Lan Huang

Cardiorespiratory function influences exercise capacity and is an important determinant of high-altitude adaptation. Some studies have investigated the characteristics of changes in cardiorespiratory fitness during high-altitude acclimatization. However, studies on changes in cardiorespiratory fitness during high-altitude de-acclimatization are still lacking and have not yet been elucidated. Furthermore, few drugs have been studied to improve cardiorespiratory function during both processes. The Shigatse CARdiorespiratory Fitness (SCARF) study is a single-center, randomized, double-blind, placebo-control clinical trial to explore the effects of ubiquinol on cardiorespiratory fitness during high-altitude acclimatization and de-acclimatization in healthy adults. Participants will be randomly assigned 1:1 to ubiquinol 200 mg daily or a placebo for 14 days before departure until the end of data collection after return in 7 days. Cardiorespiratory fitness is the primary outcome, while acute mountain sickness and high-altitude de-acclimatization symptoms are secondary endpoints. In addition, laboratory measurements, including routine blood tests and serological measurements, will be performed. To the best of our knowledge, the SCARF study will be the first to reveal the changes in the cardiorespiratory fitness characteristics during high-altitude acclimatization and de-acclimatization. Furthermore, the results of this study will contribute to exploring whether ubiquinol supplementation could be beneficial for endurance exercise capacity at different altitudes and help improve adaptation to acute hypoxia and de-acclimatization.Clinical Trial Registration: This study has been registered in the Chinese Clinical Trial Register (www.chictr.org.cn) as ChiCTR2200059900 and ChiCTR2200066328.

Background: Cardiorespiratory fitness plays an important role in coping with hypoxic stress at high altitudes. However, the association of cardiorespiratory fitness with the development of acute mountain sickness (AMS) has not yet been evaluated. Wearable technology devices provide a feasible assessment of cardiorespiratory fitness, which is quantifiable as maximum oxygen consumption (VO2max) and may contribute to AMS prediction. Objective: We aimed to determine the validity of VO2max estimated by the smartwatch test (SWT), which can be self-administered, in order to overcome the limitations of clinical VO2max measurements. We also aimed to evaluate the performance of a VO2max-SWT–based model in predicting susceptibility to AMS. Methods: Both SWT and cardiopulmonary exercise test (CPET) were performed for VO2max measurements in 46 healthy participants at low altitude (300 m) and in 41 of them at high altitude (3900 m). The characteristics of the red blood cells and hemoglobin levels in all the participants were analyzed by routine blood examination before the exercise tests. The Bland-Altman method was used for bias and precision assessment. Multivariate logistic regression was performed to analyze the correlation between AMS and the candidate variables. A receiver operating characteristic curve was used to evaluate the efficacy of VO2max in predicting AMS. Results: VO2max decreased after acute high altitude exposure, as measured by CPET (25.20 [SD 6.46] vs 30.17 [SD 5.01] at low altitude; P<.001) and SWT (26.17 [SD 6.71] vs 31.28 [SD 5.17] at low altitude; P<.001). Both at low and high altitudes, VO2max was slightly overestimated by SWT but had considerable accuracy as the mean absolute percentage error (<7%) and mean absolute error (<2 mL·kg–1·min–1), with a relatively small bias compared with VO2max-CPET. Twenty of the 46 participants developed AMS at 3900 m, and their VO2max was significantly lower than that of those without AMS (CPET: 27.80 [SD 4.55] vs 32.00 [SD 4.64], respectively; P=.004; SWT: 28.00 [IQR 25.25-32.00] vs 32.00 [IQR 30.00-37.00], respectively; P=.001). VO2max-CPET, VO2max-SWT, and red blood cell distribution width-coefficient of variation (RDW-CV) were found to be independent predictors of AMS. To increase the prediction accuracy, we used combination models. The combination of VO2max-SWT and RDW-CV showed the largest area under the curve for all parameters and models, which increased the area under the curve from 0.785 for VO2max-SWT alone to 0.839. Conclusions: Our study demonstrates that the smartwatch device can be a feasible approach for estimating VO2max. In both low and high altitudes, VO2max-SWT showed a systematic bias toward a calibration point, slightly overestimating the proper VO2max when investigated in healthy participants. The SWT-based VO2max at low altitude is an effective indicator of AMS and helps to better identify susceptible individuals following acute high-altitude exposure, particularly by combining the RDW-CV at low altitude. Trial Registration: Chinese Clinical Trial Registry ChiCTR2200059900; https://www.chictr.org.cn/showproj.html?proj=170253

Background: Atrial fibrillation (AF) is associated with an increased risk of thrombosis of the left atrial appendage (LAA). However, the molecular mechanisms underlying this site‐specificity remain poorly understood. Here, we present a comparative single‐cell transcriptional profile of paired atrial appendages from patients with AF and illustrate the chamber‐specific properties of the main cell types.Methods: Single‐cell RNA sequencing analysis of matched atrial appendage samples from three patients with persistent AF was evaluated by 10× genomics. The AF mice model was created usingTbx5knockout mice. Validation experiments were performed by glutathione S‐transferase pull‐down assays, coimmunoprecipitation (Co‐IP), cleavage assays and shear stress experiments in vitro.Results: In LAA, phenotype switching from endothelial cells to fibroblasts and inflammation associated with proinflammatory macrophage infiltration were observed. Importantly, the coagulation cascade is highly enriched in LAA endocardial endothelial cells (EECs), accompanying the up‐regulation of a disintegrin and metalloproteinase with thrombospondin motifs 1 (ADAMTS1) and the down‐regulation of the tissue factor pathway inhibitor (TFPI) and TFPI2. Similar alterations were verified in an AF mouse model (Tbx5^+/−) and EECs treated with simulated AF shear stress in vitro. Furthermore, we revealed that the cleavage of both TFPI and TFPI2 based on their interaction with ADAMTS1 would lead to loss of anticoagulant activities of EECs.Conclusions: This study highlights the decrease in the anticoagulant status of EECs in LAA as a potential mechanism underlying the propensity for thrombosis, which may aid the development of anticoagulation therapeutic approaches targeting functionally distinct cell subsets or molecules during AF.

High altitude brings a great physiological change in human beings, both during short-term exposure and in lifelong residents, especially in the cardiovascular system. Hypoxia notably induces pulmonary vasoconstriction, thus resulting in a moderate increase in pulmonary arterial pressure. Acclimatized inhabitants exhibit lower pulmonary pressure and better exercise capacity than lowlanders during short-term high-altitude exposure. Rapid ascent to high altitude without adequate acclimatization can cause high-altitude pulmonary edema in susceptible individuals, with a rapid increase in pulmonary pressure. Cardiac output increases initially following acute high-altitude exposure and returns to normal as at sea level after a few days of acclimatization. Ventricular volumes at high altitude change consistently with decreases in plasma volume. Left ventricular systolic function is enhanced after acute high-altitude exposure and during chronic acclimatization. However, there are controversies on whether right ventricular systolic function is preserved or decreases after high-altitude exposure, probably due to variable hypoxic pulmonary vasoconstriction. High altitude induces altered ventricular diastolic patterns. Recently, a new perspective has emerged, whereby ventricular intrinsic relaxation is not impaired, as assessed by untwisting through speckle-tracking imaging. Persistent hypoxic pulmonary hypertension probably induced right ventricular dilation and hypertrophy, and even right heart failure, described as high-altitude heart diseases. Descent to lower altitude should be the best treatment for them, and potential pharmacological agents majorly focus on the inhabitation of pulmonary vasoconstriction, such as phosphodiesterase-5 inhibitors and endothelin receptor antagonists. Evidence on the risks of high-altitude exposure for patients with previous cardiovascular diseases is limited, and thus they should be prudent when ascending to high altitude. Further randomized large-scale studies are needed to explore cardiac performance at high altitudes and provide more evidence for the prevention and clinical management of medical complications at high altitude.

Vascular calcification (VC) is regarded as a common feature of vascular aging. Klotho deficiency reportedly contributes to VC, which can be ameliorated by restoration of Klotho expression. However, the specific mechanisms involved remain unclear. Here, we investigated the role of autophagy in the process of Klotho‐inhibiting VC. The clinical study results indicated that, based on Agatston score, serum Klotho level was negatively associated with aortic calcification. Then, Klotho‐deficient mice exhibited aortic VC, which could be alleviated with the supplementation of Klotho protein. Moreover, autophagy increased in the aorta of Klotho‐deficient mice and protected against VC. Finally, we found that Klotho ameliorated calcification by promoting autophagy both in the aorta of Klotho‐deficient mice and in mouse vascular smooth muscle cells (MOVAS) under calcifying conditions. These findings indicate that Klotho deficiency induces increased autophagy to protect against VC and that Klotho expression further enhances autophagy to ameliorate calcification. This study is beneficial to exploring the underlying mechanisms of Klotho regulating VC, which has important guiding significance for future clinical studies in the treatment of VC.