JOURNAL
OF APPLIED
Vol. 38, No. 5,Mayl
PHYSIOLOGY 975. Printed
in U.S.A.
Effect of vibration ALEX S. SINCLAIR Department of Biophysics,
on isolated AND University
MARGOT of Western
R.
dog bronchi
ROACH
Ontario,
London,
Ontario,
Canada
METHOD
lobes were stored at 3°C allowing evaluation at different times, post mortem. One or more sections were removed from the dissected bronchus. The branches were ligated and one end attached to a cannula. The other end was fitted with a section of stiff plastic tubing which could be sealed with a rubber stopper. With this end sealed and the sample filled with fluid it was attached to the pressure-volume apparatus shown in Fig. 1. This apparatus is similar to that used by Roach and Burton (6). A Statham pressure transducer (model P23De) and a modified constant-volume infusion pump (Harvard Apparatus Co. model 600-2-200) have been added to allow continuous monitoring of pressure with volume. By attaching a precision wire-wound potentiometer (Beckman 50K Helipot) to the gear shaft of the infusion pump, a voltage signal could be obtained proportional to the volume in the pump. By feeding the pressure and volume signals into a X-Y recorder (Houston Instruments Corp. model HR-97) a pressure-volume curve could be obtained over the entire infusion-withdrawal cycle, as shown in Fig. 2. This plot can provide information on the compliance of the bronchial segment, the technique used by Martin and Proctor (3). To obtain a better estimate of the elastic properties of the wall, a 35-mm camera (Asahi Pentax Spotomotic) was mounted above the saline bath, so that photographs could be taken at different distending pressures. During the infusion phase of the fourth cycle,l 10 photographs were taken. In addition, two photographs were taken at 5 and 0 cmHz0 during the withdrawal phase, to be used as a measure of the hysteresis. The time taken for a complete cycle was at least 6 min and maintained constant for a particular sample. Tests up to 20 or 30 min revealed negligible changes in the response. From the photographic enlargements (X 5) measurements of length and external diameter could be obtained over different parts of the same sample. Coupling this information with pressure, an estimate of the wall tension could be obtained using the law of Laplace (To = P X R, circumferentially, Tr, = P X R/2, longitudinally). Thus, elastic diagrams of wall tension versus length (or radius) or strain (A~/xo, change in length over the length at zero transmural pressure) could be plotted, revealing information on the elastic behavior of the tissue. By comparison of the properties before exposure to that obtained after, the effect of wall vibration could be deduced.
Fresh lungs were obtained from large mongrel dogs (15-28 kg) and stored in saline solution with $$‘o,ooo merthiolate added to prevent bacterial growth. The central bronchus was dissected from a particular lobe and the remaining
l Several infusion-withdrawal cycles were required before the response became stable and reproducible. This condition has been noted by most people measuring the elastic properties of biological tissue.
SINCLAIR, ALEX S., AND MARGOT R. ROACH. Effect of vibration on isolated dog bronchi. J. Appl. Physiol. 38(5): 780-785. 1975.-Vibratory stress, induced by turbulent flow, has been shown to alter the structural properties in arteries. Since turbulent flow can exist in the lungs it seems important to know whether a similar effect can occur in bronchi. To answer that question air was passed through isolated dog bronchi. Turbulent flow was created by having, at one end, a cannula acting as a stenosis, producing vibrations or a “flitter” in the wall. A measure of the elastic properties was obtained by coupling pressure-volume data with photographs taken at different pressures. The results demonstrate a significant alteration in the structural properties, localized to areas under maximum vibration. A “yielding” in the direction of maximum stress was observed with a corresponding structural rearrangement (radius decreased, length increased). This effect and its relation to structural fatigue is discussed. The physiological significance of the results are that the bronchi become more resistant to deformation under positive pressures and less resistant to collapse under negative pressures. elastic
properties;
turbulence;
structural
fatigue
THERE IS CONSIDERABLE EVIDENCE that vibratory stress can result in structural fatigue or changes in the mechanical properties of elastic vessels. Roach (4, 5, 7) demonstrated that turbulence produced by an arterial stenosis was a necessary condition for poststenotic dilatation, or structural weakness. Boughner and Roach (1) have shown that vibratory stress of iliac arteries induced by a loudspeaker resulted in changes in the elastic properties and that the response was frequency dependent. Since airflow in the major bronchi can be turbulent and especially during coughing or respiratory disease, the question arises as to whether vibratory stress has a similar effect on bronchi. Turbulence seems to be involved in cases where a foreign body becomes lodged in the respiratory tract resulting in a dilatation beyond the obstruction (2). However, no direct reference to vibratory stress being a factor has been found in the literature. The purpose of this report, therefore, is to demonstrate that wall vibrations in bronchi may play a significant role in altering the structural properties in isolated segments of the bronchial tree, in particular the larger bronchi.
780
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (154.059.124.102) on January 11, 2019.
VIBRATION
OF
BRONCHI
To determine if there was any degradation of the elastic properties over a 6-h period without exposure to air, several samples were studied at Z-h intervals. The results showed a complete overlap of the tension strain diagrams and pressure-volume curves. The samples were exposed to wall vibration in the following manner. As shown in Fig. 3, the cannula was attached to an air line, resulting in a turbulent jet in the lumen. The sample was kept moist externally by covering it with saline during exposure. The length was fixed at a value slightly above resting length, less than 5 % in most cases. The transmural pressure could be varied by adjustment of the clamp.
air -
bath CANNULA
TYPES (sizes in mm )
65.
w
4.0
infusion Pump
FIG. 3. Experimental apparatus for air exposure. Narrow constriction of the sample’s cannula acted as a stenosis, creating a turbulent jet. Types of cannula used during the various exposures. Sizes of stenoses used were 0.15, 0.20, 0.26, and 0.33 for types 1-4, respec-
WALL VIBRATION ____-_--.____.-.__
Jr
water
-
both
100
to
SPECTRUM ..-_._-_-_.--___---._ 1000
Hz
manometer
pressure transducer
I to recorder
FIG.
I. Pressure-volume
apparatus
used in this study. 1000 FREQUENCY
FIG. 4. X-Y 40
SAMPLE
cardiac
Al2
PRESSURE cm
H,O
of bronchial
sound
spectra
from
sample
AI0
(left
lobe).
Thirteen samples were studied at low transmural pressures, less than a few cmHz0, while four were studied at high pressures (greater than 10 cmH20). During the latter test the driving pressure proximal to the cannula was raised to maintain a similar flow rate. Although the flow rate was not monitored, an estimate of the maximum flow rate was obtained from the pressure drop across the cannula,2 which indicated that most tests were conducted around 1.5 ml/s.
30
c.
plot
(Hz)
1
RESULTS
Vibratory exposure. For the samples that were studied at low transmural pressures a condition of dynamic instability or resonance appeared to exist, resulting in large motions of the wall. The dynamics is thought to be similar to the “flittering” reported by Rodbard and Saiki (9). When a phonocatheter (American Electronics Laboratories, model 191) was placed in the saline bath 3 cm away from the wall the sound spectrum shown in Fig. 4 was observed. This result was characteristic of that obtained on others. Note that the position of strongest vibrations could be determined by moving the phonocatheter parallel to the wall. FIG. 2. Reproduction
for one of the samples.
of a pressure-volume
plot from
X-Y recorder,
2 With all the pressure drop attributed as due to the sudden expansion and contraction of the cannula, the velocity was estimated from hL = v2/2g.
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (154.059.124.102) on January 11, 2019.
782
A. S. SINCLAIR
VOLUME FIG. 5. Pressure-volume transmural pressure before Sample was dissected from
SAMPLE
(ml)
curve during the infusion phase from zero and after exposure to airflow for 30 min. right apical lobe.
Al4 . 1
i
1
.
.l
.
after
30min
before
-
J
exposure
. 8 . .
M.
R.
ROACH
sound produced was below the threshold of the phonocatheter. Elastic properties. The first indication of whether any structural change has occurred is given by the pressurevolume curve. Figure 5 illustrates the increased stiffness (or decreased compliance) for a particular sample after 30min exposure. To obtain a measure of the change, the maximum volume at 45 cmHz0 transmural pressure is compared before and after exposure. The values are normalized by expressing the ratio of this volume after exposure to that before, for a particular sample. The mean and standard error of this normalized ratio for 10 of the samples tested (3 were found to be leaking significantly and not included) were found to be 0.75 =t 0.03. Since there was no change in the pressure-volume curves in control samples after 4 h, the result was statistically significant (P < 0.00 1). When the tension-strain data were calculated for these samples, the same structural changes were evident. Figure 6 includes the circumferential and longitudinal tensionstrain curves for another sample, illustrating a pronounced stiffening and decreased range of distension. Figure 7 displays another “elastic diagram” in which the true radius is shown. This figure illustrates that there was no change in the control test with the sample in the experimental arrangement (under tension, longitudinally) and that, when vibration occurred, the sample decreased in radius. The elastic diagrams were drawn for each of the 13 samples, and 2 measures of the structural properties recorded. These were “initial elastance” and the ccrange of distension. ” The “range of distension” was taken as the SAMPLE
Al time 0
. em
201
8: m
-C-
210
. . .. . . .
30
. . .
min (no air)
”
1 w . . . . . . . . .
(air)
”
O*Z STRAIN
AND
\ 3
’
=. m -0 F -
19
. . .
f z m c
.
.
. .’
.
y’ . e-
4:o RADIUS STRAIN
FIG. 6. Tension versus strain for the circumferential and longitudinal directions before and after 30-min exposure. Sample Al4 was dissected from left apical lobe.
If either the length of the sample was increased (increased longitudinal stress) or the pressure raised slightly (by adjustment of the clamp) during exposure, the spectrum was shifted to the right. That is, the frequency increased, demonstrating a dependence on the wall properties. When the pressure was raised further a point was reached when the large vibrations were completely absent. Palpation demonstrated that the walls were still vibrating; however, the
44 (mm)
FIG. 7. Tension versus absolute radius for sample Al (right cardiac lobe). Shown are results before exposure after three hours in bath without airflow (acting as control), and after 300min exposure to airflow.
TABLE
1. Normali
OF APPLIED
Vol. 38, No. 5,Mayl
PHYSIOLOGY 975. Printed
in U.S.A.
Effect of vibration ALEX S. SINCLAIR Department of Biophysics,
on isolated AND University
MARGOT of Western
R.
dog bronchi
ROACH
Ontario,
London,
Ontario,
Canada
METHOD
lobes were stored at 3°C allowing evaluation at different times, post mortem. One or more sections were removed from the dissected bronchus. The branches were ligated and one end attached to a cannula. The other end was fitted with a section of stiff plastic tubing which could be sealed with a rubber stopper. With this end sealed and the sample filled with fluid it was attached to the pressure-volume apparatus shown in Fig. 1. This apparatus is similar to that used by Roach and Burton (6). A Statham pressure transducer (model P23De) and a modified constant-volume infusion pump (Harvard Apparatus Co. model 600-2-200) have been added to allow continuous monitoring of pressure with volume. By attaching a precision wire-wound potentiometer (Beckman 50K Helipot) to the gear shaft of the infusion pump, a voltage signal could be obtained proportional to the volume in the pump. By feeding the pressure and volume signals into a X-Y recorder (Houston Instruments Corp. model HR-97) a pressure-volume curve could be obtained over the entire infusion-withdrawal cycle, as shown in Fig. 2. This plot can provide information on the compliance of the bronchial segment, the technique used by Martin and Proctor (3). To obtain a better estimate of the elastic properties of the wall, a 35-mm camera (Asahi Pentax Spotomotic) was mounted above the saline bath, so that photographs could be taken at different distending pressures. During the infusion phase of the fourth cycle,l 10 photographs were taken. In addition, two photographs were taken at 5 and 0 cmHz0 during the withdrawal phase, to be used as a measure of the hysteresis. The time taken for a complete cycle was at least 6 min and maintained constant for a particular sample. Tests up to 20 or 30 min revealed negligible changes in the response. From the photographic enlargements (X 5) measurements of length and external diameter could be obtained over different parts of the same sample. Coupling this information with pressure, an estimate of the wall tension could be obtained using the law of Laplace (To = P X R, circumferentially, Tr, = P X R/2, longitudinally). Thus, elastic diagrams of wall tension versus length (or radius) or strain (A~/xo, change in length over the length at zero transmural pressure) could be plotted, revealing information on the elastic behavior of the tissue. By comparison of the properties before exposure to that obtained after, the effect of wall vibration could be deduced.
Fresh lungs were obtained from large mongrel dogs (15-28 kg) and stored in saline solution with $$‘o,ooo merthiolate added to prevent bacterial growth. The central bronchus was dissected from a particular lobe and the remaining
l Several infusion-withdrawal cycles were required before the response became stable and reproducible. This condition has been noted by most people measuring the elastic properties of biological tissue.
SINCLAIR, ALEX S., AND MARGOT R. ROACH. Effect of vibration on isolated dog bronchi. J. Appl. Physiol. 38(5): 780-785. 1975.-Vibratory stress, induced by turbulent flow, has been shown to alter the structural properties in arteries. Since turbulent flow can exist in the lungs it seems important to know whether a similar effect can occur in bronchi. To answer that question air was passed through isolated dog bronchi. Turbulent flow was created by having, at one end, a cannula acting as a stenosis, producing vibrations or a “flitter” in the wall. A measure of the elastic properties was obtained by coupling pressure-volume data with photographs taken at different pressures. The results demonstrate a significant alteration in the structural properties, localized to areas under maximum vibration. A “yielding” in the direction of maximum stress was observed with a corresponding structural rearrangement (radius decreased, length increased). This effect and its relation to structural fatigue is discussed. The physiological significance of the results are that the bronchi become more resistant to deformation under positive pressures and less resistant to collapse under negative pressures. elastic
properties;
turbulence;
structural
fatigue
THERE IS CONSIDERABLE EVIDENCE that vibratory stress can result in structural fatigue or changes in the mechanical properties of elastic vessels. Roach (4, 5, 7) demonstrated that turbulence produced by an arterial stenosis was a necessary condition for poststenotic dilatation, or structural weakness. Boughner and Roach (1) have shown that vibratory stress of iliac arteries induced by a loudspeaker resulted in changes in the elastic properties and that the response was frequency dependent. Since airflow in the major bronchi can be turbulent and especially during coughing or respiratory disease, the question arises as to whether vibratory stress has a similar effect on bronchi. Turbulence seems to be involved in cases where a foreign body becomes lodged in the respiratory tract resulting in a dilatation beyond the obstruction (2). However, no direct reference to vibratory stress being a factor has been found in the literature. The purpose of this report, therefore, is to demonstrate that wall vibrations in bronchi may play a significant role in altering the structural properties in isolated segments of the bronchial tree, in particular the larger bronchi.
780
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (154.059.124.102) on January 11, 2019.
VIBRATION
OF
BRONCHI
To determine if there was any degradation of the elastic properties over a 6-h period without exposure to air, several samples were studied at Z-h intervals. The results showed a complete overlap of the tension strain diagrams and pressure-volume curves. The samples were exposed to wall vibration in the following manner. As shown in Fig. 3, the cannula was attached to an air line, resulting in a turbulent jet in the lumen. The sample was kept moist externally by covering it with saline during exposure. The length was fixed at a value slightly above resting length, less than 5 % in most cases. The transmural pressure could be varied by adjustment of the clamp.
air -
bath CANNULA
TYPES (sizes in mm )
65.
w
4.0
infusion Pump
FIG. 3. Experimental apparatus for air exposure. Narrow constriction of the sample’s cannula acted as a stenosis, creating a turbulent jet. Types of cannula used during the various exposures. Sizes of stenoses used were 0.15, 0.20, 0.26, and 0.33 for types 1-4, respec-
WALL VIBRATION ____-_--.____.-.__
Jr
water
-
both
100
to
SPECTRUM ..-_._-_-_.--___---._ 1000
Hz
manometer
pressure transducer
I to recorder
FIG.
I. Pressure-volume
apparatus
used in this study. 1000 FREQUENCY
FIG. 4. X-Y 40
SAMPLE
cardiac
Al2
PRESSURE cm
H,O
of bronchial
sound
spectra
from
sample
AI0
(left
lobe).
Thirteen samples were studied at low transmural pressures, less than a few cmHz0, while four were studied at high pressures (greater than 10 cmH20). During the latter test the driving pressure proximal to the cannula was raised to maintain a similar flow rate. Although the flow rate was not monitored, an estimate of the maximum flow rate was obtained from the pressure drop across the cannula,2 which indicated that most tests were conducted around 1.5 ml/s.
30
c.
plot
(Hz)
1
RESULTS
Vibratory exposure. For the samples that were studied at low transmural pressures a condition of dynamic instability or resonance appeared to exist, resulting in large motions of the wall. The dynamics is thought to be similar to the “flittering” reported by Rodbard and Saiki (9). When a phonocatheter (American Electronics Laboratories, model 191) was placed in the saline bath 3 cm away from the wall the sound spectrum shown in Fig. 4 was observed. This result was characteristic of that obtained on others. Note that the position of strongest vibrations could be determined by moving the phonocatheter parallel to the wall. FIG. 2. Reproduction
for one of the samples.
of a pressure-volume
plot from
X-Y recorder,
2 With all the pressure drop attributed as due to the sudden expansion and contraction of the cannula, the velocity was estimated from hL = v2/2g.
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (154.059.124.102) on January 11, 2019.
782
A. S. SINCLAIR
VOLUME FIG. 5. Pressure-volume transmural pressure before Sample was dissected from
SAMPLE
(ml)
curve during the infusion phase from zero and after exposure to airflow for 30 min. right apical lobe.
Al4 . 1
i
1
.
.l
.
after
30min
before
-
J
exposure
. 8 . .
M.
R.
ROACH
sound produced was below the threshold of the phonocatheter. Elastic properties. The first indication of whether any structural change has occurred is given by the pressurevolume curve. Figure 5 illustrates the increased stiffness (or decreased compliance) for a particular sample after 30min exposure. To obtain a measure of the change, the maximum volume at 45 cmHz0 transmural pressure is compared before and after exposure. The values are normalized by expressing the ratio of this volume after exposure to that before, for a particular sample. The mean and standard error of this normalized ratio for 10 of the samples tested (3 were found to be leaking significantly and not included) were found to be 0.75 =t 0.03. Since there was no change in the pressure-volume curves in control samples after 4 h, the result was statistically significant (P < 0.00 1). When the tension-strain data were calculated for these samples, the same structural changes were evident. Figure 6 includes the circumferential and longitudinal tensionstrain curves for another sample, illustrating a pronounced stiffening and decreased range of distension. Figure 7 displays another “elastic diagram” in which the true radius is shown. This figure illustrates that there was no change in the control test with the sample in the experimental arrangement (under tension, longitudinally) and that, when vibration occurred, the sample decreased in radius. The elastic diagrams were drawn for each of the 13 samples, and 2 measures of the structural properties recorded. These were “initial elastance” and the ccrange of distension. ” The “range of distension” was taken as the SAMPLE
Al time 0
. em
201
8: m
-C-
210
. . .. . . .
30
. . .
min (no air)
”
1 w . . . . . . . . .
(air)
”
O*Z STRAIN
AND
\ 3
’
=. m -0 F -
19
. . .
f z m c
.
.
. .’
.
y’ . e-
4:o RADIUS STRAIN
FIG. 6. Tension versus strain for the circumferential and longitudinal directions before and after 30-min exposure. Sample Al4 was dissected from left apical lobe.
If either the length of the sample was increased (increased longitudinal stress) or the pressure raised slightly (by adjustment of the clamp) during exposure, the spectrum was shifted to the right. That is, the frequency increased, demonstrating a dependence on the wall properties. When the pressure was raised further a point was reached when the large vibrations were completely absent. Palpation demonstrated that the walls were still vibrating; however, the
44 (mm)
FIG. 7. Tension versus absolute radius for sample Al (right cardiac lobe). Shown are results before exposure after three hours in bath without airflow (acting as control), and after 300min exposure to airflow.
TABLE
1. Normali
