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Mouth closure during sleep worsened airflow in some patients with obstructive sleep apnea (OSA), according to a study that cast doubt on a viral trend for "mouth taping" in an attempt to treat the condition.

When researchers manually closed the mouths of 54 study participants during a drug-induced sleep, overall inspiratory flow rose by 27.8 percentage points (1.0 L/min, 95% CI 0.4-1.9), a benefit limited to those with a moderate amount of mouth breathing, reported Daniel Vena, PhD, of Brigham & Women's Hospital and Harvard Medical School in Boston, and colleagues in .

However, manually keeping the mouth closed actually worsened airflow by some 40 percentage points for the 12 patients who relied the most on mouth breathing, dropping it by 1.86 L/min (95% CI -3.1 to -0.6) among those with more than 2.2 L/min oral airflow on a normal breath during sleep.

Given that disrupted airflow, "the study suggests caution in universally applying therapies to prevent mouth breathing in OSA patients," Vena told MedPage Today. "Further clinical studies are required. Meanwhile, clinicians should closely monitor the effect of therapies for preventing mouth breathing to ensure they are not worsening the condition."

According to a accompanying the study, thousands of TikTok videos are touting the value of mouth closure on OSA symptoms. Videos on the social media platform that use the hashtag #mouthtape -- referring to taping the mouth shut with surgical tape to prevent mouth breathing -- have drawn 7 million views, the commentary says, although it doesn't cite a source for the data.

"There's limited objective data available on forced mouth closure during sleep, and worse, on the lack of protocols and regulations to ensure its appropriate implementation," wrote commentators Jeffrey Chadwick, DDS, MSc, PhD, of the University of Texas Health Science Center at Houston, and Andrew Huang, MD, of Baylor College of Medicine in Houston.

The nonrandomized clinical study didn't specifically examine mouth taping, but instead explores its presumed effect – obstruction of mouth breathing.

Staff members induced sleep via medication in order for routine clinical endoscopies to be performed, and staff members briefly closed the mouths of subjects in order to measure the impact on airflow. "The drug-induced sleep aspect is important because it allowed us to apply pressure to the chin, using our hands to close the mouth, without the patient waking up. We knew the mouth was closed when we felt the teeth touch," Vena said.

"We did mouth closure on alternating breaths," he added. "On breath 1, we closed the mouth. Once that breath was completed, we released and allowed the mouth to resume the relaxed position for breath 2. At the end of breath 2, we then closed the mouth again for breath 3 and relaxed for breath 4. We did this as many times as we could up to about 15 breaths or so."

This strategy allowed researchers to determine whether patients were aroused due to changes in airflow.

Mouth closure was harmful to mouth-breathers and patients with severe obstruction in the soft palate, part of the airway between the nasal cavity and the oral cavity, Vena said.

"Patients with severe soft palate obstruction tended to mouth breathe the most and had a negative response to mouth closure," he told MedPage Today. "Our explanation is that severe soft palate obstruction makes it harder to breathe along the nasal route, which passes through the soft palate. These patients compensate by breathing through the mouth to bypass the soft palate obstruction. When you close the mouth and force them to breathe nasally, the obstruction at the soft palate leads to reduced airflow."

On the other hand, the most benefit tended to be among patients with collapse at the oropharyngeal lateral walls in the throat behind the mouth, he said.

The commentary authors wrote that "these findings highlight the danger of recommending the universal application of mouth taping during sleep."

For the 2021-2022 study, researchers enlisted 54 patients who were a median 55 years old, with a BMI of 28.9, and apnea-hypopnea index 26.9 events/hour, and 72.2% of whom were male. Another 54 patients were excluded because they would wake up when their mouths were closed, and 12 because their airflow was already too limited.

Researchers reported that the mouth-closure maneuver successfully stopped almost all mouth breathing.

In 32 patients with moderate levels of mouth-breathing (pre-maneuver oral airflow 0.05-2.2 L/min), mouth closure was beneficial, increasing air flow by 53.1 percentage points (2.0 L/min). It had no impact on those who usually breathed through their nose during sleep.

The researchers noted study limitations including the fact that sleep was induced by a drug (propofol). Also, it was an acute outcome of mouth closure in single breaths, "which does not reflect the longer-term outcome of mouth closure," they added. In addition, "we did not measure the contribution of nasal obstruction to open-mouth breathing, which may be important."

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