1. 2 Dept. of Anesthesia and Medicine, Massachusetts General
Correlation in Degradation of Lung Mechanics with Ventilation Distribution in Asthmatics
N. T. Tgavalekos1,2
R. S. Harris2, M.F. Vidal Melo2, G. Musch2,
T. Winkler2, K.R. Lutchen1 and J. G. Venegas2
1 Dept. of Biomedical Engineering, Boston University,
Boston, MA
2 Dept. of Anesthesia and Medicine, Massachusetts General
Hospital, Boston, MA
October 2, 2003
BMES conference

2. Evidence of Mechanical Heterogeneity in Asthma
Healthy
Mild-Moderate Asthmatic
Severe Asthmatic
RL(cmH2O/l/s)
EL(cmH2O/l)
Airway closure/Heterogeneity
Heterogeneity
Heterogeneity
Lutchen, K.R., D.W. Kaczka, E. Israel, B. Suki, E.P. Ingenito. Airway constriction pattern is a central component of asthma severity: the role of deep inspirations. Amer. J. of Resp. and Crit. Care Medicine 164: , 2001.

3. Evidence of Heterogeneity in Ventilation
Baseline
Post Challenge

4. Indices of Ventilation Dynamic Lung Mechanics
Main Goal
Are ventilation heterogeneity related to mechanical heterogeneity? l
Indices of Mechanic
Heterogeneity
Relationship?
Indices of Ventilation
PET imaging
Dynamic Lung Mechanics
RL,EL vs. freq.

5. Lung Mechanics
RL, EL estimated from lung impedance (ZL) via forced oscillations:
ZL(jw) =
Ptp (jw)
Q (jw)
RL = Re {ZL}
EL =-2pf Im {ZL}

6. Quantifying Dynamic Lung Mechanics
Rlow
Rlow-Rhigh ~ heterogeneity
Elow
Ehigh
Ehigh-Elow ~ heterogeneity/
airway shunting
Rhigh
Rhigh ~ Raw

7. Features of Lung Mechanics
** p<.001
* p<.001 * **

8. Relating Ventilation Heterogeneity to Mechanical Heterogeneity
Post Challenge
Baseline
Tracer
Retention
Airway closure/
Heterogeneity
Apnea
Washout
Time (secs)

9. Multi - Compartmental Washout
Baseline
Post Challenge
R2=.99
R2=.99
Two Compartment Model
C(t) = C1(0)e-t/t1 +C2(0)e-t/t2

10. Quantifying Ventilation Heterogeneity. .
= fraction of blood flow .
Heterogeneity Index (HI) .

11. Mechanics vs. Ventilation Heterogeneity
Baseline
Post Challenge

12. Conclusions Elevation and frequency dependence in lung mechanics is
also indicative of ventilation heterogeneity
Airway constriction in asthma is inherently heterogeneous
causing a distribution of poorly ventilated regions throughout the
lung simultaneously with degradation lung mechanics
These data sets can be combined with airway tree
models to identify what level of airways are actually
closing or constricting during asthma

13. Acknowledgements Anesthesia & Critical Care José G. Venegas, Ph.D.
R. Scott Harris, M.D.
Marcos Vidal Melo, M.D. Ph.D.
Guido Musch, M.D.
Tilo Winkler, Ph.D.
Dominick Layfield, Ph.D.
BU Respiratory Lab
K. R. Lutchen, Ph.D
Cortney Henderson, Ph.D
Carissa Bellardine, M.S.
Derek Affonce, M.S

14. Quantifying Airway Closure

15. Rlow vs. HI

16. PET Imaging in Asthmatics
End Washout :
Gas Trapping
PET functional imaging may provide useful insights into the role of gas trapping in asthma