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

+ 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

+ Impedance is the electrical resistance measured with an alternating current + Impedance is the inverse of conductance (Imp = 1/Cond) + Impedance is measured in Ohm ( Ω ) – Low impedance many ions are moving – High impedance a few ions are moving Georg Simon Ohm

+ 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.

Ohm*cm (at 1 kHz) Gastric contents 30 – 100 Bile 90 Physiologic saline solution 100 Saliva 110 Skeletal muscle Milk / Yoghurt 300 Custard-based dessert / curds 400 Drinking water 1100 Cola 1100 Esophageal wall 2000 Epidermis 2000 – Air A.J.P.M. Smout, UMC-Utrecht, The Netherlands

+ 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

+ Catheters with multiple metal rings + A ring can be used for 2 channels if the distance is not too big (2 cm) Channel Ring R1 R2 R3 R4

Oesophagus wall Pressure contraction Water bolus Air in front of bolus Impedance ring Pressure sensor

+ Baseline signal IMP PRES

+ Air in front of the bolus IMP PRES

+ Bolus IMP PRES

+ Pressure contraction (increased impedance) IMP PRES

+ Baseline signal IMP PRES

Baseline Air Bolus Contraction Baseline Bolus entry …. exit

Belching Baseline Air Baseline

+ A Wet swallow: The liquid falls down into the esophagus + B The front of the pressure wave clears the esophagus 4 sec A B WS Clearing Peak Imp Pres

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

+ BPT (Bolus Presence Time) – Time elapsed between: Bolus entry and Bolus exit using a 50% threshold. 50 % BPT

+ 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

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

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

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

Liquid swallows 80 % complete bolus transit Viscous swallows 70 % complete bolus transit Tutuian R et al. Clin Gastroenterol Hepatol 2003;1: healthy subjects solid-state manometry 10 liquid, 10 viscous swallows Normal esophageal transit when :

Manometric diagnosis N Normal transit Achalasia 24 0% Scleroderma 4 0% IEM 71 51% DES 33 55% Normal125 95% Hypertensive LES 25 96% Nutcracker 30 97% LES dysrelaxation 33100% Hypotensive LES 5100% IEM = Ineffective Esophageal Motility DES = Diffuse Esophageal Spasms

+ 40 patients with non-obstructive dysphagia + Combined manometry+impedance + Manometry findings Impedance (transit findings) + Normal 20 35% abnormal transit + Ineffective motility % abnormal transit + Esophageal spasms 4 67 % abnormal transit + Achalasia % abnormal transit + total 40

+ Normal air intake during: – Dry swallow – Wet swallow – Food intake April

+ Type I belches + Gastric belch – Normal venting of gastric air – After intake of CO 2 like Coca Cola April

+ Type II belches + Supragastric belch – Sucking air into the esophagus with immediate expulsion – Aerophagia + [A] Suck air in + [B] Belch out April AB

+ Manometry (=pressure waves) + Impedance (=transit) + Main indication: – (non-obstructive) Dysphagia – Belching – Clarify functional defects

+ 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

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

April imp pH seconds pH>4 Non-acid reflux PAIN Reflux Non-acid reflux Weakly acidic reflux Not detected by pH probe but by impedance

+ Reflux subcategories: – Acid reflux (pH falls below 4) – Super-imposed acid reflux (reflux while pH is already below 4) – Weakly acidic reflux (pH nadir >4 but <7) – Non-acid reflux (pH >7)

Off PPI On PPI 55% 97% Vela M et al. Gastroenterology 2001;120:

+ Weakly acid reflux (pH >4) 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

+ 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)

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

+ 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 April

April

April

+ 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 hr) April

+ 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 hr + Internal memory 2-3 days