Breathing pattern analysis.
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Critical Care↗
Biomedical subjects
M J Tobin
Publications and source records attributed to M J Tobin.
In vivo X-ray fluorescence of lead in bone using K X-ray excitation with 109Cd sources: radiation dosimetry studies.
Independent experiments have been performed at two centers, to evaluate the dosimetric properties of their respective 109Cd K X-ray fluorescence (XRF) bone lead measurement systems. Measurements were made of the dose to several points on the skin on the lower leg, at the surface of the tibia, in the red marrow tibia cavity, at the midcalf, and in the abdominal region occupied by the conceptus. Overall agreement between the two data sets was found. Similarities and differences are discussed. The effective dose values for an in vivo measurement of tibia lead concentration in 1-, 5-, and 10-year-old and adult subjects were calculated from one data set to be 1100, 420, 190, and 34/38 (male/female) nSv, respectively, for an in vivo median precision (one standard deviation) of 4.9 micrograms Pb (g bone mineral)-1 for a 30-min adult measurement.
Adult↗
The effect of inspiratory muscle fatigue on breathing pattern and ventilatory response to CO2.
1. The effects of inducing inspiratory muscle fatigue on the subsequent breathing pattern were examined during resting unstimulated breathing and during CO2 rebreathing. In addition, we examined whether induction of inspiratory muscle fatigue alters CO2 responsiveness. 2. Global inspiratory muscle fatigue and diaphragmatic fatigue were achieved by having subjects breathe against an inspiratory resistive load while generating a predetermined fraction of either their maximal mouth pressure or maximal transdiaphragmatic pressure until they were unable to generate the target pressure. 3. Induction of inspiratory muscle fatigue had no effect on the subsequent breathing pattern during either unstimulated breathing or during CO2 rebreathing. 4. Following induction of inspiratory muscle fatigue, the slope of the ventilatory response to CO2 was significantly decreased from 18.8 +/- 3.3 during control to 13.8 +/- 2.1 l min-1 (% end-tidal CO2 concentration)-1 with fatigue (P < 0.02).
Adult↗
The effect of hyperinflation on rib cage-abdominal motion.
Abnormalities of rib cage-abdominal motion are common in patients with chronic obstructive pulmonary disease (COPD), but the basis of the abnormal motion has not been completely determined. Although airway obstruction has been shown to be a major factor in causing abnormal chest wall motion, the effect of hyperinflation (which has numerous adverse effects on respiratory muscle function) has not been systematically examined. We induced graded levels of hyperinflation in six healthy volunteers using continuous positive airway pressure (CPAP) levels of 10, 20, and 30 cm H2O. Chest wall motion was measured by a calibrated inductive plethysmograph. Rib cage-abdominal asynchrony and paradox were quantitated by the Konno-Mead method of analysis. CPAP levels of 10, 20, and 20 cm H2O produced increases in end-expiratory lung volume of 0.98 +/- 0.14 (SE), 1.90 +/- 0.31, and 2.42 +/- 0.37 L, respectively (p < 0.0001). This corresponded to an increase in the ratio of functional residual capacity to predicted total lung capacity from 0.38 +/- 0.08 at baseline to 0.74 +/- 0.14 at 30 cm H2O CPAP-comparable to that seen in patients with COPD. Hyperinflation induced an increase in inspiratory abdominal paradox, 1.0 +/- 0.7% at baseline versus 3.6 +/- 1.7% at 30 cm H2O (p < 0.05), but this is unlikely to be clinically significant. A significant increase in asynchrony or rib cage paradox did not develop with hyperinflation. In conclusion, the primary factor contributing to abnormal chest wall motion in patients with COPD is likely to be increased airway resistance, and hyperinflation makes only a minor contribution.
Abdomen↗
Aspiration injury due to polyacrylamide.
Acute lung injury secondary to aspiration of polyacrylamide, a synthetic polymer used widely in industry, has not been previously described in man or animal. We report the case of a 26-year-old man who aspirated polyacrylamide gel while cleaning it out of a tank truck. Subsequently, severe airway obstruction and lung parenchymal damage developed, and the patient died. At autopsy, numerous polyacrylamide particles were found in the lungs, along with extensive bronchiolar and alveolar damage.
Accidents, Occupational↗
The use of mechanical ventilation via a nasal mask in myotonic dystrophy.
A 36-year-old woman with myotonic dystrophy presented with generalized weakness and daytime somnolence. Arterial blood gas analysis revealed significant hypoxemia and hypercapnia, and a polysomnogram revealed additional oxygen desaturation during sleep. For nocturnal ventilatory assistance, the patient received positive-pressure ventilation via a nasal mask. This mode of ventilation produced marked improvement in the patient's nocturnal hypoxemia.
Adult↗
A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation.
BACKGROUND: The traditional predictors of the outcome of weaning from mechanical ventilation--minute ventilation (VE) and maximal inspiratory pressure (Plmax)--are frequently inaccurate. We developed two new indexes: the first quantitates rapid shallow breathing as the ratio of respiratory frequency to tidal volume (f/VT), and the second is termed CROP, because it integrates thoracic compliance, respiratory rate, arterial oxygenation, and Plmax. METHODS: The threshold values for each index that discriminated best between a successful and an unsuccessful outcome of weaning were determined in 36 patients, and the predictive accuracy of these values was then tested prospectively in an additional 64 patients. Sensitivity and specificity were calculated, and the data were also analyzed with receiver-operating-characteristic (ROC) curves, in which the proportions of true positive results and false positive results are plotted against each other for a number of threshold values of an index; the area under the curve reflects the accuracy of the index. RESULTS: Sensitivity was highest for Plmax (1.00), followed closely by the f/VT ratio (0.97). Specificity was highest for the f/VT ratio (0.64) and lowest for Plmax (0.11). The f/VT ratio was the best predictor of successful weaning, and Plmax and the f/VT ratio were the best predictors of failure. The area under the ROC curve for the f/VT ratio (0.89) was larger than that under the curves for the CROP index (0.78, P less than 0.05), Plmax (0.61, P less than 0.001), and VE (0.40, P less than 0.001). CONCLUSIONS: Rapid shallow breathing, as reflected by the f/VT ratio, was the most accurate predictor of failure, and its absence the most accurate predictor of success, in weaning patients from mechanical ventilation.
Arteries↗
Weaning patients from mechanical ventilation. How to avoid difficulty.
The majority of patients can be easily weaned from mechanical ventilation, but a substantial minority pose considerable difficulty. In such cases, the cause of ventilator dependency should be identified and correctable factors should be rectified. An organized plan of management, a team approach, optimal pulmonary and general patient care, and nutritional supplementation are important factors in successful weaning.
Humans↗
Measurement of minute ventilation in ventilator-dependent patients: need for standardization.
OBJECTIVES: a) To determine the variation in methods used to measure minute ventilation (VE) in patients who receive mechanical ventilation; b) to determine the effect of supplemental oxygen on VE, respiratory rate (RR), and tidal volume (VT) measurements. DESIGN: Telephone survey of hospitals, and a randomized control trial. SETTING: Medical and surgical ICUs in a university hospital. PATIENTS: Thirty-three patients who had required mechanical ventilation because of the inability to sustain adequate spontaneous ventilation. All patients were considered ready to undergo a weaning trial by their physicians. INTERVENTIONS: Spontaneous VE, RR, VT, and SaO2 were measured both in the presence and absence of supplemental oxygen; measurements were obtained in a randomized manner. MEASUREMENTS AND MAIN RESULTS: a) In a telephone survey of hospitals throughout the country, we found that the measurement of VE is variably obtained during room air breathing or in the presence of supplemental oxygen. b) Measurements of VE increased from 11.0 +/- 0.8 L/min while patients received supplemental oxygen to 13.5 +/- 1.1 L/min while patients breathed room air (p less than .001). Of 15 patients who had a VE less than 10 L/min while receiving supplemental oxygen, seven developed a value greater than 10 L/min while breathing room air; thus, a weaning trial might have been inappropriately deferred in these patients. c) Mean SaO2 decreased from 95.0 +/- 0.6% while breathing supplemental oxygen to 90.2 +/- 1.1% while breathing room air (p less than .001). CONCLUSIONS: Measurements of VE in patients being considered for a weaning trial can result in significant oxygen desaturation if obtained during room air breathing, and the values obtained can significantly overestimate the patient's true ventilatory requirements, since most patients receive supplemental oxygen during a weaning trial. Standardized methods of measuring VE in critically ill patients need to be developed.
Humans↗
Effect of alterations in mental activity on the breathing pattern in healthy subjects.
The overall output from the respiratory centers is regulated by an automatic metabolic control system in the brainstem and by higher neural centers under direct voluntary control. An understanding of the constancy with which respiration is controlled can be obtained by measuring the breath-to-breath variability in breathing pattern. We hypothesized that different forms of mental activity would alter the variability of breathing pattern. To test this hypothesis, we measured breathing pattern on a breath-by-breath basis during resting wakefulness and during four conditions of altered mental activity. Measurements were obtained with a calibrated respiratory inductive plethysmograph, and variability was assessed by calculations of the coefficients of variation. We also examined the effect of the altered states of mental activity on the mean values of the breathing pattern components. We found that noxious stimulation increased the variability of all the breathing pattern indices, audiovisual stimulation tended to increase the variability of tidal volume (VT), and mental arithmetic had no effect. In addition, the variability of breathing pattern was increased during rapid eye movement sleep and decreased during Stage IV sleep. The variability of VT and expiratory time were greater than that of inspiratory time (TI) across the different states of mental activity. Significant correlations were observed between VT and TI and between VT and frequency (f) during Stage IV sleep. With regards to the mean values, mental arithmetic, audiovisual stimulation, and noxious stimulation all increased minute ventilation and mean inspiratory flow.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Respiratory monitoring.
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Blood Gas Analysis↗
Dyspnea. Pathophysiologic basis, clinical presentation, and management.
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Dyspnea↗
Apneustic breathing. A characteristic feature of brainstem compression in achondroplasia?
We have observed apneustic breathing in five patients with achondroplasia. In contrast to experimental models of apneusis, these patients appeared to have intact vagal function and no evidence of pontine disease. However, all our patients displayed clinical, structural, and electrophysiologic features of cervicomedullary compression, a well-recognized complication of achondroplasia. The degree of apneustic breathing was reduced in the majority of our patients following decompressive surgery. Traditional theories on the pathogenesis of apneustic breathing cannot satisfactorily explain the presence of apneustic breathing in our patients. We suggest that cervicomedullary compression may be capable of producing apneustic breathing in the absence of vagal or pneumotaxic center lesions.
Achondroplasia↗
Importance of respiratory rate as an indicator of respiratory dysfunction in patients with cystic fibrosis.
Bedside measurement of respiratory frequency is commonly performed in a cursory manner and judged to be of little clinical importance. However, in a recent study of patients being weaned from mechanical ventilation, we found that tachypnea was quite accurate in predicting an unsuccessful weaning outcome. The present study was undertaken to examine the relationship between nonobtrusive measurements of respiratory frequency, using a calibrated inductive plethysmograph, and detailed measurements of pulmonary function in 11 adult patients with cystic fibrosis of varying severity. Respiratory frequency was increased in the patients with cystic fibrosis compared with a group of healthy control subjects, as was minute ventilation and mean inspiratory flow. Respiratory frequency was a sensitive predictor of respiratory dysfunction, being significantly (p less than 0.05) correlated with airway obstruction (r = 0.76), hyperinflation (r = 0.52), arterial oxygenation (r = -0.59), rib cage-abdominal discoordination (r = 0.54), and maximum ventilation during exercise (r = 0.66). Despite the presence of tachypnea, the patients did not display shallow breathing; indeed, tidal volume was not correlated with any of the above abnormalities. In conclusion, respiratory rate was a useful indicator of respiratory dysfunction in this group of patients with cystic fibrosis.
Adult↗
Reliability of pulse oximetry in titrating supplemental oxygen therapy in ventilator-dependent patients.
Pulse oximetry is widely used in the critical care setting, but few studies have examined its usefulness in clinical decision making. One area where pulse oximetry might be useful is in the titration of fractional inspired O2 concentration (FIO2) in ventilator-dependent patients. Unfortunately, documented guidelines for this use do not exist, and in a survey of directors of intensive care units, we found that they employed a wide range of target O2 saturation (SpO2) values. Consequently, we undertook a study to determine if SpO2 could be reliably substituted for measurements of arterial O2 tension (PaO2) when adjusting FIO2 in ventilator-dependent patients. We examined a number of SpO2 target values in 54 critically ill patients aiming for a PaO2 of greater than or equal to 60 mm Hg, while minimizing the risk of O2 toxicity. In white patients, we found that a SpO2 target of 92 percent was reliable in predicting a satisfactory level of oxygenation. However, in black patients, such a SpO2 reading was commonly associated with significant hypoxemia (PaO2 as low as 49 mm Hg), and a higher SpO2 target, 95 percent, was required. In addition, inaccurate oximetry readings (ie, greater than 4 percent difference between SpO2 and direct SaO2 measurements) were more common in black (27 percent) than in white patients (11 percent, p less than 0.05). In conclusion, a SpO2 target of 92 percent was reliable when titrating supplemental O2 in white patients receiving mechanical ventilation; however, in black patients, such a SpO2 reading was commonly associated with significant hypoxemia, and a higher SpO2 target, 95 percent, was required to ensure a satisfactory level of oxygenation.
Black or African American↗
Respiratory monitoring during mechanical ventilation.
Continuous monitoring of important respiratory indices has the potential for predicting catastrophes and for providing an opportunity for the timely institution of lifesaving measures. Pulmonary gas exchange can be assessed by indices derived from arterial blood gas measurements, but these are limited by their invasive and intermittent nature. Intra-arterial electrodes that provide a continuous recording of blood gases are under development and appear very promising. Specially designed pulmonary artery catheters permit continuous recording of mixed venous O2 saturation, whereas continuous, non-invasive recordings of arterial oxygenation can be obtained with pulse oximetry and transcutaneous electrodes. A satisfactory method of monitoring CO2 tension does not exist. Measurements of respiratory drive can be obtained at the bedside, but their clinical usefulness remains unknown. Assessment of respiratory muscle strength is helpful in determining the need for mechanical ventilation, but a practical method of diagnosing respiratory muscle fatigue remains elusive. Recordings of the airway pressure waveform, calculation of thoracic compliance, and detailed examination of the pattern of breathing are helpful in assessing pulmonary mechanics. Although respiratory monitoring provides much useful information, it does not substitute for careful bedside examination.
Blood Gas Analysis↗
Weaning from mechanical ventilation.
Although the majority of patients can be easily weaned from mechanical ventilation, a substantial minority pose considerable difficulty. These patients account for a disproportionate amount of health care costs, and they pose enormous clinical, economic, and ethical problems. The major determinants of weaning outcome include the adequacy of pulmonary gas exchange, respiratory muscle pump function, and psychological problems. Many of the physiologic indices that have been used to predict weaning outcome are frequently inaccurate. Several techniques of weaning can be used, and there are no data to suggest the superiority of one technique over another. Management of the problem patient should be directed at the underlying cause of ventilator dependency, and an organized plan should be followed.
Humans↗