A system configured to deliver medicament to a subject, the system comprising: a respiratory medicament delivery device configured to combine breathable gas and medicament for delivery to an airway of a subject, wherein the respiratory medicament delivery device comprises a piezoelectric element, wherein the piezoelectric element has an operating frequency, and wherein the respiratory medicament delivery device emits ultrasonic energy during operation; a sensor configured to generate output signals representing one or more characteristics of the ultrasonic energy emitted by the respiratory medicament delivery device during operation; and one or more processors configured to execute computer program modules, the computer program modules comprising: a parameter determination module configured to determine, based on the generated output signals, a first spectral parameter that indicates energy amplitude of ultrasonic energy emitted by the piezoelectric element of the respiratory medicament delivery device during operation in a first ultrasonic frequency range that includes the operating frequency of the piezoelectric element, such that the first spectral parameter characterizes operation of the respiratory medicament delivery device; the system being characterized in that it further comprises: a control module configured to control the respiratory medicament delivery device during operation based on the first spectral parameter; and an inhalation flap valve configured to reduce ultrasonic energy received by the sensor during exhalation by the subject, wherein the parameter determination module is further configured to determine respiratory timing of the subject based on variations of the first spectral parameter, and wherein the control module is further configured to control delivery of medicament by the respiratory medicament delivery device based on the determined timing. a respiratory medicament delivery device configured to combine breathable gas and medicament for delivery to an airway of a subject, wherein the respiratory medicament delivery device comprises a piezoelectric element, wherein the piezoelectric element has an operating frequency, and wherein the respiratory medicament delivery device emits ultrasonic energy during operation; a sensor configured to generate output signals representing one or more characteristics of the ultrasonic energy emitted by the respiratory medicament delivery device during operation; and one or more processors configured to execute computer program modules, the computer program modules comprising: a parameter determination module configured to determine, based on the generated output signals, a first spectral parameter that indicates energy amplitude of ultrasonic energy emitted by the piezoelectric element of the respiratory medicament delivery device during operation in a first ultrasonic frequency range that includes the operating frequency of the piezoelectric element, such that the first spectral parameter characterizes operation of the respiratory medicament delivery device; the system being characterized in that it further comprises: a control module configured to control the respiratory medicament delivery device during operation based on the first spectral parameter; and an inhalation flap valve configured to reduce ultrasonic energy received by the sensor during exhalation by the subject, wherein the parameter determination module is further configured to determine respiratory timing of the subject based on variations of the first spectral parameter, and wherein the control module is further configured to control delivery of medicament by the respiratory medicament delivery device based on the determined timing. a parameter determination module configured to determine, based on the generated output signals, a first spectral parameter that indicates energy amplitude of ultrasonic energy emitted by the piezoelectric element of the respiratory medicament delivery device during operation in a first ultrasonic frequency range that includes the operating frequency of the piezoelectric element, such that the first spectral parameter characterizes operation of the respiratory medicament delivery device; the system being characterized in that it further comprises: a control module configured to control the respiratory medicament delivery device during operation based on the first spectral parameter; and an inhalation flap valve configured to reduce ultrasonic energy received by the sensor during exhalation by the subject, wherein the parameter determination module is further configured to determine respiratory timing of the subject based on variations of the first spectral parameter, and wherein the control module is further configured to control delivery of medicament by the respiratory medicament delivery device based on the determined timing. a control module configured to control the respiratory medicament delivery device during operation based on the first spectral parameter; and an inhalation flap valve configured to reduce ultrasonic energy received by the sensor during exhalation by the subject, wherein the parameter determination module is further configured to determine respiratory timing of the subject based on variations of the first spectral parameter, and wherein the control module is further configured to control delivery of medicament by the respiratory medicament delivery device based on the determined timing.