Heart Rate Variability (HRV) analysis has become an important tool in assessing human Autonomic Nervous System (ANS) activity in recent years. Orthostatic challenge is one of the most common tests to detect ANS dysfunction. In this study we looked at the changes in ANS activity of normal subjects to orthostatic challenge and compared the results of 3 different HRV analysis methods: Time-Domain Methods, HRV spectral analysis without respiratory analysis (RA) and with RA. Although all three methods have indicated an increase in sympathetic activity and a decrease in parasympathetic activity from baseline to stand, the only significant increase in sympathetic activity was observed in HRV with RA method. Additional information from RA enables isolating the sympathetic and parasympathetic branches in HRV signals and therefore reflects ANS changes more accurately. On the other hand, sympathetic and parasympathetic power may not be separated properly if respiration-dependent fluctuations in HRV are ignored. It is expected that the differences between methods would be very clear with low respiratory rates. However, we focused on studies with normal respiratory rates and have also found significant differences among the methods.

Upon assuming an upright, head up posture, a sympathetic surge is expected. Sympathetic Withdrawal (SW) is abnormal and can differentiate Orthostasis. SW, with blood pressure (BP) and heart rate (HR), can fully define the continuum that is Orthostasis, including pre-clinical forms: Orthostatic Hypotension (OH-), Orthostatic Intolerance (OI), Orthostatic Hypertension (OH+), and Postural Orthostatic Tachycardia Syndrome (POTS). Our objective was to test the therapeutic implications of SW in Orthostatic patients. Autonomic profiling of 210 consecutive Orthostatic patients recruited from ambulatory clinics was performed using the ANX-3.0 Autonomic Monitoring System (Ansar, Inc., Philadelphia, PA). The cohort (age=58.9±11.6; 30 Diabetics; 132 Females, 28 Controls) was followed over a two year period. Autonomic profiling was based on patient responses to a standard clinical study that includes a resting baseline and periods of deep (relaxed) breathing, short Valsalva maneuvers, and quick stand immediately followed by quiet standing. The control group were patients with known diagnoses. The experimental group were prescribed 2.5 mg Midodrine once a day around dinner. Control patients were administered Flourinef, or support hose, or when possible were requested to modify their diets to add salt and build fluid volume. Patients with dysautonomia, with symptoms of elevated BP when supine were omitted from the study. In 89% of the experimental cases, SW was reversed in approximately 6 months and weaned from the medication. The remaining cases were reversed and weaned before the end of the two year follow up. In the control group, 46% of the patients on Flourinef, 4% of the support hose patients and 12% of the diet modification patients corrected SW within the two year period. The application of an alpha-adrenergic agonist seems to have greater efficacy than a mineralo-corticoid, mechanical intervention, or dietary modification in correcting SW associated with Orthostasis.

Colombo, Joe; Iffrig, Kevan; Aysin, Elif; Aysin, Ben; Wo, Charles C; Shoemaker, William C; Colombo, Adam Author Information

Beat-to-beat changes in cardiac signals or heart rate variability (HRV) are controlled by the two branches of autonomic nervous system (ANS) in a very complex manner. Although traditional HRV (tHRV) analysis has shown to provide information on cardiac ANS control, it often fails to isolate the effect of two branches in HRV signals. This problem becomes more obvious especially at low respiratory rates since parasympathetic activity shifts into lower frequencies and overlaps the frequency interval where sympathetic region is defined. To investigate the effect of respiration in HRV analysis we have analyzed the data of 17 healthy subjects while they were performing normal breathing (NB) and deep breathing (DB). Data were analyzed and compared using both tHRV analysis and enhanced HRV (eHRV) analysis where we used respiration to locate the frequency interval of parasympathetic activity in HRV signal. eHRV analysis provided proper isolation and more accurate detection of parasympathetic and sympathetic control of the heart