Refined design and experimental validation of an implantable multimodal vital signs monitoring device

Background　Current vital-sign monitoring in large animals usually requires restraint or anesthesia. This makes continuous real-time monitoring in awake animals difficult. In addition, external devices are prone to detachment, displacement, or damage.Objective　To modify and develop an implantable multiparameter vital-sign monitoring device for miniature pigs and to evaluate its monitoring performance. Methods We developed an implantable vital-sign monitoring device and supporting software. The device integrated single-lead electrocardiogram (ECG), temperature monitoring, Bluetooth data transmission, and a charging module. The device was implanted into the subcutaneous tissue of the left precordial region in adult male Bama miniature pigs. Using a self-controlled paired design, heart rate and body temperature measured by the implantable device were compared with those measured by a conventional monitor under general anesthesia and sedation. Its monitoring performance in the awake state was also observed. On postoperative day 7, tissue around the implantation site was collected for hematoxylin-eosin (HE) staining to evaluate local tissue response and short-term histocompatibility.Results　The device was able to monitor ECG, heart rate, and body temperature under general anesthesia, sedation, and awake conditions, and the data could be displayed in real time on a mobile terminal. Under both general anesthesia and sedation, heart rate measured by the implantable device showed no significant difference from that measured by the conventional monitor (P＞0.05). However, the temperature measured by the implantable device was higher than the nasal temperature measured by the conventional monitor (P＜0.001). After surgery, the animals remained in good general condition. No obvious infection was found at the implantation site. Histological examination showed mild local inflammatory cell infiltration.Conclusion　The implantable vital-sign monitoring device can be used to monitor ECG, heart rate, and body temperature in miniature pigs under different conditions. Its heart-rate measurements were generally consistent with those of the conventional monitor, and it showed good short-term implantation tolerance.