Abstract: The heartbeat frequency is not constant but subject to natural variations. This change in heartbeat frequency is called the heart rate variability (HRV). A method is provided for online-displaying a HRV biofeedback signal by which the cardiovascular state of a patient can be purposefully influenced. The parameters HRVi as determined according to the invention are used for said HRV biofeedback signal, wherein, as a function of the display, the patient should alter his behaviour in such a way that a desired cardiovascular state is attained. The inventive HRVi parameters provide a HRV biofeedback signal with high dynamics which allow the patient to react quickly to changes and therewith to reliably achieve and stabilise his own desired cardiovascular state.

Abstract: The invention relates to a measuring device for optically determining the concentration of blood sugar and/or lactate in biological systems, comprising at least one IR radiation source, that radiates IR light on a volume that is to examined, and at least one measuring detector that detects light coming from the volume that is to be examined in order to determine the concentration of blood sugar and/or lactate, also by laymen in a simple manner and anywhere. According to the invention, the IR light radiated on the volume that is to be examined is supplied, prior to entry into the volume, to a reference detector.