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Biomedical subjects

A S Rebuck

Publications and source records attributed to A S Rebuck.

At least 55 records · Page 3Linked to original sources
PubMed1988

Influence of phasic afferent information on phrenic neural output during hypercapnia.

We measured the moving time average (MTA) of the phrenic neurogram before and after removal of phasic afferent information from the lungs, chest wall, and oscillations in blood gases by using constant-flow ventilation (CFV). Anesthetized dogs were studied at various levels of steady-state and progressive hypercapnia during spontaneous breathing and during CFV. When steady-state and progressive hypercapnia were compared, the frequency and height of the MTA phrenic neurogram were independent of the rate of induction of hypercapnia during each mode of ventilation. During spontaneous ventilation, the response to hypercapnia comprised mainly an increase in frequency with only a slight increase in the amplitude of the MTA phrenic waveform. During muscular paralysis and CFV, the responses were similar to those observed after vagotomy with mainly an increase in the amplitude and only a small increase in frequency. For both spontaneous breathing and CFV, increases in frequency were achieved mainly by a shortening in expiratory time with the inspiratory time remaining relatively constant. Our data support the concept of a centrally patterned respiratory generator, whose inherent pattern is modified by phasic feedback from peripheral receptors mainly of vagal origin.

Afferent Pathways↗
PubMed1988

Relative hysteresis of the airways and lung parenchyma in normal subjects.

We evaluated the mechanical properties of the airways sequentially from the glottis toward the main bronchi in 10 normal subjects. Plots of airway cross-sectional area vs. lung volume, measured during inspiration and expiration, were used to determine the relative magnitude of the airways vs. parenchymal hysteresis. Airway cross-sectional area was measured by means of the acoustic reflection technique. We found that the hysteresis of the proximal part of the trachea was greater than that of the lung parenchyma, whereas the hysteresis of the distal trachea and subcarinal segments of the airways was smaller than that of the lung parenchyma. The transition zone between the proximal and the more distal airway properties occurred 8-26 cm distal to the glottis. This transition zone was reproducible in its location on repeated testing in each subject but varied among subjects. To the extent that relative hysteresis of the airways depends on bronchomotor tone, our findings suggest that the bronchomotor tone is inhomogeneous, being maximal at the proximal part of the trachea and gradually decreasing toward the more distal trachea and subcarinal airway segments.

Acoustics↗
PubMed1988

Dichotomous airway response to exercise in asthmatic patients.

The extent and location of airway narrowing in asthmatic subjects are usually inferred from measurements of maximal expiratory flow rates and airway resistance. In the present study, we used the acoustic reflection technique to measure the airway cross-sectional area in 14 asthmatic subjects and 8 normal controls before and following treadmill exercise tests. In normal subjects, exercise caused no significant change in FEV1 and bronchial area, but did cause a significant increase in the intrathoracic tracheal area from 2.0 +/- 0.7 cm2 to 3.1 +/- 0.7 cm2 (p less than 0.002). In the asthmatics, exercise was followed by a 37 +/- 15% reduction in forced expiratory volume in 1 s(FEV1), and a 36% decrease in bronchial area from 8.5 +/- 2.8 cm2 to 5.4 +/- 1.1 cm2 (p less than 0.001); however, extra- and intrathoracic tracheal areas increased significantly. These findings provide direct and quantitative evidence that the bronchi are the main site of airway narrowing in exercise-induced asthma, and draw attention to the phenomenon of tracheal dilatation that occurs concomitant with bronchoconstriction in asthmatic patients.

Adult↗
PubMed1987

Immediate and delayed bronchoconstriction after exercise in patients with asthma.

Although an immediate asthmatic response after exercise is known to occur in some patients with asthma, the existence of a delayed asthmatic response after exercise is controversial. Accordingly, we studied 53 patients who had an immediate mean (+/- SD) decrease in forced expiratory volume at one second (FEV1) of 36 +/- 13 percent, which was maximal 13 +/- 12 minutes after the completion of treadmill exercise. Eight of these patients also had a delayed asthmatic response (a 32 +/- 5 percent decrease in FEV1 occurring 5.0 +/- 1.8 hours after exercise). During a control day, on which the FEV1 was measured serially but no exercise was performed, the same delayed asthmatic response was observed in all but one patient. This finding suggests that the delayed asthmatic response observed in these patients after exercise was not specifically related to the performance of exercise. We conclude that in patients who have bronchoconstriction immediately after exercise, a second asthmatic response occurring later after the exercise is uncommon.

Adolescent↗
PubMed1987

Corticosteroids as adjunctive therapy in treatment of Pneumocystis carinii pneumonia in patients with acquired immunodeficiency syndrome.

10 patients with the acquired immunodeficiency syndrome whose respiratory failure due to Pneumocystis carinii pneumonia (PCP) was deteriorating rapidly had 7 days of intravenous methylprednisolone added to their antibiotic regimen. 8 similar patients were treated with antibiotic therapy alone. 9 of the 10 methylprednisolone-treated patients survived their episode of PCP, compared with 2 of the 8 conventionally treated patients. Clinical improvement was evident within 2 days of the start of steroid therapy, and in none of the 10 patients did clinical deterioration or recurrence of PCP occur on cessation of steroid therapy. In 1 steroid-treated patient disseminated herpes zoster developed 2 days after discontinuation of methylprednisolone. Methylprednisolone seems to be a useful adjunctive therapeutic agent for patients with AIDS in whom Pneumocystis carinii is the sole respiratory pathogen.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Asthma: 2. Trends in pharmacologic therapy.

The most reasonable first therapy for ambulatory asthmatic patients is regular use of a selective beta 2-adrenoreceptor agonist administered with a metered-dose inhaler. When asthma is of more than mild severity, a second agent that acts through a different pharmacologic pathway is added. Although theophylline has traditionally been this second agent, recent concerns about its safety have prompted increasing use of inhalational agents such as corticosteroids, anticholinergics and mast cell stabilizers as appropriate second-line therapy. The use of such combination regimens and newer strategies such as high-dose inhaled corticosteroid therapy will reduce the proportion of patients who require systemic corticosteroid therapy for adequate control of asthma. The use of combination inhalational therapy also has a role in the management of asthma in the emergency department, the combination of a nebulized adrenoreceptor agonist and a nebulized anticholinergic being more effective than either agent alone in acute, severe asthma. The role of newer xanthine derivatives, antihistamines, calcium channel blockers and selective anti-inflammatory agents remains investigational.

Adrenal Cortex Hormones↗
PubMed1987

Asthma: 1. Pathophysiologic features and evaluation of severity.

The response of asthmatic airways to irritant stimuli is twofold: bronchoconstriction and airway inflammation. The inevitable mechanical consequence of bronchoconstriction is hyperinflation of the lungs, a phenomenon that produces characteristic clinical and radiologic signs. Hyperinflation helps to maintain airway patency at the expense of increased respiratory muscle work. Airway inflammation accounts in large part for the increased ventilatory drive of asthmatic patients, which results in alveolar hyperventilation and dyspnea. The resultant respiratory alkalosis further compromises tissue oxygen delivery both by cerebral vasoconstriction and by the leftward shift of the oxyhemoglobin dissociation curve. Optimal correction of hypoxia in the hyperventilating asthmatic patient requires delivery of oxygen at a high flow rate. Failure of patients with asthma to respond to simple bronchodilator therapy indicates the presence of continuing inflammatory activity and hence the need for anti-inflammatory therapy and frequency monitoring.

Airway Obstruction↗
PubMed1987

Nebulized anticholinergic and sympathomimetic treatment of asthma and chronic obstructive airways disease in the emergency room.

The effectiveness of nebulized anticholinergic and sympathomimetic regimens was evaluated in a double-blind study of 199 patients with acute airways obstruction. Patients were assigned to one of three treatment regimens according to a randomized schedule: 0.5 mg of ipratropium bromide, 1.25 mg of fenoterol hydrobromide, and 0.5 mg of ipratropium plus 1.25 mg of fenoterol. In 148 patients with acute exacerbations of asthma (mean one-second forced expiratory volume, 1.18 +/- 0.64 liters), all three regimens produced significant improvement in one-second forced expiratory volume (p less than 0.001). The greatest improvement followed treatment with the ipratropium-fenoterol combination (0.53 +/- 0.40 liters at 45 minutes; 0.57 +/- 0.51 liters at 90 minutes) and was significantly greater than that following either ipratropium alone (p less than 0.001) or fenoterol alone (p less than 0.05). In 51 patients with acute exacerbations of chronic obstructive pulmonary disease (mean one-second forced expiratory volume, 0.67 +/- 0.29 liter), each regimen produced significant improvement in one-second forced expiratory volume at both 45 and 90 minutes (for all, p less than 0.05), but there was no significant difference among the three treatment regimens. It is concluded that, in patients with acute asthma, combination therapy with sympathomimetic and anticholinergic agents is more efficacious than either one alone. In patients with acute exacerbations of chronic obstructive pulmonary disease, although either sympathomimetic or anticholinergic therapy provides bronchodilatation, no further benefit could be demonstrated from combination therapy.

Administration, Intranasal↗
PubMed1987

Effect of inspiratory resistive loading on control of ventilation during progressive exercise.

Eight healthy volunteers performed gradational tests to exhaustion on a mechanically braked cycle ergometer, with and without the addition of an inspiratory resistive load. Mean slopes for linear ventilatory responses during loaded and unloaded exercise [change in minute ventilation per change in CO2 output (delta VE/delta VCO2)] measured below the anaerobic threshold were 24.1 +/- 1.3 (SE) = l/l of CO2 and 26.2 +/- 1.0 l/l of CO2, respectively (P greater than 0.10). During loaded exercise, decrements in VE, tidal volume, respiratory frequency, arterial O2 saturation, and increases in end-tidal CO2 tension were observed only when work loads exceeded 65% of the unloaded maximum. There was a significant correlation between the resting ventilatory response to hypercapnia delta VE/delta PCO2 and the ventilatory response to VCO2 during exercise (delta VE/delta VCO2; r = 0.88; P less than 0.05). The maximal inspiratory pressure generated during loading correlated with CO2 sensitivity at rest (r = 0.91; P less than 0.05) and with exercise ventilation (delta VE/delta VCO2; r = 0.83; P less than 0.05). Although resistive loading did not alter O2 uptake (VO2) or heart rate (HR) as a function of work load, maximal VO2, HR, and exercise tolerance were decreased to 90% of control values. We conclude that a modest inspiratory resistive load reduces maximum exercise capacity and that CO2 responsiveness may play a role in the control of breathing during exercise when airway resistance is artificially increased.

Adult↗
PubMed1987

Airway area by acoustic response measurements and computerized tomography.

In order to determine more precisely the accuracy with which the acoustic reflection technique (ART) can infer airway area during spontaneous breathing, we compared acoustic measurements of airway area with equivalent areas measured from computerized tomographic (CT) scans of the neck and chest in 7 patients (mean age, 54 yr; range, 33 to 69 yr) with a history of upper airway abnormalities. At the time of the study, all patients were clinically stable and had no recurrent nerve palsy. Measurements of airway area by ART and CT were performed in the supine posture while patients breathed quietly at FRC. We found that there was considerable intersubject variability in area-distance functions determined by acoustic reflections. None of the subjects had a flat tracheal plateau. Once the acoustic and CT data were aligned, we compared cross-sectional areas at various distances from the glottis. Comparison points were separated by 1 cm, and as many as 13 different CT sections were used in some subjects. Mean values for all data points (n = 83) were 2.45 +/- SD = 0.69 cm2 and 2.56 +/- SD = 0.82 cm2 for the acoustic and CT methods, respectively, Z = 0.93; p greater than 0.05. Linear regression analysis revealed a correlation coefficient (r) of 0.92; p less than 0.0001. On the basis of these findings, we conclude that the acoustic reflection technique may be used reliably for clinical and physiologic studies of the upper airways in humans.

Acoustics↗
PubMed1986

Conjunctival oxygen tension and its relationship to arterial oxygen tension.

Using a miniaturized Clark electrode embedded in a polymethylmethacrylate eyepiece, we measured transconjunctival oxygen tension (PcjO2) in 5 healthy volunteer subjects at multiple levels of steady-state isocapnic hypoxia, normoxia, and hyperoxia. PcjO2 was linearly related to arterial oxygen tension (PaO2) as PaO2 ranged from 28 to 205 mm Hg (PcjO2 = 0.59 PaO2 + 0.36 mm Hg; r = 0.94; standard error of the estimate = 7.09 mm Hg). However, the relationships between PcjO2 and PaO2 varied significantly among subjects. Whereas the overall mean ratio of PcjO2 to PaO2 was 0.59, the mean ratio for subjects ranged from 0.47 to 0.79 and was significantly different among subjects (P less than 0.0001). The time response of the electrode to a step change in oxygen tension in vitro was exponential, with a 90% response time of 38 seconds after a lag of 3.7 seconds. The time responses to in vivo changes in oxygen tension were also exponential. From hypoxia to normoxia, 90% response time was 45.0 seconds after a lag of 5.1 seconds; from room air to hypoxia, 90% response time was 72.4 seconds after a lag of 30.3 seconds; from room air to hyperoxia, 90% response time was 87.2 seconds after a lag of 6.8 seconds. We conclude that, although PcjO2 measured by a miniaturized Clark electrode is linearly related to PaO2 in healthy subjects, variation in the relationship of PcjO2 to PaO2 among individuals will prevent precise estimation of PaO2 for any individual unless subject-specific calibration is performed.

Adult↗
PubMed1986

Amiodarone pulmonary toxicity: functional and ultrastructural evaluation.

Pulmonary function, chest radiographic appearances, and the cellular composition of bronchoalveolar lavage fluid were assessed in 13 patients who were receiving amiodarone treatment. Eight of the patients had developed clinical and radiological evidence of lung disease and five were symptom free. The proportions of lymphocytes (mean 8.6 (SD 6.9)) and neutrophils (mean 3.4 (3.3)) obtained by bronchoalveolar lavage were similar in patients with and without lung complications. Electron microscopic examination of alveolar macrophages showed intralysosomal inclusion bodies in all subjects, regardless of clinical state. There was no significant difference in the mean number of inclusion bodies per macrophage transection between those with and those without lung disease. The differential cell count in bronchoalveolar lavage fluid and the presence of macrophage inclusion bodies were therefore not useful as markers of disease activity. Among those who developed clinical and radiological evidence of lung disease, the cumulative drug dose per kilogram of body weight and the duration of treatment (mean 16.5 (SD 9.0) months) were significantly correlated with the degree of lung restriction as measured by total lung capacity and forced vital capacity. It is concluded that, while the severity of the restrictive pulmonary defect that is induced by amiodarone is largely dose related, the development of lung toxicity is to some extent idiosyncratic.

Adult↗
PubMed1986

Effect of CO2 concentrations on acoustic inferences of airway area.

To determine the effect of gas composition on the accuracy of measurements of airway area and distance using an acoustic reflection technique, we employed glass-tube models to simulate pharyngeal (Phar-model), laryngeal (Lar-model), and tracheal (Trach-model) regions of upper and central airways. We made repeated measurements of area-distance functions using gas mixtures containing 0, 2, 4, 6, 8, and 10% CO2, 80% He, and balance O2. The actual area of the model was calculated from the roentgenographic data and compared favorably with an area measured by acoustic reflections using a gas mixture containing 0% CO2. With the different gas mixtures, calculated area was overestimated only at the highest levels of CO2, with Phar-model area increasing from (mean +/- SD) 4.66 +/- 0.03 cm2 measured with 0% CO2 to 4.93 +/- 0.05 cm2 (P less than 0.05) measured with CO2 concentration of 10%. To assess the effect of CO2 concentration on measurements of distance, we isolated two discrete points located in the Phar-model and Lar-model regions. When measurements were performed using 10% CO2 mixture, Phar-model point was shifted by 1.02 +/- 0.03 cm and Lar-model point was shifted by 2.16 +/- 0.09 cm away from the microphone compared with their axial position determined, using 0% CO2 mixture (P less than 0.05). Differences in area-distance calculations at the higher levels of CO2 did not exceed the within-run variability of the technique (10 +/- 4%). We conclude that CO2 absorbers are not required during measurements of airway area by acoustic reflections, provided CO2 concentration does not exceed 10%.

Acoustics↗
PubMed1986

Ear oximetry during combined hypoxia and exercise.

Ear oximetry is widely used to detect arterial O2 desaturation during exercise in patients with cardiopulmonary disease. Although oximeters have been evaluated for accuracy, response time, and the influence of skin pigmentation, tests of their reliability have not been reported during strenuous exercise. Accordingly, we compared arterial O2 saturation (Sao2) measurements obtained by Hewlett-Packard (HP, model 47201A) and Biox II oximeters with those determined directly from arterial blood in six healthy volunteers during progressive exercise while rebreathing hypoxic gas mixtures. The relationship between the HP oximeter value and blood Sao2 was described by the equation: HP = 0.93 (Sao2) + 5.37 and for the Biox II: Biox = 0.55 (Sao2) + 38.97. With these equations, at a blood Sao2 value of 90%, the underestimation by both oximeters was less than 2%. At a blood value of 70%, the HP oximeter overestimated blood Sao2 by 0.7%, whereas the Biox II showed an overestimation of 10.7%. Below blood Sao2 of 83%, the Biox II tended to overestimate blood Sao2 by an amount greater than the error of the instrument, whereas the HP estimations were within the error of the instrument over all levels of blood Sao2 studied. We conclude that the HP oximeter provides valid estimates of Sao2 during exercise but that the Biox II oximeter, although reflecting qualitative changes in oxygenation that occur during exercise, does not provide accurate records of the degree of desaturation.

Adult↗
PubMed1986

Thoracoabdominal motion in response to treadmill and cycle exercise.

The present study was designed to assess differences in compartmental contributions to ventilation between cycle pedaling and treadmill walking. Eight subjects performed submaximal cycle (CE) and treadmill (TM) exercise. The mean maximal work loads were not significantly different between the 2 modes of exercise. Ventilation (VE), oxygen uptake (VO2), and respiratory inductance plethysmography (RIP) were measured continuously during both modes of exercise. During both TM and CE, VE measured by RIP was found to correlate significantly with VE measured by pneumotachometer. Although the ventilation/work load relationship for CE exceeded that for TM in all subjects, when changes in rib cage (RC) and abdominal (ABD) tidal volume responses were expressed relative to changes in VE, no significant differences were found between TM and CE (RC, p greater than 0.05; ABD, p greater than 0.05). When these changes in tidal volume were expressed relative to changes in work load and independent of ventilation, there were no significant differences between separate compartmental responses during TM or CE (RC, p greater than 0.05; ABD, p greater than 0.05). We conclude that while absolute degrees of ventilation at a given work load differ between cycling and walking, the postural and ventilatory differences between these forms of exercise do not appear to induce differences in the relative contributions of the rib cage or the abdomen to tidal breathing.

Abdomen↗