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PubMed1985

Mechanics of intercostal space and actions of external and internal intercostal muscles.

It is conventionally considered that because of their fiber orientations, the external intercostal muscles elevate the ribs, whereas the internal interosseous intercostals lower the ribs. The mechanical action of the intercostal muscles, however, has never been studied directly, and the electromyographic observations supporting this conventional thinking must be interpreted with caution. In the present studies, the external and internal interosseous intercostal muscles have been separately stimulated in different interspaces at, above, and below end-expiratory rib cage volume in anesthetized dogs. The axial (cephalo-caudal) displacements of the ribs were measured using linear displacement transducers. The results indicate that when contracting in a single interspace and other muscles are relaxed, both the external and internal intercostals have a net rib elevating action at end-expiratory rib cage volume. This action increases as rib cage volume decreases, but it progressively decreases as rib cage volume increases such that at high rib cage volumes, both the external and internal intercostals lower the ribs. Stimulating the intercostal muscles in three adjacent intercostal spaces simultaneously produced similar directional rib motion results. We conclude that (a) in contrast with the conventional thinking, the external and internal interosseous intercostals acting alone have by and large a similar effect on the ribs into which they insert; (b) this effect is very much dependent on rib cage (lung) volume; and (c) intercostal muscle action is primarily determined by the resistance of the upper ribs to caudad displacement relative to the resistance of the lower ribs to cephalad displacement. The lateral intercostals, however, might be more involved in postural movements than in respiration. Their primary involvement in rotations of the trunk might account for the presence of two differently oriented muscle layers between the ribs.

Animals↗
PubMed2004

The radiologic appearance of intercostal muscle flap.

BACKGROUND: The intercostal muscle flap (ICMF) is commonly used in airway and esophageal surgery to reinforce an anastomosis or site of closure. These flaps undergo heterotopic ossification that may result in stenosis of adjacent airways or the esophagus. We evaluated the computer tomography (CT) scan, technetium-99m-methylene diphosphonate bone scan and positron emission tomography with 2-[18F]-fluoro-2-deoxy-D-glucose (FDG-PET) findings of ICMF and the frequency of airway or esophageal stenosis. METHODS: A retrospective review was made of the radiologic records of 23 patients (9 women, 14 men) who underwent ICMF. The CT scans were obtained a mean of 36 months (range, 1 week to 58 months) after surgery and the size, morphology, and density of the ICMFs were recorded. Correlative bone scan in 13 patients and FDG-PET scans in 11 patients were reviewed. RESULTS: A discontinuous, thin, linear calcified stripe or parallel stripes (mean thickness, 4 mm; mean density, 430 Houndsfield unit [HU]) were present in all patients on CT. The flap contained fat density (mean, -59 HU) in 18 patients and soft tissue density (mean, 41 HU) in 8 patients and measured about 1 cm in thickness. The appearance of ICMF is characteristic when the ossification extends from the posterolateral chest wall to an adjacent bronchial stump. There was no increased uptake on bone scan or FDG-PET scan. None of the patients had airway or esophageal stenosis. CONCLUSIONS: The ICMF manifests on CT as a thin, linear calcified stripe or parallel stripes with central fat or soft tissue density. Airway stenosis due to ICMF is likely quite rare. We did not detect any airway stenosis.

Adult↗
PubMed2001

Respiratory effects of the external and internal intercostal muscles in humans.

The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung and the internal interosseous intercostals have an expiratory action. Recent studies in dogs, however, have shown that this notion is only approximate. In the present studies, the respiratory actions of the human external and internal intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the orientation of the muscle fibres relative to the ribs and the masses of the muscles were first assessed in cadavers. Five healthy individuals were then placed in a computed tomographic scanner to determine the geometry of the ribs and their precise transformation during passive inflation to total lung capacity. The fractional changes in length of lines with the orientation of the muscle fibres were then computed to obtain the mechanical advantages of the muscles. These values were finally multiplied by muscle mass and maximum active stress (3.0 kg cm-2) to evaluate the potential effects of the muscles on the lung. The external intercostal in the dorsal half of the second interspace was found to have a large inspiratory effect. However, this effect decreases rapidly in the caudal direction, in particular in the ventral portion of the ribcage. As a result, it is reversed into an expiratory effect in the ventral half of the sixth and eighth interspaces. The internal intercostals in the ventral half of the sixth and eighth interspaces have a large expiratory effect, but this effect decreases dorsally and cranially. The total pressure generated by all the external intercostals during a maximum contraction would be -15 cmH2O, and that generated by all the internal interosseous intercostals would be +40 cmH2O. These pressure changes are substantially greater than those induced by the parasternal intercostal and triangularis sterni muscles, respectively.

Adult↗
PubMed1998

A method for morphometric study of the intercostal muscles by high-resolution ultrasound.

Besides their main function of assisting in breathing, the intercostal muscles also play an important role in maintaining the balance of forces acting on the thoracic cage including the thoracic spine. Since it is virtually impossible to conduct a morphometric evaluation of these muscles, a study was undertaken to standardize an ultrasound method for accurate determination of the area of the intercostal muscles and hence, indirectly, their function. In a pilot study, the area of the intercostal muscles was determined on the torso of a fresh specimen of a grown-up lamb, using high-resolution ultrasound and CT, and by direct measurements of the intercostal space at two points equidistant from the midline on the left and the right sides of the back of the specimen. The size of the intercostal muscles was determined either by tracing or from the perpendiculars of the area of the muscles both on sonographs and on CT scans. The results showed that measurements derived from the perpendiculars of the muscle area on the sonographs give better estimates than those derived from CT scans, and were in good accordance with the direct measurements of the corresponding intercostal space on the specimen. To evaluate the applicability of the method in vivo the area of the intercostal muscles at maximal inhalation and exhalation was determined in one adult person. It was found that measurements at maximal inhalation were more accurate than those taken at maximal exhalation. It is concluded that ultrasonography is a reliable, safe, easy to apply and high-resolution method for measurements of the area and, indirectly, of the activity of the intercostal muscles in humans, and that the measurements are more accurate at maximal inhalation.

Adult↗
PubMed2004

The two mechanisms of intercostal muscle action on the lung.

The mechanisms of respiratory action of the intercostal muscles were studied by measuring the effect of external forces (F) applied to the ribs and by modeling the effect of F exerted by the intercostal muscles. In five dogs, with the airway occluded, cranial F were applied to individual rib pairs, from the 2nd to the 11th rib pair, and the change in airway opening pressure (Pao) was measured. The ratio Pao/F increases with increasing rib number in the upper ribs (2nd to 5th) and decreases in the lower ribs (5th to 11th). These data were incorporated into a model for the geometry of the ribs and intercostal muscles, and Pao/F was calculated from the model. For interspaces 2-8, the calculated values agree reasonably well with previously measured values. From the modeling, two mechanisms of intercostal muscle action are identified. One is the well-known Hamberger mechanism, modified to account for the three-dimensional geometry of the rib cage. This mechanism depends on the slant of an intercostal muscle relative to the ribs and on the resulting difference between the moments applied to the upper and lower ribs that bound each interspace. The second is a new mechanism that depends on the difference between the values of Pao/F for the upper and lower ribs.

Animals↗
PubMed1983

Respiratory effects of stimulation of intercostal muscles and saphenous nerve in kittens.

Effects of intercostal muscle stimulation were studied in 2- to 7-day-old kittens under ketamine-acepromazine anesthesia. Animals were vagotomized, paralyzed, and artificially ventilated. Stimuli applied during inspiration (TI) inhibited this phase. Stimulus strength necessary for TI inhibition decreased with time. However, an all-or-nothing effect was not always observed. Stimulation during expiration (TE) prolonged this phase. The responsiveness increased with increasing stimulus delay. The effects of intercostal muscle stimulation were compared with those recorded during saphenous nerve stimulation. Stimulation during TI prolonged this phase. Phrenic activity increased after a short-lasting decrease in the on-going activity. Stimulation during the first 50% of TE had variable effects, whereas stimulation with longer delay shortened this phase. Our results indicated that the pattern of breathing in newborns can be affected by both intercostal muscle and other somatic efferents. However, the mechanisms controlling respiratory timing may differ in newborns and in adults. Different effects of respiratory muscle and saphenous nerve stimulation suggest different transmitters involved or different sites of interaction of these inputs with the medullary respiratory rhythm generator.

Animals↗
PubMed2003

Distribution of inspiratory drive to the external intercostal muscles in humans.

The external intercostal muscles in humans show marked regional differences in respiratory effect, and this implies that their action on the lung during breathing is primarily determined by the spatial distribution of neural drive among them. To assess this distribution, monopolar electrodes were implanted under ultrasound guidance in different muscle areas in six healthy individuals and electromyographic recordings were made during resting breathing. The muscles in the dorsal portion of the third and fifth interspace showed phasic inspiratory activity with each breath in every subject. However, the muscle in the ventral portion of the third interspace showed inspiratory activity in only three subjects, and the muscle in the dorsal portion of the seventh interspace was almost invariably silent. Also, activity in the ventral portion of the third interspace, when present, and activity in the dorsal portion of the fifth interspace were delayed relative to the onset of activity in the dorsal portion of the third interspace. In addition, the discharge frequency of the motor units identified in the dorsal portion of the third interspace averaged (mean +/- S.E.M.) 11.9 +/- 0.3 Hz and was significantly greater than the discharge frequency of the motor units in both the ventral portion of the third interspace (6.0 +/- 0.5 Hz) and the dorsal portion of the fifth interspace (6.7 +/- 0.4 Hz). The muscle in the dorsal portion of the third interspace started firing simultaneously with the parasternal intercostal in the same interspace, and the discharge frequency of its motor units was even significantly greater (11.4 +/- 0.3 vs. 8.9 +/- 0.2 Hz). These observations indicate that the distribution of neural inspiratory drive to the external intercostals in humans takes place along dorsoventral and rostrocaudal gradients and mirrors the spatial distribution of inspiratory mechanical advantage.

Adult↗
PubMed1992

Intercostal muscles are used during rotation of the thorax in humans.

To test the idea that the lateral intercostal muscles may be more suited to aid in rotational than respiratory movements of the thorax, we inserted bipolar fine-wire electrodes in external and internal intercostal muscles in the right midaxillary line in nine sitting subjects and examined the pattern of contraction of these muscles during voluntary axial rotations of the thorax (30-35 degrees), resting breathing, and CO2-induced hyperpnea. The right external intercostal muscles were strongly recruited in rotations to the left but were not active in rotations to the right. In contrast, the right internal intercostal muscles were active in rotations to the right but not in rotations to the left. Rotations completed in 1 or 2 s were associated with an early burst of electromyographic activity, followed by a low plateau that persisted while the rotation was held. Rotations made very gradually over 5-10 s were associated with gradually rising electromyographic activity. The amplitude of activity recorded during 30-35 degrees rotations was equivalent to that measured when minute ventilation was increased by CO2 to 50 l/min. We conclude that the lateral intercostal muscles have a major role in producing axial rotations of the thorax.

Adult↗
PubMed1997

[Diffusion of bupivacaine into the intercostal muscle following interpleural analgesia].

To test the hypothesis that local anesthetic solution diffuses across the parietal pleura into the intercostal nerves in interpleural analgesia, tissue bupivacaine concentrations were assayed after interpleural injection of bupivacaine in rabbits. Thirty animals were killed at 10, 20, or 30 min after administration of 0.5% bupivacaine (1 ml.kg-1) into the left pleural cavity. The left intercostal muscle (lt-ICM), right intercostal muscle (rt-ICM) and femoral muscle (FM) were sampled immediately after killing the animals. Bupivacaine concentrations were analyzed by high-performance liquid chromatography. Mean bupivacaine concentrations in lt-ICM were 10.8 micrograms.g-1 at 10 min, 15.2 micrograms.g-1 at 20 min and 11.8 micrograms.g-1 at 30 min. On the other hand, the bupivacaine concentrations in rt-ICM and FM were less than 2.0 micrograms.g-1 at any sampling time. (P < 0.01 vs. lt-ICM). These results indicate that bupivacaine administered interpleurally diffuses from the pleural space into the ipsilateral intercostal muscle. Direct diffusion of bupivacaine could cause intercostal nerve block following interpleural analgesia.

Analgesia↗
PubMed1987

Accuracy of reinnervation of rat internal intercostal muscles by their own segmental nerves.

The positions of internal intercostal motoneurons within their motor pool were studied, following reinnervation of the intercostal muscles by their original nerves. Six to 9 weeks after proximal nerve section in 10-d-old and adult rats, 0.1 microliter injections of wheat germ agglutinin (WGA)-HRP were made in the distal part of the reinnervated internal intercostal muscle. The corresponding region of the contralateral control muscle was also injected. The positions of the retrogradely labeled motoneurons were mapped in 100 microns transverse sections of thoracic spinal cord that had been stained for HRP according to the method of Mesulam (1982). In normal rats, motoneurons innervating distal muscle fibers are found largely in the more dorsal part of the internal intercostal motoneuron pool (Hardman and Brown, 1985). In adult rats, regenerated motor axons did not show any selectivity; distal muscle fibers were innervated by motoneurons whose cell bodies were distributed throughout the internal intercostal pool. However, in rats operated on at 10 d of age, distal intercostal muscle fibers were reinnervated by motoneurons that were distributed mainly in the dorsal part of the motor pool. These results support the view that positional signals may be of importance in organizing the distribution of axon terminals within muscles during development.

Aging↗
PubMed1998

Respiratory ultrasonography of human parasternal intercostal muscle in vivo.

The parasternal intercostal muscle (PS) is phasically active during inspiration, but its mechanical function in humans is poorly understood. The aim of this study was to describe PS motion ultrasonographically during respiration. We used a 7.5-MHz curvilinear phased array transducer to obtain ultrasonograms of the second right and left interspace in the sagittal plane, 2-3 cm lateral to the sternum, in 4 seated subjects (3M, 1F), during tidal breathing and at residual volume (RV), functional residual capacity (FRC) and total lung capacity (TLC). Images were recorded on videotape and off-line, digitized, transferred to a workstation, and traced manually to outline the external and pleural borders of the PS muscle in relation to a rectangle bounded by the second and third ribs. To assess PS shape and motion, we measured inter-rib distance (Lics), PS thickness (Tps), and motion of the midpoint of the muscle relative to the midpoint of the reference rectangle (Mps). We also calculated the average radius of curvature of the external and pleural PS borders (Re, Rp) over the mid 50% of Lics, and 1/Re and 1/Rp. During tidal breathing, Mps moved ventrally by 0.42 +/- 0.06 mm (p = 0.001) against the pleural pressure gradient, and 1/Re and 1/Rp decreased by 1.1 x 10(-2) +/- 1.6 x 10(-3) mm-1 and 8.4 x 10(-3) +/- 1.4 x 10(-3) mm-1, respectively (p < 0.001). Lics and Tps did not change (p > 0.19). We conclude that, during inspiration, the PS moves ventrally and straightens, and lung volume, neural activation and pleural pressure influence PS shape and motion. The findings support an intercostal stabilizing function of the PS and suggest a novel mechanism by which the PS may contribute to the inspiratory fall in pleural pressure.

Adult↗
PubMed1988

The effect of acute hemiplegia on intercostal muscle activity.

We recorded the EMG of parasternal intercostal muscles in 25 patients with flaccid hemiplegia during quiet spontaneous breathing, voluntary hyperventilation, and CO2-induced hyperventilation. The respiratory drive was abnormal on the hemiplegic side and the function of the intercostal muscles was affected specifically during voluntary hyperventilation.

Acute Disease↗
PubMed2005

Intercostal muscle flap to buttress the bronchus at risk and the thoracic esophageal-gastric anastomosis.

BACKGROUND: We assessed our outcomes using an intercostal muscle flap harvested with cautery prior to chest retraction. METHODS: Our retrospective study was conducted using an electronic prospective database. RESULTS: There were 456 patients (348 men) over a six year period. The intercostal muscle flap was used for bronchial coverage in 391 patients. The indications for the flap were neoadjuvant radiochemotherapy in 285 patients, infection or inflammatory disease in 106, to buttress an esophageal-gastric anastomosis in 49, and for esophageal fistula in 16. There were three bronchopleural fistulas (0.7%); one after a right pneumonectomy for tuberculosis, one after a left pneumonectomy, and one after a lobectomy in a heart transplant patient for mucormycosis. The 4-week median postoperative pain score for patients who underwent an intercostal muscle flap was lower compared with historic controls who underwent similar procedures over the same time frame but did not have an intercostal muscle flap (2.4 vs 3.7, p = 0.003). Follow-up was a median of 26 months (range, 1 to 72 months) and no patients had ossification of their flap. CONCLUSIONS: An intercostal muscle flap is a versatile pedicle flap that can reach all bronchi. It is easy to harvest, adds no morbidity, and may protect the bronchi at risk. When harvested devoid of periosteum it does not ossify over time and it may reduce the pain of thoracotomy.

Adult↗
PubMed1985

Experimental use of intercostal muscle flaps for repair of induced cardiac defects.

Intercostal muscle flaps were successfully used to repair 3 cm defects of the ventricular myocardium in the mongrel dog. Early and late healing of all flaps was uncomplicated and there were no late complications related to aneurysmal formation or electrical abnormalities of the heart. The existing blood supply of the heart was unaffected. The intercostal muscle is suggested as an alternative muscle flap for use in myocardial wall reconstruction.

Animals↗
PubMed1989

Length changes of intercostal muscles during respiration in the cat.

Sonomicrometry was used to measure the length changes of intercostal muscles throughout the rib cage of anesthetized cats. The motor unit discharge in the vicinity of the length measurement was monitored with bipolar electrodes. The external intercostal muscles in the rostral spaces and the parasternals actively shortened during inspiration. The external intercostals in the caudal spaces, which were inactive, either shortened or lengthened passively due to the forces imposed on the lower rib cage by the contraction of the diaphragm. The length changes of external intercostals of the mid-thoracic spaces, which were recruited during inspiration, were variable. The internal intercostals were usually inactive in our preparation and therefore their length excursions passively followed those of the external intercostals. The information regarding the length changes is correlated with that previously gathered for the role of muscle spindles in the intercostal muscles. It is suggested that gamma motoneurons are recruited to prevent the muscle spindles from being unloaded when the intercostal muscle shortens and to increase the sensitivity of the receptors during the phase of the respiratory cycle when the muscle is active.

Animals↗
PubMed1990

Mechanical action of the interosseous intercostal muscles as a function of lung volume.

On the basis of local stimulation of individual muscles, it has been suggested that both the external (EI) and internal interosseous intercostal muscles have an inspiratory action at low lung volumes and an expiratory action at high lung volumes. In this study, we assessed the action of the interosseous intercostal muscles at different lung volumes in 19 anesthetized dogs by synchronously activating the intercostal muscles via ventral root stimulation (VRS). An electrode was positioned on the upper thoracic spinal cord according to previously described techniques. The cervical phrenic rootlets were sectioned bilaterally, the accessory muscles were sectioned from the rib cage, and the origins of the abdominal muscles were sectioned from the middle region of the rib cage. Changes in airway pressure (delta P) were monitored during the application of supramaximal stimuli after hyperventilation-induced apnea and during airway occlusion. Animals were passively inflated or deflated with a volume syringe. Precontractile airway pressure was used as an index of lung volume. External and parasternal intercostal muscle (PA) lengths were monitored by sonomicrometry in the third intercostal space. Thoracoabdominal motion was monitored by Respitrace bands. During VRS, both PA and EI shortened at all lung volumes. Mean delta P progressively decreased with increasing lung volume. At precontractile airway pressures of -10, 0, and +30 cm H2O, delta P were -25 +/- 1, -16 +/- 1, and -5 +/- 1 cm H2O, respectively. After section of the internal intercostal nerves lateral to the costochondral junctions from the first through the seventh intercostal spaces to eliminate PA action, EI shortened, whereas PA usually lengthened.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1980

Alterations in intercostal muscle morphology and biochemistry in patients with obstructive lung disease.

Twenty-two patients undergoing thoracotomy for the diagnosis or treatment of a suspected pulmonary neoplasm had separate biopsies taken from their external and internal intercostal muscles at the time of surgery. Pulmonary function abnormalities ranged from none to moderate airway obstruction. Seventeen of the twenty-two patients had morphologic changes (targeting, variation in fiber size, splitting, and atrophy) in both respiratory muscles, but not in the control latissimus dorsi. Fiber atrophy was more marked in the internal intercostal muscle and was significantly related to the degree of airway obstruction, but not to age, malignancy, or weight loss. Biochemical analyses revealed decreased adenosine triphosphate (ATP) and phosphocreatine (PC) in 47 of 52 muscles, including the latissimus dorsi. The data suggested a relation between increasing airway obstruction and decreasing amounts of phosphocreatine in both intercostal muscles. This relationship may have been enhanced by the presence of malignancy or weight loss. There was a selective decrease in muscle glycogen found only in the external intercostal muscle that was not affected by airway obstruction, malignancy, or weight loss. Intercostal muscle abnormalities are common in patients with obstructive lung disease who undergo thoracotomy, and are probably multifactorial in origin. It is possible that these abnormalities affect the natural history of lung disease in some patients.

Adenosine Triphosphate↗