Effect of Acute Hypoxia on RIght VEntRicular Function in HAPE.

Outdoor activities in the mountains are becoming increasingly popular. At higher altitudes, the air contains less oxygen, which puts extra strain on the body-especially on the heart. The right side of the heart plays a key role in pumping blood through the lungs and may need to work harder when oxygen levels are low. While the heart's response to long-term altitude exposure is relatively well known, much less is understood about how the heart reacts to short-term (acute) exposure to low oxygen, particularly during light physical activity and in individuals past HAPE.

Participants with past HAPE will be exposed to different oxygen levels that correspond to altitudes of 490 m (near sea level), 2,500 m, and 4,000 m, both at rest and during light cycling exercise. The main focus of the study is to measure changes in right ventricular function, assessed using a non-invasive heart ultrasound technique called speckle-tracking echocardiography. In addition, heart rate, blood pressure, oxygen saturation, and symptoms such as shortness of breath and leg fatigue will be recorded. The study is conducted at a single center and uses a randomized, double-blind, cross-over design, meaning that each participant undergoes all altitude conditions in a random order, and neither the participants nor the investigators know which altitude is being simulated at a given time.

Participants Only adults aged 18-80 years with diagnosed past HAPE will be included. Participants must live below 800 m above sea level and must not have been exposed to higher altitudes for more than 24 hours in the three weeks before participation. Individuals with significant other medical conditions, pregnancy, need for long-term oxygen therapy, or inability to follow the study procedures will be excluded.

Study procedures

Each study visit includes:

* 1 hour resting period * Measurement of vital signs (heart rate, blood pressure, oxygen saturation) * Heart ultrasound at rest * A 10-minute low-intensity cycling exercise * Repeated heart ultrasound during and symptom assessment after exercise * Low-oxygen conditions are created using a special gas mixture that participants breathe through a mask. Each condition is separated by at least 2 hours wash-out period to ensure recovery.

Study size and duration Based on statistical calculations, 18 participants will be recruited to allow balanced allocation across all study conditions and to account for potential dropouts. Participation may take place over two to three days, depending on the preferred schedule of the participant. The days can be spread or be spread over several weeks, depending on individual availability.

Aim of the study The goal of this study is to improve understanding of how the right side of the heart responds to short-term low-oxygen exposure at rest and during light exercise. This knowledge will help interpret future findings in patients with heart or lung disease and may contribute to safer recommendations for physical activity at altitude.

• Tricuspid annular plane systolic excursion (TAPSE) [Срок оценки: It will be assessed once at baseline in rest and during each condition three times: Once after 1 hour in the specific condition at rest, then during the 5 min of 30 Watt cycling and during the 5 min of 60 Watt cycling.]
• Right ventricular-arterial coupling [Срок оценки: It will be assessed once at baseline in rest and during each condition three times: Once after 1 hour in the specific condition at rest, then during the 5 min of 30 Watt cycling and during the 5 min of 60 Watt cycling.]
• RV/PA [Срок оценки: It will be assessed once at baseline in rest and during each condition three times: Once after 1 hour in the specific condition at rest, then during the 5 min of 30 Watt cycling and during the 5 min of 60 Watt cycling.]
• Stroke volume [Срок оценки: It will be assessed once at baseline in rest and during each condition three times: Once after 1 hour in the specific condition at rest, then during the 5 min of 30 Watt cycling and during the 5 min of 60 Watt cycling.]
• Heart rate [Срок оценки: It will be assessed at baseline and continuously measured during each condition (1 hour resting period and during the 10 minutes cycling).]
• Blood pressure [Срок оценки: It will be measured at baseline once and during each condition six times: Four times during the resting period (every 15 min) and two times during low load cycling.]
• Borg Rating of Perceived Exertion Scale (CR10) [Срок оценки: Measured at baseline and in each condition twice: Once at the end of the resting condition and again at the end of the cycling exercise.]
• Oxygen saturation [Срок оценки: It will be assessed at baseline and continuously measured during each condition (1 hour resting period and during the 10 minutes cycling).]
• Lung tissue oxygenation [Срок оценки: It will be assessed at baseline and continuously measured during each condition (1 hour resting period and during the 10 minutes cycling).]
• Brain oxygenation [Срок оценки: It will be assessed at baseline and continuously measured during the 1 hour resting period during each condition, and during the 10 minutes cycling.]
• Respiratory effort [Срок оценки: It will be assessed at baseline and continuously measured during each condition (1 hour resting period and during the 10 minutes cycling).]
• Multiomics profiles [Срок оценки: A blood sample will be collected during each condition after 1 hour of rest.]