Acute changes in cardiac dimensions, function, and longitudinal mechanics in healthy individuals with and without high-altitude induced pulmonary hypertension at 4559 m

BACKGROUND

High-altitude pulmonary hypertension (HAPH) has a prevalence of approximately 10%. Changes in cardiac morphology and function at high altitude, compared to a population that does not develop HAPH are scarce.

METHODS

Four hundred twenty-one subjects were screened in a hypoxic chamber inspiring a FiO2  = 12% for 2 h. In 33 subjects an exaggerated increase in systolic pulmonary artery pressure (sPAP) could be confirmed in two independent measurements. Twenty nine of these, and further 24 matched subjects without sPAP increase were examined at 4559 m by Doppler echocardiography including global longitudinal strain (GLS).

RESULTS

SPAP increase was higher in HAPH subjects (∆ = 10.2 vs. ∆ = 32.0 mm Hg, p < .001). LV eccentricity index (∆ = .15 vs. ∆ = .31, p = .009) increased more in HAPH. D-shaped LV (0 [0%] vs. 30 [93.8%], p = .00001) could be observed only in the HAPH group, and only in those with a sPAP ≥50 mm Hg. LV-EF (∆ = 4.5 vs. ∆ = 6.7%, p = .24) increased in both groups. LV-GLS (∆ = 1.2 vs. ∆ = 1.1 -%, p = .60) increased slightly. RV end-diastolic (∆ = 2.20 vs. ∆ = 2.7 cm2 , p = .36) and end-systolic area (∆ = 2.1 vs. ∆ = 2.7 cm2 , p = .39), as well as RA end-systolic area index (∆ = -.9 vs. ∆ = .3 cm2 /m2 , p = .01) increased, RV-FAC (∆ = -2.9 vs. ∆ = -4.7%, p = .43) decreased, this was more pronounced in HAPH, RV-GLS (∆ = 1.6 vs. ∆ = -.7 -%, p = .17) showed marginal changes.

CONCLUSIONS

LV and LA dimensions decrease and left ventricular function increases at high-altitude in subjects with and without HAPH. RV and RA dimensions increase, and RV longitudinal strain increases or remains unchanged in subjects with HAPH. Changes are negligible in those without HAPH.

Clinical Implications for Exercise at Altitude Among Individuals With Cardiovascular Disease: A Scientific Statement From the American Heart Association

An increasing number of individuals travel to mountainous environments for work and pleasure. However, oxygen availability declines at altitude, and hypoxic environments place unique stressors on the cardiovascular system. These stressors may be exacerbated by exercise at altitude, because exercise increases oxygen demand in an environment that is already relatively oxygen deplete compared with sea‐level conditions. Furthermore, the prevalence of cardiovascular disease, as well as diseases such as hypertension, heart failure, and lung disease, is high among individuals living in the United States. As such, patients who are at risk of or who have established cardiovascular disease may be at an increased risk of adverse events when sojourning to these mountainous locations. However, these risks may be minimized by appropriate pretravel assessments and planning through shared decision‐making between patients and their managing clinicians. This American Heart Association scientific statement provides a concise, yet comprehensive overview of the physiologic responses to exercise in hypoxic locations, as well as important considerations for minimizing the risk of adverse cardiovascular events during mountainous excursions.

Sporttauglichkeitsuntersuchung mit höhen- und tauchmedizinischen Aspekten

Eine Sporttauglichkeitsuntersuchung zur Identifikation von Krankheiten oder Risikofaktoren, die sich durch Sport verschlechtern oder dauerhafte Schäden bzw. einen plötzlichen Herztod verursachen können, ist bei allen sporttreibenden Personen sinnvoll. Basis ist eine sportspezifische Anamnese und Untersuchung sowie die Durchführung eines Ruhe-EKGs mit Auswertung nach standardisierten Kriterien. Bei Leistungssportlern und in höherem Alter sowie beim Vorliegen von Risikofaktoren sollte zusätzlich ein Belastungs-EKG durchgeführt werden. Bei Tauchern steht die Lunge im Fokus, da sie großen physikalischen Belastungen ausgesetzt ist – eine Lungenfunktionsprüfung ist daher obligat. Im Allgemeinen steht bei Bergsteigern und Tauchern die Feststellung eines guten Gesundheitszustandes im Mittelpunkt. Ein Belastungs-EKG kann dabei sinnvoll sein, denn diese Sportarten erfordern häufig ein Mindestmaß an körperlicher Leistungsfähigkeit. Zudem sollten die sportartspezifischen Risiken bekannt sein.

Genetic Predisposition to High-Altitude Pulmonary Edema

Background: Exaggerated pulmonary arterial hypertension (PAH) is a hallmark of high-altitude pulmonary edema (HAPE). The objective of this study was therefore to investigate genetic predisposition to HAPE by analyzing PAH candidate genes in a HAPE-susceptible (HAPE-S) family and in unrelated HAPE-S mountaineers. Materials and Methods: Eight family members and 64 mountaineers were clinically and genetically assessed using a PAH-specific gene panel for 42 genes by next-generation sequencing. Results: Two otherwise healthy family members, who developed re-entry HAPE at 3640 m during childhood, carried a likely pathogenic missense mutation (c.1198T>G p.Cys400Gly) in the Janus Kinase 2 (JAK2) gene. One of them progressed to a mild form of PAH at the age of 23 years. In two of the 64 HAPE-S mountaineers likely pathogenic variants have been detected, one missense mutation in the Cytochrome P1B1 gene, and a deletion in the Histidine-Rich Glycoprotein (HRG) gene. Conclusions: This is the first study identifying an inherited missense mutation of a gene related to PAH in a family with re-entry HAPE showing a progression to borderline PAH in the index patient. Likely pathogenic variants in 3.1% of HAPE-S mountaineers suggest a genetic predisposition in some individuals that might be linked to PAH signaling pathways.

[Acute Mountain Sickness and High-Altitude Cerebral Edema]

Zusammenfassung. Wenn unakklimatisierte Personen zu schnell in grosse Höhen aufsteigen, drohen höhenbedingte Erkrankungen wie akute Bergkrankheit (ABK), Höhenhirnödem (HHÖ) oder Höhenlungenödem (HLÖ). Am häufigsten tritt die ABK auf, die grundsätzlich harmlos und in der Regel selbstlimitierend ist. Relativ selten, aber potenziell lebensbedrohlich sind HHÖ und HLÖ. In diesem Artikel wird auf ABK und HHÖ eingegangen. Ob es sich bei ABK und HHÖ um unterschiedliche Ausprägungen der gleichen Erkrankung handelt, ist noch nicht abschliessend geklärt. Die ABK äussert sich 4 – 8 Stunden nach Aufstieg in Höhen über 2300 m durch die unspezifischen Symptome Kopfschmerzen, Inappetenz, Übelkeit, Schwindel und Schlafstörungen. Ein HHÖ deutet sich bei therapieresistenten Kopfschmerzen oder wiederholtem Erbrechen an. Wenn Bewusstseinstrübungen oder zentralneurologische Symptome wie Ataxie auftreten, liegt ein manifestes HHÖ vor. Die ABK kann mit dem Lake-Louise-Score sehr gut erfasst werden. Beste Prophylaxe aller Höhenerkrankungen sind langsamer Aufstieg und gute Vorakklimatisation. Im Allgemeinen sollte die durchschnittliche Steigerung der Schlafhöhe nicht über 300 – 500 m pro Nacht liegen. Bei hoher Wahrscheinlichkeit für das Auftreten einer ABK kann auch eine medikamentöse Prophylaxe mit Acetazolamid (2 × 125 – 250 mg / Tag) oder Corticosteroiden (Dexamethason 2 – 3 × 4 mg / Tag oder eine Äquivalenzdosis anderer Corticosteroide) erfolgen. Die leichte ABK kann symptomatisch mit gängigen nichtsteroidalen Antirheumatika und / oder Antiemetika behandelt werden, ohne dass ein Abstieg zwingend erforderlich ist. Wenn sich die Symptome dabei verschlechtern, primär eine schwere ABK oder ein HHÖ vorliegt, ist ein sofortiger Abstieg um mindestens 1000 m Therapie der Wahl. Parallel dazu sind Corticosteroide indiziert, initial 4 – 8 mg / Tag, gefolgt von 4 mg alle 6 – 8 Stunden in Abhängigkeit von der Symptomatik.

Exaggerated hypoxic pulmonary vasoconstriction without susceptibility to high altitude pulmonary edema

BACKGROUND

Abnormally high pulmonary artery pressure (PAP) in hypoxia due to exaggerated hypoxic pulmonary vasoconstriction (HPV) is a key factor for development of high-altitude pulmonary edema (HAPE). It was shown that about 10% of a healthy Caucasian population has an exaggerated HPV that is comparable to the response measured in HAPE-susceptible individuals. Therefore, we hypothesized that those with exaggerated HPV are HAPE-susceptible.

METHODS AND RESULTS

We screened 421 healthy Caucasians naïve to high altitude for HPV using Doppler echocardiography for assessment of systolic PAP in normobaric hypoxia (PASPHx; Po2 corresponding to 4500 m). Subjects with exaggerated HPV and matched controls were exposed to 4559 m with an identical protocol that causes HAPE in 62% of HAPE-S. Screening revealed 39 subjects with exaggerated HPV, of whom 33 (PASPHx 51±6 mmHg) ascended within 24 hours to 4559 m. Four (13%) of them developed HAPE during the 48 h-stay. This incidence is significantly lower than the recurrence rate of 62% previously observed in HAPE-S in the same setting. None of the control subjects (PASPHx 33±5 mmHg) developed HAPE.

CONCLUSION

An exaggerated HPV cannot be considered a surrogate maker for HAPE-susceptibility although excessively elevated PAP is a hallmark in HAPE, while a normal HPV appears to protect from HAPE in this study.

Increased hepcidin levels in high-altitude pulmonary edema

Low iron availability enhances hypoxic pulmonary vasoconstriction (HPV). Considering that reduced serum iron is caused by increased erythropoiesis, insufficient reabsorption, or elevated hepcidin levels, one might speculate that exaggerated HPV in high-altitude pulmonary edema (HAPE) is related to low serum iron. To test this notion we measured serum iron and hepcidin in blood samples obtained in previously published studies at low altitude and during 2 days at 4,559 m (HA1, HA2) from controls, individuals with HAPE, and HAPE-susceptible individuals where prophylactic dexamethasone and tadalafil prevented HAPE. As reported, at 4,559 m pulmonary arterial pressure was increased in healthy volunteers but reached higher levels in HAPE. Serum iron levels were reduced in all groups at HA2. Hepcidin levels were reduced in all groups at HA1 and HA2 except in HAPE, where hepcidin was decreased at HA1 but unexpectedly high at HA2. Elevated hepcidin in HAPE correlated with increased IL-6 at HA2, suggesting that an inflammatory response related to HAPE contributes to increased hepcidin. Likewise, platelet-derived growth factor, a regulator of hepcidin, was increased at HA1 and HA2 in controls but not in HAPE, suggesting that hypoxia-controlled factors that regulate serum iron are inappropriately expressed in HAPE. In summary, we found that HAPE is associated with inappropriate expression of hepcidin without inducing expected changes in serum iron within 2 days at HA, likely due to too short time. Although hepcidin expression is uncoupled from serum iron availability and hypoxia in individuals developing HAPE, our findings indicate that serum iron is not related with exaggerated HPV.

Sleeping in moderate hypoxia at home for prevention of acute mountain sickness (AMS): a placebo-controlled, randomized double-blind study

OBJECTIVE

Acclimatization at natural altitude effectively prevents acute mountain sickness (AMS). It is, however, unknown whether prevention of AMS is also possible by only sleeping in normobaric hypoxia.

METHODS

In a placebo-controlled, double-blind study 76 healthy unacclimatized male subjects, aged 18 to 50 years, slept for 14 consecutive nights at either a fractional inspired oxygen (Fio2) of 0.14 to 0.15 (average target altitude 3043 m; treatment group) or 0.209 (control group). Four days later, AMS scores and incidence of AMS were assessed during a 20-hour exposure in normobaric hypoxia at Fio2 = 0.12 (equivalent to 4500 m).

RESULTS

Because of technical problems with the nitrogen generators, target altitude was not achieved in the tents and only 21 of 37 subjects slept at an average altitude considered sufficient for acclimatization (>2200 m; average, 2600 m). Therefore, in a subgroup analysis these subjects were compared with the 21 subjects of the control group with the lowest sleeping altitude. This analysis showed a significantly lower AMS-C score (0.38; 95% CI, 0.21 to 0.54) vs 1.10; 95% CI, 0.57 to 1.62; P = .04) and lower Lake Louise Score (3.1; 95% CI, 2.2 to 4.1 vs 5.1; 95% CI, 3.6 to 6.6; P = .07) for the treatment subgroup. The incidence of AMS defined as an AMS-C score greater than 0.70 was also significantly lower (14% vs 52%; P < .01).

CONCLUSIONS

Sleeping 14 consecutive nights in normobaric hypoxia (equivalent to 2600 m) reduced symptoms and incidence of AMS 4 days later on exposure to 4500 m.

No correlation between plasma levels of vascular endothelial growth factor or its soluble receptor and acute mountain sickness

Increased plasma levels of vascular endothelial growth factor (VEGF) due to lower levels of its soluble receptor (sFlt-1) had been suggested to cause vasogenic brain edema and thereby to cause the symptoms of acute mountain sickness (AMS). We tested this hypothesis after active ascent to high altitude. Plasma was collected from 31 subjects at low altitude (100 m) before (LA1) and after (LA2) 4 weeks of aerobic exercise training in normobaric hypoxia or normoxia, and one night after ascent to high altitude (4559 m). Training modalities (hypoxia or normoxia) did not influence VEGF- and sFlt-1-levels. Therefore, data of both training groups were analyzed together. After one night at 4559 m, 18 subjects had AMS (AMS+), 13 had no AMS (AMS-). In AMS+ and AMS-, VEGF was 110 ± 75 (SD) pg/ml vs. 104 ± 82 (p = 0.74) at LA1, 63 ± 40 vs. 73 ± 50 (p = 0.54) at LA2, and 88 ± 62 vs. 104 ± 81 (p = 0.54) at 4559 m, respectively. Corresponding values for sFlt-1 in AMS+ and AMS- were 81 pg/ml ± 13.1 vs. 82 ± 17 (p = 0.97), 79 ± 11 vs. 80 ± 16 (p = 0.92) and 139 ± 28 vs. 135 ± 31 (p = 0.70), respectively. Absolute values or changes of VEGF were not correlated and those of sFlt-1 slightly correlated with AMS scores. These data provide no evidence for a role of plasma VEGF and sFlt-1 in the pathophysiology of AMS. They do, however, not exclude paracrine effects of VEGF in the brain.

Acute in vitro hypoxia and high-altitude (4,559 m) exposure decreases leukocyte oxygen consumption

Hypoxia impairs metabolic functions by decreasing activity and expression of ATP-consuming processes. To separate hypoxia from systemic effects, we tested whether hypoxia at high altitude affects basal and PMA-stimulated leukocyte metabolism and how this compares to acute (15 min) and 24 h of in vitro hypoxia. Leukocytes were prepared at low altitude and ∼24 h after arrival at 4559 m. Mitochondrial oxygen consumption (JO₂) was measured by respirometry, oxygen radicals by electron spin resonance spectroscopy, both at a Po₂ = 100 mmHg (JO₂,₁₀₀) and 20 mmHg (JO₂,₂₀). Acute hypoxia of leukocytes decreased JO₂ at low altitude. Exposure to high altitude decreased JO₂,₁₀₀, whereas JO₂,₂₀ was not affected. Acute hypoxia of low-altitude samples decreased the activity of complexes I, II, and III. At high altitude, activity of complexes I and III were decreased when measured in normoxia. Stimulation of leukocytes with PMA increased JO₂,₁₀₀ at low (twofold) and high altitude (five-fold). At both locations, PMA-stimulated JO₂ was decreased by acute hypoxia. Basal and PMA-stimulated reactive oxygen species (ROS) production were unchanged at high altitude. Separate in vitro experiments performed at low altitude show that ∼75% of PMA-induced increase in JO₂ was due to increased extra-mitochondrial JO₂ (JO₂(,res); in the presence of rotenone and antimycin A). JO₂(,res) was doubled by PMA. Acute hypoxia decreased basal JO₂(,res) by ∼70% and PMA-stimulated JO₂(,res) by about 50% in cells cultured in normoxia and hypoxia (1.5% O₂; 24 h). Conversely, 24 h in vitro hypoxia decreased mitochondrial JO₂,₁₀₀ and JO₂,₂₀, extra-mitochondrial, basal, and PMA-stimulated JO₂ were not affected. These results show that 24 h of high altitude but not 24 h in vitro hypoxia decreased basal leukocyte metabolism, whereas PMA-induced JO₂ and ROS formation were not affected, indicating that prolonged high-altitude hypoxia impairs mitochondrial metabolism but does not impair respiratory burst. In contrast, acute hypoxia impairs respiratory burst at either altitude.

High-altitude pulmonary hypertension is associated with a free radical-mediated reduction in pulmonary nitric oxide bioavailability

High altitude (HA)-induced pulmonary hypertension may be due to a free radical-mediated reduction in pulmonary nitric oxide (NO) bioavailability. We hypothesised that the increase in pulmonary artery systolic pressure (PASP) at HA would be associated with a net transpulmonary output of free radicals and corresponding loss of bioactive NO metabolites. Twenty-six mountaineers provided central venous and radial arterial samples at low altitude (LA) and following active ascent to 4559 m (HA). PASP was determined by Doppler echocardiography, pulmonary blood flow by inert gas re-breathing, and vasoactive exchange via the Fick principle. Acute mountain sickness (AMS) and high-altitude pulmonary oedema (HAPE) were diagnosed using clinical questionnaires and chest radiography. Electron paramagnetic resonance spectroscopy, ozone-based chemiluminescence and ELISA were employed for plasma detection of the ascorbate free radical (A(·-)), NO metabolites and 3-nitrotyrosine (3-NT). Fourteen subjects were diagnosed with AMS and three of four HAPE-susceptible subjects developed HAPE. Ascent decreased the arterio-central venous concentration difference (a-cv(D)) resulting in a net transpulmonary loss of ascorbate, α-tocopherol and bioactive NO metabolites (P < 0.05 vs. LA). This was accompanied by an increased a-cv(D) and net output of A(·-) and lipid hydroperoxides (P < 0.05 vs. sea level, SL) that correlated against the rise in PASP (r = 0.56-0.62, P < 0.05) and arterial 3-NT (r = 0.48-0.63, P < 0.05) that was more pronounced in HAPE. These findings suggest that increased PASP and vascular resistance observed at HA are associated with a free radical-mediated reduction in pulmonary NO bioavailability.

Training in normobaric hypoxia and its effects on acute mountain sickness after rapid ascent to 4559 m

In a randomized, placebo-controlled, double-blind study, we tested a 4-week program in normobaric hypoxia that is commercially offered for the prevention of acute mountain sickness (AMS). Twenty-two male and 18 female healthy subjects [mean age 33 +/- 7 (SD) years] exercised 70 min, 3 x /week for 3 weeks on a bicycle ergometer at workloads of 60% VO2max either in normoxia (normoxia group, NG) or in normobaric hypoxia (hypoxia group, HG), corresponding to altitudes of 2500, 3000, and 3500 m during weeks 1, 2, and 3, respectively. Four passive exposures of 90 min in normoxia (NG) or hypoxia corresponding to 4500 m (HG) followed in week 4. Five days after the last session, subjects ascended within 24 h from sea level to 4559 m (one overnight stay at 3611 m) and stayed there for 24 h. AMS was defined as LL (Lake Louise score) > or =5 and AMS-C > or =0.70. The AMS incidence (70% in NG vs. 60% in HG, p = 0.74), LL scores (7.1 +/- 4.3 vs. 5.9 +/- 3.4, p = 0.34), and AMS-C scores (1.50 +/- 1.22 vs. 0.93 +/- 0.81, p = 0.25) at the study endpoint were not significantly different between the groups. However, the incidence of AMS at 3611 m (6% vs. 47%, p = 0.01) and the functional LL score at 4559 m were lower in HG. SpO2 at 3611 m, heart rate during ascents, and arterial blood gases at 4559 m were not different between groups. We conclude that the tested program does not reduce the incidence of AMS within a rapid ascent to 4559 m, but our data show that it prevents AMS at lower altitudes. Whether such a program would prevent AMS at higher altitudes, but with slower ascent, remains to be tested.

Exercise reduces airway sodium ion reabsorption in cystic fibrosis but not in exercise asthma

When ventilating large volumes of air during exercise, airway fluid secretion is essential for airway function. Since these are impaired in cystic fibrosis and exercise-induced asthma, it was the aim of this study to determine how exercise affects airway Na(+) and Cl(-) transport and whether changes depend on exercise intensity. Nasal potential was measured in Ringer's solution, with amiloride to block Na(+) transport, and in low chloride-containing isoproterenol to assess Cl(-) channels. Nasal potential was measured at rest and during submaximal and maximal bicycle ergometer exercise in individuals with cystic fibrosis, exercise-induced asthma and controls. At rest, nasal potential was significantly higher in cystic fibroses than in the others. Maximal exercise decreased nasal potentials in cystic fibrosis and controls but not in exercise asthma. Submaximal exercise decreased nasal potentials only in cystic fibrosis. Cl(-) transport was not affected. Our results indicate that nasal potentials and Na(+) transport were decreased by maximal exercise in healthy and cystic fibrosis, whereas submaximal exercise decreased potentials in cystic fibrosis only. Exercise did not affect nasal potentials in asthmatics. Decreased reabsorption during exercise might favour airway fluid secretion during hyperpnoea. This protective effect appears blunted in patients with exercise-induced asthma.

Intermittent hypoxia at rest for improvement of athletic performance

Two modalities of applying hypoxia at rest are reviewed in this paper: intermittent hypoxic exposure (IHE), which consists of hypoxic air for 5-6 min alternating with breathing room air for 4-5 min during sessions lasting 60-90 min, or prolonged hypoxic exposure (PHE) to normobaric or hypobaric hypoxia over up to 3 h/day. Hypoxia with IHE is usually in the range of 12-10%, corresponding to an altitude of about 4000-6000 m. Normobaric or hypobaric hypoxia with PHE corresponds to altitudes of 4000-5500 m. Five of six studies applying IHE and all four well-controlled studies using PHE could not show a significant improvement with these modalities of hypoxic exposure for sea level performance after 14-20 sessions of exposure, with the exception of swimmers in whom there might be a slight improvement by PHE in combination with a subsequent tapering. There is no direct or indirect evidence that IHE or PHE induce any significant physiological changes that might be associated with improving athletic performance at sea level. Therefore, IHE and PHE cannot be recommended for preparation of competitions held at sea level.

Microhemorrhages in nonfatal high-altitude cerebral edema

Vasogenic edema in the corpus callosum is a characteristic finding in high-altitude cerebral edema (HACE). Furthermore, microhemorrhages have been found at autopsies in brains of HACE victims. The objective of this study was to determine if microhemorrhages also occur in nonlethal HACE. Consequently, magnetic resonance imaging (MRI) was performed in patients who had suffered from HACE and in patients who had suffered from severe acute mountain sickness (AMS) by applying imaging techniques highly susceptible to blood or blood remnants. Two experienced neuroradiologists independently evaluated the exams blinded to clinical data. The MRI was performed 2 to 31 months after the event. The MRI of the HACE patients revealed multiple hemosiderin depositions in the brain--predominantly found in the corpus callosum--indicative of microhemorrhages. These changes were not present in the three AMS patients. In summary, hemosiderin deposits detectable by MRI predominantly in the corpus callosum indicate that microhemorrhages occur in nonlethal HACE, which may serve as a novel diagnostic MRI sign for HACE even many months after the event.

Skeletal muscle dysfunction in patients with idiopathic pulmonary arterial hypertension

Dyspnea and exercise limitation are common in patients with idiopathic pulmonary arterial hypertension (IPAH). Recently, a reduction in inspiratory and expiratory muscle strength has been observed in IPAH. However, it has not been investigated whether this respiratory muscle weakness might be part of a general muscle dysfunction as observed in congestive left heart failure. Therefore, in 24 consecutive IPAH patients (16 female; age 58.7+/-16.2; WHO class II-III; systolic pulmonary artery pressure during echocardiography at rest (sPAP) 65.0+/-20.6 mmHg, and 6-min-walk test (6-MWT) 473.6+/-127.7 m), the maximal isometric forearm muscle strength (best of three hand grip manoeuvres), maximal inspiratory and expiratory mouth occlusion pressures (Pimax, Pemax) were prospectively evaluated. The isometric forearm muscle strength was significantly lower in IPAH patients (281.7+/-102.6N) than in matched 24 healthy controls (397.1+/-116.8 N; p=0.03). In IPAH patients, there was a correlation between maximal isometric forearm muscle strength and 6-MWT (r=0.67; p=0.0007) and both, Pimax (r=0.69; p=0.0003) and Pemax (r=0.63; p=0.01), respectively. There was no correlation between forearm muscle strength and sPAP (r=0.30; p=0.16). The present skeletal muscle dysfunction is a novel finding in patients with IPAH. The correlation with respiratory muscle dysfunction and severity of disease might indicate a generalised "myopathy" in IPAH.

Unchanged anaerobic and aerobic performance after short-term intermittent hypoxia

INTRODUCTION

Repeated short-term exposures to a severe degree of hypoxia, alternated with similar intervals of normoxia, are recommended for performance enhancement in sports. However, scientific evidence for the efficiency of this method is controversial with regard to anaerobic performance. Therefore, we conducted a randomized, double-blind, placebo-controlled study to investigate the effects of this new method on both anaerobic and aerobic performance.

METHODS

During 15 consecutive days, 20 endurance-trained men (V O2max (mean +/- SD) 60.2 +/- 6.8 mL x kg(-1) x min(-1)) were exposed each day to breathing (through mouthpieces) either a gas mixture (11% O2 on days 1-7 and 10% O2 on days 8-15; hypoxia group, N = 10) or compressed air (control group, N = 10), six times for 6 min, followed by 4 min of breathing room air for a total of six consecutive cycles. Before and after the treatment, an incremental cycle ergometer test to exhaustion and the Wingate anaerobic test were performed to assess aerobic and anaerobic performance.

RESULTS

Hypoxic treatment did not improve peak power or mean power during the Wingate anaerobic test, nor did it affect maximal oxygen uptake (V O2max), maximal power output (Pmax), lactate threshold or levels of heart rate (HR), minute ventilation (V E), oxygen uptake (V O2), or blood lactate concentration at the submaximal workloads during the ergometer test. Maximal lactate concentration (Lamax) after the tests and HRmax and maximal respiratory exchange ratio (RERmax) during the ergometer test were not significantly different between groups at any time.

CONCLUSION

The results of this study demonstrated that 1 h of intermittent hypoxic exposure for 15 consecutive days has no effect on aerobic or anaerobic performance.

High altitude pulmonary edema: a pressure-induced leak

High altitude pulmonary edema (HAPE) is a non-cardiogenic pulmonary edema that can occur in healthy individuals who ascend rapidly to altitudes above 3000-4000m. Excessive pulmonary artery pressure (PAP) is crucial for the development of HAPE, since lowering pulmonary artery pressure by nifedipine or tadalafil (phosphodiesterase-5-inhibitor) will in most cases prevent HAPE. Recent studies using microspheres in swine and magnetic resonance imaging in humans strongly support the concept and primacy of nonuniform hypoxic arteriolar vasoconstriction to explain how hypoxic pulmonary vasoconstriction occurring predominantly at the arteriolar level can cause leakage. Evidence is accumulating that the excessive PAP response in HAPE-susceptible individuals is due to a reduced NO bioavailability. HAPE-susceptible individuals show an endothelial dysfunction in the systemic circulation in hypoxia. Lower levels of exhaled NO in hypoxia before and during HAPE suggest that this abnormality also occurs in the lungs and polymorphisms of the eNOS gene are associated with susceptibility to HAPE in the Indian and Japanese population.

Magnetic Resonance Imaging of Uneven Pulmonary Perfusion in Hypoxia in Humans

RATIONALE

Inhomogeneous hypoxic pulmonary vasoconstriction causing regional overperfusion and high capillary pressure is postulated for explaining how high pulmonary artery pressure leads to high-altitude pulmonary edema in susceptible (HAPE-S) individuals.

OBJECTIVE

Because different species of animals also show inhomogeneous hypoxic pulmonary vasoconstriction, we hypothesized that inhomogeneity of lung perfusion in general increases in hypoxia, but is more pronounced in HAPE-S. For best temporal and spatial resolution, regional pulmonary perfusion was assessed by dynamic contrast-enhanced magnetic resonance imaging.

METHODS

Dynamic contrast-enhanced magnetic resonance imaging and echocardiography were performed during normoxia and after 2 h of hypoxia (Fi(O2) = 0.12) in 11 HAPE-S individuals and 10 control subjects. As a measure for perfusion inhomogeneity, the coefficient of variation for two perfusion parameters (peak signal intensity, time-to-peak) was determined for the whole lung and isogravitational slices.

RESULTS

There were no differences in perfusion inhomogeneity between the groups in normoxia. In hypoxia, analysis of coefficients of variation indicated a greater inhomogeneity in all subjects, which was more pronounced in HAPE-S compared with control subjects. Discrimination between HAPE-S and control subjects was best in gravity-dependent lung areas. Pulmonary artery pressure during hypoxia increased from 22 +/- 3 to 53 +/- 9 mm Hg in HAPE-S and 24 +/- 4 to 33 +/- 6 mm Hg in control subjects (mean +/- SD; p < 0.001), respectively.

CONCLUSION

This study shows that hypoxic pulmonary vasoconstriction is inhomogeneous in hypoxia in humans, particularly in HAPE-S individuals where it is accompanied by a greater increase in pulmonary artery pressure compared with control subjects. These findings support the hypothesis of exaggerated and uneven hypoxic pulmonary vasoconstriction in HAPE-S individuals.

Both tadalafil and dexamethasone may reduce the incidence of high-altitude pulmonary edema: a randomized trial

BACKGROUND

High-altitude pulmonary edema (HAPE) is caused by exaggerated hypoxic pulmonary vasoconstriction associated with decreased bioavailability of nitric oxide in the lungs and by impaired reabsorption of alveolar fluid.

OBJECTIVE

To investigate whether dexamethasone or tadalafil reduces the incidence of HAPE and acute mountain sickness (AMS) in adults with a history of HAPE.

DESIGN

Randomized, double-blind, placebo-controlled study performed in summer 2003.

SETTING

Ascent from 490 m within 24 hours and stay for 2 nights at 4559 m.

PATIENTS

29 adults with previous HAPE.

INTERVENTION

Prophylactic tadalafil (10 mg), dexamethasone (8 mg), or placebo twice daily during ascent and stay at 4559 m.

MEASUREMENTS

Chest radiography was used to diagnose HAPE. A Lake Louise score greater than 4 defined AMS. Systolic pulmonary artery pressure was measured by using Doppler echocardiography, and nasal potentials were measured as a surrogate marker of alveolar sodium transport.

RESULTS

Two participants who received tadalafil developed severe AMS on arrival at 4559 m and withdrew from the study; they did not have HAPE at that time. High-altitude pulmonary edema developed in 7 of 9 participants receiving placebo and 1 of the remaining 8 participants receiving tadalafil but in none of the 10 participants receiving dexamethasone (P = 0.007 for tadalafil vs. placebo; P < 0.001 for dexamethasone vs. placebo). Eight of 9 participants receiving placebo, 7 of 10 receiving tadalafil, and 3 of 10 receiving dexamethasone had AMS (P = 1.0 for tadalafil vs. placebo; P = 0.020 for dexamethasone vs. placebo). At high altitude, systolic pulmonary artery pressure increased less in participants receiving dexamethasone (16 mm Hg [95% CI, 9 to 23 mm Hg]) and tadalafil (13 mm Hg [CI, 6 to 20 mm Hg]) than in those receiving placebo (28 mm Hg [CI, 20 to 36 mm Hg]) (P = 0.005 for tadalafil vs. placebo; P = 0.012 for dexamethasone vs. placebo). No statistically significant difference between groups was found in change in nasal potentials and expression of leukocyte sodium transport protein messenger RNA.

LIMITATIONS

The study involved a small sample of adults with a history of HAPE.

CONCLUSIONS

Both dexamethasone and tadalafil decrease systolic pulmonary artery pressure and may reduce the incidence of HAPE in adults with a history of HAPE. Dexamethasone prophylaxis may also reduce the incidence of AMS in these adults. ClinicalTrials.gov identifier: NCT00274430.

K+ channel activation with minoxidil stimulates nasal-epithelial ion transport and blunts exaggerated hypoxic pulmonary hypertension

Increased pulmonary capillary pressure and inhibition of alveolar Na+ transport putatively contribute to the formation of pulmonary edema in alveolar hypoxia such as at high altitude. Since both events might be linked to the inhibition of K+ channels, we studied whether in vivo application of minoxidil, a stimulator of ATP-gated K channels (K+ ATP channel activator) prevents both effects. In a double- blind, placebo-controlled crossover study on 17 volunteers with no known susceptibility to high altitude pulmonary edema, we tested whether a single dose of minoxidil (5 mg) prevents pulmonary hypertension and inhibition of nasal-epithelial Na+ transport in normobaric hypoxia (12% O2, 2 h). In hypoxia, arterial SO2 was decreased to about 80%, and systolic pulmonary artery pressure (PAP) measured by Doppler echocardiography increased significantly from approximately 25 mmHg (normoxia) to approximately 38 mmHg (hypoxia; range 22 to 61 mmHg). Minoxidil decreased PAP in hypoxia in those individuals who had the highest increase in PAP in hypoxia when taking placebo. Nasal potentials decreased by about 10% in hypoxia. Although minoxidil had no effect on nasal potentials in normoxia, it increased nasal potentials significantly above normoxic control values after 2-h hypoxia. These results show that the K+ ATP activator minoxidil prevents the decrease in nasal-epithelial potential by hypoxia and seems to blunt an exaggerated increase in PAP in acute hypoxia.

Hypoxia Impairs Systemic Endothelial Function in Individuals Prone to High-Altitude Pulmonary Edema

RATIONALE

High-altitude pulmonary edema (HAPE) is characterized by excessive pulmonary vasoconstriction and is associated with decreased concentrations of nitric oxide (NO) in the lung.

OBJECTIVES

We hypothesized that individuals susceptible to HAPE (HAPE-S) would also have dysfunction of the vascular NO vasodilator pathway during hypoxia in the systemic vasculature.

METHODS

During normoxia (FI(O(2)) = 0.21) and 4 hours of normobaric hypoxia (FI(O(2)) = 0.12, corresponding to an altitude of 4,500 m above sea level) endothelium-dependent and endothelium-independent vasodilator responses to intraarterial infusion of acetylcholine (ACh) and sodium nitroprusside, respectively, were measured by forearm venous occlusion plethysmography in nine HAPE-S subjects and in nine HAPE-resistant control subjects.

MAIN RESULTS

Pulmonary artery systolic pressure increased from 22 +/- 3 to 33 +/- 6 mm Hg (p < 0.001) during hypoxia in control subjects, and from 25 +/- 4 to 50 +/- 9 mm Hg in HAPE-S subjects (p < 0.001). Despite similar responses during normoxia in both groups, ACh-induced changes in forearm blood flow markedly decreased during hypoxia in HAPE-S subjects (p = 0.01) but not in control subjects. The attenuated vascular response to ACh infusion during hypoxia inversely correlated with increased pulmonary artery systolic pressure (p = 0.04) and decreased plasma nitrite correlated with attenuated ACh-induced vasodilation in HAPE-S subjects (p = 0.02).

CONCLUSIONS

Hypoxia markedly impairs vascular endothelial function in the systemic circulation in HAPE-S subjects due to a decreased bioavailability of NO. Impairment of the NO pathway could contribute to the enhanced hypoxic pulmonary vasoconstriction that is central to the pathogenesis of HAPE.

Identification of individuals susceptible to high-altitude pulmonary oedema at low altitude

Individuals susceptible to high-altitude pulmonary oedema (HAPE) are characterised by an abnormal increase of pulmonary artery systolic pressure (PASP) in hypoxia and during normoxic exercise, reduced hypoxic ventilatory response, and smaller lung volume. In 37 mountaineers with well-documented altitude tolerance, it was investigated whether any combination of these noninvasive measurements, including exercise in hypoxia, could improve the identification of HAPE-susceptible subjects at low altitude. HAPE-susceptible subjects showed a significant higher increase of PASP during hypoxia at rest (48+/-10 mmHg) compared with controls (38+/-3 mmHg), as well as during normoxic exercise (57+/-14 versus 38+/-7 mmHg) and hypoxic exercise (69+/-13 versus 49+/-8 mmHg). PASP could not be assessed in three and eight subjects during normoxic or hypoxic exercise, respectively, due to insufficient Doppler profiles or systemic arterial hypertension. Sensitivity (77-94%) and specificity (76-93%) were not significantly different between the various testing conditions. Additional assessment of hypoxic ventilatory response and lung function parameters did not improve identification of HAPE-susceptible subjects in a multivariate analysis. Due to the greater number of missing values in pulmonary artery systolic pressure measurements during hypoxic exercise, it was concluded that pulmonary artery systolic pressure measurements at rest during hypoxia or exercise in normoxia are most feasible for the identification of high-altitude pulmonary oedema-susceptible subjects.

Cytochrome P450 enzyme-mediated drug metabolism at exposure to acute hypoxia (corresponding to an altitude of 4,500�m)

OBJECTIVE

To investigate the effect of acute hypoxia and concomitant changes in portal blood flow on the disposition of drugs mainly metabolized by the cytochrome P(450) enzymes (CYP) 3A4 (verapamil) and CYP1A2 (theophylline).

METHODS

Twenty healthy male participants were studied on two 14-h study days in a normobaric hypoxic chamber and were allocated randomly to one of two groups receiving short infusions of either theophylline (6 mg kg (-1) body weight) or verapamil (5 mg) intravenously. According to a randomized, cross-over design, participants were once exposed to normoxia and once to hypoxia (12% oxygen corresponding to the ambient( P)O(2) at an altitude of 4,500 m above sea level). The concentrations of theophylline, 1,3-dimethyluric acid, verapamil, and norverapamil were determined in serial blood samples by means of liquid chromatography-mass spectrometry (LC/MS/MS). Portal blood flow was assessed by transabdominal duplex ultrasonography.

RESULTS

Acute hypoxia did not alter the pharmacokinetics of theophylline [half-life+/-SD: 9.29+/-1.77 versus 9.39+/-1.40 (hypoxia)], 1,3-dimethyluric acid (12.9+/-4.72 versus 15.1+/-8.59), verapamil (2.00+/-0.98 versus 1.79+/-0.58), or norverapamil (7.98+/-2.94 versus 9.91+/-6.40). Individual changes of elimination half-life and changes in capillary oxygen saturation,( P)O(2), or portal vein flow were not correlated. Portal vein flow was unaffected by hypoxia.

CONCLUSIONS

Acute hypoxia corresponding to hypoxia at altitudes of 4,500 m does not impair the metabolism mediated by CYP1A2 or CYP3A4. At rapid ascent to and short-term stay at altitudes up to 4,500 m, the doses of drugs metabolized by these CYPs do therefore not require dose modification, and major changes in the disposition of already administered drugs are not to be expected.

No association between high-altitude tolerance and the ACE I/D gene polymorphism

PURPOSE

The absence (deletion allele [D]) of a 287 base-pair fragment in the ACE gene is associated with higher ACE tissue activity than its presence (insertion allele [I]) and, as such, may enhance vasoconstriction and fluid retention through increased levels of angiotensin II and aldosterone. Because fluid retention is found in acute mountain sickness (AMS) and exaggerated pulmonary hypertension is essential in the pathophysiology of high-altitude pulmonary edema (HAPE), we hypothesized that the DD genotype is associated with increased susceptibility to these illnesses.

METHODS

ACE genotype was thus determined in 83 mountaineers staying over night at 4559 m and related to AMS symptoms. Genotype was similarly determined in 76 mountaineers who had participated in previous studies at 4559 m; 38 of the latter group had a history of HAPE, and 25 had developed HAPE again during these studies.

RESULTS

The allele frequency was in Hardy-Weinberg equilibrium in both investigations. Neither the history nor the observed episodes of HAPE nor the prevalence of AMS defined as an AMS-C score >/= 0.70 (environmental symptom questionnaire) in the first study or in both studies taken together were significantly different between the genotypes DD, ID, and II.

CONCLUSION

We conclude that I/D-ACE gene polymorphism has no important effect on susceptibility to AMS or HAPE.

Erythropoiesis and performance after two weeks of living high and training low in well trained triathletes

The purpose of our study was to evaluate hematologic acclimatization during 2 weeks of intensive normoxic training with regeneration at moderate altitude (living high-training low, LHTL) and its effects on sea-level performance in well trained athletes compared to another group of equally trained athletes under control conditions (living low - training low, CONTROL). Twenty-one triathletes were ascribed either to LHTL (n = 11; age: 23.0 +/- 4.3 yrs; VO 2 max: 62.5 +/- 9.7 [ml x min -1 x kg -1]) living at 1956 m of altitude or to CONTROL (n = 10; age: 18.7 +/- 5.6 yrs; VO 2 max: 60.5 +/- 6.7 ml x min -1 x kg -1) living at 800 m. Both groups performed an equal training schedule at 800 m. VO 2 max, endurance performance, erythropoietin in serum, hemoglobin mass (Hb tot, CO-rebreathing method) and hematological quantities were measured. A tendency to improved performance in LHTL after the camp was not significant (p < 0.07). Erythropoietin concentration increased temporarily in LHTL (Delta 14.3 +/- 8.7 mU x ml -1; p < 0.012). Hb tot remained unchanged in LHTL whereas was slightly decreased from 12.5 +/- 1.3 to 11.9 +/- 1.3g x kg -1 in CONTROL (p < 0.01). As the reticulocyte number tended to higher values in LHTL than in CONTROL, it seems that a moderate stimulation of erythropoiesis during regeneration at altitude served as a compensation for an exercise-induced destruction of red cells.

Assessment of high altitude tolerance in healthy individuals

The most reliable prediction of high altitude tolerance can be derived from the clinical history of previous comparable exposures. Unfortunately, there are no reliable tests for prediction prior to first-time ascents. Although susceptibility to AMS is usually associated with a low hypoxic ventilatory response (HVR), there is too much overlap with the range of normal values, which precludes measuring HVR or O(2) saturation during brief hypoxia for reliable identification of susceptibility to AMS. A low HVR and an exaggerated rise in pulmonary artery pressure with (prolonged) hypoxia, or exercise in normoxia, are markers of susceptibility to high altitude pulmonary edema (HAPE). These tests can not be recommended for routinely determining high altitude tolerance because the prevalence of susceptibility to HAPE is low and because specificity and sensitivity of these tests are not sufficiently established. On the other hand, HAPE may be avoided in susceptible individuals by ascent rates of 300 m per day above an altitude of 2000 m. Since prediction of risk of mountain sickness is difficult, it is important during the physician consultation prior to ascent to consider the altitude profile, the type of ascent, the performance capacity, the history of previous exposures, and the medical infrastructure of the area.

Effect of exercise intensity on the changes in alveolar slopes of carbon dioxide and oxygen expiratory profiles in humans

The slope of the expired alveolar partial pressure of carbon dioxide profile increases during exercise. Its relationship to metabolic rate, however, remains to be determined at high exercise intensities. We therefore determined the slope of alveolar partial pressures of carbon dioxide and oxygen (PACO2, PAO2, respectively) during incremental cycle ergometer exercise (an increment of 40 W each minute) to exhaustion in 11 normal subjects. The PACO2 and PAO2 increased as linear functions of carbon dioxide production and oxygen uptake (VO2), respectively, up to the estimated lactate threshold (thetaLa-). At higher intensities PACO2 increased disproportionately but PAO2 continued to increase at the same rate in 7 subjects but increased more rapidly in the remainder. The rate of change in PACO2 per unit rate of change in VO2 averaged 3.15 (SD 1.05) (mmHg.s(-1)). (l.min(-1))-1 while the rate of change in PAO2 per unit rate of change in VO2 averaged -3.53 (SD 0.79) (mmHg.s(-1)) (l.min(-1))-1 over this range. The more rapid increase in PACO2 above thetaLa- was consistent with an accelerated CO2 exchange, whereas the more rapid rate of change in PAO2 in 3 of the subjects may have reflected the development of an increased distribution of the ventilation perfusion ratio in addition to the effects of hyperventilation.

Effect of "living high-training low" on the cardiac functions at sea level

Living high-training low (LHTL), living at high altitude and training at sea level, is reported to be beneficial in enhancing physical performance. Effect of LHTL on cardiac function which is one of major determinants in performance, however, was not examined. To address this issue, 21 well-trained triathletes divided into control (n = 10, living and training at sea level) and LHTL group (living at 1980 m altitude > or = 12 hrs/day and training at sea level) were Doppler echocardiographically examined before and at the end of the two-week program. Heart rate and blood pressure did not change in both groups. At end of the training, left ventricular endsystolic diameter of LHTL group was smaller than that of controls (32 vs 34 mm, P < 0.05). Shortening fraction and ejection fraction in LHTL group increased by 9% and 17 %, respectively, P < 0.05. Preejection period/ejection time was more greatly reduced in LHTL group (P < 0.05). Stroke volume and cardiac output in LHTL increased. Diastolic function was not significantly affected by LHTL. These results suggest that LHTL produced an improvement of systolic function underlined by incremented left ventricular contractility, which might be associated with increased beta-adrenergic receptor or an improved myocardial energy utilization.