## 4 Discussion
A transfusion set-pass experiment, unique to us, was used to assess RBC solution quality. We previously reported that RBC solution had hemolytic activity after filtration, which was mainly due to poor temperature control during vehicle transport that may increase the LDH levels in RBCsolutions after transport, even if LDH is not a problem due to transfusion set-pass [25]. This emphasizes the importance of measuring LDH, which passes through the transfusion filter before transfusion in clinical settings. To add about filtering, when blood is transfused, damaged red blood cells are destroyed and LDH rises. It is important to measure LDH after passing through the transfusion set (after filtering) because this means that even a small amount of red blood cell damage can be detected by LDH. Most of the previous reports on blood transport are based on blood specimens, and there are few studies that evaluate transported blood for transfusion under actual temperature control. This study had some limitations. As an indicator of hemolysis, companies in Japan do not provide tests for free hemoglobin. Therefore, the JRC itself measures free hemoglobin using an absorbance meter. However, since we did not have access to an absorbance meter, we measured the LDH levels instead, which we believe to be a low-cost and responsive test for hemolysis. For the biochemical tests, the mean was obtained using four samples. Although four samples were sufficient for this study, this may not be sufficient to accurately measure rapidly degrading substances, such as ammonia. However, an increase in the number of samples might reduce the volume of the RBC solution for the transportation trial. Vibration could not be staged due to the lack of detailed time records for each phase of the flight, including take-off, landing, and cruise flight. This was because the flight time and vibration measurement time were not linked. Both outbound and inbound flights were not under high winds, but the flight times were slightly different. The manufacturer recommends a wind speed of 10 m/s or less as a possible flight condition for the UH and does not allow it to fly in heavy rain due to wear on the carbon rotors. Strong wind and heavy rain can limit UH flights. As a matter of calculation, the maximum airspeed of the UH was 72 m/h (20 m/s), so if the tailwind is 10 m/s, the ground speed is calculated to be 108 km/h (30 m/s). Moreover, if the headwind is 10 m/s, the ground speed drops to 36 km/h (10 m/s), so excluding the time for takeoff and landing, the flight time with a headwind is three times the flight time with a tailwind. Additionally, in the event of a disaster, it will be important to transport RBC solutions by UHs to a nearby base. However, UHs may be too large for subsequent transportation to certain locations. This is similar to the disruption of transport that occurred during the COVID-19 pandemic. Therefore, we think a good way that the UH is used to reach the base where it can be installed, and the small multi-copters are used for short-range transportation to specific locations. Demonstrations of flights using large uncrewed aerial vehicles to farther, more remote areas are currently being planned, and we believe that this will provide more reliable results.