Transcutaneous PCO2 monitoring with hyperventilation during phonation in vocal cord paralysis

Objective: Hyperventilation during phonation is one of the causes of fatigue in-patients with vocal disorders. Methods: The transcutaneous (tc) PCO2 during phonation in 8 normal subjects and 12 patients with unilateral vocal cord paralysis was measured. Cases were further divided into two groups by the degree of the tcPCO2 decrease during phonation. Patients with a tcPCO2 decrease less than 3.4 mmHg during phonation were classified as group 1 (G1). Patients with a tcPCO2 decrease larger than or equal to 3.4 mmHg during phonation were classified into group 2 (G2). Results: The average changes in tcPCO2 in the G1 cases was not significantly different from that in normal subjects. The decrease in tcPCO2 during phonation in the six G2 cases was 10.7±6.2 mmHg, and was significantly different from that in normal subjects (P<0.01, t-test). The decrease of tcPCO2 during phonation in both G1 and G2 cases improved significantly after surgical treatment. Easy fatigability during phonation in two G1 cases and five G2 cases improved. Conclusions: The decrease in tcPCO2 during phonation in cases of unilateral vocal cord paralysis is well correlated with easy fatigability. It is clinically useful to classify cases into two groups using the criteria of a less than 3.4 mmHg or larger than or equal to 3.4 mmHg decrease in tcPCO2. These results also suggest that hyperventilation is one major cause for easy fatigability during phonation in cases with unilateral vocal cord paralysis. TcPCO2 changes during phonation are useful in evaluating hyperventilation and the effect of treatment.