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PubMed1998

Intercostal muscles in the rabbit: surgical anatomy and flap construction.

Demos and colleagues (1967) obtained good antireflux results from transposing an intercostal myoneurovascular pedicle around the gastro-oesophageal junction in dogs. An intact neurovascular supply is essential for the viability of a muscle flap. The aim of this study was to delineate the nerve and arterial supply to the left 11th intercostal muscle in the rabbit and to assess whether this muscle could be mobilized as a viable flap. The innervation of the muscle was studied using the methods of gross dissection in cadaveric specimens, and histological staining techniques. The arterial supply was studied using gross dissection, and aortography. In three non-recovery experiments, intercostal muscle was transposed around the gastro-oesophageal junction. The distal motor latency was recorded after electrical stimulation of the intercostal wraps. Gross dissection, histological staining techniques, and aortography showed that the left 11th intercostal muscle group in the rabbit is supplied by segmental vein, artery and nerve, running between external and internal intercostal muscles. Aortography and electrical stimulation demonstrated that the muscle group could be mobilized with an intact neurovascular supply. The left 11th intercostal muscle group has potential as a viable muscle flap for use in surgical procedures within the upper abdomen.

Animals↗
PubMed1988

Drug-induced myotonia in human intercostal muscle.

The myotonia-inducing effects of furosemide and clofibrate, two widely used pharmaceutical agents, were investigated in excised human external intercostal muscle. The effects of anthracene-9-carboxylic acid (9-AC), a well-known myotonia-producing chemical, were also tested for comparison. In the presence of these drugs the electrical threshold was lowered, and a constant current pulse produced multiple spiking. Short trains of direct stimuli were often followed by after-activity, and this caused a myotonia-like prolongation of muscle contraction. Voltage-clamp experiments showed that 0.05 mM anthracene-9-carboxylic acid, 1 mM furosemide, and 1 mM clofibrate decreased the chloride conductance of the muscle fiber membrane to 14, 18, and 40%, respectively, of the normal value, and the myotonia-inducing potency of the 3 drugs was correlated with the decreased chloride conductance. The potassium currents were not affected by these compounds.

Anthracenes↗
PubMed1975

The response to stretch of human intercostal muscle spindles studied in vitro.

1. The discharge properties of human muscle spindles have been studied in vitro in a preparation based on the biopsied external intercostal muscle. 2. The static and dynamic responsiveness of thirty-six endings in twenty visualized and histologically identified spindles have been investigated using amplitudes and velocities of stretch likely to encompass those occurring in vivo. 3. The dynamic index, measured at a stretch velocity of 3 mm/sec, ranged from 3 to 40 impulses/sec and was distributed bimodally, consitent with the presence of primary and secondary endings. 4. The relationship between the dynamic index and the velocity of stretch was approximately linear both for primary and secondary endings up to the maximum velocity tested (10 mm/sec). 5. The frequency/extension relationship was approximately linear for both primary and secondary endings. The mean values of the slope for primary and secondary endings were 16-1 +/- 8-3 S.D. of the observation and 12-1 +/- 6-5 impulses/sec per five per cent extension. 6. The slopes of the frequency/extension relationship for endings lying in the same spindle were positively correlated, significant at the 10% level. 7. It was estimated from the results in vitro that the position sensitivity of human intercostal spindles in vivo ranges from 2 to 21 impulses/sec per millimetre.

Action Potentials↗
PubMed1969

Cable properties of external intercostal muscle fibres from myotonic and nonmyotonic goats.

1. In preparations of about 200 fibres each from thirty-nine biopsies of external intercostal muscle taken from nine myotonic and six nonmyotonic goats, cable properties were determined at 38 degrees C for individual fibres with a pair of intracellular micro-electrodes.2. In each preparation the mean fibre dimensions, determined histologically and corrected for shrinkage, were used to calculate the mean membrane resistance, R(m), fibre capacitance, C(t), and myoplasmic resistivity, R(i). In the 124 nonmyotonic fibres the mean values were: R(m), 1897 Omega.cm(2), C(t), 4.1 muF/cm(2), and R(i), 112 Omega.cm. In 151 myotonic fibres R(m) was 5589 Omega.cm(2), C(t), 4.4 muF/cm(2), and R(i), 103 Omega.cm.3. Conductance of the fibre core times unit length increased with cross-sectional area, and fibre capacitance per unit length increased with perimeter. There was little correlation of membrane resistance per unit length of fibre with either fibre perimeter or resting potential.4. The principal abnormality of cable properties in the myotonic fibre is its threefold higher membrane resistance, which accounts for its decreased electrical current rheobase.

Animals↗
PubMed1993

Mechanical action of the internal intercostal muscles in dogs.

The pattern of electrical activation and muscle length changes of the internal intercostal (II) muscles (9th or 10th interspace) of the lower rib cage were evaluated in supine anesthetized dogs. Studies were performed during resting breathing and expiratory threshold loading. Results were compared with simultaneous measurements of the better-studied triangularis sterni muscle (4th interspace). In general, both muscles lengthened with passive inflation and shortened with passive deflation. During resting breathing, both the II and TS muscles were electrically active and shortened below resting length, 7.7 +/- 1.6% (SE) and 5.3 +/- 1.7%, respectively. With the addition of positive end-expiratory pressure, the degree of electrical activation and muscle shortening increased progressively for both muscles, although to a somewhat greater extent for II muscles. Isolated denervation of the II muscles eliminated their shortening during resting breathing and often resulted in muscle lengthening, indicating that II muscle shortening was secondary to its own activation. Expiration was associated with lateral inward movement of the lower rib cage below its relaxation position. This motion was not significantly affected by abdominal muscle section but was markedly reduced by bilateral II denervation (7th-11th spaces). Our results indicate that the II muscles of the lower rib cage 1) are electrically active and shorten below resting length during resting breathing, 2) respond to positive end-expiratory pressure by increasing their level of activation and degree of shortening, and 3) are primarily responsible for inward lateral motion of the lower rib cage below its relaxation position during expiration.

Abdominal Muscles↗
PubMed1996

Rostrocaudal gradient of mechanical advantage in the parasternal intercostal muscles of the dog.

1. Previous theoretical studies have led to the predictions that, in the dog, the parasternal intercostal muscles in the rostral interspaces shorten more during passive inflation than those in the caudal interspaces and have, therefore, a greater inspiratory mechanical advantage. The present studies were undertaken to test these predictions. 2. The effects of passive inflation on the length of the parasternal intercostals interspaces 1 to 7 were evaluated with markers implanted in the costal cartilages. Although the muscles in all interspaces shortened with passive inflation, the fractional shortening increased from the first to the second and third interspaces and then decreased continuously to the seventh interspace. 3. To understand this peculiar distribution, a geometric model of the parasternal area was then developed and a relation was obtained between muscle shortening and the angles that describe the orientation of the muscle and costal cartilage relative to the sternum. Measurement of these angles indicated that the rostrocaudal gradient of parasternal shortening resulted from the different orientations of the costal cartilages and their different rotations during passive inflation. 4. The changes in airway pressure generated by the parasternal intercostals in interspaces 3, 5 and 7 were finally measured during selective, maximal stimulation. The fall in pressure was invariably greatest during contraction of the third interspace and smallest during contraction of the seventh. 5. These observations indicate that, in the dog, the rostrocaudal gradient in rib rotation induces a rostrocaudal gradient of mechanical advantage in the parasternal intercostals, which has its climax in the second and third interspaces. These observations also support the concept that the respiratory effect of a given respiratory muscle can be computed from its behaviour during passive inflation.

Animals↗
PubMed1983

Phrenic activity and intercostal muscle emg during inspiratory loading in newborn kittens.

The effects of airway occlusions at functional residual capacity (FRC) on both "integrated" phrenic activity (Phr) and intercostal muscle electromyogram (intEMG) were studied in intact and vagotomized spontaneously breathing kittens during the 1st wk of life. Animals were anesthetized im with a mixture of ketamine (30 mg/kg) and acepromazine (1.1 mg/kg). In the intact kittens, inspiratory loading led to a significant increase in peak amplitudes of both Phr and intEMG and prolongation of inspiratory (TI) and expiratory (TE) times. Mean values of rate of rise of Phr and intEMG measured at 200 ms (intEMG200) from the onset of inspiration were unaffected. The results indicated that in newborns the vagal component of the load compensation is of great importance. Following vagotomy, airway occlusion produced a significant increase in mean values of TI and intEMG only. These small but significant changes suggest that most of the load compensation reflex is dependent on prolongation of TI. Increased intEMG200 during loading in the vagotomized kittens, observed during several trials, implies that the intercostal fusion-alpha interaction may operate in newborns.

Airway Obstruction↗
PubMed1990

Parasternal and external intercostal muscle shortening during eupneic breathing.

The interosseous external intercostal (EI) muscles of the upper rib cage are electrically active during inspiration, but the mechanical consequence of their activation is unclear. In 16 anesthetized dogs, we simultaneously measured EI (3rd and 4th interspaces) and parasternal intercostal (PA) (3rd interspace) electromyogram and length. Muscle length was measured by sonomicrometry and expressed as a percentage of resting length (%LR). During resting breathing, each muscle was electrically active and shortened to a similar extent. Sequential EI muscle denervation (3rd and 4th interspaces) followed by PA denervation (3rd interspace) demonstrated significant reductions in the degree of inspiratory shortening for each muscle. Mean EI muscle shortening of the third and fourth interspaces decreased from -3.4 +/- 0.5 and -3.0 +/- 0.4% LR (SE) under control conditions to -0.2 +/- 0.2 and -0.8 +/- 0.3% LR, respectively, after selective denervation of each of these muscles (P less than 0.001 for each). After selective denervation of the PA muscle, its shortening decreased from -3.5 +/- 0.3 to +0.6% LR (SE) (P less than 0.001). PA muscle denervation also caused the EI muscle in the third interspace to change from inspiratory shortening of -0.2% to inspiratory lengthening of +0.2% +/- 0.2 (P less than 0.05). We conclude that during eupneic breathing 1) the EI muscles of the upper rib cage, like the PA muscles, are inspiratory agonists and actively contribute to rib cage expansion and 2) PA muscle contraction contributes to EI muscle shortening.

Animals↗
PubMed1987

Effects of acetylcholine on internal intercostal muscle activity in the rabbit.

In pentobarbitone-anesthetized rabbits, intracarotid injections of acetylcholine (ACh, 3-30 micrograms) during inspiration led to an inhibition of internal intercostal muscle activity (IIMA). After the section of the carotid sinus nerve (CSN), ACh-induced inhibitory responses in IIMA were abolished. In addition, changes of the rabbit carotid chemoreceptor activity were studied by ACh (3-30 micrograms) given into the carotid body region during inspiration. Spontaneous chemoreceptor activity was inhibited in a dose-dependent manner by ACh. These results suggest that the inhibitory responses of IIMA to ACh are probably mediated through the carotid chemoreceptor reflexes.

Acetylcholine↗
PubMed1994

Continuous negative airway pressure increases tonic activity in diaphragm and intercostal muscles in humans.

The main objective of the present study was to quantify the increase in tonic inspiratory activity (delta TIA) in response to continuous negative airway pressure (CNAP) in humans. TIA represents the activity in inspiratory muscles at the end of expiration. In 20 subjects, electromyograms (EMGs) were recorded from the diaphragm and parasternal intercostal muscles (ICM) with surface electrodes during control and at three different levels of CNAP (-0.3, -0.6, and -0.9 kPa; 1 kPa approximately 10 cmH2O). From these recordings we determined delta TIA and the amplitudes of phasic EMG activities (EMGphas) during CNAP and control. To evaluate the effects of CNAP on functional residual capacity (FRC), respiratory frequency, tidal volume, and minute ventilation, the subjects were connected to a closed breathing circuit. When the pressure at the airway opening was -0.9 kPa, mean values of delta TIA were 53 and 49% of control EMGphas for the diaphragm and ICM, respectively. In addition, EMGphas at airway opening pressure of -0.9 kPa had increased to 195 and 162% of control EMGphas for the diaphragm and ICM, respectively. The concomitant decrease in FRC was on average 18.7% of predicted FRC. Minute ventilation had increased significantly (P < 0.05) at all levels of CNAP compared with control. We conclude that CNAP is a forceful stimulus to increase TIA in humans in both the diaphragm and the ICM.

Adolescent↗
PubMed1984

The resting membrane parameters of human intercostal muscle at low, normal, and high extracellular potassium.

Membrane parameters at the respective resting potentials in low, normal, and high extracellular potassium solutions were determined in intercostal muscle fibers from 15 patients with no known neuromuscular disease. In synthetic interstitial fluid (normal potassium concentration 3.5 mmol/liter), we found the following mean values: resting membrane potential RP = -83.3 mV, space constant lambda = 2364 micron, fiber diameter d = 49.3 micron, fiber input resistance Rin = 795 k omega, specific membrane capacitance Cm = 4.7 muF/cm2, and specific membrane resistance Rm = 5970 omega X cm2. The specific membrane conductance was gm = 168 muS/cm2, 76% of it being chloride conductance, 24% being potassium conductance. The dependence of the membrane parameters on the extracellular potassium concentration followed the predictions by the constant field theory. There was no indication of active chloride transport. The resting membrane conductance decreased with temperature with a Q10 of 1.3. Excitability parameters were nearly independent of temperature between 37 and 27 degrees C.

Action Potentials↗
PubMedDate not supplied

Electrophysiologic properties of intercostal muscle fibers in human neuromuscular diseases.

Electrophysiologic properties of biopsied normal and diseased intercostal muscle fibers were examined using intracellular microelectrode techniques. The resting potentials of all diseased muscle fibers were found to be depolarized. Those from Duchenne dystrophy patients showed the largest depolarization, followed by those from patients with myotonic muscular dystrophy, myotonia congenita, and motor neuron disease. All of the diseased fibers except those from myotonia congenita patients demonstrated an imparied ability to generate action potentials. In the latter fibers, the higher-than-normal membrane resistance was associated with hyperexcitability. When the membrane was hyperpolarized to the normal range, however, action potential characteristics in all fibers were near normal, except in motor neuron disease. All action potentials were blocked by tetrodotoxin. These findings--i.e., that all fibers were capable of generating action potentials when hyperpolarized, and that all action potentials were blocked by tetrodotoxin--suggest the relative intactness, in the disease studied here of the regenerative sodium conductance mechanism.

Action Potentials↗
PubMed1989

Histochemical characteristics of human expiratory and inspiratory intercostal muscles.

The relative occurrence of slow-twitch (ST) and fast-twitch (FTa and FTb) fibers, fiber size, and capillary supply in internal (INT) and external intercostal muscles (EXT), the costal diaphragm (DIA), and vastus lateralis muscle (VAS) was examined post-mortem in eight healthy males. The relative occurrence of ST fibers in INT [64 +/- 3% (SE)] and EXT (62 +/- 3%) was similar but higher than in DIA (49 +/- 3%) and VAS (40 +/- 6%; P less than 0.05). The occurrence of FTa fibers in expiratory INT (35 +/- 3%) was higher than in inspiratory INT and EXT (17 +/- 1%; P less than 0.05) but similar to DIA (28 +/- 6%) and VAS (32 +/- 2%). Accordingly, expiratory INT had fewer FTb fibers (1 +/- 1%) than the others (P less than 0.05). Expiratory INT had a 60% larger fiber area than inspiratory INT and EXT and DIA (P less than 0.05), but the area was similar to that of VAS. The number of capillaries per fiber was higher in expiratory INT (2.3 +/- 0.1) than in inspiratory INT and EXT (1.6 +/- 0.1), DIA (1.9 +/- 0.1), and VAS (1.8 +/- 0.2; P less than 0.05). The results suggest that the occurrence of many large capillary-rich FTa fibers in expiratory INT is bound to function (expiratory vs. inspiratory) rather than to anatomy (INT vs. EXT).

Adenosine Triphosphatases↗
PubMed2006

Parasternal intercostal muscle remodeling in severe chronic obstructive pulmonary disease.

Studies in experimental animals indicate that chronic increases in neural drive to limb muscles elicit a fast-to-slow transformation of fiber-type proportions and myofibrillar proteins. Since neural drive to the parasternal intercostal muscles (parasternals) is chronically increased in patients with severe chronic obstructive pulmonary diseases (COPDs), we carried out the present study to test the hypothesis that the parasternals of COPD patients exhibit an increase in the proportions of both slow fibers and slow myosin heavy chains (MHCs). Accordingly, we obtained full thickness parasternal muscle biopsies from the third interspace of seven COPD patients (mean +/- SE age: 59 +/- 4 yr) and seven age-matched controls (AMCs). Fiber typing was done by immunohistochemistry, and MHC proportions were determined by SDS-PAGE followed by densitometry. COPD patients exhibited higher proportions of slow fibers than AMCs (73 +/- 4 vs. 51 +/- 3%; P < 0.01). Additionally, COPD patients exhibited higher proportions of slow MHC than AMCs (56 +/- 4 vs. 46 +/- 4%, P < 0.04). We conclude that the parasternal muscles of patients with severe COPD exhibit a fast-to-slow transformation in both fiber-type and MHC proportions. Previous workers have demonstrated that remodeling of the external intercostals, another rib cage inspiratory muscle, elicited by severe COPD is characterized by a slow-to-fast transformation in both fiber types and MHC isoform proportions. The physiological significance of this difference in remodeling between these two inspiratory rib cage muscles remains to be elucidated.

Biomarkers↗
PubMed1992

Relationship between parasternal and external intercostal muscle length and load compensatory responses in dogs.

1. The effects of tracheal occlusion on peak parasternal (PA) and external intercostal (EI) (3rd interspace) EMG activities were examined at different end-expiratory lung volumes both above and below functional reserve capacity (FCR) in anaesthetized, vagotomized and spontaneously breathing dogs. 2. Parasternal (PA) and external intercostal (EI) muscle lengths were monitored in situ. The difference in peak EMG activity between free and occluded breaths (test breaths) was related to the coincident peak change in intercostal muscle length (delta L) for each muscle, respectively. 3. At FRC, tracheal occlusion resulted in compensatory augmentation of peak EI, but little change in peak PA EMG activities. At lung volumes below FRC, airway occlusion resulted in augmentation of both PA and EI activities. Responses to airway occlusion at lung volumes above FRC were variable. The magnitude and duration of these changes in EMG, however, could be linearly related to the value of delta L. With delta L = 0, there was no change in peak EI or PA EMG; for values of delta L less than 0, there was attenuation of EI and PA EMG; for delta L greater than 0, there was enhancement of EI and PA EMG activation. 4. The magnitude of the changes in EMG activity in response to tracheal occlusion was more prominent for the EI muscle compared to the PA, the latter of which are known to have much fewer muscle spindles than EI muscle. 5. Our results suggest that a difference in end-inspiratory muscle length between the control and occluded breaths is a stimulus for the intercostal response to applied loads implicating muscle spindles as the predominant receptor moderating these responses. We hypothesize that when delta L = 0, no change in EMG occurs since the spindles sense no change in muscle length. When delta L less than 0 (i.e. peak muscle length during the occluded breath is shorter than control) muscle spindles would be disengaged, resulting in a disfacilitation of EMG activity. Where delta L greater than 0 (i.e. peak muscle length during the occluded breath is longer than control), muscle spindles are stimulated, resulting in enhancement of EMG activity. 6. Additional doses of Nembutal (20 mg), which produced significant changes in breathing pattern, did not affect the magnitude of the load compensatory responses.

Animals↗
PubMed1980

Intercostal muscle reflexes and sleep breathing patterns in the human infant.

Breathing variability and apnea characteristic of rapid eye movement (REM) sleep was investigated in a newborn infant with complete interruption of intercostal to phrenic neural pathways due to intrapartem transection of the cervical spinal cord. Breath-to-breath variability in inspiratory duration (TI), breath duration (Ttot), tidal volume (VT), and ventilation (VI) was significantly greater in REM than in quiet sleep and was similar to the variability in these parameters seen in normal infants. In addition, brief periods of diaphragmeatic apnea were observed during REM sleep. The phenomenon of shortened TI during airway occlusion previously attributed to intercostal-to-phrenic reflexes was examined in the quadriplegic infant and in seven healthy term infants. The frequency of this response was increased when airway occlusion was delayed until after onset of inspiration. Shortening of TI by occlusion occurred no less frequently in the quadriplegic than in the control infants. The constant paradoxical inward movement of the rib cage during inspiration observed in the quadriplegic infant suggests that supraspinal innervation of intercostal muscle limits such paradoxical movements in the normal infant. The quadriplegic infant's end-expiratory volume was consistently above his passive functional residual capacity, as inferred from respiratory volume and pressure measurements.

Birth Injuries↗