Evaluasi Penggunaan Alat Ukur Denyut Jantung Untuk Pengukuran Beban Mental dan Kelelahan Mental

Penelitian ini bertujuan untuk mengevaluasi alat ukur denyut jantung yaitu Polar Heart Rate Monitor dalam mengukur tingkat beban mental yang berbeda-beda dan mendeteksi terjadinya kelelahan mental. Penggunaan alat ukur ini jauh lebih praktis dan ekonomis jika dibandingkan dengan ECG (Electrocardiography), yang biasanya digunakan dalam penelitian laboratorium. Penelitian ini juga bertujuan untuk mengetahui parameter yang paling sensitif dalam mendeteksi tingkat beban mental yang berbeda-beda. Beberapa parameter yang dibandingkan adalah rataan denyut jantung, standar deviasi denyut jantung, koefisien α (konstanta DFA), koefisien D (konstanta Dispersional Analysis). Sebanyak 18 reponden yang terdiri dari 9 reponden laki-laki dan 9 responden perempuan dilibatkan dalam penelitian ini. Responden melakukan aktivitas mental dalam 3 tahapan proses aritmatika, yakni penjumlahan (beban mental rendah), pengurangan (beban mental sedang) dan perkalian (beban mental tinggi) masing-masing selama 20 menit. Hasil penelitian menunjukkan bahwa Polar Heart Rate Monitor sensitif untuk mendeteksi tingkat beban mental yang berbeda dengan mencari HRV (Heart Rate Variability) yakni dengan menggunakan nilai standar deviasi denyut jantung dan koefisien α. Kelelahan mental tidak dapat dideteksi baik dengan keempat parameter denyut jantung yaitu rataan denyut jantung, standar deviasi, koefisien α dan koefisien D.

Fractal fluctuations in human respiration

The present study was designed to characterize respiratory fluctuations in awake, healthy adult humans under resting conditions. For this purpose, we recorded respiratory movements with a strain-gauge pneumograph in 20 subjects. We then used Allan factor, Fano factor, and dispersional analysis to test whether the fluctuations in the number of breaths, respiratory period, and breath amplitude were fractal (i.e., time-scale-invariant) or random in occurrence. Specifically, we measured the slopes of the power laws in the Allan factor, Fano factor, and dispersional analysis curves for original time series and compared these with the slopes of the curves for surrogates (randomized data sets). In addition, the Hurst exponent was calculated from the slope of the power law in the Allan factor curve to determine whether the long-range correlations among the fluctuations in breath number were positively or negatively correlated. The results can be summarized as follows. Fluctuations in all three parameters were fractal in nine subjects. There were four subjects in whom only the fluctuations in number of breaths and breath amplitude were fractal, three subjects in whom only the fluctuations in number of breaths were fractal, and two subjects in whom only fluctuations in breath number and respiratory period were fractal. Time-scale-invariant behavior was absent in the two remaining subjects. The results indicate that, in most cases, apparently random fluctuations in respiratory pattern are, in fact, correlated over more than one time scale. Moreover, the data suggest that fractal fluctuations in breath number, respiratory period, and breath amplitude are controlled by separate processes.

Fractal properties of human muscle sympathetic nerve activity

Muscle sympathetic nerve activity (MSNA) in resting humans is characterized by cardiac-related bursts of variable amplitude that occur sporadically or in clusters. The present study was designed to characterize the fluctuations in the number of MSNA bursts, interburst interval, and burst amplitude recorded from the peroneal nerve of 15 awake, healthy human subjects. For this purpose, we used the Allan and Fano factor analysis and dispersional analysis to test whether the fluctuations were time-scale invariant (i.e., fractal) or random in occurrence. Specifically, we measured the slopes of the power laws in the Allan factor, Fano factor, and dispersional analysis curves. In addition, the Hurst exponent was calculated from the slope of the power law in the Allan factor curve. Whether the original time series contained fractal fluctuations was decided on the basis of a comparison of the values of these parameters with those for surrogate data blocks. The results can be summarized as follows. Fluctuations in the number of MSNA bursts and interburst interval were fractal in each of the subjects, and fluctuations in burst amplitude were fractal in four of the subjects. We also found that fluctuations in the number of heartbeats and heart period (R-R interval) were fractal in each of the subjects. These results demonstrate for the first time that apparently random fluctuations in human MSNA are, in fact, dictated by a time-scale-invariant process that imparts “long-term memory” to the sequence of cardiac-related bursts. Whether sympathetic outflow to the heart also is fractal and contributes to the fractal component of heart rate variability remains an open question.

Correlation structure of end-expiratory lung volume in anesthetized rats with intact upper airway

The correlation structure of breath-to-breath fluctuations of end-expiratory lung volume (EEV) was studied in anesthetized rats with intact airways subjected to positive and negative transrespiratory pressure (i.e., PTRP and NTRP, correspondingly). The Hurst exponent, H, was estimated from EEV fluctuations using modified dispersional analysis. We found that H for EEV was 0.5362 ± 0.0763 and 0.6403 ± 0.0561 with PTRP and NTRP, respectively (mean ± SD). Both H were significantly different from those obtained after random shuffling of the original time series. Also, H with NTRP was significantly greater than that with PTRP ( P = 0.029). We conclude that in rats breathing through the upper airway, a positive long-term correlation is present in EEV that is different between PTRP and NTRP.