Haemostasis at high altitude

Clinical characteristics of venous thromboembolism onset from severe high altitude pulmonary edema in plateau regions

BACKGROUND

To investigate venous thromboembolism (VTE) in hospitalized patients with severe high altitude pulmonary edema (HAPE), we performed a single center retrospective study to evaluate its clinical characteristics, prognosis, and potential thromboprophylaxis strategies in a large referral and treatment center in plateau regions.

METHODS

We studied a total of 18 patients with severe HAPE from January 1, 2012 to December 31, 2021. Demographic and clinical data, laboratory data, including ultrasound scans of the lower extremities and cardiac ultrasound, and computed tomographic pulmonary angiography (CTPA) variables were obtained, and comparisons were made between groups with and without VTE.

RESULTS

Of the 18 patients hospitalized with severe HAPE (age 43 (range, 34-54) years, 14 [77.8%] men), 7 patients developed VTE (38.9%), including 5 with deep vein thrombosis (DVT) and pulmonary embolism (PE), 2 of whom had DVT only. Eighteen patients are all firstly rapid ascent to high altitudes which the mean altitude was 3700 m (3656-4050 m). Compared with patients who did not have VTE, patients with VTE had a longer time in hospital (13 [11, 19] versus 9 [7, 12]; P = 0.027), respiratory failure (6 [85.7%] versus 2 [18.2%]; P = 0.013), the shortened APTT (21.50 [19.00, 27.50] versus 26.30 [24.80, 30.10]; P = 0.044) and the higher level of D-dimer (7.81 [4.62, 9.60] versus 2.90 [1.75, 3.37]; P = 0.003). The proportion of thromboprophylaxis is too low in our cohort which 2 of 18 (11.1%) patients were given VTE prophylaxis. There was no statistically significant difference between the VTE and non-VTE groups (0 [0.0%] versus 2 [18.2%]; P = 0.497).

CONCLUSIONS

The prevalence of VTE is high in hospitalized patients with severe high altitude pulmonary edema (HAPE). Prophylaxis for venous thromboembolism may be protective in severe HAPE patients after admission. Our data seem to suggest that VTE is probably an additional prognostic factors in patients with severe HAPE.

Pulmonary Embolism at Extreme High Altitude: A Study of Seven Cases

Wu, Jialin, Xiaobo Han, Haiwen Ke, Li Wang, Kun Wang, Jianli Zhang, Jun Tang, Wei Yan, Guangjun Wang, and Peng Jiang. Pulmonary embolism at extreme high altitude: A study of seven cases. High Alt Med Biol. XX:000-000, 2022. Background: The incidence of venous thromboembolism (VTE) is high in high-altitude (HA) areas. We analyzed cases of pulmonary embolism (PE) in extreme HA areas to explore the epidemiological characteristics and risk factors of PE in these regions. Methods: Seven cases of PE occurring in an extreme HA region were prospectively collected at an HA (3,800 m) hospital from May to November 2020. All patients resided 5,000 m above sea level and were diagnosed with PE using computed tomography pulmonary angiography. Results: Seven patients (24 ± 3.6 years old) had symptom onset at a mean altitude of 5,200 ± 200 m, and the duration spent at HA ranged from 8 to 210 days (99.29 ± 77.31 days). Cough, expectoration, chest tightness, fever, shortness of breath, and chest pain were the most common symptoms. Six of the seven patients were initially diagnosed with pulmonary inflammation, and four were diagnosed with high-altitude pulmonary edema using computed tomography or X-ray. Most patients presented with an increased concentration of inflammatory cells and high initial D-dimer levels. Conclusions: In this study, a retrospective analysis of PE case data in extreme HA areas suggested that PE was underdiagnosed owing to misdiagnosis or masking by HA-associated disease.

Recommendations for traveling to altitude with neurological disorders

BACKGROUND

Several neurological conditions might worsen with the exposure to high altitude (HA). The aim of this review was to summarize the available knowledge on the neurological HA illnesses and the risk for people with neurological disorders to attend HA locations.

METHODS

A search of literature was conducted for several neurological disorders in PubMed and other databases since 1970. The neurological conditions searched were migraine, different cerebrovascular disease, intracranial space occupying mass, multiple sclerosis, peripheral neuropathies, neuromuscular disorders, epileptic seizures, delirium, dementia, and Parkinson's disease (PD).

RESULTS

Attempts were made to classify the risk posed by each condition and to provide recommendations regarding medical evaluation and advice for or against traveling to altitude. Individual cases should be advised after careful examination and risk evaluation performed either in an outpatient mountain medicine service or by a physician with knowledge of HA risks. Preliminary diagnostic methods and anticipation of neurological complications are needed.

CONCLUSIONS

Our recommendations suggest absolute contraindications to HA exposure for the following neurological conditions: (1) Unstable conditions-such as recent strokes, (2) Diabetic neuropathy, (3) Transient ischemic attack in the last month, (4) Brain tumors, and 5. Neuromuscular disorders with a decrease of forced vital capacity >60%. We consider the following relative contraindications where decision has to be made case by case: (1) Epilepsy based on recurrence of seizure and stabilization with the therapy, (2) PD (± obstructive sleep apnea syndrome-OSAS), (3) Mild Cognitive Impairment (± OSAS), and (4) Patent foramen ovale and migraine have to be considered risk factors for acute mountain sickness.

Modulation of lung cytoskeletal remodeling, RXR based metabolic cascades and inflammation to achieve redox homeostasis during extended exposures to lowered pO2

Extended exposure to low pO₂ has multiple effects on signaling cascades. Despite multiple exploratory studies, omics studies elucidating the signaling cascades essential for surviving extended low pO₂ exposures are lacking. In this study, we simulated low pO₂ (P_B = 40 kPa; 7620 m) exposure in male Sprague-Dawley rats for 3, 7 and 14 days. Redox stress assays and proteomics based network biology were performed using lungs and plasma. We observed that redox homeostasis was achieved after day 3 of exposure. We investigated the causative events for this. Proteo-bioinformatics analysis revealed STAT3 to be upstream of lung cytoskeletal processes and systemic lipid metabolism (RXR) derived inflammatory processes, which were the key events. Thus, during prolonged low pO₂ exposure, particularly those involving slowly decreasing pressures, redox homeostasis is achieved but energy metabolism is perturbed and this leads to an immune/inflammatory signaling impetus after third day of exposure. We found that an interplay of lung cytoskeletal elements, systemic energy metabolism and inflammatory proteins aid in achieving redox homeostasis and surviving extended low pO₂ exposures. Qualitative perturbations to cytoskeletal stability and innate immunity/inflammation were also observed during extended low pO₂ exposure in humans exposed to 14,000 ft for 7, 14 and 21 days.

Global REACH 2018: Influence of excessive erythrocytosis on coagulation and fibrinolytic factors in Andean highlanders

NEW FINDINGS

What is the central question of this study? Are coagulation and fibrinolytic factors disrupted in Andean highlanders with excessive erythrocytosis? What is the main finding and its importance? Excessive erythrocytosis is not associated with prothombotic disruptions in coagulation or the fibrinolytic system in Andean highlanders. Impairments in coagulation and fibrinolysis may not contribute to the increased vascular risk associated with excessive erythrocytosis.

ABSTRACT

Increased coagulation and reduced fibrinolysis are central factors underlying thrombotic risk and events. High altitude-induced excessive erythrocytosis (EE) is prevalent in Andean highlanders, contributing to increased cardiovascular risk. Disruption in the coagulation-fibrinolytic axis resulting in uncontrolled fibrin deposition might underlie the increased thrombotic risk associated with high-altitude EE. The experimental aim of this study was to determine whether EE is associated with a prothrombotic blood coagulation and fibrinolytic profile in Andean highlanders. Plasma coagulation factors (von Willebrand factor and factors VII, VIII and X), fibrinolytic factors [tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1)] and D-dimer levels were determined in 26 male residents of Cerro de Pasco, Peru (4340 m a.s.l.): 12 without EE (age, 40 ± 13 years; haemoglobin, 17.4 ± 1.9 g/dl) and 14 with EE (age, 43 ± 15 years; haemoglobin, 24.4 ± 1.6 g/dl). There were no significant differences in von Willebrand factor (40.5 ± 24.8 vs. 45.5 ± 22.4%), factor VII (77.0 ± 14.5 vs. 72.5 ± 8.9%), factor VIII (55.6 ± 19.8 vs. 60.7 ± 26.8%) and factor X (73.9 ± 8.3 vs. 67.3 ± 10.9%) between the Andean highlanders without or with EE. The t-PA antigen (8.5 ± 3.6 vs. 9.6 ± 5.4 ng/ml), t-PA activity (5.5 ± 2.4 vs. 5.8 ± 1.6 IU/ml), PAI antigen (45.0 ± 33.8 vs. 40.5 ± 15.8 ng/ml), PAI-1 activity (0.24 ± 0.09 vs. 0.25 ± 0.11 IU/ml) and the molar concentration ratio of active t-PA to active PAI-1 (1:0.051 ± 0.034 vs. 1:0.046 ± 0.021 mmol/l) were also similar between the groups, as were D-dimer levels (235.0 ± 126.4 vs. 268.4 ± 173.7 ng/ml). Collectively, the results of the present study indicate that EE is not associated with a hypercoagulable, hypofibrinolytic state in Andean highlanders.

Commercial Air Travel for Passengers With Cardiovascular Disease: Recommendations for Common Conditions

The exponential growth of commercial flights has resulted in an explosion of air travelers over the last few decades, including passengers with a wide range of cardiovascular conditions. Notwithstanding the ongoing COVID-19 pandemic that had set back the aviation industry for the next 1-2 years, air travel is expected to rebound fully by 2024. Guidelines and evidence-based recommendations for safe air travel in this group vary, and physicians often encounter situations where opinions and assessments on fitness for flights are sought. This article aims to provide an updated suite of recommendations for the aeromedical disposition of passenger with common cardiovascular conditions, such as ischemic heart disease, congestive heart failure, valvular heart disease, cardiomyopathies, and common arrhythmias.

Preoperative Aspirin Management in Redo Tetralogy of Fallot Population: Single Centre Experience

Purpose: Redo operations and preoperative antiplatelet/anticoagulant therapy can significantly increase surgical risk in congenital heart surgery. This is a retrospective study on the impact of preoperative aspirin therapy on the outcome of Tetralogy of Redo Fallot patients undergoing right ventricle outflow tract (RVOT) conduit implantation. Methods: Ten-years retrospective analysis of medical records was carried out. A total of 72 patients were divided into two groups: “Daily-on-ASA” group on daily therapy with aspirin (ASA) until 5 days from surgery and “No-Home-ASA” without it. Propensity match analysis was done in order to standardize the populations. Intraoperative and postoperative lengths were compared as well as the need for inotropic support. In addition, differences in blood transfusions and need for Fresh frozen plasma (FFP)/platelets (PLT) were analysed. Findings: Intraoperative lengths were similar between the groups. Not statistically significative differences about postoperative time to extubation (p = 0.34), ICU Stay (p = 0.31) or in-hospital stay (p = 0.36) were found. Drain loss was higher in the “Daily-on-ASA” group (407.9 ± 96.7 mL vs. 349.5 ± 84.3 mL; p = 0.03) as well as blood transfusions (372.7 ± 255.1 mL vs. 220.1 ± 130.3 mL, p = 0.02) and PLT/FFP need (217.7 ± 132.1 mL vs. 118.7 ± 147.1 mL, p = 0.01). No differences were found in postoperative complications or re-explorations for bleeding. Implications: We found no advantages in surgical times and hospital stay comparing redo patients who stopped aspirin versus those that didn’t take it in the last 6 months. However, our results suggest that redo patients undergoing RVOT conduit implantation who take daily aspirin are at higher risk of bleeding even if it is stopped 5 days before surgery.

Commercial Air Travel for Passengers With Cardiovascular Disease: Stressors of Flight and Aeromedical Impact

The exponential growth of commercial flights has resulted in a sharp rise of air travellers over the last 2 decades, including passengers with a wide range of cardiovascular conditions. Notwithstanding the ongoing COVID-19 pandemic that had set back the aviation industry for the next 1 to 2 years, air travel is expected to rebound fully by 2023-2024. Guidelines and evidence-based recommendations for safe air travel in this group vary, and physicians often encounter situations where opinions and assessments on fitness for flights are sought. This article aims to provide an overview of the stressors of commercial passenger flights with an impact on cardiovascular health for the general cardiologist and family practitioner, when assessing the suitability of such patients for flying fitness.

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

Redox-regulation of haemostasis in hypoxic exercising humans: a randomised double-blind placebo-controlled antioxidant study

KEY POINTS

In vitro evidence has identified that coagulation is activated by increased oxidative stress, though the link and underlying mechanism in humans have yet to be established. We conducted the first randomised controlled trial in healthy participants to examine if oral antioxidant prophylaxis alters the haemostatic responses to hypoxia and exercise given their synergistic capacity to promote free radical formation. Systemic free radical formation was shown to increase during hypoxia and was further compounded by exercise, responses that were attenuated by antioxidant prophylaxis. In contrast, antioxidant prophylaxis increased thrombin generation at rest in normoxia, and this was normalised only in the face of prevailing oxidation. Collectively, these findings suggest that human free radical formation is an adaptive phenomenon that serves to maintain vascular haemostasis.

ABSTRACT

In vitro evidence suggests that blood coagulation is activated by increased oxidative stress although the link and underlying mechanism in humans have yet to be established. We conducted the first randomised controlled trial to examine if oral antioxidant prophylaxis alters the haemostatic responses to hypoxia and exercise. Healthy males were randomly assigned double-blind to either an antioxidant (n = 20) or placebo group (n = 16). The antioxidant group ingested two capsules/day that each contained 500 mg of l-ascorbic acid and 450 international units (IU) of dl-α-tocopherol acetate for 8 weeks. The placebo group ingested capsules of identical external appearance, taste and smell (cellulose). Both groups were subsequently exposed to acute hypoxia and maximal physical exercise with venous blood sampled pre-supplementation (normoxia), post-supplementation at rest (normoxia and hypoxia) and following maximal exercise (hypoxia). Systemic free radical formation (electron paramagnetic resonance spectroscopic detection of the ascorbate radical (A^•- )) increased during hypoxia (15,152 ± 1193 AU vs. 14,076 ± 810 AU at rest, P < 0.05) and was further compounded by exercise (16,569 ± 1616 AU vs. rest, P < 0.05), responses that were attenuated by antioxidant prophylaxis. In contrast, antioxidant prophylaxis increased thrombin generation as measured by thrombin-antithrombin complex, at rest in normoxia (28.7 ± 6.4 vs. 4.3 ± 0.2 μg mL^-1 pre-intervention, P < 0.05) and was restored but only in the face of prevailing oxidation. Collectively, these findings are the first to suggest that human free radical formation likely reflects an adaptive response that serves to maintain vascular haemostasis.

Elevated Vasodilatory Cyclases and Shorter Telomere Length Contribute to High-Altitude Pulmonary Edema

Rain, Manjari, Himanshi Chaudhary, Ritushree Kukreti, Tashi Thinlas, Ghulam Mohammad, and Qadar Pasha. Elevated vasodilatory cyclases and shorter telomere length contribute to high-altitude pulmonary edema. High Alt Med Biol. 19:60-68, 2018.

AIM

High-altitude (HA) genetics is complex with respect to health and disease (HA pulmonary edema i.e., HAPE). Based on the widely recognized fact that oxidative stress is a major trigger of several physiological processes, this study was designed to establish the significance of vasodilatory cyclases and telomere length in HA physiology. The study was performed in three groups, namely HAPE-free sojourners (HAPE-f, n = 150), HAPE patients (HAPE-p, n = 150), and healthy highland natives or highlanders (HLs, n = 150). Variations in soluble guanylyl cyclase β1-subunit (GUCY1B3) and adenylyl cyclase type 6 (ADCY6) were genotyped by the SNaPshot method and/or Fluidigm SNP type genotyping. Plasma GUCY1B3 and ADCY6 levels were estimated using ELISA, and relative telomere length was estimated by qRT-PCR.

RESULTS

The rs7638AA genotype was over-represented in HLs compared with HAPE-f and HAPE-p (p = 0.035 and p = 0.012, respectively). Similarly, the rs7638A allele was prevalent in HLs compared with both groups, but significance was attained against HAPE-p (p = 0.012). Significantly elevated plasma levels of GUCY1B3 and ADCY6 were obtained in HAPE-p compared with HAPE-f (p = 0.001 and p = 0.006, respectively) and HLs (p = 3.31E-05 and p = 0.05, respectively). Shorter telomere length was observed in HAPE-p compared with HAPE-f (p > 0.05) and HLs (p = 0.017).

CONCLUSION

Elevated cyclases and shorter telomere length associate with HAPE pathophysiology.

Effect of acute exacerbations on circulating endothelial, clotting and fibrinolytic markers in COPD patients

Patients with chronic obstructive pulmonary disease (COPD) are prone to clinical exacerbations that are associated with increased airway inflammation, a potent pro-thrombotic stimulus. Limited information is available on the mechanisms underlying the putative alterations of the endothelial-coagulative system during acute exacerbations. The aim was to investigate whether the activation of the endothelial-coagulative system occurs in association with the acute inflammatory response of COPD exacerbation. We monitored the blood levels of surrogate markers of inflammation: interleukin-6 (IL-6); endothelium damage: von Willebrand's factor (vWF); clotting activation: D-dimer (D-D), and prothrombin fragment 1+2 (F1+2); fibrinolytic response: plasminogen activator inhibitor 1 (PAI-1), in COPD subjects, during hospital admission and after clinical resolution. In 30 COPD subjects, IL-6, vWF, D-D and F1+2 levels were elevated during exacerbation and decreased significantly at clinical stability (IL-6, p = 0.005; vWF, p < 0.001; D-D, p < 0.001; F1+2, p < 0.001). PAI-1 levels did not change at exacerbation compared to clinically stable situations. Positive correlations were observed between several of the markers measured. Elevation of IL-6, vWF, D-D and F1+2 levels during COPD exacerbations implies a strict association between acute inflammation, endothelial activation and clotting initiation. This was not associated with a change in PAI-1, implying an increase in the fibrinolytic response to inflammation. The pro-thrombotic nature of COPD exacerbations sustained by enhanced clotting activation appears to be mitigated by excessive fibrinolysis.

D-dimer in the diagnostic workup of suspected pulmonary thrombo-embolism at high altitude

BACKGROUND

Pulmonary thrombo-embolism (PTE) is relatively common in high altitude areas where radiological diagnostic facilities are usually not available. So this study was undertaken to use the results of D-dimer assay to determine the need for imaging studies in patients suspected of having PTE at high altitude.

METHODS

A total of 101 patients at an altitude of > 3,000 m suspected of having PTE were evacuated. D-dimer and imaging studies were carried out to confirm the diagnosis.

RESULTS

A total of 101 patients suspected of having PTE underwent D-dimer level estimation and imaging studies for PTE. Sixty-eight of these had negative findings) on D-dimer assay. All these patients with negative findings on D-dimer assay had negative findings on pulmonary imaging studies also. So this test is very sensitive with very high negative predictive value (NPV). Whereas, 17 out of 33 patients positive for D-dimer, had positive findings on imaging studies, indicating a relatively less specific test.

CONCLUSION

Clinical assessment in combination with D-dimer assay can be used for timely differentiation of PTE from other conditions such as high altitude pulmonary oedema (HAPO) especially at isolated high altitude areas/military posts, so that patients could be evacuated as early as possible by fastest means to save the precious lives and in hospital settings this test identifies patients to whom anticoagulant therapy should not be given or patients who should not be subjected to invasive imaging tests.

D-dimer is not elevated in asymptomatic high altitude climbers after descent to 5340 m: the Mount Everest Deep Venous Thrombosis Study (Ev-DVT)

We performed this study to determine the prevalence of elevated D-dimer, a marker for deep venous thrombosis (DVT), in asymptomatic high altitude climbers. On-site personnel enrolled a convenience sample of climbers at Mt. Everest Base Camp (Nepal), elevation 5340 m (17,500 ft), during a single spring climbing season. Subjects were enrolled after descent to base camp from higher elevation. The subjects completed a questionnaire to evaluate their risk factors for DVT. We then performed a D-dimer test in asymptomatic individuals. If the D-dimer test was negative, DVT was considered ruled out. Ultrasound was available to perform lower-extremity compression ultrasounds to evaluate for DVT in case the D-dimer was positive. We enrolled 76 high altitude climbers. None had a positive D-dimer test. The absence of positive D-dimer tests suggests a low prevalence of DVT in asymptomatic high altitude climbers.

Going High with Preexisting Neurological Conditions

This review presents the potential impact of high altitude exposure on preexisting neurological conditions in patients usually living at low altitude. The neurological conditions include permanent and transient ischemia of the brain, occlusive cerebral artery disease, cerebral venous thrombosis, intracranial hemorrhage and vascular malformations, multiple sclerosis, intracranial space-occupying lesions, dementia, extrapyramidal disorders, migraine and other headaches, and epileptic seizures. New developments in diagnostic work-up and treatment of preexisting neurological conditions are also mentioned where applicable. For each neurological disorder, the authors developed absolute and relative contraindications for a trip to high altitude. These recommendations are not based on the results of controlled randomized trials, but mainly on case reports, pathophysiological considerations, and extrapolations from the low altitude situation.

Low Arterial Saturation Is Associated With Increased Sensitivity to Activated Protein C in Children With Congenital Heart Disease

OBJECTIVES

Children with congenital heart disease experience both hemorrhagic and thrombotic complications. In this report the authors test the hypothesis that hypoxemia is associated with altered sensitivity to activated protein C (aPC) in pediatric patients with congenital heart lesions.

DESIGN

A retrospective genetic registry review, with statistical evaluation of factors contributing to the aPC ratio.

SETTING

Large university hospital.

PARTICIPANTS

Cohort of 92 children with congenital heart disease undergoing cardiac catheterization procedures.

INTERVENTIONS

The authors measured the aPC ratio at cardiac catheterization and evaluated the contribution of independent variables using linear regression and classification tree approaches. Independent variables included age, gender, use of aspirin, history of thrombosis, room air arterial saturation, factor VIII:C levels, presence of congestive heart failure, and heterozygosity for factor V Leiden.

MEASUREMENTS AND MAIN RESULTS

At univariate analysis, factor V Leiden, female gender, room air arterial saturation, age greater than 6 months, and plasma factor VIII:C levels were associated with a lower aPC ratio (resistance to aPC). At stepwise linear regression, arterial saturation, factor VIII:C level, female gender, and factor V Leiden were independently associated with a lower aPC ratio, and these variables explained about 49% of the variability in aPC ratio. The classification tree approach confirmed the dependence of aPC ratio on factor V genotype and arterial saturation.

CONCLUSIONS

The aPC ratio in this population is associated with hypoxemia, independent of factors previously observed in adults. Further studies are under way to determine how aPC resistance or sensitivity may independently affect perioperative hemostasis in this population.

Hypoxia-reoxygenation contributes to increased frequency of venous thromboembolism in air travellers

Commercial air travel is widespread, with close to 2 billion people traveling each year. The association between venous thromboembolism (VTE) and confined sitting has been established and a correlation between the distance traveled and its incidence had been documented. Most studies underscore stasis caused by immobility as the cause of VTE and ignore the possible contribution of additional factors including coagulation and the blood vessel wall. Recent studies indicate that hypobaric hypoxia may contribute to blood vessel wall alteration and activation of coagulation. We suggest that air travel associated hypobaric hypoxia may lead to endothelial injury and initiation of a pro-coagulatory response, effects which are augmented by the reoxygenation upon landing, thus culminating in thrombosis. Prevention of air travel associated hypoxia and reoxygenation injury may decrease the incidence of flight associated VTE.

Symptomatic portal system thrombosis in soldiers due to extended stay at extreme altitude

BACKGROUND

With induction of Indian Army to heights over 5000 m above mean sealevel (MSL), several new complications of long-term stay at extreme altitude have come to light. The authors' experience with soldiers who developed symptomatic portal system thrombosis (SPST) is described here.

METHODS

Clinical data were prospectively collected between April 1998 and April 2003, on all patients hospitalized for SPST from high-altitude areas (HAA, >3000 m above MSL) and those from non-high-altitude areas (NHAA). Site of thrombosis was confirmed by imaging and included splenic, portal, superior mesenteric, or inferior mesenteric vein thrombosis. Patients were investigated to rule out known predisposing factors and prothrombotic conditions.

RESULTS

A total of 37 cases of SPST were seen during the study period, of which 26 were from HAA. Mean age of cases from HAA was 27 +/- 4.6 years and all were male. Mean stay at high altitude was 11.7 +/- 6.2 months. First symptom was pain in abdomen in almost all the cases, later followed by gastrointestinal bleeding and fever in 14 each, and vomiting in 19. Clinical examination showed ascites (81%), splenomegaly (76.9%), and hepatomegaly (69.2%). Diagnosis was made by imaging scans (23 cases) and on surgery in three cases. A known prothrombotic state was detected in five cases from HAA and in eight cases from NHAA (P < or = 0.01). Ultrasound Doppler scan picked up collaterals as early as 12-45 days after onset of symptoms.

CONCLUSIONS

Extended stay at HAA may be a risk factor for development of symptomatic portal system thrombosis.

Moderate hypoxia suppresses exercise-induced procoagulant changes

Hypoxia has been implicated as a stimulant of coagulation. As exertion is known to affect haemostasis, we sought to control for this by using a standardized protocol. Subjects were exercised both at room air and at 12% oxygen. Exercise produced an increase in procoagulant factors, which was reduced with hypoxic exercise. Room air exercise increased fibrinolytic markers. Hypoxic exercise did not affect the increase in tissue plasminogen activator, but decreased the increase in plasminogen activator inhibitor-1 expression. Thus, it appears that hypoxia may exert an antithrombotic effect by both damping exercise-induced procoagulant changes and stimulating fibrinolysis.

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.

Endothelial dysfunction associated with chronic intravascular coagulation in secondary pulmonary hypertension

Altered endothelial anti-thrombotic properties have been observed in primary and secondary pulmonary hypertension. In the Eisenmenger syndrome, correlations of these abnormalities with the clinical status and occurrence of chronic intravascular coagulation (CIC) have not been confirmed. The purpose of this study was to investigate whether the occurrence of CIC, as determined by circulating levels of D-dimer is associated with changes in endothelial markers in Eisenmenger patients; and to identify variables that correlate with the severity of clinical presentation. Twenty-one patients were enrolled (ages, 4-52 years). Plasma levels of D-dimer, tissue plasminogen activator (t-PA), thrombomodulin, and von Willebrand factor antigen (vWF:Ag) were measured with enzyme-linked immunosorbent assay. Univariate and multivariate analyses were used to differentiate patients with stable (group 1, N=12) from those with unstable disease (group 2, N=9). Increased t-PA (p<0.0001) and vWF:Ag (p=0.001) and decreased thrombomodulin (p<0.0001) were associated with increased D-dimer levels (p=0.0201) in patients. Group 2 had a higher prevalence of affected women (p=0.0242), lower arterial oxygen saturation, and higher t-PA levels compared with group 1 (p<0.0001, discriminant analysis). t-PA and vWF:Ag correlated positively in group 2 (r=0.71, p=0.0309), but not in group 1 (r=0.25, p=NS). Two patients in group 2 but none in group 1 had episodes of pulmonary arterial thrombosis. Endothelial dysfunction is associated with evidence of CIC and correlates to some extent with the severity of symptoms in these patients.

Stroke at high altitude: Indian experience

Stroke is a common medical emergency. There is limited knowledge about stroke at high altitude. We present the clinical profile of 30 cases of stroke at high altitude seen at our center between November 1998 to July 2000. A detailed neurological and systemic examination was carried out. Cases were investigated with blood counts, lipid profile, cardiac evaluation, and CT scan/MRI. Coagulation parameters were studied in some cases. Strokes formed 13.7/1000 of hospital admissions from high altitude area, compared to 1.05/1000 in nonhigh altitude area. All our cases from high altitude area were males (serving soldiers of armed forces). Their mean high altitude stay was 10.2 months, and they were all located at heights greater than 4270 m. Age ranged from 22 to 48 years (mean 33.4 yr). Except for smoking (in four cases), they had no preexisting risk factors. Twenty-two cases were of ischemic stroke, 2 of intracerebral hemorrhage, 4 of TIA/RIND (transient ischemic attack/reversible ischemic neurological deficit), and 2 had cerebral venous thrombosis. Out of 30 cases, 28 were of "stroke in young" (<45 yr) and were compared with cases in the same age group from nonhigh altitude areas. Polycythemia with Hb ranging from 16.2 to 22 g.dL(-1) was seen in 21 of these 28 cases (75%). Protein C and S deficiency was found in 1 case in each group. CT scan showed massive infarcts involving at least 50% of one cerebral hemisphere in 12 cases. Multiple infarcts were seen in one case.

CONCLUSION

Long-term stay at high altitude is associated with higher risk of stroke. Although all types of stroke were seen, ischemic stroke was the commonest. Massive infarcts were common. Polycythemia was an important risk factor.

The scientific observatories on Mont Blanc

Since the first ascent of Mont Blanc by Jacques Balmat and Dr. Michel-Gabriel Paccard in 1786, numerous scientific events have taken place on the highest peak of Europe. Horace Benédict de Saussure, since his first ascent in 1787, made numerous observations on barometric pressure, temperature, geology, and mountain sickness on Mont Blanc. Over the next 100 years, scientists and physicians climbed Mont Blanc and made many interesting although anecdotal reports. Science on Mont Blanc exploded at the end of the 19th century. A major player at that time was Joseph Vallot (1854-1925), who constructed an observatory in 1890 at 4,358 m on the Rochers des Bosses and then moved it in 1898 to a better location at 4,350 m. There Vallot and invited scientists made observations over more than 30 years: studies in geology, glaciology, astronomy, cartography, meteorology, botany, physiology and medicine were performed and published in the seven volumes of the Annales de l'Observatoire du Mont Blanc, between 1893 and 1917, and in the Comptes Rendus de l'Académie des Sciences. While Jules Janssen and Xaver Imfeld were preparing the construction of the new observatory on the top of Mont Blanc, Dr. Jacottet died in 1891 at the Observatoire Vallot from a disease that was clearly attributed by Dr. Egli-Sinclair to the effect of high altitude. This was probably the first case of high altitude pulmonary edema documented by an autopsy and suspected to be directly due to high altitude. Extensive studies on ventilation were made from 1886 to 1900. Increase in ventilation with altitude was documented, with the phenomenon of "ventilatory acclimatization." Paul Bert's theories on the role of oxygen in acute mountain sickness were confirmed in 1903 and 1904 by studying the effects of oxygen inhalation. In 1913, Vallot documented for the first time the decrease in physical performance at the top of Mont Blanc using squirrels. After that pioneering era, few studies were done until 1984, when a team of the Association pour la Recherche en Physiologie de l'Environnement (ARPE) renovated the observatory and started to organize annual scientific expeditions.

Enhanced thromboxane biosynthesis in patients with chronic obstructive pulmonary disease. The Chronic Obstructive Bronchitis and Haemostasis Study Group

Thrombotic complications of pulmonary circulation occur in patients with chronic obstructive pulmonary disease (COPD). In the present study, we sought to evaluate in vivo platelet activation through the measurement of 11/dehydro-thromboxane (Tx) B2 TxA2 major metabolite in the urine, in 29 patients with COPD, compared with 29 sex- and age-matched healthy subjects. The urinary excretion of 11-dehydro-TxB2 was significantly higher in patients with COPD than in control subjects: median (range), 753 (277-4,409) and 275 (129-612) pg/mg creatinine, respectively; p < 0.0001). Moreover, 11-dehydro-TxB2 excretion was inversely related with arterial oxygen tension (rho = -0.46; p = 0.0145). In five of the 29 patients a short-term therapeutic course with oxygen supplementation induced a significant decrease of urinary 11-dehydro-TxB2 excretion: median range, 941 (452-2,640) to 445 (166-1,560) pg/mg creatinine. Moreover, selective inhibition of platelet cyclooxygenase activity by low-dose aspirin was associated with more than 90% inhibition of thromboxane metabolite excretion, demonstrating its being of platelet origin. Plasma levels of prothrombin fragment F1 + 2 were higher in patients than in control subjects (2.6 +/- 1.5 versus 0.9 +/- 0.4 nM, p = 0.0001). No relation between 11-dehydro-TxB2 excretion and plasma F1 + 2 levels was found. We conclude that platelet TxA2 biosynthesis is enhanced in patients with COPD and may be influenced by arterial oxygen tension changes.