Impedance Measurement Technique

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Impedance Measurement Technique

• Jia-Feng Wu, M.D.
• Division of Gastroenterology,
• Department of Pediatrics,
• National Taiwan University Children Hospital

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Impedance

• Impedance measurement is used to show the bolus
  transit in the esophagus.
• Traditional method uses X-ray to visualize the
  bolus movement (video pharyngeography)
• Because of the low price per channel many
  measuring points can be used (2 cm spacing) to
  cover the total esophagus

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What is impedance?
Georg Simon Ohm 1789-1854

• Impedance is the electrical resistance measured
  with an alternating current
• Impedance is the inverse of conductance (Imp
  1/Cond)
• Impedance is measured in Ohm ( O )
• Low impedance ? many ions are moving
• High impedance ? a few ions are moving

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Impedance

• In order to reduce the oxidation of the metal
  electrodes, an alternating current is used at 3.2
  kHz
• That means the Plus and Minus are changing 3200
  times per second.

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Impedance values

• Ohmcm (at 1 kHz)
• Gastric contents 30 100
• Bile 90
• Physiologic saline solution 100
• Saliva 110
• Skeletal muscle 250 - 700
• Milk / Yoghurt 300
• Custard-based dessert / curds 400
• Drinking water 1100
• Cola 1100
• Esophageal wall 2000
• Epidermis 2000 100.000
• Air 10.000.000

A.J.P.M. Smout,
UMC-Utrecht, The Netherlands
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Impedance measurementin the esophagus
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Measuring technique

• Use a impedance catheter
• A small electrical current is used to measure the
  impedance between the 2 rings

Ring R1 R2
Patient safe low electrical current
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Measuring technique

• Catheters with multiple metal rings
• A ring can be used for 2 channels if the distance
  is not too big (2 cm)

Ring R1 R2 R3 R4
Channel 1 2 3
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Impedance signals
Oesophagus wall Pressure contraction Water
bolus Air in front of bolus Impedance
ring Pressure sensor
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Impedance signals

• Baseline signal

IMP
PRES
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Impedance signals

• Air in front of the bolus

IMP
PRES
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Impedance signals

• Bolus

IMP
PRES
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Impedance signals

• Pressure contraction (increased impedance)

IMP
PRES
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Impedance signals

• Baseline signal

IMP
PRES
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Impedance signals
Baseline Air Bolus Contraction Baseline
Bolus entry . exit
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Impedance signals
Belching Baseline Air
Baseline
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Impedance signals
A B

• A Wet swallow The liquid falls down into the
  esophagus
• B The front of the pressure wave clears the
  esophagus

WS Clearing Peak
Imp Pres
4 sec
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Impedance catheters

• Impedance pH
• Single use
• pH antimony
• Internal reference
• 1 or 2 pH channels
• 7 or 8 rings

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Calculations impedance signals
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Calculations

• BPT (Bolus Presence Time)
• Time elapsed between
• Bolus entry and
• Bolus exit using a 50 threshold.

BPT
50
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Calculations
BHAT

• BHAT (Bolus Head Advance Time)
• Time elapsed between
• Bolus entry at top channel and
• Bolus entry at each channel
• Speed of bolus moving down

BHAT
BHAT
BHAT
BHAT
BHAT
BHAT
BHAT
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Calculations
TBTT

• TBTT (Total Bolus Transit Time)
• Time elapsed between
• Bolus entry at top channel and
• Bolus exit at lowest channel

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Calculations
STT
STT

• STT (Segment Transit Time)
• Time elapsed between
• Bolus entry at a channel and
• Bolus exit at next (lower) channel

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Clinical applications of impedance recording
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Clinical applications

• Esophagus
• bolus transit
• gas transport (air swallowing and belching)
• gastro-esophageal reflux

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Bolus transport
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Normal bolus transit
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Esophageal function testing with combined
multichannel intraluminal impedance and
manometry multicenter study in healthy volunteers
43 healthy subjects solid-state manometry 10
liquid, 10 viscous swallows
Normal esophageal transit when
Liquid swallows 80 complete bolus transit
Viscous swallows 70 complete bolus transit
Tutuian R et al. Clin Gastroenterol Hepatol
20031174-182
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Combined multichannel intraluminal impedance and
manometry clarifies esophageal function
abnormalities study in 350 patientsTutuian R,
Castell DO. Am J Gastroenterol 20042230-236
Manometric diagnosis N Normal
transit Achalasia 24 0 Scleroderma
4 0 IEM 71 51 DES 33
55 Normal 125 95 Hypertensive LES 25
96 Nutcracker 30 97 LES dysrelaxation
33 100 Hypotensive LES 5 100
IEM Ineffective Esophageal Motility DES
Diffuse Esophageal Spasms
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Non obstructive dysphagia

• 40 patients with non-obstructive dysphagia
• Combined manometryimpedance
• Manometry findings
  Impedance (transit findings)
• Normal 20
  35 abnormal transit
• Ineffective motility 13 85
  abnormal transit
• Esophageal spasms 4 67
  abnormal transit
• Achalasia 3
  100 abnormal transit
• total 40

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Gas transportair swallowing and belching
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Air swallow

• Normal air intake during
• Dry swallow
• Wet swallow
• Food intake

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Gastric belch (type I)

• Type I belches
• Gastric belch
• Normal venting of gastric air
• After intake of CO2 like Coca Cola

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Supra-gastric belch (type II)

• Type II belches
• Supragastric belch
• Sucking air into the esophagus with immediate
  expulsion
• Aerophagia
• A Suck air in
• B Belch out

A
B
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Summary of transit test

• Manometry (pressure waves)
• Impedance (transit)
• Main indication
• (non-obstructive) Dysphagia
• Belching
• Clarify functional defects

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Gastro-esophageal reflux
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Gastro-esophageal reflux (GERD)

• Reflux of gastric content into the esophagus
• Symptoms heartburn / regurgitation
• Damage to the esophageal wall (esophagitis)
• Up to 10 of world population
• Golden standard diagnostic tool
• 24 hr pH monitoring

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Gastro-esophageal reflux (GERD)

• Reflux is acid which flows from the stomach into
  the esophagus
• Detected with pH probe

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imp
Reflux
Non-acid reflux ? Weakly acidic reflux Not
detected by pH probe but by impedance
PAIN
pHgt4 Non-acid reflux
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New category (consensus meting)

• Reflux subcategories
• Acid reflux (pH falls below 4)
• Super-imposed acid reflux (reflux while pH is
  already below 4)
• Weakly acidic reflux (pH nadir gt4 but lt7)
• Non-acid reflux (pH gt7)

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Effect of omeprazole on acid and non-acid reflux
in 12 patients with reflux symptoms
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97
Off PPI On PPI
Vela M et al. Gastroenterology 20011201599-1906
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Weakly acid reflux

• Weakly acid reflux (pH gt4) can cause symptoms
• Most of the patients who visit a GI doctor
  continue to use PPI
• Weakly acid reflux cannot be analysed with a pH
  probe
• Impedance-pH detects ALL reflux episodes

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Pediatrics and infants

• Gastric content is very often not acid due to
  milk intake. Sometimes even higher than pH 7 due
  to buffering
• Reflux cannot be detected with a pH probe
• Impedance recording
• Bolus transit and reflux measured
• Reflux contents does not matter
• 24 hour (just like ambulatory pH)

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Pediatrics and infants

• 17 Infants with regurgitation, asthma, apnea
• 6-8 meals (milk) per day
• Gastric pH often gt 4
• Patient group 17 children
• 675 refluxes 185 acid
• 490
  non-acid
• 
  Skopnik et al, J.
  Pediatric Gastroenterol Nutr 1969

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Summary impedance-pH investigation

• Esophageal impedance monitoring can detect reflux
  with a pH above 4
• Weakly acid reflux
• It can detects acid and non-acid reflux episodes
• Clinical useful for evaluation of
• Symptoms under PPI
• Symptoms off PPI
• Unexplained cough
• Pediatric practice

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Equipment for impedance recording
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Ambulatory impedance - pH
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OhmegaAmbulatory impedance - pH

• ? Ohmega specs
• 8 to 13 Impedance rings
• 1 to 4 pH Antimony
• 2 glass pH 2 ISFET pH (optional)
• 4 pressure channels (optional)
• Bluetooth wireless connection (up to 50 meter)
• Memory 128 MB
• USB interface with PC
• Power supply 1 AA battery (recording time 28-35
  hr)

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Technical data Ohmega

• Data size ambulatory investigation 24 hr
• 50 MB for 24 hours
• Sample rate
• 50 samples/sec impedance channels (6 channels)
• 1 sample/sec pH channel
• MMS non destructive data compression 50 MB into
  15 MB
• Download time 5 10 minutes
• Use CD-R or DVD-R as backup
• Recording time 1 AA battery 28-35 hr
• Internal memory 2-3 days

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Stationary equipment (Solar-GI)