Consecutive Contractions Research Articles

Self-administered mixture of Entonox and isoflurane in labour

Entonox (50% nitrous oxide premixed in oxygen) was compared with a mixture of Entonox and approximately 0.25% isoflurane (Entonox-isoflurane) for pain relief in the first stage of labour in 39 mothers. An Oxford Miniature Vaporizer was incorporated as the draw-over vaporizer for adding isoflurane to Entonox. The mixture was self-administered via the Entonox on-demand valve. The two mixtures were given in random sequence for five consecutive contractions of labour to each patient. Linear analogue pain relief scores were significantly higher (P=0.001) with Entonox-isoflurane. Fourteen patients continued using Entonox-isoflurane until delivery. No adverse effect from prolonged use was noted. Entonox-isoflurane is considered worthy of further investigation.

Intertrial Reliability of Work Measurements Recorded During Concentric Isokinetic Knee Extension and Flexion in Subjects with and without Meniscal Tears

Intertrial reliability of work measurements was studied in 19 men with a partial medial meniscal tear (ME group) and in 10 men with no history of knee injury (control group). Three maximal voluntary concentric contractions of the muscles involved in knee extension (KE) and knee flexion (KF) were performed on a dynamometer at 30 degrees and 180 degrees/s using a preloading protocol. The subjects moved their legs through an arc of 90 degrees, and the work produced in the constant-velocity phase between 70 and 20 degrees of KE was computed for each trial. In ME group subjects able to perform three consecutive contractions (n = 12-14), high intertrial intraclass correlation coefficients (ICCs) were found (ICCs = .86-.92), except for KE work measurements at 180 degrees/s (ICC = .67). In the control group subjects, high ICCs were obtained for KE work measurements (ICCs = .87 and .95), whereas the low ICCs obtained for KF work measurements (ICCs = .64 and .79) increased to .86 and .93 when the first trial was removed. In both groups, a significant increase was found over the trials for KF measurements at 180 degrees/s and KE measurements at 30 degrees/s, but work measurements were shown to peak at the second trial. The results of this study suggest that the work produced on the second trial reflects a subject's maximal capacity. [Durand A, Malouin F, Richards CL, Bravo G. Intertrial reliability of work measurements recorded during concentric isokinetic knee extension and flexion in subjects with and without meniscal tears.

Gastroduodenal regulation of common duct bile flow in the dog

We investigated the relationship between the entry of individual drops of bile into the duodenum and gastroduodenal motor activity in the fasted state in 10 conscious dogs. The common bile duct was transected and a catheter was inserted through each end. The exteriorized catheters were connected to a photometric drop-flow meter. During phase III activity, bile entered the duodenum in single drops, only in between two consecutive contractions, or as a series of drops during transient inhibition of duodenal contractions by antral phase III contractions. During phase II activity bile also entered the duodenum, usually in between contractions or when the duodenum was intermittently quiescent. Bile entered the duodenum during a duodenal contraction only when the contraction amplitude was < 15% ± 1% (mean ± SE) of the maximal amplitude during phase III contractions. Bile flow into the duodenum showed a cyclic pattern with a peak during late duodenal phase II activity and a trough during duodenal phase I activity only when phase III activity originated in the duodenum and migrated caudad. There was no cyclic pattern of bile flow when phase III activity originated in the proximal jejunum and migrated caudad. The total volume of bile flow in a migrating motor complex cycle and bile flow rate were greater when phase III activity started in the proximal jejunum than when it started in the duodenum. We conclude that gastroduodenal contractions play an important role in the regulation of bile flow into the duodenum. The cyclic pattern of bile flow is altered when phase III activity starts ectopically in the jejunum.

Specificity of leg power changes to velocities used in bicycle endurance training.

Increases in leg power production resulting from 8 wk of bicycle endurance training (30 min/day, 5 times/wk) were studied using an isokinetic dynamometer. In addition, biopsies of vastus lateralis were analyzed to characterize muscle ultrastructural changes. Performance increased on the dynamometer specifically near the estimated average knee angular velocity used during the bicycle training (200 degrees/s). Power measurements were made during the first 5 contractions (maximal power: Pmax) and last 5 contractions (final power: Pend) of 25 and 50 consecutive contractions (at 60 and 240 degrees/s, respectively). Pmax and Pend increased only at 240 degrees/s but not at 60 degrees/s. These increases in Pmax (86 W) and Pend (78 W) resulted primarily from longer torque maintenance but also from increased peak torque during each contraction and were close to the increase in mechanical power output maintained on the bicycle (Pb; 78 W) during the training sessions. The specificity of these changes to the angular velocities used in the bicycle training indicates a neural basis to these adaptations. We suggest that these neural adaptations, coupled with the observed enhancement of muscle mitochondrial and capillary density (+41 and +15%, respectively) underlie the increased ability to maintain power production on a bicycle after endurance training.

Automative quantification of rat duodenal rhythmic contraction.

In (1904) Magnus described the technique of using excised segments of intest ines bathed by physiological sa l t solut ions. I n i t i a l l y , the smooth muscle ac t i v i t y was recorded by mechanical methods. Today, in addit ion to the mechanical recording under isotonic, isometric, and auxotonic condit ions, e lect r ica l ac t i v i t y is studied by i n t race l l u la r and ex t race l lu la r electrodes. Even though each method has l imi ta t ions, the information obtained has resu l t ed in advancement of smooth muscle physiology. However, the ex is t ing mechanical recording procedures have the fol lowing l imi ta t ions (I) each smooth muscle preparation must serve as i t own control , thus precluding "in vivo" exposures, (2) each evaluation of an e l i c i t ed response is based pr imari ly on visual impressions of the trace recordings, rather than automative quant i tat ive analysis and (3) the primary parameter has been the contraction, e i ther i t s presence, absence or magnitude. Studies on smooth muscle e lec t r ica l ac t i v i t y and i t s relat ionship to contract ions have suggested ( i ) that smooth muscle's e lect r ica l ac t i v i t y is composed of slow-waves and superimposed action potent ials whose combined action is required to i n i t i a t e a contraction, (2) that the slow waves(sometimes referred to as ei ther basic elect r i c rhythms or pacesetter potent ia ls) or ig inate in the long i tud i nal muscle's pacemaker cel ls and regulate the frequency of contractions, (3) that the superimposed action potent ials determine the magnitude of contraction, (4) that both longitudinal and c i rcu lar muscle layers are required for propagation of the elect r i c a l ac t i v i t y . In addit ion, Connor, et al (1976) have suggested that the slow waves are associated with cel l metabolism by means of electrogenic ion t ransport . Thus, i t appeared that "in v i t ro" measurements of the intact gut segment's frequency of contraction should be a suitable ind i rect method for monitoring smooth muscle ac t i v i t y , in par t icu lar , the slow-wave ac t i v i t y of i t s pacemaker ce l ls . This approach was fac i l i t a ted by using a microprocessor based system designed and constructed in th is laboratory. Since the frequency of contraction is the reciprocal of the intercont ract ion in terva l , the l a t t e r was measured by the microprocessor based system. The automative quant i tat ive measurements of 512 consecutive spontaneous contractions provided an i ntercont racti on interval histogram for each gut segment s imi lar to the interspike interval for neuronal spike t ra ins (MacGregory & Lewis, 1971).

Effects of hyperoxia and hypoxia on dynamic and sustained static performance of the human quadriceps muscle.

The influence of variations in inspired PO2 on dynamic and static muscle performance of the left quadriceps muscle was studied. Eight subjects performed (1) 60 maximal consecutive dynamic contractions and (2) one sustained exhaustive static contraction at 27% of maximal voluntary contraction (MVC). Breathing mixtures containing 11%, 21% or 99% O2, were administered. Peak torque as an average of the 60 knee extensions was higher (p less than 0.01) during hyperoxia (mean +/- SE = 104 +/- 4 Nm) than during normoxia (98 +/- 4 Nm), but did not differ significantly between hypoxia (95 +/- 5 Nm) and normoxia. Peak torque of individual extensions declined more rapidly during hypoxia than during normoxia, differing in the final 12 extensions by 11% from normoxic values. Static endurance time was reduced (p less than 0.02) during hypoxia (152 +/- 12 s) as compared to normoxia (189 +/- 13 s) and hyperoxia (169 +/- 11 s). No significant difference in endurance time was demonstrated between hyperoxia and normoxia. Thus, hypoxia impaired muscle performance in both dynamic and sustained static exercise, whereas acute hyperoxia improved dynamic but not static muscle performance. The results are interpreted in terms of differences in rate of intramuscular H+ accumulation.

The relationships among isokinetic endurance, initial strength level, and fiber type.

Abstract Knee extension isokinetic peak torque was assessed at angular velocities of 0, 30, 180, and 240[ddot]/sec, and isokinetic endurance was assessed by 50 consecutive contractions at 180[ddot]/sec in eight college age men. Also, muscle fiber type of the vastus lateralis was determined and related to isokinetic strength and fatigability. To determine the influence of initial strength on isokinetic endurance the 50 serial isokinetic contractions were assessed after subjects performed two bicycle exercise regimens designed to affect initial strength levels. Neither isokinetic peak torques (made relative to MVC or per Kg of body weight) nor the amount of strength loss over the 50 contractions correlated with fiber type. The peak torques at 180[ddot]/sec at the start of the 50 contractions differed over the three conditions (unfatigued and after the two bicycle exercise regimens), however, the amount of of strength loss over the 50 trials was similar for the three conditions. Also, the patterns of the thr...

Muscle strength and fatigue after selective glycogen depletion in human skeletal muscle fibers.

Two groups of male subjects were studied to examine the effects of different exercise protocols on performance of an isokinetic, short-time strength test, the performance of which is related to fast twitch (FT) muscle fiber recruitment. The laboratory group (LG) (n = 10) cycled (30 min, 70% VO2 max), ran (75 min), and performed repeated bouts of "sprint" cycling and rapid, maximal contractions of the quadriceps. The marathon group (MG) (n = 7) participated in and completed Stockholm's Marathon 1979. A strength test was performed before and within 1-2 h after completion of the group exercise protocol. The m. vastus lateralis was biopsied and muscle fibers classified as slow twitch (ST) or FT. After periodic acid-Schiff staining fibers were qualitatively classified as to glycogen content. In LG significant glycogen depletion occurred in both fiber types and in MG predominantly ST fibers were exhausted of glycogen after the exercise protocol. The glycogen exhaustion from both fiber types in LG was associated with impaired maximal muscular strength produced during a single dynamic contraction, as well as with reduced muscle fatigue patterns. When glycogen exhaustion was induced in ST muscle fibers only in the MG, no impairment was observed for maximal muscular strength but fatigue during 50 consecutive contractions was significantly increased.

Pattern in the hunger signal of hornet larvae (Vespa orientalis)

A mechanical stimulus of constant strength was applied to a single, insulated hornet larvae (Vespa orientalis). A chain of at most 140 bodily contractions resulted from the stimulus. The interval between consecutive contractions steadily increased throughout the period of response.

Variation de l'intervalle moyen entre deux battements consécutifs d'une même U.M. en fonction du travail au cours du mouvement volontaire

Variation de l'intervalle moyen entre deux battements consécutifs d'une même U.M. en fonction du travail au cours du mouvement volontaire

Quantitative study of the regularity of uterine contractile rhythm in labor

Fifty-four groups of twenty intervals of time elapsing from peak to peak of consecutive contractions recorded by amniotic pressure techniques are analyzed. The coefficients of variation of these twenty intervals are calculated. This coefficient is an “index of uterine arrhythmia”, being higher when the rhythm is more irregular. Different degrees of irregularity of rhythm are categorized. The effect of the progress of labor on the index of uterine arrhythmia is assessed. Evaluation of the response of drugs which modify uterine contractions, assessment of inertia, and true and false labor are some of the clinical applications of the index of uterine arrhythmia.

XII.—The Development of the Heart in Man.

Examination of living embryos has shown that the heart is a functionally active organ from a very early stage of its development. At all periods of life the result of the functional activity is in essentials the same, viz. the propulsion of the blood in a definite direction through the heart into the vessels arising from it; but the mechanism for effecting this propulsion undergoes profound alterations, and the heart becomes transformed from a simple continuous tube, destitute of valves, whose walls contract in a rhythmic peristaltic wave, into a complex four-chambered organ, divided into right and left portions, which are ultimately completely separated from one another, possessing valves, and contracting not in a peristaltic wave but in alternating consecutive contractions of the atria and ventricles of the right and left sides simultaneously. Coincidently with the changes in the heart itself, profound alterations occur in the vessels leading to and from the heart. In this combination of simultaneous development and functional activity the heart differs from the other organs of the body, and hence its development presents special problems involving the function as well as the structure of the different parts. Our knowledge of the development of the heart in man cannot yet be said to be complete.

"A vago-esophageal reflex"

The general knowledge of the contractions of the esophagus is confined to the peristaltic movements, that is, the consecutive contractions of the successive parts of the esophagus following a normal deglutition, or, as it was described by Meltzer at a previous meeting of this society, after an injection of liquid or insufflation of air directly into the esophagus. A simultaneous contraction of the entire esophagus can be produced only by stimulating the peripheral end of the vagus when cut in the neck.The authors discovered that in dogs a tetanic contraction of the entire esophagus can be caused also by reflex ways. When the vagus is cut in any part of the neck, an electric stimulation of its central end causes a prompt longitudinal and circular contraction of the entire esophagus, which lasts as long as the stimulation continues. Particulars and other interesting facts connected with this observation will be reported later.