Pilot study on the effects of a 2-week hiking vacation at moderate versus low altitude on plasma parameters of carbohydrate and lipid metabolism in patients with metabolic syndrome

Exposure to Normobaric Hypoxia Combined with a Mixed Diet Contributes to Improvement in Lipid Profile in Trained Cyclists

This study aimed to analyze the effects of live high-train low method (LH-TL) and intermittent hypoxic training (IHT) with a controlled mixed diet on lipid profile in cyclists. Thirty trained male cyclists at a national level with at least six years of training experience participated in the study. The LH-TL group was exposed to hypoxia (FiO2 = 16.5%) for 11-12 h a day and trained under normoxia for 3 weeks. In the IHT group, participants followed the IHT routine three times a week under hypoxia (FiO2 = 16.5%) at lactate threshold intensity. The control group (N) lived and trained under normoxia. The results showed that the 3-week LH-TL method significantly improved all lipid profile variables. The LH-TL group showed a significant increase in HDL-C by 9.0% and a decrease in total cholesterol (TC) by 9.2%, LDL-C by 18.2%, and triglycerides (TG) by 27.6%. There were no significant changes in lipid profiles in the IHT and N groups. ∆TG and ∆TC were significantly higher in the LH-TL group compared to the N group. In conclusion, hypoxic conditions combined with a mixed diet can induce beneficial changes in lipid profile even in highly trained athletes. The effectiveness of the hypoxic stimulus is closely related to the hypoxic training method.

Oxygen in Metabolic Dysfunction and Its Therapeutic Relevance

Significance: In recent years, a number of studies have shown altered oxygen partial pressure at a tissue level in metabolic disorders, and some researchers have considered oxygen to be a (macro) nutrient. Oxygen availability may be compromised in obesity and several other metabolism-related pathological conditions, including sleep apnea-hypopnea syndrome, the metabolic syndrome (which is a set of conditions), type 2 diabetes, cardiovascular disease, and cancer. Recent Advances: Strategies designed to reduce adiposity and its accompanying disorders have been mainly centered on nutritional interventions and physical activity programs. However, novel therapies are needed since these approaches have not been sufficient to counteract the worldwide increasing rates of metabolic disorders. In this regard, intermittent hypoxia training and hyperoxia could be potential treatments through oxygen-related adaptations. Moreover, living at a high altitude may have a protective effect against the development of abnormal metabolic conditions. In addition, oxygen delivery systems may be of therapeutic value for supplying the tissue-specific oxygen requirements. Critical Issues: Precise in vivo methods to measure oxygenation are vital to disentangle some of the controversies related to this research area. Further, it is evident that there is a growing need for novel in vitro models to study the potential pathways involved in metabolic dysfunction to find appropriate therapeutic targets. Future Directions: Based on the existing evidence, it is suggested that oxygen availability has a key role in obesity and its related comorbidities. Oxygen should be considered in relation to potential therapeutic strategies in the treatment and prevention of metabolic disorders. Antioxid. Redox Signal. 35, 642-687.

The impact of hypoxia exposure on glucose homeostasis in metabolically compromised humans: A systematic review

Humans living at a higher altitude are less prone to suffer from impaired glucose homeostasis and type 2 diabetes mellitus (T2DM), which might at least partly be explained by lower oxygen availability at higher altitudes. The present systematic review aimed to provide an overview of the current literature on the effects of hypoxia exposure on glucose homeostasis in metabolically compromised humans. Several databases were searched up to August 10^th, 2020. The search strategy identified 368 unique records. Following assessment for eligibility based on the selection criteria, 16 studies were included in this review. Six studies (2 controlled studies; 4 uncontrolled studies) demonstrated beneficial effects of hypoxia exposure on glucose homeostasis, while 10 studies (8 controlled studies; 2 uncontrolled studies) reported no improvement in glucose homeostasis following hypoxia exposure. Notably, passive hypoxia exposure seemed to improve glucose homeostasis, whereas hypoxic exercise training (2-8 weeks) appeared to have no additional/synergistic effects on glucose homeostasis compared to normoxia exposure. Due to the heterogeneity in study populations and intervention duration (acute studies / 2-8 wks training), it is difficult to indicate which factors may explain conflicting study outcomes. Moreover, these results should be interpreted with some caution, as several studies did not include a control group. Taken together, hypoxia exposure under resting and exercise conditions might provide a novel therapeutic strategy to improve glucose homeostasis in metabolically compromised individuals, but more randomized controlled trials are warranted before strong conclusions on the effects of hypoxia exposure on glucose homeostasis can be drawn.

Hypoxia, energy balance, and obesity: An update

Because of the enduring rise in the prevalence of obesity worldwide, there is continued interest in hypoxia as a mechanism underlying the pathophysiology of obesity and its comorbidities and as a potential therapeutic adjunct for the management of the disease. Lifelong exposure to altitude is accompanied by a lower risk for obesity, whereas altitude sojourns are generally associated with a loss of body mass. A negative energy balance upon exposure to hypoxia can be due to a combination of changes in determinants of energy expenditure (resting metabolic rate and physical activity energy expenditure) and energy intake (appetite). Over the past 15 years, the potential therapeutic interest of hypobaric or normobaric hypoxic exposure in individuals with obesity-to lower body mass and improve health status-has become an active field of research. Various protocols have been implemented, using actual altitude sojourns or intermittent normobaric hypoxic exposures, at rest or in association with physical activity. Although several studies suggest benefits on body mass and cardiovascular and metabolic variables, further investigations are required before recommending hypoxic exposure in obesity management programs. Future studies should also better clarify the effects of hypoxia on appetite, the intestinal microbiota, and finally on overall energy balance.

Effects of peripheral and different inspiratory muscle training methods in coronary artery disease patients with metabolic syndrome: A randomized-controlled trial

Background OBJECTIVE: To investigate the effects of peripheral muscle training (PMT) and different inspiratory muscle training (IMT) methods on respiratory functions, exercise capacity, and biochemistry parameters in coronary artery disease patients with metabolic syndrome.

METHODS

This prospective, single-blind, randomized-controlled study included 60 patients of stable coronary artery disease with metabolic syndrome (New York Heart Association [NYHA] Class I-II, left ventricular ejection fraction >40%). Patients were randomly divided into three groups: neuromuscular electrical stimulation (NMES) plus PMT group (NMES + PMT group, n = 20), IMT plus PMT group (IMT + PMT group, n = 20) and PMT group (PMT group, n = 20). Treatment continued for six weeks for all groups. The NMES was applied to rectus abdominis, IMT was applied with 30% of maximal inspiratory pressures, and PMT was applied at home. Spirometry, maximal inspiratory and expiratory pressure, dyspnea scores, exercise stress test, and biochemistry parameters were measured before and after training.

RESULTS

There were significant improvements in spirometric tests, respiratory muscle strength, dyspnea scores, exercise capacity, fasting blood glucose, and antistreptolysin O after treatment in all groups (p < 0.05). Significant improvements in C-reactive protein and erythrocyte sedimentation rate were observed in NMES + PMT and IMT + PMT groups (p < 0.05). Among the groups, there was a significant difference in maximal inspiratory pressure (p = 0.02) and erythrocyte sedimentation rate (p = 0.037) in favor of NMES + PMT group (p < 0.05).

CONCLUSION

Our study results showed significant improvements in respiratory functions, exercise capacity, and biochemistry markers in all groups. Different IMT methods can be used in cardiopulmonary rehabilitation to improve exercise intolerance in coronary artery disease patients with metabolic syndrome.

CLINICAL TRIAL REGISTRATION NUMBER

NCT03523026.

Limitation of Maximal Heart Rate in Hypoxia: Mechanisms and Clinical Importance

The use of exercise intervention in hypoxia has grown in popularity amongst patients, with encouraging results compared to similar intervention in normoxia. The prescription of exercise for patients largely rely on heart rate recordings (percentage of maximal heart rate (HR_max) or heart rate reserve). It is known that HR_max decreases with high altitude and the duration of the stay (acclimatization). At an altitude typically chosen for training (2,000-3,500 m) conflicting results have been found. Whether or not this decrease exists or not is of importance since the results of previous studies assessing hypoxic training based on HR may be biased due to improper intensity. By pooling the results of 86 studies, this literature review emphasizes that HR_max decreases progressively with increasing hypoxia. The dose–response is roughly linear and starts at a low altitude, but with large inter-study variabilities. Sex or age does not seem to be a major contributor in the HR_max decline with altitude. Rather, it seems that the greater the reduction in arterial oxygen saturation, the greater the reduction in HRmax, due to an over activity of the parasympathetic nervous system. Only a few studies reported HR_max at sea/low level and altitude with patients. Altogether, due to very different experimental design, it is difficult to draw firm conclusions in these different clinical categories of people. Hence, forthcoming studies in specific groups of patients are required to properly evaluate (1) the HR_max change during acute hypoxia and the contributing factors, and (2) the physiological and clinical effects of exercise training in hypoxia with adequate prescription of exercise training intensity if based on heart rate.

Different training responses to eccentric endurance exercise at low and moderate altitudes in pre-diabetic men: a pilot study

This pilot study aimed (a) to evaluate the effects of eccentric exercise training at low and moderate altitudes on physical fitness in pre-diabetic men and (b) to establish whether or not oxidative stress levels and antioxidant status were associated with performance improvements. In this crossover trial, five pre-diabetic men conducted nine downhill walking sessions (3 days/week, 3 consecutive weeks) at low altitude (from 1360 to 850 m) and one year later at moderate altitude (from 2447 to 2000 m). Exercise testing and the determination of parameters of oxidative stress and antioxidant capacity were performed pre- and post-training. The biological antioxidant activity of plasma (BAP) increased after eccentric training at moderate altitude (p < 0.001), whereas diacron reactive oxygen metabolites (dROMs) remained unchanged. Also, the BAP/dROMs ratio increased only after training at moderate-altitude training (p = 0.009). Maximum power output improved after training at low altitude and the changes were significantly related to baseline BAP/dROMs ratio (r = 0.90). No decrease was seen for fasting plasma glucose. Eccentric exercise training in pre-diabetic men improved performance only when performed at low altitude and this improvement was positively related to the baseline BAP/dROMs ratio. In contrast, 3 weeks of eccentric exercise training increased BAP levels and the BAP/dROMs ratio only at moderate altitude without improving the performance. Thus, one might speculate that the BAP/dROMs ratio has to increase before performance improvements occur at moderate altitude.

Intermittent hypoxia training in prediabetes patients: Beneficial effects on glucose homeostasis, hypoxia tolerance and gene expression

The present study aimed at examining beneficial effects of intermittent hypoxia training (IHT) under prediabetic conditions. We investigate the effects of three-week IHT on blood glucose level, tolerance to acute hypoxia, and leukocyte mRNA expression of hypoxia inducible factor 1α (HIF-1α) and its target genes, i.e. insulin receptor, facilitated glucose transporter-solute carrier family-2, and potassium voltage-gated channel subfamily J. Seven healthy and 11 prediabetic men and women (44-70 years of age) were examined before, next day and one month after three-week IHT (3 sessions per week, each session consisting 4 cycles of 5-min 12% O₂ and 5-min room air breathing). We found that IHT afforded beneficial effects on glucose homeostasis in patients with prediabetes reducing fasting glucose and during standard oral glucose tolerance test. The most pronounced positive effects were observed at one month after IHT termination. IHT also significantly increased the tolerance to acute hypoxia (i.e. SaO₂ level at 20th min of breathing with 12% O₂) and improved functional parameters of respiratory and cardiovascular systems. IHT stimulated HIF-1α mRNA expression in blood leukocytes in healthy and prediabetic subjects, but in prediabetes patients the maximum increase was lagged. The greatest changes in mRNA expression of HIF-1α target genes occurred a month after IHT and coincided with the largest decrease in blood glucose levels. The higher expression of HIF-1α was positively associated with higher tolerance to hypoxia and better glucose homeostasis. In conclusion, our results suggest that IHT may be useful for preventing the development of type 2 diabetes. Impact statement The present study investigated the beneficial effects of intermittent hypoxia training (IHT) in humans under prediabetic conditions. We found that three-week moderate IHT induced higher HIF-1α mRNA expressions as well as its target genes, which were positively correlated with higher tolerance to acute hypoxia and better glucose homeostasis in both middle-aged healthy and prediabetic subjects. This small clinical trial has provided new data suggesting a potential utility of IHT for management of prediabetes patients.

Living at a Geographically Higher Elevation Is Associated with Lower Risk of Metabolic Syndrome: Prospective Analysis of the SUN Cohort

Living in a geographically higher altitude affects oxygen availability. The possible connection between environmental factors and the development of metabolic syndrome (MetS) feature is not fully understood, being the available epidemiological evidence still very limited. The aim of the present study was to evaluate the longitudinal association between altitude and incidence of MetS and each of its components in a prospective Spanish cohort, The Seguimiento Universidad de Navarra (SUN) project. Our study included 6860 highly educated subjects (university graduates) free from any MetS criteria at baseline. The altitude of residence was imputed with the postal code of each individual subject residence according to the data of the Spanish National Cartographic Institute and participants were categorized into tertiles. MetS was defined according to the harmonized definition. Cox proportional hazards models were used to assess the association between the altitude of residence and the risk of MetS during follow-up. After a median follow-up period of 10 years, 462 incident cases of MetS were identified. When adjusting for potential confounders, subjects in the highest category of altitude (>456 m) exhibited a significantly lower risk of developing MetS compared to those in the lowest tertile (<122 m) of altitude of residence [Model 2: Hazard ratio = 0.75 (95% Confidence interval: 0.58–0.97); p for trend = 0.029]. Living at geographically higher altitude was associated with a lower risk of developing MetS in the SUN project. Our findings suggest that geographical elevation may be an important factor linked to metabolic diseases.

Intermittent hypoxia training as non-pharmacologic therapy for cardiovascular diseases: Practical analysis on methods and equipment

The global industrialization has brought profound lifestyle changes and environmental pollutions leading to higher risks of cardiovascular diseases. Such tremendous challenges outweigh the benefits of major advances in pharmacotherapies (such as statins, antihypertensive, antithrombotic drugs) and exacerbate the public healthcare burdens. One of the promising complementary non-pharmacologic therapies is the so-called intermittent hypoxia training (IHT) via activation of the human body's own natural defense through adaptation to intermittent hypoxia. This review article primarily focuses on the practical questions concerning the utilization of IHT as a non-pharmacologic therapy against cardiovascular diseases in humans. Evidence accumulated in the past five decades of research in healthy men and patients has suggested that short-term daily sessions consisting 3-4 bouts of 5-7 min exposures to 12-10% O2 alternating with normoxic durations for 2-3 weeks can result in remarkable beneficial effects in treatment of cardiovascular diseases such as hypertension, coronary heart disease, and heart failure. Special attentions are paid to the therapeutic effects of different IHT models, along with introduction of a variety of specialized facilities and equipment available for IHT, including hypobaric chambers, hypoxia gas mixture deliver equipment (rooms, tents, face masks), and portable rebreathing devices. Further clinical trials and thorough evaluations of the risks versus benefits of IHT are much needed to develop a series of standardized and practical guidelines for IHT. Taken together, we can envisage a bright future for IHT to play a more significant role in the preventive and complementary medicine against cardiovascular diseases.