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

The metabolic effects of 60-min exposure to 250-2000 mg gamma-hydroxybutyrate (GHB) per kilogram or 150-1200 mg gamma-butyrolactone (GBL) per kilogram were studied in rats by measurement of the cerebral hemisphere contents of energy phosphates and glycolytic-Krebs' cycle metabolites. A general pattern of increased glycogen and glucose with decreased pyruvate, lactate, alpha-ketoglutarate, and malate was observed. This pattern in association with unchanged adenylates and decreased energy phosphate utilization was consistent with a metabolic adaptation to a state of cerebral depression. The major qualitative difference between the two drugs was that higher doses of GBL were associated with additional decreases of citrate and glutamate. Since these doses of GBL were also associated with acute increases of arterial CO2 tension, it is proposed that these differences were secondary to hypercapnia and not due to a distinctive primary action of GBL. Derivation of the cytoplasmic NAD(P)H:NAD(P)+ ratios indicated that GHB and GBL were not associated with consistent alterations of the cytoplasmic redox state.
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PMID:A comparison of the effects of gamma-hydroxybutyrate and gamma-butyrolactone on cerebral carbohydrate metabolism. 4 Jun 77

A series of investigations suggest a specific role for BCAA in the regulation of respiration. In vitro incubation studies have shown that BCAAs improve the recovery of muscle force after fatigue. Further investigations revealed that leucine plays a key role in this action and acts in a manner not dependent on its use as an energy substrate. In humans, solutions enriched with BCAA have decreased PCO2 and stimulated the ventilatory response to hypercapnia, thereby corresponding to an enhanced ventilatory sensitivity with the administration of BCAA. The mechanisms for these actions are unknown. The most viable hypothesis is based on the ability of BCAA to decrease the synthesis of serotonin due to altered transport of AAs, including tryptophan, to the brain. Clinical studies have suggested a potency of BCAA in the treatment of respiratory dysfunction of preterm infants, as well as of patients with sleep apnea related to various disease states. The clinical applications of BCAA-enriched mixtures in respiratory diseases are still experimental, and many controversies exist concerning the validity of BCAA in clinical practice. Most TPN regimens contain BCAA approximating the average intake of BCAA in the Western diet. The question therefore remains whether additional BCAA supplementation is useful to achieve the suggested metabolic and pharmacological effects. Meticulous future studies are needed to establish the therapeutic value of BCAA in the treatment of various respiratory functions.
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PMID:Branched-chain amino acids and respiration. 142 77

With the objective to test the effect of intermittent and short term rest in respiratory muscles in patients with COPD and maintained hypercapnia we have studied 34 patients in a stable condition: 23 were part of the study group (Group I) and 11 were the control group (Group II). After a complete functional basal study, patients in Group I were treated with intermittent rest of their respiratory muscles, through a negative pressure external respirator--shield type--during three consecutive days. We got, in this study group, a significative improvement in the maximum inspiratory pressure measured at residual volume (PI max RV), which went from 66.6 +/- 15.9 to 71.2 +/- 15.2 (p < 0.005), as well as a lowering, also significative, of partial pressure of CO2 in arterial blood (PaCO2) and in expired air (EFCO2), which went from 55.2 +/- 7.2 to 52.3 +/- 3 (p < 0.0002) and 3.3 +/- 0.5 to 3.1 +/- 0.5 (p < 0.01), respectively. Maximum inspiratory pressure measured to functional residual capacity (PI max FRC) experienced an increase in the limit of statistical signification. Rest of the parameters did not significantly change. These results back the hypothesis that in stabilized COPD with CO2 retention, a chronic fatigue of respiratory muscles could exist, and that intermittent rest of these muscles could mean an hypercapnia diminution, due to the improvement in the function of respiratory muscles.
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PMID:[Short-term effects of respiration with external negative ventilation --shield-type respirator-- on the pulmonary function in COPD]. 833 62

Respiratory muscle fatigue is induced experimentally by adding high external resistances to breathing. The role played by respiratory muscle fatigue in exercise limitation and in acute respiratory failure is still unclear. The electromyogram often reflects contractions beyond the fatigue threshold, but overt force failure has been only rarely demonstrated under these circumstances. Hypercapnic ventilatory failure may possibly not result from fatigue, but rather from an adaptation of the respiratory system for avoiding fatigue. The treatment of fatigue comprises respiratory muscle support by adequate nutrition and oxygen delivery, and if needed respiratory muscle rest by mechanical ventilation.
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PMID:[Fatigue of the respiratory muscles]. 154 80

Endurance muscle performance is highly dependent on ATP production from mitochondrial oxidative phosphorylation. To study the role of the mitochondrial oxidative enzymes in muscle fatigue, we analyzed the relationship between the concentrations of substrates associated with ATP synthesis and the muscle performance of electrically stimulated rabbit muscle under CO2-induced acidosis. Two different conditions of pacing-induced muscle performance were produced in the gastrocnemius and soleus muscle groups in anesthetized rabbits by stimulating the sciatic nerve submaximally at two frequencies. Phosphorus nuclear magnetic resonance was used to measure ATP, phosphocreatine, and Pi and to provide data for a calculation of intracellular pH and free ADP. To induce acidosis, the animal was ventilated with 20% CO2. The administration of CO2 effectively reduced the intracellular pH from 6.9 to 6.7 and reduced the isometric tension-time integral (TTI) to below half the value measured in normocapnia at the low pacing frequency. A twofold increase in the pacing frequency resulted in a doubling of the TTI in normocapnia and a tripling of TTI in hypercapnia. The increases in TTI corresponded with increases in free ADP and Pi concentrations. Under the various conditions, all free ADP values were near the in vitro Michaelis-Menten constant (Km) of ADP. The Michaelis-Menten relationship of the oxidative phosphorylative enzymes was applied to the change in substrate concentrations with respect to TTI. From this relationship we observed that the in vivo Km of free ADP was 26 microM, which is close to the in nitro Km, and that Km and maximal reaction velocity did not change under hypercapnia and increased pacing frequency.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Substrate regulation of mitochondrial oxidative phosphorylation in hypercapnic rabbit muscle. 155 27

Failure of weaning from mechanical ventilation in COPD patients is often related to diaphragmatic fatigue. Whether there is a central respiratory drive fatigue and a reserve of excitability is still debated. The purpose of this study was to analyze the following in 13 COPD patients weaned from mechanical ventilation: (1) ventilatory (VE/PETCO2) and neuromuscular (P0.1/PETCO2) response to hypercapnia; (2) the maximum reserve capacity measured through changes in the VE/PETCO2 and P0.1/PETCO2 slopes after doxapram (DXP) infusion, which, given during the test, allows measurement of the maximum response capacity to overstimulation; and (3) analyze the influence of these changes on the outcome of weaning. The results show a variable P0.1/PETCO2 response and a low VE/PETCO2. DXP infusion does not change the slopes of these relations but increases the end-expiratory volume (delta FRCd); (p less than 0.02). Since there was no change in the VE/PETCO2, P0.1/PETCO2, and delta FRC values with or without DXP, there was no excitability reserve in patients who were successfully weaned. When weaning failed, DXP did not change VE/PETCO2 and P0.1/PETCO2 slope, but delta FRCd was greater the delta FRC (p less than 0.001). The excitability reserve in these patients leads to an increase in end-expiratory volume, probably worsening the diaphragm dysfunction.
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PMID:Effects of doxapram on hypercapnic response during weaning from mechanical ventilation in COPD patients. 160 Jul 86

Abnormal physical exhaustion and fatigue are often simply regarded as a natural consequence of pulmonary diseases. Apart from factors not specifically related to pulmonary diseases (e.g. consequences of infections or malignant diseases of the lungs), increased work of breathing due to impaired lung/thoracic cage mechanics, the effects of chronic hypoxia and hypercapnia, the consequences of disturbed sleep and psychosocial factors are mainly responsible for the impaired physical fitness and the fatigue in association with lung diseases. A careful case history including psychosocial aspects and a thorough physical examination are essential for an efficient diagnostic evaluation. Tests of pulmonary function not only in the awake patient at rest, but also during sleep or adequate physical exercise can reveal the causes of impaired physical performance and fatigue related to lung diseases.
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PMID:[Pulmonary causes of abnormal fatigability]. 175 70

The aim of physical exercise retraining in patients with chronic obstructive lung disease undergoing rehabilitation is to increase the anaerobic work capacity with a rise in VO2 max. Exercise programmes must take into account the duration, frequency and intensity of exercise. In these patients, numerous factors limit physical exercise, including (a) decreased ventilatory capacity and respiratory muscles fatigue; (b) decreased efficacy of the pulmonary gas exchanges; (c) altered pulmonary vascular bed with altered cardiovascular response. The most widely used training methods are walking (or running), practising on a conveyor belt and using an ergometric bicycle. The last named seems to be the best method to evaluate the physiological effects of exercise or for experimental studies. Patients who are fit to participate in a retraining programme must be in a stable period and have a stable pharmacological regimen; they must be subjected to a preliminary exercise test in order to evaluate the main physiological parameters and to obtain information on their tolerance to exercise, on the presence of lactic acidosis and on the degree of hypoxaemia and hypercapnia. In the absence of contra-indications, a training programme can be set up with 30 to 45 minutes of exercise per day at least 3 to 5 times a week during 5 to 8 weeks, with a load amounting to 50-60% of VO2 max. Two questions remain to be answered: (a) is oxygen therapy useful during retraining; (b) what effect has training on survival?
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PMID:[Indications and results of exercise rehabilitation in patients with chronic obstructive lung diseases]. 177 75

The efficacy of acupuncture and transcutaneous stimulation analgesia, supplemented by small doses of fentanyl (mean 1.2 micrograms/kg, SD 1.7) was compared with moderate-dose fentanyl anaesthesia (mean 22.9 micrograms/kg, SD 2.8) in 29 patients who underwent surgery for retroperitoneal lymph node dissection. The present study describes the anaesthetic techniques and comparison of haemodynamics, demand for analgesics after surgery, recovery and blood gases, restoration of urinary and bowel functions, convalescence in terms of self-reliance and the postoperative course in respect of fatigue and morbidity. A more rapid return of consciousness, an absence of hypercapnia and a smaller decrease in pH were observed in patients who received acupuncture and transcutaneous stimulation (p less than 0.05). No clinically relevant disadvantages attributable to the method were demonstrated.
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PMID:Acupuncture and transcutaneous stimulation analgesia in comparison with moderate-dose fentanyl anaesthesia in major surgery. Clinical efficacy and influence on recovery and morbidity. 188 9

Sleep apnea and other respiratory diseases produce hypoxemia and hypercapnia, factors that adversely affect skeletal muscle performance. To examine the effects of these chemical alterations on force production by an upper airway dilator muscle, the contractile and endurance characteristics of the geniohyoid muscle were examined in situ during severe hypoxia (arterial PO2 less than 40 Torr), mild hypoxia (PO2 45-65 Torr), and hypercapnia (PCO2 55-80 Torr) and compared with hyperoxic-normocapnic conditions in anesthetized cats. Muscles were studied at optimal length, and contractile force was assessed in response to supramaximal electrical stimulation of the hypoglossal nerve (n = 7 cats) or geniohyoid muscle (n = 2 cats). There were no significant changes in the twitch kinetics or force-frequency curve of the geniohyoid muscle during hypoxia or hypercapnia. However, the endurance of the geniohyoid, as reflected in the fatigue index (ratio of force at 2 min to initial force in response to 40-Hz stimulation at a duty cycle 0.33), was significantly reduced by severe hypoxia but not by hypercapnia or mild hypoxia. In addition, the downward shift in the force-frequency curve after the repetitive stimulation protocol was greater during hypoxia than hyperoxia, especially at higher frequencies. In conclusion, the ability of the geniohyoid muscle to maintain force output during high levels of activation is adversely affected by severe hypoxia but not mild hypoxia or hypercapnia. However, none of these chemical perturbations affected muscle contractility acutely.
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PMID:Effects of hypoxia and hypercapnia on geniohyoid contractility and endurance. 193 46


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