Heart Rate Variability (HRV) is commonly used to assess autonomic functions and responses to environmental stimuli. It is usually derived from electrocardiographic signals; however, in the last few years, photoplethysmography has been successfully used to evaluate beat-to-beat time intervals and to assess changes in the human heart rate under several conditions. The present work describes a simple design of a photoplethysmography, using a wearable earlobe sensor. Beat-to-beat time intervals were evaluated as the time between subsequent pulses,

thus generating a signal representative of heart rate variability, which was compared to RR intervals from classic electrocardiography.