Peripheral Blood Flow Responses to Pain Following a Hypnosis Intervention in Sickle Cell Disease

Introduction: Vaso-occlusive pain crises are considered the "hallmark" of sickle cell disease (SCD). Persistent occurrence is thought to lead to changes in the peripheral and central nervous system, which can then in turn lead to changes in pain sensitivity. Imaging studies have shown that hypnotic analgesia can reduce activity in supraspinal areas of the "pain matrix." To date there are no published studies looking at the effectiveness of hypnosis in altering pain perception in patients with SCD. The purpose of this study was to investigate changes in peripheral blood flow in response to a 30-minute hypnosis intervention and its relationship to pain sensitivity.

Methods: To assess the effectiveness of increasing vasodilation, a laboratory based, single session hypnosis protocol was administered to a sample of 14 SCD patients and 14 healthy controls. Continuous readings for SpO2, pulse rate and pulse waveform was monitored using a pulse oximetry transducer placed on the left thumb. Bio-behavioral pain measures were collected during a standardized pain protocol before and after a hypnosis session, performed by a trained therapist. The protocol consisted of assessing pain tolerance and threshold via a heat probe (˚C) for "pain task 1", preceded by an anticipation period. "Pain task 2" consisted of assessing pain intensity via the same heat probe (˚C) on a 1-100 visual analog scale (VAS), preceded by another anticipation period.

Results: To investigate blood-flow responses to their respective baseline (baseline vs. hypnosis), all recorded signal following these two periods was normalized respectively. Independent sample t-tests between both normalized anticipation and pain responses periods revealed controls showed no response to hypnosis for anticipation period 1(t_(23.42) = .184, p = .855, d = .072), but SCD patients showed a large increase in blood flow (t_(16.99) = 4.189, p = .0006, d = 1.79). Neither controls (t_(21.05) = .00, p = .994, d = .003) or SCD patients (t_(19.99) =.718, p = .481, d = .305) showed an effect of hypnosis in response to pain task 1. Neither controls (t_(23.96) = -.139, p = .890, d = -.05) or SCD patients (t_(18.82) = 1.035, p = .313, d = .441) showed a response to anticipation period 2, but the effect size reveals that this may be due to a lack of power. Neither controls (t_(16.52) = .258, p = .799, d = .101) or SCD patients (t_(19.63) = p = .5375, d = .268) showed no changes in response to hypnosis for pain task 2. Independent sample t-tests revealed no significant difference in pain threshold (t₍₁₃₎ = 0.941, p = .364, d = .251) or tolerance (t₍₁₃₎ = 0.937, p = 0.366, d = 0.250) in SCD patients before and after hypnosis. Differences in pain ratings were marginal but showed a decrease with medium effect (t₍₁₃₎ = -1.5315, p = 0.150, d = 0.409). The same tests revealed significant decreases in controls for pain threshold (t₍₁₃₎ = 2.825, p = 0.01, d = .755), pain tolerance (t₍₁₃₎ = 2.482, p = 0.02, d = 0.664), and pain rating (t₍₁₃₎ = 2.950, p = 0.01, d = .789).

Conclusion: Results revealed that hypnosis may be an effective treatment in helping manage vasoconstriction in SCD as a response to cognitive appraisals about pain, as well as reducing pain sensitivity. The data presented provide preliminary clinical evidence of the use of hypnosis as a treatment method to improve vasodilation in SCD patients and decreasing pain crises, thus increasing overall quality of life.