Abstract
Objective: Gagging is a problem for many dental patients, as well as patients undergoing medical procedures, such as intubation. Research to date on the gag reflex has been limited by a lack of objective measures for measuring this reflex.
Materials and Methods: A validated quantitative method was used to measure if acupuncture or transcutaneous electrical acupoint stimulation (TEAS) at Pericardium 6 (PC 6) and Stomach 36 (ST 36) suppressed the gag reflex, compared with a sham placebo. The subjects were 60 healthy adults randomly chosen to receive acupuncture, TEAS, or sham-TEAS on PC 6, located on the forearm, and ST 36, located on the lower leg. The gag reflex was measured by inserting a saliva ejector slowly down each participant's throat to determine the maximum tolerance of the gag reflex; the insertion length was used as an index of this reflex.
Results: There was a significant difference in pre- and postintervention insertion lengths in all groups (paired t-test; all groups; P < 0.001). The differences in the insertion length among the groups (P = 0.76) and the interaction effect (group × time) were not significant (P = 0.79; 2-way analysis of variance).
Conclusions: This study suggested that PC 6 and ST 36 stimulation was no different than placebo for alleviating the gag reflex.
Keywords: acupuncture, gagging, gag reflex, transcutaneous electrical acupoint stimulation, placebo
Introduction
The gag reflex is considered to be a normal, protective physiologic mechanism that occurs in order to prevent foreign objects or noxious material from entering the pharynx, larynx, or trachea.1 A proportion of the population has a profound and exaggerated gag reflex that can cause acute limitation of such patient's ability to accept dental treatment and the clinician's ability to provide it. The exact prevalence of the problem in relation to dental treatment is unknown.2 Despite a range of management strategies, some patients cannot accept even simple dental treatment.
The origin of gagging has been categorized as either somatic (initiated by sensory-nerve stimulation from direct contact) or psychogenic (modulated by higher centers in the brain). In somatic gagging, touching a trigger area induces the reflex. Although trigger areas are specific to individuals, sites such as the lateral border of the tongue and certain parts of the palate innervated by the glossopharyngeal nerve commonly elicit the gag reflex.1 Once triggered, the movement of the reflex is conducted by the motor limb of the vagus nerve.
According to Deadman's Manual of Acupuncture (2nd edition), the Ren, Lung, Spleen, Kidney, and Heart meridians end at the tongue. For throat issues, the Stomach, Gall Bladder, Large Intestine, and Small Intestine meridians are used.3
Psychogenic gagging can be induced without direct contact and the sight, sound, smell, or even the thought of dental treatment can be sufficient to induce the gag reflex in some individuals.1 Ramsay et al.4 suggested that bad dental experiences result in patients expecting—either consciously or subconsciously—to gag during future similar episodes. An unambiguous division between a somatic and a psychogenic gag reflex is not possible. Thus, some patients who have a severe somatically induced gag reflex at the dentist are able to brush their teeth, eat, and place other objects in their own mouths without problems. Other factors, such as nasal obstruction, gastrointestinal disorders, heavy smoking, ill-fitting partial or full dentures, variations in the anatomy of the soft palate, and previous unpleasant experiences during dental treatment may indirectly contribute to the exaggerated gag reflex.4–8 In an uncontrolled study in 2001,7 it was shown that auricular acupuncture was able to control the severe gag reflex of 10 patients sufficiently well to allow dental treatment to be carried out.
Acupuncture has been used successfully to control the gag reflex9–11 A controlled study showed that acupuncture at the Conception Vessel 24 (CV 24), located on the chin, could reduce the gag reflex in patients having transesophageal echocardiography.12 In a controlled study by Lu et al.,11 it was established that acupuncture at Pericardium 6 (PC 6), located on the forearm, had a significant effect to reduce the gag reflex.
Research on gag reflex has been challenging due to an inability to measure gag reflex reliably in an objective manner. In 2018, Goddard et al. developed a validated method of measuring the gag reflex using a saliva ejector.13 This method was used in a 2020 study to determine if the gag reflex was associated with tactile sensitivity and psychologic characteristics.14 This was the first known study to use this method of gag-reflex measurement to determine the effects of an intervention intended to reduce this reflex. The aim of the present study was to compare 3 interventions to reduce gag reflex. The interventions were at PC 6 and Stomach 36 (ST 36) as follows: (1) acupuncture; (2) transcutaneous electrical acupoint stimulation (TEAS); and (3) sham-TEAS. The hypothesis was that the treatments would increase gag tolerance in the following stepwise manner: Acupuncture > TEAS > Sham-TEAS.
Materials and Methods
Sixty healthy volunteers were recruited via a local recruitment effort at the University of California–Los Angeles (UCLA) School of Dentistry. Each subject gave informed consent prior to the procedure. The study was approved by the UCLA's institutional review board (IRB#: 18-000473).
The required minimum sample size was calculated with G*Power 3.1 statistical software.15 A total sample size of 42 subjects (14 per group) was required to achieve the target effect size of 0.25 at a power of 0.80, and an α level of 0.05. Using a simple randomization schedule of 60 sets of 1 number each, ranging from 1 to 3, the subjects were randomized to 1 of 3 groups: (1) acupuncture; (2) TEAS; and (3) sham-TEAS. All interventions were performed at PC 6 and ST 36.
A total of 56 subjects completed the study. Four subjects dropped out, 1 from the acupuncture group due to panic and dizziness, 1 from the TEAS group declined after giving consent, and 2 from the sham-TEAS group, one with sweating and the other declining after giving consent.
Measurement of Gag Reflex
A blinded examiner performed the gag-reflex measurement, as described by Karibe et al.13 A standard saliva ejector with a stopper made of heavy-body addition silicone impression putties was inserted into each participants' mouth at the maxillary central incisor, and gradually guided down the participant's throat along the palate. Each participant was asked to inform the examiner when maximum tolerance has been reached by pushing a button that beeped. The examiner then stopped inserting the saliva ejector, removed it, and measured the insertion distance of the saliva ejector from the maxillary central incisor with digital calipers. This distance was recorded as an index of the gag reflex.13 Subjects were also be asked to report the severity of their gagging on a numeric rating scale (NRS) of 1–10. The subjects rated their own unpleasant feelings (unpleasantness) when their maximum tolerance had been reached. The ratings of unpleasantness were obtained using the NRS ranging from 1 (not at all) to 10 (very strong).
Experimental Procedure
The examiner then left the room and the subject underwent the appropriate treatment (acupuncture, TEAS or sham-TEAS based on group allocation) for a total of 20 minutes each. The same acupuncturist performed the treatments. Following the treatment procedure, the acupuncturist removed the needles or TEAS device and the original examiner reentered the room to perform the final gag reflex measurement as described above.
Group 1 (Acupuncture)
Sterile needles were inserted into PC 6 and ST 36 bilaterally and retained for a total of 20 minutes. Halfway through the treatment, the needles were manipulated in order to recreate the acupuncture sensation. The needles were then removed after 20 minutes of treatment and prior to the second gag-reflex measurement.
Groups 2 and 3 (TEAS and Sham-TEAS, Respectively)
In both cases, gel pads were affixed to the acupuncture points PC 6 and ST 36, bilaterally. A standard transcutaneous electrical nerve stimulator (TENS) unit (TENS 3000, Roscoe Medical Inc., Middleburg Heights, OH, USA) was used to provide the TEAS and sham-TEAS interventions. The unit was set to provide a modulatory amplitude with a pulse width of 150 μs and a pulse rate of 50 Hz. For subjects assigned to TEAS only, the amplitude of the TENS device was gradually increased up to a maximum setting of 8/10, with the subject asked to notify the examiner as soon as any sensation was noticed. Once a gentle buzzing sensation was noticed, the amplitude was reduced slightly for comfort and the device remained active with this setting for 20 minutes. The pads were removed prior to the second gag-reflex measurement.
For the sham-TEAS group, identical units with severed (and physically but not electrically reattached) electrical wires were used. This allowed the unit to flash an identical light with no current delivered. The subjects were told that no sensation was required. The amplitude was turned up to a maximum setting of 8/10 and left there for 20 minutes, then the device was turned off and the pads were removed.
Final Gag Measurement
Following the treatment procedure, the acupuncturist removed the needles or TENS pads and device, and the original examiner reentered the room to perform the final gag-reflex measurement as described above. Subjects were also asked to report the severity of their gagging again on an NRS scale of 1–10.
Statistical Analysis
Before performing any analyses, the data set was tested for normality using the Shapiro–Wilk test. The ages of the participants and the NRS scores were not normally distributed (Shapiro–Wilk test; P < 0.01); however, the data were normally distributed in terms of insertion length (Shapiro–Wilk test; P > 0.05). A Kruskal–Wallis test and a Fisher's exact test were used to assess the distributions of ages and sexes among the groups.
Paired t-tests were used to compare the insertion lengths before and after the interventions to assess the gag reflex in each group. A 2-way repeated-measures analysis of variance (ANOVA) was also used to assess the differences in insertion length among the groups and the changes in the insertion length in each group. There was 1 among-subject's factor (group) with 3 levels (acupuncture, TEAS, and sham-TEAS), and 1 within-subject's factor (time) with 2 levels (before an intervention and after an intervention). A 1-way ANOVA was used to compare the percentage of change between pre- and postintervention insertion lengths among the groups. A Wilcoxon signed-rank test was used to compare the NRS scores before and after the interventions to assess the severity of gagging in each group. The Kruskal–Wallis test was used to assess the differences in the NRS scores among the groups. A P-value <0.05 was considered significant. All analyses were performed using IBM SPSS Statistics for Windows, version 21.0 (IBM Corp., Armonk, NY, USA).
Results
The ages and sex distributions of each group is shown in Table 1, with no significant difference found among the 3 groups (P = 0.41 and 0.71, respectively). The mean insertion lengths before and after the interventions are shown in Table 2. A significant difference in pre- and postintervention insertion lengths was observed in all groups (P < 0.001). A 2-way ANOVA revealed that differences in the insertion length among the groups (P = 0.76) and the interaction effect (group × time) were not significant (P = 0.79). The primary effect of time (before intervention versus after intervention) was significant for the insertion length (F [1, 54] = 88.83; P < 0.001).
Table 1.
Age and Sex Distribution of Each Group
| Characteristic | Acupuncture (n = 19) | TEAS (n = 18) | Sham-TEAS (n = 19) | P-value |
|---|---|---|---|---|
| Age (yrs) | 40.5 ± 16.1 | 34.8 ± 10.1 | 38.6 ± 11.3 | 0.41 |
| Female/male (n) | 13/6 | 14/4 | 13/6 | 0.71 |
Data are presented as mean ± standard deviation. Data were analyzed using the Kruskal–Wallis test and Fisher's exact test.
TEAS, transcutaneous electrical acupoint stimulation; yrs, years.
Table 2.
Mean Insertion Length Pre- and Postintervention in Each Group
| Intervention | Preintervention insertion length (mm) | Postintervention insertion length (mm) | P-value |
|---|---|---|---|
| Acupuncture | 75.3 ± 8.0 | 80.5 ± 9.5 | <0.001 |
| TEAS | 76.5 ± 11.6 | 82.6 ± 11.3 | <0.001 |
| Sham-TEAS | 74.2 ± 10.2 | 80.1 ± 10.3 | <0.001 |
Data are presented as mean ± standard deviation. Data were analyzed using a paired t-test.
TEAS, transcutaneous electrical acupoint stimulation.
The mean percentage of change between pre- and postintervention insertion lengths is shown in Table 3, with no significant difference found among the 3 groups (P = 0.72).
Table 3.
Mean Percentage of Change Between Pre- and Postintervention Insertion Length in Each Group
| Effect | Acupuncture | TEAS | Sham-TEAS | P-value |
|---|---|---|---|---|
| Percentage of change (%) | 6.8 ± 5.5 | 8.3 ± 6.0 | 8.3 ± 7.8 | 0.72 |
Data are presented as mean ± standard deviation. Data were analyzed using a 1-way analysis of variance.
TEAS, transcutaneous electrical acupoint stimulation.
The mean NRS scores before and after the interventions are shown in Table 4. No significant difference was observed in the pre- and postintervention NRS scores within each group (P = 0.80, 0.81, and 0.27, respectively). Additionally, there were no differences among the groups in pre- and post-NRS ratings (Kruskal–Wallis test; P = 0.60 and 0.77, respectively).
Table 4.
Mean Numeric Rating Scale Scores Before and After Intervention in Each Group
| Preintervention NRS | Postintervention NRS | P-value | |
|---|---|---|---|
| Acupuncture | 3.7 ± 2.0 | 3.6 ± 1.6 | 0.80 |
| TEAS | 3.9 ± 1.5 | 3.9 ± 1.4 | 0.81 |
| Sham-TEAS | 3.6 ± 2.2 | 3.9 ± 2.3 | 0.27 |
Data are presented as mean ± standard deviation. Data were analyzed using a Wilcoxon signed-rank test.
NRS, numeric rating scale; TEAS, transcutaneous electrical acupoint stimulation.
Discussion
There are numerous potential mechanisms by which acupuncture may have an effect on the gag reflex. Some potential mechanisms include local inhibition of somatic-nerve signaling, inhibition of motor-efferent (vagus) nerve signaling, the relaxation response, and the placebo effect. Of these, the PC 616 and ST 3617 were chosen due to their known effects on vagal-nerve activity. In addition, PC 6 is well-known for its effects on nausea.18 Sham-TEAS was chosen as an intervention to help control for the placebo effect.
Although this study produced a null effect of PC 6 and ST 36 stimulation on the gag reflex, no conclusions can be drawn regarding other acupoints, such as auricular acupoints and CV 24, that have demonstrated efficacy for treating the gag reflex.9–12 These acupoints, along with other local points—such as ST 6, San Jiao (SJ 17), SJ 21 or Gall Bladder 2—may work via different mechanisms of action—either central or somatic—but were not feasible in this particular pilot study, given the constraints of TEAS pad placement. Research into the use of these acupoints is warranted despite the null conclusions of this study.
The electrical parameters of TEAS were chosen to minimize differential endorphin responses, as low (2 Hz) and high (100 Hz) frequencies are known to elicit distinct endorphin responses. For this pilot study, an intermediate frequency was used to provide a pleomorphic effect. Future researchers may do well to consider varying the electrical stimulation to induce varying responses, and also to consider direct electrical stimulation of the inserted needles (electroacupuncture). Furthermore, this study demonstrated an unexpected pre- and postintervention measurement difference that was not seen on prior validation studies of this method of gag-reflex measurement. As reported by Karibe et al.,13 a saliva ejector can be used to determine the individual maximum tolerance of the gag reflex during the tactical stimulation of the anterior and posterior faucial pillar and soft palate to measure the gag reflex objectively. This validation study showed no differences in length of insertions during 2 separate measurements punctuated by rest periods.
The present study, by contrast, revealed a reduction in the gag reflex among all of the groups, including the placebo group. This opens the possibility of the following scenarios: (1) a noninert placebo by which the sham-TEAS provides a therapeutic effect without electrical stimulation; (2) a pronounced placebo effect relating the expectation of improvement to true reductions in gag reflex via subjective/central mechanisms; and (3) differences in the gag-reflex measurement protocol from that reported by Karibe et al.13 All three of these potential scenarios should be addressed in future studies.
The known association of gagging with fear, anxiety, and stress19–23 can explain the second scenario. Additionally, 20 minutes elapsed between the initial measurement and the last measurement, compared with the 5-minute interval studied by Karibe et al.13 It is possible that this increased time allowed the subjects to relax and potentially have reduced stress and reduced the gag reflex. This, plus other placebo factors, is particularly difficult to account for because the results of the NRS scores showed no significant differences in subjective severity of gagging between pre- and postintervention despite the measured objective differences.
Finally, there is concern that use of healthy subjects may have led to an inadequately powered study. Other studies had patients with gagging problems, such as being unable to have an upper alginate impression,24–28 for their inclusion criteria. Further studies with an inclusion group with gagging problems would shed light on this issue.
An overactive gag reflex continues to be a problem among the dental and medical communities, and, while prior research did find evidence that auricular or CV 24 stimulation could reduce the gag reflex, this study suggested that PC 6 and ST 36 stimulation was no different than placebo.
Conclusions
This study supports continued use of relaxation and stress-reduction strategies in dental settings for treating the gag reflex while further mechanistic studies on the specific acupuncture points are conducted.
Acknowledgments
The authors would like to thank Emperor's College of Traditional Oriental Medicine and UCLA School of Dentistry for the use of their facilities.
Author Disclosure Statement
No financial conflicts of interest exist.
Funding Information
Funding was provided by the Gerald Oppenheimer Family Foundation and the Shirley Hui Memorial Fund.
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