A percussive ventilation breathing head adapted to be supplied with a flow of pulsatile gas and, independently, a flow of nebulized aerosol gas, the percussive ventilation breathing head comprising: an elongated breathing head body adapted to be supplied with the pulsatile gas flow at a proximal end thereof, said breathing head body defining an interior passageway therein; a depending plenum from said breathing head body adapted to receive said nebulized gas flow thereat; an exhalation port; a reciprocating injector shuttle movably mounted in said breathing head passageway, said shuttle adapted to move back and forth, distally and proximally, respectively, due to said pulsatile gas and a bias acting on said shuttle, said shuttle having an internal flow passage from a proximal shuttle input port to a distal shuttle output port, said shuttle input port being in fluid communication with said depending plenum such that nebulized aerosol gas from the depending plenum passes into the proximal shuttle input port, through the internal flow passage and through the distal end of the elongated breathing head body, and such that when the shuttle is moved distally due to said pulsatile gas overcoming the bias acting on the shuttle, the shuttle seals against a seat of the elongated breathing head body to close the exhalation port; and an entrainment valve on said breathing head body having a one-way gas flow system from the ambient environment to an entrainment valve chamber in fluid communication with said proximal shuttle input port, wherein either said one-way gas flow system includes a flapper valve biased closed and separating the ambient from said entrainment valve chamber such that said entrainment valve permits ambient air flow during an inhalation phase and the entrainment valve body having an over-pressure valve adapted to release aerosol to said ambient environment at a predetermined pressure, or said one-way gas flow system includes a hydrophobic filter mounted in said entrainment valve body separating the ambient from said entrainment valve chamber and permitting substantially one-way ambient air flow to said entrainment valve chamber, such that said entrainment valve permits ambient air flow during an inhalation phase. an elongated breathing head body adapted to be supplied with the pulsatile gas flow at a proximal end thereof, said breathing head body defining an interior passageway therein; a depending plenum from said breathing head body adapted to receive said nebulized gas flow thereat; an exhalation port; a reciprocating injector shuttle movably mounted in said breathing head passageway, said shuttle adapted to move back and forth, distally and proximally, respectively, due to said pulsatile gas and a bias acting on said shuttle, said shuttle having an internal flow passage from a proximal shuttle input port to a distal shuttle output port, said shuttle input port being in fluid communication with said depending plenum such that nebulized aerosol gas from the depending plenum passes into the proximal shuttle input port, through the internal flow passage and through the distal end of the elongated breathing head body, and such that when the shuttle is moved distally due to said pulsatile gas overcoming the bias acting on the shuttle, the shuttle seals against a seat of the elongated breathing head body to close the exhalation port; and an entrainment valve on said breathing head body having a one-way gas flow system from the ambient environment to an entrainment valve chamber in fluid communication with said proximal shuttle input port, wherein either