Arterial Baroreceptor Physiology: Differences Between Normal Subjects and Pediatric Patients with Postural Tachycardia and Neurocardiogenic Syncope.

The arterial baroreceptor reflex in children and adolescents has not been well studied in the current literature with a lack of agreed upon normal values, particularly in postural orthostatic tachycardia syndrome (POTS) or neurocardiogenic syncope (NCS). We used the sequence method and head-up tilt test (HUTT) to evaluate baroreceptor function in 3 phases: baseline supine position for 10 min, head-up position at 70° for 30 min or until syncope, and post-tilt supine reposition for 10 min. We measured the number of baroreceptor events, baroreceptor effectiveness index (BEI), and the magnitude of sensitivity of the events at each phase of HUTT. We studied 198 individuals (49 normal subjects, 67 POTS, 82 NCS) with age ranges from 8 to 21 years. The data show a statistically significant decrease in slope and BEI in patients with POTS and NCS during the head-up phase, with an increase in activity in the lag 1 and 2 portions of all phases in patients with POTS. This study provides terminology to describe baroreceptor function and identifies the slope and BEI portions of the baroreceptor reflex as the most useful objective measures to differentiate pediatric patients with POTS and NCS from normal subjects.

Baroreceptor activity and sensitivity: normal values in children and young adults using the head up tilt test.

BACKGROUND: Baroreceptor function in children and adolescents has not been well studied in the current literature, with a lack of agreed upon normal values. The authors hypothesize that there is a significant increase in the baroreceptor activity with a decrease in the sensitivity during the upright phase in comparison to the supine phases of the head upright tilt test (HUTT) protocol. METHODS: Baroreceptor evaluation was performed using the sequence method in 49 subjects ages 8-21 years, during the 3 phases of HUTT: supine, head up, and post-tilt supine positions. Baroreceptor Effectiveness Index (BEI) and the number and slope of baroreceptor events were recorded. RESULTS: On study of the events and slope values, there was a significant difference between the three phases of the HUTT with regard to the baroreceptor activity and sensitivity. No significant difference was found in BEI. CONCLUSIONS: Our study presents normal values of baroreceptor activity, sensitivity, and BEI in pediatric patients under controlled supine and head up position. We also present new data regarding delayed heart rate responses to pressure changes in the Lag 1 and Lag 2 parameters, which may be beneficial in diagnosis and management of pediatric patients with orthostatic intolerance.