(Chest. 2001;120:397-401.)
© 2001
American College of Chest Physicians
Combined Effects of a Nasal Dilator and Nasal Prongs on Nasal Airflow Resistance*
Anne Marie Lorino, PhD;
Marie Pia d’Ortho, MD;
Estelle Dahan;
Olivier Bignani;
Carine Vastel and
Hubert Lorino, PhD
*
From INSERM U 492 et Service de Physiologie, Explorations Fonctionnelles, Hôpital Henri Mondor, AP-HP, Créteil, France.
Correspondence to: Anne Marie Lorino, PhD, Service de Physiologie, Explorations Fonctionnelles, Hôpital Henri Mondor, 94010 Créteil, France; e-mail: anne-marie.lorino{at}hmn.ap-hop-paris.fr
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Abstract
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Study objectives: Nasal prongs (NPs), when used to
assess nasal flow, can result in dramatic increases in nasal airflow
resistance (NR). The aim of this study was to investigate whether the
NP-induced increases in NR could be corrected by the simultaneous use
of an internal nasal dilator (ND).
Design: NR was
estimated by posterior rhinomanometry, in the basal state (NRb), and
while breathing with NP (NRp), with ND (NRd), and with both ND and NP
(NRd + p).
Participants: The study was performed in
15 healthy subjects.
Measurements and results: NR
(mean NRb [± SEM], 2.5 ± 0.4 cm H2O/L/s)
significantly decreased with ND (NRd = 1.4 ± 0.2 cm
H2O/L/s; p < 0.001) and significantly increased with NP
(NRp = 3.8 ± 0.8 cm H2O/L/s; p < 0.001). A
significant logarithmic relationship was found between NRd and NRb
(r2 = 0.95; p < 0.0001), and a
significant exponential relationship was found between NRp and NRb
(r2 = 0.99; p < 0.0001). While
breathing with both ND and NP, NRd + p was significantly lower than
NRb (1.9 ± 1.4 cm H2O/L/s; p < 0.02).
Conclusions: Our results demonstrate that the ND tends to
slightly overcorrect the NP-induced increase in NR and suggest that, in
view of the possible effects of NPs on upper airway resistance, the
combination of both devices might be used for nasal airflow monitoring
during nocturnal polysomnography in patients presenting with highly
resistive nares.
Key Words: nasal airflow resistance • nasal dilator • nasal prongs • posterior rhinomanometry
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Introduction
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The
diagnosis of obstructive sleep apnea syndrome (OSAS) is established on
the basis of nocturnal polysomnographic studies during which
thermistors have been routinely used for oronasal airflow monitoring.
Recommendations for measurement techniques have been
published,1
in which the use of qualitative sensors for
air flow estimation is discouraged. Airflow measured by a
pneumotachograph remains the reference signal for the detection of
obstructive sleep respiratory events, including inspiratory flow
limitation, which is a predictive index for upper airway
narrowing.2
3
Nasal pressure measured via nasal prongs
(NPs) connected to a pressure transducer is now recommended as an
alternative, since it has been demonstrated to provide a
semi-quantitative estimate of nasal airflow4
and to allow
a fair detection of flow limitation.5
6
However, a recent study7
has shown that NPs could
dramatically increase nasal airflow resistance (NR) in certain patients
presenting with high NR values due to nare narrowness and/or deviated
nasal septum. Such increases in NR, which result in additional
increases in upper airway resistance,8
might promote the
occurrence of sleep respiratory events associated with brief
arousals.9
The present study was therefore designed to
determine whether the NP-induced increase in NR could be
counterbalanced by the effect of a mechanical internal nasal dilator
(ND) that previously had been demonstrated to significantly decrease NR
in healthy subjects.10
11
For this purpose, we evaluated
the isolated and combined effects of the ND and NPs on NR assessed by
posterior rhinomanometry.
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Materials and Methods
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Subjects
The study was performed in a group of 15 asymptomatic healthy
volunteers (3 men and 12 women), aged 22 to 54 years, who had no upper
or lower respiratory complaints. Seven subjects had normal nasal
morphology, and eight subjects had nasal anatomic abnormalities such as
nare narrowness and/or deviated nasal septum.
Nasal Resistance Measurement
NR was measured by posterior rhinomanometry. The subjects
breathed quietly through a nasal mask, with the mouth occluded by a
closed mouthpiece in which a 3-mm internal diameter catheter was
inserted to measure pharyngeal pressure. Transnasal pressure (Ptn) was
measured by a differential pressure transducer (model DP 45
[± 14 cm H2O]; Validyne; Northridge, CA) with
one port connected to the nasal mask and the other to the catheter.
Nasal flow (
) was sensed by a pneumotachograph (No. 1; Fleisch;
Lausanne, Switzerland) connected to a differential pressure transducer
(model DR 45 [45 ± 2.25 cm H2O]). Pressure
and flow signals were sampled at 32 Hz by an A-D converter. To
determine the nonlinear nasal inspiratory airflow resistance, Ptn and
inspiratory data were analyzed by linear regression analysis of
Ptn over ||, according to the following equation:
 | (1) |
where K is the slope of the regression line.
NR then was calculated at an airflow of 0.5 L/s, as NR = 0.5 K. Three
to four consecutive measurements were performed within a 1-min period,
and NR was taken as the average of the NR estimates corresponding to an
r2 value of > 99%.
Experimental Protocol
In each subject, NR was measured under four conditions: (1) in
the basal state (NRb); (2) while breathing with NPs (NRp; Pro-Tech;
Woodinville, WA); (3) while breathing with a mechanical internal nasal
dilator (NRd) (Nozovent; Prevancure; Sté Pouret, France),
which consists of a plastic bar, each extremity of which ends in a tab
to be placed inside each nostril; and (4) while breathing with both the
mechanical dilator and the NPs (NRd + p). The order of the three
latter conditions was randomly selected, and for each condition a
10-min stabilization period was observed prior to NR measurements.
NPs are normally held in place with side tubing over the ears. This
tubing may induce air leaks when worn with a nasal mask. To avoid such
leaks, the NP side tubing was shortened so that subsequently it could
be placed inside the mask, and a thin strip was introduced into the
tubing for fastening to the ears. The NPs are normally connected to a
pressure transducer. The side tubing ends were sealed with silicone gel
to reproduce this arrangement. The tips of the NPs were inserted into
the nostrils. The two ends of the strip were passed over both ears and
tied together under the chin to simulate the usual placement of the
NPs. Then the nasal mask was positioned and was checked for a tight
seal.
Statistical Analysis
Statistical analysis was performed using nonlinear regression
analysis and nonparametric tests. NR values were compared by the
Friedman test (nonparametric analysis of variance) and the Wilcoxon
signed rank sum test. A p value of < 0.05 was considered to be
significant. Values are given as the mean ± SEM, except when
otherwise indicated.
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Results
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Typical Ptn– curves that were obtained in a representative
subject in the basal state and with the different devices are shown in
Figure 1
. In the basal state, NRb ranged from 0.8 to 6.5 cm
H2O/L/s, with a mean value of 2.5 ± 0.4 cm
H2O/L/s.
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Figure 1.. Illustrative Ptn- curves obtained in a
representative subject in the basal state (Base), with the internal ND,
with the NPs, and with the combination of ND and NPs (ND + NP).
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When breathing with the ND, NR significantly decreased
(NRd = 1.4 ± 0.2 cm H2O/L/s; p < 0.001)
and was 61 ± 4% of its basal value. The intersubject variability
was lower for NRd than for NRb (Fig 2
), and in 12 of the 15 subjects NRd was < 2 cm
H2O/L/s (Fig 2)
. A significant logarithmic
relationship was found between NRd and NRb
(r2 = 0.87; p < 0.0001) (Fig 3 ).
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Figure 2.. Individual values for NR observed in the 15
subjects in the basal state (Base), with the internal ND, with NPs, and
with the combination of the ND and the NPs. See the legend for Figure 1
for any abbreviations not used in the text.
* = significance at p < 0.02.
** = significance at p < 0.001.
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When breathing with the nasal prongs, NR significantly increased (NRp =
3.8 ± 0.8 cm H2O/l-1/s; p < 0.001) and was
146 ± 7% of its basal value. A wide intersubject variability was
observed for NRp (Fig. 2)
, and a significant exponential relationship
was found between NRp and NRb (r2 = 0.99; p <
0.0001) (Fig 4)
.
When breathing with both the ND and the prongs, NR was significantly
lower than NRb (NRd + p = 1.9 ± 1.4 cm
H2O/l-1/s; p < 0.02) and was 78 ± 6% of
its basal value. However, individual data analysis showed that, in one
subject, the effect of the ND undercorrected the effect of the nasal
prongs (Fig 2)
.
The difference NRb - NRp + d (22 ± 6% of NRb) was found to be
significantly lower than the differences NRb - NRd (39 ± 4%
of NRb; p < 0.01) on the one hand, and NRp - NRb (46 ± 7% of
NRb; p < 0.05) on the other hand.
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Discussion
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NPs have been demonstrated to be a convenient device for
ventilation monitoring during polysomnographic studies, because nasal
pressure provides a semiquantitative evaluation of airflow and,
thereby, allows the detection of sleep respiratory events, including
inspiratory flow limitation.12
13
However, a recent
study7
demonstrated that NPs could induce dramatic
increases in NR in certain patients who presented with high NRb values.
This suggests that the use of NPs might result in an erroneous
apnea/hypopnea index during the diagnosis night. The present study
therefore was initiated to investigate whether the NP-induced increases
in NR could be corrected by the effect of an ND.
Posterior rhinomanometry allows direct NR measurement during normal
tidal breathing. As NR is flow dependent, a choice has to be made
concerning the flow or pressure level at which it is calculated. In the
present study, NR was calculated at the 0.5-L/s flow level because this
NR index has proved suitable in previous studies for assessing the
effects of nasal mechanical dilators10
11
and
NPs7
on NR. Furthermore, the main advantage of assessing
NR at a constant flow level is that it ensures that any change in NR
only can be attributed to a modification of the nasal space available
for flow. To avoid any influence of diurnal variation on nasal
resistance,14
all our subjects were studied at the same
time of day.
The Pro-Tech NPs that were originally designed to measure the
CO2 concentration in the expired gas are
now widely used with most of the commercially available
polysomnographic recording devices. They are characterized by short and
narrow soft tips, which limit the reduction of the nasal
cross-sectional area available for airflow. Previously, their use has
been demonstrated to result in lower increases in NR than most of the
conventional O2 NPs.7
These are the
reasons why they were selected for this study. Similarly, the internal
ND was chosen because it has been proved to be more efficient in
reducing NR than an external ND.10
The wide range of our NRb values (0.8 to 6.5 cm
H2O/L/s) was due to the great diversity of our
subjects’ nose morphology and nasal anatomy. This allowed us to
investigate the potential influence of the different nasal devices on a
wide range of NRb values. It is worth noting that 20% of our 15
healthy subjects had NRb values of > 4 cm
H2O/L/s and that a higher percentage would
probably be observed in an OSAS population.
The ND resulted in a significant decrease in NR (Fig 2)
, which was in
the range of those previously observed with the same
device.10
11
The highly significant logarithmic
relationship found between NRd and NRb demonstrates that the dilator
effect on NR is all the more marked as the subject’s NRb increases
(Fig 4
) (ie, that the expanding force of the ND and the resulting
increase in the nasal cross-sectional area are all the more pronounced
as the nares are narrow).
In this connection, it is worth noting that when using NPs for airflow
monitoring, the physiologist faces a dilemma, since the higher the NRp
value, the more accurate the airflow assessment. Nevertheless, as
discussed below, it does not seem reasonable to give preference to
measure accuracy at the risk of disturbing the patient’s ventilation
and sleep, biasing the polysomnographic study.
The combination of the ND and NPs resulted in NR values significantly
lower than basal values, which illustrates the tendency of the ND to
overcorrect the effects of NPs. Interestingly, this overcorrection
could be predicted by both the NRd-NRb logarithmic relationship and the
NRp-NRb exponential relationship (see "Appendix"). In fact, the ND
undercorrected the effects of NPs on NR in only one subject (symbolized
by the diamond and the dashed line in Fig 2
). This discrepant result
might be explained by the nasal morphology of this subject, in whom
nare shortness and narrowing were associated with a deviated nasal
septum. One may indeed assume that NPs resulted in the total occlusion
of one nare, limiting the effects of the ND to the contralateral nare.
As previously mentioned, in subjects with low NRb values, NP induced
relatively small increases in NR, and in those subjects the
simultaneous use of a ND appears to be unnecessary. On the contrary, in
subjects with high NRb values, the combination of NPs and dilator might
be recommended. It has indeed been demonstrated that external resistive
loads result in increases in upper airway resistance of about 75% of
the load, during non-rapid eye movement sleep in healthy
men.8
One can therefore calculate that the total increase
in upper airway resistance resulting from the use of NPs during sleep
could exceed 12 cm H2O/L/s in the subject with
the highest NRb values. Now, it has been reported that although nasal
obstruction may not be a main factor, it can be a cofactor of OSAS
during sleep.15
Consequently, as NRd + p was found to be
closer to NRb than NRp, one may assume that the occurrence of
obstructive sleep respiratory events should be less influenced by the
decrease in NR induced by the use of both devices than by the increase
in NR induced by NPs. However, in subjects whose NRb is unknown, the
combination of NPs and dilator might be considered, since, as mentioned
above, NRd + p is closer to NRb than NRp. Furthermore, the fact that
NRd + p was found to be lower than NRb would not affect the
occurrence of obstructive sleep respiratory events in subjects with low
NRb values. Indeed, the decrease in NR presently observed with the
combination of both devices was lower than the one observed with the ND
alone, and no effect of the internal ND device on the number of
obstructive respiratory events during sleep has been reported in OSAS
patients with normal noses, despite a significant decrease in nasal
airflow resistance.16
Thus, the simultaneous use of both
devices should be preferred to the use of NPs alone in patients whose
NR values are unknown. It is worth noting that, contrary to what could
be supposed, NPs and ND are easily placed together in small and/or
narrow nares. Besides, most subjects reported a subjective increase in
ease of breathing with both devices by comparison with NPs only, which
was indeed objectified by the corresponding decrease in NR.
In conclusion, our results demonstrate that the ND tends to slightly
overcorrect the NP-induced increase in NR. However, in view of the
possible side effects of NPs on upper airway resistance and the easy
use of the ND, the combination of both devices might be recommended for
nasal airflow monitoring during polysomnographic studies in patients
whose basal NR value is either unknown or abnormally high.
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Appendix 1
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It has been found that NRd could be predicted from NRb by the
logarithmic relationship
 | (A1) |
and that NRp could be predicted from NRb by the exponential
relationship
 | (A2) |
Consequently, NRd + p can be calculated from ,
taking NRp as the new NR basal value as:
 | (A3) |
On substituting NRp from into , NRd + p
can be expressed as
 | (A4) |
thereby giving
 | (A5) |
Thus, equation 5 allows one to predict that the NRd + p value
should be lower than the NRb value for NRb values > 1.3 cm
H2O/L/s. All our subjects had NRb values > 1.3
cm H2O/L/s, except one whose NRb was 0.8 cm
H2O/L/s. In this subject, no effect of the
dilator could be observed on NR, and NRd + p was found to be equal to
NRb, probably because changes in such dramatically low NR values are
lost in the NR physiologic variability.
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Acknowledgements
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The authors wish to thank Drs. Alain Harf and
Frédéric Lofaso for their helpful review of the manuscript.
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Footnotes
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Abbreviations: ND = nasal dilator; NP = nasal
prong; NR = nasal airflow resistance; NRb = nasal airflow
resistance in the basal state; NRd = nasal airflow resistance with
nasal dilator; NRd + p = nasal airflow resistance with nasal
dilator and nasal prongs; NRp = nasal airflow resistance with nasal
prongs; OSAS = obstructive sleep apnea syndrome; Ptn = transnasal
pressure; = nasal flow
Received for publication July 7, 2000.
Accepted for publication March 2, 2001.
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TOP
Abstract
Introduction
