Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of normobaric hyperoxia on carotid body chemosensory function in the cat were studied. The hypothesis was that carotid body chemosensory function would be affected by chronic exposure to 100% O2 at sea level. It was based on the assumptions that carotid body tissue is exposed to high PO2 because of its high blood flow and that its O2 chemosensing mechanism is sensitive to O2 radical-induced reactions. Twelve cats were exposed to 100% O2 for 60-67 h, and 10 control cats were maintained in room air at sea level. They were anesthetized with pentobarbital sodium (Nembutal), and chemosensory afferents from a cut carotid sinus nerve were isolated and identified. The responses of single or a few clearly identifiable chemoreceptor afferents to isocapnic hypoxia and hypercapnia during hyperoxia and to the bolus injections of cyanide, nicotine, and dopamine were studied. We found that chronic hyperoxia severely blunted or eliminated the O2-sensitive response of the carotid chemoreceptors while augmenting the hypercapnic response. The response to cyanide but not to nicotine and dopamine were attenuated. Thus the hypoxic and hypercapnic responses that normally interact were separable. The lack of the cyanide response was consistent with the lack of the hypoxic response, suggesting a possible shared mechanism of carotid chemoreceptor response. Qualitatively normal responses to dopamine and nicotine indicated that the respective receptors were relatively intact after chronic exposure to hyperoxia and that the sensory nerves themselves were not affected by the prolonged O2 exposure.
 ...
PMID:Carotid body chemosensory function in prolonged normobaric hyperoxia in the cat. 311 Jan 24

Hypercapnia attenuates the effects of static airway pressure (Paw) on phrenic burst frequency (f) and the expiratory duration (TE) in chloralose-urethan-anesthetized dogs. Surgical removal of the carotid bodies abolishes this interaction. Since halothane anesthesia in hyperoxia greatly impairs peripheral chemoreflexes, experiments were conducted to determine whether hypercapnia would attenuate the effects of Paw on f and TE in halothane-anesthetized dogs (approximately 1.5 minimum alveolar concentration). Integrated activity of the phrenic nerve was monitored as a function of Paw (2-12 cmH2O) in a vascularly isolated left lung at varied levels of arterial PCO2 (PaCO2; 38-80 Torr) controlled by inspired gas concentrations ventilating the denervated but perfused right lung. Halothane was administered only to the right lung. The results were as follows: 1) integrated phrenic amplitude increased with PaCO2 but was unaffected by Paw; 2) f decreased as Paw increased but was not affected by PaCO2; 3) the inspiratory duration (TI) increased as PaCO2 increased but was unaffected by Paw; 4) TE increased as Paw increased but was unaffected by PaCO2; and 5) there was no phrenic response to intravenous sodium cyanide (50-100 micrograms/kg). Thus, unlike chloralose-urethan-anesthetized dogs, hypercapnia does not attenuate the effect of lung inflation on f or TE in halothane-anesthetized dogs. Furthermore, hypercapnia increases TI during halothane anesthesia, an effect found after carotid denervation but not found in intact chloralose-urethan-anesthetized dogs. It is suggested that these differences between chloralose-urethan- and halothane-anesthetized dogs may be due to functional carotid chemoreceptor denervation by halothane.
 ...
PMID:Ventilatory responses to lung inflation and arterial CO2 in halothane-anesthetized dogs. 313 47

The dependence of the carotid chemoreceptor responses to blood-borne stimuli on the ganglioglomerular nerve (GGN) activity was investigated in cats which were anesthetized, paralyzed and artificially ventilated. The activity of a few carotid chemoreceptor afferents from a slip or from the cut left carotid sinus nerve (CSN) and the activity of a few GGN fibers were recorded. The responses of the same chemoreceptor afferents to steady-state hypoxia at a constant paCO2 and to steady-state hypercapnia during hyperoxia were compared before and after the transection of the ipsilateral ganglioglomerular nerve (IGGN). Similarly the effects of IGGN transection on the responses of the same chemoreceptor afferents to graded doses of intravenous injections of sodium cyanide (20-60 micrograms) and nicotine (20-60 micrograms) at constant blood gas levels were studied. On the average, IGGN transection during normoxia only slightly changed the carotid chemoreceptor activity. Also, it did not significantly change the hypoxic and hypercapnic responses, and those to sodium cyanide and nicotine injections. Thus, the mean carotid chemoreceptor responses to physiological and pharmacological stimuli were largely independent of the GGN. However, certain GGN fibers were strongly stimulated by hypoxia and hypercapnia. Clearly, the total GGN traffic to the carotid body was not sufficiently strong to exert a significant control over the mean carotid chemoreceptor activity.
 ...
PMID:Influence of ganglioglomerular nerve on carotid chemoreceptor activity in the cat. 395 Mar 26

In decerebrate, paralyzed and vagotomized cats, we recorded activities of hypoglossal and phrenic nerves and of the mylohyoid branch of the trigeminal nerve. At normocapnia, a respiratory-modulated trigeminal discharge could be discerned in most cats. This discharge was characterized by a diminution of activity during neural inspiration and a peak in expiration. In hypercapnia or hypoxia, peak activity increased and its time of occurrence moved to late inspiration. Augmentations of peak trigeminal, hypoglossal and phrenic activities were proportional. Peak trigeminal and hypoglossal activities increased more than phrenic following administrations of protriptyline, strychnine and, in some cats, cyanide or doxapram. Peak trigeminal activity fell more than phrenic after diazepam. Pentobarbital or halothane reduced peak hypoglossal, but not trigeminal, activity more than phrenic. However, after these anesthetics, trigeminal activity became restricted to the inspiratory-expiratory junction. We conclude that trigeminal and hypoglossal activities are more dependent upon processes within the reticular formation than is the bulbospinal-phrenic system. Central and peripheral chemoreceptor influences are distributed equivalently upon trigeminal, hypoglossal and phrenic motoneurons.
 ...
PMID:Comparison of respiratory-related trigeminal, hypoglossal and phrenic activities. 407 Aug 36

1. The effects of asphyxia, hypoxia, hypercapnia, stimulation of peripheral chemoreceptors, pneumothorax and breathing through resistances have been investigated on laryngeal resistance to airflow in anaesthetized cats, with and without bilateral vagotomy below the origin of the recurrent laryngeal nerves.2. Resistance to airflow of the innervated larynx was usually measured with the larynx isolated in situ with constant flow from the trachea to a pharyngeal opening, and expressed by the relationship between translaryngeal pressure and airflow.3. Asphyxia, hypoxia and hypercapnia each stimulated breathing and decreased laryngeal resistance to airflow, in both the inspiratory and expiratory phases. After vagotomy the effect was reduced, abolished or (usually) reversed to a laryngeal constriction, especially in expiration.4. Intra-arterial injections of potassium cyanide (to stimulate carotid body chemoreceptors) caused a short apnoea or an augmented breath followed by hyperpnoea, concurrently with expiratory constrictions of the larynx. The responses were usually stronger after bilateral vagotomy.5. Pneumothorax caused tachypnoea, inspiratory dilatations and expiratory constrictions of the larynx. The responses were abolished by vagotomy.6. Imposition of respiratory resistances dilated the larynx, in inspiration and expiration, while complete closure of trachea caused expiratory constrictions of the larynx. These changes did not depend on intact vagal pathways.7. The results are discussed in terms of nervous control of the larynx in the different conditions.
 ...
PMID:Studies on laryngeal calibre during stimulation of peripheral and central chemoreceptors, pneumothorax and increased respiratory loads. 441 40

Discharges from aortic and carotid body chemoreceptor afferents were simultaneously recorded in 18 anesthetized cats to test the hypothesis that aortic chemoreceptors, because of their proximity to the heart, respond to changes in arterial blood gases before carotid chemoreceptors. We found that carotid chemoreceptor responses to the onset of hypoxia and hypercapnia, and to the intravenously administered excitatory drugs (cyanide, nicotine, and doxapram), preceded those of aortic chemoreceptors. Postulating that this unexpected result was due to differences in microcirculation and mass transport, we also investigated their relative speed of responses to changes in arterial blood pressure. The aortic chemoreceptors responded to decreases in arterial blood pressure before the carotid chemoreceptors, supporting the idea that the aortic body has microcirculatory impediments not generally present in the carotid body. These findings strengthened the concept that carotid bodies are more suited for monitoring blood gas changes due to respiration, whereas aortic bodies are for monitoring circulation.
 ...
PMID:Relative latency of responses of chemoreceptor afferents from aortic and carotid bodies. 624 48

Carotid bodies and their nerves were excised from rabbits or cats, cleaned of surrounding connective tissue and placed in a chamber through which mammalian saline equilibrated with different gas mixtures was allowed to flow. Single fibers were isolated and identified as chemosensory by their response to hypoxia, hypercapnia, or NaCN. Mass receptor potentials (recorded at some distance from the sensory nerve endings) were evoked by the same stimuli and registered as close as possible to the carotid body. Both cats and rabbits exhibited receptor depolarization and an increased discharge in response to NaCN, hypoxia, hypercapnia and cyanide. However, the effects of some pharmacological agents were quite different in rabbits and cats. In the rabbit, ACh 10-100 microgram and carbachol 1-10 microgram produced receptor hyperpolarization and discharge depression followed by discharge increase. Nicotine 0.3-20 microgram induced receptor depolarization and increased chemosensory discharge frequency. Nicotinic stimulation was antagonized by D-tubocurarine 10(-6)-10(-4) g/ml. Pilocarpine 2-50 microgram hyperpolarized the receptors and depressed discharge frequency. Pilocarpine-induced depression was reduced by atropine 10(-6) g/ml. Dopamine 5-100 microgram depolarized the receptors and increased the chemosensory discharge frequency. This effect of dopamine was reduced by haloperidol (10(-11)-10(-7) M). In the cat, ACh, carbachol and nicotine (same doses as those used in rabbits) induced receptor depolarization and increased the sensory discharge frequency. Pilocarpine (up to 50 microgram) had little effect on either discharge frequency or the receptor potential. Dopamine 5-100 microgram induced receptor hyperpolarization and depression of discharge frequency, and these effects were reduced by haloperidol.
 ...
PMID:A comparative physiological and pharmacological study of cat and rabbit carotid body chemoreceptors. 624 64

Tonic and phasic inspiratory genioglossus (GG) electromyographic activity (EMG) was recorded from 13 anesthetized rabbits during unstimulated breathing. Integrated GG EMG peaked earlier in inspiration and presented a more rounded contour than integrated diaphragmatic (DIA) EMG. Spontaneous augmented deep inspirations (sighs) showed a biphasic pattern in both GG and DIA EMGs. Hyperventilation abolished phasic inspiratory activity in the GG before the DIA, suggesting that the GG has a higher CO2 apneic point. Hypercapnia increased both EMGs; however, GG EMG increased more, as a percent of base line, than did DIA EMG. Oxygen breathing decreased GG more than DIA EMG; sodium cyanide injection and brief nitrogen breathing increased GG more than DIA EMG; carotid body denervation abolished these responses. Vagotomy abolished the Hering-Breuer inflation-inhibition reflex in both muscles, and tactile, visual, and auditory stimulation increased GG more than DIA EMG. Thus, the GG responses to chemoreceptor input and to nonspecific respiratory stimuli are qualitatively similar but quantitatively different from DIA responses. The relevance to mixed and obstructive apnea is discussed.
 ...
PMID:Control of genioglossus muscle inspiratory activity. 677 78

The purpose of this investigation was to compare the respiratory pattern of gasping with eupnea and apneusis. Decerebrate, cerebellectomized, vagotomized, paralyzed and ventilated cats were used. The ventilatory pattern, assessed by phrenic nerve activity, was reversibly altered from eupnea to apneusis or gasping by use of a cooling-for, thermode positioned inm the rostral pons or through the pontomedullary junction, respectively. Irreversible apneusis or gasping resulted from brain stem lesions or freezing at appropriate loci. Analysis of phrenic activity revealed that the rates of onset and rise of the gasp were much greater than those of the eupneic or apneustic inspiration. Moreover, in contrast to eupnea or apneusis, neither the frequency nor the intensity of gasps was altered by hypercapnia, hypocapnia, or carotid chemoreceptor stimulation by sodium cyanide. Although hypoxia caused an increase in gasping frequency, this response was transient and not dependent on carotid chemoreceptor mechanisms. These results provide no support for the concept that common mechanisms localized in medulla, underlie the neurogenesis of all automatic ventilatory patterns.
 ...
PMID:A characterization of the respiratory pattern of gasping. 678 67

In decerebrate, vagotomized, paralyzed, and ventilated cats, activities were recorded from the phrenic nerve and from respiratory units within the dorsal and ventral medullary respiratory nuclei and the pontile reticular formation. These unit activities were monitored during equivalent augmentations in peak integrated phrenic nerve activity induced by stimuli acting primarily on the peripheral or central chemoreceptors. These stimuli were intracarotid infusions of sodium cyanide or nicotine and exposure to hyperoxic hypercapnia, respectively. Both stimuli caused similar increases in activities for most dorsal nucleus inspiratory units. For units of the ventral medullary nucleus, augmentations in activity were only significant (inspiratory neurons) or were of greater magnitude (expiratory neurons) during hypercapnia. As opposed to medullary units, the discharge frequencies of many pontile units were unaltered or declined during both peripheral and central chemoreceptor stimulations. These results support the concept that excitatory influences from the peripheral and central chemoreceptors are not equally distributed among all groups of brain stem respiratory neurons.
 ...
PMID:Respiratory neuron responses to hypercapnia and carotid chemoreceptor stimulation. 729 23


<< Previous 1 2 3 4 5 Next >>