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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We tested the hypothesis that the changes in venous tone induced by changes in arterial blood oxygen or carbon dioxide require intact cardiovascular reflexes. Mongrel dogs were anesthetized with sodium pentobarbital and paralyzed with veruronium bromide. Cardiac output and central blood volume were measured by indocyanine green dilution. Mean circulatory filling pressure, an index of venous tone at constant blood volume, was estimated from the central venous pressure during transient electrical fibrillation of the heart. With intact reflexes, hypoxia (arterial PaO2 = 38 mmHg), hypercapnia (PaCO2 = 72 mmHg), or hypoxic hypercapnia (PaO2 = 41; PaCO2 = 69 mmHg) (1 mmHg = 133.32 Pa) significantly increased the mean circulatory filling pressure and cardiac output. Hypoxia, but not normoxic hypercapnia, increased the mean systemic arterial pressure and maintained the control level of total peripheral resistance. With reflexes blocked with hexamethonium and atropine, systemic arterial pressure supported with a constant infusion of norepinephrine, and the mean circulatory filling pressure restored toward control with 5 mL/kg blood, each experimental gas mixture caused a decrease in total peripheral resistance and arterial pressure, while the mean circulatory filling pressure and cardiac output were unchanged or increased slightly. We conclude that hypoxia, hypercapnia, and hypoxic hypercapnia have little direct influence on vascular capacitance, but with reflexes intact, there is a significant reflex increase in mean circulatory filling pressure.
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PMID:Reflex control of vascular capacitance during hypoxia, hypercapnia, or hypoxic hypercapnia. 232 95

The management of children with severe acute asthma who required admission to the intensive care (ICU) of this hospital during 1982 to 1988 was reviewed retrospectively. A total of 89 children were admitted to the ICU on 125 occasions. During the study period, 24% of the patients were admitted to the ICU on more than one occasion. Prior to admission to this hospital, patients had been symptomatic for a mean of 48 hours. Although all patients had received bronchodilators before admission to hospital, only 23% of patients had received oral corticosteroids. According to initial arterial blood gas values determined in the ICU, 77% of the patients had hypercapnia (PaCO2 greater than 45 mm Hg). The pharmacologic agents used in the ICU included nebulized beta 2-agonists (100% of admissions), theophylline (99%), steroids (94%), nebulized ipratropium bromide (10%), IV albuterol (38%), and IV isoproterenol (10%). Mechanical ventilation was necessary in 33% of admissions; the mean duration of ventilation was 32 hours. Ten patients had pneumothorax; in six cases, these were related to mechanical ventilation. Three of the patients who received mechanical ventilation died, representing a mortality of 7.5%. In each of these patients, sudden, severe asthma episodes had developed at home, resulting in respiratory arrest. They had evidence of hypoxic encephalopathy at the time of admission to the ICU and eventually were declared brain dead. It was concluded that delay in seeking medical care and underuse of oral corticosteroids at home may have contributed to the need for ICU admission.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Severe acute asthma in a pediatric intensive care unit: six years' experience. 231 83

Respiratory activity and airway tone can be significantly affected by perturbations confined to superficial areas of the ventrolateral surface of the medulla (VMS). It is not clear which neuromediators are responsible for these changes. Neurotensin (NT), a tridecapeptide, fulfills many of the criteria required for a neurotransmitter or a neuromodulator. In this study, we determined whether NT applied topically to the intermediocaudal area of VMS could alter tracheal tone (Ptseg) and phrenic nerve activity (Ph) in alpha-chloralose-anesthetized cats hyperventilated with O2 to neural apnea. Also, the effects of NT on the responses of tracheal tone and phrenic nerve activity to steady-state hyperoxic hypercapnia (3% CO2 in O2) and isocapnic hypoxia (12% O2) were tested. Application of pledgets containing NT (10(-5)-10(-3) M) caused significant increases in Ptseg and Ph activity without significant changes in blood pressure. Both tracheal and phrenic responses to hypercapnia and hypoxia were also increased by an earlier application of NT. Application of lidocaine (2%) to the VMS rapidly reversed NT-induced responses and prevented them on reapplication of NT. Phosphoramidon, a neutral endopeptidase inhibitor, potentiated responses to NT, suggesting that a mechanism exists at the VMS that could reverse NT effects. Earlier topical administration of hexamethonium bromide to the VMS did not influence the effects of NT, indicating that NT was not acting by causing the release of acetylcholine. Intravenous administration of atropine (1 mg/kg) blocked tracheal but not phrenic responses to NT. These findings suggest that neurotensin may be a neuromodulator involved in central chemosensitivity and that it may participate in the regulation of phrenic activity and parasympathetic tone of airway smooth muscle.
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PMID:Tracheal and phrenic responses to neurotensin applied to ventral medulla. 314 81

It is widely accepted that a tremendous increase in cerebral blood volume (CBV) due to progressive cerebral vasoparesis is an essential to the development of acute brain swelling. This study was designed to determine whether neurogenic and/or metabolic factors are predominant and how these interact with each other in producing cerebral vasoparesis. Fifty-one awake cats immobilized with pancuronium bromide were divided into 4 groups: group I, control; group II, normocapnic hypoxia (PaO2 = 50 mmHg); group III, normoxic hypercapnia (Pa-CO2 = 70 mmHg), and group IV, increased intracranial pressure (ICP = 40 mmHg) by brain compression. Systemic arterial pressure (BP), CBV (photoelectric method), and ICP (epidural pressure) were continuously recorded. The dorsomedial hypothalamic nucleus (DM) and the reticular formation of the midbrain (MB-RF) were bilaterally coagulated by a stereotaxic technique (3mA, 1 min). Therefore alterations in cerebrovascular tonus created by destruction of the cerebral vasomotor centers were examined in the animals with metabolically induced cerebral vasodilatation to various degree's. In group I, vasomotor center destruction resulted in an immediate and transient decrease in BP (DM; -14.1 +/- 6.7 mmHg, MB-RF; -10.2 +/- 4.8 mmHg) and simultaneous increase in CBV and ICP (DM; 7.6 +/- 7.0 mmHg, MB-RF; 6.0 +/- 5.6 mmHg) for 3 to 4 minutes. Increase in ICP by destruction of vasomotor centers reduced significantly in group II (DM; 2.3 +/- 2.6 mmHg, MB-RF; 1.6 +/- 1.2 mmHg) and reduced slightly in group IV (DM; 7.5 +/- 4.0 mmHg, MB-RF; 4.8 +/- 3.2 mmHg). In these 3 groups, autoregulation of cerebral blood flow and CO2 vasoreactivity were not changed by destruction of vasomotor centers.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Interaction between neurogenic and metabolic factors upon deterioration in cerebrovascular tonus--experimental study on the etiology of cerebral vasoparesis]. 344 37

Hypercapnic stimulation of the brain may account for some of the decrease in vascular capacitance (venoconstriction) seen with whole-body hypercapnia. Six mongrel dogs were anesthetized with alpha-chloralose and paralyzed with pancuronium bromide. The vagi were cut and the carotid bodies and sinuses were denervated. The head circulation was isolated and perfused with normoxic [arterial partial pressure of O2 (Pao2) = 112 mmHg], normocapnic (PaCO2 = 40 mmHg) blood, or one of three levels of normoxic, hypercapnic (PaCO2 = 56, 68, or 84 mmHg) blood. A membrane oxygenator was used to change gas tensions in the perfusate blood. The systemic circulation received normoxic, normocapnic blood (Pao2 = 107 mmHg; PaCO2 = 32 mmHg). Systemic arterial pressure increased from 111 to 134 mmHg, and heart rate decreased from 174 to 150 beats/min with a head blood PaCO2 of 84 mmHg. Central blood volume was not affected by head hypercapnia. Cardiac output significantly decreased only with a head blood PaCO2 of 84 mmHg. Mean circulatory filling pressure increased by 0.014 mmHg/1 mmHg increase in head PaCO2. The sensitivity of the total peripheral resistance to cephalic blood hypercapnia was 0.88%/mmHg, whereas that for the mean circulatory filling pressure was only 0.19%/mmHg. We conclude that stimulation of the brain, via perfusion of the head with hypercapnic blood, causes a small but significant increase in mean circulatory filling pressure, due to systemic venoconstriction.
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PMID:Vascular capacitance responses to hypercapnia of the vascularly isolated head. 372 92

The purpose of this investigation was to determine whether inhalation of a freon gas mixture, the propellant of the commercial metered-dose aerosols, consisting of freon 11, freon 12, and freon 114, reduces the bronchodilating effects of inhaled salbutamol or ipratropium bromide or causes cardiac arrhythmias in control, asthmatic and bronchitic subjects. FEV1 and flows measured at different lung volumes on the maximal effort expiratoryflow-volume curve were measured during a period of 6 h. Inhalation of freon caused no significant overall reduction in the salbutamol and ipratropium bromide response in any group. Arrhythmias only occurred among the asthmatic and bronchitic patients, and were most frequent after salbutamol. Ventricular extrasystoles occurred in three cases, all after salbutamol and in two of these in combination with freon inhalation. In one patient there was furthermore hyposia and hypercapnia. The combination of the effects of hypoxia, hypercapnia, catecholamines and freon on the heart is therefore a more likely cause of arrhythmia than the effect of freon alone.
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PMID:Effect of freon inhalation on maximal expiratoryflows and heart rhythm after treatment with salbutamol and ipratropium bromide. 644 69

1. The effect of beta-adrenergic and dopaminergic agonists and antagonists on the chemoreceptor response to graded hypoxia and hypercapnia was tested in nineteen cats and ten rabbits anaesthetized either with chloralose-urethane or pentobarbitone sodium, paralysed with pancuronium bromide and artificially ventilated.2. The inhibitory action of dopamine was confirmed. The inhibition following intra-arterial bolus injection was blocked by haloperidol; dopamine then excited and this excitation was blocked with propranolol. Adrenaline or noradrenaline caused a transient inhibition followed by a marked excitation. The inhibition was blocked with haloperidol and the excitation blocked with propranolol or metoprolol. Isoprenaline excited without inhibition and this was blocked with propranolol or metoprolol.3. A novel finding was that the chemoreceptor response to hypoxia was markedly reduced or even abolished with propranolol or metoprolol. The response was enhanced with a constant infusion of isoprenaline, adrenaline or noradrenaline in proportion to the degree of hypoxia, an effect mimicked by raising CO(2). The chemoreceptor response to hypoxia was similarly enhanced by haloperidol and depressed by a constant infusion of dopamine in proportion to the degree of hypoxia.4. The effect of these drugs on the chemoreceptor response to hypercapnia was less constant. In the majority of tests the aminergic agonists and antagonists caused a parallel shift of the CO(2) response curves in the same direction as the O(2) response curves and by amounts proportional to the degree of hypoxia. In some tests these drugs caused a change in the slope of the CO(2) response curves but only if P(a, O2) was less than 60 mmHg.5. One interpretation of these results is that hypoxia exerts a presynaptic action, causing the release of noradrenaline and dopamine from Type I cells, and that these substances act upon aminergic receptors on the sensory fibre, causing a change in potential and discharge frequency proportional to the rates of dopamine and noradrenaline release.6. An additional or alternative interpretation is that O(2) and CO(2) (the latter most probably acting on intracellular pH) alter the sensitivity of the aminergic receptors to their agonists.
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PMID:Adrenergic mechanisms and chemoreception in the carotid body of the cat and rabbit. 680 33

Morbidity and mortality derived from asthma continue to be a main public health problem in many countries, in spite of the advances in the knowledge on the disease and its treatment. There are several risk factors for asthma attack which have to be considered in the management of patients in order to prevent exacerbations and mortality. Smooth bronchial muscle constriction and inflammation with oedema of the bronchial wall are the facts that cause airway flow and resistance disturbances, with hyperinflation, leading to a bigger respiratory work. On the other hand, the bronchial obstruction leads to a ventilation-perfusion disequilibrium and hypoxia. At the beginning of the process there is hypocarbia, but when the attack progresses muscle fatigue happens, and retention of CO2, being a sing of alarm (predictive of respiratory failure) a normal and rising PaCO2. The evaluation of an acute asthmatic patient should accomplish a clinical and objective assessment (peak flow rate and saturation of O2), in order to classify the crisis in: mild, moderate or severe. Managing acute asthmatic patient includes: oxygen, bronchodilator ss2 agonists at high and even continuous doses and systemic corticosteroids to prevent the progression and to control inflammation. These procedures should be promptly instituted. Although there is less evidence on their beneficial effects other measures as intravenous aminophylline, nebulized anticholynergics, magnesium sulphate and intravenous ss2 agonists may be used when the conventional therapy is not quickly successful and the patient is in a critical situation, at a real risk of respiratory failure, and in order to avoid mechanical ventilation. If this is finally instituted, controlled hypoventilation with permissive hypercarbia is now recommended, to avoid barotrauma, which used to be a frequent complication when more aggressive attitude was the rule. Interaction between paralytic agents and corticosteroids may produce a miopathy, so the recommendation now is to try not to use paralytic agents, even with profound sedation of needed. Sixty four patients were treated on 77 occasions in the Pediatric Intensive Care Unit of our hospital. They were 0,5 to 13,9 years old, being 50% less than 5 years old. It was the first attack in 9 (14%) patients. The standard management consisted of oxygen, frequently or continuously nebulized salbutamol and intravenous methylprednisolone (1 to 6 mg/kg/day). Furthermore nebulized ipratropium bromide was administered 58 times (75%), as well as intravenous aminophylline 69 (89%), intravenous salbutamol 23 (30%), magnesium sulphate 16 (21%) and ketamine 10 (13%). Antibiotics were given 22 times (29%). Two 15 month old infants received mechanical ventilation in three occasions, and relevant complications happened (pneumothorax and myopathy, and pneumomediastinum and bronchiolitis obliterans respectively). Fifty six patients have been followed for a period of 3 to 110 months (median 48 months), and 16 (29%) have needed high doses (equal to or move than 800 mcg of budesonide or equivalent). There are data on lung function in 36 of them, FEV1 is normal (> 85% of predicted, between 86 and 127) in 26 (78%) and < 85% (65 to 84%) of predicted in 8 (22%) FEV1 rises more than 15% (16 to 23%) in four patients after the inhalation of a ss2 agonist. Inhaled anesthetic agents and heliox have been used in some pediatric cases. After a severe asthma attack the strategy of management should be reviewed, as well as the possible risk factors.
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PMID:[Round Table: Severe asthma in pediatrics: treatment of acute crises]. 1035 7

The goal of management of patients with respiratory failure is to restore them to a state of quiet breathing, without complication. This goal is often achieved by pharmacotherapy alone. Inhaled albuterol sulfate, oxygen, and systemic corticosteroids are mainstays of acute care drug management, whereas other data support the use of inhaled steroids, ipratropium bromide, magnesium sulfate, theophylline, and heliox. Assisted ventilation by face mask or endotracheal tube may be required in refractory patients. In intubated patients, a ventilatory strategy that prolongs exhalation time and accepts hypercapnia minimizes lung hyperinflation and generally results in a good outcome. Acute asthma often represents failure of outpatient management; key aspects of the outpatient program should be addressed in the acute care setting to help prevent recurrent attacks.
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PMID:Management of respiratory failure in patients with asthma. 1060 30

Sleep has well-recognized effects on breathing, including changes in central respiratory control, airways resistance, and muscular contractility, which do not have an adverse effect in healthy individuals but may cause problems in patients with COPD. Sleep-related hypoxemia and hypercapnia are well recognized in COPD and are most pronounced in rapid eye movement sleep. However, sleep studies are usually only indicated in patients with COPD when there is a possibility of sleep apnea or when cor pulmonale and/or polycythemia are not explained by the awake PaO(2) level. Management options for patients with sleep-related respiratory failure include general measures such as optimizing therapy of the underlying condition; physiotherapy and prompt treatment of infective exacerbations; supplemental oxygen; pharmacologic treatments such as bronchodilators, particularly ipratropium bromide, theophylline, and almitrine; and noninvasive positive pressure ventilation.
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PMID:Impact of sleep in COPD. 1067 75


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