HRV is a powerful, objective and noninvasive tool to explore the dynamic interactions between physiological, mental, emotional and behavioral processes. HRV can be derived from the electrocardiogram (ECG), is a measurement of these naturally occurring, beat-to-beat changes in heart rate which act in balance through neural, mechanical, humoral and other physiological mechanisms. The high amplitude peak of the ECG complex QRS (R-wave) is commonly used to trace the HRV. The RR interval is the recorded time between successive R-waves. Spectral analysis of the RR interval variability identifies three main spectral components in short-term recordings of 2 to 5 minutes: very low frequency (VLF), low frequency (LF) and high frequency (HF). The physiological explanation of the distribution of power and central frequency of LF and HF are not fixed but may vary in relation to changes in ANS modulation of heart period. Vagal activity (parasympathetic) is the major contributor to the HF component. Recent studies view LF as reflecting both sympathetic activity and vagal activity. Thus, they can be used to characterize ANS balance and the ratio (LF/HF) of the spectral powers (in normalized units) is a potentially important index of normal and pathological ANS health.

It is well established that individuals with eating disorders such as bulimia nervosa (BN) and/or anorexia nervosa (AN) characteristically present high parasympathetic tone in conjunction with low central and peripheral sympathetic tone compared to thin or normal weight women. Studies of severely compromised ED inpatients have shown subdued sympathetic activity in response to mental stress and orthostatic change. Less severely compromised ED individuals present a robust response to psychological stress but are less responsive to physiological stress.

Prospective participates will be solicited by KCC faculty as volunteers and written consent will be obtained. Potential participants will be asked to refrain from taking any stimulants or other medications prior to the study that might affect their study results. Research assistants, trained by an MD and/or physiologist to insure the safety of the participant and proper use of the recording instruments, will continuously monitor participants. Research assistants will consist of undergraduate health science students, medical students and/or biomedical graduate students.

The study is quite simple and non-invasive. Student particiapnts will be asked to fill out a questionnaire concerning bodily functions, eating, sleep and exercise activity. Participants will then be asked to relax for several minutes, following which they will be administered the initial, base-line heart rate (HR), blood pressure (BP) and HRV measurements. Next, they will be exposed to, in random order, a physiological and a psychological stressor. Participants will be informed about the stressors beforehand and reminded that they can discontinue their participation without penalty at anytime.

Immediately following the stress test the HR, BP and HRV data will be collected. The stress conditions employed are commonly used in biomedical research. They are designed to elicit brief sympathetic arousal with corresponding changes in HR, BP and HRV. Participants will be debriefed at the end of the data collection session. The recording instument that is used to measure HRV is a MiniLogger Pro that is worn as a thoracic belt and records and stores Heart RR interval data.