Pathogenesis of pulmonary edema: learning from high-altitude pulmonary edema

Protective effect of salidroside on lung tissue in rats exposed rapidly to high altitude

OBJECTIVE

To study the protective effect and mechanism of salidroside on lung tissue of rats exposed rapidly to high altitude.

METHODS

Thirty-six Wistar male rats were randomly divided into blank control group, model control group, Rhodiola rosea capsule (137 mg/kg) group, salidroside low-dose (14 mg/kg), medium-dose (28 mg/kg) and high-dose (56 mg/kg) groups, with 6 rats in each group. After 5 continuous days of drug administration in the plain lab, rats were rapidly moved to 4010 m plateau field lab. After exposure to hypoxia condition for 3 days the blood gas indexes were detected; the serum levels of inflammatory factors were measured by enzyme linked immunosorbent assay (ELISA); the oxidative stress index of lung tissue was measured; the pathological changes of lung tissue were observed by microscopy with hematoxylin and eosin (HE) staining; and the expression of occludin in lung tissues was determined by western blotting.

RESULTS

Compared with blank control group, arterial oxygen saturation (SaO 2), arterial oxygen partial pressure (PaO 2), blood pH, standard bicarbonate (SBC) and actual bicarbonate levels in model control group were significantly decreased, and hemoglobin level was significantly increased (all P<0.05). In the model control group, the contents of mast cell protease (MCP) 1, interleukin (IL)-6 and IL-1β were significantly increased, while the contents of interferon-γ were significantly decreased (all P<0.01). The contents of glutathione and total superoxide dismutase in the lung tissues of model control group were significantly decreased, while the content of malondialdehyde was significantly increased (all P<0.01). After Rhodiola rosea and salidroside were given, SaO 2, pH, hemoglobin, SBC and actual bicarbonate were improved compared with the model control group. Compared with the model control group, the Rhodiola rosea group and salidroside groups had different degrees of improvement in the contents of the above inflammatory factors and oxidative stress indexes, and the salidroside groups had better improvement in MCP-1 and IL-6 than the Rhodiola rosea group. HE staining showed that, after the administration of Rhodiola rosea capsules and salidroside at low, medium and high doses, the hypoxic injury was significantly improved, the cell wall gradually became thinner, and the alveolar wall gradually became complete. The expression of occludin in the model control group was lower than that in the blank control group ( P<0.05), while the expression of occludin in the salidroside high-dose group was significantly higher than that in the model control group ( P<0.01).

CONCLUSION

Salidroside can improve the abnormality of blood gas index, hypoxia symptoms and acid-base balance disorder, dysregulation of inflammatory factors caused by hypoxia in rats, and improve lung tissue injury and oxidative stress injury, which has a protective effect on lung tissue injury of rats exposed rapidly to the high-altitude plateau, and the effect is better than Rhodiola rosea capsule on the whole.

Congenital heart disease and air travel

The number of individuals traveling by airplanes is increasing every year. Patients with congenital heart disease and shunts, exposure to high altitude during a flight is important since it causes pulmonary vaso- constriction leading to an increase in right-to-left shunting and a decrease in arterial oxygen saturation. Patients with cyanotic congenital heart disease and Eisenmenger syndrome should be evaluated before the flight, and necessary precautions should be taken.

Qi-Long-Tian formula extract alleviates symptoms of acute high-altitude diseases via suppressing the inflammation responses in rat

Background

Chinese Yunnan Province, located in the Yunnan–Guizhou Plateau, is a famous tourist paradise where acute high-altitude illness common occurs among lowland people visitors due to non-acclimatization to the acute hypobaric hypoxia (AHH) conditions. Traditional Chinese medicine, such as Qi-Long-Tian (QLT) formula, has shown effectiveness and safety in the treatment of acute high-altitude diseases. The aim of this study was to clarify the therapeutic mechanisms of this traditional formula using a rat model in a simulated plateau environment.

Methods

Following testing, lung tissue samples were evaluated by hematoxylin–eosin staining and for biochemical characteristics. mRNA-Seq was used to compare differentially expressed genes in control rats, and in rats exposed to AHH and AHH with QLT treatment.

Results

Inflammation-related effectors induced following QLT treatment for AHH included MMP9 and TIMP1, and involved several phosphorylation signaling pathways implicated in AHH pathogenesis such as PI3K/AKT and MAPK signaling.

Conclusion

This study provides insights into the major signaling pathways induced by AHH and in the protective mechanisms involved in QLT formula activity.

Vascular homeostasis at high-altitude: role of genetic variants and transcription factors

High-altitude pulmonary edema occurs most frequently in non-acclimatized low landers on exposure to altitude ≥2500 m. High-altitude pulmonary edema is a complex condition that involves perturbation of signaling pathways in vasoconstrictors, vasodilators, anti-diuretics, and vascular growth factors. Genetic variations are instrumental in regulating these pathways and evidence is accumulating for a role of epigenetic modification in hypoxic responses. This review focuses on the crosstalk between high-altitude pulmonary edema-associated genetic variants and transcription factors, comparing high-altitude adapted and high-altitude pulmonary edema-afflicted subjects. This approach might ultimately yield biomarker information both to understand and to design therapies for high-altitude adaptation.

Nitric oxide restores peripheral blood mononuclear cell adhesion against hypoxia via NO-cGMP signalling

Hypoxia is the most detrimental threat to humans residing at high altitudes, affecting multifaceted cellular responses that are crucial for normal homeostasis. Inhalation of nitric oxide has been successfully implemented to combat the hypoxia effect in the high altitude patients. We hypothesize that nitric oxide (NO) restores the peripheral blood mononuclear cell-matrix deadhesion during hypoxia. In the present study, we investigate the cellular action of exogenous NO in the hypoxia-mediated diminution of cell-matrix adhesion of PBMNC and NO bioavailability in vitro. The result showed that NO level and cell-matrix adhesion of PBMNC were significantly reduced in hypoxia as compared with normoxia, as assessed by the DAF-FM and cell adhesion assay, respectively. In contrast, cellular oxidative damage response was indeed upregulated in hypoxic PBMNC. Further, gene expression analysis revealed that mRNA transcripts of cell adhesion molecules (Integrin α5 and β1) and eNOS expressions were significantly downregulated. The mechanistic study revealed that administration of NO and 8-Br-cGMP and overexpression of eNOS-GFP restored the basal NO level and recovers cell-matrix adhesion in PBMNC via cGMP-dependent protein kinase I (PKG I) signalling. In conclusion, NO-cGMP/PKG signalling may constitute a novel target to recover high altitude-afflicted cellular deadhesion. SIGNIFICANCE OF THIS STUDY: Cellular adhesion is a complex multistep process. The ability of cells to adhere to extracellular matrix is an essential physiological process for normal homeostasis and function. Hypoxia exposure in the PBMNC culture has been proposed to induce oxidative damage and cellular deadhesion and is generally believed to be the key factor in the reduction of NO bioavailability. In the present study, we demonstrated that NO donor or overexpression of eNOS-GFP has a protective effect against hypoxia-induced cellular deadhesion and greatly improves the redox balance by inhibiting the oxidative stress. Furthermore, this protective effect of NO is mediated by the NO-cGMP/PKG signal pathway, which may provide a potential strategy against hypoxia.

Prognostic Value of Oxidative Stress Markers in Patients with Pulmonary Arterial or Chronic Thromboembolic Pulmonary Hypertension

Oxidative stress is regarded to play a crucial role in the pathophysiology of pulmonary arterial hypertension (PAH) and inoperable chronic thromboembolic pulmonary hypertension (CTEPH). This study evaluated the prognostic value of serum oxidative stress markers (malondialdehyde (MDA), total antioxidant capacity (TAC), catalase activity (CAT), and superoxide activity (SOD)) in patients with PAH and CTEPH (n = 45). During 13 months of follow-up (median 9 months), clinical deterioration occurred in 14 patients (including 2 deaths). On the Cox regression analysis, MDA, TAC, and CAT were associated with clinical deterioration (p = 0.0068, HR = 1.42, 95% CI: 1.10-1.82; p = 0.0038, HR = 0.033, 95% CI: 0.0032-0.33; and p = 0.046, HR = 0.20, 95% CI: 0.04-0.98, respectively). There was no significant difference in SOD (p = 0.53, HR = 0.97, 95% CI: 0.87-1.08). The cut-off value derived from ROC curve analysis was 3.79 μM (p = 0.0048, AUC = 0.76, 95% CI: 0.62-0.91) for MDA, 0.49 mM (p = 0.027, AUC = 0.71, 95% CI: 0.18-0.47) for TAC, and 1.34 U/L (p = 0.029, AUC = 0.71, 95% CI: 0.55-0.86) for CAT. MDA in the group with deterioration was higher (p = 0.0041), while TAC as well as CAT were lower (p = 0.027 and p = 0.028, respectively) when compared to stable patients. Survival without clinical deterioration was significantly longer in patients with lower MDA (p = 0.037, HR = 0.37, 95% CI: 0.12-1.14, log-rank), higher TAC (p = 0.0018, HR = 0.19, 95% CI: 0.06-0.60, log-rank), and higher CAT (p = 0.044, HR = 0.31 95% CI: 0.11-0.88, log-rank). Markers of oxidative stress such as MDA, TAC, and CAT were associated with adverse clinical outcomes in patients with PAH and inoperable or residual CTEPH.

Critical hemodynamic therapy oriented resuscitation helping reduce lung water production and improve survival

BACKGROUND

Increased extravascular lung water (EVLW) in shock is common in the critically ill patients. This study aimed to explore the effect of cardiac output (CO) on EVLW and its relevant influence on prognosis.

METHODS

The hemodynamic data of 428 patients with pulse-indicated continuous CO catheterization from Department of Critical Care Medicine, Peking Union Medical College Hospital were retrospectively collected and analyzed. The patients were assigned to acute respiratory distress syndrome group, cardiogenic shock group, septic shock group, and combined shock (cardiogenic and septic) group according to their symptoms. Information on 28-day mortality and renal function was also collected.

RESULTS

The CO and EVLW index (EVLWI) in the cardiogenic and combined shock groups were lower than those in the other groups (acute respiratory distress syndrome group vs. cardiogenic shock group vs. septic shock group vs. combined shock group: CO, 5.1 [4.0, 6.2] vs. 4.7 [4.0, 5.7] vs. 5.5 [4.3, 6.7] vs. 4.6 [3.5, 5.7] at 0 to 24 h, P = 0.009; 4.6 [3.8, 5.6] vs. 4.8 [4.1, 5.7] vs. 5.3 [4.4, 6.5] vs. 4.5 [3.8, 5.3] at 24 to 48 h, P = 0.048; 4.5 [4.1, 5.4] vs. 4.8 [3.8, 5.5] vs. 5.3 [4.0, 6.4] vs. 4.0 [3.2, 5.4] at 48 to 72 h, P = 0.006; EVLWI, 11.4 [8.7, 19.1] vs. 7.9 [6.6, 10.0] vs. 8.8 [7.4, 11.0] vs. 8.2 [6.7, 11.3] at 0 to 24 h, P < 0.001; 11.8 [7.7, 17.2] vs. 7.8 [6.3, 10.2] vs. 8.7 [6.6, 12.2] vs. 8.0 [6.6, 11.1] at 24 to 48 h, P < 0.001; and 11.3 [7.7, 18.7] vs. 7.5 [6.3, 10.0] vs. 8.8 [6.3, 12.2] vs. 8.4 [6.4, 11.2] at 48 to 72 h, P < 0.001. The trend of the EVLWI in the septic shock group was higher than that in the cardiogenic shock group (P < 0.05). Moreover, there existed some difference in the pulmonary vascular permeability index among the cardiogenic shock group, the septic shock group, and the combined shock group, without statistical significance (P > 0.05). In addition, there was no significant difference in tissue perfusion or renal function among the four groups during the observation period (P > 0.05). However, the cardiogenic shock group had a higher 28-day survival rate than the other three groups [log rank (Mantel-Cox) = 31.169, P < 0.001].

CONCLUSION

Tissue-aimed lower CO could reduce the EVLWI and achieve a better prognosis.

Long-term hypoxia uncouples Ca2+ and eNOS in bradykinin-mediated pulmonary arterial relaxation

Bradykinin-induced activation of the pulmonary endothelium triggers a rise in intracellular Ca²⁺ that activates nitric oxide (NO)-dependent vasorelaxation. Chronic hypoxia is commonly associated with increased pulmonary vascular tone, which can cause pulmonary hypertension in responsive individuals. In the present study, we tested the hypothesis that long-term high-altitude hypoxia (LTH) diminishes bradykinin-induced Ca²⁺ signals and inhibits endothelial nitric oxide synthase (eNOS), prostacyclin (PGI₂), and large-conductance K⁺ (BK_Ca) channels in sheep, which are moderately responsive to LTH, resulting in decreased pulmonary arterial vasorelaxation. Pulmonary arteries were isolated from ewes kept near sea level (720 m) or at high altitude (3,801 m) for >100 days. Vessel force was measured with wire myography and endothelial intracellular Ca²⁺ with confocal microscopy. eNOS was inhibited with 100 μM N^G-nitro-l-arginine methyl ester (l-NAME), PGI₂ production was inhibited with 10 µM indomethacin that inhibits cyclooxygenase, and BK_Ca channels were blocked with 1 mM tetraethylammonium. Bradykinin-induced endothelial Ca²⁺ signals increased following LTH, but bradykinin relaxation decreased. Furthermore, some vessels contracted in response to bradykinin after LTH. l-NAME sensitivity decreased, suggesting that eNOS dysfunction played a role in uncoupling Ca²⁺ signals and bradykinin relaxation. The Ca²⁺ ionophore A-23187 (10 µM) elicited an enhanced Ca²⁺ response following LTH while relaxation was unchanged although l-NAME sensitivity increased. Additionally, BK_Ca function decreased during bradykinin relaxation following LTH. Western analysis showed that BK_Ca α-subunit expression was increased by LTH while that for the β₁ subunit was unchanged. Overall, these results suggest that those even moderately responsive to LTH can have impaired endothelial function.

Developmental Origins of Hypoxic Pulmonary Hypertension and Systemic Vascular Dysfunction: Evidence from Humans

Epidemiological studies have shown an association between pathologic events occurring during fetal/perinatal life and the development of cardiovascular and metabolic disease in adulthood. These observations have led to the so-called developmental origin of adult disease hypothesis. More recently, evidence has been provided that the pulmonary circulation is also an important target for the developmental programming of adult disease in both experimental animal models and in humans. Here we will review this evidence and provide insight into mechanisms that may play a pathogenic role.

Novel Insights into Cardiovascular Regulation in Patients with Chronic Mountain Sickness

Studies of high-altitude populations, and in particular of maladapted subgroups, may provide important insight into underlying mechanisms involved in the pathogenesis of hypoxemia-related disease in general. Chronic mountain sickness (CMS) is a major public health problem in mountainous regions of the world affecting many millions of high-altitude dwellers. It is characterized by exaggerated chronic hypoxemia, erythrocytosis, and mild pulmonary hypertension. In later stages these patients often present with right heart failure and are predisposed to systemic cardiovascular disease, but the underlying mechanisms are poorly understood. Here, we present recent new data providing insight into underlying mechanisms that may cause these complications.

Sympathetic crashing acute pulmonary edema

Sympathetic crashing acute pulmonary edema (SCAPE) is the extreme end of the spectrum of acute pulmonary edema. It is important to understand this disease as it is relatively common in the emergency department (ED) and has better outcomes when managed appropriately. The patients have an abrupt redistribution of fluid in the lungs, and when treated promptly and effectively, these patients will rapidly recover. Noninvasive ventilation and intravenous nitrates are the mainstay of treatment which should be started within minutes of the patient's arrival to the ED. Use of morphine and intravenous loop diuretics, although popular, has poor scientific evidence.

Thoracic ultrasound: Potential new tool for physiotherapists in respiratory management. A narrative review

The use of diagnostic ultrasound by physiotherapists is not a new concept; it is frequently performed in musculoskeletal physiotherapy. Physiotherapists currently lack accurate, reliable, sensitive, and valid measurements for the assessment of the indications and effectiveness of chest physiotherapy. Thoracic ultrasound may be a promising tool for the physiotherapist and could be routinely performed at patients' bedsides to provide real-time and accurate information on the status of pleura, lungs, and diaphragm; this would allow for assessment of lung aeration from interstitial syndrome to lung consolidation with much better accuracy than chest x-rays or auscultation. Diaphragm excursion and contractility may also be assessed by ultrasound. This narrative review refers to lung and diaphragm ultrasound semiology and describes how physiotherapists could use this tool in their clinical decision-making processes in various cases of respiratory disorders. The use of thoracic ultrasound semiology alongside typical examinations may allow for the guiding, monitoring, and evaluating of chest physiotherapy treatments. Thoracic ultrasound is a potential new tool for physiotherapists.

Saturation diving; physiology and pathophysiology

In saturation diving, divers stay under pressure until most of their tissues are saturated with breathing gas. Divers spend a long time in isolation exposed to increased partial pressure of oxygen, potentially toxic gases, bacteria, and bubble formation during decompression combined with shift work and long periods of relative inactivity. Hyperoxia may lead to the production of reactive oxygen species (ROS) that interact with cell structures, causing damage to proteins, lipids, and nucleic acid. Vascular gas-bubble formation and hyperoxia may lead to dysfunction of the endothelium. The antioxidant status of the diver is an important mechanism in the protection against injury and is influenced both by diet and genetic factors. The factors mentioned above may lead to production of heat shock proteins (HSP) that also may have a negative effect on endothelial function. On the other hand, there is a great deal of evidence that HSPs may also have a "conditioning" effect, thus protecting against injury. As people age, their ability to produce antioxidants decreases. We do not currently know the capacity for antioxidant defense, but it is reasonable to assume that it has a limit. Many studies have linked ROS to disease states such as cancer, insulin resistance, diabetes mellitus, cardiovascular diseases, and atherosclerosis as well as to old age. However, ROS are also involved in a number of protective mechanisms, for instance immune defense, antibacterial action, vascular tone, and signal transduction. Low-grade oxidative stress can increase antioxidant production. While under pressure, divers change depth frequently. After such changes and at the end of the dive, divers must follow procedures to decompress safely. Decompression sickness (DCS) used to be one of the major causes of injury in saturation diving. Improved decompression procedures have significantly reduced the number of reported incidents; however, data indicate considerable underreporting of injuries. Furthermore, divers who are required to return to the surface quickly are under higher risk of serious injury as no adequate decompression procedures for such situations are available. Decompression also leads to the production of endothelial microparticles that may reduce endothelial function. As good endothelial function is a documented indicator of health that can be influenced by regular exercise, regular physical exercise is recommended for saturation divers. Nowadays, saturation diving is a reasonably safe and well controlled method for working under water. Until now, no long-term impact on health due to diving has been documented. However, we still have limited knowledge about the pathophysiologic mechanisms involved. In particular we know little about the effect of long exposure to hyperoxia and microparticles on the endothelium.

Role of posterior hypothalamus in hypobaric hypoxia induced pulmonary edema

To investigate the role of posterior hypothalamus and central neurotransmitters in the pulmonary edema due to hypobaric hypoxia, rats were placed in a high altitude simulation chamber (barometric pressure-294.4 mmHg) for 24 h. Exposure to hypobaric hypoxia resulted in increases in mean arterial blood pressure, renal sympathetic nerve activity, right ventricular systolic pressure, lung wet to dry weight ratio and Evans blue dye leakage. There was a significant attenuation in these responses to hypobaric hypoxia (a) after lesioning posterior hypothalamus and (b) after chronic infusion of GABAA receptor agonist muscimol into posterior hypothalamus. No such attenuation was evident with the chronic infusion of the nitric oxide donor SNAP into the posterior hypothalamus. It is concluded that in hypobaric hypoxia, there is over-activity of posterior hypothalamic neurons probably due to a local decrease in GABA-ergic inhibition which increases the sympathetic drive causing pulmonary hypertension and edema.

Is reversal of endothelial dysfunction still an attractive target in modern cardiology?

Although the endothelium has a number of important functions, the term endothelial dysfunction is commonly used to describe impairment in its vasodilatory capacity. There have been numerous studies evaluating the relationship between endothelial dysfunction and cardiovascular disease, however assessment of endothelial function is perhaps still primarily thought of as a research tool and has not reached widespread clinical acceptance. In this review we explore the relationship between endothelial dysfunction and cardiovascular disease, its prognostic significance, methods of pharmacological reversal of endothelial dysfunction, and ask the question, is reversal of endothelial dysfunction still an attractive target in modern cardiology?

Acute heart failure: patient characteristics and pathophysiology

The number of hospitalizations for acute heart failure (HF) continues to increase and it remains the most common discharge diagnosis among Medicare beneficiaries. Prognosis after hospitalization for HF is poor, with high in-hospital mortality and even higher post-discharge mortality and rehospitalization rates. It is a complex clinical syndrome that varies widely with respect to clinical presentation and underlying pathophysiology. This paper reviews what is documented in the literature regarding the known pathophysiologic mechanisms reported in patients hospitalized for HF.

Reactive species and pulmonary edema

Pulmonary edema occurs when fluid flux into the lung interstitium exceeds its removal, resulting in hypoxemia and even death. Noncardiogenic pulmonary edema (NPE) generally results when microvascular and alveolar permeability to plasma proteins increase, one possible etiology being oxidant injury. Reactive oxygen and nitrogen species (RONS) can modify or damage ion channels, such as epithelial sodium channels, which alters fluid balance. Experimental systems in which either RONS are increased or protective antioxidant mechanisms are decreased result in alterations of epithelial sodium channel activity and support the hypothesis that RONS are important in NPE. Both basic and clinical studies are needed to critically define the RONS-NPE connection and the capacity of antioxidant therapy (either alone or as a supplement to β-agonists) to improve patient outcome.

Hypoxia and hypoxia mimetics decrease aquaporin 5 (AQP5) expression through both hypoxia inducible factor-1α and proteasome-mediated pathways

The alveolar epithelium plays a central role in gas exchange and fluid transport, and is therefore critical for normal lung function. Since the bulk of water flux across this epithelium depends on the membrane water channel Aquaporin 5 (AQP5), we asked whether hypoxia had any effect on AQP5 expression. We show that hypoxia causes a significant (70%) decrease in AQP5 expression in the lungs of mice exposed to hypoxia. Hypoxia and the hypoxia mimetic, cobalt, also caused similar decreases in AQP5 mRNA and protein expression in the mouse lung epithelial cell line MLE-12. The action of hypoxia and cobalt on AQP5 transcription was demonstrated by directly quantifying heternonuclear RNA by real-time PCR. Dominant negative mutants of Hypoxia Inducible Factor (HIF-1α) and HIF-1α siRNA blocked the action of cobalt, showing that HIF-1α is a key component in this mechanism. The proteasome inhibitors, lactacystin or proteasome inhibitor-III completely abolished the effect of hypoxia and cobalt both at the protein and mRNA level indicating that the proteasome pathway is probably involved not only for the stability of HIF-1α protein, but for the stability of unidentified transcription factors that regulate AQP5 transcription. These studies reveal a potentially important physiological mechanism linking hypoxic stress and membrane water channels.

Endothelial dysfunction, arterial stiffness, and heart failure

Outcomes for heart failure (HF) patients remain suboptimal. No known therapy improves mortality in acute HF and HF with preserved ejection fraction; the most recent HF trial results have been negative or neutral. Improvement in surrogate markers has not necessarily translated into better outcomes. To translate breakthroughs with potential therapies into clinical benefit, a better understanding of the pathophysiology establishing the foundation of benefit is necessary. Vascular function plays a central role in the development and progression of HF. Endothelial function and nitric oxide availability affect myocardial function, systemic and pulmonary hemodynamics, and coronary and renal circulation. Arterial stiffness modulates ventricular loading conditions and diastolic function, key components of HF with preserved ejection. Endothelial function and arterial stiffness may therefore serve as important physiological targets for new HF therapies and facilitate patient selection for improved application of existing agents.

Reading chest radiographs in the critically ill (Part II): Radiography of lung pathologies common in the ICU patient

This is part II of two series review of reading chest radiographs in the critically ill. Conventional chest radiography remains the cornerstone of day to day management of the critically ill occasionally supplemented by computed tomography or ultrasound for specific indications. In this second review we discuss radiographic findings of cardiopulmonary disorders common in the intensive care patient and suggest guidelines for interpretation based not only on imaging but also on the pathophysiology and clinical grounds.

Assessment of extravascular lung water and cardiac function in trimix SCUBA diving

An increasing number of recreational self-contained underwater breathing apparatus (SCUBA) divers use trimix of oxygen, helium, and nitrogen for dives deeper than 60 m of sea water. Although it was seldom linked to the development of pulmonary edema, whether SCUBA diving affects the extravascular lung water (EVLW) accumulation is largely unexplored.

METHODS

Seven divers performed six dives on consecutive days using compressed gas mixture of oxygen, helium, and nitrogen (trimix), with diving depths ranging from 55 to 80 m. The echocardiographic parameters (bubble grade, lung comets, mean pulmonary arterial pressure (PAP), and left ventricular function) and the blood levels of the N-terminal part of pro-brain natriuretic peptide (NT-proBNP) were assessed before and after each dive.

RESULTS

Venous gas bubbling was detected after each dive with mean probability of decompression sickness ranging from 1.77% to 3.12%. After each dive, several ultrasonographically detected lung comets rose significantly, which was paralleled by increased pulmonary artery pressure (PAP) and decreased left ventricular contractility (reduced ejection fraction at higher end-systolic and end-diastolic volumes) as well as the elevated NT-proBNP. The number of ultrasound lung comets and mean PAP did not return to baseline values after each dive.

CONCLUSIONS

This is the first report that asymptomatic SCUBA dives are associated with accumulation of EVLW with concomitant increase in PAP, diminished left ventricular contractility, and increased release of NT-proBNP, suggesting a significant cardiopulmonary strain. EVLW and PAP did not return to baseline during repetitive dives, indicating possible cumulative effect with increasing the risk for pulmonary edema.

Pulmonary and Systemic Vascular Dysfunction in Young Offspring of Mothers With Preeclampsia

Background— Adverse events in utero may predispose to cardiovascular disease in adulthood. The underlying mechanisms are unknown. During preeclampsia, vasculotoxic factors are released into the maternal circulation by the diseased placenta. We speculated that these factors pass the placental barrier and leave a defect in the circulation of the offspring that predisposes to a pathological response later in life. The hypoxia associated with high-altitude exposure is expected to facilitate the detection of this problem.

Methods and Results— We assessed pulmonary artery pressure (by Doppler echocardiography) and flow-mediated dilation of the brachial artery in 48 offspring of women with preeclampsia and 90 offspring of women with normal pregnancies born and permanently living at the same high-altitude location (3600 m). Pulmonary artery pressure was roughly 30% higher (mean±SD, 32.1±5.6 versus 25.3±4.7 mm Hg; P <0.001) and flow-mediated dilation was 30% smaller (6.3±1.2% versus 8.3±1.4%; P <0.0001) in offspring of mothers with preeclampsia than in control subjects. A strong inverse relationship existed between flow-mediated dilation and pulmonary artery pressure ( r =−0.61, P <0.001). The vascular dysfunction was related to preeclampsia itself because siblings of offspring of mothers with preeclampsia who were born after a normal pregnancy had normal vascular function. Augmented oxidative stress may represent an underlying mechanism because thiobarbituric acid-reactive substances plasma concentration was increased in offspring of mothers with preeclampsia.

Conclusions— Preeclampsia leaves a persistent defect in the systemic and the pulmonary circulation of the offspring. This defect predisposes to exaggerated hypoxic pulmonary hypertension already during childhood and may contribute to premature cardiovascular disease in the systemic circulation later in life.

High altitude, a natural research laboratory for the study of cardiovascular physiology and pathophysiology

High altitude constitutes an exciting natural laboratory for medical research. Although initially, the aim of high-altitude research was to understand the adaption of the organism to hypoxia and find treatments for altitude-related diseases, during the past decade or so, the scope of this research has broadened considerably. Two important observations led the foundation for the broadening of the scientific scope of high-altitude research. First, high-altitude pulmonary edema represents a unique model that allows studying fundamental mechanisms of pulmonary hypertension and lung edema in humans. Second, the ambient hypoxia associated with high-altitude exposure facilitates the detection of pulmonary and systemic vascular dysfunction at an early stage. Here, we will review studies that, by capitalizing on these observations, have led to the description of novel mechanisms underpinning lung edema and pulmonary hypertension and to the first direct demonstration of fetal programming of vascular dysfunction in humans.

Ultrasonic evidence of acute interstitial lung edema after SCUBA diving is resolved within 2-3h

Recently, an increase in extravascular lung water (EVLW) accumulation with diminished left ventricular contractility within 60 min after SCUBA diving was reported. We have observed previously that diving was associated with reduced diffusing lung capacity for carbon monoxide (DLCO) and arterial oxygen pressure for up to 60-80 min postdive. Here we investigated whether increased EVLW persists 2-3h after successive deep dives in a group of seven male divers. The echocardiographic indices of pulmonary water accumulation (ultrasound lung comets (ULC)) and left ventricular function, respiratory functional measurements and arterial oxygen saturation (SaO(2)) were assessed 2-3h post diving, while venous gas bubbles (VGB) and the blood levels of NT-proBNP and proANP were analyzed 40 min after surfacing. Spirometry values, flow-volume, DLCO, SaO(2) and ULC were unchanged after each dive, except for significant increase in ULC after the second dive. Left ventricular function was reduced, while NT-proBNP and proANP levels were significantly elevated after majority of dives, suggesting a cardiac strain.

The von Hippel-Lindau Chuvash mutation promotes pulmonary hypertension and fibrosis in mice

Mutation of the von Hippel-Lindau (VHL) tumor suppressor protein at codon 200 (R200W) is associated with a disease known as Chuvash polycythemia. In addition to polycythemia, Chuvash patients have pulmonary hypertension and increased respiratory rates, although the pathophysiological basis of these symptoms is unclear. Here we sought to address this issue by studying mice homozygous for the R200W Vhl mutation (VhlR/R mice) as a model for Chuvash disease. These mice developed pulmonary hypertension independently of polycythemia and enhanced normoxic respiration similar to Chuvash patients, further validating VhlR/R mice as a model for Chuvash disease. Lungs from VhlR/R mice exhibited pulmonary vascular remodeling, hemorrhage, edema, and macrophage infiltration, and lungs from older mice also exhibited fibrosis. HIF-2alpha activity was increased in lungs from VhlR/R mice, and heterozygosity for Hif2a, but not Hif1a, genetically suppressed both the polycythemia and pulmonary hypertension in the VhlR/R mice. Furthermore, Hif2a heterozygosity resulted in partial protection against vascular remodeling, hemorrhage, and edema, but not inflammation, in VhlR/R lungs, suggesting a selective role for HIF-2alpha in the pulmonary pathology and thereby providing insight into the mechanisms underlying pulmonary hypertension. These findings strongly support a dependency of the Chuvash phenotype on HIF-2alpha and suggest potential treatments for Chuvash patients.

Flash pulmonary edema

Flash pulmonary edema (FPE) is a general clinical term used to describe a particularly dramatic form of acute decompensated heart failure. Well-established risk factors for heart failure such as hypertension, coronary ischemia, valvular heart disease, and diastolic dysfunction are associated with acute decompensated heart failure as well as with FPE. However, endothelial dysfunction possibly secondary to an excessive activity of renin-angiotensin-aldosterone system, impaired nitric oxide synthesis, increased endothelin levels, and/or excessive circulating catecholamines may cause excessive pulmonary capillary permeability and facilitate FPE formation. Renal artery stenosis particularly when bilateral has been identified has a common cause of FPE. Lack of diurnal variation in blood pressure and a widened pulse pressure have been identified as risk factors for FPE. This review is an attempt to delineate clinical and pathophysiological mechanisms responsible for FPE and to distinguish pathophysiologic, clinical, and therapeutic aspects of FPE from those of acute decompensated heart failure.

Altitude and the heart: is going high safe for your cardiac patient?

Our aging population combined with the ease of travel and the interest in high altitude recreation pursuits exposes more patients to the acute physiologic effects of high altitude and lower oxygen availability. Acute exposure to high altitude is associated with significant alterations to the cardiovascular system. These may be important in patients with underlying cardiovascular disease who are not able to compensate to such physiologic changes. Exacerbating factors pertinent to patients with cardiovascular disease include acute hypoxia, increased myocardial work, increased epinephrine release, and increased pulmonary artery pressures. This review summarizes the physiology and clinical evidence regarding acute altitude exposure on the cardiopulmonary system with practical recommendations to address the question: "Is it safe for me to ski in the Rockies or climb Mt. Kilimanjaro?"

Chest sonography detects lung water accumulation in healthy elite apnea divers

BACKGROUND

Ultrasound lung comets (ULCs) detected by chest sonography are a simple, noninvasive, semiquantitative sign of increased extravascular lung water. Pulmonary edema may occur in elite apnea divers, possibly triggered by centralization of blood flow from the periphery to pulmonary vessels. We assessed the prevalence of ULCs in top-level breath-hold divers after immersion.

METHODS

We evaluated 31 consecutive healthy, top-level, breath-hold divers (10 female, 21 male; age 31 +/- 5 years) participating in a yearly international apnea diving contest in Sharm-el-Sheik, Egypt, November 1 to 3, 2007. We performed chest and cardiac sonography with a transthoracic probe (2.5-3.5 MHz, Esaote Mylab) in all divers, both on the day before and 10 +/- 9 minutes after immersion. In a subset of 4 divers, chest scan was also repeated at 24 hours after immersion. ULCs were evaluated on the anterior and posterior chest at 61 predefined scanning sites. An independent sonographer, blind to both patient identity and status (pre- or post-diving), scored ULCs.

RESULTS

Diving depth ranged from 31 to 112 m. Duration of immersion ranged from 120 to 225 seconds. The ULC score was 0.5 +/- 1.5 at baseline and 13 +/- 21 after diving (P = .012). At individual patient analysis, ULCs appeared in 14 athletes (45%) after diving. Of these 14 athletes, 4 were asymptomatic, 6 showed aspecific symptoms with transient loss of motor control ("Samba"), 2 had palpitations with frequent premature ventricular contractions, and 2 had persistent cough with hemoptysis and pulmonary crackles. In a subset of 4 athletes with post-diving ULCs in whom late follow-up study also was available, chest sonography findings fully normalized at 24 hours of follow-up.

CONCLUSION

In top-level breath-hold divers, chest sonography frequently reveals an increased number of ULCs after immersion, indicating a relatively high prevalence of (often subclinical) reversible extravascular lung water accumulation.

Type I epithelial cells are the main target of whole-body hypoxic preconditioning in the lung

Whole-body hypoxic preconditioning (WHPC) prolongs survival of mice exposed to severe hypoxia by attenuating pulmonary edema and preserving gas exchange. However, the cellular and molecular mechanism(s) of this protection remains unclear. The objective of this study was to identify the cellular target(s) of WHPC in the lung. Conscious mice were exposed to hypoxia (7% O(2)) for 6 hours with or without pretreatment of WHPC ([8% O(2)] x 10 min/[21% O(2)] x 10 min; 6 cycles). Hypoxia caused severe lung injury, as shown by the development of high-permeability-type pulmonary edema and the release of lactate dehydrogenase and creatine kinase into the airspace and the circulation. All these signs of hypoxic lung injury were significantly attenuated by WHPC. Hypoxia also caused a remarkable release of type I cell markers (caveolin-2 and receptor for advanced glycation end products) in lung lavage that was almost completely abolished by WHPC. Conversely, hypoxia-induced release of type II cell markers (surfactant-associated proteins A and D) was only marginal, and was unaffected by WHPC. Electron microscopic analysis demonstrated considerable hypoxic damage in alveolar type I cells and vascular endothelial cells. Notably, WHPC completely eliminated hypoxic damage in the former and alleviated it in the latter. Type II cells appeared normal. Furthermore, WHPC up-regulated protein expression of cytoprotective genes in the lung, such as heat shock proteins and manganese superoxide dismutase. Thus, WHPC attenuates hypoxic lung injury through protection of cells constituting the respiratory membrane, especially hypoxia-vulnerable type I epithelial cells. This beneficial effect may involve up-regulation of cytoprotective genes.

Patterns of alveolar fluid clearance in heart failure

Alveolar fluid clearance (AFC) is important in keeping the airspaces free of edema. This process is accomplished via passive and active transport of Na(+) across the alveolo-capillary barrier mostly by apical Na(+) channels and basolateral Na,K-ATPases, respectively. Patterns of alveolar fluid clearance were found to be decreased in acutely elevated left atrial pressures, possibly due to the inhibition of alveolar epithelial active sodium transport. On the other hand, chronic elevation of pulmonary capillary pressure, such as seen in experimental and clinical congestive heart failure, increases alveolar fluid clearance most likely secondary to upregulation of active sodium transport.

Nitric oxide/cGMP protects endothelial cells from hypoxia-mediated leakiness

Leakiness of the endothelial bed is attributed to the over-perfusion of the pulmonary bed, which leads to high altitude pulmonary edema (HAPE). Inhalation of nitric oxide has been successfully employed to treat HAPE patients. We hypothesize that nitric oxide intervenes in the permeability of the pulmonary macrovascular endothelial bed to rectify the leaky bed under hypoxia. Our present work explores the underlying mechanism of 'hypoxia-mediated' endothelial malfunction by using human umbilical cord-derived immortalized endothelial cells, ECV-304, and bovine pulmonary artery primary endothelial cells. The leakiness of the endothelial monolayer was increased by two-fold under hypoxia in comparison to cells under normoxia, while optical tweezers-based tethering assays reported a higher membrane tension of endothelial cells under hypoxia. Phalloidin staining demonstrated depolymerization of F-actin stress fibers and highly polarized F-actin patterns in endothelial cells under hypoxia. Nitric oxide, 8-Br-cGMP and sildenafil citrate (phosphodiesterase type 5 inhibitor) led to recovery from hypoxia-induced leakiness of the endothelial monolayers. Results of the present study also suggest that 'hypoxia-induced' cytoskeletal rearrangements and membrane leakiness are associated with the low nitric oxide availability under hypoxia. We conclude that nitric oxide-based recovery of hypoxia-induced leakiness of endothelial cells is a cyclic guanosine monophosphate (cGMP)-dependent phenomenon.