Conditions Of Controlled Ventilation Research Articles

Gaseous effluents from the combustion of nanocomposites in controlled-ventilation conditions

Composite materials are more and more used every day. In order to further enhance their attractive mechanical and physico chemical performances, the last generation of these materials largely makes use of nanomaterials.Various nanofillers are eligible for such a purpose, the best ones depending on the associated matrices. One favorite field of application of these nanomaterials is fire retardancy and fire behavior of nanocomposites. In the context of the ANR research project NanoFeu, various technical analyses have been performed [1]. One focuses on the characterization of the dispersion of nanofillers in the matrix; another deals with the characterization of the fire behavior of samples including the study of the composition of the gaseous effluents, the characterization of the emitted soot [2]. A third part of the work focused on molecular modeling of observed phenomena within the matrices. This paper focuses mainly on the combustion of nanocomposite samples under various ventilation conditions.Tests have been performed with the Fire Propagation Apparatus (FPA). Samples are based on poly(methyl methacrylate); various nanofillers were used: carbon nanotubes, alumina and silica. Efficiency of fillers is compared to the classical ammonium polyphosphate in equal proportions. During testing, the ventilation-controlled conditions were obtained by adjusting the combustion air flow rate entering the apparatus. Gaseous effluents were analyzed by Fourier Transform Infra-Red spectrometer.Fire behavior is characterized in terms of fire parameters and chemical composition of gaseous effluents. The influence of ventilation conditions is especially significant in terms of amount of gases released: much more important production of specific gases is generally observed in case of under ventilation regime as compared to the well ventilated case.

I-GEL(TM) VS. AURAONCE(TM) LARYNGEAL MASK FOR GENERAL ANAESTHESIA WITH CONTROLLED VENTILATION IN PARALYZED PATIENTS

The i-gel™ and the AuraOnce™ laryngeal mask are supraglottic airway devices used for airway management during general anaesthesia. Both devices are cheap, disposable and widely used. They may be used with both spontaneous and controlled ventilation. This study compared differences in the seal and peak pressures, and postoperative complications in these devices when used in paralyzed patients under controlled ventilation. A prospective randomized trial was designed to compare the i-gel™ and the AuraOnce™ in paralyzed adult patients under conditions of controlled ventilation. Two hundred and four patients (ASA class 1-3, age 18-89, weight 46-115 kg) were enrolled in the study. Standardized anaesthesia (fentanyl, propofol and sevoflurane in air-oxygen) was administered including neuromuscular blockade. The primary outcome measure was the difference in seal airway pressures between the two devices. Secondary outcome measures included peak airway pressures, insertion data and postoperative profiles--the incidence of sore throat, swallowing difficulties, numb tongue, hearing difficulties, neck pain, nausea and vomiting. First time insertions were 85.6% (i-gel) and 82% (AuraOnce) with overall success rates 96.3% (i-gel) and 94.2% (AuraOnce) (p=0.54). Average insertion times were 11.0 s (i-gel) and 11.6 s (AuraOnce) (p=0.19). Seal pressures were 30.4 cmH(2)O (i-gel) and 27.8 cmH(2)O (AuraOnce) (p=0.007). Peak pressures were 15.3 cmH(2)O (i-gel) and 15.6 cmH(2)O (AuraOnce) (p=0.57). Traumatic insertion occurred in 5.8% of i-gel™ and 2% of AuraOnce™ insertions. The overall incidence of postoperative complications was low, with the i-gel™ causing less sore throat and difficulty swallowing at 24h. Conclusion. Both devices provided effective seals for ventilation under positive pressure. I-gel™ may be a better alternative for the procedures with controlled ventilation because of higher seal pressures and lower incidence of sore throat postoperatively.

Comparison of responses to CO2 under the conditions of natural respiration and controlled artificial pulmonary ventilation

The relationship between the sensation of lack of air caused by the addition of carbon dioxide to inhaled air and minute pulmonary ventilation was studied in eight healthy male volunteers. Under the conditions of both natural respiration and controlled artificial ventilation of the lungs, ventilation increased in proportion to the increase in the partial pressure of CO2 in the end-tidal exhaled air. The individual differences in the ventilation responses to CO2 under the conditions of controlled ventilation and natural ventilation are regarded as a property of voluntary control.

Revising a Dogma: Ketamine for Patients with Neurological Injury?

We evaluated reports of randomized clinical trials in the perioperative and intensive care setting concerning ketamine's effects on the brain in patients with, or at risk for, neurological injury. We also reviewed other studies in humans on the drug's effects on the brain, and reports that examined ketamine in experimental brain injury. In the clinical setting, level II evidence indicates that ketamine does not increase intracranial pressure when used under conditions of controlled ventilation, coadministration of a gamma-aminobutyric acid (GABA) receptor agonist, and without nitrous oxide. Ketamine may thus safely be used in neurologically impaired patients. Compared with other anesthetics or sedatives, level II and III evidence indicates that hemodynamic stimulation induced by ketamine may improve cerebral perfusion; this could make the drug a preferred choice in sedative regimes after brain injury. In the laboratory, ketamine has neuroprotective, and S(+)-ketamine additional neuroregenerative effects, even when administered after onset of a cerebral insult. However, improved outcomes were only reported in studies with brief recovery observation intervals. In developing animals, and in certain brain areas of adult rats without cerebral injury, neurotoxic effects were noted after large-dose ketamine. These were prevented by coadministration of GABA receptor agonists. Ketamine can be used safely in neurologically impaired patients under conditions of controlled ventilation, coadministration of a {gamma}-aminobutyric acid receptor agonist, and avoidance of nitrous oxide. Its beneficial circulatory effects and preclinical data demonstrating neuroprotection merit further animal and patient investigation.

Cardiac and respiratory activity at arousal from sleep under controlled ventilation conditions.

Arousal from sleep is associated with elevated cardiac and respiratory activity. It is unclear whether this occurs because of homeostatic mechanisms or a reflex activation response associated with arousal. Cardiorespiratory activity was measured during spontaneous arousals from sleep in subjects breathing passively on a ventilator. Under such conditions, homeostatic mechanisms are eliminated. Ventilation, end-tidal PCO2, mask pressure, diaphragmatic electromyograph, heart rate, and blood pressure were measured in four normal subjects under two conditions: assisted ventilation and a normal ventilation control condition. In the control condition, there was a normal, sleep-related fall in ventilation and rise in end-tidal PCO2. Subsequently, at an arousal, there was an increase in respiratory and cardiac activity. In the ventilator condition, a vigorous cardiorespiratory response to a spontaneous arousal from sleep remained. These results indicate that sleep-related respiratory stimuli are not necessary for the occurrence of elevated cardiorespiratory activity at an arousal from sleep and are consistent with the hypothesis that such activity is at least in part due to a reflex activation response.

Cyclooxygenase mediated airway response to leukotriene D 4 in the cat

The effects of leukotriene D 4 (LTD 4) on pulmonary mechanics were investigated in anesthetized, paralyzed cats under conditions of controlled ventilation. Intravenous injections of LTD 4 in doses of 3, 10, and 30 μg caused significant increases in transpulmonary pressure (P TP) and lung resistance (R L) while decreasing dynamic compliance (C dyn). LTD 4 also increased systemic arterial pressure (P A0). The changes in P TP, R L, and C dyn in response to LTD 4 were blocked by sodium meclofenamate, a cyclooxygenase inhibitor. However, there was no significant change in the increase in P A0 following cyclooxygenase blockade. U 46619, a thromboxane mimic, was 30 to 100 times more potent than LTD 4 in increasing P TP, R L and decreasing C dyn in the cat. These data show that LTD 4 has significant smooth muscle constrictor activity in central airways as well as peripheral portions of the feline lung. In addition, these data suggest that in the cat the actions of intravenously administered LTD 4 on lung mechanics are mediated by release of cyclooxygenase products while the systemic pressor effects are not dependent upon the integrity of the cyclooxygenase pathway.

The fate and distribution of chlorpropham when applied to stored potatoes as a sprout suppressant

AbstractTwo varieties of potato were treated with 14C‐ or 36Cl‐radiolabelled chlorpropham to suppress sprouting, and stored under controlled ventilation conditions in the laboratory for up to 6 months at 10°C. The migration of chlorpropham into the potato tubers was studied at intervals by autoradiography and analysis of tuber extracts. Little penetration of chlorpropham beyond the peel layer occurred even after storage for 6 months. No identifiable degradation product of chlorpropham was detected in the extracts, although there was evidence of bound non‐extractable residues. Volatile compounds lost by ventilation through the storage containers were collected in cold traps and analysed by liquid scintillation counting. Loss of chlorpropham by volatilisation from the tuber surface was very small.

Brain blood flow and O2 delivery during hemorrhagic hypotension in the piglet.

Summary: We have previously demonstrated regional differences in brain blood flow reduction when hemorrhagic hypotension was induced in spontaneously breathing newborn piglets. Both the mean arterial blood pressure and Paco2 correlated with the changes in brain blood flow. To determine if changes in brain blood flow during hypotension can be attributed to alterations of mean arterial blood pressure alone, eight newborn piglets were studied under conditions of controlled ventilation. Regional brain blood flow was measured by microspheres and the blood pressure was varied by phlebotomy. After baseline determinations, three measurements of blood flow were performed during hypotension. Hypotension produced a significant reduction in blood brain flow confirming the independent effect of mean arterial blood pressure in autoregulation of cerebral circulation. Significantly different regional blood flow responses occurred in response to hypotension (P < 0.05). The % reduction from control blood flow was greatest to the cerebrum, less to the cerebellum, and least to the brainstem. Furthermore, the blood flow was consistently decreased in the cerebral hemispheres during the entire exposure to hypotension (mean ± S.E.: −36 ± 10%, −18 ± 11%, and −33 ± 11% change from control) whereas the brainstem demonstrated an intial reduction and then an increase in blood flow (mean ± SE: −14 ± 12%, +16 ± 15%, and +5.5 ± 13% change from control). The cerebellar responses were intermediate between those of the cerebrum and brainstem. O2 delivery was significantly decreased to all brain regions during hypotension, maintaining the same rank order of the regions as when blood flow reductions occurred. Speculation: Newborn piglets subjected to profound hypotension demonstrate regional differences in the reduction of brain blood flow. Cranial window studies of the microvasculature in adult cats clearly demonstrate that precapillary vessels in the brain do not respond in an identical manner to hypotension but rather react in a size dependent fashion. The observed differences in brain regional blood flow are possibly a manifestation of the relative composition (with respect to vessel size) of the regional parenchymal arterial beds.

HAEMODYNAMICS AND MYOCARDIAL OXYGEN CONSUMPTION DURING ISOFLURANE (FORANE) ANAESTHESIA IN GERIATRIC PATIENTS

The influence of isoflurane on haemodynamics and myocardial oxygen consumption was examined in seven geriatric patients under conditions of controlled ventilation and a normal arterial carbon dioxide tension. During isoflurane/nitrous oxide in oxygen anaesthesia (0.75 and 1.5 vol% inspired isoflurane) no significant changes occurred in cardiac output, stroke volume, heart rate, central venous and pulmonary artery pressure. Arterial pressure decreased, as did total peripheral resistance. A reduction in left ventricular maximum dp/dt (18-39%) was, at least in part, a result of changes in loading conditions. Total body (CaO2--CVO2) and base excess values remained within the normal range. We consider that the oxygen supply was adequate to meet the metabolic demands of the body as a whole. Myocardial oxygen consumption decreased by 25% during 0.75 vol% inspired isoflurane and by 43.5% with deepening of anaesthesia (1.5 vol% isoflurane).

Effects of induction of anaesthesia and muscle paralysis on functional residual capacity of the lungs

A helium dilution method of measuring FRC under conditions of controlled ventilation is described. Using this method the effect on FRC of premedication and of induction of anaesthesia and muscle paralysis has been investigated. No significant change in FRC was found with premedication alone. A significant fall (p < .01) was observed with the induction of anaesthesia and muscle paralysis. The combined effect of premedication and induction of anaesthesia and muscle paralysis also produced a significant fall in FRC (p < .05).

Reflex effects of carotid body chemoreceptor stimulation on the heart rate of the rabbit.

SummaryThe isolated carotid bifurcation regions of the rabbit were perfused with blood. Stimulation of the chemoreceptors in the carotid bodies was achieved by perfusion with hypoxic blood from a donor rabbit. Under conditions of controlled ventilation, chemoreceptor stimulation caused a slowing of the heart. This response was considerably modified by hyperventilation, either occurring spontaneously with the chemoreceptor excitation or induced artificially. The responses occurred whether the aortic depressor nerves were intact or not. The bradycardia of chemoreceptor origin was mediated both by vagal efferent pathways and by sympathetic fibres to the heart.

Hemodynamic responses to controlled 100% oxygen breathing in emphysema

Cardiopulmonary hemodynamic responses to breathing 100% oxygen for 20 min were studied in 13 patients with moderate to severe chronic obstructive emphysema under conditions of controlled ventilation. A technique for regulating the level of ventilation in the unanesthetized subject is described. Cardiac output was measured by the indicator-dilution method. Arterial blood gas analysis and pH were performed in each phase of the study. A slight but statistically significant decrease in cardiac index occurred. There was a highly significant reduction in pulmonary arterial pressure and pulmonary vascular resistance. No change in heart rate, pulmonary wedge pressure, or aortic pressure occurred. It is concluded that oxygen breathing caused a release, in part at least, of a pulmonary vasoconstrictive element in these patients. pulmonary circulation; oxygen in pulmonary hypertension; hypoxia and pulmonary vasoconstriction; controlled ventilation during oxygen inhalation Submitted on May 27, 1964