Enhanced synthesis of albumin and fibrinogen at high altitude

Ferroptosis and aerobic training in ageing: A review

 Ferroptosis is a form of programmed cell death that plays a significant role in causing several diseases such as heart attack and heart failure, through alterations in fat, amino acid, and iron metabolism. Comprehending the regulatory mechanisms of ferroptosis signaling is critical because it has a considerable effect on the elderly's mortality. Conversely, age-related changes in substrate metabolism and metabolite levels are recognized to give rise to obesity. Furthermore, research has proposed that aging and obesity-related changes in substrate metabolism may aggravate ferroptosis. The suppression of ferroptosis holds potential as a successful therapeutic approach for managing different diseases, including sarcopenia, cardiovascular diseases, and central nervous system diseases. However, the pathologic and biological mechanisms behind the function of ferroptosis are not fully comprehended yet. Physical activity could affect lipid, amino acid, and iron metabolism to modulate ferroptosis. The aim of this study is to showcase the current understanding of the molecular mechanisms leading to ferroptosis and discuss the role of aging and physical activity in this phenomenon.

Partial Pressure of Arterial Oxygen in Healthy Adults at High Altitudes: A Systematic Review and Meta-Analysis

Importance

With increasing altitude, the partial pressure of inspired oxygen decreases and, consequently, the Pao2 decreases. Even though this phenomenon is well known, the extent of the reduction as a function of altitude remains unknown.

Objective

To calculate an effect size estimate for the decrease in Pao2 with each kilometer of vertical gain among healthy unacclimatized adults and to identify factors associated with Pao2 at high altitude (HA).

Data Sources

A systematic search of PubMed and Embase was performed from database inception to April 11, 2023. Search terms included arterial blood gases and altitude.

Study Selection

A total of 53 peer-reviewed prospective studies in healthy adults providing results of arterial blood gas analysis at low altitude (<1500 m) and within the first 3 days at the target altitude (≥1500 m) were analyzed.

Data Extraction and Synthesis

Primary and secondary outcomes as well as study characteristics were extracted from the included studies, and individual participant data (IPD) were requested. Estimates were pooled using a random-effects DerSimonian-Laird model for the meta-analysis.

Main Outcomes and Measures

Mean effect size estimates and 95% CIs for reduction in Pao2 at HA and factors associated with Pao2 at HA in healthy adults.

Results

All of the 53 studies involving 777 adults (mean [SD] age, 36.2 [10.5] years; 510 men [65.6%]) reporting 115 group ascents to altitudes between 1524 m and 8730 m were included in the aggregated data analysis; 13 of those studies involving 305 individuals (mean [SD] age, 39.8 [13.6] years; 185 men [60.7%]) reporting 29 ascents were included in the IPD analysis. The estimated effect size of Pao2 was -1.60 kPa (95% CI, -1.73 to -1.47 kPa) for each 1000 m of altitude gain (τ2 = 0.14; I2 = 86%). The Pao2 estimation model based on IPD data revealed that target altitude (-1.53 kPa per 1000 m; 95% CI, -1.63 to -1.42 kPa per 1000 m), age (-0.01 kPa per year; 95% CI, -0.02 to -0.003 kPa per year), and time spent at an altitude of 1500 m or higher (0.16 kPa per day; 95% CI, 0.11-0.21 kPa per day) were significantly associated with Pao2.

Conclusions and Relevance

In this systematic review and meta-analysis, the mean decrease in Pao2 was 1.60 kPa per 1000 m of vertical ascent. This effect size estimate may improve the understanding of physiological mechanisms, assist in the clinical interpretation of acute altitude illness in healthy individuals, and serve as a reference for physicians counseling patients with cardiorespiratory disease who are traveling to HA regions.

Organophosphorus Poisoning: Acute Respiratory Distress Syndrome (ARDS) and Cardiac Failure as Cause of Death in Hospitalized Patients

Industrial production of food for animals and humans needs increasing amounts of pesticides, especially of organophosphates, which are now easily available worldwide. More than 3 million cases of acute severe poisoning are estimated to occur worldwide every year, and even more cases remain unreported, while 200,000–350,000 incidentally or intentionally poisoned people die every year. Diagnostic and therapeutic procedures in organophosphate poisoning have, however, remained unchanged. In addition to several neurologic symptoms (miosis, fasciculations), hypersecretion of salivary, bronchial, and sweat glands, vomiting, diarrhea, and loss of urine rapidly induce dehydration, hypovolemia, loss of conscience and respiratory distress. Within hours, signs of acidosis due to systemic hypoxia can be observed at first laboratory investigation after hospitalization. While determination of serum-cholinesterase does not have any diagnostic value, it has been established that hypoalbuminemia alone or accompanied by an increase in creatinine, lactate, or C-reactive protein serum levels has negative prognostic value. Increased serum levels of C-reactive protein are a sign of systemic ischemia. Protective mechanical ventilation should be avoided, if possible. In fact, acute respiratory distress syndrome characterized by congestion and increased weight of the lung, accompanied by heart failure, may become the cause of death. As the excess of acetylcholine at the neuronal level can persist for weeks until enough newly, locally synthesized acetylcholinesterase becomes available (the value of oximes in reducing this time is still under debate), after atropine administration, intravenous albumin and fluid infusion should be the first therapeutic interventions to reestablish normal blood volume and normal tissue oxygenation, avoiding death by cardiac arrest.

Hypoxia briefly increases diuresis but reduces plasma volume by fluid redistribution in women

We have recently reported that hypobaric hypoxia (HH) reduces plasma volume (PV) in men by decreasing total circulating plasma protein (TCPP). Here, we investigated whether this applies to women and whether an inflammatory response and/or endothelial glycocalyx shedding could facilitate the TCCP reduction. We further investigated whether acute HH induces a short-lived diuretic response that was overlooked in our recent study, where only 24-h urine volumes were evaluated. In a strictly controlled crossover protocol, 12 women underwent two 4-day sojourns in a hypobaric chamber: one in normoxia (NX) and one in HH equivalent to 3,500-m altitude. PV, urine output, TCPP, and markers for inflammation and glycocalyx shedding were repeatedly measured. Total body water (TBW) was determined pre- and postsojourns by deuterium dilution. PV was reduced after 12 h of HH and thereafter remained 230-330 mL lower than in NX (P < 0.0001). Urine flow was 45% higher in HH than in NX throughout the first 6 h (P = 0.01) but lower during the second half of the first day (P < 0.001). Twenty-four-hour urine volumes (P ≥ 0.37) and TBW (P ≥ 0.14) were not different between the sojourns. TCPP was lower in HH than in NX at the same time points as PV (P < 0.001), but inflammatory or glycocalyx shedding markers were not consistently increased. As in men, and despite initially increased diuresis, HH-induced PV contraction in women is driven by a loss of TCPP and ensuing fluid redistribution, rather than by fluid loss. The mechanism underlying the TCPP reduction remains unclear but does not seem to involve inflammation or glycocalyx shedding.NEW & NOTEWORTHY This study is the first to investigate the mechanisms underlying plasma volume (PV) contraction in response to hypoxia in women while strictly controlling for confounders. PV contraction in women has a similar time course and magnitude as in men and is driven by the same mechanism, namely, oncotically driven redistribution rather than loss of fluid. We further report that hypoxia facilitates an increase in diuresis, that is, however, short-lived and of little relevance for PV regulation.

Hypoxia and hemorheological properties in older individuals

Hypoxia is caused by insufficient oxygen availability for the organism leading to reduced oxygen delivery to tissues and cells. It has been regarded as a severe threat to human health and it is indeed implicated in pathophysiological mechanisms involved in the development and progression of many diseases. Nevertheless, the potential of controlled hypoxia interventions (i.e. hypoxia conditioning) for improving cardio-vascular health is gaining increased attention. However, blood rheology is often a forgotten factor for vascular health while aging and hypoxia exposure are both suspected to alter hemorheological properties. These changes in blood rheology may influence the benefits-risks balance of hypoxia exposure in older individuals. The benefits of hypoxia exposure for vascular health are mainly reported for healthy populations and the combined impact of aging and hypoxia on blood rheology could therefore be deleterious in older individuals. This review discusses evidence of hypoxia-related and aging-related changes in blood viscosity and its determinants. It draws upon an extensive literature search on the effects of hypoxia/altitude and aging on blood rheology. Aging increases blood viscosity mainly through a rise in plasma viscosity, red blood cell (RBC) aggregation and a decrease in RBC deformability. Hypoxia also causes an increase in RBC aggregation and plasma viscosity. In addition, hypoxia exposure may increase hematocrit and modulate RBC deformability, depending on the hypoxic dose, i.e, beneficial effect of intermittent hypoxia with moderate dose vs deleterious effect of chronic continuous or intermittent hypoxia or if the hypoxic dose is too high. Special attention is directed toward the risks vs. benefits of hemorheological changes during hypoxia exposure in older individuals, and its clinical relevance for vascular disorders.

The Impact of Nocebo and Placebo Effects on Reported Incidence of Acute Mountain Sickness

Bärtsch Peter. The impact of nocebo and placebo effects on reported incidence of acute mountain sickness. High Alt Med Biol 00:000-000, 2021. Well comparable studies reporting acute mountain sickness (AMS) in nonacclimatized, acutely exposed individuals performed at 3,450-3,650 m (9 studies) and 4,559-4,675 m (18 studies) at real altitude or in hypobaric or in normobaric hypoxic chambers were analyzed with the hypothesis that the study design impacts occurrence of AMS. Individual symptoms and overall scores of AMS were not different between the three modalities of exposure to a comparable degree of hypoxia, indicating that hypobaria has, if at all, minimal influence on AMS. Studies not focusing versus those focusing on AMS report lower scores and prevalence of AMS at 3,500 m, but not at 4,559 m, while frequent assessment may be associated with more severe AMS. These data suggest that focusing on AMS creates expectations of getting AMS (nocebo effects) and increases its prevalence, while not paying attention reduces negative expectations and thus AMS. On the other hand, interventions promising improvement may cause positive expectations (placebo effect). Information about purpose and dangers of a study, repeated assessments for AMS, previous experiences of AMS, and observation of illness in other study participants are major factors contributing to negative expectations and thus nocebo effects increasing AMS. They should be considered when designing studies and subject information and be reported in detail in publications of studies on AMS.

Albumin Infusion in Critically Ill COVID-19 Patients: Hemodilution and Anticoagulation

Hypercoagulation is one of the major risk factors for ICU treatment, mechanical ventilation, and death in critically ill patients infected with SARS-CoV-2. At the same time, hypoalbuminemia is one risk factor in such patients, independent of age and comorbidities. Especially in patients with severe SARS-CoV-2-infection, albumin infusion may be essential to improve hemodynamics and to reduce the plasma level of the main marker of thromboembolism, namely, the D-dimer plasma level, as suggested by a recent report. Albumin is responsible for 80% of the oncotic pressure in the vessels. This is necessary to keep enough water within the systemic circulatory system and for the maintenance of sufficient blood pressure, as well as for sufficient blood supply for vital organs like the brain, lungs, heart, and kidney. The liver reacts to a decrease in oncotic pressure with an increase in albumin synthesis. This is normally possible through the use of amino acids from the proteins introduced with the nutrients reaching the portal blood. If these are not sufficiently provided with the diet, amino acids are delivered to the liver from muscular proteins by systemic circulation. The liver is also the source of coagulation proteins, such as fibrinogen, fibronectin, and most of the v WF VIII, which are physiological components of the extracellular matrix of the vessel wall. While albumin is the main negative acute-phase protein, fibrinogen, fibronectin, and v WF VIII are positive acute-phase proteins. Acute illnesses cause the activation of defense mechanisms (acute-phase reaction) that may lead to an increase of fibrinolysis and an increase of plasma level of fibrinogen breakdown products, mainly fibrin and D-dimer. The measurement of the plasma level of the D-dimer has been used as a marker for venous thromboembolism, where a fourfold increase of the D-dimer plasma level was used as a negative prognostic marker in critically ill SARS-CoV-2 hospitalized patients. Increased fibrinolysis can take place in ischemic peripheral sites, where the mentioned coagulation proteins can become part of the provisional clot (e.g., in the lungs). Although critically ill SARS-CoV-2-infected patients are considered septic shock patients, albumin infusions have not been considered for hemodynamic resuscitation and as anticoagulants. The role of coagulation factors as provisional components of the extracellular matrix in case of generalized peripheral ischemia due to hypoalbuminemia and hypovolemia is discussed in this review.

Altitude Cardiomyopathy Is Associated With Impaired Stress Electrocardiogram and Increased Circulating Inflammation Makers

Many sea-level residents suffer from acute mountain sickness (AMS) when first visiting altitudes above 4,000 m. Exercise tolerance also decreases as altitude increases. We observed exercise capacity at sea level and under a simulated hypobaric hypoxia condition (SHHC) to explore whether the response to exercise intensity represented by physiological variables could predict AMS development in young men. Eighty young men from a military academy underwent a standard treadmill exercise test (TET) and biochemical blood test at sea level, SHHC, and 4,000-m altitude, sequentially, between December 2015 and March 2016. Exercise-related variables and 12-lead electrocardiogram parameters were obtained. Exercise intensity and AMS development were investigated. After exposure to high altitude, the count of white blood cells, alkaline phosphatase and serum albumin were increased (P < 0.05). There were no significant differences in exercise time and metabolic equivalents (METs) between SHHC and high-altitude exposures (7.05 ± 1.02 vs. 7.22 ± 0.96 min, P = 0.235; 9.62 ± 1.11 vs. 9.38 ± 1.12, P = 0.126, respectively). However, these variables were relatively higher at sea level (8.03 ± 0.24 min, P < 0.01; 10.05 ± 0.31, P < 0.01, respectively). Thus, subjects displayed an equivalent exercise tolerance upon acute exposure to high altitude and to SHHC. The trends of cardiovascular hemodynamics during exercise under the three different conditions were similar. However, both systolic blood pressure and the rate-pressure product at every TET stage were higher at high altitude and under the SHHC than at sea level. After acute exposure to high altitude, 19 (23.8%) subjects developed AMS. Multivariate logistic regression analysis showed that METs under the SHHC {odds ratio (OR) 0.355 per unit increment [95% confidence intervals (CI) 0.159-0.793], P = 0.011}, diastolic blood pressure (DBP) at rest under SHHC [OR 0.893 per mmHg (95%CI 0.805-0.991), P = 0.030], and recovery DBP 3 min after exercise at sea level [OR 1.179 per mmHg (95%CI 1.043-1.333), P = 0.008] were independently associated with AMS. The predictive model had an area under the receiver operating characteristic curve of 0.886 (95%CI 0.803-0.969, P < 0.001). Thus, young men have similar exercise tolerance in acute exposure to high altitude and to SHHC. Moreover, AMS can be predicted with superior accuracy using characteristics easily obtainable with TET.

Haematological and biochemical profiling of Ladakhi cow: A native cattle of high altitude Leh-Ladakh, India

Ladakhi cattle is a native breed of cattle which is well adapted to hypobaric-hypoxia and cold-stress conditions prevalent at high altitude. These cattle are the main source of A2 quality milk. However, their utility, health and dairy production managements were not standardised for optimum dairy farm economics. Moreover, the haematological and biochemical parameters have not been investigated in details in adult Ladakhi cows, which is the primary requirement of farm health managements. Thus, the objective of this study was to examine the haematology and biochemical parameters in adult Ladakhi cow to establish baseline reference values. Clinically healthy female Ladakhi cattle (10) were selected from the Ladakhi cattle research section, DIHAR, Leh. The resulted haematological and biochemical parameters were compared with already reported reference values for low lander cattle and high lander native and crossbred cattle. Haematological findings revealed that RBC, Hb, heamatocrit, MCV and WBC were within the reference range, rather MCH and MCHC values were more than the reference range. Biochemical findings revealed that albumin, glucose, creatinine, uric acid, alkaline phosphatase, and aspartate aminotransferase were within the reference range limits of low lander. However, urea, triglycerides, total protein values were higher than the reference range and calcium was less than the reference range. These findings indicated that the native Ladakhi cattle are in healthy condition and metabolically adapted to high altitude stress. Hence, these hemato-biochemical profile could be the good biomarkers to evaluate their health status in high altitude stress condition.

Evolution of blood rheology and its relationship to pulmonary hemodynamic during the first days of exposure to moderate altitude

Blood rheology and hemodynamic parameters have never been explored together during acclimatization to altitude. This study aimed to investigate changes in blood rheology parameters and pulmonary hemodynamics during the first days of real moderate altitude exposure.Seventeen athletes were tested at sea-level, 20 hours after their arrival at 2,400 meters of altitude (H1) and five days later (H2). Blood was sampled to analyze red blood cell (RBC) aggregation, blood viscosity and hematocrit. Pulmonary arterial pressure (PAP), pulmonary capillary pressure (Pcap) and pulmonary vascular resistance (PVR) were assessed by echocardiography.We observed a rise in hematocrit, blood viscosity, RBC aggregation, PAP, Pcap and PVR between sea-level and H1. In H2, RBC aggregation, hematocrit, PAP, Pcap and PVR remained different compared to sea-level and no difference was observed between H1 and H2. Blood viscosity decreased in H2 and returned to sea-level values.Our results suggest that hemoconcentration occurring within the first hours of altitude exposure increased blood viscosity, which contributed to the changes in pulmonary hemodynamic. When blood viscosity decreased in H2, no change occurred in pulmonary hemodynamic parameters suggesting that hypoxic pulmonary vasoconstriction was still present. The elevated RBC aggregation observed after in H2 could participate in the increase of Pcap.

Circulating fibrinogen levels are elevated in patients with obstructive sleep apnea: a systemic review and meta-analysis

OBJECTIVE

Fibrinogen is believed to play a role in the pathophysiology of obstructive sleep apnea (OSA) and many studies have assessed circulating fibrinogen concentrations in OSA patients. However, the results from these studies were not consistent. To assess the association of circulating fibrinogen levels and OSA, a meta-analysis was performed.

METHODS

PubMed, Embase and Web of Science databases were searched for eligible studies. Data were extracted, and then weighted mean differences (WMDs) with 95% confidence intervals (CIs) were calculated.

RESULTS

A total of 25 studies involving 1480 cases and 2312 controls were included in this meta-analysis. Combined data indicated that the circulating fibrinogen levels were higher in OSA patients than in controls (WMD: 0.38 g/L, 95% CI [0.29-0.47 g/L], p < 0.001; I² = 80.3%, p < 0.001). In the subgroup analyses by disease severity, there were similar results in mild-moderate OSA patients (WMD: 0.27 g/L, 95% CI [0.14-0.41 g/L], p < 0.001; I² = 29.3%, p = 0.185) and severe OSA patients (WMD: 0.54 g/L, 95% CI [0.28-0.79 g/L], p < 0.001; I² = 65.9%, p = 0.012). Furthermore, in another subgroup analysis, the circulating fibrinogen levels were higher in OSA patients than those in controls who were matched for important potential confounders (WMD: 0.41 g/L, 95% CI [0.21-0.60 g/L], p < 0.001; I² = 62.0%, p = 0.003).

CONCLUSIONS

This systematic review and meta-analysis reveals that circulating fibrinogen levels are elevated in patients with OSA.

Ventilatory and cerebrovascular regulation and integration at high-altitude

Ascent to high-altitude elicits compensatory physiological adaptations in order to improve oxygenation throughout the body. The brain is particularly vulnerable to the hypoxemia of terrestrial altitude exposure. Herein we review the ventilatory and cerebrovascular changes at altitude and how they are both implicated in the maintenance of oxygen delivery to the brain. Further, the interdependence of ventilation and cerebral blood flow at altitude is discussed. Following the acute hypoxic ventilatory response, acclimatization leads to progressive increases in ventilation, and a partial mitigation of hypoxemia. Simultaneously, cerebral blood flow increases during initial exposure to altitude when hypoxemia is the greatest. Following ventilatory acclimatization to altitude, and an increase in hemoglobin concentration-which both underscore improvements in arterial oxygen content over time at altitude-cerebral blood flow progressively decreases back to sea-level values. The complimentary nature of these responses (ventilatory, hematological and cerebral) lead to a tightly maintained cerebral oxygen delivery while at altitude. Despite this general maintenance of global cerebral oxygen delivery, the manner in which this occurs reflects integration of these physiological responses. Indeed, ventilation directly influences cerebral blood flow by determining the prevailing blood gas and acid/base stimuli at altitude, but cerebral blood flow may also influence ventilation by altering central chemoreceptor stimulation via central CO₂ washout. The causes and consequences of the integration of ventilatory and cerebral blood flow regulation at high altitude are outlined.

ACUTE PHASE PROTEIN INCREASE IN HIGH ALTITUDE MOUNTAINEERS

ABSTRACT Introduction: Many middle-aged Turks go hiking in mountains to breathe some fresh air or to maintain fitness. Objective: This study investigated the effects of regular high altitude mountain climbing on the metabolic and hematological responses of mountaineers. Methods: Hematological and biochemical parameters were studied, as well as some hormonal values of 21 mountaineers and 16 healthy age-matched sedentary volunteers. Results: The neutrophil to lymphocyte ratio (NLR) was significantly lower (p<0.04) in mountaineers compared with the sedentary group. Total protein (p<0.001) and albumin (p<0.001) were lower, while the levels of ferritin (p<0.04), creatine (p<0.03) and creatine phosphokinase (p<0.01) were higher in mountaineers. Other hematological and biochemical parameters, i.e., erythrocytes, leukocytes, hemoglobin and hematocrit, did not change significantly. Conclusion: Our results show that regular exposure to high altitude increased the serum levels of some acute phase proteins with anti-inflammatory properties.

A step towards removing plasma volume variance from the Athlete's Biological Passport: The use of biomarkers to describe vascular volumes from a simple blood test

The haematological module of the Athlete's Biological Passport (ABP) has significantly impacted the prevalence of blood manipulations in elite sports. However, the ABP relies on a number of concentration-based markers of erythropoiesis, such as haemoglobin concentration ([Hb]), which are influenced by shifts in plasma volume (PV). Fluctuations in PV contribute to the majority of biological variance associated with volumetric ABP markers. Our laboratory recently identified a panel of common chemistry markers (from a simple blood test) capable of describing ca 67% of PV variance, presenting an applicable method to account for volume shifts within anti-doping practices. Here, this novel PV marker was included into the ABP adaptive model. Over a six-month period (one test per month), 33 healthy, active males provided blood samples and performed the CO-rebreathing method to record PV (control). In the final month participants performed a single maximal exercise effort to promote a PV shift (mean PV decrease -17%, 95% CI -9.75 to -18.13%). Applying the ABP adaptive model, individualized reference limits for [Hb] and the OFF-score were created, with and without the PV correction. With the PV correction, an average of 66% of [Hb] within-subject variance is explained, narrowing the predicted reference limits, and reducing the number of atypical ABP findings post-exercise. Despite an increase in sensitivity there was no observed loss of specificity with the addition of the PV correction. The novel PV marker presented here has the potential to improve the ABP's rate of correct doping detection by removing the confounding effects of PV variance.

Regulation of blood volume in lowlanders exposed to high altitude

Humans ascending to high altitude (HA) experience a reduction in arterial oxyhemoglobin saturation and, as a result, arterial O₂ content ([Formula: see text]). As HA exposure extends, this reduction in [Formula: see text] is counteracted by an increase in arterial hemoglobin concentration. Initially, hemoconcentration is exclusively related to a reduction in plasma volume (PV), whereas after several weeks a progressive expansion in total red blood cell volume (RCV) contributes, although often to a modest extent. Since the decrease in PV is more rapid and usually more pronounced than the expansion in RCV, at least during the first weeks of exposure, a reduction in circulating blood volume is common at HA. Although the regulation of hematological responses to HA has been investigated for decades, it remains incompletely understood. This is not only related to the large number of mechanisms that could be involved and the complexity of their interplay but also to the difficulty of conducting comprehensive experiments in the often secluded HA environment. In this review, we present our understanding of the kinetics, the mechanisms and the physiological relevance of the HA-induced reduction in PV and expansion in RCV.

Blood biomarkers of endocrine, immune, inflammatory, and metabolic systems in obstructive sleep apnea

OBJECTIVE/BACKGROUND

Obstructive sleep apnea (OSA) is a common disorder, affecting over 100 million adults. Untreated OSA leads to serious health consequences and perturbations in endocrine, immune, inflammatory, and metabolic systems. Study objectives are to evaluate the association between OSA and biomarkers, and to test the hypothesis that a combination of markers may be useful in screening for OSA.

PATIENTS/METHODS

A multicenter trial was conducted enrolling symptomatic male patients with suspected OSA. All subjects underwent in-laboratory overnight polysomnography. A non-symptomatic control group was also obtained. Eleven biomarkers were tested: HbA1c, CRP, EPO, IL-6, uric acid, cortisol, hGH, prolactin, testosterone, DHEA (Beckman Coulter UniCel DxC 600i Synchron® Access® Clinical Systems), IGF-1.

RESULTS

73 male subjects were enrolled; 26 had moderate/severe OSA. ROC curve analysis showed HbA1c, CRP, EPO, IL-6, and Uric Acid (AUCs: 0.76, 0.73, 0.65, 0.65, 0.61) were superior to the Epworth Sleepiness Scale (AUC: 0.52). Concurrent elevation of HbA1c and CRP provide even greater predictive power. A combination of elevated HbA1c, CRP, and EPO provided 0.08 increase in AUC (0.84 [0.75 - 0.94]) over individual markers (p<0.05), with high sensitivity (85%), and specificity (79%) for moderate/severe OSA.

CONCLUSIONS

OSA induces characteristic endocrine, immune, inflammatory, and metabolic disturbances that can be detected with blood biomarkers. These biomarkers are superior to standard screening questionnaires. Various clusters of these biomarkers have an even greater association with OSA and thus may represent physiologic signatures of the disorder that may have value in initial screening for OSA as well as for follow-up of therapy response.

Remote ischemic preconditioning for prevention of high-altitude diseases: fact or fiction?

Preconditioning refers to exposure to brief episodes of potentially adverse stimuli and protects against injury during subsequent exposures. This was first described in the heart, where episodes of ischemia/reperfusion render the myocardium resistant to subsequent ischemic injury, which is likely caused by reactive oxygen species (ROS) and proinflammatory processes. Protection of the heart was also found when preconditioning was performed in an organ different from the target, which is called remote ischemic preconditioning (RIPC). The mechanisms causing protection seem to include stimulation of nitric oxide (NO) synthase, increase in antioxidant enzymes, and downregulation of proinflammatory cytokines. These pathways are also thought to play a role in high-altitude diseases: high-altitude pulmonary edema (HAPE) is associated with decreased bioavailability of NO and increased generation of ROS, whereas mechanisms causing acute mountain sickness (AMS) and high-altitude cerebral edema (HACE) seem to involve cytotoxic effects by ROS and inflammation. Based on these apparent similarities between ischemic damage and AMS, HACE, and HAPE, it is reasonable to assume that RIPC might be protective and improve altitude tolerance. In studies addressing high-altitude/hypoxia tolerance, RIPC has been shown to decrease pulmonary arterial systolic pressure in normobaric hypoxia (13% O2) and at high altitude (4,342 m). Our own results indicate that RIPC transiently decreases the severity of AMS at 12% O2. Thus preliminary studies show some benefit, but clearly, further experiments to establish the efficacy and potential mechanism of RIPC are needed.

Acute hyperhydration reduces athlete biological passport OFF-hr score

Anecdotal evidence suggests that athletes hyperhydrate to mask prohibited substances in urine and potentially counteract suspicious fluctuations in blood parameters in the athlete biological passport (ABP). It is examined if acute hyperhydration changes parameters included in the ABP. Twenty subjects received recombinant human erythropoietin (rhEPO) for 3 weeks. After 10 days of rhEPO washout, 10 subjects ingested normal amount of water (∼ 270 mL), whereas the remaining 10 ingested a 1000 mL bolus of water. Blood variables were measured 20, 40, 60, and 80 min after ingestion. Three days later, the subjects were crossed-over with regard to water ingestion and the procedure was repeated. OFF-hr was reduced by ∼ 4%, ∼ 3%, and ∼ 2% at 40, 60, and 80 min, respectively, after drinking 1000 mL of water, compared with normal water ingestion (P < 0.05). Forty percent of the subjects were identified with atypical blood profiles (99% specificity level) before drinking 1000 mL of water, whereas 11% (n = 18), 10% and 11% (n = 18) were identified 40, 60, and 80 min, respectively, after ingestion. This was different (P < 0.05) compared with normal water intake, where 45% of the subjects were identified before ingestion, and 54% (n = 19), 45%, and 47% (n = 19) were identified 40, 60, and 80 min, respectively, after ingestion. In conclusion, acute hyperhydration reduces ABP OFF-hr and reduces ABP sensitivity.

Biomarkers to improve diagnosis and monitoring of obstructive sleep apnea syndrome: current status and future perspectives

Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent episodes of upper airway collapse associated with oxygen desaturation and sleep disruption. It is proposed that these periodic changes lead to molecular variations that can be detected by assessing serum biomarkers. Studies have identified inflammatory, oxidative, and metabolic perturbations attributable to sleep-disordered breathing. Given that OSAS is associated with increased cardiovascular and cerebrovascular morbidity, the ideal biomarker should enable timely recognition with the possibility of intervention. There is accumulating data on the utility of serum biomarkers for the evaluation of disease severity, prognosis, and response to treatment. However, current knowledge is limited by data collection techniques, disease complexity, and potential confounding factors. The current paper reviews the literature on the use of serum biomarkers in OSAS. It is concluded that the ideal serum biomarker still needs to be discovered, while caution is needed in the interpretation of hitherto available results.

AltitudeOmics: rapid hemoglobin mass alterations with early acclimatization to and de-acclimatization from 5260 m in healthy humans

It is classically thought that increases in hemoglobin mass (Hbmass) take several weeks to develop upon ascent to high altitude and are lost gradually following descent. However, the early time course of these erythropoietic adaptations has not been thoroughly investigated and data are lacking at elevations greater than 5000 m, where the hypoxic stimulus is dramatically increased. As part of the AltitudeOmics project, we examined Hbmass in healthy men and women at sea level (SL) and 5260 m following 1, 7, and 16 days of high altitude exposure (ALT1/ALT7/ALT16). Subjects were also studied upon return to 5260 m following descent to 1525 m for either 7 or 21 days. Compared to SL, absolute Hbmass was not different at ALT1 but increased by 3.7±5.8% (mean ± SD; n = 20; p<0.01) at ALT7 and 7.6±6.6% (n = 21; p<0.001) at ALT16. Following descent to 1525 m, Hbmass was reduced compared to ALT16 (−6.0±3.7%; n = 20; p = 0.001) and not different compared to SL, with no difference in the loss in Hbmass between groups that descended for 7 (−6.3±3.0%; n = 13) versus 21 days (−5.7±5.0; n = 7). The loss in Hbmass following 7 days at 1525 m was correlated with an increase in serum ferritin (r = −0.64; n = 13; p<0.05), suggesting increased red blood cell destruction. Our novel findings demonstrate that Hbmass increases within 7 days of ascent to 5260 m but that the altitude-induced Hbmass adaptation is lost within 7 days of descent to 1525 m. The rapid time course of these adaptations contrasts with the classical dogma, suggesting the need to further examine mechanisms responsible for Hbmass adaptations in response to severe hypoxia.

Severity of obstructive sleep apnea is associated with elevated plasma fibrinogen in otherwise healthy patients

PURPOSE

Obstructive sleep apnea (OSA) has been implicated in both cardiovascular and cerebrovascular diseases. Systemic inflammation and coagulation may be related to cardiovascular pathophysiology in patients with OSA. Fibrinogen is a major coagulation protein associated with inflammation, and long-term elevated plasma fibrinogen is associated with an increased risk of major cardiovascular diseases. We assessed whether severity of OSA is associated with levels of fibrinogen in newly diagnosed, untreated, and otherwise healthy OSA patients.

METHODS

We studied 36 men with OSA and 18 male control subjects (apnea-hypopnea index [AHI]<5 events/h). OSA patients were divided into mild (AHI≥5<15 events/h) and severe (AHI≥15 events/h) OSA groups. Morning fibrinogen levels in OSA patients were compared to those in control subjects of similar age, body mass index, blood pressure, smoking habits, and alcohol consumption.

RESULTS

Fibrinogen levels were significantly elevated in patients with severe OSA compared to both control (P=0.003) and mild OSA (P=0.02) subjects after adjustment for covariates. However, there were no significant differences in fibrinogen levels between mild OSA and control subjects. Fibrinogen levels were directly related to AHI and arousal index and inversely related to mean and lowest oxygen saturation during sleep.

CONCLUSIONS

Severity of OSA was associated with increased fibrinogen level independent of other factors, suggesting that apneic events and oxygen desaturation during sleep are mechanisms for increased fibrinogen levels in patients with OSA.

High-altitude pulmonary edema

High-altitude pulmonary edema (HAPE), a not uncommon form of acute altitude illness, can occur within days of ascent above 2500 to 3000 m. Although life-threatening, it is avoidable by slow ascent to permit acclimatization or with drug prophylaxis. The critical pathophysiology is an excessive rise in pulmonary vascular resistance or hypoxic pulmonary vasoconstriction (HPV) leading to increased microvascular pressures. The resultant hydrostatic stress causes dynamic changes in the permeability of the alveolar capillary barrier and mechanical injurious damage leading to leakage of large proteins and erythrocytes into the alveolar space in the absence of inflammation. Bronchoalveolar lavage and hemodynamic pressure measurements in humans confirm that elevated capillary pressure induces a high-permeability noninflammatory lung edema. Reduced nitric oxide availability and increased endothelin in hypoxia are the major determinants of excessive HPV in HAPE-susceptible individuals. Other hypoxia-dependent differences in ventilatory control, sympathetic nervous system activation, endothelial function, and alveolar epithelial active fluid reabsorption likely contribute additionally to HAPE susceptibility. Recent studies strongly suggest nonuniform regional hypoxic arteriolar vasoconstriction as an explanation for how HPV occurring predominantly at the arteriolar level causes leakage. In areas of high blood flow due to lesser HPV, edema develops due to pressures that exceed the dynamic and structural capacity of the alveolar capillary barrier to maintain normal fluid balance. This article will review the pathophysiology of the vasculature, alveolar epithelium, innervation, immune response, and genetics of the lung at high altitude, as well as therapeutic and prophylactic strategies to reduce the morbidity and mortality of HAPE.

Serum inflammatory markers in obstructive sleep apnea: a meta-analysis

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) has been linked to and is associated with increased cardiovascular and cerebrovascular morbidity. Ongoing inflammatory responses play an important role in this association. Multiple small size studies addressing the profile of the inflammatory markers in OSA are available therefore we performed a meta-analysis.

METHODS

Systematic review of medical literature was conducted using PubMed, Cochrane, and EMBASE databases from 1968 to 2011 by utilizing the key words obstructive sleep apnea, C-Reactive protein, tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), interleukin 8 (IL-8), intercellular adhesion molecule (ICAM), vascular cell adhesion molecule (VCAM) and Selectins. Inclusion criteria were: full text English articles; studies with adult population; reported values for at least one of the markers of interest; with at least two separate groups (subjects with OSA and control group); OSA was defined as AHI of ≥ 5/h.

RESULTS

Five hundred and twelve studies were reviewed for inclusion with 51 studies pooled for analysis (30 studies for CRP, 19 studies for TNF-α, 8 studies for ICAM, 18 studies for IL-6, six studies for VCAM and 5 studies for Selectins). The levels of inflammatory markers were higher in patients with OSA compared to control group. Standardized pooled Mean differences were calculated to be 1.77 for CRP, 1.03 for TNF-α, 2.16 for IL-6, 4.22 for IL-8, 2.93 for ICAM, 1.45 for Selectins and 2.08 for VCAM.

CONCLUSIONS

In this meta-analysis, the levels of systemic inflammatory markers were found to be higher in OSA patients compared to control subjects.

High-altitude diving in river otters: coping with combined hypoxic stresses

River otters (Lontra canadensis) are highly active, semi-aquatic mammals indigenous to a range of elevations and represent an appropriate model for assessing the physiological responses to diving at altitude. In this study, we performed blood gas analyses and compared blood chemistry of river otters from a high-elevation (2357 m) population at Yellowstone Lake with a sea-level population along the Pacific coast. Comparisons of oxygen dissociation curves (ODC) revealed no significant difference in hemoglobin-oxygen (Hb-O(2)) binding affinity between the two populations - potentially because of demands for tissue oxygenation. Instead, high-elevation otters had greater Hb concentrations (18.7 g dl(-1)) than sea-level otters (15.6 g dl(-1)). Yellowstone otters displayed higher levels of the vasodilator nitric oxide (NO), and half the concentration of the serum protein albumin, possibly to compensate for increased blood viscosity. Despite compensation in several hematological and serological parameters, theoretical aerobic dive limits (ADL) were similar between high-elevation and sea-level otters because of the lower availability of O(2) at altitude. Our results suggest that recent disruptions to the Yellowstone Lake food web could be detrimental to otters because at this high elevation, constraints on diving may limit their ability to switch to prey in a deep-water environment.

Measurement of apolipoprotein E and amyloid β clearance rates in the mouse brain using bolus stable isotope labeling

Background

Abnormal proteostasis due to alterations in protein turnover has been postulated to play a central role in several neurodegenerative diseases. Therefore, the development of techniques to quantify protein turnover in the brain is critical for understanding the pathogenic mechanisms of these diseases. We have developed a bolus stable isotope-labeling kinetics (SILK) technique coupled with multiple reaction monitoring mass spectrometry to measure the clearance of proteins in the mouse brain.

Results

Cohorts of mice were pulse labeled with ¹³ C₆-leucine and the brains were isolated after pre-determined time points. The extent of label incorporation was measured over time using mass spectrometry to measure the ratio of labeled to unlabeled apolipoprotein E (apoE) and amyloid β (Aβ). The fractional clearance rate (FCR) was then calculated by analyzing the time course of disappearance for the labeled protein species. To validate the technique, apoE clearance was measured in mice that overexpress the low-density lipoprotein receptor (LDLR). The FCR in these mice was 2.7-fold faster than wild-type mice. To demonstrate the potential of this technique for understanding the pathogenesis of neurodegenerative disease, we applied our SILK technique to determine the effect of ATP binding cassette A1 (ABCA1) on both apoE and Aβ clearance. ABCA1 had previously been shown to regulate both the amount of apoE in the brain, along with the extent of Aβ deposition, and represents a potential molecular target for lowering brain amyloid levels in Alzheimer's disease patients. The FCR of apoE was increased by 1.9- and 1.5-fold in mice that either lacked or overexpressed ABCA1, respectively. However, ABCA1 had no effect on the FCR of Aβ, suggesting that ABCA1 does not regulate Aβ metabolism in the brain.

Conclusions

Our SILK strategy represents a straightforward, cost-effective, and efficient method to measure the clearance of proteins in the mouse brain. We expect that this technique will be applicable to the study of protein dynamics in the pathogenesis of several neurodegenerative diseases, and could aid in the evaluation of novel therapeutic agents.

Plasma adipokine and hormone changes in mountaineers on ascent to 5300 meters

OBJECTIVE

The current study evaluated multiple metabolic and inflammatory hormone responses in recreational climbers (7 men and 3 women, age 26-49 years) over 9 days. In particular, acylation-stimulating protein (ASP), which influences fat storage in adipose tissue, has not been measured at high altitude.

METHODS

Serial measurements were taken at sea level (SL), or 353 m, on day 0, 4000 m on day 3, 4750 m on day 6, and 5300 m on day 9 of the expedition.

RESULTS

Body mass index (BMI) decreased upon ascent to 5300 m from SL (SL 23.2 ± 1.5 kg/m(2); 4000 m 23.2 ± 1.4 kg/m(2); 4750 m 22.9 ± 1.3 kg/m(2); 5300 m 22.3 ± 1.2 kg/m(2); P<.001). Similarly, plasma non-esterified fatty acids and triglycerides increased, while HDL cholesterol decreased (P<.05 to <.001) from SL to 5300 m. Acylation-stimulating protein (SL 42.2 ± 40.2 nm; 4000 m 117.0 ± 69.6 nm; 4750 m 107.9 ± 44.5 nm; 5300 m 82.2 ± 20.2 nm; P=.019) and adiponectin (SL 10.4 ± 6.5 ng/mL, 4000 m 13.9 ± 8.5 ng/mL, 4750 m 18.3 ± 8.3 ng/mL, 5300 m 14.7 ± 8.0 ng/mL; P=.015) increased, as did insulin and Interleukin-6 (IL-6) levels (up to 71% and 168%, respectively; P<.05) with no change in leptin, complement C3 (C3), high sensitivity C-reactive protein (hsCRP) or cortisol levels throughout the mountain ascent from SL to 5300 m.

CONCLUSION

Acylation-stimulating protein and adiponectin are increased during a 9-day period of high altitude (SL to 5300 m) exposure despite weight loss in healthy mountaineers.

High-Altitude Pulmonary Edema

High-altitude pulmonary edema (HAPE) is an uncommon form of pulmonary edema that occurs in healthy individuals within a few days of arrival at altitudes above 2,500–3,000 m. The crucial pathophysiology is an excessive hypoxia-mediated rise in pulmonary vascular resistance (PVR) or hypoxic pulmonary vasoconstriction (HPV) leading to increased microvascular hydrostatic pressures despite normal left atrial pressure. The resultant hydrostatic stress can cause both dynamic changes in the permeability of the alveolar capillary barrier and mechanical damage leading to leakage of large proteins and erythrocytes into the alveolar space in the absence of inflammation. Bronchoalveolar lavage (BAL) and pulmonary artery (PA) and microvascular pressure measurements in humans confirm that high capillary pressure induces a high-permeability non-inflammatory-type lung edema; a concept termed “capillary stress failure.” Measurements of endothelin and nitric oxide (NO) in exhaled air, NO metabolites in BAL fluid, and NO-dependent endothelial function in the systemic circulation all point to reduced NO availability and increased endothelin in hypoxia as a major cause of the excessive hypoxic PA pressure rise in HAPE-susceptible individuals. Other hypoxia-dependent differences in ventilatory control, sympathetic nervous system activation, endothelial function, and alveolar epithelial sodium and water reabsorption likely contribute additionally to the phenotype of HAPE susceptibility. Recent studies using magnetic resonance imaging in humans strongly suggest nonuniform regional hypoxic arteriolar vasoconstriction as an explanation for how HPV occurring predominantly at the arteriolar level can cause leakage. This compelling but not yet fully proven mechanism predicts that in areas of high blood flow due to lesser vasoconstriction edema will develop owing to pressures that exceed the structural and dynamic capacity of the alveolar capillary barrier to maintain normal alveolar fluid balance. Numerous strategies aimed at lowering HPV and possibly enhancing active alveolar fluid reabsorption are effective in preventing and treating HAPE. Much has been learned about HAPE in the past four decades such that what was once a mysterious alpine malady is now a well-characterized and preventable lung disease. This chapter will relate the history, pathophysiology, and treatment of HAPE, using it not only to illuminate the condition, but also for the broader lessons it offers in understanding pulmonary vascular regulation and lung fluid balance.

Enhanced albumin synthesis in severely burned adults

Albumin plays an important role in maintaining physiological homeostasis. Although decreased albumin concentration has been well described as an acute-phase response following injury, it is unclear whether the decrease is due to compromised synthesis of albumin, dilution, or imbalance between synthesis and breakdown rates, particularly after injury. We investigated changes in albumin synthesis in severely burned patients using stable isotope infusion techniques. Five patients (29 ± 3 years; 80 ± 7 kg) with burn of 48% ± 4% total body surface area (TBSA) were enrolled and studied in the ICU at the Burn Unit of the US Army Institute of Surgical Research. Five age- and sex-matched healthy volunteers (33 ± 5 years; 81 ± 6 kg) were included as controls. On the study day (13 ± 3 days after burn), a primed constant infusion (4 h) of stable isotope d5-phenlylalanine and d3-ketoisocaproic acid was given. Hourly arterial blood samples were drawn during the infusion to determine albumin synthesis rates, using gas chromatography-mass spectrometry analysis. Burned patients had higher heart and respiration rates. Plasma total protein in burn patients (4.5 ± 0.3 g · dL-1) was lower compared with controls (6.8 ± 0.2 g · dL-1). Plasma albumin concentration in burn patients (1.1 ± 0.1 g · dL-1) was also lower compared with controls (3.8 ± 0.1 g · dL-1; both P < 0.05). Albumin synthesis rate in burn patients (4.6 ± 0.2 mg · kg-1 · h-1) was enhanced compared with controls (2.2 ± 0.2 mg · kg-1 · h-1; P < 0.05). Despite the decrease in albumin concentration, albumin synthesis was enhanced in severely burned patients during the flow phase.

Plasticity of the muscle proteome to exercise at altitude

The ascent of humans to the summits of the highest peaks on Earth initiated a spurt of explorations into the physiological consequences of physical activity at altitude. The past three decades have demonstrated that the resetting of respiratory and cardiovascular control with chronic exposure to altitudes above 4000 m is accompanied by important structural-functional adjustments of skeletal muscle. The fully altitude-adapted phenotype preserves energy charge at reduced aerobic capacity through the promotion of anaerobic substrate flux and tighter metabolic control, often at the expense of muscle mass. In seeming contrast, intense physical activity at moderate hypoxia (2500 to 4000 m) modifies this response in both low and high altitude natives through metabolic compensation by elevating local aerobic capacity and possibly preventing muscle fiber atrophy. The combined use of classical morphometry and contemporary proteomic technology provides a highly resolved picture of the temporal control of hypoxia-induced muscular adaptations. The muscle proteome signature identifies mitochondrial autophagy and protein degradation as prime adaptive mechanisms to passive altitude exposure and ascent to extreme altitude. Protein measures also explain the lactate paradox by a sparing of glycolytic enzymes from general muscle wasting. Enhanced mitochondrial and angiogenic protein expression in human muscle with exercise up to 4000 m is related to the reduction in intramuscular oxygen content below 1% (8 torr), when the master regulator of hypoxia-dependent gene expression, HIF-1alpha, is stabilized. Accordingly, it is proposed here that the catabolic consequences of chronic hypoxia exposure reflect the insufficient activation of hypoxia-sensitive signaling and the suppression of energy-consuming protein translation.

Appropriate use of nasal continuous positive airway pressure decreases elevated C-reactive protein in patients with obstructive sleep apnea

BACKGROUND

C-reactive protein (CRP) is an important risk factor for cardiovascular disease. Furthermore, it has been reported that levels of CRP are increased in patients with obstructive sleep apnea (OSA). The aim of this study was to examine the effects of long-term therapy with nasal continuous positive airway pressure (nCPAP) on CRP levels and to investigate whether compliance with nCPAP therapy more effectively attenuated markers of systemic inflammation in patients with OSA.

METHODS AND RESULTS

Fifty-five patients (mean [+/- SEM] age, 55 +/- 2 years; 44 male patients, 11 female patients) with newly diagnosed moderate-to-severe OSA (apnea-hypopnea index > 20 events/h) were studied before and after 6 months of nCPAP treatment. There was a significant reduction in CRP levels after nCPAP therapy (before nCPAP therapy, 0.23 +/- 0.03 mg/dL; after nCPAP therapy, 0.17 +/- 0.02 mg/dL; p < 0.01). Additionally, we divided these patients into two groups based on adherence to nCPAP therapy. A group of patients using nCPAP > 4 h/d and > 5 d/wk were designated as the good compliance group. The decrease in CRP concentration was significant (before nCPAP therapy, 0.23 +/- 0.04 mg/dL; after nCPAP therapy, 0.16 +/- 0.03 mg/dL; p < 0.05) in the good compliance group but not in the poor compliance group (before nCPAP therapy, 0.24 +/- 0.05 mg/dL; after nCPAP therapy, 0.20 +/- 0.05 mg/dL; p = 0.21). Furthermore, we divided those patients into a high CRP group (>/= 0.2 mg/dL) and a normal CRP group (< 0.2 mg/dL) before nCPAP therapy. The significant decrease in CRP levels in the good compliance group was evident only in those patients with an initially elevated CRP level (before nCPAP therapy, 0.48 +/- 0.08 mg/dL; after nCPAP therapy, 0.29 +/- 0.06 mg/dL; p < 0.05).

CONCLUSION

Appropriate use of nCPAP in patients with OSA may be required to decrease elevated CRP levels, with possible implications for cardiovascular morbidity and mortality.

Effects of the Fusarium toxin deoxynivalenol from naturally contaminated wheat given subchronically or as one single dose on the in vivo protein synthesis of peripheral blood lymphocytes and plasma proteins in the pig

Trichothecenes, such as deoxynivalenol (DON), are known to inhibit the protein synthesis in vitro by binding at the 60S subunit of eukaryotic ribosomes. Therefore, cells and tissues with high protein turnover, such as lymphocytes and the liver (albumin and fibrinogen synthesis), were suggested to react most sensitively to DON. However, to the author's knowledge this observation was not proven in vivo in pigs, which were regarded as the farm animals most susceptible to DON. A total of 31 castrated male, crossbred German Landrace x Pietrain pigs weighing approx. 40 kg were fed a DON contaminated diet (5.7 mg/kg) either acutely (one single dose) or subchronically (4 weeks) or a control diet (0.1 mg/kg). In addition, one group received an intravenous injection of 53 microg DON/kg LW. One hour after feeding, a "flooding dose" of the stable isotope l-[(2)H(5)]-phenylalanine (125 mg/kg LW) was given and frequent blood samples (permanent catheter) were collected over a 60 min period. The molar percent excess (MPE) of plasma free and protein-bound phenylalanine were measured by GC/MS. No differences could be observed in the plasma concentrations of total protein, albumin, fibrinogen and serum enzymes between the groups. On the other hand, fractional synthesis rates (FSR, %/d) of albumin were significantly decreased by 43%, 45% and 26% and FSR of lymphocytes declined by 27%, 19% and 24%, whereas fibrinogen was not significantly affected after subchronic or one single oral and intravenous DON exposure, respectively. Additionally, the absolute synthesis rate (ASR, g/d) of albumin and the proportion of albumin to total body protein synthesis were reduced in the same manner, whereas the albumin secretion time ranged between 6.8 and 34.4 min and was not affected by treatment. In conclusion, the flooding dose technique appeared to be suitable for distinguishing DON-related effects on the protein synthesis, while determination of plasma protein concentrations seemed not to be an appropriate parameter.

Skeletal Muscle Protein Synthesis after Active or Passive Ascent to High Altitude

INTRODUCTION

The effects of acute exposure to high altitude on muscle protein synthesis rates in human volunteers were examined after active and passive ascent.

METHODS

Measurements were made initially at low altitude (550 m) and again after ascent to high altitude (4,559 m). To be able to separate the contribution of physical exercise, one group was flown by helicopter (air group, N=8), whereas the other group climbed to high altitude (foot group, N=9). Fractional rates of muscle protein synthesis rates (FSR) were determined from the incorporation of isotope into protein after injection of [H5ring] phenylalanine.

RESULTS

In the air group, there was no change in FSR at high altitude, whereas in the foot group, there was a 35% increase in FSR (P<0.05 for interaction) measured 19-23 h after the end of climbing. At high altitude, the degree of hypoxia and alkalosis were not different between the groups. The plasma concentration of insulin-like growth factor-1, free thyroxin, free triiodothyronine, and thyroid-stimulating hormone were not different between the groups. Urinary 24-h cortisol excretion increased significantly in both groups after ascent, but the increase in the foot group was significantly higher compared with the air group.

CONCLUSION

Physical exercise appeared to be responsible for the observed increase in muscle FSR. The significantly higher increase of 24-h cortisol excretion in the foot group suggests that the increase in FSR occurred despite higher levels of glucocorticoids, which generally affect muscle protein turnover by inhibiting protein synthesis.

Effect of high altitude and exercise on microvascular parameters in acclimatized subjects

The role of microvascular fluid shifts in the adaptation to hypobaric hypoxia and its contribution to the pathophysiology of AMS (acute mountain sickness) is unresolved. In a systematic prospective study, we investigated the effects of hypobaric hypoxia and physical exercise alone, and in combination, on microvascular fluid exchange and related factors. We used computer-assisted VCP (venous congestion plethysmography) on the calves of ten altitude-acclimatized volunteers. We investigated the effects of: (i) actively climbing to an altitude of 3196 m, (ii) airlifting these subjects to the same altitude, and (iii) exercise at low altitude. CFC (capillary filtration capacity), Pvi (isovolumetric venous pressure) and Qa (calf blood flow) were assessed before and after each procedure and then repeated after an overnight rest. Measurements of CFC showed no evidence of increased microvascular permeability after any of the procedures. Pvi was significantly decreased (P<0.001) from 20.3±4.4 to 8.9±4.3 mmHg after active ascent, and was still significantly lower (P=0.009) after overnight rest at high altitude (13.6±5.9 mmHg). No such changes were observed after the passive ascent (16.7±4.0 mmHg at baseline; 17.3±4.5 mmHg after passive ascent; and 19.9±5.3 mmHg after overnight rest) or after exercise at low altitude. After the active ascent, Qa was significantly increased. We also found a significant correlation between Qa, Pvi and the number of circulating white blood cells. In conclusion, we found evidence to support the hypothesis that increased microvascular permeability associated with AMS does not occur in acclimatized subjects. We also observed that the microvascular equilibrium pressure (Pvi) fell in inverse relation to the increase in Qa, especially in hypoxic exercise. We hypothesize that this inverse relationship reflects the haemodynamic changes at the microvascular interface, possibly attributable to the flow-induced increases in endothelial surface shear forces.

Role of acid-base balance in the chemoreflex control of breathing

This paper uses a steady-state modeling approach to describe the effects of changes in acid-base balance on the chemoreflex control of breathing. First, a mathematical model is presented, which describes the control of breathing by the respiratory chemoreflexes; equations express the dependence of pulmonary ventilation on Pco(2) and Po(2) at the central and peripheral chemoreceptors. These equations, with Pco(2) values as inputs to the chemoreceptors, are transformed to equations with hydrogen ion concentrations [H(+)] in brain interstitial fluid and arterial blood as inputs, using the Stewart approach to acid-base balance. Examples illustrate the use of the model to explain the regulation of breathing during acid-base disturbances. They include diet-induced changes in sodium and chloride, altitude acclimatization, and respiratory disturbances of acid-base balance due to chronic hyperventilation and carbon dioxide retention. The examples demonstrate that the relationship between Pco(2) and [H(+)] should not be neglected when modeling the chemoreflex control of breathing. Because pulmonary ventilation controls Pco(2) rather than the actual stimulus to the chemoreceptors, [H(+)], changes in their relationship will alter the ventilatory recruitment threshold Pco(2), and thereby the steady-state resting ventilation and Pco(2).

The effect of rosiglitazone on novel atherosclerotic risk factors in patients with type 2 diabetes mellitus and hypertension. An open-label observational study

Thiazolidinediones are antidiabetic agents that decrease insulin resistance. Emerging evidence indicates that they present beneficial effects for the vasculature beyond glycemic control. The aim of this open-label observational study was to determine the effect of the thiazolidinedione rosiglitazone on novel cardiovascular risk factors, namely, lipoprotein(a) [Lp(a)], C-reactive protein (CRP), homocysteine, and fibrinogen in patients with type 2 diabetes and hypertension. A total of 40 type 2 diabetic patients already on treatment with 15 mg of glibenclamide daily and with poorly controlled or newly diagnosed hypertension were included in the study. Twenty of them received 4 mg of rosiglitazone daily as added-on therapy, whereas the rest remained on the preexisting antidiabetic treatment for 26 weeks. At baseline and the end of the study, subjects gave blood tests for the determination of Lp(a), CRP, homocysteine, fibrinogen, serum lipids, apolipoprotein (apo) A-I, and apo B. At the end of the study, rosiglitazone treatment was associated with significant reductions in Lp(a) (10.5 [8.9-54.1] to 9.8 [8.0-42.0] mg/dL, P<.05) and CRP levels (0.33 [0.07-2.05] to 0.25 [0.05-1.84] mg/dL, P<.05) vs baseline. Homocysteine levels were not affected but plasma fibrinogen presented a significant increase (303.5+/-75.1 to 387.5+/-70.4 mg/dL, P<.01) with rosiglitazone. Although no significant changes were observed in the rosiglitazone group for triglycerides, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein (LDL) cholesterol, both apo A-I and apo B presented small significant reductions and the LDL-apo B ratio was significantly increased. None of the above parameters were changed in the control group. In conclusion, rosiglitazone treatment had a beneficial impact on Lp(a), CRP, and LDL particles' lipid content in type 2 diabetic hypertensive patients but not on homocysteine and fibrinogen. The overall effect of rosiglitazone on cardiovascular risk factors seems positive but must be further evaluated.

Changes in respiratory control after 5 days at altitude

These experiments examined changes in the chemoreflex control of breathing and acid-base balance after 5 days at altitude (3480 m) in six healthy males. The partial pressures of carbon dioxide (P(CO2)) at which ventilation increased during isoxic hypoxic and hyperoxic modified rebreathing tests at sea level fell significantly at altitude by mean+/-S.E.M. of 12.8+/-2.51 mmHg and 9.5+/-1.77 mmHg, respectively, but response slopes above threshold were unchanged. Altitude exposure produced a respiratory alkalosis evidenced by a decrease in mean resting end-tidal P(CO2) from 41+/-0.84 mmHg at sea level to 32+/-2.04 mmHg at altitude, but pH did not increase significantly from its sea level value. Blood samples were analyzed to discover acid-base changes, using a modification of the equations for acid-base balance proposed by [Stewart, P.A., 1983. Modern quantitative acid-base chemistry. Can. J. Physiol. Pharmacol. 61, 1444-1461]. While strong ion difference at altitude was not significantly different from its sea level value, albumin concentration was increased significantly from 38.6+/-0.30 g L(-1) to 49.8+/-0.76 g L(-1). We suggest that the respiratory alkalosis was produced by a fall in the chemoreflex threshold and pH was corrected by an elevation in the concentration of weakly dissociated protein anions.

POOR NUTRITIONAL STATUS AND INFLAMMATION: Serum Albumin: Relationship to Inflammation and Nutrition

Hypoalbuminemia is the result of the combined effects of inflammation and inadequate protein and caloric intake in patients with chronic disease such as chronic renal failure. Inflammation and malnutrition both reduce albumin concentration by decreasing its rate of synthesis, while inflammation alone is associated with a greater fractional catabolic rate (FCR) and, when extreme, increased transfer of albumin out of the vascular compartment. A vicious cascade of events ensues in which inflammation induces anorexia and reduces the effective use of dietary protein and energy intake and augments catabolism of the key somatic protein, albumin. Hypoalbuminemia is a powerful predictor of mortality in patients with chronic renal failure, and the major cause of death in this population is due to cardiovascular events. Inflammation is associated with vascular disease and likely causes injury to the vascular endothelium, and hypoalbuminemia as two separate expressions of the inflammatory process. Albumin has a myriad of important physiologic effects that are essential for normal health. However, simply administering albumin to critically ill patients with hypoalbuminemia has not been shown to improve survival or reduce morbidity. Thus the inference from these clinical studies suggests that the cause of hypoalbuminemia, rather than low albumin levels specifically, is responsible for morbidity and mortality.

Postexercise protein metabolism in older and younger men following moderate-intensity aerobic exercise

Regular aerobic exercise strongly influences muscle metabolism in elderly and young; however, the acute effects of aerobic exercise on protein metabolism are not fully understood. We investigated the effect of a single bout of moderate walking (45 min at approximately 40% of peak O2 consumption) on postexercise (POST-EX) muscle metabolism and synthesis of plasma proteins [albumin (ALB) and fibrinogen (FIB)] in untrained older (n = 6) and younger (n = 6) men. We measured muscle phenylalanine (Phe) kinetics before (REST) and POST-EX (10, 60, and 180 min) using l-[ring-2H5]phenylalanine infusion, femoral arteriovenous blood samples, and muscle biopsies. All data are presented as the difference from REST (at 10, 60, and 180 min POST-EX). Mixed muscle fractional synthesis rate (FSR) increased significantly at 10 min POST-EX in both the younger (0.0363%/h) and older men (0.0830%/h), with the younger men staying elevated through 60 min POST-EX (0.0253%/h). ALB FSR increased at 10 min POST-EX in the younger men only (2.30%/day), whereas FIB FSR was elevated in both groups through 180 min POST-EX (younger men = 4.149, older men = 4.107%/day). Muscle protein turnover was also increased, with increases in synthesis and breakdown in younger and older men. Phe rate of disappearance (synthesis) was increased in both groups at 10 min POST-EX and remained elevated through 60 min POST-EX in the older men. A bout of moderate-intensity aerobic exercise induces short-term increases in muscle and plasma protein synthesis in both younger and older men. Aging per se does not diminish the protein metabolic capacity of the elderly to respond to acute aerobic exercise.

Hemostatic Alterations in Patients With Obstructive Sleep Apnea and the Implications for Cardiovascular Disease *

STUDY OBJECTIVES

Patients with obstructive sleep apnea (OSA) are at increased risk for coronary artery and cerebrovascular diseases. Numerous studies suggest that a hypercoagulable state is prospectively related to atherothrombotic events. This review explores whether changes in hemostasis may constitute one biological link between OSA and vascular disease.

DESIGN

Ten studies on hemostatic variables in OSA were located by electronic library search and descriptively reviewed. Work on hemostatic function with physiologic conditions similar to those found in OSA (hypoxemia and hyperactivity of the sympathetic nervous system) was considered to discuss potential molecular mechanisms of procoagulant disturbances in OSA.

MEASUREMENTS AND RESULTS

The reviewed data suggest that, as compared to non-OSA control subjects, patients with OSA have elevated plasma fibrinogen levels, exaggerated platelet activity, and reduced fibrinolytic capacity. Although not consistently shown, severity of OSA (ie, apnea-hypopnea index) and plasma epinephrine were independent predictors of platelet activity, and average minimal oxygen saturation was an independent predictor of fibrinogen. In some studies, treatment with continuous positive airway pressure decreased platelet activity, plasma fibrinogen levels, and activity of clotting factor VII.

CONCLUSIONS

There is some evidence for a hypercoagulable state in OSA, which might help explain the increased prevalence of vascular diseases in this population. To further confirm such a notion, future studies need to be performed on sufficiently large samples to be able to control for confounders of hemostatic activity. Prospective studies are needed to examine the association between hemostasis molecules and strong vascular end points.

Factors that affect albumin concentration in dialysis patients and their relationship to vascular disease

INTRODUCTION

Hypoalbuminemia is a powerful risk factor for cardiovascular mortality in hemodialysis patients (HD). Inflammation causes a decrease in albumin synthesis and an increase in albumin fractional catabolic rate, providing two mechanisms for hypoalbuminemia. The inflammatory response alters the endothelium and plasma protein composition in ways that favor vascular injury. Plasma volume is expanded in HD patients, providing another mechanism for hypoalbuminemia. Fibrinogen levels are an independent risk factor for cardiovascular disease (CVD) in HD patients, and fibrinogen levels are increased in HD patients. Plasma volume expansion is also an independent risk factor for CVD.

METHODS

Albumin synthesis was measured in 74 HD patients as the disappearance of [125I] human albumin over six weeks. Fibrinogen was measured in plasma. Plasma fibrinogen mass was the product of fibrinogen concentration and plasma volume.

RESULTS

Albumin synthesis correlated positively with plasma volume (P < 0.001). Fibrinogen concentration and plasma fibrinogen mass both correlated positively with albumin synthesis (P < 0.001).

CONCLUSION

Albumin levels are reduced as part of the acute-phase response in HD. Plasma volume expansion also tends to decrease albumin concentration, but elicits an increase in its rate of synthesis, which, in turn, is associated with increased fibrinogen levels. Thus, both inflammation and plasma volume expansion factors that reduce albumin concentration and are independent cardiovascular risk factors, independently increase fibrinogen levels.

Impact of albumin synthesis rate and the acute phase response in the dual regulation of fibrinogen levels in hemodialysis patients

BACKGROUND

Fibrinogen is a risk factor for cardiovascular disease. It also is an acute phase protein (APP) and its plasma concentration increases with inflammation. Fibrinogen synthesis correlates with albumin synthesis in nephrotic patients and in patients with an expanded plasma volume even when serum albumin is normal and there is no inflammatory disease. The relationships among albumin synthesis, the acute phase response and plasma fibrinogen levels in hemodialysis patients are unknown.

METHODS

In 74 hemodialysis patients, albumin synthesis, plasma volume (PV) and acute phase proteins (APPs) C-reactive protein (CRP), alpha1 acid glycoprotein (alpha1 AG), ceruloplasmin (Cer), and interleukin 6 (IL-6) were measured in serum and fibrinogen in plasma, and the results analyzed by multiple regression analysis. CRP, IL-6, alpha1 AG, Cer and fibrinogen were measured monthly, which enabled us to determine whether changes in these APPs correlated with the levels of and variability in plasma fibrinogen over time using a longitudinal modeling approach. Length of follow-up for the 74 patients ranged from 3.25 to 67.5 months.

RESULTS

Baseline fibrinogen (548.6 +/- 106. 4 mg/dL) was significantly greater than levels reported for normal adults and correlated positively with albumin synthesis (P < 0.001), age (P < 0.001) and log CRP (P = 0.002) and negatively with PV (P < 0.001). Longitudinally, fibrinogen varied positively with long-lived APPs, Cer and alpha1 AG, as well as the short-lived APP, CRP.

CONCLUSION

Plasma fibrinogen concentration is high in HD patients and directly correlates with increased albumin synthesis rates and the serum levels of APPs. Fibrinogen levels also correlate negatively with PV. Fibrinogen levels vary over time in synchrony with levels of other long-lived APPs, supporting the hypothesis that fibrinogen is regulated in part as a component of the acute phase response and in part by factors that increase albumin synthesis.

Measurement of muscle protein fractional synthesis and breakdown rates from a pulse tracer injection

We have developed a new method to determine the fractional synthesis rate (FSR) and breakdown rate (FBR) of muscle protein. This method involves a pulse tracer injection and measurement of enrichment in the arterial blood and muscle at three time points. The calculations of FSR and FBR are based on the precursor-product principle. To test this method, we gave a pulse injection of L-[ring-(13)C(6)]phenylalanine of 4-6 mg/kg in five rabbits. The measured FBR value (0.233 +/- 0.060%/h) was almost identical (P = 0.35) to that (0.217 +/- 0.078%/h) estimated from a leg arteriovenous balance model (Biolo G, Chinkes D, Zhang X-J, and Wolfe RR. J Parenter Enteral Nutr 16: 305-315, 1992). The measured FSR value tended to be lower than that estimated from the leg model (0.125 +/- 0.036 vs. 0.185 +/- 0.086%/h; P = 0.14), possibly because the new method measures only muscle FSR, whereas the leg balance model also includes skin and bone contributions. The pulse tracer injection did not affect muscle protein kinetics as measured by leucine and phenylalanine kinetics in the leg. In another five rabbits, we demonstrated that sampling could be reduced to either one or two muscle biopsies when multiple pulse injections were used. This method can be completed in 1 h with one muscle biopsy and has technical advantages over currently used methods.

Metabolic and osmoregulatory function at low and high (3800 m) altitude

Altitude evokes physiological adjustments that include not only respiratory and cardiovascular properties, but also metabolic function, renal and endocrine responses. The purpose of the present study was designed to expand our understanding of the physiological process involved with acclimatisation to high altitude in equids. The study examined temporal effects on metabolic and osmoregulatory function in horses (n = 6) at rest and postexercise at 3800 m. Animals were studied at 225 m (Pb = 743 mmHg) and during a 10 day stay at altitude (Pb = 487 mmHg). Rest samples were taken 90 min postprandial at 0830 h and immediately after the gallop phase of a standard exercise test. Changes in glucose, insulin, cortisol, thyroxine, sodium, potassium, chloride and total protein were assessed at both altitudes. Exercise stimulated increases in cortisol, thyroxine, potassium, and chloride; while the concentrations of glucose, insulin, sodium and total protein (regardless of altitude) decreased. Acute (Day 2) altitude exposure (following transport stress) produced significant increases in glucose, cortisol, thyroxine, chloride and protein at rest and exercise. All variables (except cortisol) appeared to stabilise by Day 4 of altitude exposure. Observations from these data (coupled with haematological and blood gases data) indicate that equids acutely acclimate within 2-3 days to this altitude.

Relationships among inflammation nutrition and physiologic mechanisms establishing albumin levels in hemodialysis patients

BACKGROUND

Serum albumin concentration is a balance among its synthesis rate, fractional catabolic rate (FCR), distribution, dilution in the plasma pool and external loss. The physiologic bases for establishing the level of serum albumin in hemodialysis patients have not been defined despite the association of hypoalbuminemia with excess mortality. Albumin concentration is associated with the levels of several acute phase proteins (APPs), C-reactive protein (CRP), alpha1 acid glycoprotein (alpha1 AG), or ceruloplasmin, and with nutritional markers, such as normalized protein catabolic rate (nPCR).

METHODS

To establish the relationship among parameters that regulate albumin levels and markers of nutrition and inflammation, we injected [125I]-albumin, into 64 hemodialysis patients enrolled in the HEMO study to measure albumin distribution, synthesis and FCR. These variables were related to the levels of acute phase proteins (APPs), nPCR, body mass index (BMI), external albumin loss as well as demographic variables. Albumin distribution, synthesis and FCR were calculated from kinetic modeling, as was the initial plasma volume (PV). Serum albumin, transferrin, CRP, ceruloplasmin and alpha1 AG were measured weekly. Dialysate was collected during one dialysis each week to measure albumin loss. Results were analyzed by multiple linear regression.

RESULTS

Albumin concentration correlated with its synthesis rate and FCR, but not with PV or its distribution between the vascular and extravascular pools. Albumin concentration also correlated with nPCR and alpha1 AG. However, albumin synthesis was directly related most strongly to PV and BMI (or nPCR), but not to levels of APPs. By contrast, albumin FCR correlated positively with both alpha1 AG and ceruloplasmin.

CONCLUSION

Albumin concentration in dialysis patients changes with inflammation and nutritional status through their effects on albumin catabolism and synthesis, respectively. Within the range of albumin levels in these patients, nutritional variables primarily affected albumin synthesis while inflammation caused hypoalbuminemia by increasing albumin FCR. Albumin synthesis also increased in proportion to PV. The result of this is that PV expansion does not contribute to hypoalbuminemia.