‘RFa’ is known to be a measure of Parasympathetic activity and ‘LFa’ is known to be a measure of Sympathetic activity, based on reference: Colombo J, Arora RR, DePace NL, Vinik AI, Clinical Autonomic Dysfunction: Measurement, Indications, Therapies, and Outcomes. Springer Science + Business Media, New York, NY; 2014.