Measurement of ventilation and cardiac related impedance changes with electrical impedance tomography.
BACKGROUND
Electrical impedance tomography (EIT) has been shown to be able to distinguish both ventilation and perfusion. With adequate filtering the regional distributions of both ventilation and perfusion and their relationships could be analysed. Several methods of separation have been suggested previously, including breath holding, electrocardiograph (ECG) gating and frequency filtering. Many of these methods require interventions inappropriate in a clinical setting. This study therefore aims to extend a previously reported frequency filtering technique to a spontaneously breathing cohort and assess the regional distributions of ventilation and perfusion and their relationship.


METHODS
Ten healthy adults were measured during a breath hold and while spontaneously breathing in supine, prone, left and right lateral positions. EIT data were analysed with and without filtering at the respiratory and heart rate. Profiles of ventilation, perfusion and ventilation/perfusion related impedance change were generated and regions of ventilation and pulmonary perfusion were identified and compared.


RESULTS
Analysis of the filtration technique demonstrated its ability to separate the ventilation and cardiac related impedance signals without negative impact. It was, therefore, deemed suitable for use in this spontaneously breathing cohort.Regional distributions of ventilation, perfusion and the combined ΔZV/ΔZQ were calculated along the gravity axis and anatomically in each position. Along the gravity axis, gravity dependence was seen only in the lateral positions in ventilation distribution, with the dependent lung being better ventilated regardless of position. This gravity dependence was not seen in perfusion.When looking anatomically, differences were only apparent in the lateral positions. The lateral position ventilation distributions showed a difference in the left lung, with the right lung maintaining a similar distribution in both lateral positions. This is likely caused by more pronounced anatomical changes in the left lung when changing positions.


CONCLUSIONS
The modified filtration technique was demonstrated to be effective in separating the ventilation and perfusion signals in spontaneously breathing subjects. Gravity dependence was seen only in ventilation distribution in the left lung in lateral positions, suggesting gravity based shifts in anatomical structures. Gravity dependence was not seen in any perfusion distributions.
Paediatric Critical Care Research Group, Paediatric Intensive Care Unit, Mater Children's Hospital, 550 Stanley Street, South Brisbane, Queensland 4101, Australia. Caroline.Grant@mater.org.au
Caroline A
CA
Grant
Trang
T
Pham
Judith
J
Hough
Thomas
T
Riedel
Christian
C
Stocker
Andreas
A
Schibler
D000328:Adult; D017097:Electric Impedance; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D011187:Posture / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology*; D015203:Reproducibility of Results; D012119:Respiration; D014054:Tomography / Q000379:methods*; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*; D055815:Young Adult
IEEE Trans Med Imaging. 2002 Jun;21(6):646-52
12166861
Physiol Meas. 2006 Nov;27(11):1151-65
17028408
J Appl Physiol (1985). 2001 Apr;90(4):1342-8
11247933
Intensive Care Med. 2005 Nov;31(11):1522-8
16195908
J Appl Physiol (1985). 2006 Sep;101(3):763-70
16627672
Crit Care Med. 2009 Feb;37(2):713-24
19114889
Physiol Meas. 2000 May;21(2):285-93
10847195
Intensive Care Med. 2010 Dec;36(12):2101-8
20857279
Respir Physiol. 1984 May;56(2):169-82
6463424
Acta Anaesthesiol Scand. 2009 Feb;53(2):152-8
19175575
Physiol Meas. 2001 Feb;22(1):159-66
11236876
Physiol Meas. 2006 May;27(5):S115-27
16636403
Physiol Meas. 2008 Jun;29(6):S1-14
18544813
Intensive Care Med. 2003 Dec;29(12):2312-2316
14566457
Crit Care. 2009;13(2):R34
19265527
Physiol Meas. 1998 May;19(2):263-73
9626690
Respiration. 2009;77(3):282-91
19147986
J Appl Physiol (1985). 1999 Feb;86(2):623-32
9931200