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Biomedical subjects

B Duron

Publications and source records attributed to B Duron.

At least 73 records · Page 4Linked to original sources
PubMed1983

Dose effect of pentobarbital sodium on control of breathing in cats.

The dose effect of pentobarbital sodium on integrated ("moving time average") phrenic activity (EPHR), transdiaphragmatic pressure (Pdi), gastric pressure (Pga), changes in lung volume (V), and mechanical properties of the respiratory system was studied in six cats breathing room air. Increased pentobarbital dose from an initial value of 35 mg/kg ip, had no substantial effect on the relationship between EPHR and Pdi during both unoccluded and occluded inspirations, indicating that the diaphragmatic excitation-contraction coupling was not affected. Similarly, increased anesthetic dose had no effect on the relationship between EPHR and delta Pga during both occluded and unoccluded breaths, suggesting that the contribution of the diaphragm to the breathing movements did not change with increasing depth of anesthesia. Although the time course of phrenic activity showed substantial interanimal differences, the shape of the phrenic neurogram did not change substantially with increased pentobarbital dose in any of the cats studied. Increased anesthetic dose depressed, in the same proportion, the rate of rise of EPHR, Pdi, and V, but the mechanical properties of the respiratory system remained unchanged. The depression of ventilation with increased anesthetic dose was not proportional to the drop in central inspiratory activity, as quantified in terms of rate of rise of EPHR.

Airway Obstruction↗
PubMed1982

Spinal localization of the intercostal motoneurones innervating the upper thoracic spaces.

At the rostral level of the thorax, the intercostal muscles participate both in postural and respiratory functions to a variable degree depending upon the considered muscle: external intercostal, intercartilaginous, internal intercostal, and triangularis sterni. In order to determine if these physiological properties are related to a special organization at the spinal cord level, we have used the retrograde transport of horseradish peroxidase as a tool for studying the spinal distribution of intercostal motor cells in the adult cat. Results suggest that the intercostal motoneurones could be distributed, in the ventral grey horn, among two areas according to the respiratory or postural muscle specialization.

Animals↗
PubMed1982

Functional localization of pulmonary stretch receptors in the tracheobronchial tree of the kitten.

Seven kittens age 5 to 8 days were anaesthetized with ketamine, tracheotomized, cannulated just below the larynx, paralyzed, and ventilated. The thorax was widely opened and an expiratory load equal to the transpulmonary pressure at functional residual capacity (PLFRC) added. Single vagal fibers were dissected from the peripheral cut end of the right vagus nerve. Thirty-eight receptor discharges modulated during the respiratory cycle (pulmonary stretch receptors, PSR) were studied; 4 (10.5%) were tonically active at PLFRC while the remaining 34 had a mean threshold at 3.2 cmH2O. All the receptors progressively increased their discharge frequency with higher pressures reaching a plateau between 8-10 cmH2O. By occluding the airways at different levels of the tracheobronchial tree 32 PSR were functionally localized: none were found in the extrathoracic trachea; 3 (9.5%) were located in the intrathoracic trachea, 12 (37.5%) at the carina, main bronchi, and lobar bronchi, and 17 (53%) inside the lobes. All three tracheal receptors were tonic PSR. Previously obtained data from adult mammals indicate that 27-60% of PSR are tonically active and most of these are located in the trachea. The low incidence of tonically active PSR in the kitten may suggest a delayed functional maturation of the tracheal receptors.

Animals↗
PubMed1982

Anatomical organization of cat intercostal motor nuclei as demonstrated by HRP retrograde labelling.

1. Intercostal muscles participate both in postural and respiratory functions to a variable degree dependent upon the specific interspace or muscle. In order to determine if these physiological properties are related to a special organization at the spinal cord level, we have used the retrograde transport of HRP as a tool for studying the spinal distribution and morphology of intercostal motor cells in the adult cat. 2. Results obtained after intramuscular injections of the enzyme suggest that the intercostal motor columns could be distributed, in thoracic spinal segments, among two areas according to the respiratory or postural muscle specialization. Moreover, it appears that both postural and respiratory muscles are innervated by motor cells whose size is not related to histological or functional characteristics of the muscle.

Animals↗
PubMed1981

Postnatal development of the discharge pattern of phrenic motor units in the kitten.

The postnatal change of the mean frequency (F), the maximal frequency (FM) and the onset frequency (FO) of discharge of kitten phrenic motor units was studied and compared to adult values. The latency (recruitment time) and duration of discharge of phrenic units were also analyzed. In kittens less than 3 weeks old, there were relatively few early units (latency less than or equal to 10% of phrenic discharge duration), TI). The duration of discharge of early and late units, expressed in percentage of TI, was the same in kittens and adult cats, and the duration of discharge of the early units was greater than that of the late units. In kittens, F, FM and FO of the early and late units were always greater than in adult cats. In adult cat, as in Kittens, F, FM and FO of early units were not significantly greater than those of late units. In conclusion, the relatively small number of early units in kittens may reflect either a small number of active early bulbo-spinal neurons or may be linked to the electrical and morphological properties of phrenic motoneurons in the kitten.

Action Potentials↗
PubMed1981

Phrenic activity, respiratory pressures, and volume changes in cats.

In eight anesthetized cats we measured the integrated ("moving time average") phrenic activity [using phrenic electroneurogram (EPHR)] and the active transdiaphragmatic pressure [Pdi(mus)] during room air breathing, hypoxia, and hypercapnia. The relationship between Pdi(mus) and EPHR was unaffected by either hypoxic or hypercapnic stimulation of breathing, suggesting that in spontaneously breathing cats the pressure losses are negligible. In all cats, however, there was a substantial volume-related decrease in Pdi(mus), indicating that with increasing lung volume the effectiveness of the diaphragm as a pressure generator decreases. In addition, we have developed a model that allows prediction of the time course changes in lung volume for different morphology of inspiratory driving pressure. This model explains many of the features of control of breathing found experimentally in our cats.

Animals↗
PubMed1981

Time course of phrenic activity and respiratory pressures during airway occlusion in cats.

The morphology of integrated ("moving time average") phrenic electroneurograms (EPHR) and of tracheal (Ptr) and transdiaphragmatic (Pdi) pressure waves during occluded inspirations was studied in eight anesthetized cats breathing air and various hypercapnic and hypoxic mixtures. The shape of the rising part of EPR-, Ptr-, and Pdi-time profiles varied between animals (from convex to concave), but in each animal it remained virtually unchanged by hypoxia and hypercapnia. The shape of the Ptr and Pdi occlusion waves reflected the shape of EPHR. The relationship of EPHR to Pdi and Ptr did not change with chemical drive. It is concluded that central inspiratory activity (CIA) (as reflected by EPHR and its mechanical transforms Pdi and Ptr) increases in amplitude with stimulation of breathing but that the profile of CIA remains essentially unchanged. However, substantial differences in the time course development of phrenic activity, Pdi, and Ptr exist between cats. The fixed interrelationships among EPHR, Pdi, and Ptr indicate a proportional increase in activity among all inspiratory muscles with increased chemical drive.

Airway Obstruction↗
PubMed1980

The non-myelinated fibers of the phrenic and the intercostal nerves in the cat.

The aim of this work was obtaining quantitative data relative to the non-myelinated fibers of some thoracic nerves of the cat. The study has been done both through the utilization of the light and the electron microscope. A comparative analysis of the results obtained from the muscle nerves (external intercostal nerve and phrenic nerve), cutaneous nerve (lateral collateral branch of the internal intercostal nerve) and mixed nerves (internal intercostal) has been made. The C muscle fibers have a smaller diameter than the C cutaneous fibers. Some of the non-myelinated fibers of the phrenic nerve are probably involved in the innervation of the pleura or of the peritoneum. The relative number of non-myelinated fibers varies according to the nerves. The factor linking the diameter of the non-myelinated fibers to their conduction velocity is approximately equal to 0.7.

Animals↗
PubMed1979

Segmental motor innervation of the cat diaphragm.

In ten anaesthetized adult cats, bipolar recording electrodes were inserted in different muscular bundles of each hemi-diaphragm. Both stimulation and section of the phrenic cervical branches were made. The upper phrenic cervical branch innervates both the sternal and lateral portions of the diaphragm whereas the lower phrenic cervical branch innervates both the lateral and dorso-caudal portions.

Animals↗
PubMed1979

Somatotopy in the phrenic motor nucleus of the cat as revealed by retrograde transport of horseradish peroxidase.

Cats received unilateral or bilateral horseradish peroxidase (HRP) injections into various portions of the diaphragm. In two experiments one of the cut cervical roots of the phrenic nerve was immersed in HRP. The phrenic motoneurons located in the fifth and occasionally the fourth cervical segment send their axons, via the upper phrenic root, to pars sternalis and pars costalis of the diaphragmatic dome whereas the neurons of the sixth segment innervate preferentially the dorsal portion both crura and dome. No evidence of contralateral innervation of the diaphragm was obtained.

Animals↗
PubMed1979

Postnatal maturation of phrenic, vagus, and intercostal nerves in the kitten.

In the present work, we have compared the histological maturation of the phrenic nerve, the internal and external intercostal nerves of the 8th space and the vagus nerve. At least three nerves from each category have been taken from different kittens each week during the first 2 months of postnatal life, and each month for kittens aged between 2 and 8 months. Compared to references obtained in the adult animal, the development of the number and diameter of myelinated fibers has been studied for each nerve. Moreover, the maturation of unmyelinated fibers of the phrenic nerve has been studied with the electrom microscope. There is a possibility of a cephalo-caudal maturation in the somatic nerves. Important differences exist between somatic nerve maturation and that of the vagus nerve.

Animals↗
PubMed1979

Postnatal development of vagal control of breathing in the kitten.

At birth, the number of vagal myelinated fibers represents about 10% of the corresponding adult value. Their diameters range between 1 micron and 5 micron. The conduction velocities, calculated from the bimodal vagus nerve action potential, are 20 m.sec--1 (range 16--30 m.sec--1) and 6 m.sec--1 (range 1--10 m.sec--1) respectively. The discharge patterns of the vagal afferent units are similar to those described in adult cat for the various pulmonary mecano receptors. The proportion (9%) of low threshold broncho-pulmonary stretch receptors is smaller than that given by Paintal (1973) for the adult cat (50%). Nevertheless, the inhibitory action of the pulmonary stretch receptors is very potent at birth. Various experimental procedures (bivagotomy, vagal stimulation and lung deflation) which reinforce the central inspiratory activity in the adult cat provoke essentially a lengthening of expiration in the newborn. The predominance of expiratory activity can be seen as part of the general motor behaviour which in the newborn is essentially characterized by activation of flexor muscles.

Animals↗
PubMed1978

Myelinated nerve fiber supply and muscle spindles in the respiratory muscles of cat: quantitative study.

The present study was undertaken to provide quantitative data on the myelinated fibers of the phrenic and intercostal nerves and the number of spindles in the main respiratory muscles of the cat. The myelinated component of the phrenic and intercostal nerves was studied in the cat. Histograms of sequency distributions as a function of nerve fiber diameter were established for normal nerves. Certain nerves were then examined 35 to 40 days after excision of the dorsal spinal ganglia. The muscle spindles of the corresponding muscles were counted and localized, and, on the basis of several morphological criteria, were classified with those usually described in the interosseous muscles. The study of the nerves, as that of the spindles, demonstrates clear differences of proprioceptive innervation among the respirator muscles. The lateral part of the diaphragm and the Triangularis sterni have practically no spindles. The external muscles of the first thoracic spaces are very rich in spindles. Respiratory muscles can be ranged in an almost continuous manner between these two extremes.

Animals↗