A new device for ambulatory cough recording

Abstract

Nocturnal cough reporting on diary cards has been shown to be unreliable and inconsistent. Whether subjective reporting of daytime cough is equally unreliable remains unknown. We have, therefore, developed a new and easily portable device (RBC-7) that records electromyographic (EMG) and audio cough signals for at least a 24-hr period, with a capacity of over 48 hr. Additional information is obtained from electrocardiographic (ECG) signals, and from an accelerometer indicating the level of the subject's activity. The RBC-7 can be set up with the aid of a notebook computer at the subjects home, school or workplace. Initial studies utilizing a prototype device were performed to determine the optimal position of the EMG leads and the microphone. The optimal position for the EMG leads was determined as the positive electrode in the sixth intercostal space (ICS) in the midclavicular line on the left, the negative electrode in the same position on the right, and the reference electrode in the midline over the abdomen. This position was shown to give the highest EMG voltages and the greatest difference in voltages between cough and other signals. The optimal microphone position for signal strength and comfort was over the first ICS, either right or left, close to the sternum. Recordings were performed simultaneously in 20 subjects with conventional tape recorders and the multiparametric cough monitoring system (RBC-7). Conventional tape recordings limited the duration of the studies due to the inherent restrictions. No significant difference in the number of single coughs recorded by each system was detected (correlation coefficient = 0.996). The RBC-7 offers a unique opportunity to obtain objective information on cough in ambulatory subjects over at least a 24-hr period, and to relate cough to time, activity and heart rate, while normal activities are pursued.