Human muscle afferent responses to tendon taps. I. Characteristics of the waveform recorded with transcutaneous electrodes

Responses of muscle afferent nerve fibres to tendon taps of digital muscles in the human can be recorded with surface electrodes attached to the skin over the nerve at the wrist. Using an effectively monopolar recording method, a considerable improvement in signal amplitude is achieved with simultaneous reduction in mechanical artefacts using differential amplification techniques. The characteristics of the afferent waveform (latency and duration) are discussed in relation to the applied stimulus. The contribution to the afferent response from receptors other than in the muscle have been shown to be minimal. Afferent fibres from primary muscle spindle endings are thought to be the major contributors to the afferent waveforms recorded by this technique.

Human muscle afferent responses to tendon taps. 2. Effects of variations in fusimotor bias

The effect of varying the fusimotor bias on the muscle spindle responses to light tendon taps has been studied in normal human volunteers using surface electrodes at the wrist for recording whole nerve activity. Reinforcement manoeuvres were found to increase the sensitivity of the afferent responses to the mechanical stimulus. Such sensitisation was found to be exhibited more commonly as a decrease in the latency of the peak of the afferent waveform than as an increase in amplitude. Increase in amplitude of the response was seen in cases where the subject was well relaxed and the test muscle quiescent. A change in furimotor drive was also achieved by asking the subjects to close their eyes voluntarily during the test, thus depriving themselves of the visual feedback. The results under these conditions were found to be variable, though showing considerable changes from control recordings. The effect of reinforcement manoeuvres may perhaps result in increasing the dynamic fusimotor drive. Such an effect may be simulated on occluding the blood supply to the test muscle since ischaemia produces an immediate rise in the rate of afferent discharge. The method of recording is suggested as a convenient technique for clinical use.

Effect of shear mixing on in vitro drug release of capsule formulations containing lubricants

The influence of shear mixing on the in vitro dissolution properties of several experimental capsule formulations containing lubricants was investigated. The studies were carried out in 2.8-liter laboratory V-blender equipped with a high-speed intensifier bar, using nitrofurantoin and procainamide hydrochloride as active drugs, powdered lactose and starch as excipients, and magnesium stearate and magnesium lauryl sulfate as lubricants. These studies revealed a pronounced inhibitory effect on drug dissolution due to shear in powder mixtures containing magnesium stearate; even at the maximum lubricant level of only 2%, high mixing markedly altered the in vitro dissolution rate. In systems with magnesium lauryl sulfate, the shear effect was less pronounced (nitrofurantoin blends) or absent (procainamide hydrochloride blends). The poor dissolution characteristics noted with magnesium stearate--shear combinations seem to result from the formation of a hydrophobic film around the powder mass, preventing wetting and deaggregation.