[Echogram of the upper airway].
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Acoustics↗
Biomedical subjects
N Zamel
Publications and source records attributed to N Zamel.
The effects of air pollution on allergic bronchial responsiveness.
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Air Pollution↗
Heterogeneous airway tone in asthmatic subjects.
We examined the effect of volume history on the dynamic relationship between airways and lung parenchyma (relative hysteresis) in 20 asthmatic subjects. The acoustic reflection technique was employed to evaluate changes in airway cross-sectional areas during a slow continuous expiration from total lung capacity to residual volume and inspiration back to total lung capacity. Lung volume was measured continuously during this quasi-static maneuver. We studied three anatomic airway segments: extra- and intrathoracic tracheal and main bronchial segments. Plots of airway area vs. lung volume were obtained for each segment to assess the relative magnitude and direction of the airway and parenchymal hysteresis. We also performed maximal expiratory flow-volume and partial expiratory flow-volume curves and calculated the ratio of maximal to partial flow rates (M/P) at 30% of the vital capacity. We found that 10 subjects (group I) showed a significant predominance of airway over parenchymal hysteresis (P < 0.005) at the extra- and intrathoracic tracheal and main bronchial segments; these subjects had high M/P ratios [1.53 +/- 0.27 (SD)]. The other 10 subjects (group II) showed similar airway and parenchymal hysteresis for all three segments and significantly lower M/P ratios (1.16 +/- 0.20, P < 0.01). We conclude that the effect of volume history on the relative hysteresis of airway and lung parenchyma and M/P ratio at 30% of vital capacity in nonprovoked asthmatic subjects is variable. We suggest that our findings may result from heterogeneous airway tone in asthmatic subjects.
Adolescent↗
Maximal exercise testing in single and double lung transplant recipients.
Patients with end-stage pulmonary and pulmonary vascular disease can now be offered single-lung (SLT), double-lung (DLT), or heart-lung (HLT) transplantation. Long-term survival with greatly improved pulmonary function has been reported with all three procedures. Little has been reported of the exercise capacity after transplantation. This report documents Stage 1 exercise test results in six SLT (five males and one female; age 50.7 +/- 4.4; FEV1.0 75.5 +/- 6.7% of predicted) and seven DLT (three males and four females; age 37.3 +/- 6.7; FEV1.0 85.1 +/- 10.3% of predicted) recipients, early (3 months) and late (1 to 2 yr) following transplantation. The results show low work rates and VO2max in both SLT and DLT recipients at 3 months after transplant. Heart rate and minute ventilation did not appear limiting. There was no significant improvement when retested 1 to 2 yr after transplant. At 3 months, VO2max was 46% of predicted for SLT and 50% of predicted for DLT recipients. It is concluded that considerable exercise limitation persists after transplantation and does not appear to improve with time. These limitations are similar for both SLT and DLT and are not related to ventilation. The results may suggest chronic muscle deconditioning after long-term pretransplant debilitation.
Adult↗
Changes in cross-sectional airway areas induced by methacholine, histamine, and LTC4 in asthmatic subjects.
To examine whether leukotrienes, histamine, and methacholine have different sites of bronchoconstrictor action, we studied 8 stable asthmatic subjects (mean age +/- SD, 26 +/- 5 yr) on 3 different days. On each day, a randomized challenge with LTC4, methacholine, or histamine was performed until the dose that provoked a fall of 20% in FEV1 (PC20) was obtained. Complete and partial flow-volume curves as well as area-distance profiles generated by the acoustic reflection technique (ART) at a fixed lung volume were obtained in all subjects before and after each inhalation challenge. No significant differences were found in pulmonary function or baseline cross-sectional airway areas for the different study days. The three agonists provoked significant (p less than 0.05) bronchoconstriction at the level of the main bronchi when identical falls of FEV1 were achieved. Similarly, equal reductions of V30p were elicited by the three agonists. However, LTC4 and methacholine induced additional tracheal constriction but histamine inhalation did not. These differences in the degree of tracheal constriction were statistically significant (p less than 0.05; ANOVA). These results may be explained by distinct pharmacologic properties of the agents used and may have relevance in the understanding of the pathophysiology of asthma.
Analysis of Variance↗
Physiologic studies of tracheobronchial stents in airway obstruction.
When airway obstruction is due to extraluminal compression and/or dynamic collapse, metal and silicone rubber prosthetic stents may stabilize the affected airway. Through a rigid bronchoscope, we inserted three metal stents in two patients and 18 silicone stents in 15 adult patients with symptomatic tracheobronchial compression and dynamic airway collapse. The underlying cause was malignancy in three patients; benign tracheobronchial malacia in three patients, two of whom refused surgical resection; and tracheobronchial stenosis that developed at the anastomotic site following lung transplantation in 11 patients. Clinical status and lung function studies were analyzed before and after stent insertion. Following stent insertion, airway diameter at least doubled and near normal patency of the affected tracheobronchial tree was achieved in every patient using stents of axial length 4 to 5 cm. The stents were well tolerated clinically, and all patients noted immediate relief of dyspnea. Following stent insertion, the forced vital capacity (FVC) increased from 64 +/- 21% predicted (mean +/- 1 SD) to 73 +/- 19% predicted, p less than 0.1; the forced expiratory volume in 1 s (FEV1) from 49 +/- 25% predicted to 72 +/- 26% predicted, p less than 0.02; the ratio of the FEV1/FVC from 59 +/- 16% to 78 +/- 15%, p less than 0.01; and the maximum flow at 50% expired FVC from 38 +/- 26% predicted to 72 +/- 31% predicted, p less than 0.01.
Adult↗
Hypercapnic ventilatory response in recipients of double-lung transplants.
Ten survivors of double lung transplantation using a tracheal anastomosis underwent assessment of their ventilatory responses to hypercapnia (HCVR) at least 3 months postsurgery. At the time of HCVR testing, pulmonary functions were normal in four and abnormal in six patients who demonstrated degrees of obstruction, restriction, or mixed defects. Arterial blood gas measurements were normal. Postoperatively, hypercapnic responses were low or low normal. Mean changes in tidal volume and mean change in respiratory frequency in response to hypercapnia postoperatively were not different in patients with normocapnic versus hypercapnic preoperative blood gases. Neither postoperative resting PCO2 nor muscle strength (as measured by MIP) were predictive of the degree or character of the patients' ventilatory responses to hypercapnia. The factors resulting in the observed blunting of the hypercapnic response in this denervated population require further clarification; however, comparison of data between this patient population and recipients of heart-lung transplantation reported elsewhere suggests that alterations in pulmonary function correlate with the observed depression in HCVR.
Carbon Dioxide↗
Effect of low concentrations of ozone on inhaled allergen responses in asthmatic subjects.
The relation between inhalation of ambient concentrations of ozone and airway reactivity to inhaled allergens may be important in asthma, since both agents can produce inflammatory changes in the airways. Seven asthmatic patients (mean age 40 [SD 13] years), with seasonal symptoms of asthma and positive skin tests for ragweed or grass, took part in a study to investigate whether exposure to low concentrations of ozone potentiates the airway allergic response. The patients were studied during 4 separate weeks in the winter. In each week there were 3 study days: on days 1 and 3 methacholine challenges were carried out; and on day 2 the subject received one of four combined challenges in a single-blind design--air breathing followed by inhalation of allergen diluent (placebo); ozone followed by inhalation of allergen diluent; air followed by allergen; or ozone followed by allergen. The ozone concentration was 0.12 ppm during 1 h of tidal breathing at rest, and allergens were inhaled until the forced expiratory volume in 1 s (FEV1) had fallen by 15% (PC15). There were no significant differences in baseline FEV1 after exposure to ozone but PC15 was significantly reduced when allergen was preceded by ozone inhalation: the mean PC15 after air was 0.013 (SD 0.017) mg/ml compared with 0.0056 (0.0062) mg/ml after ozone (p = 0.042). Thus, low ozone concentrations, similar to those commonly occurring in urban areas, can increase the bronchial responsiveness to allergen in atopic asthmatic subjects. This effect does not seem to be the result of changes in baseline airway function.
Adult↗
Absence of effects of hypoxia on small airway function in humans.
We measured the effects of sustained isocapnic hypoxia (PAO2 = 40--50 Torr; PACO2 = 38--42 Torr) on tests sensitive to small airway function in healthy human subjects. Maximum expiratory flow-volume curves on air, nitrogen-hypoxic, helium-normoxic, and helium-hypoxic mixtures as well as closing volumes while subjects breathed air and a hypoxic mixture were obtained. We then measured total lung capacity (TLC), both plethysmographically and by inert gas dilution, and used the nonplethysmographic method to measure the effects of hypoxia on TLC. In none of these tests were there any statistically significant changes when values obtained during hypoxia were compared with those during normoxia. It is suggested that previous reports that indicated that TLC was increased by hypoxia might have arisen from a plethysmographic artifact.
Adult↗
Volume-displacement body plethysmograph using a large flowmeter without pressure compensation.
A modification of the conventional volume-displacement whole-body plethysmograph was done using a low-resistance flow element and integrating the plethysmographic pressure signal. A flow element with a resistance of 0.036 cmH2O/(l/s), linear to 75 l/s was fitted to a 440-liter plethysmograph, resulting in an instrument with a volume-amplitude-frequency response flat to 15 Hz and in phase with mouth flow and esophageal catheter-balloon to at least 15 Hz without pressure compensation.
Humans↗
Regulation of airway smooth muscle tone in sleeping dogs.
We examined the influence of sleep state on airway smooth muscle tone in 4 unanesthetized dogs that were trained to sleep in the laboratory. The dogs had been prepared with a permanent side-hole tracheostomy and bilateral cervical vagal loops. During the studies, the dogs breathed through a cuffed endotracheal tube inserted through the tracheostomy. To monitor changes in tracheal smooth muscle tone, we measured the pressure in the water-filled cuff of the endotracheal tube. The technique was validated by examining changes in cuff pressure after administration to the dogs of a series of chemical agents and physiologic stimuli known to constrict or relax tracheobronchial smooth muscle. Sleep state of the dogs was determined by behavioral, electroencephalographic, and electromyographic criteria. During quiet wakefulness, tracheal smooth muscle tone was stable. With the onset and progression of sleep through the nonrapid-eye movement stages, airway smooth muscle tone relaxed (decrease in cuff pressure of 20 to 40 cm H2O), reaching a new steady level during slow-wave sleep. In contrast, during rapid-eye-movement sleep, tracheal smooth muscle tone fluctuated markedly and erratically, as reflected by changes in cuff pressure as large as 90 cm H2O. Partial blockade of the vagus nerves, by cooling the exteriorized cervical vagal loops, decreased or abolished the fluctuations in tracheal smooth muscle tone during rapid-eye-movement sleep at temperatures that did not abolish resting tone, demonstrating that the changes in tone during rapid-eye-movement sleep were related to variability in neural control of airway smooth muscle.
Animals↗
Decrease in lung recoil pressure after cessation of smoking.
Tests of lung mechanics and single-breath carbon monoxide diffusing capacity (DLCO) were done in 26 apparently healthy cigarette smokers before and 2 months after cessation of smoking. There was a significant increase in vital capacity and 1-sec forced expiratory volume as well as improvement in frequency dependence of lung dynamic compliance. Slope and phase III and density dependence of maximal expiratory flow showed a borderline improvement DLCO did not change. Static lung pressure-volume curves showed a small but significant (P less than 0.01) shift toward lower pressures. We concluded that the previously reported decrease in lung recoil pressure observed in smokers is even more accentuated after cessation of smoking.
Adult↗
Pulmonary function in identical twins: comparison of nonsmokers and smokers.
Forty-five apparently normal pairs of identical twins were given pulmonary function tests to determine the role of genetics in bronchial susceptibility to cigarette smoke. Maximal expiratory flow at 60 per cent of total lung capacity (Vmax60) was the best discriminator of smokers from nonsmokers among pairs in which one member smoked and the other did not. The intrapair difference of Vmax60 values in pairs in which both members smoked was the same as in pairs in which both members did not smoke. These data support the view that genetic factors are important in determining the vulnerability of the airways to cigarette smoke.
Adult↗
Evaluation of the single-breath diffusing capacity in asthma and cystic fibrosis.
To explain why the single-breath carbon monoxide diffusing capacity (Dsb) was, on the average, elevated in 163 asthmatic subjects and 175 patients with cystic fibrosis, we simulated this elevation in ten normal subjects by having them perform the test for Dsb through an inspiratory obstruction. This resulted in an 18 percent increase in Dsb corrected for pulmonary volume. Inhalation of a bronchodilator drug was associated with relief of obstruction and a fall in the corrected Dsb in 31 asthmatic subjects but did not change either the obstruction or the corrected Dsb in 17 patients with cystic fibrosis. We suggest that elevated Dsb in asthma and cystic fibrosis is partly due to maximal inspiration against obstructed airways. This requires abnormally negative intrathoracic pressures, increasing the pulmonary capillary blood volume, and, thereby, increasing the Dsb.
Adolescent↗
Reproducibility of maximum expiratory flow in severe chronic obstructive pulmonary disease.
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Adult↗
Abnormalities in pulmonary function after brief exposure to toxic metal fumes.
A 26-year-old welder became ill after exposure to zinc and cadmium fumes at work. His initial clinical course was consistent with that of metal fume fever, but persistence of symptoms and signs beyond the usual duration in this condition led to suspicion of a toxic pulmonary reaction to cadmium. The finding of high percentages of both metals in the urine confirmed this diagnosis. Pulmonary function tests showed restriction of lung volumes, with increased elastic recoil and reduced diffusion, but no evidence of airways obstruction. Chest roentgenograms indicated central pulmonary edema, which cleared in 6 days. Follow-up assessment 2 years later showed incomplete improvement of the restrictive ventilatory defect.
Adult↗
Interaction of metabolic and behavioral respiratory control during hypercapnia and speech.
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Adult↗
Effect of body position on carbon monoxide diffusing capacity in asymptomatic smokers and nonsmokers.
We measured carbon monoxide diffusion capacity (DLCO) in the sitting and supine position in 73 apparently normal subjects (41 nonsmokers and 32 smokers). The coefficient of DLCO standardized for alveolar volume (KCO) was less in the smokers than in the nonsmokers (P less than 0.05) in the sitting position, but the separation was wider in the supine posture (P less than 0.01). The per cent changes between supine and sitting KCO (deltaKCO) were shown to be age dependent in both nonsmokers and smokers, but this age dependence was more accentuated in the latter group. Only 3 smokers were below the 95 per cent confidence limit of nonsmokers for KCO in the sitting position, but there were 7 smokers below that limit for deltaKCO. An attempt was made, using intravenous injection of xenon-133, to study the mechanism of this impairment. Persons who failed to increase KCO in the supine posture showed an ability to increase apical blood flow in that position. The mechanisms of impairment in deltaKCO remain to be explained and may be due either to a predominant apical defect or to a widespread abnormality of the pulmonary capillary bed.
Adult↗