We consider a two-user binary multiple access setup suitable for pulse based communications. The link from each user to the receiver is modeled by independent time-varying Z-channel. We consider the cross-over probabilities of the Z-channels as the state of the process. Each user has access only to its own state process and is unaware of the other user's states. The receiver observes the superposition of the symbols from the links. Assuming a block fading state process, we propose adaptive communication schemes, which also ensure outage-free communication in any transmission block. Furthermore, the proposed strategies turn out to be throughput optimal for highly dispersive systems. {\textcopyright} 2014 IEEE.