Patch-based physiological sensor

A sensor for measuring a photoplethysmogram (PPG) waveform, a phonocardiogram (PCG) waveform, an impedance plethysmogram (IPG) waveform, and an electrocardiogram (ECG) waveform from a patient's chest, the sensor comprising:

• a housing configured to be located on the patient's chest;
• a reflective optical sensor for measuring the PPG waveform;
• a digital microphone for measuring the PCG waveform;
• a buzzer disposed in the housing, adjacent to the digital microphone, configured to generate an acoustic sound at a known amplitude and frequency;
• a processor disposed within the housing;
• and
• a set of electrodes that attach the optical sensor and the digital microphone to the patient's chest, with the set of electrodes connected to an ECG sensor configured to measure the ECG waveform,
• wherein the set of electrodes is further attached to an IPG sensor, the IPG sensor configured to measure the IPG waveform,
• wherein the IPG sensor is configured to inject current into the patient's chest, and further configured to measure the current to determine the IPG waveform,
• wherein the digital microphone is configured to compare the acoustic sound generated by the buzzer with the PCG waveform to determine a quality of patient-sensor adhesion between the sensor and a surface of the patient's chest, and
• wherein the processor uses time-domain analysis and frequency-domain analysis of the IPG waveform and uses time-domain analysis and frequency-domain analysis of the PCG waveform to collectively determine one of a coughing event, a wheezing event, and an apnea event by identifying amplitude modulation in the IPG waveform.