Effect of oral levodopa treatment on articulatory function in Parkinson's disease: preliminary results

To quantify lip function in 16 patients with Parkinson's disease, a computerized semiconductor lip pressure transducer system was used prior to subjects being administered oral levodopa and at approximately 0.5 hr, 1.5 hr, and 3.0 hr postmedication. Two blood samples were taken from each subject at varying times during the levodopa dosage interval, and the exact time and dosage of levodopa were noted. Lip function measurements were expressed as percentage changes from baseline and were plotted for each subject against time and levodopa concentrations to determine the effects of levodopa therapy on articulatory function. The results supported the effectiveness of levodopa therapy in improving lip function. In particular, lip pressures recorded during both speech and nonspeech tasks tended to improve after levodopa administration, the lip measures improving somewhat in parallel with the rise and fall of blood plasma levodopa concentrations. Evidence of a hysteresis effect was noted.