Exploring the acute cardiovascular effects of Floatation-REST

Abstract

The central nervous system (CNS) exerts a strong regulatory influence over the cardiovascular system in response to environmental demands. Floatation-REST (Reduced Environmental Stimulation Therapy) is an intervention that minimizes stimulation from the environment, yet little is known about the autonomic consequences of reducing external sensory input to the CNS. We recently found that Floatation-REST induces a strong anxiolytic effect in anxious patients while paradoxically enhancing their interoceptive awareness for cardiorespiratory sensations. To further investigate the physiologic nature of this anxiolytic effect, the present study measured acute cardiovascular changes during Floatation-REST using wireless and waterproof equipment that allowed for concurrent measurement of heart rate, heart rate variability (HRV), breathing rate, and blood pressure. Using a within-subjects crossover design, 37 clinically anxious participants with high levels of anxiety sensitivity and 20 non-anxious comparison participants were randomly assigned to undergo a 90-min session of either Floatation-REST or an exteroceptive comparison condition that entailed watching a relaxing nature film. Measures of state anxiety and serenity were collected before and after each session, while indices of autonomic activity were measured throughout each session. HRV was calculated using both time-series and frequency domain analyses. Linear mixed-effects modeling revealed a significant main effect of condition such that relative to the film condition, Floatation-REST elicited significant decreases (p < 0.001) in diastolic blood pressure, systolic blood pressure, breathing rate, and certain metrics of HRV including the standard deviation of the interbeat interval (SDNN), low-frequency HRV, and very low-frequency HRV. Heart rate showed a non-significant trend (p = 0.073) toward being lower in the float condition, especially toward the beginning of the session. The only metric that showed a significant increase during Floatation-REST was normalized high-frequency HRV (p < 0.001). The observed physiological changes were consistent across both anxious and non-anxious participants, and there were no significant group by condition interactions. Blood pressure was the only cardiac metric significantly associated with float-related reductions in state anxiety and increases in serenity. These findings suggest that Floatation-REST lowers sympathetic arousal and alters the balance of the autonomic nervous system toward a more parasympathetic state.

Clinical trial registration: [https://clinicaltrials.gov/show/NCT03051074], identifier [NCT03051074].

Keywords: anxiety; autonomic; blood pressure; heart rate variability; interoception.

FIGURE 1

Concurrent physiological measurement during Floatation-REST (Reduced Environmental Stimulation Therapy). In order to collect physiological data during the float session, small non-invasive wireless sensors were attached to the participant. To measure heart rate, breathing rate, and HRV, a Zephyr BioPatch ECG system was attached to the chest with a layer of waterproof Tegaderm. To measure blood pressure, a QardioArm monitor was placed around the upper left arm with a waterproof cast. We also collected electroencephalography (EEG) using a wireless system that was placed on the forehead, in addition to accelerometry using accelerometers attached to each wrist; these data will be part of a separate publication. Of note, participants floated without any clothing on. The same sensors and setup were also used to collect physiological data during the film condition.

FIGURE 2

Cardiovascular effects of Floatation-REST as compared to the film condition. Mean physiological response as broken down by condition (blue = float; orange = film) across all participants for panel (A) heart rate, (B) systolic blood pressure, (C) diastolic blood pressure, (D) absolute very low frequency HRV, (E) normalized low frequency HRV, (F) normalized high frequency HRV, (G) SDNN, (H) RMSSD, and (I) breathing rate. The shaded region represents the standard error of the mean. The x-axis represents time (in minutes) since the start of the float or film. With the exception of blood pressure (which were single point measurements), data are graphed in 5-min bins such that timepoint 0 is the average from 0 to 5 min, and timepoint 75 is the average from 75 to 80 min. Significant differences were found between conditions for all variables except heart rate.

FIGURE 3

Mean change in state anxiety and serenity. Mean change scores from pre- to post-float/film were computed for each group and condition (orange = film; blue = float) for panel (A) state anxiety, and (B) serenity. Error bars represent the standard error of the mean.

FIGURE 4

Significant interactions between blood pressure and change in state anxiety and serenity. Each point represents a single blood pressure measurement for one participant, and each trend line shows the correlation between blood pressure and change in state anxiety and serenity broken down for each condition (orange = film; blue = float). Significant interactions (p < 0.001) were found between (A) state anxiety change and systolic blood pressure, (B) serenity change and systolic blood pressure, (C) state anxiety change and diastolic blood pressure, and (D) serenity change and diastolic blood pressure.