Reduced Environmental Stimulation in Anorexia Nervosa: An Early-Phase Clinical Trial

Abstract

Reduced Environmental Stimulation Therapy (REST) alters the balance of sensory input to the nervous system by systematically attenuating sensory signals from visual, auditory, thermal, tactile, vestibular, and proprioceptive channels. Previous research from our group has shown that REST via floatation acutely reduces anxiety and blood pressure (BP) while simultaneously heightening interoceptive awareness in clinically anxious populations. Anorexia nervosa (AN) is an eating disorder characterized by elevated anxiety, distorted body representation, and abnormal interoception, raising the question of whether REST might positively impact these symptoms. However, this approach has never been studied in eating disorders, and it is unknown whether exposure to floatation REST might worsen AN symptoms. To examine these possibilities, we conducted an open-label study to investigate the safety and tolerability of REST in AN. We also explored the acute impact of REST on BP, affective symptoms, body image disturbance, and interoception. Twenty-one partially weight-restored AN outpatients completed a protocol involving four sequential sessions of REST: reclining in a zero-gravity chair, floating in an open pool, and two sessions of floating in an enclosed pool. All sessions were 90 min, approximately 1 week apart. We measured orthostatic BP before and immediately after each session (primary outcome), in addition to collecting BP readings every 10 min during the session using a wireless waterproof system as a secondary outcome measure. Each participant's affective state, awareness of interoceptive sensations, and body image were assessed before and after every session (exploratory outcomes). There was no evidence of orthostatic hypotension following floating, and no adverse events (primary outcome). Secondary analyses revealed that REST induced statistically significant reductions in BP (p < 0.001; Cohen's d, 0.2-0.5), anxiety (p < 0.001; Cohen's d, >1) and negative affect (p < 0.01; Cohen's d, >0.5), heightened awareness of cardiorespiratory (p < 0.01; Cohen's d, 0.2-0.5) but not gastrointestinal sensations, and reduced body image dissatisfaction (p < 0.001; Cohen's d, >0.5). The findings from this initial trial suggest that individuals with AN can safely tolerate the physical effects of REST via floatation. Future randomized controlled trials will need to investigate whether these initial observations of improved anxiety, interoception, and body image disturbance occur in acutely ill AN populations.

Clinical trial registration: ClinicalTrials.gov; Identifier: NCT02801084 (April 01, 2016).

Keywords: body awareness; body image; eating disorder; floatation therapy; interoception; interoceptive awareness; stress.

FIGURE 1

REST at LIBR. (Left) Chair-REST. (Middle) Floatation-REST in an open pool. (Right) Floatation-REST in an enclosed pool. The open (middle) and enclosed (right) pools are both 2.44 m in diameter and 0.28 m in depth. The domed pool contains an enclosure with a 2.44-m domed ceiling. Each pool contains 11 in. of reverse osmosis water saturated with ∼816 kg of USP grade Epsom salt (magnesium sulfate), creating a dense saltwater solution that is maintained at a specific gravity of ∼1.26, allowing participants to effortlessly float on their back while the water hovers just above the ears. The temperature of the water and the temperature of the air are both calibrated to match the temperature of the skin (∼35.0°C). For more details about how our float pools were engineered to minimize exteroceptive sensory stimulation to the nervous system, please see Feinstein et al. (2018a; 2018b).

FIGURE 2

Approximate timeline of assessments during each REST session. Sensor application included the application of a wireless blood pressure monitor and waterproof cast. The total duration of each session was approximately 3.5 h.

FIGURE 3

Consort flow diagram. This figure illustrates the number of participants included in enrollment, the number allocated to the REST intervention, the number withdrawn, and the number included in the data analysis.

FIGURE 4

Individual orthostatic blood pressure changes. (A) The figure displays each individual’s change in systolic blood pressure (BP) from lying to standing at the end of each REST session. There was no evidence of systolic orthostatic hypotension in any individual, i.e., a reduction in systolic BP below 20 mmHg (red dashed line). (B) The figure displays each individual’s change in diastolic BP from lying to standing at the end of each REST session. There was no evidence of diastolic orthostatic hypotension in any individual, i.e., a reduction in systolic BP below 10 mmHg (red dashed line). Note that BP was not measured during the second pool session and is therefore unlisted.

FIGURE 5

Group summary of orthostatic blood pressure measures. Each figure displays the mean and standard error for the lying, sitting, and standing blood pressure measurements, at pre- and postsession intervals for the (A) chair-REST (B) the first and (C) final floatation-REST sessions.

FIGURE 6

Blood pressure responses during REST. (A) Systolic BP. (B) Diastolic BP. Significant reductions in both systolic and diastolic BP occurred between the 25th and 65th minutes of REST.

FIGURE 7

Effect size estimates for the secondary outcome measures. Note that there were no blood pressure measures taken during the second pool float, and therefore that field is blank. A table showing the exact effect size estimates and associated confidence intervals is located in the Supplementary Material.