A comparison of cognitive functions in non-hypoxemic chronic obstructive pulmonary disease (COPD) patients and age-matched healthy volunteers using mini-mental state examination questionnaire and event-related potential, P300 analysis

Abstract

Objective: To assess sub-clinical cognitive dysfunctions in stable chronic obstructive pulmonary disease (COPD) patients having no hypoxemia vs. age-matched healthy volunteers using (i) an electrophysiological test: Auditory event related potential, P300 test and (ii) a questionnaire tool: Mini-mental state examination (MMSE) questionnaire.

Materials and methods: EIGHTY MALE SUBJECTS WERE INCLUDED: 40 stable COPD patients (smoking history >20 pack years) and 40 healthy volunteers (HVs). Age, duration of illness, smoking pack years, and spirometric indices were assessed. MMSE scores were evaluated in these groups. Latency of P300 wave and amplitude of P300 wave were studied in both groups to detect P300 abnormalities in COPD group. Correlations of P300 abnormalities with patient characteristic parameters and MMSE scores were assessed. In addition, individual COPD patients having significant cognitive dysfunctions beyond cut-off value of 99(th) percentile of HVs were analyzed.

Results: We observed significantly prolonged P300 latency (P < 0.001) and decreased P300 amplitude (P < 0.001) in COPD group. MMSE scores were significantly reduced in COPD group (P < 0.001). 10/40 COPD patients had prolongation of P300 latency, and 27/40 COPD patients had reduced MMSE scores beyond 99(th) percentile of HV. However, we did not observe any statistically significant correlation between P300 abnormalities and patients' characteristics or MMSE scores (P > 0.05 for all).

Conclusions: Our study explores cognitive dysfunctions in stable COPD patients with no hypoxemia. This study highlights the relative importance of using MMSE and P300. Cognitive dysfunctions were detected both by MMSE and P300; however, MMSE abnormalities were more frequent compared to P300 abnormalities (27/40 vs. 10/40) in COPD patients.

Keywords: Chronic obstructive pulmonary disease; P300; cognitive functions; event-related potential; mini-mental state examination.

Figure 1

The electrophysiological assessment was done in response to auditory stimuli given with a frequency of 1 stimulus/s. They were of two types: Frequent tone stimuli [80% of total stimuli] and rare tone stimuli [20% of total stimuli]. Event-related potential wave pattern observed with a frequent tone stimulus is shown here: A negative N1 wave is followed by positive P2 vertex potential

Figure 2

Event-related potential pattern with a rare tone stimulus: A negative N1, followed by positive apparent P2, again followed by negative N2–positive P300 complex (representing, in part, the event-related response) is seen. The latency of N2–P300 and amplitude of P300 wave is used for analysis purpose.