Mikrovibration und Muskeltonus des Säuglings in Abhängigkeit vom Schlafstadium

Summary

The effect of quiet (NREM) and active (REM) sleep on accelerometric recorded hand microvibration was studied in infants (N = 10) at the age of 2, 6, and 12 months. Additionally to microvibration, masseter surface EMC as a measure of resting muscle tone, electrocardiogram as a measure of cardiac activity, and EEC for estimation of sleep state were recorded in a whole-night polysomnography. Root mean square amplitudes of microvibration were calculated in the frequency bands of 3-7 Hz (B1), 7-13 Hz (B2) and 13-30 Hz (B3). Additionally, mean frequency of microvibration, integrated EMC and heart rate were calculated.

In quiet sleep the microvibration signal clearly shows the mechanical action of the heart beat followed by a complex oscillatory component. In active sleep, both, action of the heart beat and the oscillatory component was reduced (Fig. 1, 2). This was expressed by a decrease of B2 (-15 %), B1, B2 and mean frequency of microvibration remained unchanged (Fig. 4). Integrated EMG was decreased (-10 %) and heart rate was not significantly increased in active sleep (Fig. 3, 5). Further B1, B2, B3 and heart rate decreased with age, no effect was found with sleep duration.

From these results it was concluded that reduction of elastic coupling in the musculoskeletal system (= mucle tone) is responsible for the reduction of the 7-13 Hz component of microvibration during active sleep. On the one hand reduction of muscle tone reduces transmission of cardiac impulses to distal parts of the body, and on the other hand musculoskeletal resonances which were excited by the heart beat became more damped. Other factors contributing to microvibration, like resonance properties of the wrist joint and of the skin-transducer are discussed. The parallel decrease of microvibration and heart rate with age, indicates that microvibration depends on heart rate too.

Zusammenfassung

Zur Untersuchung der Mikrovibration in Abhängigkeit von der muskulären Grundspannung im Körper (IEMG = integriertes EMG) wurden Mikrovibrations-Signale aus ruhigen (NREM) und aktiven (REM) Schlafphasen von zehn Säuglingen im Alter von zwei, sechs und zwölf Monaten verglichen. Im aktiven Schlaf war die Amplitude der Mikrovibration reduziert, wobei sowohl der im Mikrovibrations-Signal erkennbare Herzschlag als auch ein Schwingungsmuster mit einer Frequenzkomponente im Bereich zwischen 7-13 Hz betroffen war. Da die Reduktion der Mikrovibration (-15 %) mit der Reduktion der muskulären Grundspannung im Körper (-10 %) einhergeht, ist anzunehmen, daß die elastische Kopplung im Muskel-Skelettsystem (= Muskeltonus) während des aktiven Schlafs reduziert ist. Als Folge nimmt die Übertragung des Herzschlags an die Körperperipherie (Hand) ab, weiters verringert sich damit auch die Schwingungsneigung im Muskel-Skelettsystem. Die Amplitude der Mikrovibration nimmt mit dem Alter ab, es wurde aber kein Einfluß der Schlafdauer festgestellt.

Key words:

Musculoskeletal stiffness - Transmission of cardiac impulse - Resonance properties - Accelerometry