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PubMed1999

Accuracy of MR phase mapping for temperature monitoring during interstitial laser coagulation (ILC) in the liver at rest and simulated respiration.

The chemical shift or proton-resonance frequency (phase mapping) can be used to measure temperature changes. As a subtraction technique, it requires scans at exactly the same location, making it prone to respiration-induced artifacts. The accuracy of magnetic resonance (MR) phase mapping for temperature monitoring of interstitial laser coagulation (ILC) was therefore investigated in two ex vivo models with simulated respiration. MR temperatures were calibrated to interstitially measured temperature. Gradual cooling of a homogenous medium (gel) was monitored for four starting temperatures (room temperature, 40 degrees C, 50 degrees C, and 60 degrees C) during 30 min. Temperature increases were measured during ILC in ex vivo porcine liver with Nd:YAG for 6 min with 5 Watt. Experiments were performed at rest and with simulated respiratory motion (both n = 5). In liver, accuracy did not decrease with respiration simulation (P = 0.32), whereas a significant decline was found in the gel model (P = 0.002). In all experiments a small drift over time was observed between temperature determined with MR and thermoprobes. Correction for temperature-independent phase-shift at a reference location did not enhance agreement. Temperatures could be determined correctly by MR in the moving liver within a range of +/-3.5 degrees C after 6 min of laser application (95% confidence interval), justifying further pre-clinical studies.

Analysis of Variance↗
PubMed1987

The effect of the respiratory cycle on mediastinal and lung dimensions in Hodgkin's disease. Implications for radiotherapy gated to respiration.

Changes in mediastinal and lung dimensions during respiration were studied to assess the potential of radiotherapy gated to respiration to minimize normal tissue irradiation. Twelve patients with mediastinal Hodgkin's disease were assessed using chest radiographs and thoracic computed tomography (CT) scans both during quiet breathing and at maximum inspiration in the standing, supine, and prone positions. A simple measure of the bulk of mediastinal disease, the ratio of the width of mediastinal mass to thoracic diameter, was determined from posteroanterior (PA) chest radiographs. The volumes of mediastinum, irradiated and protected lung if anteroposterior (AP) and PA mantle fields were used were determined from sequential thoracic CT scans and three-dimensional treatment planning and compared at quiet breathing and deep inspiration. The mediastinal width to thoracic diameter ratio decreased from quiet breathing to deep inspiration an average of 3%, 9%, and 11% for the standing, supine, and prone positions, respectively. Lung volumes as measured from the thoracic CT scans showed that on average, 8% more lung was protected at deep inspiration than at quiet breathing, independent of treatment position. The maximum increase in the percentage of protected lung from quiet breathing to deep inspiration was seen in patients with extensive mediastinal adenopathy suggesting that radiotherapy gated to respiration may be most advantageous in the subset of patients.

Hodgkin Disease↗
PubMed1988

Determinants of pattern of breathing during respirator use.

The relationship between the pattern of breathing in response to respirator-type loads and an individual's psychophysiologic sensitivity to loads (load scaling sensitivity, LSS) was investigated in the study of 11 normal volunteers. LSS was measured by having the subjects numerically rate a series of resistors; Steven's Psychophysical Law was used to evaluate sensitivity as the slope relating log (sensation) to log (stimulus). Peak pressure and actual added resistance were the stimuli. Inspiratory time, peak pressure, duty cycle, and tidal volume were inversely related to independently measured LSS during exercise and with a respiratory-type dead space and inspiratory resistance load. Because the need for changes in respiratory timing is a major adaptation in respirator use, it suggests that workers who are very sensitive to loads may have limited ability to adapt to respirator use.

Adult↗
PubMedDate not supplied

Inhibition of mitochondrial respiration by nitric oxide is independent of membrane fluidity modulation or oxidation of sulfhydryl groups.

Nitric oxide (NO) modulates the fluidity of a variety of membranes. Thus, the aim of the present work was to study if the inhibitory effect of NO on mitochondrial respiration is associated with its effects on membrane fluidity. Liver mitochondria and an inner mitochondrial membrane fraction (IMMF) were isolated from male Wistar rats by differential centrifugation. Oxygen consumption was measured polarographically and fluidity by the fluorescence polarization method. S-nitroso-N-acetylpenicillamine (SNAP) was used as a NO donor. It was observed that NO decreased IMMF fluidity and oxygen consumption in a concentration dependent fashion. However, SAM a fluidizing agent that prevented the decrement in fluidity produced by SNAP, failed to preserve oxygen consumption. Protection of sulfhydryl groups with dithiotreitol was utilized to evaluate the role of oxidation of these groups on IMMF respiration. Incubation with dithiotreitol did not preserve IMMF oxygen consumption. The data shown herein suggest that NO inhibits the respiratory chain by a mechanism not involving the modulation of membrane fluidity or the oxidation of sulfhydryl groups. Thus, it seems that the mechanism by which NO modulates mitochondrial respiration is by cytochrome oxidase inhibition, because (as reported by others) low concentrations of NO specifically inhibit reversibly cytochrome oxidase in competition with oxygen.

Animals↗
PubMed1986

Respiration of F344 rats in nose-only inhalation exposure tubes.

The respiration of naive F344 rats confined in nose-only inhalation exposure tubes was measured to obtain data for normal adult rats of different ages and to evaluate the tubes for exposures lasting several hours. Exposure tubes were modified for use as volume-displacement plethysmographs. Respiration of 10 male and 10 female rats at 3, 6, 12 and 24 months of age was measured in the tubes during simulated exposures of up to 6 h duration. Measurements included respiratory frequency, tidal volume, minute volume and body surface temperature. The mean respiratory frequencies of 3, 6, 12 and 24 month old rats during the first hour of exposure were 172, 152, 123 and 136 breaths min-1, respectively. Minute volumes were 1.40, 0.89, 0.67 and 0.82 ml g-1 body weight, respectively. Both frequency and minute volumes g-1 body weight were significantly greater for the youngest group, declined with age to 12 months and then increased at 24 months. Minute volumes g-1 body weight were similar for males and females. Minute volume and respiratory frequency of 3 and 12 month old rats declined progressively between 1 and 6 h of confinement in the tubes. Surface temperature did not increase after the first hour. The age and sex-specific data provide a basis for predicting respiration of naive tube-confined rats during inhalation exposures to non-irritating materials.

Age Factors↗
PubMed1995

The effect of respiration on the contrast and sharpness of liver lesions in MRI.

This work demonstrates the effects of through-plane motion due to respiration on contrast and sharpness of liver lesions in MRI. The effects of slice coverage with and without such respiratory motion is also reported. This work is comprised of two parts: a theoretical prediction of liver-lesion contrast and blur with and without respiration and an experimental validation using gel phantoms of the predicted results. Both theory and experiment show a loss of contrast, increasing with amplitude of the peak-to-peak motion. The loss of contrast for a 5-mm lesion at normal respiration of 15 mm peak-to-peak superior-inferior motion is approximately 10% with a low order sorted respiratory ordered phase encoding acquisition and approximately 50% for an unsorted acquisition. Lesion blur is greatest for the low order sorted acquisition while the unsorted and high sort acquisitions maintain edge definition. Breath-hold imaging is potentially superior to nonbreath-hold imaging in liver lesion contrast and edge definition, but is more sensitive to inadequate slice coverage.

Artifacts↗
PubMed1995

Error in MR volumetric flow measurements due to ordered phase encoding in the presence of flow varying with respiration.

Respiratory ordered phase encoding is often employed in MRI studies to reduce image artifacts due to breathing motion. The purpose of this work was to evaluate error caused by the use of respiratory ordering of phase encoding in MR cine phase-contrast (CPC) volumetric flow measurements when the flow rate is sensitive to respiration. It was hypothesized that this effect is due to the systematic biasing of a respiratory-induced phase modulation function in k-space. A theoretical model for the effects of respiration was developed and then tested in flow phantom studies and in normal volunteer studies. In phantom experiments, the use of respiratory ordering induced an error of as much as 13% in CPC volumetric flow measurements. In preliminary volunteer studies, error was as high as 26% in superior vena cava flow measurements versus less than 1% error in the ascending aorta. It is concluded that a potential for error exists in CPC volumetric flow measurements obtained with the use of respiratory ordering schemes. Volunteer studies with larger numbers are warranted. Clinical applications in which this effect may be important include flow measurements in vessels subject to variations in flow due to respiration, such as the venae cavae, pulmonary vasculature, and portal vein.

Aorta↗
PubMed2003

Dynamic calibration and dissolved gas analysis using membrane inlet mass spectrometry for the quantification of cell respiration.

A membrane inlet mass spectrometer connected to a miniaturized reactor was applied for dynamic dissolved gas analysis. Cell samples were taken from 7 mL shake flask cultures of Corynebacterium glutamicum ATCC 13032, and transferred to the 12 mL miniaturized reactor. There, oxygen uptake and carbon dioxide and its mass isotopomer production rates were determined using a new experimental procedure and applying nonlinear model equations. A novel dynamic method for the calibration of the membrane inlet mass spectrometer using first-order dynamics was developed. To derive total dissolved concentration of all carbon dioxide species (C(T)) from dissolved carbon dioxide concentration ([CO(2)](aq)), the ratio of C(T) to [CO(2)](aq) was determined by nonlinear parameter estimation, whereas the mass transfer coefficient of CO(2) was determined by the Wilke-Chang correlation. Subsequently, the suitability of the model equations for respiration measurements was examined using residual analysis and the Jarque-Bera hypothesis test. The resulting residuals were found to be random with normal distribution, which proved the adequacy of the application of the model for cell respiration analysis. Hence, dynamic changes in respiration activities could be accurately analyzed using membrane inlet mass spectrometry with the novel calibration method.

Algorithms↗
PubMed1999

Cytochrome p450nor, a novel class of mitochondrial cytochrome P450 involved in nitrate respiration in the fungus Fusarium oxysporum.

Fusarium oxysporum, an imperfect filamentous fungus performs nitrate respiration under limited oxygen. In the respiratory system, Cytochrome P450nor (P450nor) is thought to catalyze the last step; reduction of nitric oxide to nitrous oxide. We examined its intracellular localization using enzymatic, spectroscopic, and immunological analyses to show that P450nor is found in both the mitochondria and the cytosol. Translational fusions between the putative mitochondrial targeting signal on the amino terminus of P450nor and Escherichia coli beta-galactosidase resulted in significant beta-galactosidase activity in the mitochondrial fraction of nitrate-respiring cells, suggesting that one of the isoforms of P450nor (P450norA) is in anaerobic mitochondrion of F. oxysporum and acts as nitric oxide reductase. Furthermore, these findings suggest the involvement of P450nor in nitrate respiration in mitochondria.

Aerobiosis↗
PubMed1997

Very high CO2 reduces photosynthesis, dark respiration and yield in wheat.

Although terrestrial CO2 concentrations, [CO2] are not expected to reach 1000 micromoles mol-1 for many decades, CO2 levels in closed systems such as growth chambers and glasshouses, can easily exceed this concentration. CO2 levels in life support systems in space can exceed 10000 micromoles mol-1 (1%). Here we studied the effect of six CO2 concentrations, from ambient up to 10000 micromoles mol-1, on seed yield, growth and gas exchange of two wheat cultivars (USU-Apogee and Veery-l0). Elevating [CO2] from 350 to 1000 micromoles mol-1 increased seed yield (by 33%), vegetative biomass (by 25%) and number of heads m-2 (by 34%) of wheat plants. Elevation of [CO2] from 1000 to 10000 micromoles mol-1 decreased seed yield (by 37%), harvest index (by 14%), mass per seed (by 9%) and number of seeds per head (by 29%). This very high [CO2] had a negligible, non-significant effect on vegetative biomass, number of heads m-2 and seed mass per head. A sharp decrease in seed yield, harvest index and seeds per head occurred by elevating [CO2] from 1000 to 2600 micromoles mol-1. Further elevation of [CO2] from 2600 to 10000 micromoles mol-1 caused a further but smaller decrease. The effect of CO2 on both wheat cultivars was similar for all growth parameters. Similarly there were no differences in the response to high [CO2] between wheat grown hydroponically in growth chambers under fluorescent lights and those grown in soilless media in a glasshouse under sunlight and high pressure sodium lamps. There was no correlation between high [CO2] and ethylene production by flag leaves or by wheat heads. Therefore, the reduction in seed set in wheat plants is not mediated by ethylene. The photosynthetic rate of whole wheat plants was 8% lower and dark respiration of the wheat heads 25% lower when exposed to 2600 micromoles mol-1 CO2 compared to ambient [CO2]. It is concluded that the reduction in the seed set can be mainly explained by the reduction in the dark respiration in wheat heads, when most of the respiration is functional and is needed for seed development.

Biomass↗
PubMed1994

Dependency of overall fractionation effect of respiration on hemoglobin concentration within blood at rest.

In this study it was investigated in which way varying hemoglobin concentrations within blood influence overall fractionation effect of respiration, meaning a change in composition of isotopic oxygen molecules 16O2 and 16O18O within oxygen transported during entire respiration. Since overall fractionation effect of respiration is known to consist of different fractionating and non-fractionating processes, measuring it under condition of anemia could be useful in relating changes in isotopic compositions of oxygen to limitations of entire oxygen transport caused by one or more of these processes. Experiments were performed on 6 patients suffering from various degrees of anemia of a variety of etiologies and on 6 healthy humans. All test subjects breathed air at rest. Samples from inspiratory and expiratory gas were taken in order to analyse 16O18O/16O2 ratios with the aid of respiratory mass spectrometry. Values of overall fractionation effect decreased with respect to a drop in hemoglobin concentration from 17.6 to 6.6 g/100 ml in terms of a linear relationship (r = 0.79) provided that values of overall fractionation effect were normalized so as to exclude the influence of varying ventilatory conditions. It could be shown that at a value of hemoglobin content of 6.6 g/100 ml, 16O2 was transported in preference to 16O18O with a 0.57% higher rate compared to a value of 0.78% obtained at a hemoglobin concentration of 17.6 g/100 ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Anemia↗
PubMed1993

Origin of the central entrainment of respiration by locomotion facilitated by MK 801 in the decerebrate rabbit.

In order to establish the origin of the central coupling between locomotion and respiration which operates in freely moving mammals during galloping, we sought experimental conditions that readily lead to such a coupling in decerebrate and curarised rabbit preparations. In such preparations, stimulation of the mesencephalic locomotor region (MLR) evokes locomotor activities, recorded from hindlimb muscle nerves, that are rarely totally coordinated with phrenic inspiratory activity. However, low doses (0.2 mg/kg i.v.) of MK 801, a non-competitive NMDA antagonist which has been shown to increase the activity of the spinal locomotion generators (Fenaux et al. 1991), dramatically enhanced this coupling during MLR stimulation in most experiments: 1/1 coupling was dominant but 2/1 and 3/1 couplings (i.e. two or three locomotor cycles per respiratory cycle) were also obtained. Compared with spontaneous respiratory activity, which was apneustic under these conditions, the respiratory period was drastically decreased during coupling. However, a further transection of the spinal cord at the C6 or C7 level, which isolated the spinal locomotion generators from the supraspinal levels, totally suppressed this reduction of the inspiratory period during MLR stimulation in the presence of MK 801. In experiments where locomotor activity was simultaneously recorded at forelimb and hindlimb levels, the 1/1 evoked locomotor-respiratory coupling remained after the lumbar cord had been isolated by L1 spinal transection. The present data do show that intact spinal mechanisms are required for entrainment to occur. They suggest either tha a common supraspinal drive cannot entrain locomotion and respiration when being depressed, or that respiration is entrained at the locomotor rate by the spinal locomotion generators.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

[Motor rhythms synchronous with respiration in the decerebration syndrome of man].

Rhythmical somatomotor discharges in the EMG from arms and legs are recorded together with the respiration in decerebrated patients. The rhythms of 7-18/min are synchronous with respiration. The slow activations of 0.3-0.8/min are related to periods of acceleration with higher amplitudes of respiration. The quick rhythms above 2/min correlate with single respiratory movements. They are interpreted as a phenomenon of disinhibition of lower brain stem structures.

Adult↗
PubMed1980

Naloxone increases carbon dioxide stimulated respiration in the rabbit.

1. The effects were studied of morphine and naloxone on the respiratory minute volume and the minute volume stimulated by carbon dioxide in the anaesthetized rabbit. 2. The respiratory minute volume is reduced by morphine (2 mg/kg) to about 60% of control. The effect of morphine is abolished by naloxone (5 mg/kg); the minute volume depressed by morphine transiently becomes larger after naloxone than prior to morphine. Also the minute volume stimulated by carbon dioxide becomes larger after naloxone than that prior to the period of depression produced by morphine. 3. Naloxone (0.5 mg and 5 mg/kg i.v.) enhances the sensitivity of respiration to carbon dioxide by about 21% and 28%, respectively. 0.5 mg/kg naloxone itself had no influence, 5 mg/kg for about 5 min increases basal respiratory minute volume. 4. It is assumed that endogenous opiates modulate respiration and, like exogenously administered opiates, reduce the sensitivity of respiration to carbon dioxide. 5. The hypothesis is discussed that endogenous opiates are involved in regulation of biological functions which are known to be inhibited by opiates and which belong to the "protective system" postulated by O. Schaumann.

Animals↗
PubMed1976

The effect of respiration on the monitoring of stroke volume and cardiac output by the electrical impedance technique.

In six volunteers (5 male, 1 female) it has been shown that normal respiration made no statistical difference to the estimates of the mean stroke volume and the mean cardiac output as determined by the electrical impedance method of Kubicek et al, (1966). The coefficient of variation was usually increased by respiration. The use of those stroke volumes which occur only at end-expiration was not shown to yield a greater reproducibility with 3 other male volunteers. In the female subject it was found that the use of a digital averager triggered from the preceding R-wave of the ECG gave values for the mean stroke volume and cardiac output which were always lower than the conventional mean values obtained from a number of strokes. The expense of either of these approaches does not appear to be justified as a means of compensating for the effects of normal respiration on the impedance dZ/dt waveform.

Adult↗
PubMed1985

Organization of inputs to motoneurons during fictive respiration in the isolated lamprey brain.

The intracellular activity of motoneurons during 'fictive' respiration in the isolated lamprey brain was investigated. In association with each respiratory cycle three distinct PSP phases were observed: an early, low amplitude EPSP phase; a large, brief EPSP phase that drove action potentials; and a subsequent IPSP phase. Selective midline and trigeminal lesions, and trigeminal stimulation, demonstrated that the large excitatory and inhibitory phases were generated by a previously described pair of central pattern generators located in the trigeminal region of the medulla. Lesion studies further showed that the low amplitude excitatory input could be produced independently of the trigeminal pacemakers, near the region of the medulla that contains the respiratory motoneurons. In addition to 'normal' fictive respiration, the isolated brain was found to produce several variations of the respiratory pattern. These motor programs, 'coughs', 'arousal breathing', and 'weak breathing', were distinguished from the normal respiratory pattern by their much longer burst durations, distinctive underlying synaptic input, and separate coordinating mechanism. Activity similar to these motor programs could be independently produced by the caudal medulla after both trigeminal central pattern generators had been removed. Lesion studies, and the observation that respiratory-related neural activity ceased in the trigeminal region during the production of these long-duration programs, suggest that the caudal medulla also contains paired central pattern generators involved in lamprey respiration.

Animals↗
PubMed1995

Simulation of mechanical respiration using a multicompartment model for ventilation mechanics and gas exchange.

The mechanical respiration of intubated patients is a process which is influenced by many parameters and, through its many interactions, is extremely complex. Taken by itself the logical analysis of this complexity is extraordinarily difficult and leads very often to false conclusions. For that reason computer simulation of complex systems by means of the computer is an important tool in the analysis of these processes. Required is a model which describes the actual behavior of the system. However, it should not be overlooked that a model always describes only a portion of reality. Models having exclusively to do with ventilation mechanics or with gas exchange cannot simulate the interactions between the two. To accomplish this purpose, an improved model is necessary, including both partial processes and thereby capturing the complexity of the system. Accordingly, both ventilation mechanics and gas exchange have been integrated equally into the newly developed model for the simulation program Simu Vent. The core of the program builds a functional multicompartment model of the lungs and considers the partial processes ventilation mechanics, gas transport, gas mixing and gas exchange. Further considered are the respirator, blood circulation and peripheral compartments. The program runs under a graphical user interface, allowing its easy use. Responsible for this ease is the user's ability to interact with the program while simulation is in progress and the specially designed graphic screen mask. Comparing measured with simulated values demonstrated that the measured curve can be simulated with minimal error. Furthermore, the multicompartment model describes disruptions in distribution. Simu Vent's application is especially well advised in the description and analysis of the theoretical fundamentals of mechanical respiration. This aspect is meaningful above all in education and research, rendering these two the model's main areas of use.

Computer Simulation↗
PubMed1976

[Pulmonary changes in cranio-cerebral injuries and respiration with high oxygen concentrations].

In 131 cases of craniocerebral trauma it was shown in what respect definite changes in the lungs, demonstrated by clinical course, radiographs and blood gas analyses, occurred in proportion to the severity of the trauma. The causes of these changes were considered and the possibility of complicating the course of the illness by administering oxygen in high concentrations was investigated. In 98 patients was an indication for treatment with a respirator. 41 patients were so treated for longer than 5 days (mean 17.7 days). The need for respirator treatment rose with the increasing severity of the trauma. Frequency and severity of tracheobronchial aspiration increased in proportion to the depth of unconsciousness. It occurred in 50-60% of cases with severe trauma. Minor pulmonary lesions developed in 13% of those patients who only had minor disturbances of consciousness. Patients who had aspirated had lower arterial oxygen tensions than those who had not aspirated. In a high percentage of cases considerable improvement could be achieved, despite lung changes. In patients treated with the respirator mean inspiratory oxygen concentrations of 75% were necessary to achieve arterial oxygen tensions of 150-200 mm Hg. No evidence of oxygen toxicity was found, despite long periods of treatment with high oxygen concentrations. Very often cases of craniocerebral injury are followed both by tracheobronchial aspiration, causing lung damage, hypoxia and acidosis, and by disturbances of coagulation. These disorders are to be considered as most important, each needing specific therapy.

Brain Injuries↗