P wave duration and dispersion in Holter electrocardiography of patients with obstructive sleep apnea.

PURPOSE: The underlying mechanisms of the association between obstructive sleep apnea (OSA) and atrial fibrillation (AF) remained unclear. We investigated P wave parameters as indicators of atrial conduction status among OSA patients. METHODS: We studied 42 untreated OSA patients, categorized into mild (6), moderate (18), and severe (18) OSA based on the apnea/hypopnea index (AHI) and 18 healthy controls. Twenty-four-hour Holter electrocardiography was applied to measure P wave parameters including P wave duration and P wave dispersion; difference between the maximum (P-max) and minimum (P-min) measured P wave duration. RESULTS: Mean P wave duration ranged from 110.2 ± 9.3 ms in mild OSA patients to 121.1 ± 15.4 ms in severe OSA patients and was 113.4 ± 10.0 ms in controls with no significant difference among the groups, P = 0.281. P wave dispersion and P-max were significantly longer in those with moderate OSA (68.0 ± 9.3 and 154.2 ± 9.3 ms) and those with severe OSA (71.6 ± 13.7 and 157.2 ± 13.3 ms) than controls (52.6 ± 15.3 and 142.1 ± 15.4 ms), P < 0.05. AHI was significantly correlated with P-max (r = 0.407, P = 0.012) and P wave dispersion (r = 0.431, P = 0.008). With linear regression analysis controlling for age, gender, and BMI, the AHI was independently associated with P wave dispersion (ß = 0.482, P = 0.002). CONCLUSIONS: Using Holter monitoring for measurement of P wave parameters, this study showed an association of OSA with prolonged P-max and P wave dispersion. These results indicate that patients with OSA have disturbances in atrial conduction associated with OSA severity. Repeating this study in a larger sample of patients is warranted.

Designing a Low-noise, High-resolution, and Portable Four Channel Acquisition System for Recording Surface Electromyographic Signal.

In current years, the application of biopotential signals has received a lot of attention in literature. One of these signals is an electromyogram (EMG) generated by active muscles. Surface EMG (sEMG) signal is recorded over the skin, as the representative of the muscle activity. Since its amplitude can be as low as 50 µV, it is sensitive to undesirable noise signals such as power-line interferences. This study aims at designing a battery-powered portable four-channel sEMG signal acquisition system. The performance of the proposed system was assessed in terms of the input voltage and current noise, noise distribution, synchronization and input noise level among different channels. The results indicated that the designed system had several inbuilt operational merits such as low referred to input noise (lower than 0.56 µV between 8 Hz and 1000 Hz), considerable elimination of power-line interference and satisfactory recorded signal quality in terms of signal-to-noise ratio. The muscle conduction velocity was also estimated using the proposed system on the brachial biceps muscle during isometric contraction. The estimated values were in then normal ranges. In addition, the system included a modular configuration to increase the number of recording channels up to 96.