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Biomedical subjects

N Zamel

Publications and source records attributed to N Zamel.

At least 73 records · Page 4Linked to original sources
PubMed1992

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↗
PubMed1991

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↗
PubMed1991

Pharyngeal function and snoring characteristics in apneic and nonapneic snorers.

Abnormalities in pharyngeal function, manifested even when the patients are awake, are thought to play an important role in the pathogenesis of sleep apnea. Tests of awake pharyngeal function continue to stimulate interest because it is hoped that they may allow physicians to distinguish patients with sleep apnea from those without it, and therefore reduce the number of unnecessary sleep studies. We elected to study two measures of pharyngeal function: changes in pharyngeal area with lung volume (PLVD) and changes in pharyngeal area in response to externally applied positive pressure, i.e., pharyngeal distensibility (Cph). Both measurements have been employed for assessment of pharyngeal function, and both are thought to reflect pharyngeal "floppiness." Measurement of PLVD is technically very simple, whereas the measurement of Cph is technically more complex. If the two measurements are highly correlated, it might be possible to replace the technically more difficult one by the simpler one. Consequently, the purpose of this study was two-fold: first, to examine the relationship between pharyngeal distensibility and lung volume dependence of pharyngeal area, and second, to compare these parameters in a large group of confirmed snorers with and without obstructive sleep apnea (OSA). We studied 75 unselected patients referred for the investigation of snoring and suspected sleep apnea. All patients had nocturnal polysomnography, pulmonary function tests, and measurement of pharyngeal areas at TLC, FRC, and residual volume (RV) employing the acoustic reflection technique. The area measurement at FRC was performed at zero and at 4.1 cm H2O positive airway pressure to calculate pharyngeal distensibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Airflow limitation in morbidly obese, nonsmoking men.

STUDY OBJECTIVE: To determine the effect of obesity on pulmonary function. DESIGN: Case-control study, using nonobese, age- and height-matched [corrected] nonsmokers. SETTING: Metabolic and obesity clinics of two major teaching hospitals. PATIENTS: One hundred and three obese, lifelong nonsmokers without cardiopulmonary disease. CONTROLS: One hundred and ninety healthy, nonobese nonsmokers recruited from among hospital personnel. MEASUREMENTS AND MAIN RESULTS: Complete pulmonary function measurements in all patients and controls. These measurements included maximum expiratory flow-volume curve, lung volumes and airway resistance using body plethysmograph, single-breath diffusing capacity for carbon monoxide, and total lung capacity using the helium dilution technique. Obese persons were found to have lower functional residual capacity, expiratory reserve volume, and total lung capacity by helium dilution than nonobese controls. In addition, residual volume and diffusing capacity were higher in the obese group. Finally, we found that obese men, but not women, had reduced maximum expiratory flow rates at 50% and 75% of exhaled vital capacity. CONCLUSION: Obesity may contribute independently of smoking habits to chronic airflow limitation in men.

Adult↗
PubMed1990

Results of single-lung transplantation for bilateral pulmonary fibrosis. The Toronto Lung Transplant Group.

Between November 1983 and August 1989, we performed single-lung transplantation for end-stage pulmonary fibrosis in 20 patients. Nine patients (45 percent) who survived for more than one year form the basis of this report. Before surgery, the nine survivors had severe restrictive lung disease, with a mean (+/- SD) vital capacity (VC) of 43 +/- 9 percent, a forced expiratory volume in one second (FEV1) of 50 +/- 9 percent, and a single-breath diffusing capacity (DLCO) of 36 +/- 9 percent of predicted values. One year after transplantation, the patients' VC had reached 69 +/- 10 percent, FEV1 79 +/- 15 percent, and DLCO 62 +/- 16 percent of predicted values. Relative perfusion to the transplanted lung rose from 63 +/- 14 percent (three days after surgery) to 77 +/- 7 percent within three months and stayed constant or increased slightly thereafter. Before surgery, despite supplemental oxygen at flow rates varying from 1 to 9 liters per minute, none of the patients could exercise beyond stage 1/2 (2.7 km [1.7 miles] per hour, 5 percent grade) on a modified Bruce treadmill-exercise protocol. All eight patients tested one year or more after transplantation achieved at least stage 1 (2.7 km [1.7 miles] per hour, 10 percent grade), and usually a higher stage, without supplemental oxygen. Arterial oxygen tension returned to normal values in most patients (87 +/- 13 mm Hg), and supplemental oxygen, which all patients required before surgery, was no longer needed by any patient after transplantation. We conclude that in carefully selected patients with end-stage pulmonary fibrosis, single-lung transplantation is an effective treatment.

Adolescent↗
PubMed1990

Mechanisms of gas exchange with different gases during constant-flow ventilation.

To investigate the mechanisms responsible for the difference in gas exchange during constant-flow ventilation (CFV) when using gases with different physical properties, we used mixtures of 70% N2-30% O2 (N2-O2) and 70% He-30% O2 (He-O2) as the insufflating gases in 12 dogs. All dogs but one had higher arterial PCO2 (PaCO2) with He-O2 compared with N2-O2. At a flow of 0.37 +/- 0.12 l/s, the mean PaCO2's with N2-O2 and He-O2 were 41.3 +/- 13.9 and 53.7 +/- 20.3 Torr, respectively (P less than 0.01); at a flow rate of 0.84 +/- 0.17 l/s, the mean PaCO2's were 29.1 +/- 11.3 and 35.3 +/- 13.6 Torr, respectively (P less than 0.01). The chest was then opened to alter the apposition between heart and the lungs, thereby reducing the extent of cardiogenic oscillations by 58.4 +/- 18.4%. This intervention did not significantly alter the difference in PaCO2 between N2-O2 and He-O2 from that observed in the intact animals, although the individual PaCO2 values for each gas mixture did increase. When the PaCO2 was plotted against stagnation pressure (rho V2), the difference in PaCO2 between N2-O2 and He-O2 was nearly abolished in both the closed- and open-chest animals. These findings suggest that the different PaCO2's obtained by insufflating gases with different physical properties at a fixed flow rate, catheter position, and lung volume result mainly from a difference in the properties of the jet.

Animals↗
PubMed1990

Do patients with obstructive sleep apnea have thick necks?

During physical examination of patients with suspected obstructive sleep apnea (OSA), a comment is frequently made that they appear to have a short and fat neck. To confirm this subjective impression by objective measurements, we studied a group of 123 patients referred to us because of snoring and suspected OSA, all of whom had nocturnal polysomnography and measurements of external and internal neck circumference. The external neck circumference was measured at the level of the superior border of the cricothyroid cartilage. Internal neck circumferences were calculated from the measurements of pharyngeal, glottic, and tracheal areas obtained by the acoustic reflection technique. Internal pharyngeal circumference was further subdivided into the proximal, middle, and distal thirds. The acoustic technique also permitted us to measure the distance between the teeth and the glottic minimum, which reflects the length of the upper airway. Stepwise multiple linear regression analysis revealed that the apnea/hypopnea index (AHI) correlated only with the external neck circumference, the body mass index, and the internal circumference of the distal pharynx; these three variables accounted for 39% of the variability in AHI. We conclude that the external and internal neck circumferences and the degree of obesity are important predictors of sleep apnea; it is possible that obesity produces its effect via fat in the neck. We speculate that the static pharyngeal size modulated by the dynamic loading of the airway due to the weight of fatty tissue of the neck may contribute to the pathogenesis of OSA.

Adult↗
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↗
PubMed1989

Glottic dimensions in healthy men and women.

Glottic aperture is important in modulating respiratory system resistance. Male patients with obstructive sleep apnea (OSA) have a smaller glottic cross-sectional area compared to controls. Since OSA has a strong male predominance, we reasoned that glottic dimensions may differ between healthy men and women. Therefore, we utilized the acoustic reflection to measure glottic cross-sectional area in 44 non-smoking, non-obese, healthy subjects, 25 men and 19 women. Glottic area was measured during a continuous slow expiration from total lung capacity (TLC) to residual volume (RV). We compared glottic areas in men and women at three lung volumes: TLC, 50% of vital capacity (VC), and RV. We found that in all but 2 subjects, glottic areas at TLC was greater than at 50% VC or RV. At any given lung volume, there was no significant difference in glottic area between men and women. The reduction in glottic area between TLC and RV was also similar between men and women (36 +/- 24% and 33 +/- 21%, respectively). However, this reduction in glottic area occurred mainly at low lung volumes in women, and more uniformly throughout the vital capacity range in men. We conclude that changes in glottic dimensions are dependent on lung volume, that healthy men and women have similar glottic areas, and that the glottic aperture shows similar variation with lung volume among both sexes.

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

Glottic and cervical tracheal narrowing in patients with obstructive sleep apnea.

There are several studies showing that patients with idiopathic obstructive sleep apnea (OSA) have a narrow and collapsible pharynx that may predispose them to repeated upper airway occlusions during sleep. We hypothesized that this structural abnormality may also extend to the glottic and tracheal region. Consequently, we measured pharyngeal (Aph), glottic (Agl), cervical tracheal (Atr1), midtracheal (Atr2), and distal (Atr3) tracheal areas during tidal breathing in 66 patients with OSA (16 nonobese and 50 obese) and 8 nonapneic controls. We found that Aph, Agl, and Atr1, but not Atr2 or Atr3, were significantly smaller in the OSA group than in the control group. Obese patients with OSA had the smallest upper airway area, although the nonapneic controls had the largest areas. Multiple linear regression analysis revealed that the pharyngeal area, cervical tracheal area, and body mass index were all independent determinants of the apnea-hypopnea index, accounting for 31% of the variability in apnea-hypopnea index. Aph, Agl, and Atr showed significant correlation with the body mass index. We conclude that sleep-disordered breathing is associated with diffuse upper airway narrowing and that obesity contributes to this narrowing. Furthermore, we speculate that a common pathophysiological mechanism may be responsible for this reduction in upper airway area extending from the pharynx to the proximal trachea.

Adult↗
PubMed1989

Airway hyperreactivity in patients undergoing lung and heart/lung transplantation.

To assess airway reactivity in lung transplant patients, three heart/lung, three double lung, and eight single lung transplant patients underwent airway challenge tests. All patients were assessed by methacholine aerosol challenge and thirteen were also assessed by histamine aerosol challenge at least three months after transplant surgery. The airways of patients with bilaterally denervated lungs (heart/lung and double lung transplants) were significantly more reactive to both methacholine and histamine (p less than 0.01) than were the airways of patients with unilaterally denervated (single lung transplants) lungs. Inflammatory changes in the airway mucosal biopsies were minimal in three patients and absent in all others. These studies raise questions about the role of central innervation in the maintenance of normal airway function as well as the mechanisms of action of both methacholine and histamine in causing bronchoconstriction.

Adolescent↗
PubMed1989

Flow-volume curves in snoring patients with and without obstructive sleep apnea.

To examine the usefulness of flow-volume curves as a screening test for the diagnosis of obstructive sleep apnea (OSA), we studied 405 consecutive patients referred for evaluation of possible OSA. All patients had full pulmonary function studies, which included measurements of maximal inspiratory and expiratory flow-volume curves, and nocturnal polysomnography, including continuous monitoring of snoring sounds. When the results were analyzed, of the 405 patients studied, 207 had OSA (apnea/hypopnea index [AHI] greater than 10) and 198 did not. Flow-volume curves were examined for the presence of upper airway obstruction defined as midvital capacity flow ratio (MVCFR = ratio of the maximal expiratory flow at 50% of vital capacity to maximal inspiratory flow at 50% of vital capacity) greater than 1.0. We found no significant difference in the values of MVCFR between the two groups: MVCFR was equal to 0.69 +/- 0.31 for nonapneic snorers, and 0.68 +/- 0.29 for the apneic snorers. Furthermore, we redefined the apneic and nonapneic groups using different cutoff values of AHI: 20, 30, 40, and 50. Independently of the AHI cutoff used, we found no significant difference in the MVCFR between the two groups. Linear regression analysis for the entire group of 405 patients revealed no significant correlation between MVCFR and the AHI or the snoring indices. We calculated the sensitivity, specificity, and predictive values of MVCFR for the diagnosis of OSA. We found that this test had 12% sensitivity, 86% specificity, 47% positive predictive value, and 46% negative predictive value.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
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

Changes in pharyngeal properties after uvulopalatopharyngoplasty.

Uvulopalatopharyngoplasty is a commonly used modality for surgical treatment of snoring and obstructive sleep apnea. Although this procedure is thought to alter pharyngeal properties, its effect on pharyngeal mechanics has not been studied. The acoustic reflection technique was used to measure pharyngeal area at functional residual capacity and residual volume before and after uvulopalatopharyngoplasty in eight patients referred because of loud snoring. We also calculated the lung volume dependence of pharyngeal area, defined as the percent change in pharyngeal area between functional residual capacity and residual volume, normalized to the area at functional residual capacity. This parameter, which may be related to pharyngeal collapsibility, was obtained before and after uvulopalatopharyngoplasty. Preoperative sleep studies showed that one patient had obstructive sleep apnea (apnea index greater than 10). Uvulopalatopharyngoplasty resulted in a significant increase (p less than 0.01) in pharyngeal area (from 3.14 +/- 0.71 cm2 to 4.25 +/- 1.07 cm2) and residual volume (from 2.49 +/- 0.53 cm2 to 3.91 +/- 0.83 cm2). Following uvulopalatopharyngoplasty, the pharynx became stiffer, as manifested by a reduction in lung volume dependence of pharyngeal area from 19 +/- 12% to 8 +/- 13% (p less than 0.05). Six patients, including the patient with obstructive sleep apnea, reported improvement in snoring. Two patients reported worsening in snoring. One of the two was found to have reduction in pharyngeal area and lung volume dependence of pharyngeal area, and an increase in apnea index from 3 to 33. In selected snorers, uvulopalatopharyngoplasty results in improvement in snoring with a concomitant increase in pharyngeal area and a tendency toward lower pharyngeal collapsibility.

Adult↗
PubMed1988

Single breath of CO2 as a clinical test of the peripheral chemoreflex.

Peripheral chemoreceptor responsiveness is usually examined clinically by hypoxic testing, but the usefulness of this approach is limited by safety considerations, and the interpretation of results may be confounded by the direct central nervous system effects of hypoxia. Therefore we examined the single-breath (SB) CO2 test to determine its reproducibility and applicability as a clinical test of peripheral chemoreceptor function. The technique involved the inhalation of a SB of 13% CO2 in air. The ventilatory response was determined from the increase in ventilation (VE) during the first 20 s after the test breath and from the difference in end-tidal PCO2 between the test breath and preceding control breaths. The peak increase in VE occurred during the second or third breath after the test breath, corresponding to a delay of approximately 10 s. The mean of 10 SB tests administered at 2- to 3-min intervals was taken as the subject's response. Five healthy subjects were tested in this manner on each of 6 consecutive days with the response having an interday coefficient of variation of 25 +/- 6% (SD). The response in 26 healthy females (aged 22-61 yr) was 0.32 +/- 0.11 l.min-1.Torr-1, and in 26 healthy males (aged 24-69 yr) the response was 0.38 +/- 0.14 (P NS). No significant correlation was found between the age of the subjects and their ventilatory response. Thirty-six of the subjects also underwent hyperoxic CO2 rebreathing tests, the response to which is dependent on central chemoreceptor function. No correlation was found between rebreathing and SB tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗