Adapted from: Peper, E. & Harvey, R. (2022). Nausea and GI discomfort: A biofeedback assessment model to create a rational for training. Biofeedback, 50(1), 24–32. https://doi.org/10.5298/1081-5937-50.1.05
Abdominal discomfort and pain such as functional abdominal pain, acid reflux or irritable bowel affects many people. Teaching slower biofeedback-assisted HRV breathing with biofeedback is a useful strategy by which the person may be able to reduce symptoms. This essay provides detailed instruction for a first session assessment for clients who have abdominal discomfort (functional abdominal pain). Descriptions include how the physiological recording can be used to understand a possible etiology of the illness, to create a biological/evolutionary based explanation that is readily understood by the client, and finally to offer self-regulation suggestions to improve health.
Background of abdominal discomfort (irritable bowel syndrome, acid reflux, functional abdominal pain, recurrent abdominal pain)
Irritable bowel syndrome (IBS) affects 7% to 21% of the general population in Western cultures with a global prevalence estimated at around 11% (Fairbrass, Costantino, Gracie, & Ford, 2020). The chronic symptoms (i.e., lasting more than 30 days) usually include abdominal cramping, discomfort or pain, bloating, loose or frequent stools and constipation, which can significantly reduce the quality of life (Chey et al., 2015). A precursor of IBS in children is called recurrent abdominal pain (RAP), which affects 0.3% to 19% of school children (Chitkara et al., 2005). Both IBS and RAP appear to be functional illnesses, as no organic causes have been identified to explain the symptoms. IBS and RAP are contrasted to various types of diseases such as Crohn’s disease, inflammatory bowel disease or ulcerative colitis.
Multiple factors may contribute to IBS, such as genetics, food allergies, previous treatment with antibiotics, infections, psychological status and stress. More recently, dietary factors contributing to changes in the intestinal and colonic microbiome resulting in small intestine bacterial overgrowth have been suggested as another risk factor (Dupont, 2014). Generally, standard medical treatments (reassurance, dietary manipulation and of pharmacological therapy) are often ineffective in reducing IBS symptoms (Chey et al., 2015). On the other hand, complementary and alternative approaches such as biofeedback-assisted relaxation techniques (Davidoff & Whitehead, 1996; Goldenberg et al., 2019; Stern et al. 2014), autogenic training (Luthe & Schultz, 1969) and cognitive therapy are more effective than traditional medical treatment (Vlieger et al., 2008).
Biofeedback-assisted relaxation training typically moderates IBS or RAP symptoms by restoring balance in the nervous system (sympathetic/parasympathetic autonomic balance), such as through heart rate variability (HRV) breathing training. For example, Sowder et al. (2010) as well as Sun et al. (2016) demonstrated that functional abdominal pain can be reduced with HRV feedback training. In most cases, increased vagal tone was achieved by breathing at about six breaths per minute. While Taneja et al. (2004) reported that yogic breathing decreased diarrhea-predominant irritable bowel syndrome symptoms significantly more than conventional treatment in a randomized control study.Sympathetic/parasympathetic balance can be enhanced by increasing HRV, which occurs when a person breathes at their resonant frequency, which is usually 5–7 breaths per minute. For most people, the HRV training means breathing at much slower rate. A benefit of slow abdominal breathing appears to be a self-control strategy that can reduce symptoms of IBS, RAP and similar functional abdominal pain symptoms.
Mastery of effortless diaphragmatic breathing can be affected by injury, surgery or similar insults to the abdominal area (Peper et al., 2015). In addition, dysregulation of diaphragm, which is enervated by the phrenic nerve and the vagus nerve, along with dysregulation of other abdominal muscles appears to be associated with irritable bowel syndrome (Bordoni & Morabito, 2018). It is likely that slower biofeedback-assisted HRV breathing training restores abdominal muscles and diaphragmatic movement, theoretically by tonic and phasic regulation of the phrenic and vagal nerve activity (cf. Marchenko et al., 2015; Streeter et al., 2012). The theory, simply stated, is that HRV breathing training at an individual’s resonant frequency produces increases in regulatory neurotransmitters, particularly gamma amino butyric acid (GABA). Many of our students who complain of abdominal discomfort report reductions of symptoms following HRV breathing training.
Consistently for more than 40 years, we have taught undergraduate students a semester-long integrated stress management program that includes modified progressive relaxation, slow diaphragmatic breathing and changing internal language as outlined in the book, Make Health Happen, by Peper, Gibney & Holt (2002). At the end of each semester, numerous students report that their anxiety, gastrointestinal distress and other symptoms related to self-described IBS or RAP have decreased or disappeared (Peper et al., 2014; Peper, Miceli, & Harvey, 2016; Peper, Mason, Huey, 2017; Peper et al., 2020). Abdominal discomfort is prevalent experience of distress by college students. In our recent survey of 99 undergraduate students, 41% self-reported abdominal discomfort (25% irritable bowel or acid reflux), 86% self-reported anxiety, 70% neck and shoulder tension and 48% headaches. After practicing slower breathing (i.e., typically directing them to breath abdominally at a rate of about six breaths a minute) and focus on slower exhalation and allowing the air to flow in without effort as the abdominal wall expands, as a homework assignment for a week, many reported that their symptoms significantly decreased (Peper, Harvey, Cuellar, & Membrila, in press).
Case example illustrating how to use the physiological recording to guide the client discussion and provide motivation
A 16-year-old high school junior suffered from abdomen discomfort for years. The symptoms mainly consisted of frequent constipation, and when it occurred, great discomfort from nausea. After having been diagnosed and undergoing all the necessary tests by the gastroenterologist, there was no identifiable cause of the chief complaints. Biofeedback was suggested as an alternative to medications for symptom reduction. During the biofeedback assessment and training session, the client discussed what she would like to learn from the session. It was challenging for her to respond to those questions. Not being able to report what the client would like from a training session is also a very common experience when working with students. A useful strategy is to describe experiences of other students that the clients could relate to, and imply that their abdominal discomfort is somewhat commonplace in other students.
Discussed during the session was the link between being very sensitive and reactive to other people’s feeling and being concerned about what others think of her. The client nodded her head in agreement. When describing herself, she discussed being very perfectionistic using a scale from being lackadaisical/undemanding to being perfectionistic (i.e., self-oriented perfectionism, self-worth contingencies, concern over mistakes, doubts about actions, self-criticism, socially prescribed perfectionism, other-oriented perfectionism, hypercriticism; see Smith, Saklofske, Stoeber, & Sherry, 2016).
Furthermore, the client sat slouched in the chair. Possibly her slouched posture implied a state of powerlessness instead of empowerment, a state of being ready to react and protect (Carney, Cuddy, & Yap, 2010; Cuddy, 2012; Peper, Lin, & Harvey, 2017).
Working hypotheses. The client was very sensitive and continuously reacted to external and internal signals with sympathetic arousal, while masking her reactions. These ongoing flight/flight responses would decrease intestinal peristalsis and abdominal blood flow, which would result in nausea, constipation and abdominal distress. Namely, the body reacts to the stimuli as signals of danger and blood flow is shunted away from the abdomen into the large muscles to run and fight. To paraphrase Stanford University professor Robert Sapolsky (2004): Why should the body digest food and repair itself, if it is going to be the predator’s lunch? It is only when we are safe that we can digest and regenerate.
The session began by exploring how pressure on the abdomen could potentially affect experiences of nausea and abdominal distress. After explaining how the diaphragm descends and how abdominal content in the stomach can be displaced (spread out) during inhalation, we systematically changed her posture by placing and adjusting a small pillow behind her middle back so that she could sit tall. The tall posture resulted in an open feeling of empowerment not felt during slouching. She observed that breathing was slightly easier and felt there was more space in her abdomen. As she began to feel more comfortable during the training session, we discussed the impact of posture on the body. We also discussed the relationship between thoughts of perfectionism and abdominal discomfort. The discussion also included an exploration of why some people tend to curl-up and slouch in a protective posture (e.g., head down to protect the neck region and big bones of the arms and legs positioned to protect the core organs) when feeling self-consciousness or perfectionistic about body image.
Biofeedback monitoring for assessment
Psychophysiology was recorded with multichannel physiological system (Procomp Infinity System running Biograph Infinity software version 6.7.1, Thought Technology Ltd). Respiration was monitored with strain-gauge sensors placed around the abdomen and thoracic regions (for a discussion on sensor placement see Peper et al., 2016 and Chu et al., 2019). Blood volume pulse was recorded with the sensor placed on the left thumb. The thumb was used because the participant had small and cold fingers (for a discussion about blood volume pulse, see Peper et al, 2007 and Peper, Shafer, & Lin, 2010). Skin conductance was recorded with the sensor wrapped around the left index and middle fingers with the electrodes on the finger pads (for a discussion about skin conductance and normal values, see Khazan, 2019, and Shafer et al, 2016).
After sensors were attached and the signals explained, the client sat comfortably while looking at the screen. Unexpectedly the clinician clapped his hands and made a loud noise. The client reacted with a momentary startle and smile. The physiological response, showed an increase in skin conductance, decrease in pulse amplitude, decrease in abdominal diameter, and increase in heart rate, is shown in Figure 1.
Figure 1. Physiological response to a loud noise (clap) (1) increased skin conductance, (2) decrease in pulse amplitude, (3) decrease in decreased abdominal circumference, and (4) increased heart rate and decreased heart rate variability.
The client was aware that she reacted to the clap; however, she was totally unaware how much her body responded. The computer screen display of her physiological reaction made the invisible visible. It provided the opportunity to discuss how various body reactions related to heart rate, breathing, and skin conductance could contribute to experiences of abdominal discomfort.
She was unaware that skin conductance did not return to baseline levels for more than 20 minutes. An elevated skin conductance level may mean that the body’s reaction to the hand-clap noise triggered a defense reaction and maintained the increased sympathetic activity for more than 20 minutes. Having a sustained flight/fight reaction to external stimuli such as a hand-clap would most likely affect digestive and peristalsis processes, contributing to symptoms found in IBS and RAP. The observations made during biofeedback monitoring led to a discussion of how sympathetic activation affects the gastrointestinal track.
Blood volume pulse amplitude decreased, which indicated a decrease in blood flow through her hands, which would decrease hand temperature and again indicated a systemic sympathetic activation.
Abdominal circumference decreased, which indicated that she tightened her abdominal muscles as a protective response to the hand-clap. She was unaware of the abdominal muscles tightening; however, she stated that she was aware that her breathing had changed. The abdominal muscle, which pulled the abdomen in, took almost two minutes to relax. The sustained muscle constriction around the abdomen increased pressure around the core organs, which may contribute to ongoing abdominal discomfort. A fight-flight reaction includes body bracing (e.g. tightened muscles, head down to protect the neck, big bones of arms and legs curled to protect core organs), and she confirmed that she experienced neck and shoulder tensions.
The discussion of abdominal muscle tension led to another discussion of how holding your stomach in may relate to self-image. For example, tight clothing can contribute to constricted movement around the abdomen. Wearing corsets contributed to psychophysiological symptoms, mainly for women in the late 19th and early 20th centuries, during a time when women who wore very tight corsets were diagnosed with neurasthenia. Simply stated, neurasthenia was characterized as a condition of mental and/or physical fatigue with at least two of the following symptoms: dyspepsia, dizziness, muscular aches or pains, tension headaches, inability to relax, irritability and sleep disturbance.
“Dyspepsia” was the commonly reported symptom of neurasthenia, which included upset stomach, a gnawing or burning stomach pain, heartburn, bloating, and or burping, nausea, and vomiting. The constricted waist region that resulted from wearing a corset in the name of fashion compromises the functions of both digestion and breathing. When the person inhales, the abdomen cannot expand as the diaphragm is flattening and pushing downward. Thus, the person is forced to breathe more shallowly by lifting their ribs; this increases neck and shoulder tension as well as the risk of anxiety, heart palpitation, and fatigue (Cohen & White, 1947; Courtney, 2009).
It also can contribute to abdominal discomfort since the abdomen is being squeezed by the corset and forcing the abdominal organs upward. Even architects of the Victorian era recognized a need for a place to position a chair or chaise lounge, such as at the top of some stairs, because people wearing corsets could faint, pass out or otherwise experience breathlessness through the effort of climbing the stairs with restrictive clothing around their abdomen (Melissa, 2015). Many of these symptoms could be easily reduced by wearing looser clothing and learning slower diaphragmatic breathing. In modern times, a related phenomenon results when people wear items of clothing that are too tight around their waist or abdomen (e.g., tight jeans) in service to fashion trends often labeled as designer jean syndrome (MacHose & Peper, 1991; Stonehewer, 2009). Similarly, when people wear garments that are too tight around their chest or thoracic region (e.g., tight vests) in service to external protection (e.g., athletes, industrial workers, police or soldiers wearing heavy, restrictive gear), then restrictive ventilatory disorders can occur (Harty et al., 1999). Simply stated, when the muscles related to breathing are restricted from moving, respiration is affected.
The client’s heart rate increased and stayed high for more than 30 seconds. The first decrease in heart rate at about 20 seconds after the hand-clap was a long sigh of relief as breathing (i.e., oxygen/carbon dioxide exchange) started again. It took almost 90 seconds before breathing and heart rate returned to normal as reflected by measures of HRV. The computer screen showing increased heart rate was reviewed with the client to explain how her body reacted with a fight-flight response to the hand-clap, as well as how regulating breathing through biofeedback training could lower the heart rate and reduce the sympathetic activation and enhance the parasympathetic activation.
Body responds to cognitive stressful thoughts
After discussion about the psychophysiological response to the hand-clap (a physical external stressor) and how other external stressors (e.g., startling noise) or internal stressors (e.g., perfectionistic ruminations) could trigger a similar response of abdominal muscle tightening, the assessment was repeated by having her relax and then think about a mental stressor, as shown in Figure 2.
Figure 2. Physiological responses to thinking about a past stressor (1) increased skin conductance, (2) decreased pulse amplitude, (3) decreased abdominal circumference, and (4) increased heart rate and decreased HRV.
The physiological response pattern to thinking about a past stressor was similar to the bodily reaction to a loud noise. The skin conductance increased and blood volume pulse amplitude decreased immediately after hearing (e.g., anticipating) the task of evoking/thinking of a past stressor. Most likely, the initial response was triggered by performance anxiety, then 6 seconds later the heart rate increased and breathing changed as she began experiencing the somatic reaction evoked by the recall of a negative stressor. The recordings also showed that her pulse amplitude decreased. The decrease in pulse amplitude suggested that her hands would probably become colder, which was confirmed by her self-report that she often experienced cold hands and feet. She reported being aware of the feeling an emotional reaction, but mainly noticing the change of breathing in her chest, and she was unaware of the abdominal changes. The client was surprised by how her body reacted to emotional thoughts. The recording viewed on the computer screen demonstrated objectively that her thoughts (initial performance anxiety) had a physical effect on her body. Specifically, experiencing the emotions that were evoked by recalling the stressful memory had a direct effect on the body in the same way that a physical external threat leads to a fight-flight response.
Building a psychophysiological model
Using these recorded computer images reflecting physical reactions to the hand clap and emotional thoughts, the discussion focused on how abdominal discomfort could be the result of activating a normal biological survival response. Survival responses would occur hundreds of times throughout a day, especially when worrying. Each thought would evoke the response, and the awareness of body reaction would evoke another reaction. Similar to how awareness of blushing amplifies blushing.
The client shared that she was very sensitive and reactive especially when other people were upset. She reported feeling “cursed” by their sensitivity and reactivity. The linguistic metaphor that could be used to describe her reactions is “she could not stomach what was going on.”
The discussion about physiological reactions provided the client with a model how her disorder (IBS and RAP) could have developed and been maintained over the years. The model matched her subjective experience: when stressed, the discomfort often increased. The discussion shifted to reframing her internal labels. Instead of describing her sensitivity as a curse, the sensitivity was reframed and labeled a gift; namely, she could sense many people’s emotional reactions, to which they would react in a variety of ways. She just needed to learn how to manage this sensitivity. Once she learned to manage it, she would have many advantages in interpersonal relations at home and at work. She would be able to sense what other people are experiencing. By reframing her symptoms as a result of a survival physiological response pattern, it reduces self- blame and offers solutions about how to master and change reactions and thereby have more control in the world.
Training to demonstrate control is possible.
The discussion was followed by teaching her diaphragmatic breathing in sitting and lying down positions. As she had no history of abdominal injuries, similar to many of our students, she rapidly demonstrated slower diaphragmatic breathing as shown in Figures 3 and 4.
Figure 3. The client practiced a few slower diaphragmatic breaths in the sitting and reclining position, which increased heart rate variability, decreased skin conductance and increased blood volume pulse amplitude.
Figure 4. Practicing slower diaphragmatic breathing at about six breaths per minute in a reclining position increased HRV.
With tactile coaching, she demonstrated that she could breathe at about six breaths per minute with the heart rate increasing during inhalation and decreasing during exhalation. She reported feeling more relaxed and that the sensations of nausea had disappeared. Additionally, her hands felt warmer. This recording provided proof that there was hope and that she could do something about her body’s psychophysiological responses.
The discussion focused on how breathing affecting heart rate variability. Namely, if she allowed exhalation to occur without effort, her heart rate decreased (the vagal response of slowing the heart) and thereby increased the parasympathetic activation that would support digestion and gastrointestinal functioning. Often when people practice effortless diaphragmatic breathing, abdominal noises (borborygmus)– the gurgling, rumbling, or squeaking noise from the abdomen–occur and indicate that intestinal activity is being activated, and that food, liquids and digestive juice are moving through the intestines. It is usually a positive indicator that the person is relaxing and sympathetic activity has been reduced.
During the last part of session, we reviewed how posture affects physiology, emotions and cognitions, as well as how posture and breathing would be the first step in beginning to reduce symptoms and enhance health. To provide additional information using video and bibliotherapy/education, we suggested that she watches the embedded videos in the blogs listed at the end of the article.
Recommendations for future sessions and home practice
The recommended strategies for future sessions would focus on teaching the client to master slow diaphragmatic breathing and practicing that for 10–20 minutes per day. The teaching techniques would incorporate imagery to imagine air flowing down their arms and legs as she exhaled. . More importantly, the focus would shift to generalize the skill during the day; namely, whenever she would become aware of feeling stressed or observed herself holding her breath or breathing in her chest, she would use that as the cue to shift to slower abdominal breathing. Had the client continued training, future sessions would focus on mastering slower diaphragmatic breathing. The training would include relaxing the lower abdominal muscles during inhalation, increasing control of HRV, practicing imagining stress and use image to trigger slower breathing, and cognitive reframing practices to interrupt worrying and promote self-acceptance. The final goal is to generalize these skills into daily life as illustrated in the successful cases described in the following blogs
Blogs on posture:
Bordoni, B. & Morabito, B. (2018). Symptomatology correlations between the diaphragm and irritable bowel syndrome. Cureus, 10(7), e3036. https://doi.org/10.7759/cureus.3036
Carney, D. R., Cuddy, A. J., & Yap, A. J. (2010). Power posing: brief nonverbal displays affect neuroendocrine levels and risk tolerance. Psychological Science, 10, 1363-1368. https://dx.doi.org/10.1177/0956797610383437
Chitkara, D. K., Rawat, D. J., & Talley, N. J. (2005). The epidemiology of childhood recurrent abdominal pain in Western countries: a systematic review. American journal of Gastroenterology, 100(8), 1868–1875. https://doi.org/10.1111/j.1572-0241.2005.41893.x
Chu, M., Nguyen, T., Pandey, V., Zhou, Y., Pham, H. N., Bar-Yoseph, R., Radom-Aizik, S., Jain, R., Cooper, D. M., & Khine, M. (2019). Respiration rate and volume measurements using wearable strain sensors. NPJ digital medicine, 2(1), 1–9. https://doi.org/10.1038/s41746-019-0083-3
Cohen, M. E. & White, P. D. (1947). Studies of breathing, pulmonary ventilation and subjective awareness of shortness of breath (dyspnea) in neurocirculatory asthenia, effort syndrome, anxiety neurosis. Journal of Clinical Investigation, 26(3), 520–529. https://doi.org/10.1172/JCI101836
Courtney, R. (2009). The functions of breathing and its dysfunctions and their relationship to breathing therapy. International Journal of Osteopathic Medicine, 12, 78–85. https://doi.org/10.1016/j.ijosm.2009.04.002
Cuddy, A. (2012). Your body language shapes who you are. Technology, Entertainment, and Design (TED) Talk, available at: http://www.ted.com/talks/amy_cuddy_your_body_language_shapes_who_you_are
Davidoff, A. L., & Whitehead, W. E. (1996). Biofeedback, relaxation training, and cognitive behavior modification: Treatments for functional GI disorders, In Olden, K, W. (ed). Handbook of Functional Gastrointestinal Disorders. CRC Press, 361–384.
Dupont, H. L. (2014). Review article: evidence for the role of gut microbiota in irritable bowel syndrome and its potential influence on therapeutic targets. Alimentary Pharmacology & Therapeutics, 39(10), 1033–1042. https://doi.org/10.1111/apt.12728
Fairbrass, K. M., Costantino, S. J., Gracie, D. J., & Ford, A. C. (2020). Prevalence of irritable bowel syndrome-type symptoms in patients with inflammatory bowel disease in remission: a systematic review and meta-analysis. The Lancet Gastroenterology & Hepatology, 5(12), 1053–162. https://doi.org/10.1016/s2468-1253(20)30300-9
Goldenberg, J. Z., Brignall, M., Hamilton, M., Beardsley, J., Batson, R. D., Hawrelak, J., Lichtenstein, B., & Johnston, B. C. (2019). Biofeedback for treatment of irritable bowel syndrome. Cochrane Database of Systematic Reviews, (11). https://doi.org/10.1002/14651858.CD012530.pub2
Harty, H. R., Corfield, D. R., Schwartzstein, R. M., & Adams, L. (1999). External thoracic restriction, respiratory sensation, and ventilation during exercise in men. Journal of Applied Physiology, 86(4), 1142–1150. https://doi.org/10.1152/jappl.19220.127.116.112
Khazan, I. (2019). A guide to normal values for biofeedback. Biofeedback, 47(1), 2–5. https://doi.org/10.5298/1081-5937-47.1.03
Luthe, W. & Schultz, J. H. (1969). Autogenic Therapy Volume II: Medical Applications. Grune & Stratton.
MacHose, M., & Peper, E. (1991). The effect of clothing on inhalation volume. Biofeedback and Self-Regulation, 16(3), 261–265. https://doi.org/10.1007/BF01000020
Marchenko, V., Ghali, M. G., & Rogers, R. F. (2015). The role of spinal GABAergic circuits in the control of phrenic nerve motor output. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 308(11), R916–R926. https://doi.org/10.1152/ajpregu.00244.2014
Melissa. (2015). Why women fainted so much in the 19th century. May 20, 2015. Downloaded October 2, 2021. http://www.todayifoundout.com/index.php/2015/05/women-fainted-much-19th-century/
Peper, E., Gibney, K. H., & Holt, C. F. (2002). Make Health Happen—Training Yourself to Create Wellness. Kendall/Hunt Publishing Company.
Peper, E., Gilbert, C. D., Harvey, R. & Lin, I-M. (2015). Did you ask about abdominal surgery or injury? A learned disuse risk factor for breathing dysfunction. Biofeedback. 34(4), 173–179. https://doi.org/10.5298/1081-5937-43.4.06
Peper, E., Groshans, G. H., Johnston, J., Harvey, R., & Shaffer, F. (2016). Calibrating respiratory strain gauges: What the numbers mean for monitoring respiration. Biofeedback, 44(2), 101–105. https://doi.org/10.5298/1081-5937-44.2.06
Peper, E., Harvey, R., Cuellar, Y., & Membrila, C.(in press). Reduce anxiety. NeuroRegulation.
Peper, E., Harvey, R., Lin, I. M., Tylova, H., & Moss, D. (2007). Is there more to blood volume pulse than heart rate variability, respiratory sinus arrhythmia, and cardiorespiratory synchrony? Biofeedback, 35(2), 54–61. https://www.researchgate.net/publication/259560204_Is_There_More_to_Blood_Volume_Pulse_Than_Heart_Rate_Variability_Respiratory_Sinus_Arrhythmia_and_Cardiorespiratory_Synchrony
Peper, E., Lin, I-M, & Harvey, R. (2017). Posture and mood: Implications and applications to therapy. Biofeedback, 35(2), 42–48. https://doi.org/10.5298/1081-5937-45.2.03
Peper, E., Lin, I-M, Harvey, R., Gilbert, M., Gubbala, P., Ratkovich, A., & Fletcher, F. (2014). Transforming chained behaviors: Case studies of overcoming smoking, eczema and hair pulling (trichotillomania). Biofeedback, 42(4), 154–160. https://doi.org/10.5298/1081-5937-42.4.06
Peper, E., Mason, L., Harvey, R., Wolski, L, & Torres, J. (2020). Can acid reflux be reduced by breathing? Townsend Letters-The Examiner of Alternative Medicine, 445/446, 44–47. https://www.townsendletter.com/article/445-6-acid-reflux-reduced-by-breathing/
Peper, E., Mason, L., Huey, C. (2017). Healing irritable bowel syndrome with diaphragmatic breathing. Biofeedback, 45(4), 83–87. https://doi.org/10.5298/1081-5937-45.4.04
Peper, E., Miceli, B., & Harvey, R. (2016). Educational model for self-healing: Eliminating a chronic migraine with electromyography, autogenic training, posture, and mindfulness. Biofeedback, 44(3), 130–137. https://www.aapb.org/files/publications/biofeedback/2016/biof-44-03-130-137.pdf
Peper, E., Shaffer, F., & Lin, I. M. (2010). Garbage in; Garbage out—Identify blood volume pulse (BVP) artifacts before analyzing and interpreting BVP, blood volume pulse amplitude, and heart rate/respiratory sinus arrhythmia data. Biofeedback, 38(1), 19–23. https://doi.org/10.5298/1081-5937-38.1.19
Sapolsky, R. (2004). Why Zebras Don’t Get Ulcers. Owl Books ISBN: 978-0805073690
Shaffer, F., Combatalade, D., Peper, E., & Meehan, Z. M. (2016). A guide to cleaner electrodermal activity measurements. Biofeedback, 44( 2), 90–100. https://doi.org/10.5298/1081-5937-44.2.01
Smith, M. M., Saklofske, D. H., Stoeber, J., & Sherry, S. B. (2016). The big three perfectionism scale: A new measure of perfectionism. Journal of Psychoeducational Assessment, 34(7), 670–687. https://doi.org/10.1177/0734282916651539
Sowder, E., Gevirtz, R., Shapiro, W., & Ebert, C. (2010). Restoration of vagal tone: a possible mechanism for functional abdominal pain. Applied Psychophysiology and Biofeedback, 35(3), 199–206. https://doi.org/10.1007/s10484-010-9128-8
Stern, M. J., Guiles, R. A., & Gevirtz, R. (2014). HRV biofeedback for pediatric irritable bowel syndrome and functional abdominal pain: A clinical replication series. Applied Psychophysiology and Biofeedback, 39(3), 287–291. https://doi.org/10.1007/s10484-014-9261-x
Stonehewer, L. (2009). Dysfunctional breathing for women’s health physiotherapists. Journal of the Association of Chartered Physiotherapists in Women’s Health, 104, 38–40. https://pogp.csp.org.uk/system/files/stonehewer_hr.pdf
Streeter, C. C., Gerbarg, P. L., Saper, R. B., Ciraulo, D. A., & Brown, R. P. (2012). Effects of yoga on the autonomic nervous system, gamma-aminobutyric-acid, and allostasis in epilepsy, depression, and post-traumatic stress disorder. Medical hypotheses, 78(5), 571–579. https://doi.org/10.1016/j.mehy.2012.01.021
Sun, X., Shang, W., Wang, Z., Liu, X., Fang, X., & Ke, M. (2016). Short-term and long-term effect of diaphragm biofeedback training in gastroesophageal reflux disease: An open-label, pilot, randomized trial. Diseases of the Esophagus, 29(7), 829–836. https://doi.org/10.1111/dote.12390
Taneja. I., Deepak, K.K., Poojary, G., Acharya, I.N., Pandey, R.M., & Sharma, M.P. (2004). Yogic versus conventional treatment in diarrhea-predominant irritable bowel syndrome: a randomized control study. Appl Psychophysiol Biofeedback, 29(1), 19-33. https://doi.org/10.1023/b:apbi.0000017861.60439.95
Vlieger, A. M., Blink, M., Tromp, E., & Benninga, M. A. (2008). Use of complementary and alternative medicine by pediatric patients with functional and organic gastrointestinal diseases: results from a multicenter survey. Pediatrics, 122(2), e446–e451. https://doi.org/10.1542/peds.2008-0266