A method, a system, or an apparatus for resuscitation can include a first sensor having a first output configured to provide a first sensor signal corresponding to optical attenuation of tissue at a site. The method, the system, or the apparatus can include a processor coupled to the first output. The processor can be configured to generate an output signal. The output signal can be determined based on a first parameter of the optical attenuation. The first parameter can correspond to blood circulation associated with externally applied stimulation of a cardiovascular organ. The method, the system, or the apparatus can include a system output coupled to the processor. The system output can be configured to provide a control signal determined using the output signal.
