How does humming increase nitric oxide (NO) production in the body?

How Humming Increases Nitric Oxide Production

Humming significantly increases nasal nitric oxide (NO) levels by enhancing gas exchange between the paranasal sinuses and the nasal cavity, causing a rapid washout of NO accumulated in the sinuses. 1

Mechanism of Action

• The paranasal sinuses are major producers of nitric oxide in the upper respiratory tract 1
• During humming, oscillating sound waves create pressure fluctuations that facilitate gas exchange between the sinuses and nasal cavity 1
• This acoustic activity promotes mixing of sinus gases (high in NO) with nasal gases, resulting in a dramatic increase in measurable nasal NO levels 2
• Humming can increase nasal NO output up to 15-fold compared to quiet exhalation 2

Physiological Characteristics of the Humming Effect

• The humming maneuver produces a large initial peak in nasal NO output, followed by a progressive decline 3
• With repeated consecutive humming, the NO peak decreases in a step-wise manner but recovers completely after a silent period of approximately 3 minutes 3, 4
• Nasal NO levels measured immediately after repeated humming are 5-50% lower than baseline silent exhalation, suggesting variable continuous contribution from the sinuses to nasal NO 3

Factors Affecting NO Release During Humming

• Ostium size (opening between sinuses and nasal cavity) is the most critical factor influencing NO release during humming 3
• Humming frequency also affects the magnitude of NO release 3
• Topical application of NO synthase inhibitors reduces baseline nasal NO by >50% but does not affect the increase evoked by humming, confirming that the humming effect is primarily due to enhanced release of pre-formed NO from the sinuses 3

Clinical Applications and Measurement Techniques

• Nasal NO measurement during humming may serve as a non-invasive test for:

  • Sinus NO production 2
  • Ostial patency (openness of sinus passages) 2, 5
  • Evaluation of sinonasal diseases 5

• Two recommended measurement methods:

  1. Parallel technique: Active exhalation through the nose with closed mouth (more reliable) 6
  2. Serial technique: Passive aspiration of nasal gas with closed velopharynx 6

• For optimal measurement during humming:

  • Subject should blow their nose before testing to ensure free airflow in both nostrils 1
  • Measurement should be performed at a flow rate between 45-55 mL/s 1
  • A plateau should be established at 10 seconds 1

Clinical Significance

• Combined nasal NO measurement with and without humming can help:

  • Estimate sinus ventilation 3
  • Distinguish between nasal mucosal NO output and sinus NO contribution 3, 4
  • Screen for conditions like primary ciliary dyskinesia (PCD), which shows abnormally low nasal NO 1

• Potential applications in monitoring:

  • Sinus ostial patency 2
  • Response to treatments affecting sinonasal conditions 5
  • Inflammatory processes in the upper airways 5

Limitations and Considerations

• Measurement techniques are not yet fully standardized 1
• The optimal sound frequency for humming requires further research 1
• Various factors can affect nasal NO measurements, including:
  • Exercise (should refrain 1 hour before testing) 1
  • Medications (decongestants, steroids) 1
  • Smoking (causes small decrease in nasal NO) 1