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* From the Department of Pulmonology Dekkerswald (Drs. van de Ven and Folgering) and the Department of Physiology (Drs. Colier, Oeseburg, and Vis and Mr. van der Sluijs), Faculty of Medical Sciences, University Medical Center Nijmegen, The Netherlands.
Correspondence to: Marjo J. T. van de Ven, MD, Department of Pulmonology Dekkerswald, University Medical Center Nijmegen, PO Box 9001, 6560 GB Groesbeek, The Netherlands; e-mail: m_vandeven60{at}hotmail.com
Study objectives: Effects of chronic metabolic alkalosis and acidosis and their relation to central chemoregulation may differ between normocapnic and chronic hypercapnic patients with COPD. The relationship between responses of inspired ventilation (VI), mouth occlusion pressure (P0.1), and cerebral blood volume (CBV), to short-term changes in arterial PCO2 was measured.
Patients and
methods: Seventeen patients with chronic hypercapnia and COPD
(PaCO2 > 6.0 kPa) and 16 normocapnic patients
with COPD (PaCO2
6.0 kPa)
[FEV1 27% predicted] were studied under baseline
metabolic conditions and after 1 week of treatment with oral
furosemide, 40 mg/d, or acetazolamide, 500 mg/d. Hypercapnia (change in
end-tidal carbon dioxide > 1 kPa) was induced by administering
adequate amounts of carbon dioxide in the inspired air. CBV was
measured using near-infrared spectroscopy.
Results:
Compared with baseline metabolic condition, chronic metabolic acidosis
and alkalosis did not change ventilatory
(
VI/
PaCO2) and
cerebrovascular (
CBV/
PaCO2) reactivity.
Base excess (BE) decreased by 6.8 ± 1.1 mEq/L and 6.9 ± 1.6
mEq/L, respectively, in the normocapnic and chronic hypercapnic COPD
groups during metabolic acidosis, resulting in a not-quite-significant
leftward shift of both the ventilatory and cerebrovascular carbon
dioxide response curve. BE increased by 2.3 ± 1.2 mEq/L and
1.2 ± 1.3 mEq/L, respectively, during chronic metabolic alkalosis in
both COPD groups, without concomitant shift. Poor correlations between
ventilatory and cerebrovascular carbon dioxide responsiveness
(
CBV/
PaCO2 and
VI/
PaCO2,
CBV/
PaCO2 and
P0.1/
PaCO2, respectively)
were found irrespective of baseline, respiratory condition, and induced
metabolic state.
Conclusions: Normocapnic and chronic hypercapnic COPD patients have the same ventilatory and cerebrovascular carbon dioxide responsiveness irrespective of induced metabolic state.
Key Words: acid-base central chemosensitivity cerebral blood volume control of breathing COPD metabolic acidosis metabolic alkalosis mouth occlusion pressure near-infrared spectroscopy
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