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Biomedical subjects

A S Rebuck

Publications and source records attributed to A S Rebuck.

At least 37 records · Page 2Linked to original sources
PubMed1991

Emergency room care of asthmatics: a comparison between Auckland and Toronto.

We compared emergency room visits for the treatment of asthma in two large downtown teaching hospitals: one in Auckland, New Zealand and one in Toronto, Canada. We wished to determine whether the differences in asthma mortality between New Zealand and Canada were reflected in different patterns of emergency room use or physician management. Emergency room use during the past decade was enumerated in both hospitals, and charts containing the sole diagnosis of asthma were reviewed in detail for a defined study period in 1986. In both Toronto and Auckland, the number of emergency visits for asthma had increased significantly in the past decade (P less than .015 but the rate of rise was significantly higher in Auckland (P less than .05). In Auckland, 27% of asthmatics were admitted whereas in Toronto significantly fewer (16%) were admitted (P less than .0005). Objective measures of pulmonary function were documented more frequently by emergency room physicians in New Zealand than in Canada (90% versus 48%; P less than .0005). Pulmonary function measurement was primarily by peak flow meter in Auckland and most commonly by spirometer in Toronto so that pulmonary function measurements could not be compared directly between centers. In both centers, however, admitted patients had significantly lower pulmonary function indices than discharged patients. In New Zealand, mean peak flow was 38% of the predicted value among all asthmatics assessed; in Toronto, mean FEV1 was 47% of predicted. In Toronto, pulmonary function measurements were most likely to be missing among presumably healthier discharged patients. Pulse rate, respiratory rate, and pulsus paradoxus were documented more consistently in Auckland than in Toronto.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

A 3-month evaluation of the efficacy of nedocromil sodium in asthma: a randomized, double-blind, placebo-controlled trial of nedocromil sodium conducted by a Canadian multicenter study group.

Nedocromil sodium is a pyranoquinoline dicarboxylic acid derivative, formulated in a metered-dose inhaler. Because nedocromil sodium has in vitro and in vivo anti-inflammatory properties, it was evaluated in a group of steroid-dependent patients with asthma to observe how well it might be tolerated and for evidence of any beneficial effects. In a double-blind, group-comparative study, 127 patients received nedocromil sodium and 61 received placebo, administered as two puffs of 2 mg, four times per day, for 12 weeks. Ten patients developed adverse reactions, seven receiving active drug and three patients receiving placebo. Two patients of each group withdrew because of worsening asthma. Despite selecting patients whose asthma was stable, when they were receiving established therapeutic regimens that included steroids and bronchodilators, it was found that diary-card symptom scores, morning and evening peak expiratory flow rate values, and inhaled beta-agonist usage all demonstrated slight but significant benefit with addition of nedocromil sodium. It is concluded that the inhaled, anti-inflammatory agent, nedocromil sodium, may be added to asthma-treatment regimens with the reasonable expectation of further modest symptomatic benefit.

Adult↗
PubMed1990

Ventilatory responses to hypercapnia and hypoxia in patients with eucapnic morbid obesity before and after weight loss.

1. To examine the relationship between eucapnic morbid obesity and ventilatory responsiveness to chemical stimuli, we measured hypercapnic and hypoxic ventilatory responses in 29 patients (26 women, three men) before and 3-6 months after gastroplasty. No subject demonstrated resting awake hypercapnia and non suffered from sleep-disordered breathing. 2. Mean weight fell significantly (122.8 +/- 21.4 vs 102.2 +/- 22.8 kg, P less than 0.0001) and functional residual capacity rose slightly but significantly (1.94 +/- 0.58 vs 2.18 +/- 0.64 litres; P less than 0.05) after weight loss. 3. The hypercapnic ventilatory response slope fell significantly after weight loss (2.88 +/- 2.27 vs 2.24 +/- 1.06 litres min-1 mmHg-1, P less than 0.05) with a significant shift of the ventilatory response curve to the right. There were no statistically significant changes in the patterns of ventilatory response. 4. In addition, isocapnic hypoxic ventilatory response slopes, measured at two levels of carbon dioxide partial pressure, fell significantly after weight loss. These changes were accompanied by significant shifts of the ventilatory response curves to the left, such that, for a given oxygen saturation, mean ventilation was significantly lower in the less obese state. Similarly to hypercapnic responses, there were no statistically significant changes in ventilatory pattern despite the changes in overall ventilatory response. 5. We conclude that ventilatory responsiveness to chemical stimuli is increased in obese subjects who maintain adequate alveolar ventilation while awake.

Adult↗
PubMed1990

Effects of oxygen withdrawal on catecholamine release in patients on home oxygen therapy.

1. Long-term oxygen therapy in appropriate patients prolongs survival and corrects neuropsychological function. Some tests of mental function paradoxically improve during short periods of oxygen withdrawal in patients on long-term oxygen therapy, although the mechanism of this response is unknown. 2. To evaluate the effects of transient hypoxaemia on plasma adrenaline and noradrenaline levels, we studied eight oxygen-dependent patients who underwent either a 4 h period of oxygen withdrawal or their routine therapy, in a randomized, blinded fashion, on 2 separate days. 3. Plasma noradrenaline did not differ at baseline between study days. During normoxic conditions, plasma noradrenaline levels did not increase significantly with time. By contrast, under hypoxic conditions, plasma levels of noradrenaline rose significantly from 0 to 4 h (P less than 0.05). The magnitude of the noradrenaline response was correlated with baseline noradrenaline such that subjects with the highest resting levels had the largest increase during hypoxia (r = 0.95, P less than 0.001). 4. Plasma adrenaline did not differ at baseline between study days and there were no significant effects of hypoxia on plasma adrenaline levels. 5. We conclude that the sympathetic nervous system, but not the adrenal medulla, is stimulated in chronically oxygen-dependent subjects made acutely hypoxaemic. The magnitude of this stimulation appears to be related to the state of sympathetic nervous system activity at baseline. Improvement in some tests of mental function during transient periods of oxygen withdrawal may be due to non-specific arousal caused by a catecholamine surge.

Aged↗
PubMed1990

Respiratory rate during acute asthma.

Asthmatic patients hyperventilate during acute attacks, but controversy persists as to whether they breathe rapidly, deeply or both. We monitored respiratory rate under the three following conditions: (1) asthma treated in the emergency room; (2) airways obstruction provoked by methacholine inhalation; and (3) airways obstruction provoked by exercise. In 47 acutely ill asthmatic patients, respiratory rate was higher than in 42 nonasthmatic control patients in the emergency room. Pretreatment respiratory rate correlated with peak expiratory flow rate and forced expired volume in one second. In 17 asthmatic patients and 16 healthy volunteers, breathing pattern was monitored by respiratory inductance plethysmography. Methacholine inhalation and exercise provoked significant airways obstruction in asthmatic patients but not in control subjects. In asthmatic patients, minute ventilation and tidal volume increased above that of control subjects following methacholine and exercise, but the rate was no higher than in control subjects. We conclude that the respiratory rate is increased in naturally occurring asthma, but not when acute airways obstruction is induced transiently in the laboratory. In the former setting, the respiratory rate is correlated with spirometric measures of airflow obstruction, but the weakness of the correlation does not allow the respiratory rate to be used as a substitute for spirometry.

Acute Disease↗
PubMed1990

An evaluation of flow-volume curves as a screening test for obstructive sleep apnea.

We examined flow-volume curves for their potential as screening tests for obstructive sleep apnea (OSA) in 401 patients referred for investigation of snoring. In all patients, we performed nocturnal polysomnography, maximum inspiratory and maximum expiratory flow-volume curves. The curves were examined for two features: 1) presence of flow oscillations (the "saw-tooth" sign), and 2) changes in their configuration that might suggest upper airway obstruction as documented by the expiratory/inspiratory flow ratios calculated at 50 and 75 percent of exhaled vital capacity (FR50 and FR25, respectively). Based on the results of nocturnal polysomnography, the patients were stratified according to severity into apnea groups, and the flow ratios and flow oscillations were compared among these groups. We found that neither the FR50 nor FR25 were significantly different among the groups. Inspiratory and expiratory flow oscillations were seen infrequently (32 patients) and tended to occur in patients with more severe sleep apnea. Neither the flow ratios nor the flow oscillations had good predictive values for snoring or sleep apnea. The sensitivity of the flow volume curve abnormalities ranged between 0 and 14 percent, but the specificity was high, ranging between 93 and 95 percent. We conclude that because of low sensitivity, flow-volume loops are not a useful screening test for the diagnosis of OSA in snoring patients.

Adult↗
PubMed1990

Cyclosporine and chronic sarcoidosis.

Two patients with progressive sarcoidosis who had poor responses and side effects from corticosteroid therapy were treated with cyclosporine. Cyclosporine suppressed conventional markers of inflammation and there was clinical improvement in one patient, but the disease recurred when therapy was discontinued. The second patient who had diabetes mellitus developed unstable glucose metabolism when given cyclosporine. This unstable diabetes mellitus together with side effects of nausea and vomiting resulted in weight loss and inadequate serum therapeutic levels that was associated with a poor therapeutic response to the cyclosporine. The major side effects in both patients were headache and gastrointestinal symptoms, but there was no renal dysfunction. We conclude that while corticosteroids remain the mainstay of sarcoid therapy, when these drugs have not been successful for the skin manifestations of the disease, a trial of cyclosporine may be justified.

Adult↗
PubMed1990

Ventilatory effects of nasal continuous positive airway pressure.

Nasal continuous positive airway pressure (nCPAP) improved arterial oxygenation in patients with sleep apnoea as well as those with acute pulmonary processes such as Pneumocystis carinii pneumonia. Despite an expanding pool of clinical information, little if any attempt seems to have been made to see whether nCPAP alters ventilatory patterns. The effect of nCPAP was assessed by respiratory inductance plethysmography in 14 healthy males. nCPAP reduced respiratory rate (14.3 +/- 1.47 to 9.7 +/- 1.98, p less than 0.0001) but increased tidal volume (0.483 +/- 0.090 to 0.602 +/- 0.140 l, p = 0.01). Accordingly, minute ventilation decreased (6.91 +/- 1.20 to 5.64 +/- 0.93 l.min-1, p = 0.0002). Duty cycle (TI/TTOT) decreased from 0.43 +/- 0.04 to 0.35 +/- 0.05 s during nCPAP (p less than 0.0001). Mean inspiratory time and mean expiratory time increased with nCPAP (1.79 +/- 0.19 to 2.20 +/- 0.41 and 2.44 +/- 0.38 to 4.27 +/- 1.07 s, respectively, p less than 0.02), but there were no significant changes in mean inspiratory flow rate or partitioning of rib cage and abdominal/diaphragmatic contributions to tidal volume. We conclude that nCPAP effects ventilatory pattern in a manner similar to that described for expiratory threshold loading; that is, by decreasing respiratory frequency and minute ventilation. nCPAP does not appear to stimulate healthy subjects to increase their level of ventilation.

Adult↗
PubMed1989

Tracheal hysteresis in sleep apnea.

The collapsibility of pharyngeal walls, characteristic of patients with obstructive sleep apnea, likely results from reduced tone of the pharyngeal muscles. This reduction in the upper airway muscle tone may not end at the pharynx but may extend further distally, e.g., into the trachea. Because tracheal tone cannot be measured directly in conscious humans, we inferred the tone from the relative hysteresis of the tracheal area compared with the lung. Relative hysteresis was measured by plotting the cross-sectional area of a tracheal segment obtained by the acoustic reflection technique vs. lung volume. All measurements were performed during wakefulness. We found that in 42 patients with obstructive sleep apnea (apnea/hypopnea index greater than 10), relative hysteresis of the proximal trachea was predominantly clockwise, i.e., smaller than that of the lung parenchyma; in the 33 nonapneic patients (apnea/hypopnea index less than or equal to 10), it was predominantly counter-clockwise, i.e., larger than that of the lung parenchyma. For the distal trachea all patients, apneic and nonapneic, had similar, clockwise, relative hysteresis. We conclude that reduction in the upper airway muscle tone in patients with obstructive sleep apnea extends into the trachea.

Adolescent↗
PubMed1989

Expiratory glottic widening in asthmatic subjects during exercise-induced bronchoconstriction.

Glottic caliber is modulated in a way that optimizes the airway resistance and the work of breathing. The midexpiratory glottic narrowing that normally occurs during tidal breathing is enhanced during histamine- or methacholine-induced airway narrowing. Exercise is associated with increased ventilatory demand and midexpiratory glottic widening in healthy subjects. However, the relative contribution of glottic aperture to airflow limitation during exercise-induced asthma is unknown. Consequently, we used the acoustic reflection technique to test whether a decrease in midexpiratory glottic size occurred also during exercise-induced bronchoconstriction in seven asthmatic subjects. Exercise resulted in a 38 +/- 16% (SD) fall in FEV1 from the baseline value (p less than 0.001) and a significant increase in midexpiratory glottic cross-sectional area from 1.89 +/- 0.45 cm2 before to 2.36 +/- 0.71 cm2 during bronchoconstriction (p less than 0.05). This midexpiratory glottic widening was also associated with increased tidal flow rates. We conclude that in marked contrast to airway obstruction induced by histamine or methacholine, exercise-induced asthma is associated with midexpiratory glottic widening, which occurs concomitantly with a decrease in lower airway caliber. We suggest that modulation of glottic aperture during acute asthma is heterogeneous and depends partly on the initiating stimulus.

Adult↗
PubMed1989

Cardiovascular response to acute airway obstruction and hypoxia.

We wished to evaluate the role of hypoxia in the production of cardiovascular manifestations of acute airway obstruction. We monitored blood pressure, electrocardiogram, and radionuclide ejection fraction in 14 healthy volunteers on exposure to four experimental conditions: expiratory resistive loading while breathing room air (RAL), expiratory resistive loading while hypoxic (HL), hypoxia alone (H), and expiratory resistive loading while voluntarily hyperventilating in a pattern similar to HL trials (VL). Mean respiratory-related oscillation in systolic blood pressure (pulsus paradoxus) increased significantly under each experimental condition compared with those at baseline (2 +/- 2.3 mm Hg): for RAL, 21 +/- 8.4 mm Hg; for HL, 34 +/- 16.3 mm Hg; for H, 10 +/- 5.4 mm Hg; for VL 26 +/- 13.4 mm Hg. Pulsus paradoxus was significantly greater under conditions of moderate hypoxia (saturation, 80%) than of mild hypoxia (saturation, 90%). Electrocardiographic changes were more marked under HL and H conditions than under RAL and VL conditions. HL induced changes in blood pressure and frontal QRS axis that were qualitatively similar to those seen in naturally occurring asthma. Radionuclide ejection fraction showed no dramatic change with any experimental condition. We conclude that hypoxia magnifies the cardiovascular changes induced by acute expiratory resistive loads and may contribute to the degree of pulsus paradoxus seen in severe asthma.

Acute Disease↗
PubMed1989

Management of chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is characterised by insidiously progressive airflow limitation. The necessarily multifactorial management programme should include smoking cessation, prevention of infections, bronchodilator and steroid therapy, supplemental oxygen, physical therapy, pulmonary rehabilitation programmes, psychosocial support and treatment of concomitant disease. There have been many advances in medical therapy but some of the notorious controversies remain. New sympathomimetic agents and methylxanthines, as well as the availability of inhaled anticholinergic medications free of toxicity, have led to improvement in symptoms and complications related to COPD. There is a clear place for the judicious use of systemic steroids.

Administration, Inhalation↗
PubMed1989

Treatment of the recalcitrant asthmatic.

Treatment of "difficult" asthma requires good doctor-patient communication, patient education, and attention to precipitating factors as well as an aggressive drug regimen. Specific medications include inhaled sympathomimetic and anti-cholinergic bronchodilators, inhaled, oral and/or intravenous corticosteroids and, in certain circumstances, mast cell stabilizing drugs such as cromolyn sodium. The use of systemic theophyllines is currently undergoing critical reevaluation. There have been a number of recent developments in the search for steroid-sparing agents and drugs that inhibit inflammatory mediators felt to be important in the pathophysiology of asthma. Most of these drugs are still undergoing evaluation in multicentre clinical trials. The newer antiinflammatory agents, methotrexate and gold, should probably not be used on a routine basis except as part of randomized, ethically approved clinical trials.

Administration, Inhalation↗
PubMed1989

Acute asthma: observations regarding the management of a pediatric emergency room.

Because inadequate assessment and inappropriate treatment of acute asthma have been implicated as contributing factors in morbidity and even deaths, the management of acute asthma, as practiced in an emergency room, were reviewed. The study population comprised 1,864 children (mean age 5.6 years; 65% boys) who attended the emergency room with acute asthma on 3,358 occasions during a 16-month period. Visits occurred more commonly in winter and usually in the evenings; 93% were self-referred and the mean duration of symptoms was 41 hours. Most acute episodes were associated with infection. Although chest auscultation, heart rate, and respiratory rate were recorded during the majority of visits, evidence that pulsus paradoxus had been measured could be found for only 1% of visits. Results of lung function and blood gas values were rarely recorded, but chest radiographs were obtained in 18% of visits. Drugs used in the emergency room included beta 2-agonists (93% of visits), theophylline (16%), and systemic steroids (4%), but no child received anticholinergic therapy. In 26% of patient visits, admission to hospital occurred; one patient died. The erratic fashion in which asthma severity appears to have been assessed and the failure to document whether lung function had been measured are causes for concern. The surprisingly high hospitalization rate may have been avoided if bronchodilators and corticosteroids had not been underused in the emergency room.

Acute Disease↗
PubMed1988

Nasal continuous positive airway pressure in Pneumocystis carinii pneumonia.

10 cm H2O of nasal continuous positive airway pressure (CPAP) was applied in nine subjects with Pneumocystis carinii pneumonia and the acquired immunodeficiency syndrome, all of whom had presented with bilateral pulmonary infiltrates and hypoxaemia. The procedure was tolerated well by eight patients and none of the nine had complications. 20 minutes of nasal CPAP without supplemental oxygen increased mean PaO2 from 55.9 to 68.4 mm Hg and decreased the calculated alveolar-arterial oxygen gradient from 48.3 to 34.3 mm Hg. In one patient who was breathing oxygen at 4 litres per minute, PaO2 increased by 35 mm Hg. Nasal CPAP could be a useful method for augmenting oxygenation in P carinii pneumonia.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Comparison of glottic areas measured by acoustic reflections vs. computerized tomography.

We compared measurements of glottic area obtained by acoustic reflection technique with anatomically equivalent area measured from computerized tomographic (CT) scans of the neck in 11 subjects with glottic pathology. Both measurements were performed in the supine position during tidal breathing at functional residual capacity. We found excellent agreement in glottic areas obtained by both methods: the mean (+/- SD) values were 1.8 +/- 0.8 cm2 for the acoustic method and 1.7 +/- 0.9 cm2 for the CT method. Linear regression analysis revealed the following relationship between the area measured by acoustic technique (AAC) and that measured by CT (ACT): AAC = 0.81.ACT + 0.36. There was a significant correlation between the two measurements of glottic area (r = 0.95, P less than 0.0001). We conclude that the acoustic reflection technique may be used reliably in clinical and physiological studies concerned with glottic geometry.

Acoustics↗
PubMed1988

Assessment of maximal expiratory pressure in healthy adults.

Maximal static expiratory pressure developed at the mouth (PEmax) provides a useful clinical index of expiratory muscle function; however, the range of normal values among laboratories shows considerable variation. We examined the hypothesis that the wide variability could be attributable to the differences in technique among laboratories. We measured PEmax at functional residual capacity (PEmax FRC) in 28 healthy subjects using the following five techniques: 1) using a scuba-type mouthpiece with the cheeks supported by the hands ("hands on"), 2) without supporting the cheeks ("no hands"), 3) using a rigid, circular mouthpiece (2.8 cm ID, "tube"), 4) using the scuba-type mouthpiece but with the cheeks supported by an observer ("other hands"), and 5) using a large-bore circular mouthpiece (4.1 cm ID, "new tube"). Mean PEmax FRC obtained with hands on was significantly higher than no-hands and tube methods. PEmax FRC values obtained by the other-hands and new-tube maneuvers were similar to the hands-on maneuver. We conclude that the technique used to measure PEmax FRC can significantly affect the results and suggest that it should be measured using a large-bore circular mouthpiece or a scuba-diving mouthpiece with the cheeks supported.

Adult↗