Impedance Measurement Technique

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

2. 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

3. 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 ( Ω ) • Low impedance ► many ions are moving • High impedance ► a few ions are moving

4. 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.

5. Ohm*cm (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 Impedance values A.J.P.M. Smout, UMC-Utrecht, The Netherlands

6. Impedance measurementin the esophagus

7. 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

8. 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

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

10. Impedance signals • Baseline signal IMP PRES

11. Impedance signals • Air in front of the bolus IMP PRES

12. Impedance signals • Bolus IMP PRES

13. Impedance signals • Pressure contraction (increased impedance) IMP PRES

14. Impedance signals • Baseline signal IMP PRES

15. Impedance signals Baseline Air Bolus Contraction Baseline Bolus entry …. exit

16. Impedance signals Belching Baseline Air Baseline

17. 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

18. Impedance catheters • Impedance + pH • Single use • pH antimony • Internal reference • 1 or 2 pH channels • 7 or 8 rings

19. Calculations impedance signals

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

21. 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

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

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

24. Clinical applications of impedance recording

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

26. Bolus transport

27. Normal bolus transit

28. 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 : Tutuian R et al. Clin Gastroenterol Hepatol 2003;1:174-182

29. ‘Combined multichannel intraluminal impedance and manometry clarifies esophageal function abnormalities: study in 350 patients’Tutuian R, Castell DO. Am J Gastroenterol 2004;2:230-236 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

30. Non obstructive dysphagia • 40 patients with non-obstructive dysphagia • Combined manometry+impedance • 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

31. Gas transportair swallowing and belching

32. Air swallow • Normal air intake during: • Dry swallow • Wet swallow • Food intake 32

33. Gastric belch (type I) • Type I belches • Gastric belch • Normal venting of gastric air • After intake of CO2 like Coca Cola 33

34. 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 34

35. Summary of transit test • Manometry (=pressure waves) • Impedance (=transit) • Main indication: • (non-obstructive) Dysphagia • Belching • Clarify functional defects

36. Gastro-esophageal reflux

37. 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

38. Gastro-esophageal reflux (GERD) • Reflux is acid which flows from the stomach into the esophagus • Detected with pH probe

39. 7 pH 4 0 60 seconds imp Reflux Non-acid reflux  Weakly acidic reflux Not detected by pH probe but by impedance PAIN pH>4 ‘Non-acid’ reflux 39

40. 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 >4 but <7) • Non-acid reflux (pH >7)

41. Effect of omeprazole on acid and non-acid reflux in 12 patients with reflux symptoms 55% 97% Off PPI On PPI Vela M et al. Gastroenterology 2001;120:1599-1906

42. Weakly acid reflux • 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

43. 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)

44. Pediatrics and infants • 17 Infants with regurgitation, asthma, apnea • 6-8 meals (milk) per day • Gastric pH often > 4 • Patient group: 17 children • 675 refluxes185 acid 490 non-acid Skopnik et al, J. Pediatric Gastroenterol Nutr 1969

45. 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 45

46. Equipment for impedance recording 46

47. Ambulatory impedance - pH 47

48. OhmegaAmbulatory impedance - pH • Ω 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) 48

49. 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

50. Stationary equipment (Solar-GI)