Effect of moderate altitude with and without nocturnal oxygen therapy on the next-day cerebrovascular function in patients with chronic obstructive pulmonary disease – A randomized, cross-over trial at 2048 m
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Background
This study investigated whether nocturnal oxygen therapy (NOT) improves next-day cerebrovascular function in lowlanders with COPD staying at moderate altitude.
Methods
This randomized, placebo-controlled crossover trial was performed in stable patients with moderate to severe COPD (FEV 1 /FVC <0.7 and FEV 1 30-80%predicted), living <800m and pulse oximetry (SpO 2 ) ≥92%. Patients underwent assessments at 490m and during 2 stays of 2 days at 2048m while NOT or placebo (each at 3L min −1 through nasal cannula) were applied according to a randomized cross-over design. At both altitudes, SpO 2 , cerebral tissue oxygenation (CTO, near-infrared spectroscopy), mean arterial blood pressure (MAP, finger plethysmography) and middle cerebral artery systolic peak blood flow velocity (sMCAv, transcranial Doppler ultrasound) were assessed while patients were (0) quietly breathing FiO 2 0.21; (i) quietly breathing FiO 2 1.0, (ii) voluntarily hyperventilating, (iii) voluntarily hyperventilating under FiO 2 1.0, and (iv) during head-up tilting. Indices of cerebrovascular responsiveness to changes in blood gases and blood pressure were computed.
Results
A total of 18 patients (8 women aged mean±SD 65±5y, FEV 1 54.7±13.9%predicted) were analyzed. At 2048m under placebo, patients became hypoxemic, mean±SE SpO 2 90.3±0.4% vs. 93.7±0.4% at 490m, while MAP, CTO and sMCAv remained unchanged compared to 490m. All ventilatory maneuvers at 2048 m induced greater increases in SpO 2 compared to 490m while changes in MAP, CTO and sMCAv were similar. Head-up tilting induced a similar blood pressure fall at 2048m compared to 490m, whereas cerebral blood flow velocity changed less in response to systemic hypotension (mean±SE ΔsMCAv/ΔMAP 0.9±0.3 vs. 2.3±0.4cm s −1 mmHg −1 ) at 2048m. No alteration in cerebrovascular function as a treatment effect of NOT was observed in either maneuver.
Conclusion
This randomized clinical trial in moderate-to-severe COPD patients ascending to 2048m showed that moderate daytime systemic hypoxemia does not translate to cerebral hypoxia nor cerebrovascular autoregulatory impairments while at rest or under ventilatory or orthostatic challenges.
