High concentrations of free fatty acids (FFA) depolarize the resting muscle cell membrane and decrease the membrane resistance. In contrast, low concentrations have a "membrane stabilizing effect" which decreases action potential (AP) and voltage-dependent ionic currents. The changes of AP may result in a decrease of excitation-induced Ca++ release from cellular stores. This may be a causal factor for depression of contraction by FFA.
The NARCOguide algorithm calculates an EEG-derived index to monitor the hypnotic component of anaesthesia. This study evaluates the accuracy of the index calculated by NARCOguide against the Narcotrend index as a reference. Secondly, the automatic detection of burst-suppression patterns as represented by the burst suppression ratio was compared. Comparative study to assess the agreement between two medical devices. At two study centres, patient data were collected from a total of 40 adults receiving general anaesthesia or sedation with propofol. Patients underwent either general anaesthesia for oral surgery with propofol/remifentanil/rocuronium (study centre 1) or light general anaesthesia/deep sedation with propofol alone for laryngoscopic upper airway exploration (study centre 2). In a posthoc analysis, the NARCOguide index was compared with the Narcotrend index. Comparison was made after averaging over 1 min at defined clinical markers using classic linear least squares regression and Bland-Altman plots. Precision and recall for the detection of burst suppression were determined using human scoring as a reference. Data analysis showed good agreement [Bland-Altman mean difference (MD) = -2.3; limits of agreement = -27.1, to +22.4; n = 1209] and high correlation (r 2 = 0.76) between the depth of anaesthesia index calculated by NARCOguide and Narcotrend. The precision and recall of NARCOguide and Narcotrend for the detection of burst suppression were in a similar range. Over the entire dataset, the NARCOguide algorithm showed higher precision and recall than the Narcotrend algorithm (56% vs. 36% and 68% vs. 58%, respectively). The NARCOguide index can be used to monitor the hypnotic component of anaesthesia in patients undergoing general anaesthesia or sedation with propofol, with a performance similar to that of the Narcotrend index. Trial registration number: 18020, regulatory authority: Ethikkommission der bayerischen Landesärztekammer, chairman: Dr med. Gerald Quitterer, applicant: Dr Gert Küchler, date of approval: 12. Jun 2018, completion of data collection: 12 December 2018, study completion: 31 March 2022.
A study was made to reinvestigate the general validity of the force/endurance relation of isometric contractions. Relative force development, mean bioelectrical muscle activity and circulatory responses (blood pressure, interbeat interval) during isometric contractions of different muscle groups were compared. 6 men performed maximum isometric contractions of foot plantar- and dorsalflexors and hand flexors lasting 10 minutes. The hydrostatic blood pressure was varied by placing subject's arms and legs in two different positions, high and low. 9 Women performed plantarflexion and dorsalflexion with maximum strength and at constant load of 60% MVC to exhaustion. The results confirm that the force/endurance relationship during isometric exercise is not a biological constant, applicable for all muscles. The fibre composition of the muscle and the blood pressure varied by different hydrostatic components are discussed as factors causing differences in force/endurance relationship.
The influence of butyric, hexanoic, octanoic, and decanoic acid on the membrane resting potential of isolated frog skeletal muscles were studied and the osmotic effects of n-alkanoic acids tested. 1. n-alkanoic acids cause osmotic effects like impermeable non-electrolytes (sucrose). Therefore, the permeability to alkanoic acids of the resting muscle cell membrane seems to be small. There are no differences between the acids tested. 2. The membrane resting potential is differently affected. Butyric acid in high concentration effects a hyperpolarization of the membrane whereas higher homologues (C6--C10) cause a depolarization. The depolarizing action increases with increasing concentration, exposure, and with the length of the hydrocarbon chain of the alkanoic acids. 3. It is suggested that osmotic effects are the cause for hyperpolarization of the membrane by high concentrations of butyric acid. 4. The depolarizing action of hexanoic, octanoic, and decanoic acid is discussed with regard to alterations induced by alkanoic acids in the membrane permeability and/or in the metabolism of the cells.
Auditory evoked brain potentials (AEP), galvanic skin responses (GSR) and auditory evoked bioelectrical muscular responses were recorded in 16 male human subjects during voluntary isometric contraction of m. triceps brachii dexter. The electromygraphically controlled strength of muscular innervation corresponded to 20, 30, 40 and 50% of the maximal voluntary contraction. The trials were organized according to a change-over design. The following results could be obtained: The stepwise increase of the strength of muscular innervation effected an increase of the mean amplitude of auditory evoked EMG responses. The N1-P2 amplitudes of the AEP decreased with increasing strength of muscular innervation. The mean amplitude of the auditory evoked galvanic skin response was not changed significantly by the strength of muscular innervation, however, the spontaneous changes in galvanic skin resistance increased monotonously. Habituation effects were evident regarding amplitudes of AEP and GSR. The results indicate that muscular activity affects sensory information processing.
The present study describes a new method which allows the determination of muscle elasticity by applying quick releases at one end of a muscle and measuring the resulting tension drops at both ends, and simultaneously the propagation time of the mechanical impulse. The elasticity determined by both methods was examined on resting as well as on tetanized frog muscles (Rana esculenta, M. flexor hallucis brevis) in relation to muscle length and at two different temperatures 1 degree C and 20 degrees C. The average propagation velocity of the mechanical impulse of resting muscle was 55.7 +/- 4.7 m/s and of the contracting muscle 104.8 +/- 24.7 m/s at 1 degree C (L0, n = 6), which corresponds to elasticities of 3.3 +/- 0.5 N/mm2 and 14.4 +/- 6.2 N/mm2, respectively. The elasticity modulus calculated from the tension drop was for the resting muscle 2.3 +/- 0.5 N/mm2 and for the contracting muscle 11.1 +/- 2.1 N/mm2 (L0, 1 degree C, n = 6). When the muscle length is varied, the elasticity modulus corresponds to the length-tension relation of the resting and the isometrically contracting muscle. There is a strong correlation between the elasticity moduli which was determined by both methods for measurement of resting (r = 0.99, n = 19, p less than 0.05) and contracting muscle (r = 0.97, n = 19, p less than 0.05). This relation between elasticity and tetanic tension, i.e. filament overlap at constant temperature, can be interpreted in accordance with the sliding filament theory. But if the temperature is increased from 1 degree C to 20 degrees C, an increase of the tetanic tension (Q10 = 1.56) and a decrease of the elasticity measured by both methods (Q10 of 0.86 and 0.84) were obtained. This suggests that the increased tetanic force is generated by a smaller number of attached cross-bridges, but with a higher amount of force generated by each cross-bridge.
