RESUMO
The study was undertaken on 150 healthy human subjects of both the sexes in the age group of 18- 38 years to assess the effect of graded head-up tilt (HUT) and head-reverse tilt (HRT) on sympathetic nervous system Vs parasympathetic nervous system. The tilt positions used were 00, 300, 600, 300R and 00R. The parameters and test performed were pulse rate, blood pressure, cold pressor test, QTC interval, valsalva ratio and expiratory-inspiratory (E:I) ratio. On graded head-up tilt (600) pulse rate and diastolic blood pressure showed significant increase. Cold pressor test and QTc interval showed significant increase from 300 to 600 tilt. The valsalva and E:I ratios did not show any significant change on graded HUT. On reversal of tilt all the parameters showing significant increase returned to near pre-tilt values. These responses clearly indicate that graded HUT leads to decrease in parasympathetic reactivity but increase in sympathetic reactivity, which is more significant during higher tilt levels (300 to 600). On reversal of tilt both the parasympathetic reactivity and the sympathetic reactivity i.e. autonomic reactivity return to normal pre-tilt level.