Heart rate variability in prolonged head up tilt in healthy adults

Abstract

Tilt table testing is taken as a safe and effective modality for subjecting a person to strong orthostatic stimulus. HRV (Heart rate variability) has the potential to provide valuable insight into physiological variations occurring in relation to postural changes. This study compares the supine basal, entire 30 minutes (Prolonged tilt), early 10 and last10 minutes (early and late tilt respectively) tilt HRV among themselves.13 healthy adults were subjected to 30 minutes head up tilt at 60 degree angle. 10 minutes basal supine HRV was compared with entire 30 minutes, early 10 minutes and last 10 minutes tilt HRV. Stastical analysis was done using one way Anova with repeated measures and LSD post hoc tests. Among the time domain measures Mean±SEM RR interval in seconds showed significant decrease during prolonged, early and late tilt (0.73±0.02,0.72±0.02,0.69±0.02 respectively) as compared to the basal (0.81±0.02).The Mean±SEM heart rate in beats per minute showed significant increase during prolonged, early and late tilt (84.13±2.49, 84.64 ±2.71, 87.69±2.70 respectively) as compared to basal (75.22±2.60). The parametric frequency domain measures showed significant difference between basal and late tilt. The Mean±SEM Lf power in normalised units or LFNU was 40.95±5.31 and 70.20±6.75 between basal and late tilt respectively, and LF/HF%was 2.27±0.50 and 11.33±1.92 between basal and late tilt respectively. They showed significant increase during the late tilt. The Hf power in percentage or HF % (35.41±5.23 and 9.80±2.14 between basal and late tilt respectively) and Hf power in normalised units or HFNU (32.19±6.13 and 8.68±1.74 between basal and late tilt respectively) showed significant decrease during late tilt. The non parametric frequency domain measures showed similar significant difference between late tilt and basal, late tilt and prolonged tilt as well as between late tilt and early tilt. This indicates sympathetic predominance during prolonged HUT.