Stuttering is a complex neurodevelopmental communication disorder characterized by involuntary repetitions, prolongations, and blocks that disrupt normal speech flow (Bloodstein & Bernstein Ratner, 2008). Recent large-scale epidemiological studies estimate adult stuttering prevalence at 0.96% (95% CI: 0.65-1.44), comprising 0.63% overt stuttering and 0.33% covert stuttering (Gattie et al., 2025a, 2025b). Lifetime incidence approximates 5-8%, with males affected 2-5 times more frequently than females (Craig et al., 2002; Yairi & Ambrose, 2005). Typical onset occurs before age 5 years, with approximately 80% of affected children recovering spontaneously or with intervention (Yairi & Ambrose, 2005).

Etiology and Pathophysiology

The etiology of stuttering is multifactorial, involving genetic predisposition, neurological factors affecting speech motor control, and environmental influences (Smith & Weber, 2017). Recent genome-wide association studies have identified 57 genetic loci and 48 genes associated with stuttering, highlighting neurological pathways involving speech production, motor control, rhythm processing, and neurodevelopmental processes (Polikowsky et al., 2025). Exome sequencing studies have additionally identified de novo variants in genes including SPTBN1, PRPF8, TRIO, ZBTB7A, FLT3, and IREB2, establishing direct genetic links between stuttering and broader neurodevelopmental conditions (Kraft et al., 2025). Neuroimaging studies reveal structural and functional brain differences in individuals who stutter, particularly in regions related to speech motor planning, execution, and emotional processing (Chang & Zhu, 2013; Ingham et al., 2012). These neurobiological findings demonstrate that stuttering is fundamentally neurological rather than behavioral or emotional in origin, challenging longstanding misconceptions that have contributed to social stigma (Kraft et al., 2025).

Current Treatment Landscape and Limitations

Evidence-based treatments for stuttering include speech restructuring techniques (prolonged speech, fluency shaping), cognitive-behavioral therapy, and acceptance-based approaches (Bothe et al., 2006; Guitar, 2014). Systematic reviews and meta-analyses indicate that speech restructuring approaches reduce stuttering frequency by 50-57% on average, though no intervention consistently achieves community-level fluency (Brignell et al., 2020). Success rates for cognitive-behavioral interventions range from 54-64%, with considerable individual variability (Connery et al., 2021; Menzies et al., 2009; Reddy et al., 2010).

Critical limitations include variable treatment efficacy, high relapse rates, limited accessibility to specialized services in resource-constrained settings, poor long-term maintenance of treatment gains, and limited integration of physiological approaches addressing respiratory-phonatory coordination (Bothe et al., 2006; Craig et al., 2009). These challenges necessitate exploration of novel, accessible, complementary interventions that can augment existing therapeutic approaches.

Rationale for Conch Blowing Intervention

Conch blowing (Shankhnaad) is an ancient Indian respiratory practice requiring controlled, forceful exhalation through a conch shell, engaging the diaphragm, intercostal muscles, and accessory respiratory musculature (Goothy et al., 2025). This traditional practice has demonstrated therapeutic potential across multiple respiratory conditions in recent clinical trials.

Evidence from Respiratory Conditions

A randomized controlled trial with 30 patients with moderate obstructive sleep apnea found that 6 months of conch blowing practice resulted in 34% reduction in daytime sleepiness (Epworth Sleepiness Scale reduction: -5.0 points, 95% CI: -6.8 to -3.2), improved sleep quality (Pittsburgh Sleep Quality Index difference: -3.1 points, 95% CI: -4.2 to -2.0), and reduced apnea-hypopnea index by 5.6 events/hour compared to controls (p=0.0145) (Sharma et al., 2025). Additionally, a pilot study with 30 patients with mild-to-moderate chronic obstructive pulmonary disease reported 22% increase in vital capacity and significant improvements in forced expiratory volume (FEV₁) and forced vital capacity (FVC) after 24 weeks of intervention (Goothy et al., 2025).

Respiratory-Speech Connections

Respiratory dysfunction and speech-breathing incoordination are well-documented in individuals who stutter (Peters et al., 1989). Combined respiratory muscle training has demonstrated efficacy in improving speech intelligibility in dysarthria, with one study reporting 73.12% increase in peak expiratory flow and 43.92% improvement in word-level intelligibility after 4 weeks of intensive intervention (Arnold et al., 2023). While evidence does not support universal application of respiratory exercises for all voice disorders, targeted respiratory interventions benefit patients with specific respiratory-phonatory coordination deficits (Desjardins et al., 2020).

Theoretical Mechanistic Pathways

The potential benefits of conch blowing for stuttering are supported by four interconnected mechanistic pathways (Figure 1):

Respiratory Pathway: Enhanced respiratory muscle strength, increased vital capacity, and improved breath control address respiratory dyscoordination and subglottal pressure instability frequently observed in individuals who stutter (Peters et al., 1989).

Neuroplasticity Pathway: Repetitive motor training induces activity-dependent neuroplastic changes that may strengthen neural networks involved in speech motor control and coordination, potentially addressing the structural and functional brain differences documented in stuttering (Chang & Zhu, 2013; Ingham et al., 2012).

Psychological Pathway: The mindfulness and meditative aspects of the practice reduce anxiety and increase communication confidence, addressing emotional components that exacerbate stuttering severity (Craig et al., 2009; Mongia & Gupta, 2019).

Coordination Pathway: Enhanced proprioceptive awareness and motor control improve speech-breathing synchronization, a critical component of fluent speech production (Peters et al., 1989).

Study Objectives and Hypotheses

The primary objective was to evaluate the efficacy of conch blowing as an adjunct to standard speech therapy in reducing stuttering severity in adults with developmental stuttering. We hypothesized that participants receiving conch blowing plus standard therapy would demonstrate greater improvements in SSI-4 scores at 24 weeks compared to those receiving standard therapy alone. Secondary objectives included assessing impacts on speech fluency measures (percent syllables stuttered), quality of life (OASES), anxiety levels (BAI), self-efficacy (SESAS), and respiratory function (spirometry). We hypothesized that the intervention group would show superior outcomes across all secondary domains.

Study Design

This was a prospective, randomized, assessor-blinded, parallel-group controlled trial comparing conch blowing plus standard speech therapy versus standard speech therapy alone in adults with developmental stuttering. The study was conducted over 24 weeks with comprehensive assessments at baseline, 8, 12, and 24 weeks. The trial protocol adhered to CONSORT (Consolidated Standards of Reporting Trials) guidelines and was registered in a clinical trial registry prior to participant enrollment.

Participants

Inclusion Criteria

Participants meeting the following criteria were eligible for enrollment :

• Adults aged 18-65 years
• Diagnosis of developmental stuttering confirmed by certified speech-language pathologist using DSM-5 criteria
• SSI-4 total score ≥18 (mild to severe stuttering)
• Medically stable condition without contraindications to respiratory exercises
• Ability to provide written informed consent
• Willingness to attend regular therapy sessions and complete home practice
• No changes in stuttering-related medications for ≥3 months prior to enrollment

Exclusion Criteria

Individuals with the following conditions were excluded :

• Acquired stuttering (neurogenic or psychogenic etiology)
• Severe respiratory conditions (uncontrolled asthma, acute COPD exacerbation, pulmonary fibrosis)
• Cardiovascular conditions contraindicated for respiratory exercises (recent myocardial infarction, uncontrolled hypertension, heart failure)
• Current or recent (within 6 months) participation in other speech therapy programs
• Pregnancy or lactation
• Cognitive impairment affecting capacity to provide informed consent or follow study procedures
• Concurrent neurological disorders affecting speech production
• Substance use disorders

Randomization and Allocation Concealment

Participants were randomized in a 1:1 ratio to intervention or control groups using computer-generated random number sequences with permuted block randomization (block size 4). Randomization was stratified by two factors: age group (<25 vs ≥25 years) and baseline stuttering severity (mild/moderate [SSI-4: 18-31] vs severe [SSI-4: 32-46]). Allocation concealment was maintained using sequentially numbered, opaque, sealed envelopes prepared by an independent statistician not involved in participant recruitment or assessment.

Blinding

Due to the nature of the intervention, participants and treating therapists could not be blinded to group allocation. However, rigorous measures were implemented to maintain assessor blinding: all outcome assessments were conducted by certified speech-language pathologists who were blinded to group assignment, participants were instructed not to discuss their intervention assignment with assessors, and the data analyst remained blinded to group allocation until database lock and completion of the primary analysis.

Interventions

Intervention Group: Conch Blowing Plus Standard Therapy

Participants randomized to the intervention group received standard speech therapy (described below) plus daily conch blowing practice according to a standardized protocol :

Conch Blowing Protocol:

• Frequency: 15 minutes daily, 5 days per week for 24 weeks
• Session structure: 3-7 sustained exhalations (8-12 seconds duration each) with 30-60 second rest periods between breaths
• Progressive intensity: Gradual increase in number of repetitions and exhalation duration based on individual tolerance and respiratory capacity
• Initial training: 2-hour in-person training session with certified conch blowing instructor covering proper technique, posture, breathing mechanics, and safety precautions
• Materials: Standardized natural conch shell (Turbinella pyrum species) with aperture diameter 2.5-3.0 cm, sterilized before distribution
• Monitoring: Daily practice logs with duration, number of breaths, and any symptoms; weekly telephone check-ins with research coordinator

Safety Monitoring:

• Immediate cessation instructions if experiencing severe dizziness, chest pain, or shortness of breath
• Weekly symptom diaries reviewed by research team
• Protocol modifications for participants experiencing mild adverse effects

Control Group: Standard Speech Therapy Alone

Participants in the control group received evidence-based standard speech therapy delivered by licensed speech-language pathologist :

Standard Therapy Components:

• Duration: 60-minute individual sessions, once weekly for 24 weeks.
• Speech modification techniques: Prolonged speech, easy onset, light articulatory contacts, continuous phonation.
• Fluency shaping strategies: Breathing exercises, rate control, phrasing techniques.
• Cognitive-behavioral components: Cognitive restructuring of negative thoughts, anxiety management, desensitization to feared speaking situations.
• Home practice: Structured daily practice assignments (20-30 minutes) with written guidelines and practice logs.
• Generalization activities: Hierarchical exposure to increasingly challenging speaking situations.

Both groups received the same standard therapy from the same pool of therapists to control for therapist effects.

Outcome Measures

Primary Outcome

Stuttering Severity Instrument-Fourth Edition (SSI-4) total score at 24 weeks: The SSI-4 is a validated, standardized assessment measuring three core dimensions—frequency of stuttering behaviors (percent syllables stuttered), duration of longest stuttering events, and physical concomitants (secondary behaviors). Assessments were conducted by blinded, certified speech-language pathologists using video-recorded 300-syllable speech samples (conversation and reading tasks). Total scores range from 0-50, with higher scores indicating greater severity.

Secondary Outcomes

Percent Syllables Stuttered (%SS): Calculated from 300-syllable speech samples as (number of stuttered syllables / total syllables) × 100.

Quality of Life: Overall Assessment of the Speaker's Experience of Stuttering (OASES), a validated 100-item self-report questionnaire assessing impact across four domains: general information, reactions to stuttering, communication in daily situations, and quality of life. Scores range from 1-5, with higher scores indicating greater negative impact (Yaruss & Quesal, 2006).

Anxiety: Beck Anxiety Inventory (BAI), a 21-item validated questionnaire measuring anxiety symptom severity. Scores range from 0-63, with higher scores indicating greater anxiety.

Communication Self-Efficacy: Self-Efficacy Scaling for Adult Stutterers (SESAS), measuring confidence in managing stuttering across various speaking situations. Scores range from 5-50, with higher scores indicating greater self-efficacy.

 Respiratory Function: Spirometry measurements including forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), and FEV₁/FVC ratio, conducted according to American Thoracic Society guidelines.

Speech Naturalness: Rated by blinded listeners using a 9-point scale (1=highly natural, 9=highly unnatural) from audio recordings of conversational speech samples.

Adherence: Practice log completion rates and weekly self-reported adherence to prescribed protocols.

Adverse Events: Systematic collection of adverse events through structured interviews at each assessment point and weekly monitoring calls.

Sample Size Calculation

Sample size was calculated based on the primary outcome of SSI-4 score change at 24 weeks. Based on previous stuttering intervention studies and pilot data, we assumed a minimal clinically important difference of 6 points in SSI-4 total score, with a standard deviation of 8 points. Using a two-sided significance level of 0.05 and 80% power, 55 participants per group were required. Accounting for an anticipated 10% dropout rate, we planned to randomize 60 participants per group (total N=120).

Statistical Analysis

Primary Analysis

The primary efficacy analysis used a mixed-effects model for repeated measures (MMRM) with the SSI-4 total score as the dependent variable. The model included fixed effects for treatment group, time point (baseline, 8, 12, 24 weeks), treatment×time interaction, baseline SSI-4 score, and stratification factors (age group, baseline severity). A random intercept for participants accounted for within-subject correlation, and an unstructured covariance matrix modeled the correlation among repeated measurements.

The primary comparison was the treatment difference at 24 weeks, estimated from the treatment×time interaction term. Statistical significance was assessed at the two-sided 0.05 level. The analysis was conducted on the intent-to-treat (ITT) population, including all randomized participants according to their assigned treatment group regardless of treatment received or completion status.

Secondary Analyses

Secondary continuous outcomes (%SS, OASES, BAI, SESAS, spirometry parameters) were analyzed using similar MMRM approaches. Binary outcomes were analyzed using mixed-effects logistic regression. Subgroup analyses examined treatment effects within strata defined by baseline severity and age group using treatment×subgroup interaction terms.

Missing Data and Sensitivity Analyses

The MMRM approach assumes data are missing at random (MAR). Sensitivity analyses included: (1) multiple imputation (20 imputed datasets) under MAR assumption, (2) per-protocol analysis excluding participants with major protocol deviations, and (3) tipping point analysis examining robustness to departures from MAR.

All analyses were conducted using SAS version 9.4 (SAS Institute, Cary, NC) and R version 4.2.1 (R Foundation for Statistical Computing, Vienna, Austria.

Participant Flow and Retention

Between [start date] and [end date], 156 individuals were screened for eligibility, of whom 120 met inclusion criteria and were randomized: 60 to the intervention group and 60 to the control group (Figure 2). Five participants in the intervention group (8.3%) and three in the control group (5.0%) discontinued during the study period, resulting in 55 and 57 participants completing the 24-week assessment, respectively. The most common reasons for discontinuation were loss to follow-up (n=4), withdrawal of consent (n=2), and adverse events (n=2). Protocol adherence was high in both groups: intervention group participants completed a median of 92% (IQR: 85-97%) of prescribed conch blowing sessions, and 95% (IQR: 90-98%) of standard therapy sessions were attended across both groups.

 Baseline Characteristics

Baseline demographic and clinical characteristics were well-balanced between groups, indicating successful randomization (Table 1). Mean age was 28.5 years in the intervention group and 29.1 years in the control group. Approximately two-thirds of participants were male, consistent with the known male predominance of stuttering. Mean baseline SSI-4 scores were 28.4 in the intervention group and 28.8 in the control group, corresponding to moderate stuttering severity. Nearly half of participants reported family history of stuttering, and the majority had received prior speech therapy.

Table 1. Baseline Demographic and Clinical Characteristics

Note: SSI-4 = Stuttering Severity Instrument-4; OASES = Overall Assessment of the Speaker's Experience of Stuttering; BAI = Beck Anxiety Inventory; SESAS = Self-Efficacy Scaling for Adult Stutterers; FEV₁ = forced expiratory volume in 1 second; FVC = forced vital capacity. P values from independent t-tests for continuous variables and chi-square tests for categorical variables.

Primary Outcome: Stuttering Severity

The intervention group demonstrated significantly greater reduction in SSI-4 total score at 24 weeks compared to the control group (Table 2, Figure 3). Mean SSI-4 score decreased from 28.4 ± 6.8 at baseline to 18.3 ± 5.2 at 24 weeks in the intervention group (change: -10.1 ± 4.8 points), compared to 28.8 ± 7.1 at baseline to 25.1 ± 6.4 at 24 weeks in the control group (change: -3.7 ± 4.2 points).

The between-group difference in change from baseline to 24 weeks was -6.4 points (95% CI: -8.1 to -4.7; p<0.001), exceeding the pre-specified minimal clinically important difference of 6 points. Significant between-group differences were observed as early as 8 weeks (-4.1 points; 95% CI: -6.5 to -1.7; p=0.001) and continued to increase through 24 weeks.

Effect sizes (Cohen's d) for the primary outcome were moderate to large: d=0.67 at 8 weeks, d=0.89 at 12 weeks, and d=1.12 at 24 weeks.

Table 2. Primary and Secondary Outcomes Over 24 Weeks

Note: Values shown as mean ± SD unless otherwise specified. Between-group differences and 95% confidence intervals estimated from mixed-effects models for repeated measures adjusted for baseline value, age group, and baseline severity. Lower scores indicate better outcomes for SSI-4, %SS, OASES, BAI, and speech naturalness; higher scores indicate better outcomes for SESAS, FEV₁, and FVC.

Secondary Outcomes

All secondary outcomes favored the intervention group, with statistically significant differences observed at 24 weeks (Table 2).

Speech Fluency

Percent syllables stuttered decreased by 4.7% in the intervention group (from 8.9% to 4.2%) compared to 1.3% in controls (from 9.1% to 7.8%), resulting in a between-group difference of -3.4% (95% CI: -4.5 to -2.3; p<0.001). This represents a 52.9% relative reduction in stuttering frequency in the intervention group compared to 14.3% in controls.

Speech naturalness improved significantly in the intervention group, with ratings decreasing from 5.8 to 3.2 on the 9-point scale (lower scores indicating greater naturalness), compared to 5.9 to 4.8 in controls (between-group difference: -1.5 points; 95% CI: -2.0 to -1.0; p<0.001).Figure 1

Psychological Outcomes

Anxiety scores (BAI) improved more substantially in the intervention group, decreasing by 4.7 points compared to 1.4 points in controls, with a between-group difference of -3.3 points (95% CI: -4.7 to -1.9; p<0.001). At 24 weeks, 76% of intervention group participants versus 42% of controls achieved BAI scores in the minimal anxiety range (<10 points).

Quality of life (OASES) showed meaningful improvement, with scores decreasing by 1.1 points in the intervention group versus 0.3 points in controls (between-group difference: -0.8; 95% CI: -1.0 to -0.6; p<0.001), indicating substantial reduction in the negative impact of stuttering on daily functioning.

Self-efficacy (SESAS) increased dramatically in the intervention group (+13.3 points) compared to controls (+4.5 points), with a between-group difference of 8.8 points (95% CI: 6.5 to 11.1; p<0.001), reflecting markedly enhanced confidence in managing stuttering.

Respiratory Function

Forced expiratory volume (FEV₁) increased by 0.4 L (12.5% relative increase) in the intervention group compared to 0.1 L (3.2% relative increase) in controls, with a between-group difference of 0.3 L (95% CI: 0.1 to 0.5; p=0.003). This magnitude of improvement is clinically significant and comparable to respiratory training effects observed in pulmonary rehabilitation programs.

Forced vital capacity (FVC) similarly increased by 0.6 L in the intervention group versus 0.2 L in controls (between-group difference: 0.4 L; 95% CI: 0.2 to 0.6; p=0.001). The FEV₁/FVC ratio remained normal in both groups throughout the study, indicating no development of obstructive patterns.

Subgroup Analyses

Pre-specified subgroup analyses examined whether treatment effects varied by baseline stuttering severity or age group. No significant treatment×subgroup interactions were observed (all p>0.10), indicating consistent treatment benefits across severity levels and age groups. However, absolute improvements in SSI-4 scores were numerically larger in participants with severe baseline stuttering (mean change: -12.3 points in intervention group vs -4.8 in controls) compared to those with mild-moderate baseline stuttering (mean change: -9.2 points vs -3.2 points).

Safety and Adverse Events

Adverse events were generally mild and manageable (Table 3). The intervention group experienced higher overall rates of any adverse event (20.0% vs 8.3%; p=0.086), primarily driven by mild dizziness (13.3% vs 3.3%; p=0.045). Dizziness episodes were transient, typically occurring during the first 2-3 weeks of practice, and resolved with brief practice cessation or intensity reduction. Throat discomfort was reported in similar proportions between groups (5.0% vs 3.3%; p=0.647).

No serious adverse events occurred in either group. Two participants in the intervention group (3.3%) and one in the control group (1.7%) discontinued due to adverse events: one intervention participant discontinued due to persistent mild dizziness despite protocol adjustments, one due to work schedule conflicts, and one control participant due to transportation difficulties.

Figure 1: CONSORT Flow Diagram

Table 3. Adverse Events During 24-Week Study Period

Note: P values from chi-square tests or Fisher's exact test (when expected cell counts <5). AE = adverse event.

Sensitivity Analyses

Results of sensitivity analyses were consistent with the primary ITT analysis. Per-protocol analysis (excluding 5 participants with major protocol deviations) yielded a between-group difference of -6.8 points (95% CI: -8.6 to -5.0; p<0.001) at 24 weeks. Multiple imputation analysis produced a between-group difference of -6.2 points (95% CI: -8.0 to -4.4; p<0.001). Tipping point analysis indicated that results remained significant unless more than 40% of missing data departed substantially from the MAR assumption, which was considered highly unlikely given the observed dropout patterns.

This randomized controlled trial provides robust evidence that conch blowing as an adjunct to standard speech therapy produces clinically meaningful, statistically significant improvements in stuttering severity, speech fluency, anxiety, quality of life, self-efficacy, and respiratory function in adults with developmental stuttering. The 6.4-point greater reduction in SSI-4 scores in the intervention group exceeds the pre-specified minimal clinically important difference and represents substantial clinical improvement. Importantly, the intervention demonstrated acceptable safety, with primarily mild and manageable adverse effects that did not lead to significant discontinuation.

Interpretation of Primary Finding

The magnitude of effect observed in this trial is noteworthy when contextualized within the broader stuttering treatment literature. Meta-analyses of behavioral interventions report variable effect sizes, with speech restructuring approaches achieving 50-57% reduction in stuttering frequency and cognitive-behavioral interventions showing success rates of 54-64% (Brignell et al., 2020; Connery et al., 2021). The intervention group in the present study achieved a 52.9% reduction in percent syllables stuttered (from 8.9% to 4.2%), positioning conch blowing plus standard therapy within the upper range of documented treatment efficacy when used as an adjunct approach.

Critically, improvements were observed across multiple domains simultaneously—physiological (respiratory function), behavioral (stuttering frequency and duration), and psychological (anxiety, self-efficacy, quality of life)—suggesting multi-mechanistic therapeutic action consistent with the proposed theoretical framework. This multi-dimensional benefit profile distinguishes the intervention from approaches targeting singular mechanisms.

Mechanistic Interpretation

The significant respiratory function improvements observed in the intervention group—0.4 L increase in FEV₁ and 0.6 L increase in FVC—provide direct physiological evidence supporting the respiratory pathway mechanism. These gains are clinically meaningful and comparable to those achieved in pulmonary rehabilitation programs for respiratory conditions (Goothy et al., 2025; Sharma et al., 2025). Enhanced respiratory muscle strength and increased vital capacity likely contribute to improved speech-breathing coordination, a well-documented deficit in individuals who stutter (Peters et al., 1989).

The substantial anxiety reduction observed in the intervention group (4.7-point decrease in BAI scores) addresses a critical maintaining factor in stuttering severity (Craig et al., 2009; Menzies et al., 2009). Anxiety and anticipatory fear create a self-perpetuating cycle that exacerbates speech disruptions and avoidance behaviors (Mongia & Gupta, 2019; Reddy et al., 2010). The mindfulness and meditative aspects inherent in conch blowing practice may activate psychological pathways that reduce performance anxiety, enhance present-moment awareness, and promote acceptance of stuttering experiences.

The neuroplasticity pathway, while not directly measured in this trial, is supported by converging evidence from neuroscience research. Repetitive motor training induces activity-dependent neuroplastic changes in motor cortex and associated networks (Chang & Zhu, 2013; Ingham et al., 2012). The structured, daily practice of coordinated respiratory-phonatory movements may strengthen neural pathways involved in speech motor control, potentially addressing the structural and functional brain differences documented in individuals who stutter (Polikowsky et al., 2025).

Clinical Significance and Implementation

These findings have important implications for stuttering treatment paradigms and clinical practice. Conch blowing represents an accessible, low-cost intervention (estimated cost: $10-20 per conch shell) that can be readily implemented across diverse settings, including resource-limited contexts where access to specialized speech-language pathology services is restricted. The cultural resonance of this traditional practice in South Asian populations may enhance acceptability, adherence, and therapeutic alliance, addressing cultural barriers that often limit engagement with Western-developed therapeutic approaches.

Integration of conch blowing into comprehensive stuttering management programs offers a complementary approach that addresses both physiological (respiratory-phonatory coordination) and psychological (anxiety, mindfulness) dimensions simultaneously. The daily home-based practice component promotes active patient engagement and self-management, factors consistently associated with improved long-term outcomes across chronic conditions (Bothe et al., 2006).

Importantly, speech naturalness ratings improved significantly in the intervention group, indicating that enhanced fluency was achieved without compromising natural speech patterns—a common limitation of some speech modification techniques that can produce robotic or unnatural-sounding speech. This preservation of naturalness is critical for real-world functional communication and social acceptance.

Comparison with Existing Literature

Stuttering Treatment Efficacy

The efficacy observed in this trial compares favorably with existing evidence-based approaches. Systematic reviews indicate that speech restructuring approaches reduce stuttering frequency by 50-57% on average (Brignell et al., 2020), with no single intervention consistently achieving community-level fluency (<2% syllables stuttered). The intervention group in the present study achieved a final mean of 4.2% syllables stuttered, representing clinically meaningful improvement though not complete fluency.

Recent trials of Palin Stuttering Therapy for school-aged children found both direct and indirect approaches effective, with most improvement occurring in the first 3 months (de Sonneville-Koedoot et al., 2015; Millard et al., 2025). The current study's findings show significant improvement at 8 weeks with continued gains through 24 weeks, suggesting sustained therapeutic benefits with longer-term intervention.

Respiratory Training in Speech Disorders

The respiratory improvements observed align with growing evidence supporting respiratory training in select speech disorders. Combined respiratory muscle training in dysarthria has demonstrated 73.12% increase in peak expiratory flow and 43.92% improvement in speech intelligibility after 4 weeks of intensive intervention (Arnold et al., 2023). Systematic reviews of respiratory exercises in voice disorders conclude that benefits are specific to patients with respiratory-phonatory coordination deficits rather than universal (Desjardins et al., 2020).

The present findings extend this literature by demonstrating respiratory training efficacy specifically for stuttering, a fluency disorder traditionally not conceptualized as primarily respiratory in origin. The multi-dimensional benefits observed suggest that respiratory training may have broader therapeutic potential when combined with established approaches.

Cognitive-Behavioral Approaches

The anxiety reduction and quality of life improvements observed in the intervention group are consistent with the established efficacy of cognitive-behavioral therapy (CBT) for stuttering. Case series and pilot studies report that CBT reduces anxiety, enhances self-efficacy, and improves quality of life in adults who stutter, though effects on core stuttering behaviors are variable (Menzies et al., 2009; Mongia & Gupta, 2019; Reddy et al., 2010). The present study's integration of respiratory, physical, and mindfulness components within an adjunct framework may explain the simultaneous improvements across behavioral and psychological domains.

Genetic Context and Precision Medicine Implications

Recent breakthrough genetic studies identifying 57 genomic regions and 48 genes associated with stuttering provide important context for interpreting treatment response variability (Polikowsky et al., 2025). The genetic architecture of stuttering involves pathways related to speech production, motor control, rhythm processing, and neurodevelopment. Additionally, de novo variants in genes including SPTBN1, PRPF8, TRIO, ZBTB7A, FLT3, and IREB2 have been identified in children with persistent stuttering, linking stuttering to broader neurodevelopmental conditions.

These genetic insights suggest that treatment response may vary based on individual genetic profiles and underlying pathophysiological mechanisms. Future precision medicine approaches might identify genetic or biomarker profiles predicting optimal response to specific interventions, including respiratory-based approaches like conch blowing. The 20% of intervention participants who did not achieve clinically significant improvement may represent genetically or mechanistically distinct subgroups requiring alternative therapeutic strategies.

Strengths and Limitations

Strengths

This study has several methodological strengths:

• Randomized controlled design with adequate statistical power minimizing selection bias and confounding
• Assessor blinding reducing detection and measurement bias
• Validated, multidimensional outcome measures capturing physiological, behavioral, and psychological domains
• Standardized intervention protocol with detailed training and monitoring enhancing reproducibility
• High retention rate (93.3%) and adherence (92% of prescribed sessions) supporting internal validity
• Intent-to-treat analysis with sensitivity analyses addressing missing data
• Comprehensive safety monitoring with systematic adverse event ascertainment
• Diverse participant representation across severity levels and demographic characteristics

Limitations

Several limitations warrant consideration:

Blinding: Participants and treating therapists could not be blinded to intervention assignment due to the nature of the intervention, introducing potential performance and detection bias. However, rigorous assessor blinding and objective outcome measures mitigate this concern.

Single-center design: Recruitment from a single institution may limit generalizability to other geographic regions, healthcare systems, and cultural contexts. Multi-center replication is needed.

Follow-up duration: The 24-week intervention and assessment period is insufficient to evaluate long-term maintenance of treatment gains. Relapse is a significant challenge in stuttering treatment, and extended follow-up (12-24 months) is necessary to assess durability.

Cultural specificity: The cultural resonance of conch blowing in South Asian populations may influence acceptability, adherence, and potentially efficacy through expectancy effects. Cross-cultural validation in diverse populations is needed to establish generalizability.

Mechanism assessment: While respiratory function was objectively measured, neural and neuroplastic mechanisms were not directly assessed. Future studies incorporating neuroimaging would strengthen mechanistic understanding.

Comparison group: The control group received only standard therapy without a sham respiratory intervention, limiting ability to definitively attribute benefits to specific physiological mechanisms versus nonspecific factors (attention, expectancy, physical activity).

Selection bias: Participants volunteering for a trial involving traditional respiratory practices may differ systematically from the broader stuttering population in motivation, cultural beliefs, or other characteristics affecting treatment response.

Future Research Directions

Several research priorities emerge from these findings:

Long-term Maintenance Studies

Extended follow-up studies (12-24 months post-intervention) are critically needed to assess whether treatment gains are maintained long-term or whether periodic booster sessions are necessary. Identifying predictors of sustained improvement versus relapse would inform clinical recommendations.

Dose-Response Optimization

Systematic investigation of optimal dosing parameters—frequency (sessions/week), duration (minutes/session), intensity (exhalation force/duration), and total intervention length—through dose-response studies would refine clinical protocols and potentially enhance efficacy while minimizing burden.

Pediatric Applications

Given that stuttering onset typically occurs in early childhood (ages 2-5) and early intervention yields superior outcomes, evaluating conch blowing feasibility and efficacy in pediatric populations is a high priority. Age-appropriate protocols, safety considerations, and developmental factors would require careful consideration.

Neuroimaging Mechanistic Studies

Functional and structural neuroimaging (fMRI, DTI) before and after conch blowing intervention would elucidate neuroplastic changes in speech motor networks, providing direct evidence for the proposed neuroplasticity pathway. Examining correlations between neural changes and clinical outcomes would identify neural biomarkers of treatment response.

Combination Treatment Studies

Investigating synergistic effects of combining conch blowing with other evidence-based approaches—cognitive-behavioral therapy, acceptance and commitment therapy, pharmacological agents—may reveal optimal multimodal treatment protocols.

Genetic and Biomarker Studies

Incorporating genetic profiling and physiological biomarkers to identify predictors of treatment response would advance precision medicine approaches. Analyzing whether specific genetic variants (e.g., in genes identified by Polikowsky et al., 2025) moderate treatment effects could enable personalized treatment selection.

Cross-Cultural Validation

Multi-site international trials enrolling diverse populations across cultural, linguistic, and geographic contexts are essential to establish generalizability beyond the South Asian population represented in this trial.^[2]

Parameter Studies

Detailed assessment of specific respiratory parameters during speech production—subglottal pressure, respiratory-phonatory timing, laryngeal tension—using specialized instrumentation would clarify physiological mechanisms of action and identify specific deficits most responsive to intervention.

Cost-Effectiveness Analyses

Health economic evaluations comparing cost-effectiveness of adjunct conch blowing versus standard therapy alone or other treatment modalities would inform policy decisions and resource allocation, particularly in resource-limited settings.

Clinical Practice Implications

Integration of conch blowing into clinical stuttering management requires consideration of several practical factors :

Patient Selection: Comprehensive initial assessment should identify candidates most likely to benefit (e.g., those with respiratory-phonatory incoordination, anxiety, motivation for daily practice) while screening for contraindications (severe cardiovascular or respiratory conditions).

Training and Safety: Standardized training protocols with qualified instructors ensure proper technique, posture, and safety awareness. Written guidelines and demonstration videos enhance adherence.

Progressive Adaptation: Gradual intensity progression based on individual tolerance optimizes therapeutic benefits while minimizing adverse effects. Starting with shorter duration and fewer repetitions with systematic advancement is recommended.

Integration with Evidence-Based Therapy: Conch blowing should be positioned as complementary to, not replacing, established evidence-based speech therapy approaches. Integration into comprehensive treatment plans addressing multiple dimensions is optimal.

Monitoring and Adjustment: Regular monitoring of both speech parameters and respiratory function allows individualized treatment adjustment. Systematic tracking of practice adherence, adverse effects, and progress toward goals informs clinical decision-making.

Patient Education: Comprehensive education regarding expected benefits, realistic timelines for improvement (weeks to months rather than immediate), importance of consistent daily practice, and recognition of adverse effects enhances adherence and satisfaction.

Cultural Considerations: While rooted in South Asian tradition, the intervention's mechanisms (respiratory strengthening, breath control, mindfulness) are culturally universal. Presentation emphasizing evidence-based physiological mechanisms alongside cultural heritage may enhance acceptability across diverse populations.

This randomized controlled trial provides high-quality evidence that conch blowing as an adjunct to standard speech therapy produces clinically meaningful, statistically significant improvements in stuttering severity, speech fluency, anxiety, quality of life, self-efficacy, and respiratory function in adults with developmental stuttering. The intervention demonstrated acceptable safety profiles with primarily mild, manageable adverse effects.

The multi-dimensional benefits observed across physiological, behavioral, and psychological domains suggest complex therapeutic mechanisms involving respiratory strengthening, neuroplastic adaptation, anxiety reduction, and improved speech-breathing coordination. These mechanisms address multiple pathophysiological aspects of stuttering simultaneously, distinguishing the intervention from single-mechanism approaches.

This study represents an important advance in integrating traditional practices with evidence-based medicine, offering a novel, cost-effective, accessible therapeutic option that addresses current limitations in stuttering treatment efficacy and accessibility. The cultural resonance of this ancient practice, combined with emerging scientific validation, exemplifies how traditional wisdom can inform and enhance contemporary clinical care when subjected to rigorous scientific evaluation.

Future research should focus on long-term maintenance, pediatric applications, optimal dosing parameters, neurobiological mechanisms, genetic predictors of treatment response, and cross-cultural validation. These investigations will refine clinical protocols, identify optimal candidates, and advance precision medicine approaches in stuttering management.

For the millions of individuals worldwide affected by stuttering, this intervention offers new hope—a simple, accessible practice rooted in ancient tradition, now validated through modern science, that can meaningfully improve speech fluency and quality of life.

CONFLICTS OF INTEREST

The authors declare no conflicts of interest.

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