Effects of levodopa on pulmonary function in Parkinson's disease

Upper-airway obstruction (UAO) may be present in patients with Parkinson's disease (PD), and its reversibility after levodopa therapy has been suggested. To investigate the effects of oral intake of levodopa on pulmonary function and UAO criteria in patients with PD, we studied 22 patients with PD.

Pulmonary function tests were performed after a 12-h withdrawal of levodopa therapy, and 1 h after oral intake of placebo or levodopa, according to a double-blind, placebo-controlled, crossover study. Six UAO criteria were recorded to detect UAO in patients. UAO was found in 5 of 21 patients on baseline conditions (1 patient could not perform all tests).

Among the patients with UAO, after levodopa therapy three of five patients did not meet the four of six required criteria for defining UAO. Levodopa produced its effects on UAO criteria by means of a saw-tooth pattern improvement and/or a decrease below the defined thresholds of the peak inspiratory flow and the FEV(1)/peak expiratory flow (PEF) and FEV(1)/forced expiratory flow after 50% of the FVC (FEV(0.5)) ratios. Levodopa PEF increased by 0.85 L/s in patients with UAO and by 0.24 L/s in patients without UAO, while after placebo it increased by 0.03 L/s in patients with UAO and decreased by 0.16 L/s in patients without UAO (p = 0.02). Whereas in patients without UAO an increase of the FEV(1)/PEF and FEV(1)/FEV(0.5) ratios was observed after placebo and levodopa intake, these ratios decreased after levodopa and increased after placebo in patients with UAO.

These results show that levodopa administration in patients with PD induces significant variations in PEF and UAO ratios (FEV(1)/PEF and FEV(1)/FEV(0.5)).