This is an exploratory interventional study. The aim of the investigation is to identify and quantify contributing factors to local bioimpedance spectroscopy (BIS) measured by a wearable sensor patch, particularly the effect of fluid shifts caused by postural changes and lower body negative pressure (LBNP).

The investigational devices (patches) will perform near-continuous measurements of multifrequency bioimpedance (BIS), temperature, and body orientation (accelerometer) during the entire period of wear (2 days). Patches will be mounted at the upper body (back and thorax) and calf. The primary objective is to assess the effect of prolonged lower body negative pressure (LBNP) on the BIS of the calf. The target population is healthy volunteers between 18-50 years old.

Inclusion Criteria:

• 18 to 50 years of age, at the time of signing the informed consent
• Overtly healthy as determined by medical evaluation including medical history, physical examination and focused cardiac ultrasound.
• Use of adequate birth control for women of childbearing potential. Inclusion is possible when an acceptable effective contraceptive measure is used (combined (estrogen and progestogen containing) hormonal contraception, progestogen-only hormonal contraception associated with inhibition of ovulation, intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, vasectomised partner or sexual abstinence).
• Capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol.

Exclusion Criteria:

• Known allergies or skin sensitivities to electrode hydrogel and/or acrylic adhesives
• Breached skin at patch mounting area.
• Implantable pulse generators such as pacemakers and defibrillators, and/or use of other electrical medical equipment for which an interaction effect with the investigational device cannot be ruled out.
• Planned magnetic resonance (MR) imaging during the investigation period
• Any medical condition limiting physical exertional capacity or requiring regular medication (allergy and contraceptives excepted).
• Pregnancy
• Breastfeeding
• History of syncope (syncope of presumed vasovagal nature with known precipitating factor excepted).
• Any known cardiac disease that, at the investigator's discretion, warrants exclusion from the study, including but not limited to cardiac arrhythmia, esophageal varices, and aneurysms.