Frequency of acoustic myography during isometric contraction of fresh and fatigued muscle and during dynamic contractions

The frequency of the acoustic myographic (AMG) signal was examined during fresh and fatigued isometric contractions of quadriceps and during dynamic contractions of biceps brachii (BB) in healthy subjects. Recordings were obtained from quadriceps over a range of forces between 10% and 100% maximal voluntary contraction prior to, and 15 minutes after, a fatiguing exercise. Recordings from BB were obtained over a range of submaximal forces (0–8.5 kg) during concentric and eccentric contractions. The mean power frequency (MPF) of the AMG signal was analyzed during each of these contractions by fast-Fourier transform (FFT). The MPF was not significantly different (P > 0.05) during fresh and fatigued contractions of quadriceps and increased quadratically with force in both states (r = 0.81, fresh; r = 0.77, fatiqued). During concentric contractions of BB the MPF initially with force, but then decreased at the heavier loads (>5.5 kg). The MPF of eccentric contractions did not significantly (P > 0.05) alter with force. The AMG MPF was within a similar low frequency range for both muscles, during different types of contraction, and was unaltered with fatigue. © 1993 John Wiley & Sons, Inc.     

Sleep in Parkinson's disease

Two major sources of dissatisfaction with the quality of life among Parkinsonian patients are the "locomotor disability" and the "nature of their sleep". The main focus of research was directed towards the locomotor disability, but in the last two decades some progress has been made towards the understanding of sleep in PD patients. Sleep in Parkinson's disease is light and fragmented due to an increased skeletal muscle activity, disturbed breathing, impaired biological rhythm and REM-nonREM variations of the dopaminergic receptor sensitivity.     

Evidence that naloxonazine produces prolonged antagonism of central delta opioid receptor activity in vivo

Intracerebroventricular (i.c.v.) administrations of the postulated μ₁ opioid receptor antagonist naloxonazine produced an increase in the frequency of urinary bladder contractions recorded isometrically in the anesthetized rat. This substance also antagonized the inhibition of spontaneous bladder contractions produced by submaximal i.c.v. doses of the highly selective μ opioid agonist [D-Ala²-MePhe⁴,Gly-(ol)⁵]enkephalin (DAGO) and the δ opioid agonist [D-Pen²,D-Pen⁵]enkephalin (DPDPE). The antagonism of DAGO was reversible but that of DPDPE lasted up to 30 h. These data suggest that endogenous opioids are involved in the central control of bladder motility and that naloxonazine is a long-lasting δ opioid receptor antagonist.     

The inhibitory effect of X537A on vascular and intestinal smooth muscle contraction

Summary the effects of X537A (Lasalocid) on contractions induced in vascular and intestinal smooth muscles were examined. High K-induced sustained contractions were inhibited by X537A with an IC50 of 2.8·10^–6 M in rabbit aorta and 8.8·10^–8 M in guinea-pig Taenia coli. Changing the Ca concentration in the medium did not modify the effect of X537A. X537A also inhibited the noradrenaline-induced contraction in aorta (IC50=7.0·10^–8 M). In a solution without added glucose, the inhibitory effect of X537A on the K-induced contraction in aorta was augmented (IC50=1.5·10^–8 M). Under hypoxic conditions, the inhibitory effects of X537A on the noradrenaline-induced contractions in aorta and on the K-induced contraction in T. coli were decreased (IC50>10^–5 M and 3.2·10^–6 M, respectively). X537A inhibited the K-induced increase in cellular ⁴⁵Ca content in aorta measured by a modified lanthanum method. However, the IC50 for ⁴⁵Ca uptake (6.6·10^–7 M) was lower than that for K-induced contraction. In both tissues, X537A decreased the ATP content. Oxygen consumption of rat liver mitochondria was inhibited by X537A. From these results, it is concluded that the inhibitory effect of X537A on the noradrenaline-induced contraction in aorta and the K-induced contraction in T. coli, but not the K-induced contractions in aorta, may be due to the inhibition of aerobic metabolism.     

Plasma aldosterone,renin activity,and cortisol responses to heat exposure in sodium depleted and repleted subjects

Summary Fatigue of the vastus lateralis muscle was studied in healthy well-conditioned students, who differed considerably regarding their muscle fibre type distribution. Muscle force decline during repeated maximum voluntary knee extensions at a constant angular velocity (180×s^–1 or rad×s^–1), using isokinetic equipment, was taken as the criterion for the degree of fatigue. In an attempt to study quantitative as well as qualitative changes in the EMG pattern, integrated EMG (IEMG) and the frequency of the mean power (MPF), computed from the power spectral density function (PSDF), were analysed. It was found that individuals with muscles made up of a high proportion of fast twitch (FT) muscle fibres demonstrated higher peak knee extension torque, and a greater susceptibility to fatigue than did individuals with muscles mainly composed of slow twitch (ST) muscle fibres. An IEMG decline (p<0.01) was demonstrated during 100 contractions in individuals rich in FT fibres. Only a slight, but not significant, reduction in IEMG occurred in individuals with a high percentage of ST fibres. Concomitantly, MPF decreased (p<0.001) in individuals with a high percentage of FT fibres, while their opposites demonstrated only a slight decrease (non-significant). It is suggested that muscle contraction failure might also be related to qualitative changes in the motor unit recruitment pattern, and that these changes occur more rapidly in muscles composed of a high proportion of FT muscle fibres than in muscles composed of a high proportion of ST fibres.     

Regression analysis applied to PVC histories: a statistical procedure for evaluating antiarrhythmic drug efficacy

Suppression of premature ventricular contractions (PVCs) is one of the goals of antiarrhythmic therapy. In a clinical trial, however, it may be difficult to distinguish antiarrhythmic drug effect from spontaneous variation in PVCs. We propose the application of linear regression to PVC histories to ascertain drug effect in individual patients. The model determines which variables are important in explaining a patient's PVCs. One such variable indicates the presence or absence of the drug; the model determines whether the drug has an effect on the patient's PVCs, while compensating for the other explanatory variables. In addition to determining the statistical significance of any drug effect, the model estimates the strength of the effect for each patient. We demonstrate the method with data from a three-day clinical trial which used 24-hour Holter monitoring. The method is flexible and can be modified to apply to any clinical study design. It allows for inferences concerning populations and subpopulations of patients.     

Isometric fatigue induced by different levels of rhythmic exercise

Summary Three subjects were trained in leg extensor isometric contractions and in cycling. They then cycled for three consecutive bouts, each of 2.75 min at a constant level of , from 20 to 80% max. Fifteen seconds after each bout of cycling the subjects exerted an isometric contraction of the right leg at 40% of the maximum voluntary contraction. In each experiment, the duration of the three successive isometric contractions decreased as in hand-grip contractions. There was also a linear reduction in isometric endurance as the severity of the preceding rhythmic exercise increased. In other experiments, after three bouts of rhythmic exercise at 20% max (each followed by a fatiguing contraction at 40% MVC), further bouts of cycling at increasing levels of severity up to 60% max resulted in a linear fall in isometric endurance which could be reversed by interposing a lighter level of cycling. The heart rates during these experiments showed a steady increase during the isometric exercise, to about 150 beats·min⁻¹, as the bouts of preceding rhythmic exercise became progressively more severe. The isometric contractions had little influence on the heart rate during cycling. But the rhythmic cycling exercise markedly increased the heart rate achieved at the end of the isometric contractions while decreasing theincrement in heart rateduring the contraction. Supported by HEW Contract HSM 99-71-21, and U.S.N. Grant N00014-77-0640     

Development and regeneration of motor systems under the influence of ACTH peptides

ACTH peptides exert quantitative and qualitative influences on the formation and maturation of motor units in developing and regenerating neuromuscular systems. ACTH 4–10, administered daily (10 μg/kg.s.c.) from the day of birth, accelerated the rate at which muscle strength developed in the immature rat, the effect of this peptide being most marked in animals 11–15 days old. A similar increase in grasping time occurred in ACTH 4–10 treated animals, indicating that the peptide affects neuronal maturation at a time in development when organization and maturation of the neuromuscular system is most active. The synthetic analogue of ACTH 4–9 (Org 2766), administered in the same dosage, had little effect on these parameters, indicating a differential sensitivity to these similar peptides. Elevated circulating titers of ACTH, whether exogenous (0.2 U ACTH 1–39 IP daily), or endogenous (adrenalectomy), stimulated the formation of more functional motor units, as indicated by increased amplitude of muscle action potentials and tetanic tension following nerve stimulation. ACTH appears to favor the recovery of high threshold, small-size motor units. Fine control of muscle function in peptide-treated animals is partially restored, as indicated by the return of stepwise recruitment to an extent not seen in the reinnervated, saline-treated controls.     

‘Frequent’ ventricular bigeminy – A reversible cause of dilated cardiomyopathy. How frequent is ‘frequent’?

An interesting development in the field of heart failure has been the link between frequent premature ventricular contractions and cardiomyopathy. We report a patient whose frequent ventricular bigeminy resulted in left ventricular impairment that resolved after the use of non-contact mapping during radiofrequency ablation. A review of the literature regarding possible mechanisms is discussed. For the practicing clinician, the question of 'frequent' should be taken in context of symptoms and LV function. A single 24-h Holter monitor may not truly reflect the ectopic load. We recommend that if there is associated LV dysfunction and a causal link to frequent PVCs then suppression with radiofrequency ablation is a safe and effective treatment strategy.