TECHNICAL NOTE

A multimodal laser Doppler and endosonographic

distension device for studying mechanosensation and

mucosal blood flow in the oesophagus

D. A. L. HOFF,*�§ H. GREGERSEN,*– S. ODEGAARD,*� L. B. NESJE,*� K. OEVREBOE,� T. HAUSKEN,*� O. H. GILJA,*�

K. MATRE* & J. G. HATLEBAKK*�

*Institute of Medicine, University of Bergen, Bergen, Norway �Institute of Surgical Sciences, University of Bergen, Bergen, Norway

�National Centre of Ultrasound in Gastroenterology, Haukeland University Hospital, Bergen, Norway §Department of Medicine,

Aalesund Hospital, Aalesund, Norway –Centre for Visceral Biomechanics and Pain, Aalborg Hospital, SMI, Aalborg University,

Aalborg, Denmark

Abstract We describe the development of a multimo-

dal device combining bag distension, manometry,

high frequency intraluminal ultrasound, laser Doppler

flowmetry and symptom registration. Bench tests

showed that the different modalities did not influence

each other. During bag distension we obtained high

quality images of the oesophageal wall for computing

biomechanical parameters, and laser Doppler signals

showing variation in mucosal perfusion. We conclude

that the principle of measurement is sound and that

the device can provide a basis for further studies.

Keywords bag distension, biomechanics, blood flow,

endosonography, ischemia, laser Doppler flowmetry.

INTRODUCTION

Functional chest pain of presumed oesophageal origin1

is incompletely understood. Distending a bag in the

oesophageal body typically reproduces the painful

sensation2–5 but the exact mechanism is unknown.

Over the past four decades the concept of intramural

tension receptors, in series or in parallel with the

muscle, has evolved without actual evidence that

tension is the direct stimulus.6 Alternatively ischemia

may, through its biochemical consequences, excite

sympathetic afferent nerves.

We aimed to design a multimodal device for study-

ing biomechanics and mucosal blood flow during bag

distension. We chose to include endosonography (ES)

as the imaging tool7 and laser Doppler flowmetry (LDF)

for measurements of perfusion.8

MATERIALS AND METHODS

The development of the technology went through

three steps; bench testing, animal trials and a human

feasibility trial. The Norwegian Animal Health

Authority approved the animal study protocol, which

was conducted in accordance with laws and regu-

lations. The Regional Committee for Medical

Research Ethics approved the protocol for the human

study and it was performed according to the Declar-

ation of Helsinki. Informed, written consent was

obtained.

Catheter

A specially designed catheter with an outer diameter of

6 mm, six separated lumens, and a bag attached at its

distal part. However, the configuration differed for

animal and human studies (Figs 1A and 2).

Endosonography

A radial 20 MHz miniature ultrasound probe with a

diameter of 2.6 mm (UM-3R, Olympus Corp., Tokyo,

Address for correspondenceDag Arne Lihaug Hoff, Institute of Medicine, HaukelandUniversity Hospital, NO-5021 Bergen, Norway.Tel: +47 40 04 52 44; fax: +47 55 97 29 50;e-mail: dag.hoff@helse-bergen.noReceived: 8 October 2005Accepted for publication: 16 October 2005

Neurogastroenterol Motil (2006) 18, 243–248 doi: 10.1111/j.1365-2982.2005.00738.x

� 2005 The AuthorsJournal compilation � 2006 Blackwell Publishing Ltd 243

Japan) was connected to a processor (EU-M20,

Olympus Corp.) and a digital video camera.

Repeated measures ANOVA was used in order to esti-

mate intraobserver variation of oesophageal wall

thickness.

Laser Doppler flowmetry

The laser Doppler probe [LDP-415-253 (size

10 · 6 · 4.5 mm, fibre diameter 140 lm and separation

250 lm, wavelength 780 nm) Perimed AB, Stockholm,

Sweden] was connected to a PF 5001 main unit with a

PF 5010 LDPM Unit (Perimed AB). Calibration was

performed in accordance with established procedures

and dedicated software (Perisoft 2.0, Perimed AB) was

used for recordings.

Bench testing

Taping the LDP transducer to a 25 lm thick poly-

estherurethane film we obtained reproducible and

stable flow signals from the thenar region of a hand.

When lowering the hand and the miniature ultra-

sound probe simultaneously in a water bath we

demonstrated no interference between LDF and

ultrasound signals. Stability of the ultrasound probe

in the centre of the bag as well as attenuation of the

ultrasound signals was important issues. After trying

A B

CD

Figure 1 (A) The multimodal device for the animal experiments. The oesophageal pressure was recorded at P1 and the BP at P2.The ultrasound signal (US) was acquired from a transducer inside the bag. The LDF was acquired from a transducer in the peripheryof the bag. (B) A typical BP tracing during distension. (C) An ultrasound image of a full distend bag. Ultrasound layers arecorresponding mainly to mucosa (1 + 2), submucosa (3), muscularis propria (4) and adventitia (5). (D) A typical LDF tracingduring distension. Perfusion is defined as the number of blood cells moving in the measured volume multiplied by mean speedof these cells.

D. A. L. Hoff et al. Neurogastroenterology and Motility

� 2005 The AuthorsJournal compilation � 2006 Blackwell Publishing Ltd244

several materials we discovered that polyethylene

pipettes did not attenuate the ultrasound signal

significantly and gave excellent centring of the US

probe as well. This was implemented in the catheter

for human use.

Animal studies

The catheter prototype had a 65 mm long and 30 mm

wide bag attached at the end (Fig. 1A). The LDF

transducer was fixed with double-sided tape to the

inner surface of the bag. The largest lumen was used

for filling and emptying water and for insertion of the

ultrasound probe. Two small lumens were used for

pressure recordings. The pressure channels were con-

nected to external transducers through a low compli-

ance perfused manometric system using a flow rate of

1 mL min)1. An overtube was used for insertion the

device into the oesophagus.

Three pigs were fasted overnight, airways intubated

and continuously anaesthetized. The pigs were placed

in the supine position. The device was inserted into the

distal oesophagus. Fluoroscopy and ES were used to

verify the position. The bag was distended using sterile

water at rates ranging from 2.5 to 20 mL min)1 using a

60 mL syringe driver pump (Harvard Apparatus Inc.,

Holliston, MA, USA). The bag volume was controlled

to an accuracy of 0.5 mL and the pressure recordings

had an accuracy of 0.25 cm H2O.

Human study

A six-lumen catheter (GMC Medical, Hornslet, Den-

mark) was used (Fig. 2), which had separate lumens for

the ultrasound probe, water infusion and the LDP as

well as three lumens for manometry. The bag attached

was 95 mm long and 45 mm wide.

One healthy female subject, aged 25 years, was

studied. The pharynx was sprayed with lidocain

(Xylocain�, AstraZeneca, Aderslund, Sweden) before

the device was inserted through the mouth into the

stomach, and retracted to the oesophagus, with the tip

of the bag approximately 8 cm proximal to the upper

border of the lower oesophageal sphincter, as deter-

mined with manometry and ultrasound. A total of six

distensions were performed at a bag infusion rate of

15 mL min)1. The inflations were reversed when a

score of 70 was reached on an electronic 100 mm

visual analogue scale for retrosternal discomfort, where

0 indicated no sensation and 50 the pain threshold. The

fifth distension was started 1 min after an intravenous

injection of 20 mg butylscopolaminebromide (Busco-

pan,� Boehringer Ingelheim, Ingelheim am Rhein,

Germany).

Data acquisition and analysis

The pressure transducers were connected to a multi-

channel amplifier (Impedance planimeter Version

Figure 2 The multimodal device forhuman use. Openings for the mano-metric pressure channel are inside thebag and on the distal part of thecatheter (P1 and P2). The end of thesix-lumen catheter is attached to afenestrated cone of a polyethylenepipette. The distal end of the cone wasattached to a smaller end mountcatheter (anchoring-tube) for distalattachment for the bag. The transducerof the LDP was fixed with double-sidedtape to the inner surface of the bag. Theultrasound probe was placed in thecentre of the bag.

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� 2005 The AuthorsJournal compilation � 2006 Blackwell Publishing Ltd 245

3300, GMC Medical), calibration and recordings were

done using dedicated software (Openlab, GMC Med-

ical). All pressure and perfusion data were exported to

Microsoft Excel 2003, (Microsoft Corp., Redmond, WA,

USA). Endosonography recordings were analysed at

maximum inflation in an image analysis program

(SigmaScan Pro 5.0, Systat Inc., Richmond, CA,

USA). Luminal cross-sectional area (CSAL) was deter-

mined from the interface between the liquid and

the bag. Total CSA (CSAT) was determined from the

interface between the longitudinal muscle and the

adventitia. The average wall thickness was calculated

using the equation hW¼(CSAT/p)1/2 ) (CSAL/p)

1/2.

RESULTS

Animal study

High resolution manometric, LDF and endosonograph-

ic signals were achieved during all the 32 distensions

we performed (Fig. 1B–D). With increasing distension

we observed a decreasing discrimination of wall

layers. The thickness of the muscularis propria, both

the inner circular and the outer longitudinal muscle

layer could be identified throughout the bag disten-

sions.

Variation due to the respiratory cycle was recorded

by manometry and the pulse cycle with LDF. The LDF

signal fell abruptly to zero at an average bag pressure

(BP) of 90 and 30 cm H2O and a volume of 10 and

17 mL in pigs 2 and 3, respectively. The LDF signal

reappeared during bag emptying, usually at a lower

pressure and bag volume than when they disappeared.

Human study

High quality signals from manometry, LDF, ES and

VAS were achieved (Fig. 3). Measurement of CSA and

thickness of the wall in multiple views proved to be

consistent with an acceptable intraobserver variation,

P ¼ 0.20.

The BP increased slowly during all bag distensions

and fluctuations were seen due to respiration, primary

peristalsis and distension-induced contractions (Fig. 3C).

The LDF signal decreased during bag distensions

(Fig. 3C). Contractions characterized by high ampli-

tudes and long duration was associated with a decrease

in mucosal perfusion (Fig. 3C) but minor fluctuation

was also observed without contractile activity.

The symptom level increased toward the maximum

filling of the bag. After reversal of the pump, the

symptom level stayed at the same level for some time

(Fig. 3D). During injection of 20 mg butyl scopolamine

bromide, fewer contractions were recorded and the

LDF signal fluctuated less.

DISCUSSION AND PERSPECTIVES

We demonstrated that simultaneous measurements of

pressure, perfusion and ultrasound could be obtained

from the oesophagus, when using a new multimodal

device combining these modalities with bag disten-

sion. The quality of the data indicates that new insight

can be obtained from larger studies in healthy volun-

teers and patients with functional chest pain.

The multimodal catheter concept in gastroenterol-

ogy was introduced in 2002 by Drewes et al.,4 who

integrated electrical, mechanical, cold and warmth

stimuli in the same device measurements. In this

study, we further developed the concept and technol-

ogy to include real time imaging and tissue perfusion.

After bench testing, a simple device was constructed

for the animal experiments. Based on this experience,

the device was further improved for human experi-

ments with better centring of the ultrasound probe in

the bag, less ultrasound signal attenuation and im-

proved attachment of the bag.

All data were of such quality that they could be used

for further analysis. High frequency intraluminal

ultrasound allowed detection of lumen geometry dur-

ing distension.9 Such data are important for 3D-defor-

mation analysis with computation of strains and the

stress distribution in the wall. In the human study

only, due to primary and secondary peristalsis, con-

tractions interfered with endosonographic imaging, but

did not affect the evaluation of the images significantly

nor did distension affect the ability to differentiate the

oesophageal wall layers.9

Laser Doppler flowmetry signals can usually be

obtained up to a depth of 1 mm.8 Hence, presumably

at all degrees of distension, signals will originate

primarily from the mucosa. Animal experiments have

demonstrated residual stresses of compressive nature

in the mucosa-submucosa and of tensile nature in the

muscle layers. This indicates more evenly distributed

stress and strain throughout the oesophageal wall as

also demonstrated in a study of the multilayered

composite oesophagus by Liao et al.10 It is therefore

likely that changes in perfusion throughout the wall

are also evenly distributed. No current method can

provide reliable flow data from the entire human

oesophageal wall. LDF seems to be the best choice

but it must be emphasized that LDF does not provide

absolute flow data but rather arbitrary perfusion units

(PU). Our data show that continuous data sampling can

be done, but the LDF technology depends on several

D. A. L. Hoff et al. Neurogastroenterology and Motility

� 2005 The AuthorsJournal compilation � 2006 Blackwell Publishing Ltd246

factors for obtaining adequate and reproducible re-

sults.8 Although in vitro recordings from a calibration

standard or from a physical model have shown LDF

signals to be highly reproducible,11,12 LDF in vivo is

dependent on factors such as probe design, calibration

options, temperature, blood pressure, pressure applied

at site of measurement and the heterogeneity of the

microvascular anatomy.

It is not clear why the LDF signal was lost abruptly

in the animal experiments whereas continuous record-

ing could be obtained in the human study, in spite of

the peristaltic activity. Bag pressures were approxi-

mately the same. It may be of importance that the

animals were under anaesthesia and the oesophageal

muscles without tone. This might cause over-stretch-

ing of the oesophageal wall during distension. It is also

a possibility that mechanical disruption or angulation

of the LDF transducer led to loss of wall contact in the

animal study, whereas the improved device used in the

human design stabilized the LDF transducer.

This is, to our knowledge, the first time LDF has

been included in a multimodal device for measuring

perfusion in the oesophagus. The study shows the

feasibility of the method but obviously the present

A B

C D

5 mm 5 mm

Figure 3 Two ultrasound images of the oesophagus wall in a human subject. The bag was distended with 10 ml fluid (A) and 25 mlfluid (B). The ultrasound probe was centrally placed. Oesophageal wall layers could be visualized. The ultrasound layers arecorresponding mainly to the mucosa (1), submucosa (2), muscularis propria (3) and adventitia (4). A shadow corresponding to theLDP transducer can be seen at 7 o’clock. The PU plotted together with BP (C) and the VAS symptom score (D). The data areobtained during ramp distension in the human volunteer.

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� 2005 The AuthorsJournal compilation � 2006 Blackwell Publishing Ltd 247

material does not allow firm conclusions yet, whether

gastrointestinal pain is mechanical or ischemic. Fur-

ther studies to look into ischemic- or strain-dependent

mechanisms, need to take advanced distension proto-

cols such as strain softening protocols into considera-

tion.

ACKNOWLEDGMENTS

We wish to express our gratitude to Jens Frøkjær at the

Centre for Visceral Biomechanics and Pain, Aalborg

Hospital, Denmark, for his contribution to design and

development of the present catheter. The same apply to

Perimed AB for their professional handling of our needs

regarding LDP design. The study was supported by

Innovest, Helse-Vest RHF, Helse-Sunnmøre HF and

the Norwegian Research Council.

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