The effects of acute yoga on anxiety symptoms in response to a carbon dioxide inhalation task in women
Introduction
The practice of yoga is becoming increasingly popular as an alternative approach for reduction and prevention of anxiety symptoms.1 As a physical practice, yoga involves stretching, balance and strength movements, in addition to breathing and meditation. In certain yoga styles, such as vinyasa, there is deliberate attention on linking breath to movement to increase awareness and control of breathing and bodily sensations.2 This is particularly relevant for considering yoga as an approach for anxiety reduction(i.e., anxiolysis), given the evidence that individuals with anxiety are also more likely to have heightened sensitivity to changes in their breathing and other bodily sensations that might be misconstrued.3
There is a small body of literature examining the acute effects of yoga on anxiety using controlled experimental designs. Two existing studies 4,5 were conducted under naturalistic settings using convenience samples and reported statistically significant reductions in anxiety post-yoga. The lack of a true control condition and randomization, and risk of significant selection bias in these studies limit the quality and therefore the interpretability of the results. Regarding the chronic anxiolytic effects of yoga, a meta-analytic review6 of 6 randomized controlled studies reported evidence for small, short-term effects of yoga on anxiety compared with no treatment based on a standardized mean difference (SMD) of -0.43, and larger effects were observed compared with active comparators (SMD=-0.86). Collectively, these findings suggest that yoga might be a feasible, and effective approach for anxiety management, especially among those with clinically meaningful levels of anxiety (e.g., clinical diagnosis of an anxiety disorder).6 The research supports further studies that investigate the anxiolytic effects of yoga under controlled conditions and ideally using potential physiological correlates of this relationship that may delineate the possible mechanisms of action.
Anxiolytic effects of yoga can be studied under controlled laboratory conditions using biological human models of generalized anxiety and panic, namely the carbon dioxide(CO2) inhalation task. The CO2-inhalation task is a well-established, validated protocol for anxiety induction and reliably induces anxiety symptoms as well as panic in both healthy and clinical populations.7., 8., 9., 10., 11. The existing studies investigating the CO2-inhalation paradigm12., 13., 14., 15., 16. in the context of physical activity manipulations have all administered a single vital-capacity 35% CO2 inhalation procedure to induce panic disorder symptoms. However, no studies have used a longer (e.g., ∼5 min) CO2-inhalation protocol to assess symptoms of more generalized anxiety for a possible anxiolytic effect. The anxiety-inducing (i.e., anxiogenic) effect of this longer stimulus might mimic real-life and more generalized anxiety situations (e.g., trait anxiety and anxiety sensitivity) more accurately, and remains to be investigated.
The CO2-inhalation task to date has not been used to investigate change in response over time to control for possible baseline differences across participants before the task is administered. This can be accomplished by assessing symptom severity before and after the inhalation, therefore making the unit of analysis change in response(i.e., Δanxiety). Similar previous studies examining this anxiolytic effect only administered a single or double CO2-inhalation challenge immediately after the physical activity stimulus.12., 13., 14., 15., 16. Investigation of whether the anxiolytic effects of the stimulus sustains at later time points(e.g., 1 h post-condition) can help determine the duration of such anxiolytic effects and subsequently help inform future study designs.
This study investigated the immediate and delayed anxiolytic effects of acute (one bout) yoga, compared with an active control condition of light stretching, in response to a 5-minute anxiogenic CO2-inhalation task. Our target demographic were women, who are significantly more likely to suffer from anxiety symptoms and high anxiety sensitivity (AS), which is defined as the tendency to misconstrue physical sensations/experiences that others judge as a normal response in such a way as to elicit intense feelings of panic and fear.17 We hypothesized that yoga would significantly attenuate the anxiogenic responses to the CO2-inhalation task when compared with an active control(e.g., light stretching) condition. We further expected acute attenuations in respiratory rate(RR) and ventilation(VE) and increase in tidal volume(Vt), that would accompany the improvements in self-reported anxiety symptoms.
Section snippets
Participants
Prospective participants were recruited from the University campus, and the study protocol was initially described via telephone. If interested, potential participants were screened following study inclusion criteria (provided in Supplemental File 1), which included good overall health and no contraindications to yoga or physical activity. As our target demographic were women with increased AS, Anxiety Sensitivity Index-3 (ASI-3)18,19 was used to screen individuals with clinically meaningful
Study recruitment and enrollment
Ninety-three women initially contacted our laboratory via email or phone expressing interest in in the study. Forty-six of them expressed further interest and were screened. Twenty-four individuals met the criteria for inclusion, 2 individuals decided not to continue due to the required time commitment for the study and therefore 22 participants were scheduled for testing. Three participants were not able to complete the full 5 min of breathing of the 7.5% CO2-air mixture during the baseline
Discussion
The goal of this study was to investigate the immediate and delayed anxiolytic effects of a single session of guided yoga in response to a 5-minute anxiety-inducing CO2-inhalation task in a sample of women with high AS. Our main hypothesis was not supported in that the yoga condition did not induce a larger attenuation in anxiety symptoms compared to the control condition. However, there was an attenuation in self-reported anxiety symptoms over time independent of condition and inhalation task,
Conclusion
In conclusion, our findings do not support our primary hypothesis and suggest that both vinyasa style yoga and light stretching activities might induce similar effects of general physical activity for acute anxiolysis. However, our assessment of whether self-reported anxiety patterns follow physiological patterns associated to anxiety following an acute session of yoga indicate a disassociation of cognitive symptoms of anxiety from its physiological correlates.
Source of funding
No funding sources have been used to support this study or the preparation of this manuscript.
Declaration of Competing Interest
All authors declare no potential conflict of interest related to the data collection for the study and the preparation of this manuscript. Parts of this study were completed in partial fulfillment of the first author’s doctoral degree.
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