Most patients exhibit changes in their vital signs hours before an adverse event, sometimes as much as six hours before.
In ICUs, vital signs are continuously monitored by wired devices, but in the step-down units, they are often measured intermittently by the unit's clinical staff. A wireless sensor network could monitor vital signs tens or hundreds of times more frequently.
The computer scientists were focused on ensuring the network would always function and never go down. "To a technology guy, what's most interesting is that the network reliably delivers data to the endpoints, even if a few relays went silent," Lu says.
The relay nodes were programmed as a self-organizing mesh network, meaning that if one node dropped out, data packets took another path to the base.
And indeed nodes did sometimes drop out, if only because the cleaning staff unplugged them to plug in floor cleaning machines.
The sensor and relay nodes both included a radio chip. The sensor nodes were battery powered, and the relay nodes were energized by USB-to-power adapters plugged into electrical outlets.
Because the scientists knew they couldn't expect the nurses to take on extra duties like changing batteries, the sensor nodes hoarded power. A node turned on the radio only when it had a data packet to transmit, and turned off the radio as soon as a relay node acknowledged receipt of the packet.
When it first powered up, a sensor node "discovered" the relay nodes within its communication range and added them to a "neighbor table." Then when it had data to transmit, it selected the neighbor at the start of the "lowest-cost" path to the base station for the first data hop.
If ambulatory patients w
|Contact: Diana Lutz|
Washington University in St. Louis