An initial version of the software has been finished, so its time for a first case study. As biofeedback is a method for visualization of physical body reactions, stress should be a good stimulus. And which type of stress can be generated instantly? Right! Don't breathe! ;-)

The following diagram displays a recorded period about 1 minute with no breathing. The two vertical black lines mark the beginning and end of the period:

• Yellow line: Galvanic Skin Response (GSR). Falling line means increased skin sweat production
• Blue line: Heart Rate Variability (HRV) - the varying time delta (in milliseconds) between two heart beats
• Red line: classical Heart Rate

Some facts that I noticed and that I could reproduce:

• Heart rate does not increase as much as expected
• HRV is much more regular than before
• Heart rate is more constant than before
• GSR line: fall - rise - fall pattern