis or arterial stiffness contribute to pathogenesis of early-onset CIS.

Arterial Stiffness, Subendocardial Impairment, and 30-Day Readmission in Heart Failure Older Patients

Arterial stiffness and subendocardial perfusion impairment may play a significant role in heart failure (HF) outcomes. The aim of the study was to examine the main predictors of 30-day readmission in geriatric patients, hospitalized with HF, explore hemodynamical parameters, arterial stiffness indexes, and subendocardial viability ratio (SEVR). In total, 41 hospitalized patients, affected by HF, were included; they underwent clinical evaluation, routine laboratory testing, and echocardiography. At the time of admission, after the achievement of clinical stability (defined as switching from intravenous to oral diuretic therapy), and at discharge, arterial tonometry was performed to evaluate carotid-femoral pulse wave velocity (PWVcf) and SEVR (then corrected for hemoglobin concentration and oxygen saturation). Through the evaluations, a significant progressive decrease in PWVcf was described (17.79 ± 4.49, 13.54 ± 4.54, and 9.94 ± 3.73 m/s), even after adjustment for age, gender, mean arterial pressure (MAP) variation, and left ventricular ejection fraction (LVEF). A significant improvement was registered for both SEVR (83.48 ± 24.43, 97.94 ± 26.84, and 113.29 ± 38.02) and corrected SEVR (12.74 ± 4.69, 15.71 ± 5.30, and 18.55 ± 6.66) values, and it was still significant when adjusted for age, gender, MAP variation, and LVEF. After discharge, 26.8% of patients were readmitted within 30 days. In a multivariate binary logistic regression analysis, PWVcf at discharge was the only predictor of 30-day readmission (odds ratio [OR] 1.957, 95% CI 1.112–3.443). In conclusion, medical therapy seems to improve arterial stiffness and subendocardial perfusion in geriatric patients hospitalized with heart failure. Furthermore, PWVcf is a valid predictor of 30-day readmission. Its feasibility in clinical practice may provide an instrument to detect patients with HF at high risk of rehospitalization.

Cardiovascular risk in high-hazard occupations: the role of occupational cardiology

Work is beneficial for health, but many individuals develop cardiovascular disease (CVD) during their working lives. Occupational cardiology is an emerging field that combines traditional cardiology sub-specialisms with prevention and risk management unique to specific employment characteristics and conditions. In some occupational settings incapacitation through CVD has the potential to be catastrophic due to the nature of work and/or the working environment. These are often termed 'hazardous' or 'high-hazard' occupations. Consequently, many organizations that employ individuals in high-hazard roles undertake pre-employment medicals and periodic medical examinations to screen for CVD. The identification of CVD that exceeds predefined employer (or regulatory body) risk thresholds can result in occupational restriction, or disqualification, which may be temporary or permanent. This article will review the evidence related to occupational cardiology for several high-hazard occupations related to aviation and space, diving, high altitude, emergency workers, commercial transportation, and the military. The article will focus on environmental risk, screening, surveillance, and risk management for the prevention of events precipitated by CVD. Occupational cardiology is a challenging field that requires a broad understanding of general cardiology, environmental, and occupational medicine principles. There is a current lack of consensus and contemporary evidence which requires further research. Provision of evidence-based, but individualized, risk stratification and treatment plans is required from specialists that understand the complex interaction between work and the cardiovascular system. There is a current lack of consensus and contemporary evidence in occupational cardiology and further research is required.

Impaired subendocardial perfusion in patients with metabolic syndrome

BACKGROUND

Metabolic Syndrome (MS) is associated to vascular damage, increased arterial stiffness, and impaired myocardial perfusion. Subendocardial viability ratio (SEVR) is a noninvasive estimation of myocardial workload, oxygen supply, and perfusion. The aim of the study was to describe the relation between arterial stiffness, SEVR, and cardio-metabolic risk factors.

METHODS

A cohort of 55 patients, aged 59.9 ± 10.8 years, was studied; 28 subjects (50.9%) had metabolic syndrome. All patients underwent a clinical evaluation and blood venous sampling, to assess glico-lipid profile. Applanation tonometry was performed, to obtain pulse wave analysis and SEVR values.

RESULTS

In the overall study population, SEVR showed negative associations with mean (r = -0.301; p = 0.026) and systolic (borderline relation, r = -0.257; p = 0.058) arterial pressure. Metabolic syndrome patients presented lower level of SEVR (p = 0.012), even after adjusting for age, sex, and mean arterial pressure (p = 0.040). Subdividing the study population by the number of metabolic syndrome components, SEVR significantly decreased as the number of Metabolic Syndrome components increased (p for trend 0.005). In a logistic backward regression analysis, both metabolic syndrome and mean arterial pressure resulted significant predictors of SEVR, accounting for 18% of variance.

CONCLUSION

The reduced SEVR in metabolic syndrome patients could be an important pathophysiological determinant of the increased cardiovascular risk.

Efficacy of acetazolamide for the prophylaxis of acute mountain sickness: A systematic review, meta-analysis, and trial sequential analysis of randomized clinical trials

BACKGROUND

Acute mountain sickness (AMS) is a benign and self-limiting syndrome, but can progress to life-threatening conditions if leave untreated. This study aimed to assess the efficacy of acetazolamide for the prophylaxis of AMS, and disclose factors that affect the treatment effect of acetazolamide.

METHODS

Randomized controlled trials comparing the use of acetazolamide versus placebo for the prevention of AMS were included. The incidence of AMS was our primary endpoint. Meta-regression analysis was conducted to explore factors that associated with acetazolamide efficacy. Trial sequential analyses were conducted to estimate the statistical power of the available data.

RESULTS

A total of 22 trials were included. Acetazolamide at 125, 250, and 375 mg/bid significantly reduced incidence of AMS compared to placebo. TAS indicated that the current evidence was adequate confirming the efficacy of acetazolamide at 125, 250, and 375 mg/bid in lowering incidence of AMS. There was no evidence of an association between efficacy and dose of acetazolamide, timing at start of acetazolamide treatment, mode of ascent, AMS assessment score, timing of AMS assessment, baseline altitude, and endpoint altitude.

CONCLUSION

Acetazolamide is effective prophylaxis for the prevention of AMS at 125, 250, and 375 mg/bid. Future investigation should focus on personal characteristics, disclosing the correlation between acetazolamide efficacy and body mass, height, degree of prior acclimatization, individual inborn susceptibility, and history of AMS.

Blood Pressure Response in Miners Exposed to Chronic Intermittent Hypoxia in Chile

Introduction: Limited information is available on blood pressure (BP) behavior in workers exposed to chronic intermittent hypoxia (CIH), and even less is known regarding effects of CIH on 24-h ambulatory BP in those affected by arterial hypertension at sea level (SL). The aims of this study were to assess clinic and 24-h ambulatory BP at SL and at high altitude (HA; 3,870 m above SL) in workers exposed to CIH, and to compare BP response to HA exposure between normotensive and hypertensive workers.

Methods: Nineteen normotensive and 18 pharmacologically treated hypertensive miners acclimatized to CIH were included, whose work was organized according to a “7 days-on−7 days-off” shift pattern between SL and HA. All measurements were performed on the second and seventh day of their HA shift and after the second day of SL sojourn.

Results: Compared to SL, 24-h systolic BP (SBP) and diastolic BP (DBP) increased at HA [+14.7 ± 12.6 mmHg (p < 0.001) and +8.7 ± 7.2 mmHg (p < 0.001), respectively], and SBP nocturnal fall decreased consistently (−4.1 ± 9.8%; p < 0.05) in all participants, with hypertensives showing higher nocturnal DBP than normotensives (p < 0.05) despite the current therapy. Also, heart rate (HR) nocturnal fall tended to be reduced at HA. In addition, the 24-h SBP/DBP hypertension threshold of ≥130/80 mmHg was exceeded by 39% of workers at SL and by 89% at HA. Clinic HR, SBP, and DBP were significantly higher on the second day of work at HA compared with SL, the increase being more pronounced for SBP in hypertensives (p < 0.05) and accompanied by, on average, mild altitude sickness in both groups. These symptoms and the values of all cardiovascular variables decreased on the seventh day at HA (p < 0.05) regardless of CIH exposure duration.

Conclusion: Long history of work at HA according to scheduled CIH did not prevent the occurrence of acute cardiovascular changes at HA during the first days of exposure. The BP response to HA tended to be more pronounced in hypertensive than in normotensive workers despite being already treated; the BP changes were more evident for 24-h ambulatory BP. Twenty-four-hour ABP monitoring is a useful tool for an appropriate evaluation of BP in CIH workers.

Relationships between subendocardial perfusion impairment, arterial stiffness and orthostatic hypotension in hospitalized elderly individuals

BACKGROUND

Orthostatic hypotension is an independent risk factor for cardiovascular morbidity and mortality. Arterial stiffness has been shown to be a pathophysiological mechanism linking orthostatic hypotension and increased cardiovascular risk. This study aims to evaluate the relationship between arterial stiffness, orthostatic hypotension and subendocardial viability ratio (SEVR) and moreover to identify the main predictors of orthostatic hypotension, carotid-femoral pulse wave velocity (PWV-cf) and SEVR.

METHODS

Seventy-five patients were enrolled (mean age 82.95 ± 6.45) in Verona's AOUI Geriatric ward. They underwent blood pressure, heart rate, body weight measurements and also comorbidity, arterial stiffness (PWV-cf measured by applanation tonometry), SEVR and biochemical indexes.

RESULTS

Prevalence of orthostatic hypotension was 46.6%. Even after adjustment for age, sex, glomerular filtration rate and mean arterial pressure, SEVR values corrected for arterial oxygen and haemoglobin content were statistically lower in orthostatic hypotension patients (P = 0.05) and PWV-cf values were statistically higher in orthostatic hypotension individuals (P = 0.042). In a binary logistic regression, PWV-cf was the only significant predictor of orthostatic hypotension (odds ratio 1.123; P = 0.039; confidence interval = 1.006--1.17).In a backward logistic regression model sex, creatinine clearance and orthostatic hypotension were significant predictors of SEVR corrected for O2 content. Mean arterial pressure, creatinine clearance and orthostatic hypotension were significant predictors of PWV-cf.

CONCLUSION

This study shows that orthostatic hypotension is related to increased arterial stiffness, confirming its higher prevalence in elderly patients. Orthostatic hypotension was also associated with reduced values of corrected SEVR, showing a relevant consequence of orthostatic hypotension on subendocardial perfusion impairment.

Measures of ejection duration and subendocardial viability ratio in normal weight and overweight adolescent children

The aim of our study was to determine how being overweight (OW) affects measures of ejection duration (ED), subendocardial viability ratio (SEVR), and central arterial health in a sample of adolescent children. Thirty‐four sex and age‐matched adolescent children (n = 34, 17 OW, age = 14 ± 2 years) participated in one laboratory visit. Anthropometric measures, body composition, and cardiovascular measures including resting heart rate, aortic systolic blood pressure (ASBP), carotid‐femoral pulse wave velocity (cf‐PWV), ED (EDms absolute vs. relative ED%), and the SEVR were ascertained. Transfer functions were applied to obtain ASBP. ED was measured as the time from the beginning of the upstroke of the pulse wave and the dicrotic notch, SEVR as the quotient of the diastolic pressure‐time area to the systolic pressure‐time area, and cf‐PWV as the quotient of distance between carotid‐femoral measurement sites and the transit time of the pulse wave. cf‐PWV was significantly higher in OW compared to normal weight participants (5.13 ± 0.85 vs. 4.53 ± 0.46 m/s respectively; p = 0.015, d = 0.51). OW adolescents also reported significantly higher values for ASBP (103.1 ± 11.8 vs. 95.7 ± 8.2 mmHg respectively; p = 0.043, d = 0.72) and significantly lower values of SEVR (114.4 ± 25.9% vs. 132.2 ± 22.0% respectively; p = 0.038; d = 0.33). Overweight adolescents demonstrated higher cf‐PWV, ASBP, and SEVR then normal weight peers.

[Blood pressure and high altitude: physiological response and clinical management]

High altitude is an extreme environment that challenges human beings exposed because of work, recreational activities, or habitat. Exposure to hypobaric hypoxia results in physiological adaptations in response to the geography and the associated extreme environmental conditions. These acclimatization responses can be diverse and result from evolutionary changes and comorbidities. In this context, this review aims to identify the available evidence on the effects of high altitude on blood pressurefrom the physiological to clinical aspects at rest and during exerciseand the underlying mechanisms and possible clinical implications of acute and chronic intermittent hypoxia.

Efficacy of Acetazolamide for the Prophylaxis of Acute Mountain Sickness: A Systematic Review, Meta-Analysis and Trial Sequential Analysis of Randomized Clinical Trials

BACKGROUND

Acute mountain sickness (AMS) is a benign and self-limiting syndrome but can progress to life-threatening conditions if leave untreated. This study aimed to assess the efficacy of acetazolamide for the prophylaxis of AMS and disclose potential factors that affect the treatment effect of acetazolamide.

MATERIALS AND METHODS

Randomized controlled trials comparing the use of acetazolamide versus placebo for the prevention of AMS were included. The incidence of AMS was the primary endpoint. Meta-regression analysis was conducted to explore potential factors associated with acetazolamide efficacy. Trial sequential analysis (TSA) was conducted to estimate the statistical power of the available data.

RESULTS

A total of 22 trials were included. Acetazolamide at 125, 250, and 375 mg/ twice daily (bid) significantly reduced incidence of AMS compared to placebo. TAS indicated that the current evidence was adequate confirming the efficacy of acetazolamide at 125, 250, and 375 mg/bid in lowering incidence of AMS. There was no evidence of an association between efficacy and dose of acetazolamide, timing at start of acetazolamide treatment, mode of ascent, AMS assessment score, timing of AMS assessment, baseline altitude, and endpoint altitude.

CONCLUSION

Acetazolamide is effective prophylaxis for the prevention of AMS in doses of 125, 250, and 375 mg/bid. Future investigations should focus on personal characteristics, disclosing the correlation between acetazolamide efficacy and body mass, height, degree of prior acclimatization, individual inborn susceptibility, and history of AMS.

Acetazolamide for OSA and Central Sleep Apnea: A Comprehensive Systematic Review and Meta-Analysis

BACKGROUND

Therapy options for OSA and central sleep apnea (CSA) are limited, thus many patients remain untreated. Clinically, acetazolamide is sometimes used for CSA; however, given overlapping pathophysiologic properties of OSA and CSA, we hypothesized that acetazolamide is equally effective for both types. Prior reviews focused on specific subtypes of sleep apnea, study designs, and languages, thus including few studies (typically ≤3) limiting insights.

RESEARCH QUESTION

How efficacious is acetazolamide for sleep apnea, and is its effect modified by sleep apnea type or acetazolamide dose?

STUDY DESIGN AND METHODS

We queried MEDLINE, EMBASE, and ClinicalTrials.gov from inception until March 11, 2019. Any study in which adults with OSA/CSA received oral acetazolamide vs no acetazolamide (control) that reported sleep apnea-related outcomes was eligible, independent of study design or language. Two reviewers independently assessed eligibility and abstracted data. Primary outcomes were apnea-hypopnea index (AHI) and oxygen saturation nadir. Quality of evidence (QoE) was rated with the use of Grades of Recommendation Assessment, Development and Evaluation methods.

RESULTS

We included 28 studies (13 OSA/15 CSA; N_{Subjects,Acetazolamide} = 542; N_{Subjects,Control} = 553) that enabled meta-analyses for 24 outcomes. Acetazolamide doses ranged from 36 to 1000 mg/d and treatment duration from 1 to 90 d (median, 6 d). Overall, acetazolamide vs control lowered the AHI by -0.7 effect sizes (95% CI, -0.83 to -0.58; I² = 0%; moderate QoE) that corresponded to a reduction of 37.7% (95% CI, -44.7 to -31.3) or 13.8/h (95% CI, -16.3 to -11.4; AHI_Control = 36.5/h). The AHI reduction was similar in OSA vs CSA, but significantly greater with higher doses (at least up to 500 mg/d). Furthermore, acetazolamide improved oxygen saturation nadir by +4.4% (95% CI, 2.3 to 6.5; I² = 63%; no evidence of effect modification; very low QoE) and several secondary outcomes that included sleep quality measures and BP (mostly low QoE).

INTERPRETATION

Short-term acetazolamide improved both OSA and CSA. Rigorous studies with long-term follow up are warranted to assess Acetazolamide's value for the chronic treatment of patients with sleep apnea.

CLINICAL TRIAL REGISTRATION

PROSPERO (CRD42019147504).

Clinical recommendations for high altitude exposure of individuals with pre-existing cardiovascular conditions: A joint statement by the European Society of Cardiology, the Council on Hypertension of the European Society of Cardiology, the European Society of Hypertension, the International Society of Mountain Medicine, the Italian Society of Hypertension and the Italian Society of Mountain Medicine

Take home figure

Systolic time intervals assessed from analysis of the carotid pressure waveform

OBJECTIVE

The timing of mechanical cardiac events is usually evaluated by conventional echocardiography as an index of cardiac systolic function and predictor of cardiovascular outcomes. We aimed to measure the systolic time intervals, namely the isovolumetric contraction time (ICT) and pre-ejection period (PEP), by arterial tonometry.

APPROACH

Sixty-two healthy volunteers (age 47  ±  17 years) and 42 patients with heart failure and reduced ejection fraction were enrolled (age 66  ±  14 years). Pulse waves were recorded at the carotid artery by arterial tonometry together with simultaneous aortic transvalvular flow by Doppler-echocardiography, synchronized by electrocardiographic gating. The ICT was determined from the time delay between the electrical R wave and the carotid pressure waveform, after adjustment for the pulse transit time from the aortic valve to the carotid artery site, estimated by an algorithm based on the carotid-femoral pulse wave velocity. The PEP was evaluated by adding the electrical QR duration to the ICT.

MAIN RESULTS

The ICT derived from carotid pulse wave analysis was closely related to that measured by echocardiography (r  =  0.90, p  <  0.0001), with homogeneous distribution in Bland-Altman analysis (mean difference and 95% confidence interval  =  0.2 from  -14.2 to 14.5 ms). ICT and PEP were higher in cardiac patients than in healthy volunteers (p  <  0.0001). The ratio between PEP and left ventricular ejection time was related to the ejection fraction measured with echocardiography (r  =  0.555, p  <  0.0001).

SIGNIFICANCE

The timing of electro-mechanical cardiac events can be reliably obtained from the carotid pulse waveform and carotid-femoral PWV, evaluated using arterial tonometry. Systolic time intervals assessed with this approach showed good agreement with measurements performed with conventional echocardiography and may represent a promising additional application of arterial tonometry.

Aortic dilatation in Marfan syndrome: role of arterial stiffness and fibrillin-1 variants

OBJECTIVE

Marfan syndrome (MFS) is an autosomal dominant genetic disorder characterized by aortic root dilation and dissection and an abnormal fibrillin-1 synthesis. In this observational study, we evaluated aortic stiffness in MFS and its association with ascending aorta diameters and fibrillin-1 genotype.

METHODS

A total of 116 Marfan adult patients without history of cardiovascular surgery, and 144 age, sex, blood pressure and heart rate matched controls were enrolled. All patients underwent arterial stiffness evaluation through carotid-femoral pulse wave velocity (PWV) and central blood pressure waveform analysis (PulsePen tonometer). Fibrillin-1 mutations were classified based on the effect on the protein, into 'dominant negative' and 'haploinsufficient' mutations.

RESULTS

PWV and central pulse pressure were significantly higher in MFS patients than in controls [respectively 7.31 (6.81-7.44) vs. 6.69 (6.52-6.86) m/s, P = 0.0008; 41.3 (39.1-43.5) vs. 34.0 (32.7-35.3) mmHg, P < 0.0001], with a higher age-related increase of PWV in MFS (β 0.062 vs. 0.036). Pressure amplification was significantly reduced in MFS [18.2 (15.9-20.5) vs. 33.4 (31.6-35.2)%, P < 0.0001]. Central pressure profile was altered even in MFS patients without aortic dilatation. Multiple linear regression models showed that PWV independently predicted aortic diameters at the sinuses of Valsalva (ß = 0.243, P = 0.002) and at the sinotubular junction (ß = 0.186, P = 0.048). PWV was higher in 'dominant negative' than 'haploinsufficient' fibrillin-1 mutations [7.37 (7.04-7.70) vs. 6.60 (5.97-7.23) m/s, P = 0.035], although this difference was not significant after adjustment.

CONCLUSION

Aortic stiffness is increased in MFS, independently from fibrillin-1 genotype and is associated with diameters of ascending aorta. Alterations in central hemodynamics are present even when aortic diameter is within normal limits. Our findings suggest an accelerated arterial aging in MFS.

Cardioprotection after acute exposure to simulated high altitude in rats. Role of nitric oxide

AIM

In previous studies, upregulation of NOS during acclimatization of rats to sustained hypobaric hypoxia was associated to cardioprotection, evaluated as an increased tolerance of myocardium to hypoxia/reoxygenation. The objective of the present work was to investigate the effect of acute hypobaric hypoxia and the role of endogenous NO concerning cardiac tolerance to hypoxia/reoxygenation under β-adrenergic stimulation.

METHODS

Rats were submitted to 58.7 kPa in a hypopressure chamber for 48 h whereas their normoxic controls remained at 101.3 kPa. By adding NOS substrate L-arg, or blocker L-NNA, isometric mechanical activity of papillary muscles isolated from left ventricle was evaluated at maximal or minimal production of NO, respectively, under β-adrenergic stimulation by isoproterenol, followed by 60/30 min of hypoxia/reoxygenation. Activities of NOS and cytochrome oxidase were evaluated by spectrophotometric methods and expression of HIF1-α and NOS isoforms by western blot. Eosin and hematoxiline staining were used for histological studies.

RESULTS

Cytosolic expression of HIF1-α, nNOS and eNOS, and NO production were higher in left ventricle of hypoxic rats. Mitochondrial cytochrome oxidase activity was decreased by hypobaric hypoxia and this effect was reversed by L-NNA. After H/R, recovery of developed tension in papillary muscles from normoxic rats was 51-60% (regardless NO modulation) while in hypobaric hypoxia was 70% ± 3 (L-arg) and 54% ± 1 (L-NNA). Other mechanical parameters showed similar results. Preserved histological architecture was observed only in L-arg papillary muscles of hypoxic rats.

CONCLUSION

Exposure of rats to hypobaric hypoxia for only 2 days increased NO synthesis leading to cardioprotection.

Renin–Angiotensin–Aldosterone System Is Not Involved in the Arterial Stiffening Induced by Acute and Prolonged Exposure to High Altitude

This randomized, double-blind, placebo-controlled study was designed to explore the effects of exposure to very high altitude hypoxia on vascular wall properties and to clarify the role of renin–angiotensin–aldosterone system inhibition on these vascular changes. Forty-seven healthy subjects were included in this study: 22 randomized to telmisartan (age, 40.3±10.8 years; 7 women) and 25 to placebo (age, 39.3±9.8 years; 7 women). Tests were performed at sea level, pre- and post-treatment, during acute exposure to 3400 and 5400-m altitude (Mt. Everest Base Camp), and after 2 weeks, at 5400 m. The effects of hypobaric hypoxia on mechanical properties of large arteries were assessed by applanation tonometry, measuring carotid–femoral pulse wave velocity, analyzing arterial pulse waveforms, and evaluating subendocardial oxygen supply/demand index. No differences in hemodynamic changes during acute and prolonged exposure to 5400-m altitude were found between telmisartan and placebo groups. Aortic pulse wave velocity significantly increased with altitude ( P <0.001) from 7.41±1.25 m/s at sea level to 7.70±1.13 m/s at 3400 m and to 8.52±1.59 m/s at arrival at 5400 m ( P <0.0001), remaining elevated during prolonged exposure to this altitude (8.41±1.12 m/s; P <0.0001). Subendocardial oxygen supply/demand index significantly decreased with acute exposure to 3400 m: from 1.72±0.30 m/s at sea level to 1.41±0.27 m/s at 3400 m ( P <0.001), remaining significantly although slightly less reduced after reaching 5400 m (1.52±0.33) and after prolonged exposure to this altitude (1.53±0.25; P <0.001). In conclusion, the acute exposure to hypobaric hypoxia induces aortic stiffening and reduction in subendocardial oxygen supply/demand index. Renin–angiotensin–aldosterone system does not seem to play any significant role in these hemodynamic changes.

Clinical Trial Registration—

URL: https://www.clinicaltrialsregister.eu/ . Unique identifier: 2008-000540-14.

Interventions for preventing high altitude illness: Part 1. Commonly-used classes of drugs

BACKGROUND

High altitude illness (HAI) is a term used to describe a group of cerebral and pulmonary syndromes that can occur during travel to elevations above 2500 metres (8202 feet). Acute hypoxia, acute mountain sickness (AMS), high altitude cerebral oedema (HACE) and high altitude pulmonary oedema (HAPE) are reported as potential medical problems associated with high altitude. In this review, the first in a series of three about preventive strategies for HAI, we assess the effectiveness of six of the most recommended classes of pharmacological interventions.

OBJECTIVES

To assess the clinical effectiveness and adverse events of commonly-used pharmacological interventions for preventing acute HAI.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OVID), Embase (OVID), LILACS and trial registries in January 2017. We adapted the MEDLINE strategy for searching the other databases. We used a combination of thesaurus-based and free-text terms to search.

SELECTION CRITERIA

We included randomized-controlled and cross-over trials conducted in any setting where commonly-used classes of drugs were used to prevent acute HAI.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures as expected by Cochrane.

MAIN RESULTS

We included 64 studies (78 references) and 4547 participants in this review, and classified 12 additional studies as ongoing. A further 12 studies await classification, as we were unable to obtain the full texts. Most of the studies were conducted in high altitude mountain areas, while the rest used low pressure (hypobaric) chambers to simulate altitude exposure. Twenty-four trials provided the intervention between three and five days prior to the ascent, and 23 trials, between one and two days beforehand. Most of the included studies reached a final altitude of between 4001 and 5000 metres above sea level. Risks of bias were unclear for several domains, and a considerable number of studies did not report adverse events of the evaluated interventions. We found 26 comparisons, 15 of them comparing commonly-used drugs versus placebo. We report results for the three most important comparisons: Acetazolamide versus placebo (28 parallel studies; 2345 participants)The risk of AMS was reduced with acetazolamide (risk ratio (RR) 0.47, 95% confidence interval (CI) 0.39 to 0.56; I² = 0%; 16 studies; 2301 participants; moderate quality of evidence). No events of HAPE were reported and only one event of HACE (RR 0.32, 95% CI 0.01 to 7.48; 6 parallel studies; 1126 participants; moderate quality of evidence). Few studies reported side effects for this comparison, and they showed an increase in the risk of paraesthesia with the intake of acetazolamide (RR 5.53, 95% CI 2.81 to 10.88, I² = 60%; 5 studies, 789 participants; low quality of evidence). Budenoside versus placebo (2 parallel studies; 132 participants)Data on budenoside showed a reduction in the incidence of AMS compared with placebo (RR 0.37, 95% CI 0.23 to 0.61; I² = 0%; 2 studies, 132 participants; low quality of evidence). Studies included did not report events of HAPE or HACE, and they did not find side effects (low quality of evidence). Dexamethasone versus placebo (7 parallel studies; 205 participants)For dexamethasone, the data did not show benefits at any dosage (RR 0.60, 95% CI 0.36 to 1.00; I2 = 39%; 4 trials, 176 participants; low quality of evidence). Included studies did not report events of HAPE or HACE, and we rated the evidence about adverse events as of very low quality.

AUTHORS' CONCLUSIONS

Our assessment of the most commonly-used pharmacological interventions suggests that acetazolamide is an effective pharmacological agent to prevent acute HAI in dosages of 250 to 750 mg/day. This information is based on evidence of moderate quality. Acetazolamide is associated with an increased risk of paraesthesia, although there are few reports about other adverse events from the available evidence. The clinical benefits and harms of other pharmacological interventions such as ibuprofen, budenoside and dexamethasone are unclear. Large multicentre studies are needed for most of the pharmacological agents evaluated in this review, to evaluate their effectiveness and safety.

Ventricular-vascular dynamics in pediatric patients with heart failure and preserved ejection fraction

OBJECTIVE

The details of the ventricular-vascular dynamics of heart failure with preserved ejection fraction (HFpEF) in children remain poorly understood. We tested the hypothesis that pediatric HFpEF patients have ventricular systolic, diastolic, and arterial stiffening at rest as well as impaired reserve function associated with coronary supply/demand imbalance.

METHODS

We studied the ventricular pressure-area relationship in 22 pediatric HFpEF patients and 22 control subjects before and after dobutamine infusion and during abdominal compression. Coronary supply/demand balance was assessed by subendocardial viability ratio (SEVR) calculated from the aortic pressure waveform.

RESULTS

Compared with controls, the HFpEF patients had significantly higher end-systolic (Ees) and arterial (Ea) elastance. Increased ventricular diastolic stiffness also occurred in the HFpEF patients, resulting in modest elevation of end-diastolic pressure (EDP) at rest (13.6±4.3 vs. 7.3±2.3mmHg, P<0.0001). The difference in EDP became more evident with a preload increase through abdominal compression, indicating a limited diastolic reserve in HFpEF patients (EDP changes; 11.3±6.2 for HFpEF vs. 3.4±0.6mmHg for controls, P=0.016). The HFpEF patients exhibited impaired beta-adrenergic reserve in ventricular contractility and ventricular-arterial coupling in response to dobutamine infusion. SEVR was significantly lower in the HFpEF (0.64±0.11) than in the control (0.79±0.07, P<0.0001) and was significantly correlated with LV diastolic stiffness and dobutamine-induced changes in ventricular contractility.

CONCLUSIONS

HFpEF in children involves higher ventricular-arterial stiffness at rest as well as impaired systolic and diastolic reserve, which closely correlate with impaired coronary supply/demand balance.

Baseline subendocardial viability ratio influences left ventricular systolic improvement with cardiac rehabilitation

OBJECTIVE

Subendocardial viability ratio (SEVR), defined as diastolic to systolic pressure-time integral ratio, is a useful tool reflecting the balance between coronary perfusion and arterial load. Suboptimal SEVR creating a supply-demand imbalance may limit favorable cardiac response to cardiac rehabilitation (CR). To explore this hypothesis, we designed a study to analyze the relationship between baseline SEVR and response to CR in patients with coronary artery disease (CAD).

METHODS

In this prospectively study, after baseline arterial tonometry, echocardiography, and cardiopulmonary exercise tests (CPETs), patients undergone 20 sessions of CR. Post-CR echocardiographic and CPET measurements were obtained for comparison.

RESULTS

Final study population was comprised of fifty subjects. Study population was divided into two subgroups by median SEVR value (1.45, interquartile range 0.38). Although both groups showed significant improvements in peak VO2, significant improvements in oxygen pulse (πO2) (from 16.1±3.4 to 19.1±4.8 mL O2.kg-1.beat-1; p<0.001) and stroke volume index (from 31±5 to 35±6 mL; p=0.008) were observed in only the patients in the above-median subgroup. The change in πO2 was also significantly higher in the above-median SEVR subgroup (2.9±3.3 vs. 0.5±2.4; p=0.007).

CONCLUSION

Our study shows that baseline supply-demand imbalance may limit systolic improvement response to CR in patients with CAD.

Vulnerability of Coronary Circulation After Norwood Operation

BACKGROUND

We hypothesized that the myocardial oxygen supply-demand balance is impaired in patients after a Norwood procedure and that an abnormal oxygen supply-demand balance is associated with pronounced activation of the renin-angiotensin-aldosterone system and worse clinical outcome after this procedure.

METHODS

To investigate the myocardial oxygen supply-demand balance, the subendocardial viability ratio (SEVR) was measured in 29 hypoplastic left heart syndrome patients after the Norwood procedure, in 27 patients with pulmonary atresia whose pulmonary blood flow was supplied from the aortopulmonary (AP) shunt, and in 30 control patients who were considered to have normal biventricular circulation. The SEVR in Norwood (0.57 ± 0.18) and AP shunt (0.66 ± 0.10) patients was significantly reduced compared with that in controls (0.94 ± 0.25, p < 0.001 vs Norwood and AP shunt).

RESULTS

After controlling for heart rate, the SEVR was significantly lower in Norwood than in AP shunt patients (p < 0.001). Importantly, the SEVR was significantly lower in Norwood patients with poor clinical outcomes (cardiac arrest before second-stage operation, progressive tricuspid regurgitation, or reduction of ejection fraction <0.35) than in the remaining Norwood patients (0.51 ± 0.12 vs 0.69 ± 0.22, p < 0.01). An SEVR of less than 0.52 had a more than 76% probability of having a poor outcome (p < 0.05). Furthermore, a lower SEVR was significantly correlated with more pronounced renin-angiotensin-aldosterone system activation and elevated natriuretic peptides in serum. Multiple regression analysis revealed that increased aortic stiffness and a smaller neoaorta relative to the native descending aorta were independent determinants of reduced SEVR.

CONCLUSIONS

Myocardial oxygen supply-demand imbalance is intrinsic to Norwood circulation but may be improved by technical refinement of aortic reconstruction or afterload-reducing medication with renin-angiotensin-aldosterone system blockade.

Sex and acetazolamide effects on chemoreflex and periodic breathing during sleep at altitude

OBJECTIVE

Nocturnal periodic breathing occurs more frequently in men than in women with various clinical and pathophysiologic conditions. The mechanisms accounting for this sex-related difference are not completely understood. Acetazolamide effectively counteracts nocturnal periodic breathing, but it has been investigated almost exclusively in men. Our aim was to explore possible determinants of nocturnal periodic breathing in a high-altitude setting both in men and in women. We hypothesized that increased hypoxic chemosensitivity in men could be associated with the development of nocturnal periodic breathing at altitude more frequently than in women, and that acetazolamide, by leftward shifting the CO2 ventilatory response, could improve nocturnal periodic breathing at altitude in a sex-independent manner.

METHODS

Forty-four healthy lowlanders (21 women), randomized to acetazolamide or placebo, underwent cardiorespiratory sleep studies at sea level off treatment and under treatment on the first night after arrival at a 4,559-m altitude. Hypoxic and hypercapnic chemosensitivities were assessed at sea level.

RESULTS

Men, more frequently than women, exhibited increased hypoxic chemosensitivity and displayed nocturnal periodic breathing at altitude. Acetazolamide leftward shifted the CO2 set point and, at altitude, improved oxygenation and reduced periodic breathing in both sexes, but to a larger extent in men. Hypoxic chemosensitivity directly correlated with the number of apneas/hypopneas at altitude in the placebo group but not in the acetazolamide group.

CONCLUSIONS

The greater severity of periodic breathing during sleep displayed by men at altitude could be attributed to their increased hypoxic chemosensitivity. Acetazolamide counteracted the occurrence of periodic breathing at altitude in both sexes, modifying the apneic threshold and improving oxygenation.

TRIAL REGISTRY

EU Clinical Trials Register, EudraCT; No.: 2010-019986-27; URL: https://www.clinicaltrialsregister.eu.

Visit-to-visit variability in systolic blood pressure: correlated with the changes of arterial stiffness and myocardial perfusion in on-treated hypertensive patients

BACKGROUND

Visit-to-visit variability in blood pressure (BP) was demonstrated to correlate with cardiovascular events independent of mean BP. The goal of the present study was to investigate the correlation of visit-to-visit BP variability with artery stiffness and myocardial perfusion in on-treated hypertensive patients.

METHODS

BP was measured in 271 hypertensive patients at every visit over the course of the antihypertensive treatment, and the standard deviation (SD), coefficient of variation (CV), maximum, and minimum in serial BP were calculated. Non-invasive pulse wave analysis was performed in all patients.

RESULTS

Compared with baseline, carotid-femoral pulse wave velocity (cfPWV), aortic augmentation index (Aix) and Aix adjusted to a "standard heart rate" of 75 beats/min (Aix@HR75) were markedly declined, and sub-endocardial viability ratio (SEVR) was obviously increased in each group (p < 0.001). The changes of cfPWV, SEVR, Aix and Aix@HR75 in patients with lower SD of systolic blood pressure (SBP) were significantly greater than those in patients with higher SD of SBP. And the changes were statistically correlated with both SD and CV of serial SBP during follow-up, even after adjusted for mean SBP and mean diastolic blood pressure (DBP).

CONCLUSION

Visit-to-visit SBP variability is independently correlated with changes of artery stiffness and myocardial perfusion in on-treated hypertensive patients.

Ambulatory and central haemodynamics during progressive ascent to high-altitude and associated hypoxia

High-altitude hypoxia causes major cardiovascular changes, which may result in raised resting brachial blood pressure (BP). However, the effect of high-altitude hypoxia on more sensitive measures of BP control (such as 24 h ambulatory BP and resting central BP) is largely unknown. This study aimed to assess this and compare high-altitude responses to resting brachial BP, as well as determine the haemodynamic correlates of acute mountain sickness (AMS) during a progressive trekking ascent to high-altitude. Measures of oxygen saturation (pulse oximetry), 24 h ambulatory BP, resting brachial and central BP (Pulsecor) were recorded in 10 adults (aged 27±4, 30% male) during a 9-day trek to Mount Everest base camp, Nepal. Data were recorded at sea level (stage 1; <450 m above sea level (ASL)) and at progressive ascension to 3440 m ASL (stage 2), 4350 m ASL (stage 3) and 5164 m ASL (stage 4). The Lake Louise score (LLS) was used to quantify AMS symptoms. Total LLS increased stepwise from sea level to stage 4 (0.3±0.7 vs 4.4±2.0, P=0.012), whereas oxygen saturation decreased to 77±9% (P=0.001). The highest recordings of 24 h ambulatory, daytime, night time, brachial and central systolic BP and diastolic BP were achieved at stage 3, which were significantly greater than at sea level (P<0.005 for all). Twenty-four-hour ambulatory heart rate (HR) and night HR correlated with oxygen saturation (r=-0.741 and -0.608, both P<0.001) and total LLS (r=0.648 and r=0.493, both P<0.001). We conclude that 24 h ambulatory BP, central BP and HR are elevated during high-altitude hypoxia, but AMS symptoms are only related to tachycardia.