Characterization of Flow-resistant Tubes Used for Semi-occluded Vocal Tract Voice Training and Therapy.
Simeon L Smith, Ingo R Titze
PMID 27133001WHAT IT FOUND
Tube diameter, not length, mainly controls pressure behind the lips during semi-occluded voice training.
Diameter 2.5 to 4.9 mm gave higher pressures at speech-like flows, and mouth shape changed pressure only slightly.
Key findings
01Tube diameter is the main dimension controlling flow resistance and oral pressure. For a 4.9 mm tube, doubling length from 6 cm to 12 cm raised pressure by about 20%, while doubling diameter from 3.3 mm to 6.5 mm reduced pressure by a factor of 10.
02Tubes from 2.5 to 4.9 mm diameter gave higher pressures at speech-like flows, and tested dimensions could produce pressures from 0 to 7 kPa at flows from 0 to 1 L/s.
03Mouth shape behind the tube had a small effect on pressure, but the effect grew when tube diameter approached the upstream pipe diameter.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
It tested tubes with compressed air, not patients, so it does not show what pressure helps a person's voice. The upstream pipe only approximates the mouth behind the lips, and the setup used a square reduction, not a real mouth. Discrepancies were largest for the 1.8 mm and 8.1 mm tubes, while the equations were more accurate for the common 2 to 6 mm range. Tube entrance shape was not varied, and the authors say it could change pressure somewhat.
The easy way to misread this
Do not read this as evidence that flow-resistant tubes improve voice. It measured air pressure through plastic tubes, not patients or voice outcomes.