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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Twenty-nine patients scheduled for postnatal tubal ligation by minilaparotomy under general anaesthesia were studied. Arterial and end-tidal carbon dioxide tensions were determined during anaesthesia. The mean arterial to end-tidal carbon dioxide tension difference was 0.08 kPa (SEM 0.05). Thirty-one percent of the patients had negative values. These results were similar to those observed during Caesarean section. The physiological changes responsible for reduced arterial to end-tidal carbon dioxide values, persist into the postnatal period. It is predicted from the regression analysis of the time between delivery and anaesthesia for tubal ligation and arterial to end-tidal CO2 difference, that the values might return to normal nonpregnant levels by 8 days following delivery.
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PMID:Arterial to end-tidal carbon dioxide tension difference during anaesthesia for tubal ligation. 310 74

We analyzed biochemical data derived from 911 patients with renal insufficiency observed at our institution for periods up to 7 years. During early renal failure (RF) (creatinine less than 5 mg/dL), the rate of change of hematocrit, total CO2 (tCO2) and urea per unit change of creatinine was significantly higher than during moderate (creatinine between 5 and 10 mg/dL) or advanced (creatinine greater than 10 mg/dL) RF. For example, the rate of change of hematocrit (%, volume/volume [v/v]) was (mean +/- SEM) -2.15 +/- 0.15% for each 1 mg/dL increase in creatinine in the range of creatinine less than 5 mg/dL, whereas for the range of creatinine greater than 10 mg/dL, the rate of change was only -0.48 +/- 0.06% (P less than 0.001). Similarly, the rate of change of tCO2 was -1.68 +/- 0.09 mEq/L for each 1 mg/dL increment in creatinine concentration during early RF, and -0.19 +/- 0.09 mEq/L per unit increase in creatinine during advanced RF (P less than 0.001). Chloride concentration initially increased as a function of creatinine in early RF, but decreased in advanced RF, whereas the anion gap increased throughout the course of RF. Mean serum phosphate concentration also increased steadily, but remained below the upper range of normal (4.7 mg/dL) during early RF without the use of phosphate binders. These data suggest that different biochemical parameters change at different rates as a function of the severity of renal dysfunction, and that although phosphate retention may occur, hyperphosphatemia is not a hallmark of early RF.
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PMID:Biochemical parameters in chronic renal failure. 312 41

Regional (frontal, parietal, occipital, cortical, and basal ganglia) cerebral blood flow (rCBF) was examined at 1.5 and 3.5 MAC inspired isoflurane/O2 anesthesia in the rat using the radioactive microsphere technique to determine the effects of controlled hypotension with deep isoflurane anesthesia on rCBF and the response of rCBF to changes in PaCO2 when mean blood pressure (BP) was decreased to levels below the lower limit of the autoregulatory threshold. Four groups of six rats were studied with rCBF 1 determined at 1.5 MAC (mean BP 80-90 mm Hg) followed by two rCBF determinations at 3.5 MAC (mean BP 46-48 mm Hg). For CBF 1 the regional CO2 response was a 3.1-3.9% increase in rCBF/mm Hg increase in CO2. Regional cerebral blood flow (ml/g/min) ranged from 0.64 +/- 0.05-0.83 +/- 0.15 at PaCO2 of 19 mm Hg to 1.34 +/- 0.11-1.80 +/- 0.33 at PaCO2 of 41 mm Hg to 2.61 +/- 0.26-3.72 +/- 0.37 at PaCO2 of 59 mm Hg (mean +/- SEM). With controlled hypotension (CBF 2) rCBF was unchanged during normocarbia, increased 100% during hypocarbia, P less than 0.01 vs CBF 1 and decreased 30% during hypercarbia, P less than 0.01 vs CBF 1. For rCBF 3 measurements, the BP and inspired concentration of isoflurane were kept constant, while PaCO2 was increased in two and decreased in two of the four groups. Within-group comparisons between rCBF 2 and rCBF 3 results demonstrated loss of CO2 responsiveness of the rat cerebrovasculature in every region during controlled hypotension to below the autoregulatory threshold at 3.5 MAC isoflurane/O2 anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Regional cerebral blood flow and response to carbon dioxide during controlled hypotension with isoflurane anesthesia in the rat. 312 43

The authors measured the rate of carbon dioxide elimination (VCO2) in 25 pediatric patients (age 2 days to 9 yr) during total cardiopulmonary bypass at average venous blood temperatures ranging from 19.5 to 35.9 degrees C. A multiplexed mass spectrometer was connected to the gas inlet and exhaust ports of the bubble oxygenator, and the gas-phase Fick principle was used to determine VCO2. A curvilinear relationship was found between log VCO2 and venous blood temperature, and a quadratic regression equation (r2 = 0.74) was fit to the data. Q10 (the ratio of VCO2 before and after a 10 degree C temperature change) was estimated to be 2.7 or 3.0, depending on the analytic method used. Venous blood temperature as a predictor variable explained a greater proportion of the variability of log VCO2 than did nasopharyngeal or rectal temperatures. Analysis of covariance revealed that total circulatory arrest during bypass (utilized in 10 patients for 34 +/- 4 min, mean +/- SEM) affected the relationship of venous blood temperature with log VCO2, by increasing the y-intercept (P = .008) but not the slope. These data, with associated 95% prediction intervals, define the expected CO2 elimination rates at various temperatures during standard bypass conditions in our patients. Real-time measurement of VCO2 using mass spectrometry can be a useful routine monitor during CPB that may help to assess patient metabolic function, adequacy of perfusion, and oxygenator performance.
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PMID:Carbon dioxide elimination during total cardiopulmonary bypass in infants and children. 313 83

Hypocarbia results in an increase in brain adenosine concentrations, presumably because of brain hypoxia associated with hypocarbic vasoconstriction. It was hypothesized that adenosine limits the degree of hypocarbic vasoconstriction. To test this hypothesis, the effects of dipyridamole and theophylline on CO2 reactivity during hypocarbia were investigated in anesthetized rats. Dipyridamole should reduce the vasoconstriction by potentiating adenosine action, whereas theophylline should increase the vasoconstriction by blocking adenosine receptors. Cortical pial arterioles of mechanically ventilated and anesthetized rats were displayed on a video monitor system through a closed cranial window. Arterial blood pressure and oxygen tension were stable. CO2 reactivity, formulated as 100 X [delta diameter (micron)/resting diameter (micron)]/delta PaCO2 (mmHg), in the hypocarbic phase was calculated before and after topical superfusion of dipyridamole (10(-6) M; n = 7) and theophylline (5 X 10(-5) M; n = 6). CO2 reactivity was significantly decreased after superfusion of dipyridamole (0.57 +/- 0.08; mean +/- SEM) as compared with mock cerebrospinal fluid (CSF) (0.97 +/- 0.17, p less than 0.05, n = 7). On the other hand, CO2 reactivity after superfusion of theophylline was increased (1.63 +/- 0.28) as compared with mock CSF (1.00 +/- 0.20, p less than 0.05, n = 6), indicating that adenosine is involved in hypocarbic vasoconstriction.
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PMID:The effects of dipyridamole and theophylline on rat pial vessels during hypocarbia. 314 92

In order to investigate the effect of a CO2 laser on dental tissues, 51 healthy human teeth were lased and prepared for macroscopic, histological and SEM examination using standardized methods. The alterations induced by the thermic shock varied according to the tissue's composition and the lasing's intensity. The effects generally appeared as cracks with fragmentation of the superficial enamel, and a carbonization of the cavity. The underlying pulp showed a disintegration of the odontoblastic layer and an oedema, the severity of which depended on the residual dentinal thickness and the lasing's intensity. The study's results, divergent from those often found promising in the abundant literature, bring to light the biological incompatibility of this type of hard laser regarding the dental organ and suggest caution concerning eventual therapeutic indications.
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PMID:[Action of a CO2 laser on dental tissues]. 314 12

In patients with obstructive apnea, it was hypothesized that stimulation of the ventilatory system by hypercapnia during sleep would increase pharyngeal inspiratory muscle activity and thereby increase upper airway caliber. We predicted that this increase in caliber would decrease the number of apneas and sleep time spent apneic. In contrast, suppression of the ventilatory system activity with hyperoxia was predicted to decrease both inspiratory muscle activity and pharyngeal caliber and thereby increase the number of apneas and apnea time. In all 7 patients with symptomatic obstructive sleep apnea studied, 3 with upper airway narrowing obvious during wakefulness, inhalation of 3 to 6% CO2 preferentially stimulated upper airway inspiratory muscle tonic electrical activity relative to the activity of chest wall inspiratory muscles and diminished periodic breathing. Apnea time decreased from 60 +/- 2% (mean +/- SEM) of sleep time during ambient air inhalation to 12 +/- 3% during CO2 inhalation; 50% O2 had the reverse effect on inspiratory muscle tonic electrical activity and increased apnea time to 75 +/- 5% of sleep time. We conclude that manipulation of inspiratory muscle tonic activity and alteration of the pattern of breathing by CO2 and O2 inhalation lead to significant changes in the pattern of upper airway inspiratory collapse during sleep. We speculate that physiologic variables related to the control of upper airway inspiratory muscle function are instrumental in the pathophysiology of obstructive sleep apnea.
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PMID:Alteration in obstructive apnea pattern induced by changes in oxygen- and carbon-dioxide-inspired concentrations. 314 3

Elimination of CO2 during liquid ventilation is dependent on flow, diffusion, and the liquid's capacitance for CO2. Maximum expiratory flow (Vmax) and diffusion dead space were measured in vivo in 12 young cats during liquid fluorocarbon (FC-80) ventilation to determine the effect of breathing frequency on maximum CO2 elimination. All animals were maintained (PaO2 = 255 +/- 19 SEM mm Hg, PaCO2 = 35 +/- 1 SEM mm Hg, pH = 7.31 +/- 0.01 SEM) within physiologic range during 1-4 h of liquid ventilation. The Vmax in air (26 +/- 1 SEM liter/min) and in liquid (1.2 +/- 0.2 SEM liter/min) was determined by volume displacement plethysmography. Diffusion dead space (VDdiff) during liquid ventilation as a ratio of alveolar volume (VA) was well correlated (r = 0.84, p less than 0.005) with the average time (tav) the liquid was in the lung [VDdiff/VA = 0.89 e (-0.053 tav)]. Alveolar ventilation, CO2 elimination (VCO2), and PaCO2 were not affected by breathing frequency (f) when tidal volume was adjusted appropriately during steady state liquid ventilation. Predicted maximum CO2 elimination (VCO2max) determined from Vmax and VDdiff was 24 ml/min at a f of 3-3.5 breaths/min. The maximum was found to be strongly dependent on f with much less dependency on fixed dead space (anatomic plus equipment) and wave shape characteristics. Elimination of CO2 decreased at low values of f due to inadequate ventilation and at high values of f due to inadequate diffusion time. From a comparison of experimentally determined steady state VCO2 to theoretically predicted VCO2max, the results demonstrate a f-related functional reserve capacity for CO2 elimination during liquid ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Fluorocarbon ventilation: maximal expiratory flows and CO2 elimination. 314 82

The effects of airway CO2 and pressure on pulmonary vagal afferent fibers were studied in seven anesthetized alligators Alligator mississippiensis, at room temperature (24 degrees C). Of 49 receptors which fired in phase with ventilation, 13 behaved like mammalian rapidly adapting pulmonary stretch receptors, 19 like mammalian slowly adapting pulmonary stretch receptors (PSR), and 17 like avian intrapulmonary CO2-sensitive chemoreceptors (IPC). PSR and IPC were positively localized to the lung by punctate stimulation or response to airway CO2 changes during pulmonary artery occlusion. PSR discharge frequency (fPSR) was measured at airway pressures (Paw) from 0 to 15 cm H2O at FICO2 = 0.01 in 14 receptors. fPSR increased in all receptors throughout the range of Paw studied. In 13 PSR, increasing FICO2 from 0.01 to 0.07 decreased fPSR 23 +/- 13% (+/- SEM) at Paw = 2 cm H2O and 14 +/- 7% at 15 cm H2O. IPC discharge frequency (fIPC) decreased as FICO2 increased and most discharged less than 1 sec-1 at FICO2 = 0.03. In 7 IPC at FICO2 = 0.01, increasing Paw from 2 to 15 cm H2O increased fIPC 17 +/- 5% after pulmonary artery occlusion demonstrating some mechanosensitivity in alligator IPC. Although both IPC and PSR showed mechanosensitivity and CO2-sensitivity, the two receptor types were distinct. PSR were 13 times more sensitive to Paw changes than IPC and IPC were 14 times more sensitive to FICO2 changes than PSR. We did not find any receptors with intermediate CO2- or mechanosensitivities that could represent a transitional form of receptor. These results predict that IPC and PSR may have different roles in reflex ventilatory control.
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PMID:Effects of intrapulmonary CO2 and airway pressure on pulmonary vagal afferent activity in the alligator. 314 84

We compared the response of ventricular muscle from adult and neonatal rats to hypercapnic acidosis. In adult muscle, acidosis caused an initial rapid fall of developed tension to 30 +/- 5% of control (mean +/- SEM, n = 6). However, tension recovered slowly to a steady state that was 56 +/- 6% of control. In neonatal muscle, acidosis caused a significantly smaller initial fall in tension to 43 +/- 3% (n = 8, p less than 0.05), but the tension then showed a subsequent slower fall to a steady state that was 29 +/- 4% of control, significantly less than in the adult (p less than 0.01). We have attempted to identify the mechanisms underlying these differences in response. In detergent-skinned myofibrils, reducing the pH from 7.0 to 6.5 caused a reduction in the pCa50 of 0.61 units in the adult muscle, but only 0.27 units in the neonatal ventricular muscle. Myofibrillar Ca2+ sensitivity in neonatal ventricular muscle is thus less susceptible to the effects of acidic pH than that of adult muscle. Since intracellular pH decreases rapidly on application of increased external CO2, these results are consistent with the finding that, initially, developed tension in neonatal muscles is less sensitive to the effects of acidosis. Sodium dodecylsulfate gel electrophoresis of myofibrillar preparations from adult and neonatal rats demonstrated differences in thin filament proteins, including troponin I, which may underlie the observed differences in Ca2+ sensitivity. In adult rat ventricular muscles, the slow recovery of tension during acidosis is associated with an increase in the amplitude of the Ca2+ transients to 263 +/- 34% of control (n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of acidosis on ventricular muscle from adult and neonatal rats. 316 78


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