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PubMed1993

Mechanisms of fatigue in normal intercostal muscle and muscle from patients with myasthenia gravis.

Fatigue mechanisms in normal intercostal muscle and muscle from patients with myasthenia gravis (MG) were evaluated by monitoring the compound muscle action potential (CMAP) and tetanic tension responses to repetitive nerve or muscle stimulation in vitro. When fatigue was induced by nerve stimulation at 30 Hz for 0.5 s every 2.5 s, about half of the original tension decreased after 30 min in normal muscle and 5 min in MG muscle. Analysis of the changes in area of CMAPs and tension indicated that impairment of neuromuscular transmission, muscle membrane excitation, and excitation-contraction (E-C) coupling and contractility accounted for 40%, 29%, and 31% of fatigue in normal muscle, and 83%, 0%, and 17% of fatigue in MG muscle. When fatigue was induced by muscle stimulation at 30 Hz, tension declined by a quarter after 30 min in normal muscle, but by a half after 17 min in MG muscle. Impairment of muscle membrane excitation and E-C coupling and contractility accounted for 58% and 42% of fatigue in normal muscle, and 22% and 78% of fatigue in MG muscle. Thus, fatigue of normal muscle is caused by impairment of at least four processes, and enhanced fatigue of MG muscle is caused by greater impairment of neuromuscular transmission, E-C coupling, and contractility.

Action Potentials↗
PubMed1996

Activity of the intercostal muscle spindle afferents in the lower thoracic segments during spontaneous breathing in the cat.

Intraaxonal recordings of 33 spindle afferents from the inspiratory (n = 8) and expiratory (n = 25) intercostal muscles in the lower thoracic segment (T9-11), were made during spontaneous breathing in the anesthetized cat. All of them showed respiration-related activity. However, only three spindle afferents (one from the inspiratory and two from the expiratory intercostal muscles) showed higher firing frequency during the active contraction phase of the receptor-bearing muscle. The remaining 30 spindle afferents (seven from the inspiratory and 23 from the expiratory muscles) showed the maximum firing discharge during the passive stretch phase of the parent muscles. On the other hand, in the middle thoracic segments (T6-7), five of six spindle afferents from the inspiratory muscles and four of nine spindle afferents from the expiratory muscles showed maximum firing rate during parent muscle contraction in agreement with previous study. These results suggest that the spindle activity in the lower thoracic segments is dominated by muscle length changes, whereas that in the middle thoracic segments is largely via the fusimotor pathway.

Animals↗
PubMed1982

Role of intercostal muscles in the rib cage distortions produced by inspiratory loads.

We studied the patterns of rib cage (RC) deformation in six normal subjects breathing against different resistive and elastic inspiratory loads, and we examined, with concentric needle electrodes, the role played by the inspiratory intercostal muscles in the development of these patterns. Four of the subjects deformed their RC to a more elliptical shape during loaded inspirations; RC anteroposterior diameter became smaller and RC lateral diameter became larger. The RC deformation increased as the load increased, but it appeared to be independent of the nature of the load. Moreover these deformations were associated with a marked increase in the inspiratory activity of the intercostals situated in the lateral parts of the RC and a striking diminution of the activity in the parasternal area. On the other hand, two subjects invariably breathed along their RC relaxation characteristic, and they showed an increased inspiratory activity in all regions of the intercostal musculature. These findings indicate that 1) the pattern of RC deformation during loaded inspirations is closely related to the activity and coordination of the various inspiratory intercostal muscles, and 2) the parasternal intercostals are not necessarily representative of all the inspiratory intercostals. They are also strong evidence against the concept that the parasternal intercostal electrical activity normally recorded during quiet breathing is an excitatory reflex activity.

Adult↗
PubMed1985

The three-dimensional structure of motor endplates in different fiber types of rat intercostal muscle. A scanning electron-microscopic study.

The three-dimensional organization of the motor end plates in the red, white and intermediate striated muscle fibers of the rat intercostal muscle was observed under a field-emission type scanning electron microscope after removal of connective tissue components by HCl hydrolysis. The motor endplate of the white fiber had terminal branches (or axon terminals), which were large, long and thin, and small but numerous nerve swellings (or terminal boutons). The motor endplate of the red fiber had terminal branches, which were small, short and thick, and had large but fewer nerve swellings. The motor endplate of the intermediate fiber was intermediate in size and structure between these two. In detached nerve-ending preparations, primary synaptic grooves with slit-like openings of the junctional folds appeared on the surface of the muscle fibers. The primary synaptic grooves were more developed in the white fiber than in the red fiber, and they were intermediate in the intermediate fiber. The numerical ratio of slit-like openings was 1:1.8:3.5 in the red, intermediate and white fiber, respectively. The Schwann cells and their processes were observed on the surface of the motor endplate, with the processes covering the upper orifices of the primary synaptic grooves and sealing the terminal branches. The number of Schwann cells was usually three in the white fiber, two in the intermediate fiber and one in the red fiber.

Animals↗
PubMed1984

[Possible inspiratory or expiratory synergism between various external and internal intercostal muscles in cats].

The electrical activities of the lateral parts of the external and internal intercostal muscles were recorded in decerebrated cats during eupnea and in the course of artificially induced dyspnoea, elicited in order to reinforce the inspiratory or expiratory central drive. Our results indicate that in the cephalic spaces (1st to 5th rib), external and internal intercostals are synergists during inspiration. In the caudal spaces (9th to 13th rib), the same muscles are activated during expiration only. In the intermediate part of the thorax (5th to 9th rib), external intercostals are inspiratory muscles, internal intercostals are expiratory muscles.

Animals↗
PubMed1982

Intercostal muscle and myo-osseous flaps in difficult pediatric thoracic problems.

Intercostal muscle pedicle flaps have been successfully utilized in the treatment of recurrent tracheoesophageal fistulae and esophageal perforations in the pediatric age group. An intercostal myo-osseous pedicle flap was also created to repair a distal congenital tracheal stenosis at the carina. The viable intercostal flap has the advantage of multiplicity of uses and of considerable mobility. The presence of a blood supply assures healing. The option of retaining periosteum on the flap encourages bone regeneration at the site of tracheal or bronchial repair. The pleura of the flap provides an epithelial surface for intratracheal repair. The rib graft prevents stricture at the site of tracheal repair.

Child, Preschool↗
PubMed1989

Projection of low-threshold afferents from human intercostal muscles to the cerebral cortex.

Low-threshold afferents from human limb muscles are known to project to the sensorimotor cortex and to contribute to proprioception. However, there are few data on the cortical projection of afferents from human respiratory muscles. The present study employed evoked-potential techniques to determine whether low-threshold muscle afferents from the chest wall project to cortical levels in conscious human subjects. In four subjects intramuscular afferents of the second parasternal and fifth lateral intercostal muscles were selectively stimulated through an insulated microelectrode inserted percutaneously at the respective motor point. Evoked potentials were recorded and averaged from eight scalp sites. The initial cortical component of the cerebral response to intramuscular stimulation of the second and fifth interspaces was a negative potential commencing at 19.2 +/- 2.1 msec and 20.7 +/- 1.1 msec respectively. The dominant early cortical potential was largest at the vertex, and was comparable in amplitude (0.58 +/- 0.23 microV) to that for individual muscles of the upper and lower limbs. The cortical focus was distributed differently from that for cutaneous afferents of the chest wall and for both muscle and cutaneous afferents from the upper and lower limbs. This study provides direct evidence for a short-latency projection from intercostal muscle afferents (group I and/or II) to the human cerebral cortex.

Adult↗
PubMed1997

Actions of the inspiratory intercostal muscles in flail chest.

We have previously shown in dogs that the ribs in flail chest move paradoxically inward during inspiration but continue to move cranially. We have also shown that flail elicits, probably via an increased activation of the muscle spindles, a threefold to fourfold increase in external intercostal inspiratory EMG activity without inducing any changes in parasternal intercostal activity. Therefore, the present studies were undertaken to test the hypothesis that the persistent cranial motion of the fractured ribs resulted primarily from the action of the external intercostals. A flail was induced in seven supine anesthetized animals by fracturing both dorsally and ventrally ribs 3 to 6 on the right side of the chest, after which the external intercostal muscles in interspaces 1 to 7 were severed. Severing the external intercostals caused a small increase in the inspiratory inward displacement of the fractured ribs, from 2.76 +/- 0.31 to 3.25 +/- 0.38 mm (p < 0.05), but it did not affect the parasternal intercostal EMG activity or the cranial rib displacement (before, 3.61 +/- 1.03 mm; after, 3.22 +/- 1.43 mm; NS). However, when the parasternal intercostals in interspaces 1 to 7 were also denervated, the inspiratory inward displacement of the ribs increased markedly to 5.95 +/- 0.48 mm (p < 0.01), and their inspiratory cranial displacement was reversed into a 1.05 +/- 0.58 mm inspiratory caudal displacement (p < 0.01). We conclude, therefore, that in dogs with flail chest the respiratory displacements of the ribs are still primarily determined, besides pleural pressure, by the action of the parasternal intercostals. These observations also suggest that in anesthetized dogs, spindle-induced excitation of the external intercostals has little impact on the mechanical behavior of the ribs.

Animals↗
PubMedDate not supplied

Benign solitary fibrous tumor of the parietal pleura which invaded the intercostal muscle.

A 29-year-old woman who underwent evaluation for a 3-month history of left-sided back pain proved to have a left pleural tumor accompanied by a bloody pleural effusion (cytological class II). Three years previously, a chest roentgenogram had been normal. The tumor originated from the parietal pleura at the level of the first three intercostal muscles and was excised completely in continuity with these muscles, including a margin of normal muscle. The tumor measured 15x12 cm and the pathologic diagnosis was benign solitary fibrous tumor; while the tumor invaded the intercostal muscles, no histologically malignant features were present. Long-term follow-up is planned because a possibility of local recurrence exists.

Adult↗
PubMed1989

Inspiratory action of separate external and parasternal intercostal muscle contraction.

We have previously shown that electrical stimulation of the thoracic spinal cord produces near maximal activation of the inspiratory intercostal muscles. In the present investigation, we used this technique to evaluate the relative capacity of separate external (EI) and parasternal intercostal (PA) muscle contraction to produce changes in airway pressure and inspired volume. Studies were performed in 23 anesthetized phrenicotomized dogs. Electrical stimuli were applied to the spinal cord after hyperventilation-induced apnea, before and after sequentially severing either the PA or EI muscles from the first through sixth intercostal spaces. During spinal cord stimulation (SCS), measurements were made of inspired volume (delta V) with the airway open and negative airway pressure (delta P) during tracheal occlusion. Compared with control values, sectioning of the PA muscles resulted in a 40.9% reduction in delta P and 35.7% reduction in delta V during SCS. In other animals, initial sectioning of the EI muscles produced reductions in delta P and delta V of 67.4 and 63.0, respectively, during SCS. After subsequent section of the PA muscles, SCS produced only negligible inspired volumes and changes in airway pressure. We conclude that 1) the EI and PA muscles are each capable of generating substantial changes in airway pressure and large inspired volumes and 2) the ventilatory capacity of the EI muscles exceeds that of the PA muscles.

Animals↗
PubMed1975

Intercostal muscle biopsy in human neuromuscular disease. Histochemical and electron microscopic studies.

External intercostal muscle biopsies were examined histochemically and by electron microscopy. The use of this muscle allowed correlation with physiological and pharmacological studies on the same specimens. Changes observed in musclar dystrophy and motor neurone disease resembled those previously described in biopsied limb muscle and underline the particular usefulness of this preparation in the study of human neuromuscular disease.

Adenosine Triphosphatases↗
PubMed1992

Spike trains from single motor units in human parasternal intercostal muscles.

Recordings of single motor unit activity were obtained from parasternal intercostal muscles of normal humans during quiet breathing. Spike trains from 52 individual motor units were analyzed. All these units were low threshold ones, recruited at low inspired volumes and therefore at low tension thresholds. Mean frequency of firing at onset was 7.8 Hz and mean increase in frequency through the breath was 3.6 Hz. Onset and peak frequencies were positively correlated with inspiratory flow rate. Alternation of interspike intervals between long and short was found in the spike trains of 6 of 13 units tested and this occurred at frequencies of 6-12/s. Doublet discharges at the beginnings of spike trains were seen during voluntary neck flexion but never in quiet breathing or voluntary deep breaths. The pattern of activity in these human intercostal motor units was similar to that reported for low threshold, slow twitch units in other mammalian skeletal muscles, including respiratory muscles.

Action Potentials↗
PubMed1980

Respiratory mechanics in quadriplegia. The respiratory function of the intercostal muscles.

Pulmonary mechanics and inspiratory muscle pressures were studied in relation to electromyograms (EMG) of the respiratory muscles in 10 chronic quadriplegic patients . Transdiaphragmatic pressures at maximal inflation were normal, but minimal pleural pressures at functional residual capacity (FRC) were reduced to about one half the normal values. On the basis of the parasternal intercostal EMG results, 2 groups were defined. In 8 patients (Group I), no electromyographic activity was found in the intercostal muscles, even during large inspiratory maneuvers. In 2 patients (Group II), both intercostal and diaphragmatic activities were recorded during inspiration, and intercostal EMG activity increased with increasing inspiratory volume. Group 1 patients had reduced FRC, transpulmonary pressure at FRC, and static expiratory compliance; therefore, the pressure-volume curves of the lungs resembled those obtained in patients with generalized weakness of the respiratory muscles. Specific compliance was normal in each patient, suggesting that the low compliance resulted in large part from the collapse of air spaces. Group 2 patients had FRC, transpulmonary pressure at FRC, and lung compliance values within normal limits. We concluded that longstanding paralysis of intercostal muscles causes marked alterations in the elastic properties of the lungs and reduces the passive (outward) recoil of the chest wall. These findings suggested that the intercostal muscles normally stabilize the chest wall and prevent lung collapse. Moreover, intercostal surface EMG recordings may help to identify tetraplegic patients who may be at risk of developing respiratory failure during rather minor insults to the respiratory system.

Adult↗
PubMed1985

Selective reinnervation of intercostal muscles transplanted from different segmental levels to a common site.

We transplanted external intercostal muscles from one of several thoracic (T) levels to the neck of adult rats. The cervical sympathetic trunk, which innervates the superior cervical ganglion, was cut, and its proximal end was apposed to the muscle. Preganglionic axons in the trunk reinnervated muscle fibers in the transplants. We determined the segmental origin of synaptic inputs to transplanted muscles by recording intracellularly from muscle fibers while stimulating individual ventral roots which supply axons to the trunk. In one series of experiments, T2 or T8 muscles were transplanted from the thorax to the neck of the same rat. While T2 and T8 muscles were reinnervated to a similar extent, they differed in the segmental origin of the innervation they received: T2 muscles received more inputs from rostral segments (T1 and T2) than did T8 muscles, and T8 muscles received more inputs from caudal segments (T4 to T6) than did T2 muscles. This difference between reinnervation of T2 and T8 muscles was detected both 2 to 4 weeks and 10 to 14 weeks after surgery. In a separate series, using rats of an inbred strain, T3, T4, or T5 muscles were transplanted from one rat to a separate host. Again, the average segmental origin of inputs to transplants from different levels differed systematically: it was most rostral to T3 muscles, intermediate to T4 muscles, and most caudal to T5 muscles. Finally, T3 and T5 muscles were soaked in a myotoxin, Marcaine, before reimplantation. This treatment kills muscle fibers but not myoblastic satellite cells; therefore, muscle fibers were replaced by regeneration. Marcaine-treated T3 and T5 muscles were successfully reinnervated but did not differ significantly in the segmental origin of their inputs. Our results show that adult mammalian muscles can be selectively reinnervated, and they raise the possibility that the selectivity is based on some positional quality that matches axons and muscles from corresponding segments. However, while differences among muscles survive denervation and transplantation, their expression or accessibility may change during regeneration.

Animals↗
PubMed1991

Regional blood flow to canine parietal pleura and internal intercostal muscle.

Transcapillary Starling forces in the parietal pleura and the underlying interstitium may potentially contribute to the exchange of fluid across this barrier. However, the extent of blood flow to the parietal pleura has not been measured. Thus, using standard microsphere techniques, we compared blood flow to the parietal pleura, including the subpleural interstitium, with blood flow to the adjacent internal intercostal muscle, as well as with flows to other serous tissues, including mediastinal pleura, pericardium, and parietal peritoneum, in anesthetized dogs that were either breathing spontaneously (n = 9) or ventilated to control arterial PCO2 (n = 5). Blood flow (ml.min-1.g-1) was measured after 20 min of equilibration in four successive body positions: right lateral decubitus, supine, left lateral decubitus, and prone. Overall, flow to parietal pleura was not different in spontaneous [1.07 +/- 0.14 (SE)] and mechanically ventilated animals (0.74 +/- 0.11). Flow to the internal intercostal muscle was significantly less than pleural blood flow, averaging 0.24 +/- 0.03 and 0.16 +/- 0.03 in the same groups, although again there was no effect of ventilation mode. Blood flow to other serous tissues in the thoracic cavity, specifically the mediastinal pleura (0.67 +/- 0.14) and pericardium (0.88 +/- 0.22), was similar to parietal pleural flow, whereas that to the parietal peritoneum was an order of magnitude lower (0.09 +/- 0.02, P less than 0.05). Changing body position had no effect on blood flow to any of the sampled tissues. Blood flow to the dorsal aspect of the chest wall muscle in spontaneously breathing animals tended to be greater than that to lateral or ventral portions of the chest wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Using intercostal muscle EMG to quantify maternal expulsive efforts during vaginal delivery: a pilot study.

AIMS: The expulsive forces of childbirth can be included among the many potential risk factors implicated in the subsequent development of stress urinary incontinence (SUI) in women. The objective of this study was to devise a non-invasive way to measure abdominal pushing that would accurately represent the expulsive forces during childbirth. METHODS: By means of intravesical and intrauterine manometry, and electromyography (EMG) of intercostal muscles, we quantified these forces in 21 women during vaginal delivery. RESULTS: A mathematical analysis of variance (ANOVA) model showed the integral of intravesical pressure to be significantly associated (P < 0.001) with the integral of intercostal muscle electrical activity during the first six uterine contractions during the phase of fetal expulsion. CONCLUSIONS: EMG is a non-invasive measurement that can replace intravesical determinations to quantify these forces as it reflects the real intra-abdominal pressure.

Adult↗