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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have emphasized the mechanisms and consequences of sleep state effects on the manifestation of a sensitive apneic threshold. In the absence of the stabilizing influences of wakefulness, even the healthy person is vulnerable to instabilities and ventilatory control as maintenance of a rhythmic breathing pattern becomes overwhelmingly dependent on CO2. This sleep-induced unmasking of the depressant effects of hypocapnia contrasts with the relatively minor effects of sleep on the ventilatory response to a wide variety of other acute or chronic ventilatory stimuli or inhibitors. This combination of an apneic threshold with a maintained hypoxic (and asphyxic) responsiveness during non-REM sleep probably explains much of the periodic breathing in hypoxic sleep in adults and in newborns. Furthermore, applying acute hypoxia to persons with upper airways that are susceptible to collapse, i.e., snorers, showed that fluctuating chemical stimuli and the accompanying instability in ventilatory control during sleep can cause obstructive apnea, at least under conditions where chemoreceptor stimuli are sufficient to initiate some inspiratory effort but insufficient to insure a completely patent upper airway. We emphasize that chemoreceptor-induced instability and/or apnea probably plays little or no role in the induction of many other varieties of sleep apnea including most obstructive sleep apneas and perhaps even in some types of nonobstructive apnea. The consequences of these chemoreceptor-induced instabilities are, of course, substantial in terms of impairment of pulmonary gas exchange and the precipitation of events that contribute significantly to the development of chronic cor pulmonale.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:A sleep-induced apneic threshold and its consequences. 371 65

1. The reflex effects of alterations in lung volume on systemic vascular resistance have been studied in anaesthetized dogs under conditions in which the systemic circulation was perfused at constant blood flow. The pressures in the isolated perfused carotid sinuses and aortic arch, and the arterial blood P(O2) and P(CO2) were maintained constant.2. A maintained inflation of the lungs produced by injection of air into the trachea caused a fall in systemic arterial perfusion pressure, indicating vasodilatation. The size of the systemic vasodilator response varied directly with the pressure and volume of gas used to inflate the lungs. A similar effect was observed when the tidal volume of lungs ventilated by an intermittent positive pressure was increased.3. Collapse of the lungs by creating a pneumothorax in closed-chest spontaneously breathing animals evoked a systemic vasoconstrictor response which was reversed when the lungs were re-expanded.4. These vasodilator responses were abolished by dividing the pulmonary branches of the thoracic vagosympathetic nerves. Evidence is presented that the afferent fibres run in the cervical vagosympathetic nerves and through the stellate ganglia.5. The responses were unaffected by atropine, but were abolished by hexamethonium, guanethidine and by bretylium tosylate, indicating that they are mediated via the sympathetic nervous system.6. Evidence is presented that the lungs are a constant course of afferent impulses inhibiting the ;vasomotor centre', and that the lung inflation-systemic vasodilator reflex is a potential mechanism operating in eupnoeic breathing.
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PMID:The reflex effects of alterations in lung volume on systemic vascular resistance in the dog. 603 4

The bowfin, Amia calva is a facultative air breathing fish restricted to North America and is reported to estivate. The relative and functional gill surface areas of A. calva are not reduced, as in many amphibious fish, but have areas comparable to many completely aquatic species. The secondary lamellae are fused to form a lattice-work of rectangular pores, a gill arrangement unique among fresh-water fishes. This highly modified gill structure imparts considerable rigidity such that these do not collapse upon air exposure. In vivo blood gas measurements from air exposed Amia reveal that these gills must be free of water, since there is both O2 uptake and CO2 excretion across them. The observed ventilatory motions therefore pass air over the secondary lamellae for diffusive gas exchange during air exposure. In the artificial conditions of our experiments, however, air exposure was associated with a marked acidosis and the fish died within 2 hours of being returned to normoxic water.
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PMID:Functional morphology of the gills of the bowfin, Amia calva L., with special reference to their significance during air exposure. 679 74

A method is described for liquid filling lungs without collapse by ventilating them on CO2 and then absorbing this gas with isotonic Tris buffer solution. The gas retained in each of 16 liquid-filled lungs has been measured by their compression in a dilatometer and averages 0.13% of lung volume. The liquid filling method has the advantage that it can be used either for lungs in situ or excised; total elimination of any retained gas, if desired, can be ensured by subsequent compression to 8.3 ATA for 10 min.
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PMID:Methods for liquid filling inflated lungs and measuring any retained gas. 679 6

In 24 patients with cystic fibrosis (6-20 years old), divided into two groups, we studied indices of airways obstruction before, 20-30 min and 2 h after chest physiotherapy. The physiotherapy lasted for 30 min and included expectoration of 2-10 ml of sputum. In one group of 14 patients, studies were made only 30 min after chest physiotherapy. No significant improvements of the ventilatory tests occurred. In fact, Vmax at 25% of VC deteriorated (P less than 0.05) in this group as a whole. In some patients also CV/VC increased, and N2 and CO2 alveolar slopes became steeper. Only Gaw/TGV improved in 20% of the patients by more than 10% of the control value. In the second group of 10 patients, ventilatory studies were repeated 3 times at one month intervals. They did not change significantly at 20 min and 2 h after chest physiotherapy. Gaw/TGV value improved by more than 10% in 20% of the patients. During chest physiotherapy, the patients were stimulated to cough. This might contribute to the immediate negative effects on ventilatory function by causing collapse of the central airways, as documented by cinebronchographic studies in 8 patients.
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PMID:Chest physiotherapy and airway obstruction in patients with cystic fibrosis - a negative report. 688 55

Studies on the activation and excystation of I. felis and I. rivolta sporozoites revealed that, although some differences were apparent between the two, both were capable of activation under a wide range of conditions. Activation of both species took place in trypsin and bile between 21 and 43 C (the range tested) occurring rapidly at 39 C. Although the presence of bile appeared to be essential for this process that of trypsin did not. Neither the concentration of bile (above 5%), the type of bile, nor the hydrogen ion concentration had a marked effect on the level of activation. Pretreatment of oocysts in aqueous cysteine hydrochloride under CO2 or with sodium hypochlorite before exposure to trypsin and bile was not an essential prerequisite for the activation of I. felis and I. rivolta. However, higher levels of activation were attained when pretreatment was used. But for I. rivolta, the level of activation appeared to be less dependent on pretreatment for oocysts stored in sulfuric acid than for those stored in potassium dichromate. The process of activation and excystation of both species was essentially similar to that described for other species of disporocystic coccidia with heteroxenous life cycles. Sporozoites escaped following the collapse of the sporocyst wall and completed excystation through indentations and fractures at one or both ends of the oocyst.
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PMID:Activation and excystation of Isospora felis and Isospora rivolta sporozoites. 707 58

We have examined the umbilical cord of ten newborn children of nonsmoking (five) and of smoking (five) mothers (10-20 cigarettes/day). The patients chosen for the study resulted "normal" before and during pregnancy. Immediately after delivery the umbilical cords were tied (to avoid collapse) and cut about 10 cm from the placenta. Umbilical cords were submitted to pressure-perfusion-fixation according to Kjelsen and Thomsen (7). Three randomly chosen specimens for SEM were cut and postfixation was performed in 1% buffered osmium tetroxide (pH 7.4) and after dehydration, were submitted to critical point drying (CO2), coated with gold palladium (sputtering technique), and observed by means of a Super ISI Mini SEM at 7,5 Kv. Luminal surfaces of umbilical arteries and veins from non-smoking mothers revealed a regular endothelial layer all over the surface. Large disendothelialised areas were instead found not only in arteries (1) but also in veins from newborn children of smoking mothers.
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PMID:[Scanning electron microscopic studies of the umbilical arteries and veins of newborn infants of smoking mothers]. 733 42

Better understanding of the physiopathology of ventilatory mechanisms associated with ARDS and the recent re-evaluation of the iatrogenic potential of mechanical ventilation (MV) brings us closer to the best suited ventilatory mode for these patients. In severely ill ARDS patients, only a small lung volume is ventilated, and remains available for the totality of the gas exchanges (baby lung concept). The goal of MV is to restore and maintain an optimal exchange volume while limiting mechanical agression of the lung tissue. Analysis of the ARDS related pressure-volume relationship (P/V) is helpful in specifying the tolerable limits of the ventilatory pressure regimen. The lower limit (end expiratory pressure) must be kept above the lower inflexion point of the curve, in order to increase the ventilated lung volume and avoid distal airway collapse. Under this limit, gas exchanges are altered by the shunt effect, and shear stress lesions result from the repeated opening and closing of the distal airways. The upper limit (end inspiratory pressure) must be situated below the upper inflexion point of the curve, in order to avoid lesions resulting from surdistension of the alveolocapillary membranes and barotraumatisms. The only way to position MV in such a narrow pressure window, is to greatly reduce the tidal volume (VT). Though CO2 retention would inevitably occur under conventional MV conditions, high frequency ventilation (HFV) seems better adapted to these theoreotical objectives; small VT's are injected under a limited amplitude pressure regimen and a satisfactory CO2 clearance is maintained. This ventilatory mode, existing since more than 15 years, has recently benefited from many technical improvements as well as the concept of oscillating the ventilation around a selected mean pressure in the central region of the P/V curve. In the past, HFV was applied using low pressure regimens, situated below the lower inflexion point of the curve. The resulting failures are, a posteriori, explained by insufficient lung volumes, unable to maintain adequate gas exchanges. Current work is aimed at re-evaluating HFV, using higher mean airway pressure levels. Combined HFV is another advance towards the theoretical goal of restoring and maintaining optimally ventilated lung volumes. Though HFV alone can maintain lung volumes oscillating around a mean value, it cannot re-expand atelectatic areas. The small VT's used are insufficient to overcome these area's elevated opening pressures. Volume recruitment by periodic hyperinflations, or sighs, though generally considered useless in conventional MV, have been shown to be of great benefit in HFV.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:[High frequency jet ventilation combined with conventional mechanical ventilation in the treatment of adult respiratory distress syndrome]. 748 98

Hydrogen peroxide is used to cleanse and irrigate wounds. As it decomposes immediately into water and oxygen on contact with organic tissue, it is usually regarded as a safe agent. We report a case of oxygen embolism associated with hydrogen peroxide irrigation of the surgical field during anterior fusion of the cervical vertebrae. It was accompanied by precipitous hypotension and decrease in pulse oximetry oxygen saturation and end-tidal CO2 tension. Semi-closed spaces formed under the apatite dowel and between the apatite dowel and vertebral bodies may have precipitated the absorption of oxygen bubbles into the vasculature. Although this case was associated with a rapid recovery and uneventful sequelae, it discourages the use of hydrogen peroxide in this procedure because of the potential hazards including cardiovascular collapse.
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PMID:Oxygen embolism due to hydrogen peroxide irrigation during cervical spinal surgery. 774 77

A hydraulic pump with an adjustable stroke delivering up to 145 ml at 1 to 45 Hz has been used to ventilate adult pigs of a weight between 60 and 140 kg. After tracheotomy the curarized animals were connected to the pump by a metallic tube through which a bias flow was directed. This flow (FiO2 0.35) was humidified by a special ceramic device and aspirated at the distal end of the tube. It was demonstrated that under these conditions gaz exchange was well maintained with oscillations between 15 and 35 Hz. Higher frequencies were needed for the heavier animals. Blood gas measurements of samples from segmental pulmonary veins demonstrated regional differences in gas exchange. These could be modified by adjusting the oscillation frequency. Reinhalation of gas could be prevented by an increase of the bias flow. Alveolar recruitment by initial pulmonary inflation by a pressure of 18 +/- 2 cm H2O is required for adequate oxygenation. Maintenance of adequate elimination of CO2 required a bias flow of 35 +/- 5 l/min. Mean pressure in the airways was maintained at 12 +/- 1 cm H2O. This pressure determines the value of PaO2. Ordinary endotracheal tubes tend to collapse during the sucking phase of the pressure cycle. Rigid or armed tubes are required. They must allow for aspiration of the bias flow from the distal end of the tube.
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PMID:[Ventilation by high frequency oscillations in adults. An experimental study of conditions and methods]. 781 53


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