J Appl Physiol 95: 497-503, 2003.
First published April 11, 2003; doi:10.1152/japplphysiol.00718.2002
8750-7587/03 $5.00
Nasal contribution to breathing with exercise: effect of race and gender
William D. Bennett,1
Kirby L. Zeman,1 and
Annie M. Jarabek2
1Center for Environmental Medicine, Asthma and
Lung Biology, University of North Carolina at Chapel Hill, Chapel Hill 27599;
and 2National Center for Environmental Assessment, US
Environmental Protection Agency, Research Triangle Park, North Carolina
27709
Submitted 5 August 2002
; accepted in final form 7 April 2003
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ABSTRACT
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Because the nose acts as a filter to prevent penetration of toxic particles
and gases to the lower respiratory tract, the route of breathing, oral vs.
nasal, may be an important determinant of toxicant dose to the lungs. Using
respiratory inductance plethysmography and a nasal mask fitted with flowmeter,
we measured the nasal contribution to breathing at rest and during exercise
(to 60% maximum workload) in healthy young adults (men/women = 11/11 and
Caucasian/African-American = 11/11). We found that the nasal contribution to
breathing is less during submaximal exercise in the Caucasians vs.
African-Americans (e.g., at 60% maximum workload, mean nasal-to-total
ventilation ratio = 0.40 ± 0.21 and 0.65 ± 0.24, respectively,
P < 0.05). This difference is likely due to the African-Americans'
ability to achieve higher maximal inspiratory flows through their nose than
the Caucasians. Men also had a lesser nasal contribution to breathing during
exercise compared with women. This is likely due to greater minute
ventilations at any given percentage of maximum workload in men vs. women.
oronasal breathing; exercise ventilation; nasal resistance
THE MODE OF BREATHING, ORAL vs. nasal, is an important
determinant of deposited dose of inhaled particles and gases to the lungs
(1). The nose can act as an
effective filter to prevent penetration of particles and gases to the lower
respiratory tract. Gases that are very water soluble or reactive, e.g.,
SO2, aldehydes, organic esters, and ozone, can be extracted in the
nose by up to 95% during resting breathing
(18,
32). Very large (>5-µm
aerodynamic diameter) and very small (<0.01 µm) particles are deposited
very efficiently in the nose by inertial impaction and diffusion,
respectively, during nasal breathing
(8,
33). In addition, the nose
effectively conditions inspired air to near body temperature and 98–100%
relative humidity before it enters the lungs
(9). The ability of the nose to
condition ambient air in these ways serves as a protective mechanism against
toxicity to the lower respiratory tract.
Ventilation rate is a key determinant of both inhaled particle deposition
and gas uptake in the respiratory tract. Ventilation rate is linked to
activity, e.g., with exertion or strenuous activity, people who typically
breathe through their nose will augment their nasal ventilation and also
breathe through their mouth (oronasal breathing). The mode of breathing, i.e.,
via the mouth or nose, dramatically alters airflow dynamics in the upper
respiratory tract and influences particle deposition and gas uptake. The
capability of the nose to filter or condition inspired air is diminished as
airflow is diverted from nasal to mouth breathing during exercise. The level
of ventilation at which this switch from nasal to oronasal breathing occurs
has been previously referred to as the "oronasal switching point"
(21). A number of studies,
however, have shown that oronasal breathing occurs at resting ventilation in
some individuals (3,
7,
14). Characterizing the
ventilation level and variability across individuals for the relative
contribution of nasal to total breathing is critical to the construction of
ventilation activity patterns for accurately constructing the airflow
apportionment (nasal or mouth) at various ventilation rates associated with
different activities. Ventilation activity patterns (e.g., 10-h rest, 8-h
sitting, 5-h light work, and 1-h heavy exercise in a 24-h day) are beginning
to be used in risk assessment to link exposure profiles to internal dose for
more accurate dose-response assessment. For example, Snipes et al.
(29) recently used different
ventilatory patterns to illustrate that age, gender, and disease state may be
important determinants of susceptibility to inhaled particles.
Characterization of the variability in ventilation is an important
consideration to determine the magnitude of the intrahuman variability
uncertainty factor applied in inhalation risk assessment
(15).
The level of exercise at which the oronasal switching point occurs and the
relative contributions of oral vs. nasal breathing at rest and during exercise
have been studied by a number of investigators
(3,
7,
14,
21,
22,
25,
27,
31). The physiological
determinants of the relative contributions to nasal and oral breathing during
exercise are still not well understood. Presumably, nasal resistance
(Rnose) to airflow should determine the relative work of breathing
between nasal and mouth breathing and thus the switch from nasal to oronasal
breathing during exercise
(27). Schultz and Horvath
(27) showed that, within an
individual, nasal work of breathing was the most repeatable variable at
cross-over to oral breathing in subjects and thus a potential candidate for
determining the initiation of oral augmentation during exercise. Many previous
studies, however, have not found good correlations between Rnose
and the switch to oronasal breathing
(7,
14,
25) between individuals,
perhaps because the maximal inspiratory flow through the nose
(MIFnose) may be determined by more than Rnose as
measured under resting flow conditions
(5,
6,
24). Bridger and Proctor
(5,
6) suggested that
collapsibility of the nasal valve (referred to as alar collapse) plays a role
in MIFnose that is independent of Rnose downstream of
the collapse point (i.e., flow-limiting segment). After noting that the few
African-American subjects studied were able to achieve higher maximum nasal
flow rates, they further suggested that differences in nasal structure
associated with race (10,
11) may translate into
different maximal flow capacities.
Similarly, modest gender differences in nasal structure have also been
observed (10) and may
translate into gender-dependent oronasal switching with exercise. More
importantly, on average, women have lower maximal physical work capacities
(PWCmax) and associated ventilation rates. Thus, at a given work
effort (as %PWCmax), women might be expected to have a greater
nasal contribution to breathing than men. Gender differences in these relative
contributions of nasal breathing are important for assessing relative risks
associated with inhaled toxicants.
The purpose of our study was to determine whether the relative contribution
of nasal and oral breathing during light-to-moderate exercise is dependent on
race or gender in adults. Previous studies of this type have not addressed
race as a factor in oronasal breathing. Neither have they reported data
comparing gender in terms of relative contribution of nasal breathing as a
function of work effort. Second, we attempted to better elucidate how
parameters of nasal physiology, i.e., resistance and MIFnose, might
determine the relative contributions to nasal and oral breathing during
exercise.
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METHODS
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A group of 11 Caucasian (6 men/5 women) and 11 African-American (5 men/6
women) healthy, nonsmoking adults, age 18–31 yr, were studied. The
subjects had no smoking history, no history of lung disease, and no recent
history of acute respiratory infection or viral illness within the previous 4
wk. A few subjects reported seasonal nasal allergies and associated rhinitis
but were asymptomatic during the time of study. Forced expiratory volume in 1
s and forced vital capacity were determined for each subject by spirometry.
Informed consent was obtained from each volunteer; the study had the approval
of the University of North Carolina Committee on the Protection of the Rights
of Human Subjects.
A measure of each subject's predicted maximum exercise capacity on a cycle
ergometer (2) was determined.
While being monitored by a three-lead ECG, subjects performed graded
submaximal exercise at three increasing workloads (in W) while maintaining a
pedal rate of 60–70 rpm. Each workload trial lasted 5 min. The maximum
of the three workloads did not exceed a heart rate of 170 beats/min. By linear
extrapolation of the workload-heart rate relationship to each subject's
age-related predicted maximum heart rate
(2,
21), the subject's
PWCmax was determined.
On a subsequent study day, the relative contributions of oral vs. nasal
breathing were measured at rest and during incrementally graded submaximal
exercise on the cycle ergometer (10% increments from 0–60%
PWCmax for each subject)
(21,
22). The subject was fitted
with a nasal mask (Respironics, Murrysville, PA) (approximate dead space of 60
ml) that was similar to that used in pulmonary sleep laboratories and modified
to allow insertion of a mass flowmeter (Korr Medical Technologies, Salt Lake
City, UT) to detect nasal airflow
(21,
22). Total ventilation
(
E) was determined by respiratory
inductance plethysmography (Respitrace) (calibrated by spirometry)
(4,
7,
30). The Respitrace bands
(abdomen and rib cage) were fixed to the subject's torso with adhesive tape to
minimize slippage during exercise. The changes in inductance of these bands
with expansion and contraction were calibrated to spirometry for each subject,
according to the procedure of Tobin et al.
(30). Oral airflow was
determined as the difference between total (Respitrace) and nasal (nasal
mask). Subjects maintained a 60- to 70-rpm pedal rate at each 10% increment of
effort for 2 min. Flow characteristics during the last 30 s of each 2-min
period were recorded at 20-Hz sampling rate and analyzed on a MacIntosh
computer by using Superscope (GW Instruments) data-acquisition and analysis
software. To calibrate volumes obtained from respiratory inductance
plethysmography with the nasal flowmeter, we compared both signals to a volume
signal from a spirometer through which the subject rebreathed
(4) postexercise via the nose
only with the obstructed mouthpiece (mouth plug) in place. We did this
calibration postexercise so that the subject would be as unbiased as possible
with regard to nasal vs. oral breathing during the exercise session. In a few
initial, pilot subjects (data not included here), we found that having them
perform measurements with nose mask and mouth plug in place before the
exercise session created a bias in oronasal breathing. These subjects thought
they were to try to breathe through their nose during the exercise session
with the nasal mask in place but without a mouth plug. We tried to remove any
bias toward nasal or oral breathing by letting the subjects relax with the
Respitrace and nasal mask in place for a few minutes before beginning their
graded exercise and asking them not to think about their breathing during the
session.
Immediately after measurements of oral-nasal breathing during exercise
(within 15 min), measurements of airway resistance in the body plethysmograph
were made while the subject panted through a mouthpiece (with nose plug) and
then through the nasal mask (with mouth plug) described above
(23). Rnose was
then determined as the absolute difference between the mouthpiece and nasal
mask measure of total airway resistance. The assumption associated with this
technique is that the mouth adds very little to the measure of total airway
resistance. This technique for measuring Rnose has been shown to
correlate well with posterior rhinometry
(23), is easier for subjects
to perform, and is more realistic to conditions associated with exercise
breathing (i.e., cyclic panting) than posterior rhinometry (i.e., constant
inspired flow). Also, after the exercise session (within 15 min postexercise),
we had subjects perform maximal inspiratory flow maneuvers via their nose by
slowly exhaling to near residual volume and then rapidly inhaling through
their nose at maximal effort with the nose mask and mouth plug in place
(24). MIFnose
associated with these maneuvers was determined as the peak flow for each
maneuver.
Statistical analysis. Group comparisons, i.e., Caucasians vs.
African-Americans and men vs. women, for all variables reported were made by
independent sample t-test. As an exploratory analysis, we also
performed multivariate backward and forward stepwise regression for %nasal
contribution at rest and at 20, 40, and 60% PWCmax, considering the
following independent variables: race, gender, Rnose,
MIFnose, and E at that
workload. Due to our limited data set, we did not consider interactions
between variables for this exploratory analysis. Statistical criteria for a
variable to enter and stay in the stepwise model was set at P =
0.15.
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RESULTS
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Figure 1 shows the average
total and nasal E as a function of
%PWCmax in all subjects studied.
E increased linearly with increasing
workload to 60% PWCmax, whereas nasal ventilation increased more
slowly with increasing workload.
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Fig. 1. Mean total (+SD) and nasal ventilation (-SD) [minute ventilation
(E); in l/min] as a function of
relative workload [percentage of maximal physical work capacities
(%PWCmax)].
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Table 1 summarizes the
racial comparison of subject exercise capacities,
E, and lung and nasal function. Only
forced vital capacity and MIFnose were significantly different
between the two groups. There was a tendency for Rnose to be less
in the African-Americans vs. the Caucasians (P = 0.08).
Rnose tended toward a negative correlation with MIFnose
(r = -0.41, P = 0.06).
Figure 2 illustrates the nasal
contribution to breathing (in %E) as
a function of workload in %PWCmax for Caucasians and
African-Americans. At 20 and 60% PWCmax, the Caucasians had
significantly less nasal contribution to breathing than African-Americans
(P < 0.01 and 0.05, respectively). There was also a tendency
toward a racial difference at 40% PWCmax (P = 0.06).
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Fig. 2. Percent nasal contribution to breathing at rest and at 20, 40, and 60%
PWCmax for Caucasians vs. African-Americans. Values are means
± SD. Significant difference: #P < 0.01 and
*P < 0.05.
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Table 2 summarizes the
gender comparison of subject exercise capacities,
E, and lung and nasal function. The
women had a significantly less PWCmax compared with the men and, as
a result, also had a lesser E at 60%
PWCmax. Figure 3
illustrates the nasal contribution to breathing (in
%E) as a function of workload (in
%PWCmax) for men vs. women. At 40% PWCmax, the men had
significantly less nasal contribution to breathing than women (P <
0.05). There was also a tendency toward a gender difference at 20%
PWCmax (P = 0.06). Because there was a gender difference
in work capacity, we also compared the men and women at a given workload. All
subjects had a workload at or near 50 W during their exercise (a workload
associated with 
20% PWCmax in men and 40% PWCmax in
women), at which women and men had a
E of 22.1 ± 2.4 (SD) and 23.5
± 5.3 l/min respectively [not significant (NS)]. At this workload,
women had a nasal contribution to breathing of 79 ± 21% compared with
67 ± 28% for men (NS).
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Fig. 3. Percent nasal contribution to breathing at rest and at 20, 40, and 60%
PWCmax for women vs. men. Values are means ± SD.
*Significant difference, P < 0.05.
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The results of multivariate stepwise regression analysis for %nasal
contribution to breathing at rest showed no significant variables at the
P = 0.15 level. The same analysis at 20% PWCmax showed
significance for 1) E at
this workload (P = 0.001) and 2) race (P = 0.007;
r2 = 0.62 for the regression). Similarly, at 40%
PWCmax, the regression analysis showed significance for 1)
E at this workload (P <
0.001) and 2) race (P = 0.028; r2 = 0.62
for the regression). Finally, at 60% PWCmax, the regression
analysis showed %nasal contribution to breathing dependence on 1)
E at this workload (P <
0.001) and 2) race (P = 0.003; r2 = 0.59
for regression). Neither Rnose nor MIFnose was a
significant predictor of %nasal contribution to breathing at any exercise
level.
Figure 4 illustrates the
relationship between E and the
%nasal contribution at 40% and 60% PWCmax. For comparison to
previous work, the "switching point" reported by Niinimaa et al.
(21),
E = 35 l/min, is delineated. Below
E = 35 l/min, there is considerable
variation in %nasal contribution to breathing (30–100%), with
African-Americans clearly having a greater nasal contribution than Caucasians.
Above E = 35 l/min, the %nasal
contribution drops to <40% in all of the Caucasians, whereas four of the
African-Americans maintain %nasal contributions of >40%.
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Fig. 4. Relationship between E rate and
the percent contribution of nasal breathing at 40% and 60% PWCmax.
The "switching point" from Niinimaa et al.
(21) is shown for
comparison.
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DISCUSSION
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As in previous studies (3,
7,
14,
21,
22,
25,
31), our laboratory has shown
that the nasal contribution to breathing decreases with increasing exercise
(Fig. 1). Consequently, the air
entering the lower respiratory tract is less conditioned and filtered of
inhaled toxicants than it is otherwise
(1,
9), thus subjecting the lower
respiratory tract to potential insult. Others have also shown an average 50%
nasal contribution to E at a mean
E of 40 l/min
(7,
22,
31). Whereas our data and that
of others suggest that the %nasal contribution plateaus as total
E increases, absolute nasal
ventilation rates may continue to rise, reaching mean peak values of 40 l/min
(25). Unlike some previous
findings (21,
22), we did not find a
distinct switching point for a change from nasal to oronasal breathing;
rather, subjects generally tended to gradually increase their oral
contribution to breathing as exercise levels increased. Nevertheless, a
comparison of the switching point of Niinimaa et al.
(21) (35 ± 10 l/min)
with our nasal contributions and ventilation rates
(Fig. 4) shows that, for
ventilation rates >30 l/min, all subjects had nasal breathing that falls
<90% of total. It is also true that, above the switching point of 35 l/min
(Fig. 4), except for two
outliers, all subjects' nasal contribution to breathing fell <50%. However,
below that ventilation rate there was considerable variability in the nasal
contribution to breathing (i.e., 30–100%). Other studies
(7,
14) have also found a more
variable switching between nasal and oronasal breathing as we have found here.
Some of the differences between studies may be due to different measurement
techniques but also may be due to the "blindedness" of the
subjects toward the test's objectives. We found in pilot studies that, if
subjects thought we wanted them to breathe through their nose (based on
posttest questioning), they were more likely to maintain nasal breathing
solely until reaching a switching point, where, despite their best efforts,
they needed to orally supplement their breathing. In fact some subjects who
were less fit than others never achieved ventilation rates where switching
occurred.
We also found that the degree of nasal breathing at rest was correlated
with %nasal contribution to breathing during exercise. The best simple
regression between resting nasal contribution and nasal contribution during
exercise occurred at the 20% PWCmax level (r = 0.51,
P < 0.05) and diminished by 60% PWCmax (r =
0.38, NS). So while there may have been some effect of subject's baseline
nasal contribution at rest, this effect or relationship was not significant at
the higher workloads and thus could not explain the racial differences seen as
exercise progressed. Furthermore, there was no significant racial difference
in nasal contribution to breathing at rest (P = 0.20). We chose to
characterize nasal contribution to breathing as a function of relative
(14,
21,
22) rather than absolute
(7,
25) workload for reasons
associated with risk assessment. Because individuals have variable fitness
levels, they will generally exercise at their own capacities (or fraction of
their PWCmax). Thus the breathing patterns for these relative
workloads should be considered when attempting to model and/or assess risk
associated with inhaled toxicants. Using relative workloads to compare nasal
contribution to breathing as a function of race did not affect our findings,
because the PWCmax and E
at any relative workload were similar between African-Americans and
Caucasians. However, the same comparison between men and women was affected
because the latter had significantly lower PWCmax and thus lower
ventilation rates at a given %PWCmax.
Previous investigators have not distinguished their subjects by race and
their associated differences in nasal function. We have shown here that
African-Americans have a greater nasal contribution to breathing with exercise
compared with Caucasians. This difference was greatest as exercise level
increased. Whereas there was only a tendency for Rnose to be less
in the African-Americans compared with Caucasians
(Table 1), there was a clear
difference in the MIFnose, with African-Americans able to achieve
33% higher maximal nasal flows. This was true, despite their having
significantly smaller vital capacities
(Table 1) than Caucasians
(18).
Figure 4 shows that, after
switching to oronasal breathing, most African-American subjects were
maintaining higher levels of %nasal contribution than most of the Caucasians.
Two African-Americans had nasal contributions of 75% at
E as high as 40 l/min
(Fig. 4).
A clear relationship between either MIFnose (which differed by
race) or Rnose and nasal contribution to breathing was not evident
in our study. This may be due, in part, to the fact that both
MIFnose and Rnose were measured immediately
postexercise, at rest. Whether or not we obtained a true reflection of
Rnose during the exercise period is open to question. First, we
measured an average Rnose (inspiratory and expiratory) over the
flow range of ±0.5 l/s postexercise. The resistance at different phases
of the breathing cycle may vary and be important for determining maximal nasal
ventilation during exercise. For example, Shi et al.
(28) showed hysteresis in the
inspiratory resistance during hyperpnea, i.e., lesser Rnose during
increasing vs. decreasing inspiratory flow. They further showed that voluntary
flaring of the nostrils reduced the hysteresis and overall Rnose.
The degree to which their results with voluntary hyperventilation can be
extrapolated to the exercise condition is not clear, however. Second, total
Rnose at a given flow rate is known to be reduced with exercise,
depending on the workload
(12). We tried to capture the
Rnose associated with each subject's exercise state by measuring it
immediately postexercise, in each case within 15 min. However, it is not known
how much change in Rnose occurred for each subject in association
with the exercise protocol. Nor were we able to ascertain the degree to which
each subject maintained nasal dilatation postexercise. We chose not to measure
preexercise Rnose and MIFnose so that subjects would be
as naive as possible with regard to oronasal breathing during the exercise
protocol (discussed in METHODS). Future studies using other
measures or indexes of Rnose that do not require use of the nasal
mask, e.g., acoustic rhinometry, may allow for these pre- and postmeasures
while also not biasing subjects with regard to their oronasal breathing during
the exercise protocol.
Our findings suggest that Caucasians may be at greater risk for inhalation
of toxic gases and particles than African-Americans because of their lower
nasal contribution to overall breathing. However, it may also be that there
are racial differences in nasal efficiencies for removing these gases and
particles. Some recent studies suggest that this may in fact be the case for
inhaled particles. Kesavanathan et al.
(16,
17) attempted to link specific
nasal characteristics with total and regional particle deposition in the adult
nose. They showed that nasal particle deposition efficiency for 2–6
µm was increased with decreased minimal cross-sectional area of the nasal
passages and increasing ellipticity of the nostrils, with the latter being
significantly greater in Caucasians than in African-Americans. Others have
shown that the minimal cross-sectional area of the nasal passages is
significantly larger in African-Americans than Caucasians as well
(10). So the advantage of
greater nasal contribution to breathing observed by us may be offset by a less
efficient nasal filtering capacity in African-Americans. Differences in nasal
efficiency associated with race require further study, especially for gaseous
pollutants and conditioning of inspired air.
Our finding of lesser nasal contribution to breathing with exercise for men
vs. women is likely due to the different ventilation rates (due to different
workloads) at each level of exercise (Table
2). The regression analysis showed that, at each level of
exercise, %nasal contribution to breathing was most significantly associated
with E. From a risk assessment
perspective, the men may be at greater risk (i.e., more susceptible) to
inhalation of toxic gases and particles compared with women exercising at
similar effort levels. On the other hand, when we matched workload (at 50
W) and E between men and women,
there was not a significant gender difference in nasal contribution to
breathing. We also found no gender difference in nasal function
(Table 2), which is supported
by other measures of internal nasal structure as well
(10).
A few models have incorporated values for nasal ventilation fractions to
predict particle deposition in the lower respiratory tract
(13,
20,
26). In each case, model
inputs were based on the previous study of Niinimaa et al.
(22) and do not take into
account racial or gender differences discussed here. For example, the most
recent International Commission on Radiological Protection model
(13) incorporated fixed
fractions of nasal ventilation for all adults, either "normal
augmenters," i.e., those who breathe nasally at rest, or "habitual
mouth breathers," depending on their type of activity (e.g., sleep,
sitting, light exercise, and heavy exercise). For the light-exercise
condition, normal augmenters and habitual mouth breathers were predicted to
have a nasal ventilation fraction of 1.0 and 0.4, respectively. Our data
(e.g., Figs. 2 and
3) may provide input of more
realistic average nasal ventilation fractions in the adult population that
will vary as a function of race and gender. For example, a comparison of the
light-exercise condition (20% PWCmax) in African-Americans vs.
Caucasians shows nasal fractions of 1.0 and 0.7
(Fig. 2) that can be used to
predict respiratory tract deposition differences between these two groups.
However, to be accurate, these models must also consider the relative
scrubbing efficiency of the noses as a function of race and gender.
Conclusion. Like others, we have shown that the contribution of
nasal breathing to E diminishes with
increasing exercise effort. However, we have also found that nasal ventilation
during exercise varies as a function of both race and gender.
African-Americans have a greater nasal contribution to breathing during
exercise than Caucasians. It may be that this interracial difference is due to
the former's ability to achieve greater maximal flow rates through their nose,
although this dependence requires further investigation. At relative exercise
efforts (i.e., as a %maximum work capacity), the women also had a greater
nasal contribution to breathing during exercise than men. This gender
difference is explained by the fact that the women achieved lower
E than men at a given percentage of
their maximum work capacity. Because oral augmentation during exercise was
shown to be a function of E, the
women did not need to augment their breathing orally until much later in their
relative work effort. These racial and gender-related differences in route of
breathing during exercise may be important for determining relative risks of
individuals to environmental or occupational exposures of potentially toxic
gases or particulate matter.
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DISCLOSURES
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This study was supported by US Environmental Protection Agency Cooperative
Agreement 824915/829522.
Disclaimer: This study was performed in laboratories of the US
Environmental Protection Agency. The views expressed in this paper are those
of the authors and do not necessarily reflect the views or policies of the
Agency, and no official endorsement should be inferred. Mention of trade names
or commercial products does not constitute endorsement or recommendation for
use.
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FOOTNOTES
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Address for reprint requests and other correspondence: W. D. Bennett, Center
for Environmental Medicine, Asthma and Lung Biology, CB 7310, 104 Mason Farm
Rd., Univ. of North Carolina at Chapel Hill, Chapel Hill, NC 27599 (E-mail:
William_Bennett{at}med.unc.edu).
The costs of publication of this article were defrayed in part by the
payment of page charges. The article must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section 1734
solely to indicate this fact.
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