The effect of 18 h of simulated high altitude on left ventricular function

Preconditioning with Ginsenoside Rg3 mitigates cardiac injury induced by high-altitude hypobaric hypoxia exposure in mice by suppressing ferroptosis through inhibition of the RhoA/ROCK signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Ginseng has historically been utilized as a conventional herbal remedy and dietary supplement to enhance physical stamina and alleviate fatigue. The primary active component of Ginseng, Ginsenoside Rg3 (GS-Rg3), possesses diverse pharmacological properties including immune modulation and anti-inflammatory effects. Furthermore, GS-Rg3 has demonstrated efficacy in mitigating tissue and organ damage associated with metabolic disorders such as hypertension, hyperglycemia, and hyperlipidemia. Nevertheless, its potential impact on high-altitude cardiac injury (HACI) remains insufficiently explored.

AIM OF THE STUDY

The aim of this study was to examine the potential cardioprotective effects of Ginsenoside Rg3, and to investigate how Ginsenoside Rg3 preconditioning can enhance high-altitude cardiac injury by inhibiting the RhoA/ROCK pathway and ferroptosis in cardiac tissue. The findings of this study may contribute to the development of novel therapeutic strategies using traditional Chinese medicine for high-altitude cardiac injury, based on experimental evidence.

MATERIALS AND METHODS

A hypobaric hypoxia chamber was employed to simulate hypobaric hypoxia conditions equivalent to an altitude of 6000 m. Through a randomization process, groups of six male mice were assigned to receive either saline, Ginsenoside Rg3 at doses of 15 mg/kg or 30 mg/kg, or lysophosphatidic acid (LPA) at 1 mg/kg. The impact of Ginsenoside Rg3 on high altitude-induced arrhythmias was evaluated using electrocardiography. Cardiac pathology sections stained with hematoxylin and eosin were evaluated for damage, with the extent of cardiomyocyte damage observed via transmission electron microscopy. The impact of Ginsenoside Rg3 on high-altitude cardiac injury was investigated through analysis of serum biomarkers for cardiac injury (CK-MB, BNP), inflammatory cytokines (TNF, IL-6, IL-1β), reactive oxygen species (ROS) and glutathione (GSH). The expression levels of hypoxia and hypoxia-related proteins in myocardial tissues from each experimental group were assessed using Western blot analysis. Following a review of the existing literature, the traditional regulatory mechanisms of ferroptosis were examined. Immunofluorescence staining of cardiac tissues and Western blotting techniques were utilized to investigate the impact of Ginsenoside Rg3 on cardiomyocyte ferroptosis through the RhoA/ROCK signaling pathway under conditions of hypobaric hypoxia exposure.

RESULTS

Pre-treatment with Ginsenoside Rg3 improved high altitude-induced arrhythmias, reduced cardiomyocyte damage, decreased cardiac injury biomarkers and inflammatory cytokines, and lowered the expression of hypoxia-related proteins in myocardial tissues. Both Western blotting and immunofluorescence staining of cardiac tissues demonstrated that exposure to high-altitude hypobaric hypoxia results in elevated expression of ferroptosis and proteins related to the RhoA/ROCK pathway. Experimental validation corroborated that the role of the RhoA/ROCK signaling pathway in mediating ferroptosis.

CONCLUSIONS

The findings of our study suggest that preconditioning with Ginsenoside Rg3 may attenuate cardiac injury caused by high-altitude hypobaric hypoxia exposure in mice by inhibiting ferroptosis through the suppression of the RhoA/ROCK signaling pathway. These findings contribute to the current knowledge of Ginsenoside Rg3 and high-altitude cardiac injury, suggesting that Ginsenoside Rg3 shows potential as a therapeutic agent for high-altitude cardiac injury.

Extreme altitude induces divergent mass reduction of right and left ventricle in mountain climbers

Mountain climbing at high altitude implies exposure to low levels of oxygen, low temperature, wind, physical and psychological stress, and nutritional insufficiencies. We examined whether right ventricular (RV) and left ventricular (LV) myocardial masses were reversibly altered by exposure to extreme altitude. Magnetic resonance imaging and echocardiography of the heart, dual x‐ray absorptiometry scan of body composition, and blood samples were obtained from ten mountain climbers before departure to Mount Everest or Dhaulagiri (baseline), 13.5 ± 1.5 days after peaking the mountain (post‐hypoxia), and six weeks and six months after expeditions exceeding 8000 meters above sea level. RV mass was unaltered after extreme altitude, in contrast to a reduction in LV mass by 11.8 ± 3.4 g post‐hypoxia (p = 0.001). The reduction in LV mass correlated with a reduction in skeletal muscle mass. After six weeks, LV myocardial mass was restored to baseline values. Extreme altitude induced a reduction in LV end‐diastolic volume (20.8 ± 7.7 ml, p = 0.011) and reduced E’, indicating diastolic dysfunction, which were restored after six weeks follow‐up. Elevated circulating interleukin‐18 after extreme altitude compared to follow‐up levels, might have contributed to reduced muscle mass and diastolic dysfunction. In conclusion, the mass of the RV, possibly exposed to elevated afterload, was not changed after extreme altitude, whereas LV mass was reduced. The reduction in LV mass correlated with reduced skeletal muscle mass, indicating a common denominator, and elevated circulating interleukin‐18 might be a mechanism for reduced muscle mass after extreme altitude.

Low Stroke Volume Index in Healthy Young Men Is Associated with the Incidence of Acute Mountain Sickness after an Ascent by Airplane: A Case-Control Study

Background

The aims of this study were to explore the characteristics of left ventricular (LV) functional changes in subjects with or without acute mountain sickness (AMS) and their associations with AMS incidence.

Methods

A total of 589 healthy men were enrolled and took a trip from Chengdu (500 m, above sea level (asl)) to Lhasa (3700 m, asl) by airplane. Basic characteristics, physiological data, and echocardiographic parameters were collected both at Chengdu and Lhasa, respectively. AMS was identified by the Lake Louise Questionnaire Score.

Results

The oxygen saturation (SpO₂), end-systolic volume index, end-diastolic volume index (EDVi), stroke volume index (SVi), E-wave velocity, and E/A ratio were decreased, whereas the heart rate (HR), ejection fraction, cardiac index (CI), and A-wave velocity were increased at the third day after arrival, as evaluated by an oximeter and echocardiography. However, AMS patients showed higher HR and lower EDVi, SVi, CI, E-wave velocity, and E/A ratio than AMS-free subjects. Among them, SVi, which is mainly correlated with the changes of EDVi and altered LV filling pattern, was the most valuable factor associated with AMS incidence following receiver-operator characteristic curves and linear and Poisson regression. Compared with subjects in the highest SVi tertile, subjects in the middle SVi tertile showed higher multivariable Incidence Rate Ratios (IRR) for AMS with higher incidences of mild headache and gastrointestinal symptoms, whereas subjects in the lowest SVi tertile showed even higher multivariable IRR with higher incidences of all the symptoms.

Conclusions

This relatively large-scale case-control study revealed that the reduction of SVi correlated with the altered LV filling pattern was associated with the incidence and clinical severity of AMS.

Impairment of left atrial mechanics does not contribute to the reduction in stroke volume after active ascent to 4559 m

Hypoxia challenges left ventricular (LV) function due to reduced energy supply. Conflicting results exist whether high‐altitude exposure impairs LV diastolic function and thus contributes to the high altitude‐induced increase in systolic pulmonary artery pressure (sPAP) and reduction in stroke volume (SV). This study aimed to assess LV diastolic function, LV end‐diastolic pressure (LVEDP), and LA mechanics using comprehensive echocardiographic imaging in healthy volunteers at 4559 m. Fifty subjects performed rapid (<20 hours) and active ascent from 1130 m to 4559 m (high). All participants underwent echocardiography during baseline examination at 424 m (low) as well as 7, 20 and 44 hours after arrival at high altitude. Heart rate (HR), sPAP, and comprehensive volumetric‐ and Doppler‐ as well as speckle tracking‐derived LA strain parameters were obtained to assess LV diastolic function, LA mechanics, and LVEDP in a multiparametric approach. Data for final analyses were available in 46 subjects. HR (low: 64 ± 11 vs high: 79 ± 14 beats/min, P < 0.001) and sPAP (low: 24.4 ± 3.8 vs high: 38.5 ± 8.2 mm Hg, P < 0.001) increased following ascent and remained elevated at high altitude. Stroke volume (low: 64.5 ± 15.0 vs high: 58.1 ± 16.4 mL, P < 0.001) and EDV decreased following ascent and remained decreased at high altitude due to decreased LV passive filling volume, whereas LA mechanics were preserved. There was no case of LV diastolic dysfunction or increased LVEDP estimates. In summary, this study shows that rapid and active ascent of healthy individuals to 4559 m impairs passive filling and SV of the LV. These alterations were not related to changes in LV and LA mechanics.

Physiological Changes to the Cardiovascular System at High Altitude and Its Effects on Cardiovascular Disease

Riley, Callum James, and Matthew Gavin. Physiological changes to the cardiovascular system at high altitude and its effects on cardiovascular disease. High Alt Med Biol. 18:102-113, 2017.-The physiological changes to the cardiovascular system in response to the high altitude environment are well understood. More recently, we have begun to understand how these changes may affect and cause detriment to cardiovascular disease. In addition to this, the increasing availability of altitude simulation has dramatically improved our understanding of the physiology of high altitude. This has allowed further study on the effect of altitude in those with cardiovascular disease in a safe and controlled environment as well as in healthy individuals. Using a thorough PubMed search, this review aims to integrate recent advances in cardiovascular physiology at altitude with previous understanding, as well as its potential implications on cardiovascular disease. Altogether, it was found that the changes at altitude to cardiovascular physiology are profound enough to have a noteworthy effect on many forms of cardiovascular disease. While often asymptomatic, there is some risk in high altitude exposure for individuals with certain cardiovascular diseases. Although controlled research in patients with cardiovascular disease was largely lacking, meaning firm conclusions cannot be drawn, these risks should be a consideration to both the individual and their physician.

The altitude at which a calf is born and raised influences the rate at which mean pulmonary arterial pressure increases with age

Right heart failure secondary to pulmonary hypertension is a leading cause of mortality among suckling beef calves in the Rocky Mountain region. The objective of this study was to track changes in pulmonary arterial pressures (PAP) in healthy calves born and raised at altitudes ranging from 1,470 to 2,730 m. It was hypothesized that calves located at higher altitudes would show a greater increase in mean PAP (mPAP) with age than would be experienced by calves located at lower altitudes. The rationale is that high altitude hypobaric hypoxia causes a greater rate of vascular remodeling and, consequently, greater resistance to blood flow than calves located at lower altitudes. A prospective study was conducted on 5 cohorts of suckling calves from 4 herds located at altitudes of 1,470, 2,010, 2,170, and 2,730 m. In total, 470 PAP measurements were obtained from 258 calves. As hypothesized, calves located at altitudes ≥2,170 m showed a significant increase in mPAP with age ( ≤ 0.002) whereas calves at 1,470 m did not ( = 0.16). Except for calves at 2,170 m ( < 0.001), systolic PAP did not increase with age ( ≥ 0.16). Diastolic PAP increased with age at altitudes ≥ 2,170 m ( ≤ 0.09) but did not change in calves at 1,470 m ( = 0.20). In summary, mPAP and the rate at which mPAP increases with age are positively associated with the altitude at which calves are born and raised.

Oral Coenzyme Q10 supplementation does not prevent cardiac alterations during a high altitude trek to everest base cAMP

Exposure to high altitude is associated with sustained, but reversible, changes in cardiac mass, diastolic function, and high-energy phosphate metabolism. Whilst the underlying mechanisms remain elusive, tissue hypoxia increases generation of reactive oxygen species (ROS), which can stabilize hypoxia-inducible factor (HIF) transcription factors, bringing about transcriptional changes that suppress oxidative phosphorylation and activate autophagy. We therefore investigated whether oral supplementation with an antioxidant, Coenzyme Q10, prevented the cardiac perturbations associated with altitude exposure. Twenty-three volunteers (10 male, 13 female, 46±3 years) were recruited from the 2009 Caudwell Xtreme Everest Research Treks and studied before, and within 48 h of return from, a 17-day trek to Everest Base Camp, with subjects receiving either no intervention (controls) or 300 mg Coenzyme Q10 per day throughout altitude exposure. Cardiac magnetic resonance imaging and echocardiography were used to assess cardiac morphology and function. Following altitude exposure, body mass fell by 3 kg in all subjects (p<0.001), associated with a loss of body fat and a fall in BMI. Post-trek, left ventricular mass had decreased by 11% in controls (p<0.05) and by 16% in Coenzyme Q10-treated subjects (p<0.001), whereas mitral inflow E/A had decreased by 18% in controls (p<0.05) and by 21% in Coenzyme Q10-treated subjects (p<0.05). Coenzyme Q10 supplementation did not, therefore, prevent the loss of left ventricular mass or change in diastolic function that occurred following a trek to Everest Base Camp.

Effects of hypobaric hypoxia exposure at high altitude on left ventricular twist in healthy subjects: data from HIGHCARE study on Mount Everest

AIMS

Previous studies investigating the effect of hypoxia on left ventricle focused on its global function, an approach that may not detect a selective dysfunction of subendocardial layers that are most sensitive to an inadequate oxygen supply. In the HIGHCARE study, aimed at exploring the effects of high altitude hypoxia on multiple biological variables and their modulation by an angiotensin receptor blocker, we addressed the effects of hypobaric hypoxia on both systolic and diastolic left ventricular geometry and function, focusing on echocardiographic assessment of left ventricle twist to indirectly examine subendocardial left ventricular systolic function.

METHODS AND RESULTS

In 39 healthy subjects, physiological and echocardiographic variables, including left ventricular twist and a simplified torsion-to-shortening ratio (sTSR), were recorded at sea level, at 3400 m, and at 5400 m altitude (Mount Everest base camp). Both left ventricular twist and sTSR were greater at 5400 m than at sea level (12.6° vs. 9.6° and 0.285 vs. 0.202, P < 0.05 for both), were linearly related to the reduction in arterial oxygen partial pressure (P < 0.01 for both), and were associated with significant changes in LV dimensions and contractility. No effects of angiotensin receptor blockade were observed on these variables throughout the study.

CONCLUSION

Our study, for the first time, demonstrates an increase in left ventricular twist at high altitude in healthy subjects exposed to high altitude hypoxia, suggesting the occurrence of subendocardial systolic dysfunction in such condition.

Left ventricular function during acute high-altitude exposure in a large group of healthy young Chinese men

OBJECTIVE

The purpose of this study was to observe left ventricular function during acute high-altitude exposure in a large group of healthy young males.

METHODS

A prospective trial was conducted in Szechwan and Tibet from June to August, 2012. By Doppler echocardiography, left ventricular function was examined in 139 healthy young Chinese men at sea level; within 24 hours after arrival in Lhasa, Tibet, at 3700 m; and on day 7 following an ascent to Yangbajing at 4400 m after 7 days of acclimatization at 3700 m. The resting oxygen saturation (SaO2), heart rate (HR) and blood pressure (BP) were also measured at the above mentioned three time points.

RESULTS

Within 24 hours of arrival at 3700 m, the HR, ejection fraction (EF), fractional shortening (FS), stroke volume (SV), cardiac output (CO), and left ventricular (LV) Tei index were significantly increased, but the LV end-systolic dimension (ESD), end-systolic volume (ESV), SaO2, E/A ratio, and ejection time (ET) were significantly decreased compared to the baseline levels in all subjects. On day 7 at 4400 m, the SV and CO were significantly decreased; the EF and FS Tei were not decreased compared with the values at 3700 m; the HR was further elevated; and the SaO2, ESV, ESD, and ET were further reduced. Additionally, the E/A ratio was significantly increased on day 7 but was still lower than it was at low altitude.

CONCLUSION

Upon acute high-altitude exposure, left ventricular systolic function was elevated with increased stroke volume, but diastolic function was decreased in healthy young males. With higher altitude exposure and prolonged acclimatization, the left ventricular systolic function was preserved with reduced stroke volume and improved diastolic function.

Left ventricular adaptation to acute hypoxia: a speckle-tracking echocardiography study

BACKGROUND

Hypoxia depresses myocardial contractility in vitro but does not affect or may even improve indices of myocardial performance in vivo, possibly through associated changes in autonomic nervous system tone. The aim of this study was to explore the effects of hypoxic breathing on speckle-tracking echocardiographic indices of left ventricular function, with and without β1-adrenergic inhibition.

METHODS

Speckle-tracking echocardiography was performed in 21 healthy volunteers in normoxia and after 30 min of hypoxic breathing (fraction of inspired oxygen, 0.12). Measurements were also obtained after the administration of atropine in normoxia (n = 21) and after bisoprolol intake in normoxia (n = 6) and in hypoxia (n = 10).

RESULTS

Hypoxia increased heart rate (from 68 ± 11 to 74 ± 9 beats/min, P = .001), without changing mean blood pressure (P = NS), and decreased total peripheral resistance (P = .003). Myocardial deformation magnitude increased (circumferential strain, -19.6 ± 1.9% vs -21.2 ± 2.5%; radial strain, 19.2 ± 3.7% vs 22.6 ± 4.1%, P < .05; longitudinal and circumferential strain rate, -0.88 ± 0.11 vs -0.99 ± 0.15 sec(-1) and -1.03 ± 0.16 vs -1.18 ± 0.18 sec(-1), respectively, P < .05 for both; peak twist, 8.98 ± 3.2° vs 11.1 ± 2.9°, P < .05). Except for peak twist, these deformation parameters were correlated with total peripheral resistance (P < .05). Atropine increased only longitudinal strain rate magnitude (-0.88 ± 0.11 vs -0.97 ± 0.14 sec(-1), P < .05). The increased magnitude of myocardial deformation persisted in hypoxia under bisoprolol (P < .05). In normoxia, bisoprolol decreased heart rate (73 ± 10 vs 54 ± 7 beats/min, P = .0005), mean blood pressure (88 ± 7 vs 81 ± 4 mm Hg, P = .0027), without altering deformation.

CONCLUSIONS

Hypoxic breathing increases left ventricular deformation magnitude in normal subjects, and this effect may not be attributed to hypoxia-induced tachycardia or β1-adrenergic pathway changes but to hypoxia-induced systemic vasodilation.

Dynasore protects mitochondria and improves cardiac lusitropy in Langendorff perfused mouse heart

Background

Heart failure due to diastolic dysfunction exacts a major economic, morbidity and mortality burden in the United States. Therapeutic agents to improve diastolic dysfunction are limited. It was recently found that Dynamin related protein 1 (Drp1) mediates mitochondrial fission during ischemia/reperfusion (I/R) injury, whereas inhibition of Drp1 decreases myocardial infarct size. We hypothesized that Dynasore, a small noncompetitive dynamin GTPase inhibitor, could have beneficial effects on cardiac physiology during I/R injury.

Methods and Results

In Langendorff perfused mouse hearts subjected to I/R (30 minutes of global ischemia followed by 1 hour of reperfusion), pretreatment with 1 µM Dynasore prevented I/R induced elevation of left ventricular end diastolic pressure (LVEDP), indicating a significant and specific lusitropic effect. Dynasore also decreased cardiac troponin I efflux during reperfusion and reduced infarct size. In cultured adult mouse cardiomyocytes subjected to oxidative stress, Dynasore increased cardiomyocyte survival and viability identified by trypan blue exclusion assay and reduced cellular Adenosine triphosphate(ATP) depletion. Moreover, in cultured cells, Dynasore pretreatment protected mitochondrial fragmentation induced by oxidative stress.

Conclusion

Dynasore protects cardiac lusitropy and limits cell damage through a mechanism that maintains mitochondrial morphology and intracellular ATP in stressed cells. Mitochondrial protection through an agent such as Dynasore can have clinical benefit by positively influencing the energetics of diastolic dysfunction.

Severe acute mountain sickness, brain natriuretic peptide and NT-proBNP in humans

AIM

To examine the response of brain natriuretic peptide (BNP) and NT-proBNP to high altitude (HA) both at rest and following exercise.

METHODS

We measured NT-proBNP and BNP and Lake Louise (LL) acute mountain sickness (AMS) scores in 20 subjects at rest in Kathmandu (Kat; 1300 m), following exercise and at rest at 4270 and 5150 m.

RESULTS

BNP and NT-proBNP (pg ml(-1) , mean ± SEM) rose significantly from Kat (9.2 ± 2 and 36.9 ± 6.6, respectively) to arrival at 4270 m after exercise (16.6 ± 4 and 152 ± 56.1, P=0.008 and P<0.001, respectively) and remained elevated the next morning at rest (28.9 ± 9 and 207.4 ± 65.1, P = 0.004 and P<0.001 respectively). At 5150, immediately following ascent/descent to 5643 m, BNP and NT-proBNP were 32.3 ± 8.8 and 301.1 ± 96.3 (P=0.003 and P<0.001 vs. Kat, respectively) and at rest the following morning were 33.3 ± 9.7 and 258.9 ± 89.5 (P=0.008 and P=0.001 vs. Kat respectively). NT-proBNP and BNP correlated strongly at 5150 m (ρ 0.905, P<0.001 and ρ 0.914, P<0.001 for resting and post-exercise samples respectively). At 5150 m, BNP levels were significantly higher among the four subjects with severe (LL score>6) AMS (58.4 ± 18.7) compared with those without (BNP 22.7 ± 8.6, P=0.048). There were significant correlations between change in body water from baseline to 5150 m with both BNP and NT-proBNP (ρ 0.77, P=0.001, ρ 0.745, P=0.002 respectively).

CONCLUSION

In conclusion, these data suggest that BNP and NT-proBNP increase with ascent to HA both after exercise and at rest. We also report the novel finding that BNP is significantly greater in those with severe AMS at 5150 m.

Normobaric hypoxia impairs human cardiac energetics

Hypoxia causes left ventricular dysfunction in the human heart, but the biochemical mechanism is poorly understood. Here, we tested whether short-term normobaric hypoxia leads to changes in cardiac energetics and early cardiac dysfunction. Healthy male volunteers (n=12, age 24 ± 2 yr) were exposed to normobaric hypoxia in a purpose-built hypoxic chamber. The partial pressure of oxygen during end-tidal expiration (P(ET)o₂) was kept between 50 and 60 mmHg, and peripheral oxygen saturation (Sao₂) was kept above 80%. Cardiac morphology and function were assessed using magnetic resonance imaging and echocardiography, both before and after 20 h of hypoxic exposure, and high-energy phosphate metabolism [measured as the phosphocreatine (PCr)/ATP ratio] was measured using ³¹P magnetic resonance spectroscopy. During hypoxia, P(ET)o₂ and Sao₂ averaged 55 ± 1 mmHg and 83.6 ± 0.4%, respectively. Hypoxia caused a 15% reduction in cardiac PCr/ATP (from 2.0 ± 0.1 to 1.7 ± 0.1, P<0.01) and reduced diastolic function (measured as E/E', rising from 6.1 ± 0.4 to 7.5 ± 0.7, P<0.01). Normobaric hypoxia causes a rapid decrease in high-energy phosphate metabolism in the human cardiac left ventricle, which may lead to a decline in diastolic function. These findings are important in understanding the response of normal individuals to environmental hypoxia, and to situations in which disease reduces cardiac oxygen delivery.

Pulmonary capillary recruitment in response to hypoxia in healthy humans: a possible role for hypoxic pulmonary venoconstriction?

We examined mechanisms by which hypoxia may elicit pulmonary capillary recruitment in humans. On separate occasions, twenty-five healthy adults underwent exposure to intravenous saline infusion (30 ml/kg ∼ 15 min) or 17-h normobaric hypoxia ( [FIO2 = 12.5%). Cardiac output (Q) and pulmonary capillary blood volume (Vc) were measured before and after saline infusion and hypoxic-exposure by a rebreathing method. Pulmonary artery systolic pressure (sPpa) and left ventricular (LV) diastolic function were assessed before and after hypoxic-exposure via echocardiography. Saline infusion increased Q and Vc (P < 0.05) with no change in Vc/Q (P = 0.97). Hypoxic-exposure increased Vc (P < 0.01) despite no change in Q (P = 0.25), increased sPpa (P < 0.01), and impaired LV relaxation. Multiple regression suggested that ∼ 37% of the hypoxia-mediated increase in Vc was attributable to alterations in Q, sPpa and LV diastolic function. In conclusion, hypoxia-induced pulmonary capillary recruitment in humans is only partly accounted for by changes in Q, sPpa and LV diastolic function. We speculate that hypoxic pulmonary venoconstriction may play a role in such recruitment.

Cardiac response to hypobaric hypoxia: persistent changes in cardiac mass, function, and energy metabolism after a trek to Mt. Everest Base Camp

We postulated that changes in cardiac high-energy phosphate metabolism may underlie the myocardial dysfunction caused by hypobaric hypoxia. Healthy volunteers (n=14) were studied immediately before, and within 4 d of return from, a 17-d trek to Mt. Everest Base Camp (5300 m). (31)P magnetic resonance (MR) spectroscopy was used to measure cardiac phosphocreatine (PCr)/ATP, and MR imaging and echocardiography were used to assess cardiac volumes, mass, and function. Immediately after returning from Mt. Everest, total body weight had fallen by 3% (P<0.05), but left ventricular mass, adjusted for changes in body surface area, had disproportionately decreased by 11% (P<0.05). Alterations in diastolic function were also observed, with a reduction in peak left ventricular filling rates and mitral inflow E/A, by 17% (P<0.05) and 24% (P<0.01), respectively, with no change in hydration status. Compared with pretrek, cardiac PCr/ATP ratio had decreased by 18% (P<0.01). Whether the abnormalities were even greater at altitude is unknown, but all had returned to pretrek levels after 6 mo. The alterations in cardiac morphology, function, and energetics are similar to findings in patients with chronic hypoxia. Thus, a decrease in cardiac PCr/ATP may be a universal response to periods of sustained low oxygen availability, underlying hypoxia-induced cardiac dysfunction in healthy human heart and in patients with cardiopulmonary diseases.

Evaluating the safety of high-altitude travel in patients with adult congenital heart disease

As medical management and surgical techniques continue to improve, patients with congenital heart disease are surviving further into adulthood and seeking to participate in multiple activities. Given the increasing popularity of adventure recreation, it is likely that many of these individuals will express interest in travel to and activities at high altitude. At first glance, the hypoxia associated with acute altitude exposure would appear to pose high risks for patients with underlying cardiopulmonary disease, but few studies have systematically addressed these concerns in the adult congenital heart disease population. In this review, we consider the safety of high-altitude travel in these patients. After reviewing the primary cardiopulmonary responses to acute hypoxia and the risks of high altitude in all individuals regardless of their underlying health status, we consider the risks in adult congenital heart disease patients, in particular. We focus on broad concerns that should be considered in all patients such as whether they have underlying pulmonary hypertension, the adequacy of their ventilatory responses, and their ability to compensate for hypoxemia and right-to-left shunting. We then conclude by providing basic recommendations for pretravel assessment in patients with congenital heart disease of moderate or great complexity.

Impact of high altitude on echocardiographically determined cardiac morphology and function in patients with coronary artery disease and healthy controls

AIMS

To evaluate the impact of high altitude on cardiac morphology and function in patients with coronary artery disease (CAD) and healthy controls.

METHODS AND RESULTS

Eight patients with a history of acute myocardial infarction [53 +/- 8 years, left ventricular (LV) ejection fraction 54 +/- 6%] and a low risk score were compared with seven healthy controls (41 +/- 16 years) during the Dutch Heart Expedition 2007 at the Aconcagua (6960 m) in Argentina. An exercise test and echocardiography were performed at sea level and at base camp (4200 m). In the apical four-chamber view, right ventricular (RV) diameter, tricuspid annular plane systolic excursion (TAPSE), early transmitral inflow peak velocity (E), atrial transmitral inflow peak velocity (A), and peak tissue velocity during early diastole (E') were obtained. Changes in global LV function and wall motion score index (WMSI) were used as markers of ischaemia. There were no significant differences in individual global LV function and WMSI at high altitude compared with sea level in both groups. A significant increase in RV diameter was observed in the patient group at 4200 m compared with sea level and a trend towards the same result in the control group. A decrease in TAPSE was observed. Measurements of the E' showed a significant decrease in the LV septum and lateral wall at high altitude compared with sea level in both groups.

CONCLUSION

Symptoms and echocardiographic signs of myocardial ischaemia were absent in low-risk patients with a history of CAD during and after exercise up to an altitude of 4200 m. Patients and healthy controls showed comparable changes at high altitude compared with sea level with an increase in RV diameter, a decrease in TAPSE, and decreased E' as early signs of pulmonary hypertension and LV diastolic dysfunction. As these alterations are most likely physiological adaptation to high altitude, the results seem to affirm current guidelines. The safety of expanding previous recommendations to patients with low-risk CAD to an altitude ascent of 4200 m requires confirmation in a larger study with appropriately defined clinical endpoints.

Diastolic dysfunction: a link between hypertension and heart failure

Diastolic heart failure is characterized by the symptoms and signs of heart failure, a preserved ejection fraction and abnormal left ventricular (LV) diastolic function caused by a decreased LV compliance and relaxation. The signs and symptoms of diastolic heart failure are indistinguishable from those of heart failure related to systolic dysfunction; therefore, the diagnosis of diastolic heart failure is often one of exclusion. The majority of patients with heart failure and preserved ejection fraction have a history of hypertension. Hypertension induces a compensatory thickening of the ventricular wall in an attempt to normalize wall stress, which results in LV concentric hypertrophy, which in turn decreases LV compliance and LV diastolic filling. There is an abnormal accumulation of fibrillar collagen accompanying the hypertension-induced LV hypertrophy, which is also associated with decreased compliance and LV diastolic dysfunction. There are no specific guidelines for treating diastolic heart failure, but pharmacological treatment should be directed at normalizing blood pressure, promoting regression of LV hypertrophy, preventing tachycardia and treating symptoms of congestion. Preventive strategies directed toward an early and aggressive blood pressure control are likely to offer the greatest promise for reducing the incidence of diastolic heart failure.

Evidence supportive of impaired myocardial blood flow reserve at high altitude in subjects developing high-altitude pulmonary edema

An exaggerated increase in pulmonary arterial pressure is the hallmark of high-altitude pulmonary edema (HAPE) and is associated with endothelial dysfunction of the pulmonary vasculature. Whether the myocardial circulation is affected as well is not known. The aim of this study was, therefore, to investigate whether myocardial blood flow reserve (MBFr) is altered in mountaineers developing HAPE. Healthy mountaineers taking part in a trial of prophylactic treatment of HAPE were examined at low (490 m) and high altitude (4,559 m). MBFr was derived from low mechanical index contrast echocardiography, performed at rest and during submaximal exercise. Among 24 subjects evaluated for MBFr, 9 were HAPE-susceptible individuals on prophylactic treatment with dexamethasone or tadalafil, 6 were HAPE-susceptible individuals on placebo, and 9 persons without HAPE susceptibility served as controls. At low altitude, MBFr did not differ between groups. At high altitude, MBFr increased significantly in HAPE-susceptible individuals on treatment (from 2.2 ± 0.8 at low to 2.9 ± 1.0 at high altitude, P = 0.04) and in control persons (from 1.9 ± 0.8 to 2.8 ± 1.0, P = 0.02), but not in HAPE-susceptible individuals on placebo (2.5 ± 0.3 and 2.0 ± 1.3 at low and high altitude, respectively, P > 0.1). The response to high altitude was significantly different between the two groups ( P = 0.01). There was a significant inverse relation between the increase in the pressure gradient across the tricuspid valve and the change in myocardial blood flow reserve. HAPE-susceptible individuals not taking prophylactic treatment exhibit a reduced MBFr compared with either treated HAPE-susceptible individuals or healthy controls at high altitude.

Right ventricular function with hypoxic exercise: effects of sildenafil

The effect of sildenafil on right ventricular contractility in hypoxic exercise is unknown, whereas reports have shown that sildenafil is associated with a smaller increase in pulmonary vascular resistance and right ventricular systolic pressure (RVSP) with exercise at high altitude. The present study evaluates the changes induced by controlled hypoxia on right ventricular pressure and performance with and without sildenafil administration. Tricuspid annular isovolumic acceleration (IVA) and annular velocities were measured in 14 healthy subjects at rest and after maximal exercise in a cross-over, double blind placebo controlled trial in three situations: normoxia, normobaric hypoxia with, and normobaric hypoxia without the administration of 100 mg sildenafil. RVSP, assessed by Doppler echocardiography, was determined from the peak tricuspid regurgitation pressure gradient. RVSP during rest increased from 26.9 +/- 2.3 mmHg in normoxia to 37.8 +/- 6.9 mmHg in hypoxia, p < 0.01; sildenafil administration reduced RVSP in hypoxia to 30.5 +/- 5.6, p < 0.01. Compared to normoxia at rest, IVA increased similarly with peak exercise in normoxia and hypoxia(sildenafil) (by 2.37 and 1.90 m/s(2), respectively), but the observed increase in IVA during exercise was smaller (0.86 m/s(2), p < 0.05) in hypoxia(placebo). Right ventricular contractility, as estimated by IVA at peak exercise is increased with the administration of sildenafil as compared to placebo, and is not different from the values seen during exercise in normoxia. This effect seems independent of the effect of sildenafil on RVSP.