Healthy Adults Aged 18-55, Three Ukrainian Windlass Tourniquets (SICH, DNIPRO GEN 2, PULS) Compared With CAT Gen 7, and Complete Limb Arterial Occlusion Confirmed by Doppler.

The goal of this clinical trial is to learn if three Ukrainian-made windlass tourniquets (SICH, DNIPRO GEN 2 and PULS) stop arterial blood flow in the arm or leg as well as the Combat Application Tourniquet (CAT Gen 7) does. The trial is in healthy adult volunteers, men and women aged 18 to 55 years. Limb tourniquets are used to stop life-threatening bleeding from an arm or leg. The results will support a national standard for windlass tourniquets in Ukraine. The main question it aims to answer is: Does each Ukrainian tourniquet completely stop arterial blood flow below the tourniquet within 120 seconds as often as CAT Gen 7? Stopped blood flow will be confirmed by Doppler ultrasound. Investigators will compare each Ukrainian tourniquet with CAT Gen 7 in the same participant, using one device on the arm and the other on the leg. They will look at whether blood flow is completely stopped and how quickly. They will also compare: * pain and comfort during and after use; * how fast normal blood flow returns after the tourniquet is removed; * how reliably each device can be applied; * any device problems and side effects. Participants will: Attend a screening visit with a medical history, physical examination, vital signs, ECG, tests for hepatitis B (HBsAg) and hepatitis C (anti-HCV) on the blood sample, and a rapid HIV test using a mouth swabblood, urine tests including pregnancy test (only for women). Be randomly assigned to one pair of devices: CAT Gen 7 with SICH, CAT Gen 7 with DNIPRO GEN 2, or CAT Gen 7 with PULS. The order in which the two devices are used will also be chosen at random. Have a tourniquet applied by trained study staff on two visits at least 24 hours apart. Each time, a different device is used on a different limb (upper arm or thigh), for no longer than 120 seconds. Have blood flow checked with Doppler ultrasound by a doctor who does not know which device is being used. Have skin temperature measured, and rate their pain and comfort. Receive follow-up phone calls about 24 hours and 72 hours after the second application. A clinic visit is arranged only if a side effect is reported.