2004 OPEN FORUM Abstracts
EFFECT OF HIGH NASAL GAS FLOW ON UPPER AIRWAY PRESSURE.
Owen
Bamford, PhD and David Lain, Ph.D, FCCP (Vapotherm Inc. ,
Stevensville, MD)
Background:
at BTPS, high-flow breathing gas administered by nasal cannula is
well tolerated. Oxygen at up to 40 lpm can be given nasally rather
than by mask, with reported improvement in patient oxygenation and
comfort. Although clinical experience has been positive, the effects
of high nasal flows on airway conditions are not well understood.
This study measured changes in upper airway pressures at nasal
cannula air flows up to 40 lpm.
Methods:
6 healthy adult subjects were studied. Oropharyngeal pressure was
recorded via an air-filled 1/16” i.d. vinyl tube held in the
closed mouth, and connected to a pressure transducer (Abbott). The
transducer output was amplified (Grass Instruments) and displayed and
digitized (Windaq). Room air at BTPS (Vapotherm 2000i) flowed
through a nasal cannula (Vapotherm MA1700) at between 0 and 40 lpm.
Respiratory pressure waveforms were monitored to confirm valid data.
Mean values for mean, peak expiratory and minimum inspiratory
airway pressures were calculated for periods of steady breathing for
each subject at each flow rate.
Results:
pressures in the oropharynx increased linearly with nasal flow rate.
Correlation coefficients were highly significant (r=0.92-0.99;
p<0.001). However, the absolute increases were small. At 40 lpm
the mean peak expiratory pressure was 4.5 cm H20, vs. 1.1
cm at zero flow. The Figure shows mean ± SEM for peak
expiratory, mean, and minimum inspiratory pressures.
Conclusions:
High nasal flow through a non-occluding cannula induced a small but
consistent absolute increase in oropharyngeal pressure during all
phases of the respiratory cycle. The increase was statistically
highly correlated with flow rate.
Speculation:
The change in inspiratory minimum pressure suggests a reduction in
the nasal resistance component of inspiratory work of breathing as
flow increases.