This paper proposes a mathematical framework for evaluating the throughput of an 802.11 Distributed Wireless Network (DWN) when the system allows Multi-Packet Reception (MPR) in asynchronous operating mode. Differently from previous studies on MPR, which assume a certain synchronization between the different sources at the beginning of the respective transmissions, this work analyzes a fully distributed scenario, where each node can access to the medium in a completely asynchronous way. More precisely, a new transmission may begin in an already busy channel, as long as the current channel load is within a given threshold. The presented model, which includes the synchronous scenario as a particular case, is employed to investigate the influence of the number of allowed communications, of the load threshold, and of the minimum contention window on the network performance.