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Biomedical subjects

N H Secher

Publications and source records attributed to N H Secher.

At least 235 records · Page 13Linked to original sources
PubMed1985

Heart rate at the onset of static exercise in man with partial neuromuscular blockade.

In human subjects the length of the first complete cardiac cycle after the onset of static finger or hand muscle contractions was recorded. Graded contractions as well as maximal contractions in which muscle fatigue was provoked by ischaemia were studied. Maximal finger muscle contractions were also weakened by partial neuromuscular blockade with either decamethonium or tubocurarine. The change in R-R interval at the onset of exercise was variable and in part dependent on the length of the last R-R interval before the onset of exercise. The largest decreases were seen when the preceding R-R interval was long. During graded submaximal and maximal contractions a correlation was demonstrated between the change of the R-R interval at the onset of exercise and the contraction intensity. At the onset of the weakest contractions a 3% prolongation of the R-R interval was seen while the strongest contractions were associated with a shortening of 8%. At the onset of all maximal contractions, whether fatigued due to ischaemia or weakened by decamethonium or tubocurarine, a decrease in R-R interval was seen independent of the force developed. When compared at the same resting R-R interval, contractions performed with hand muscles elicited a greater shortening of R-R interval than contractions with finger muscles. The results suggest that the initial change in heart rate at the onset of static muscle contractions is related to the voluntary effort rather than to the force developed, the state of the working muscles or to the type of muscle fibres involved. It may thus be elicited by 'cortical irradiation' rather than by a 'muscle-heart reflex'. Its size depends on the length of the preceding R-R interval, the intended contraction intensity and the muscle mass involved.

Adult↗
PubMed1985

Inspiratory resistance versus general physical training in patients with chronic obstructive pulmonary disease.

The effect of inspiratory muscle training (IMT) three times daily for 6 weeks was compared with that of general physical training (PT) (stair climbing) in 10 out-patients with severe chronic obstructive pulmonary disease (COPD). PT improved 12 min walking distance (12MWD) by 19% (1-28), stair climbing ability (SCA) over four floors at maximum speed by 11% (3-50), maximum oxygen uptake by 10% (2-33), inspiratory flow by 85% (19-113) and improved an index of breathlessness by 44% (3-786). During IMT, 12MWD and SCA decreased by 8% (0-33) and 10% (0-161), respectively, and the other variables decreased by 6-10%. No changes were seen in ventilation during maximum exercise, in maximum inspiratory and expiratory pressures, or in variables measured during spirometry. Thus work capacity can be improved by training in COPD maybe because of an increase in inspiratory flow rate, but without a change in maximum exercise ventilation.

Aged↗
PubMed1984

Fade in voluntary muscle contractions of patients with sequelae after poliomyelitis.

The isometric contraction pattern was followed in three female and two male patients with lower motoneuron paralysis due to sequelae from poliomyelitis in 1942-48. In uninstructed contractions, force increased slowly to an almost horizontal level which could be kept up for as long as desired. During rapid maximal voluntary contractions, a "biphasic" mechanogram was seen in 49% of 204 contractions, with a first maximum after 0.3 s (0.1-0.9), separated by a notch from a second maximum after 1.1 s (0.3-2.3). In the rest of the contractions, force could not be generated rapidly, despite the intention of the subjects, and a single maximum in the mechanogram was seen after 0.9 s (0.2-2.4). In contractions where a biphasic contraction pattern was seen, the electromyographic activity was greatest during approximately the first one half second of the contraction. In the other contractions the electromyographic activity was about the same during the whole contraction. The results suggest that the mechanograms are composed of a high innervation threshold, fast phasically active component, and a low innervation threshold, slow tonically active component. Fade represents the waning of tension in the phasically active component present in some contractions, while this component appears to be eliminated by poliomyelitis in other muscle contractions.

Adult↗
PubMed1984

Effect of tubocurarine on static and dynamic muscle contractions in man.

The effect of a bolus injection of tubocurarine (0.1 mg X kg-1 i.v.) was followed in six young subjects by registration of static, and slow (30 degrees X s-1) and fast (150 degrees X s-1) dynamic (isokinetic) maximal voluntary leg extensions. Mechanograms from both unblocked and curarized muscle contractions showed a "notch" after about 440 ms separating two relative maxima. The mechanograms were divided by an arbitrary straight line connecting the starting point of the contraction curve and the notch. The line separated an area (Nm X s) above and to the left (alpha-component) from an area below and to the right (beta-component) of the line. Tubocurarine affected the beta-component selectively until about 70% reduced in the static contractions. With further curarization the alpha-component was also reduced in size. The alpha-component was equally affected during the three types of contractions, while the faster the contraction the more the beta-component was reduced. The results suggest that static as well as dynamic human muscle contractions can be divided into two parts with a different sensitivity for tubocurarine, one of which seems to have a sensitivity which depends on the contraction velocity.

Adult↗
PubMed1984

Fatigue of voluntary contractions in normal and myasthenic human subjects.

The effect of fatigue developed during 96 repeated rapid maximal voluntary finger muscle contractions (MVC), 12 contractions per minute, was followed in 4 control subjects and 4 myasthenic patients. The tension-time integral (T-TI) was determined during either the first 1 or 1.25 s of each contraction. Fatigue decreased the T-TI by 21% in the control subjects and by 65% in the patients. While ordinary MVC showed a slow rate of rise of tension and gradually increasing electromyographic activity, rapid MVC from both groups showed a steep rate of rise of tension, a 'notch' after about 0.3-0.4 s separating two relative maxima and a larger electromyographic activity during the first half second of the contraction. The mechanograms from rapid MVC were divided by an arbitrary straight line connecting the starting pint of the contraction curve and the notch. The line separated an area (N X s) above and to the left (alpha-component) from an area below and to the right (beta-component of the line. Fatigue affected the beta-component selectively in both control subjects and myasthenic patients. Only when the beta-component was reduced by more than 80%, was a reduction of the alpha-component also seen. At any time during a sustained contraction, the patients could briefly increase their instantaneous strength, but for only about one half second. The results suggest that human muscle contractions can be divided into two parts with a different sensitivity to fatigue in both control subjects and myasthenic patients.

Adolescent↗
PubMed1984

Bradycardia during severe but reversible hypovolemic shock in man.

Severe bleeding and hypovolemic shock causing hypotension are most often associated with tachycardia. In response to passive head-up tilt, five healthy men exhibited an increase in heart rate (HR) from 62 to 79 beats X min-1 and a gradual increase in the plasma concentration of aldosterone and protein. The increase in HR was followed by a decrease of 29 beats X min-1 (range 11-46) at the time when blood pressure decreased 38 mmHg (6-73). When tilted back to 0 degree, blood pressure immediately reversed while HR remained unchanged. Hypotension was associated with large but variable increases in plasma vasopressin (86 +/- 28 pg X ml-1) accompanied by peripheral vasoconstriction. In two cases where patients with internal bleeding presented with a moderate HR of 96 beats X min-1, the ensuing fall in blood pressure was associated with a decrease in HR to 68 and 76 beats X min-1, respectively. Administration of albumin solution and blood normalized cardiovascular function. Two other patients showing initial HR of 130 and 100 beats X min-1, respectively, also developed relative bradycardia in conjunction with a decrease in blood pressure. Administration of ephedrine and atropine increased HR temporarily from 56 to 90 and from 36 to 110 beats X min-1, respectively. The latter two patients died in extreme bradycardia and autopsies revealed severe internal bleeding. It is concluded that although hypovolemic shock is most often associated with an increase in HR, the increase is modest and a paradoxical bradycardia develops in severe but potentially reversible hypotensive hypovolemic shock.

Adult↗
PubMed1983

Rowing performance, a mathematical model based on analysis of body dimensions as exemplified by body weight.

The theory of body dimensional influence on muscular work is employed for calculating the racing time of heavy- and lightweight male, and female rowers. The developed equation predicts racing results with an accuracy of 1 s +/- 1.7 (SE). The prediction of a 2.6% advantage of the heavyweights (average bodyweight) 93 kg over the lightweights (70 kg) is in excellent agreement with observations (2.5%). Significant implications of the equation would be to row without a coxswain, to reduce boat weight to a minimum, and to increase racing distance e.g., for females to the racing distance rowed by the males (2,000 m) in order to reduce the influence of body dimensions on rowing performance.

Aerobiosis↗
PubMed1983

Effect of tubocurarine and decamethonium on voluntary muscle contractions in man.

Six healthy, young male subjects performed repeated brisk maximal voluntary muscle contractions (MVC) with the knee and hip extensors. Three MVCs were performed every minute. On separate days decamethonium 0.03 mg X kg-1 and tubocurarine 0.01 mg X kg-1 were administered intravenously during repeated MVCs. While ordinary MVCs showed a slow rate of rise of tension over approximately 1 s, brisk MVCs showed a steep rate of rise of tension and a biphasic configuration appeared, as a notch was seen 370-480 ms after the initiation of the contraction curve. An arbitrary straight line was drawn connecting the starting point of the contraction curve and the notch. The tension time integral to the left and above this line (alpha component), respectively to the right and below the line (beta component) was measured during the first 600 ms of the contraction. Tubocurarine affected the beta component until 70% reduced. With further curarization, the remainder of the beta component was reduced together with the alpha component. Decamethonium, in contrast, affected the alpha component together with 30% of the beta component. Thereafter, the rest of the beta component was increasingly affected. The results suggest that the isometric mechanogram is composed of a phasically active component with a high innervation threshold primarily sensitive to decamethonium, and a tonically active component with a lower innervation threshold, and primarily sensitive to tubocurarine.

Decamethonium Compounds↗
PubMed1982

Effect of tubocurarine on human soleus and gastrocnemius muscles.

The effect of a bolus injection of tubocurarine (0.1-0.13 mg X kg-1 i.v.) was followed in six young male subjects by registration of the rectified smoothed electromyogram (rsEMG) from the m. soleus (71 +/- 5.1 (s.e. mean) % slow twitch muscle fibers) and from the m. gastrocnemius (54 +/- 3.1% slow twitch muscle fibers). Volitional muscle strength was recorded in isometric plantar flexions with the knee fully (0 degrees) extended where m. soleus and m. gastrocnemius both are active, and with the knee bent 90 degrees where m. soleus is dominating force development. During maximal action of the drug, the rsEMG from the soleus muscle was reduced to 30 +/- 4.0% of the control value, while the rsEMG from the gastrocnemius muscle was reduced to 53 +/- 5.2% (P less than 0.01). Muscle strength with the knee extended showed 53 +/- 7.5% force left, while 44 +/- 6.4% of the muscle strength remained when the knee was bent (P less than 0.01). The results suggest that tubocurarine affects human muscles in proportion to their slow twitch muscle fiber content.

Adult↗
PubMed1982

Central and regional circulatory adaptations to one-leg training.

Six young healthy male subjects performed submaximal and maximal exercise on bicycle ergometers with one leg and two legs before and after 8 wk of one-leg training with each of both legs. The following variables were measured during one- and two-leg exercise: oxygen uptake, heart rate, mean arterial blood pressure, cardiac output, leg blood flow, and iliac arteriovenous differences for oxygen and lactate. After training the maximal oxygen uptake during one- and two-leg exercise was increased by 19 and 11%, respectively. The corresponding cardiac outputs increased by 16 and 11%, respectively. During submaximal one-leg exercise, heart rate decreased by 11%, whereas a decrease of only 2% was seen during submaximal two-leg exercise. Mean blood pressure decreased by about 10 Torr in both types of exercise and during both submaximal and maximal exercise. Maximal leg blood flow increased only by 1.2 l/min during one-leg exercise. Leg blood flow and leg oxygen uptake were smaller during two-leg exercise than during one-leg exercise and more so after training. These findings indicate that one-leg exercise, compared with two-leg exercise, involves circulatory adaptations that respond differently to one-leg training. The findings further imply that oxygen supply to one large muscle group of exercising muscles may be limited by vasoconstriction when another large group of muscles is exercising simultaneously.

Adaptation, Physiological↗
PubMed1981

Heart rate and ventilatory frequency as dimension-dependent variables.

Heart rate (HR) and ventilatory frequency (f) were determined at rest in 79 boys and 91 girls aged 0.07-20 years and with a range in heights from 54-198 cm to establish the relationship between decrease in HR and f during early life with increase in body dimensions. From theoretical considerations it is assumed that frequencies such as HR and f are proportional to a characteristic linear dimension of the subjects in minus first power (approximately equal to rho-1). In the present material resting HR and f decreased with increasing height of the subjects according to the equations HR = 6,408 . height-0.9015 (r = 0.8983) and f = 5,969 . height-1.1691 (r = 0.8471). These results suggest that the decrease in resting HR and f during childhood and adolescence corresponds well with increase in body dimensions. A similar equation was developed for HRmax within the range of heights from 149-198 cm. Only a slight dependency on height was observed (HRmax = rho-0.1642, r = 0.3796).

Adolescent↗
PubMed1981

Paradoxical influence of encouragement on muscle fatigue.

A comparison between the fatigue developed during encouraged and non-encouraged maximum voluntary contractions (MVC) was carried out. Six subjects performed 150 isometric leg extension MVCs with the right and the left leg separately, and seven subjects performed 150 isometric MVCs with both legs simultaneously. Force and rectified smoothed electromyography (rsEMG) were followed during the contraction series. No significant difference was found in the initial force between the encouraged and the non-encouraged contraction series. Irrespective of the type of exercise performed, the relative strength in the encouraged contractions decreased more than the relative strength in the non-encouraged contractions. In all subjects a decrease in rsEMG was seen, and the ratio between rsEMG and strength remained constant throughout the 150 MVCs. The results suggest that part of the fatigue produced during repeated MVCs originates within the central nervous system, and is influenced by the presence and the encouragement given by the experimenters.

Adult↗
PubMed1981

Inspiratory resistance training in severe chronic obstructive pulmonary disease.

Twenty-eight patients with stable chronic obstructive pulmonary disease (COPD) undertook a training program with a simple respiratory apparatus for 15 min three times daily for 6 weeks. Fourteen patients were allocated to an inspiratory resistance training program and 14 to a control group. In all subjects the median FEV1 was 0.72 and the median FEV1/FVC was 39%. There was no difference in FEV1 or FEV1/FVC between the control and the test groups. In both groups of patients FEV1 FVC and the corresponding values during inspiration, FIV1 and FIVC, as well as MVV, were found unchanged following the training period. Inspiratory resistance tolerance increased in both groups but no significant difference in the improvement could be observed between the two groups. Both groups also showed a similar increase, 23 (76-10) %, in stair-climbing ability. There was no correlation between increases in inspiratory load tolerance and stair-climbing ability. It is suggested that both inspiratory load tolerance and work ability can be improved in COPD patients, but that inspiratory resistance training does not contribute to these improvements.

Adult↗
PubMed1978

Contralateral influence on recruitment of curarized muscle fibres during maximal voluntary extension of the legs.

The force of maximal voluntary contraction (MVC) was compared during extension of one leg alone and during simultaneous extension of both legs. In 6 subjects MVC of two legs extension was 75 +/- 3.6 (S.E.)% of the sum of the single one leg MVC. This may indicate a reduced muscle fibre involvement during two leg extension as compared with one leg extension. We investigated the possibility that either red (type I) or white (type II) muscle fibre recruitment was restricted during two leg extension. The neuromuscular transmission in the two types of fibres was partially blocked with d-tubocurarine (dtc) or decamethonium (C10) for either type I or II, respectively. In 5 subjects receiving dtc the ratio between the reduced two leg and one leg extension forces (75 +/- 2.3%) did not change. During administration of C10, however, this ratio decreased by 16 +/- 3.1%. Partial blocking with dtc caused a two component curve during tension development with a first maximum at 0.22 s, and another maximum at 1.03 s of a 3 s attempt to reach MVC. During partial blocking with C10 results in muscle contractions where a relatively large amount of type I muscle fibres are contributing to the force developed. The experiment suggests that type I fibre recruitment is restricted during severe static exercise in normal muscles. Furthermore, it demonstrates that fibre recruitment can vary in the same muscle function performed with one leg or two legs.

Adult↗