Wearable wireless medical sensors beneficially impact the healthcare sector, and this market is experiencing rapid growth. Globally, the digital health market is forecast to increase from $80 billion in 2015 to $200 billion in 2020. Medical body area networks (MBANs) improve the mobility of patients and medical personnel during surgery, accelerate the patients' recovery, while facilitating the remote monitoring of patients suffering from chronic diseases. Currently, MBANs are being introduced in unlicensed frequency bands, where the risk of mutual interference with other electronic devices can be high. Techniques developed during the evolution of cognitive radio (CR) can potentially alleviate these problems in medical communication environments. In addition, these techniques can help increase the efficiency of spectrum usage to accommodate the rapidly growing demand for wireless MBAN solutions and enhance coexistence with other collocated wireless systems. A viable architecture of an MBAN with practical CR features is proposed in this work. Additionally, ultra wideband (UWB) radio for the implementation of CR offers many advantages to MBANs, and some features of this technology can be exploited for effective implementation of CR. Conceptual aspects associated with energy harvesting and practical identification of spectrum opportunities for radio frequency (RF) energy scavenging motivates the options taken in the development of the protocols. The physical (PHY) and medium access control (MAC) layer aspects of the proposal are proposed in addition to their implementation challenges in the context of CR.