Gas exchange in stable patients with moderate-to-severe lung disease from cystic fibrosis.
BACKGROUND
Studies using the multiple inert gas elimination technique (MIGET) to characterise the mechanisms of impaired gas exchange in CF, provide conflicting results on the importance of ventilation-perfusion (VA/Q) inequality over shunt. We hypothesise that the mechanisms of gas exchange abnormality have changed with changing CF management over the last two decades.


METHODS
Detailed gas exchange was evaluated by MIGET with venous sampling in stable patients, age > 20 years, FEV1% predicted < or = 50.


RESULTS
Fifteen (14 male) subjects were studied with a mean +/- SD age 28.1 +/- 8.4 years, FEV1% 32.6 +/- 10.3, TLC% 111.5 +/- 12.9, PaO2 9.3 +/- 1.3 kPa, (69.5 +/- 9.6 mm Hg), and PaCO2 6.2 +/- 0.7 kPa, (45.9 +/- 5.3 mm Hg). The predominant gas exchange abnormality was VA/Q inequality with a log SD of the distributions of perfusion 0.91 +/- 0.30 and of ventilation 0.60 +/- 0.14. Unimodal distributions were seen in nine subjects, a low VA/Q mode in five and one subject had a bimodal distribution, mean intrapulmonary shunt was negligible.


CONCLUSIONS
Subjects had a lower FEV1% by comparison with previously published studies and demonstrated severe VA/Q inequality and negligible shunt. This suggests a low degree of complete obstruction of airways in adults with CF and severe stable pulmonary disease. The primary mechanism of hypoxaemia in CF subjects reaching adulthood today appears to have changed with modern management over the last two decades.
Soni
Rajeev
R
Department of Respiratory Medicine, Gosford Hospital, Gosford, NSW, 2250, Australia. Electronic address: rsoni@nsccahs.health.nsw.gov.au.
Dobbin
Catherine J
CJ
Department of Respiratory Medicine, Royal Prince Alfred Hospital, Sydney, NSW, 2050, Australia. Electronic address: cathd@med.usyd.edu.au.
Milross
Maree A
MA
Department of Respiratory Medicine, Royal Prince Alfred Hospital, Sydney, NSW, 2050, Australia. Electronic address: mareem@med.usyd.edu.au.
Young
Iven H
IH
Department of Respiratory Medicine, Royal Prince Alfred Hospital, Sydney, NSW, 2050, Australia. Electronic address: iveny@med.usyd.edu.au.
Bye
Peter P T
PPT
Department of Respiratory Medicine, Royal Prince Alfred Hospital, Sydney, NSW, 2050, Australia. Electronic address: peterb@med.usyd.edu.au.
D000328:Adult; D001784:Blood Gas Analysis; D015331:Cohort Studies; D003550:Cystic Fibrosis / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*; D055815:Young Adult