Repetitive pain experiences modulate feedforward control of hemodynamics and modification by nitrous oxide/oxygen inhalation in humans

Figures

• 

  Fig. 1. Timelines for the repetitive cardiovascular response tests in which the participants immersed their hand in cold water (∼4 °C) as pain stimulation for 2 min (CPT). The experiment consists of three trials: the first CPT (CPT[1st]), the second CPT (CPT + CC), and the placebo test with warm water (∼35 °C) (PLCB + CC) under two conditions: room air (RA) and 40 % nitrous oxide/oxygen (N2O) inhalation. Participants performed the 5-min baseline, 30-s countdown (CD) before the stimulation, 2-min CPT/PLCB, and 3-min recovery in each trial.

• 

  Fig. 2. Time course changes (Δ) from baseline in systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and finger arterial stiffness (β-stiffness) and cumulative values during CPT/PLCB in CPT[1st], CPT + CC, and PLCB + CC under RA and N2O. Values are means ± S.D. *, vs BL at p < 0.05; #, vs CPT [1st] at p < 0.05; †, vs PLCB + CC at p < 0.05.

• 

  Fig. 3. Changes (Δ) in SBP (A), DBP (B), HR (C), and β-stiffness (D) by 30-s CD before the stimulation in CPT[1st], CPT + CC, and PLCB + CC under RA and N2O, respectively. Values are means ± S.D. A significant difference from RA is indicated at the level of p < 0.05 (Tukey test).

• 

  Fig. 4. Relationship between subjective pain intensity and cardiovascular changes during pain stimulation and that between subjective pain intensity and feedforward cardiovascular changes after conditioning by experiencing pain stimulation. Linear regression analysis of the inter-individual relationships between visual analog scale (VAS) and cumulative values of ΔHR (A) and Δβ-stiffness (B) and those between VAS and ΔHR (C) and Δβ-stiffness (D) during CD under RA. Bivariate correlations were examined using the Pearson correlation coefficient.

• 

  Fig. 5. Cardiac baroreflex sensitivity (BRS) determined from the sequence method of the short-term HR and SBP variabilities for 15 participants at baseline and around the onset of CPT/PLCB under RA and N2O in CPT[1st] (A) and CPT + CC (B), respectively. Values are means ± S.D. A significant difference from baseline at the level of p < 0.05 (Tukey test) was observed around the onset of CPT under RA in CPT + CC.

• 

  Fig. 6. The schema illustrates the co-relationship between central command before and after pain experience during CD, peripheral reflex induced by pain stimulation, and the effectors involved in the pressor mechanism during CPT under RA and 40 % N2O.