Fig. 2From: Indirect measures of human vagal withdrawal during head-up tilt with and without a respiratory acidosisRelation between the change (Δ) in the high frequency (HFNU) component of heart rate variability and the change (Δ) in R–R interval when moving from supine to a head-up tilt, with (open circle, solid line) and without (crosses, dashed line) a respiratory acidosis induced by inhalation of 5%CO2 in normoxic air. Linear regression equations with accompanying coefficients of determination are shown for both relationsBack to article page