Pulmonary vascular responses to hypoxia and hyperoxia in healthy volunteers and COPD patients measured by electrical impedance tomography.
BACKGROUND
Electrical impedance tomography (EIT) is a noninvasive imaging technique using impedance to visualize and measure blood volume changes.


OBJECTIVE
To examine the validity of EIT in the measurement of hypoxic pulmonary vasoconstriction (HPV) and hyperoxic pulmonary vasodilation in healthy volunteers and COPD patients.


METHODS
Group 1 consisted of seven healthy volunteers (mean age, 46 years; age range, 36 to 53 years). Group 2 comprised six clinically stable COPD patients (mean age, 65 years; age range, 50 to 74 years).


METHODS
EIT measurements were performed in healthy subjects while they were breathing room air, 14% oxygen (ie, hypoxia), and 100% oxygen (ie, hyperoxia) through a mouthpiece. Maximal impedance change during systole (DeltaZsys) was used as a measure of pulmonary perfusion-related impedance changes. Stroke volume (SV) was measured by means of MRI. In the COPD group, EIT and SV also were determined, but only in room air and under hyperoxic conditions.


RESULTS
The data were statistically compared to data for the room air baseline condition. In the volunteers, the mean (+/- SD) DeltaZsys for the group was 352 +/- 53 arbitrary units (AU) while breathing room air, 309 +/- 75 AU in hypoxia (p < 0.05), and 341 +/- 69 AU in hyperoxia (not significant [NS]). The mean MRI-measured SV was 83 +/- 21 mL while breathing room air, 90 +/- 29) mL in hypoxia (NS), and 94 +/- 19 mL in hyperoxia (p < 0.05). In the COPD patients, the mean DeltaZsys for this group was 222 +/- 84 AU while breathing room air and 255 +/- 83 AU in hyperoxia (p < 0.05). In this group, the SV was 59 +/- 16 mL while breathing room air and 61 +/- 13 mL in hyperoxia (NS). Thus, the volunteer EIT response to hypoxia is not caused by decreased SV, because SV did not show a significant decrease. Similarly, in COPD patients the EIT response to hyperoxia is not caused by increased SV, because SV showed only a minor change.


CONCLUSIONS
EIT can detect blood volume changes due to HPV noninvasively in healthy subjects and hyperoxic vasodilation in COPD patients.
Smit
Henk J
HJ
Department of Pulmonary Medicine, Vrije Universiteit Medical Center, Amsterdam, the Netherlands. HJ.Smit@VUmc.nl
Vonk-Noordegraaf
Anton
A
Marcus
J Tim
JT
van der Weijden
Saskia
S
Postmus
Pieter E
PE
de Vries
Peter M J M
PM
Boonstra
Anco
A
D000328:Adult; D000368:Aged; D017097:Electric Impedance; D006801:Humans; D018496:Hyperoxia / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008875:Middle Aged; D011652:Pulmonary Circulation / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D014054:Tomography / Q000379:methods*; D014661:Vasoconstriction / Q000502:physiology