Mouth Leak With Nasal Continuous Positive Airway Pressure (CPAP) Increases Nasal Airway Resistance

The following information is provided by: Fisher & Paykel Healthcare

By Dr. Vanessa MB Jordan Ph.D., Research Scientist, Fisher & Paykel Healthcare

G.N. Richards, P.A. Cistulli, R.G. Ungar, M. Berthon-Jones and C.E. Sullivan
Am J Respir Crit Care Med 1996; 154: 182-6

Key Points

• Mouth leak during CPAP causes unidirectional nasal airflow.
• Nasal resistance increases when a mouth leak is simulated during CPAP use.
• During mouth leak, using heated humidification in conjunction with CPAP will attenuate and largely prevent increases in nasal airway resistance.
• Cold passover humidification, in conjunction with CPAP, did not prevent increases in nasal airway resistance.
• This study suggests that CPAP treatment if not tempered by humidification will irritate nasal mucosa increasing nasal airway resistance. The increased resistance would promote mouth breathing, increase unidirectional airflow and exacerbate the effect on the nasal mucosa.
• Although a pilot study, the increase in nasal resistance with room temperature CPAP was witnessed, to varying degrees, in all of the participants.
• This study adds weight to the building evidence that nasal CPAP when administered without heated humidification causes drying of the nasal mucosa. This results in increased blood flux which in turn produces increased nasal airway resistance.

Aim

• To determine the effect of mouth leak with CPAP on nasal airway resistance.
• To determine the influence of humidification on the above effect.

Method

Six healthy subjects were presented with a nasal airway challenge when using CPAP with room air, CPAP with cold passover humidification and CPAP with heated humidification. Nasal airway resistance was measured prior to the challenge, to determine a baseline value, and then every two minutes following the challenge for 20 minutes.

Nasal Airway Challenge

The challenge was produced by asking the participants to simulate a mouth leak by mouth breathing for ten minutes while on CPAP. This allowed air to pass through their nose and out through their mouths between breaths, causing unidirectional airflow.

Seven tests were carried out - the first and last of which only required nasal breathing during the challenge period. The remaining five challenges consisted of simulated mouth leak:

• Challenge 2: without humidification
• Challenge 3: with cold passover humidification
• Challenge 4: with heated humidification (end of hose temperature 230C)
• Challenge 5: with heated humidification (end of hose temperature 300C)
• Challenge 6: with heated humidification (end of hose temperature 370C)

Challenges were carried out on separate days in random order.

Results

When breathing room air using nasal CPAP without a mouth leak, in challenge one and seven, there were no apparent increases in nasal airflow resistance, from baseline recordings, for any of the participants.

After mouth breathing with room air during CPAP (challenge two) nasal airway resistance increased from the baseline measurement in all participants (figure 1). A similar increase in resistance was seen in challenge three, when CPAP was used in conjunction with cold passover humidification (figure 2).

Heated humidification used in conjunction with nasal CPAP (challenge four) prevented the large increase in nasal airway resistance that was observed in challenges two and three (figure 2).

Challenges four, five and six were compared in order to ascertain if air temperature or humidity was the main determinant in reducing the effect of mouth leak on nasal resistance. It was demonstrated that changing the end of hose temperature produced little further benefit (figure 3).

This study also illustrated that once increased, nasal resistance did not remain amplified, but rather returned to the baseline value 40-60 minutes after the challenge had ceased. The transient nature of the rise in nasal airway resistance remained even after repetitive challenges (figure 4).

Conclusions

Simulating a mouth leak during nasal CPAP without humidification causes an increase in nasal airway resistance.

Cold passover humidification does not prevent the observed increase in nasal airway resistance.

Heated humidification used in conjunction with nasal CPAP during simulated mouth leak, prevents nasal airway resistance from substantially increasing.