Effects of altitude on exercise level and heart rate in patients with coronary artery disease and healthy controls

The effect of high altitude (2500 m) on incremental cycling exercise in patients with pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension: a randomised controlled crossover trial

BACKGROUND

Our objective was to investigate the effect of a day-long exposure to high altitude on peak exercise capacity and safety in stable patients with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

In a randomised controlled crossover trial, stable patients with PAH or distal CTEPH without resting hypoxaemia at low altitude performed two incremental exercise tests to exhaustion: one after 3-5 h at high altitude (2500 m) and one at low altitude (470 m).

RESULTS

In 27 patients with PAH/CTEPH (44% females, mean±sd age 62±14 years), maximal work rate was 110±64 W at 2500 m and 123±64 W at 470 m (-11%, 95% CI -16- -11%; p<0.001). Oxygen saturation measured by pulse oximetry and arterial oxygen tension at end-exercise were 83±6% versus 91±6% and 6.1±1.9 versus 8.6±1.9 kPa (-8% and -29%; both p<0.001) at 2500 versus 470 m, respectively. Maximal oxygen uptake was 17.8±7.5 L·min-1·kg-1 at high altitude versus 20±7.4 L·min-1·kg-1 at low altitude (-11%; p<0.001). At end-exercise, the ventilatory equivalent for carbon dioxide was 43±9 at 2500 m versus 39±9 at 470 m (9%, 95% CI 2-6%; p=0.002). No adverse events occurred during or after exercise.

CONCLUSIONS

Among predominantly low-risk patients with stable PAH/CTEPH, cycling exercise during the first day at 2500 m was well tolerated, but peak exercise capacity, blood oxygenation and ventilatory efficiency were lower compared with 470 m.

Physiological and Morphometric Differences in Resident Moderate-Altitude vs. Sea-Level Mice

INTRODUCTION: High-altitude [>2400 m (7874 ft)] acclimatization has been well studied with physiological adaptations like reductions in body weight and exercise capacity. However, despite the significance of moderate altitude [MA, 1524-2438 m (5000-8000 ft)], acclimatization at this elevation is not well described. We aimed to investigate differences in mice reared at MA compared to sea level (SL). We hypothesized that MA mice would be smaller and leaner and voluntarily run less than SL mice.METHODS: C57BL/6 mice reared for at least three generations in Laramie, WY [2194 m (7198 ft), MA], were compared to C57BL/6J mice from Bar Harbor, ME [20 m (66 ft), SL]. We quantified body composition and exercise outputs as well as cardiopulmonary morphometrics. Subsets of MA and SL mice were analyzed to determine differences in neuronal activation after exercise.RESULTS: When body weight was normalized to tibia length, SL animals weighed 1.30 g ⋅ mm-1 while MA mice weighed 1.13 g · mm-1. Total fat % and trunk fat % were higher in MA mice with values of 41% and 39%, respectively, compared to SL mice with values of 28% and 26%, respectively. However, no differences were noted in leg fat %. MA animals had higher heart mass (119 mg) and lower lung mass (160 mg) compared to SL mice heart mass (100 mg) and lung mass (177 mg). MA mice engaged in about 40% less voluntary wheel-running activity than SL animals.DISCUSSION: Physiological differences are apparent between MA and SL mice, prompting a need to further understand larger scale implications of residence at moderate altitude.O'Connor AE, Hatzenbiler DM, Flom LT, Bobadilla A-C, Bruns DR, Schmitt EE. Physiological and morphometric differences in resident moderate-altitude vs. sea-level mice. Aerosp Med Hum Perform. 2023; 94(12):887-893.

Coronary Syndromes and High-Altitude Exposure—A Comprehensive Review

The aim of this review is to identify a preventive strategy in order to minimize the risk of adverse events in patients with coronary syndromes and acute exposure to high-altitude. For this purpose we searched the electronic database of PubMed, EMBASE, and Web of Science for studies published in the last 30 years in this field. The conclusions of this review are: patients with stable coronary artery disease on optimal treatment and in a good physical condition can tolerate traveling to high altitude up to 3500 m; on the other hand, patients with unstable angina or recent myocardial infarction no older than 6 months should take less interest in hiking or any activity involving high altitude. Air-traveling is contraindicated for patients with myocardial infarction within previous 2 weeks, angioplasty or intracoronary stent placement within previous 2 weeks, and unstable angina or coronary artery bypass grafting within previous 3 weeks. The main trigger for sudden cardiac death is the lack of gradual acclimatization to high-altitude and to the exercise activity, and the most important risk factor is prior myocardial infarction.

Effects of Acute Exposure and Acclimatization to High-Altitude on Oxygen Saturation and Related Cardiorespiratory Fitness in Health and Disease

Maximal values of aerobic power (VO₂max) and peripheral oxygen saturation (SpO₂max) decline in parallel with gain in altitude. Whereas this relationship has been well investigated when acutely exposed to high altitude, potential benefits of acclimatization on SpO₂ and related VO₂max in healthy and diseased individuals have been much less considered. Therefore, this narrative review was primarily aimed to identify relevant literature reporting altitude-dependent changes in determinants, in particular SpO₂, of VO₂max and effects of acclimatization in athletes, healthy non-athletes, and patients suffering from cardiovascular, respiratory and/or metabolic diseases. Moreover, focus was set on potential differences with regard to baseline exercise performance, age and sex. Main findings of this review emphasize the close association between individual SpO₂ and VO₂max, and demonstrate similar altitude effects (acute and during acclimatization) in healthy people and those suffering from cardiovascular and metabolic diseases. However, in patients with ventilatory constrains, i.e., chronic obstructive pulmonary disease, steep decline in SpO₂ and V̇O₂max and reduced potential to acclimatize stress the already low exercise performance. Finally, implications for prevention and therapy are briefly discussed.

Effect of a day-trip to altitude (2500 m) on exercise performance in pulmonary hypertension: randomised crossover trial

Question addressed by the study

To investigate exercise performance and hypoxia-related health effects in patients with pulmonary hypertension (PH) during a high-altitude sojourn.

Patients and methods

In a randomised crossover trial in stable (same therapy for >4 weeks) patients with pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH) with resting arterial oxygen tension (P_aO2) ≥7.3 kPa, we compared symptom-limited constant work-rate exercise test (CWRET) cycling time during a day-trip to 2500 m versus 470 m. Further outcomes were symptoms, oxygenation and echocardiography. For safety, patients with sustained hypoxaemia at altitude (peripheral oxygen saturation <80% for >30 min or <75% for >15 min) received oxygen therapy.

Results

28 PAH/CTEPH patients (n=15/n=13); 13 females; mean±sd age 63±15 years were included. After >3 h at 2500 m versus 470 m, CWRET-time was reduced to 17±11 versus 24±9 min (mean difference −6, 95% CI −10 to −3), corresponding to −27.6% (−41.1 to −14.1; p<0.001), but similar Borg dyspnoea scale. At altitude, P_aO2 was significantly lower (7.3±0.8 versus 10.4±1.5 kPa; mean difference −3.2 kPa, 95% CI −3.6 to −2.8 kPa), whereas heart rate and tricuspid regurgitation pressure gradient (TRPG) were higher (86±18 versus 71±16 beats·min⁻¹, mean difference 15 beats·min⁻¹, 95% CI 7 to 23 beats·min⁻¹) and 56±25 versus 40±15 mmHg (mean difference 17 mmHg, 95% CI 9 to 24 mmHg), respectively, and remained so until end-exercise (all p<0.001). The TRPG/cardiac output slope during exercise was similar at both altitudes. Overall, three (11%) out of 28 patients received oxygen at 2500 m due to hypoxaemia.

Conclusion

This randomised crossover study showed that the majority of PH patients tolerate a day-trip to 2500 m well. At high versus low altitude, the mean exercise time was reduced, albeit with a high interindividual variability, and pulmonary artery pressure at rest and during exercise increased, but pressure–flow slope and dyspnoea were unchanged.

Short-time exposure to high altitude in pulmonary hypertension induces hypoxaemia, reduces constant work-rate cycle time compared to ambient air and is well tolerated overallhttps://bit.ly/3xUAFMs

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.

Observational study to compare the effect of altitude on cardiopulmonary reserves of different individuals staying more than 6 weeks at 10,000 ft and 15,000 ft

Background

The variation in heights beyond high altitude has different effects on the cardiorespiratory profile of individuals because of variation in oxygen density with every thousand feet. This study was planned to analyze and compare the effects of difference in altitudes on cardiorespiratory profile from anesthesiologist's point of view.

Methods

A multicenter observational study was done involving two different groups of 600 patients at 10,000 ft (Group A) and 15,000 ft (Group B). Observation and comparison of oxygen saturation, 6-min walk test, and breath holding time was carried out.

Results

Fifty-five percent of subjects in Group A had oxygen saturation of more than 93% in comparison to 5.5% in Group B. This was statistically significant (P < 0.001). Two percent of subjects in Group A in comparison to 63.5% of Group B had oxygen saturation of less than 88% (P < 0.001). Percentage increase of more than 15% of heart rate was found to be statistically significant in all the age groups. Overall, 3.8% of individuals in Group A had breath holding time less than 15 s in comparison to 16.6% of individuals in Group B (P value < 0.001).

Conclusion

The study demonstrates that there is a significant fall in oxygen saturation, significant rise in the heart rate in 6-min walk test, and significant fall in the breath holding time in the group located at 15,000 ft. Heights beyond 10,000 ft should be restricted to life and limb saving surgeries, and logistics should be focused more on "scoop and run" than "stay and play" policy.

[Heart Patients and Exposure to Altitude]

Overall, heart patients should be advised individually with respect to their tolerance of altitudes. However, the historical reflex that altitude 'per se' is bad for heart patients should become a thing of the past. Adequately treated and stable patients can usually go up to an altitude of 2500 m without any restrictions. Higher altitudes are also possible for a large number of patients, but may require an adaptation of the medication and further clarification. This is especially the case when physical work is to be performed at great heights.

Effect of Normobaric Hypoxia on Exercise Performance in Pulmonary Hypertension: Randomized Trial

BACKGROUND

Many patients with pulmonary arterial or chronic thromboembolic pulmonary hypertension (PH) wish to travel to altitude or by airplane, but their risk of hypoxia-related adverse health effects is insufficiently explored.

RESEARCH QUESTION

How does hypoxia, compared with normoxia, affect constant work-rate exercise test (CWRET) time in patients with PH, and which physiologic mechanisms are involved?

STUDY DESIGN AND METHODS

Stable patients with PH with resting Pao₂ ≥ 7.3 kPa underwent symptom-limited cycling CWRET (60% of maximal workload) while breathing normobaric hypoxic air (hypoxia; Fio₂, 15%) and ambient air (normoxia; Fio₂, 21%) in a randomized cross-over design. Borg dyspnea score, arterial blood gases, tricuspid regurgitation pressure gradient, and mean pulmonary artery pressure/cardiac output ratio (mean PAP/CO) by echocardiography were assessed before and during end-CWRET.

RESULTS

Twenty-eight patients (13 women) were included: median (quartiles) age, 66 (54; 74) years; mean pulmonary artery pressure, 41 (29; 49) mm Hg; and pulmonary vascular resistance, 5.4 (4; 8) Wood units. Under normoxia and hypoxia, CWRET times were 16.9 (8.0; 30.0) and 6.7 (5.5; 27.3) min, respectively, with a median difference (95% CI) of -0.7 (-3.1 to 0.0) min corresponding to -7 (-32 to 0.0)% (P = .006). At end-exercise in normoxia and hypoxia, respectively, median values and differences in corresponding variables were as follows: Pao₂: 8.0 vs 6.4, -1.7 (-2.7 to -1.1) kPa; arterial oxygen content: 19.2 vs 17.2, -1.7 (-3 to -0.1) mL/dL; Paco₂: 4.7 vs 4.3, -0.3 (-0.5 to -0.1) kPa; lactate: 3.7 vs 3.7, 0.9 (0.1 to 1.6) mM (P < .05 all differences). Values for Borg scale score: 7 vs 6, 0.5 (0 to 1); tricuspid pressure gradient: 89 vs 77, -3 (-9 to 16) mm Hg; and mean PAP/CO: 4.5 vs 3.3, 0.3 (-0.8 to 1.4) Wood units remained unchanged. In multivariable regression, baseline pulmonary vascular resistance was the sole predictor of hypoxia-induced change in CWRET time.

INTERPRETATION

In patients with PH, short-time exposure to hypoxia was well tolerated but reduced CWRET time compared with normoxia in association with hypoxemia, lactacidemia, and hypocapnia. Because pulmonary hemodynamics and dyspnea at end-exercise remained unaltered, the hypoxia-induced exercise limitation may be due to a reduced oxygen delivery causing peripheral tissue hypoxia, augmented lactic acid loading and hyperventilation.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT03592927; URL: www.clinicaltrials.gov.

Altitude Travel in Patients With Pulmonary Hypertension: Randomized Pilot-Trial Evaluating Nocturnal Oxygen Therapy

Introduction: Stable patients with pulmonary arterial or chronic thromboembolic pulmonary hypertension (PH) wish to undergo altitude sojourns or air travel but fear disease worsening. This pilot study investigates health effects of altitude sojourns and potential benefits of nocturnal oxygen therapy (NOT) in PH patients. Methods: Nine stable PH patients, age 65 (47; 71) years, 5 women, in NYHA class II, on optimized medication, were investigated at 490 m and during two sojourns of 2 days/nights at 2,048 m, once using NOT, once placebo (ambient air), 3 L/min per nasal cannula, according to a randomized crossover design with 2 weeks washout at <800 m. Assessments included safety, nocturnal pulse oximetry (SpO₂), 6-min walk distance (6 MWD), and echocardiography. Results: At 2,048 m, two of nine patients required medical intervention, one for exercise-induced syncope, one for excessive nocturnal hypoxemia (SpO₂ < 75% for >30 min). Both recovered immediately with oxygen therapy. Two patients suffered from acute mountain sickness. In 6 patients with complete data, nocturnal mean SpO₂ and cyclic SpO₂ dips reflecting sleep apnea significantly differed from 490 to 2,048 m with placebo, and 2,048 m with NOT (medians, quartiles): SpO₂ 93 (91; 95)%, 89 (85; 90)%, 97 (95; 97)%; SpO₂ dips 10.4/h (3.1; 26.9), 34.0/h (5.3; 81.3), 0.3/h (0.1; 2.3). 6 MWD at 490, 2,048 m without and with NOT was 620 m (563; 720), 583 m (467; 696), and 561 m (501; 688). Echocardiographic indices of heart function and PH were unchanged at 2,048 m with/without NOT vs. 490 m. Conclusions: 7/9 PH patients stayed safely at 2,048 m but revealed hypoxemia, sleep apnea, and reduced 6 MWD. Hemodynamic changes were trivial. NOT improved oxygenation and sleep apnea. The current pilot trial is important for designing further studies on altitude tolerance of PH patients.

Clinical recommendations for high altitude exposure of individuals with pre-existing cardiovascular conditions: A joint statement by the European Society of Cardiology, the Council on Hypertension of the European Society of Cardiology, the European Society of Hypertension, the International Society of Mountain Medicine, the Italian Society of Hypertension and the Italian Society of Mountain Medicine

Take home figure

Out of air: Is going to high altitude safe for your patient?

As more people travel to high altitudes for recreation or work, more travelers with underlying medical conditions will need advice before traveling or treatment for altitude illness. This article focuses on the two main issues for travelers: whether travel to a high altitude will have a negative effect on their underlying medical condition and whether the medical condition increases the patient's risk of developing altitude illness. Although patients with severe pulmonary or cardiac conditions are most at risk in the hypoxic environment, other conditions such as diabetes and pregnancy warrant attention as well.

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.

Supplemental oxygen attenuates the increase in wound bacterial growth during simulated aeromedical evacuation in goats

BACKGROUND

Bacterial growth in soft tissue and open fractures is a known risk factor for tissue loss and complications in contaminated musculoskeletal wounds. Current care for battlefield casualties with soft tissue and musculoskeletal wounds includes tactical and strategic aeromedical evacuation (AE). This exposes patients to a hypobaric, hypoxic environment. In this study, we sought to determine whether exposure to AE alters bacterial growth in contaminated complex musculoskeletal wounds and whether supplemental oxygen had any effect on wound infections during simulated AE.

METHODS

A caprine model of a contaminated complex musculoskeletal wound was used. Complex musculoskeletal wounds were created and inoculated with bioluminescent Pseudomonas aeruginosa. Goats were divided into three experimental groups: ground control, simulated AE, and simulated AE with supplemental oxygen. Simulated AE was induced in a hypobaric chamber pressurized to 8,800 feet for 7 hours. Bacterial luminescence was measured using a photon counting camera at three time points: preflight (20 hours postsurgery), postflight (7 hours from preflight and 27 hours postsurgery), and necropsy (24 hours from preflight and 44 hours postsurgery).

RESULTS

There was a significant increase in bacterial growth in the AE group compared with the ground control group measured postflight and at necropsy. Simulated AE induced hypoxia with oxygen saturation less than 93%. Supplemental oxygen corrected the hypoxia and significantly reduced bacterial growth in wounds at necropsy.

CONCLUSIONS

Hypoxia induced during simulated AE enhances bacterial growth in complex musculoskeletal wounds which can be prevented with the application of supplemental oxygen to the host.

Effects of altitude on exercise level and heart rate in patients with coronary artery disease and healthy controls

Background. To evaluate the safety and effects of high altitude on exercise level and heart rate in patients with coronary artery disease compared with healthy controls.Methods. Eight patients with a history of an acute myocardial infarction (ejection fraction >5%) with a low-risk score were compared with seven healthy subjects during the Dutch Heart Expedition at the Aconcagua in Argentina in March 2007. All subjects underwent a maximum exercise test with a cycle ergometer at sea level and base camp, after ten days of acclimatisation, at an altitude of 4200 m. Exercise capacity and maximum heart rate were compared between groups and within subjects.Results. There was a significant decrease in maximum heart rate at high altitude compared with sea level in both the patient and the control group (166 vs. 139 beats/min, p<0.001 and 181 vs. 150 beats/min, p<0.001). There was no significant difference in the decrease of the exercise level and maximum heart rate between patients and healthy controls (-31 vs. -30%, p=0.673).Conclusion. Both patients and healthy controls showed a similar decrease in exercise capacity and maximum heart rate at 4200 m compared with sea level, suggesting that patients with a history of coronary artery disease may tolerate stay and exercise at high altitude similarly to healthy controls. (Neth Heart J 2010;18:118-21.).