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Biomedical subjects

N Zamel

Publications and source records attributed to N Zamel.

At least 127 records · Page 7Linked to original sources
PubMed1984

Impaired detection of added inspiratory resistance in patients with obstructive sleep apnea.

The ability to detect added inspiratory flow-resistive loads during wakefulness was examined in 5 men with laboratory-documented obstructive sleep apnea. The patients were eucapnic, and standard measurements of lung volumes and flow rates were within the normal range. The patients breathed through a circuit, to which each of 5 flow resistances of 0.12 to 5.5 cm H2O/L/s was added at 20- to 30-s intervals for 1 inspiration, following a cue. Each resistance was presented 10 times in random sequence, and the percentage of trials in which each load was detected by the patient was calculated. The threshold level of load detection, defined as the change in resistance that could be detected 50% of the time, was higher in the patients (2.37 +/- 0.41 cmH2O/L/s, mean +/- SE) than in 9 healthy subjects (0.65 +/- 0.08; p less than 0.001), and this difference persisted when the threshold load was corrected for background resistance (1.05 +/- 0.11 versus 0.45 +/- 0.07; p less than 0.001). In addition, the ventilatory response to hypercapnia was less in the patients (1.82 +/- 0.22 L/min/mm Hg) than in the normal subjects (3.87 +/- 0.40; p less than 0.005), and there was a significant negative correlation (r = 0.97; p less than 0.001) between the load detection threshold and the ventilatory response to CO2. The results add to the developing concept that subtle defects in respiratory control can be demonstrated even during wakefulness in eucapnic patients with obstructive sleep apnea.

Adult↗
PubMed1984

Upper airway morphology in patients with idiopathic obstructive sleep apnea.

Fundamental to the pathogenesis of obstructive sleep apnea (OSA) is the interaction of physiologic and anatomic alterations of the upper airway. However, many patients with OSA have no identifiable abnormality of the upper airway, and they have been termed idiopathic. In an attempt to find a structural deviation in upper airway anatomy, we performed acoustic echography and cephalometric roentgenograms in 9 male patients with OSA and no clinical evidence of upper airway abnormality. Mean cross-sectional area of the pharynx by acoustic reflection was less in these patients (3.7 +/- 0.8 cm2) than in subjects in a control group (5.3 +/- 0.6 cm2) (p less than 0.001). Mean glottic cross-sectional area was less in the patient group (1.5 +/- 0.5 cm2) than in the control group (2.7 +/- 0.5) (p less than 0.001). There was a significant correlation between the number of apneas per sleep hour and pharyngeal cross-sectional area (r = 0.87, p less than 0.01). Cephalometric analysis indicated that the patients had smaller mandibles by a mean of 5.4 +/- 6.6 mm (p less than 0.05). The overall posterior displacement of the mandibular symphysis, which is representative of the skeletal support of the anterior pharyngeal wall and is dependent on both mandibular size and position, was highly significant (6.4 +/- 4.7 mm) (p less than 0.01). Furthermore, there was a significant correlation between the number of apnea episodes per sleep hour and the total posterior displacement (r = 0.67, p less than 0.05). This study indicates that patients with so-called idiopathic OSA may have an anatomic predisposition to the development of upper airway occlusion that may not be detectable on clinical examination.

Adult↗
PubMed1984

Lung volume dependence of pharyngeal cross-sectional area in patients with obstructive sleep apnea.

We examined the relationship between lung volume and pharyngeal cross-sectional area in 9 obese patients with obstructive sleep apnea and 10 age-matched, obese subjects without sleep apnea. Pharyngeal area was measured in the upright, seated posture using an acoustic reflection technique. Measurements were made at a rate of 5 per second during a slow exhalation from total lung capacity (TLC) to residual volume (RV). In the control subjects, the mean +/- SE pharyngeal area was 5.6 +/- 0.2 cm2 at TLC, and decreased by 30 +/- 5% over the vital capacity range to 3.9 +/- 0.3 cm2 at RV. In contrast to the control subjects, in patients with obstructive sleep apnea, pharyngeal area was 5.0 +/- 0.2 cm2 at TLC, and decreased by 54 +/- 6% over the vital capacity range to 2.3 +/- 0.3 cm2 at RV. The difference in pharyngeal area between the patients and control subjects was significant at all lung volumes below TLC, as was the difference in the magnitude of change in pharyngeal area with change in lung volume. The results indicate that in obese patients with obstructive sleep apnea, pharyngeal cross-sectional area is abnormally small, and varies considerably with changes in lung volume. The beneficial effects of weight reduction in such patients may relate to the coincident increase in functional residual capacity, causing an increase in upper airway size.

Adult↗
PubMed1984

Tracheal stenosis measured by the acoustic reflection technique.

We examined the usefulness of the acoustic reflection technique for measurement of airway area in 6 patients with tracheal stenosis. In each patient, we obtained airway area by acoustic reflections in the upright position, maximal expiratory and inspiratory flow-volume curve, and radiographs of the trachea. We identified acoustic and radiographic stenotic segments and compared their length, their distances from the glottis, and their cross-sectional areas. We found that (1) in all subjects except one, flow-volume curves did not suggest upper airway obstruction, (2) tracheal stenosis was confirmed by acoustic and radiographic measurements in all subjects, and (3) area of the stenotic segment showed less variation with lung volume than that of the nonstenotic segment. Length of the stenotic segment (mean +/- SE) was found to be 4.9 +/- 0.2 cm (acoustic versus 4.8 +/- 0.3 cm (radiographic); distance between the midglottis and maximal stenosis was 5.7 +/- 0.4 cm (acoustic) and 5.6 +/- 0.6 cm (radiographic); minimal acoustic cross-sectional area was 1.7 +/- 0.1 cm2 versus a radiographic circular cross-sectional area of 1.2 +/- 0.1 cm2. During slow expiration from total lung capacity to residual volume, average cross-sectional area of the stenotic segment decreased by 19.5 +/- 3.0% (mean +/- SE), whereas that of the distal nonstenotic segment decreased by 48.5 +/- 2.2% and that of the proximal nonstenotic segment by 43.6 +/- 5%. We conclude that the acoustic technique, which is rapid and noninvasive, is useful in confirming tracheal stenosis in patients with normal flow-volume curves, and in assessing elastic properties of the trachea.

Acoustics↗
PubMed1984

Estimation of changes in alveolar-arterial oxygen gradient induced by hypoxia.

The alveolar-arterial oxygen tension difference provides a useful clinical indication of ventilation-blood flow mismatching in the lungs. In some clinical situations involving alveolar hypoxia (e.g., patients with chronic obstructive lung disease flying in commercial aircraft or normal humans at high altitudes) it would be useful to know this tension difference to predict the likely arterial PO2 under such potentially stressful conditions. Such estimates would require multiple arterial punctures performed under a variety of trying circumstances, conditions usually far distant from a suitable analytic facility. Consequently, we induced controlled hypoxia in 23 healthy humans and calculated changes in the alveolar-arterial oxygen tension difference during the hypoxic challenge test. We plotted this difference as a function of the alveolar oxygen tension over a range from 35 to 110 mm Hg. In addition to a series of control studies in which multiple arterial blood samples were obtained, we calculated arterial PO2 by converting the arterial oxyhemoglobin saturation (measured with an ear oximeter) into partial pressure of oxygen. During hypoxic procedures in which levels of oxygenation fell on the steep section of the oxyhemoglobin dissociation curve, fixing PCO2 at constant predetermined levels allowed accurate predictions of arterial PO2. We were able to demonstrate that the alveolar-arterial oxygen tension difference narrowed with decreasing alveolar oxygen tension, and that measurement with an ear oximeter provided data that allowed a reasonable estimate of the tension difference during hypoxic conditions.

Adult↗
PubMed1983

Partial and complete maximum expiratory flow-volume curves in asthmatic patients with spontaneous bronchospasm.

Bronchodilatation follows a deep inspiration in normal subjects with pharmacologically induced bronchoconstriction. To determine to what extent this occurs in asthmatic patients with spontaneous bronchospasm, we obtained partial (PEFV) and complete (MEFV) maximum expiratory flow volume curves in 20 adults (helium-oxygen responders and nonresponders) and 13 children with asthma. We measured maximum expiratory flow at 25 percent of forced vital capacity from the partial (Vmax - p) and complete (Vmax - c) flow-volume curves and expressed this relationship as the Vmax - p/Vmax - c ratio. Three of the adult subjects and one of the children had a V max-p/V max-c less than 1.0. Following inhalation of nebulized bronchodilators, none of the children or adults had a Vmax - p/Vmax - c ratio less than 1.0. Reasons for Vmax - p to be higher than Vmax - c include bronchoconstriction, decreased lung elastic recoil following a deep inspiration, and time dependence of maximum expiratory flow due to lung inhomogeneity. We conclude that asthmatic patients with spontaneous bronchospasm are only seldom able to obtain bronchodilation following a deep inspiration.

Adolescent↗
PubMed1982

Pulmonary function in identical twins raised apart.

As part of the Minnesota Study of Twins Raised Apart, we measured pulmonary function in 15 pairs of monozygotic twins and one set of monozygotic triplets who were separated at an average age of 3.8 months. Six pairs of twins were concordant for nonsmoking, 3 pairs and the triplets were concordant for cigarette smoking, and 6 pairs were discordant for respiratory problems (5 pairs for smoking, 1 pair for asthma). Thirteen pulmonary function tests were done on each twin; however, only 2 tests of pulmonary function, the FEF25-75% and V75, could separate smokers from nonsmokers to a statistically significant degree. One additional test, the FEV1, was the most sensitive way to separate smoking from nonsmoking twins when only paired data from twin pairs discordant for smoking were used. Intratwin differences between twins of a pair for these three pulmonary function tests were small and virtually identical for both concordant groups, whereas the intratwin differences in the discordant group were large and distinctly different from the concordant groups. These results, together with those of previous studies in identical twins raised together, support the conclusion that genetic factors are important in determining susceptibility to airway obstruction from cigarette smoke.

Adolescent↗
PubMed1982

Beneficial effect of oxygen in primary alveolar hypoventilation with central sleep apnea.

A 58-yr-old man with primary alveolar hypoventilation, central sleep apnea, and secondary polycythemia failed to improve when treated with respiratory stimulant medications, including oxtriphylline, acetazolamide, and medroxyprogesterone. In contrast, after institution of treatment with low-flow nocturnal oxygen, there was a marked decrease in the number and duration of sleep apneas, and an increase in the level of ventilation during sleep. These changes were sustained during 5 months of nocturnal oxygen therapy. The improvement produced by oxygen may have been due to the fact that the patient had no demonstrable ventilatory response to hypoxia during wakefulness, and therefore may have developed hypoxic brainstem depression during sleep. The findings suggest that oxygen therapy during sleep may be beneficial in patients with primary alveolar hypoventilation and central sleep apnea who demonstrate no ventilatory response to hypoxia during wakefulness.

Humans↗
PubMed1982

Obstructive apneas during sleep in patients with seasonal allergic rhinitis.

The possible role of high nasal airway resistance in the pathogenesis of obstructive sleep apnea has been examined in 7 patients with seasonal (ragweed) allergic rhinitis, a naturally occurring model of reversible nasal obstruction. Measurements of nasal resistance and overnight polysomnographic studies were performed during the ragweed season when the patients complained of nasal obstruction; and 6 to 8 wk later when the symptoms had subsided (control study). During the symptomatic phase, mean (+/- SE) nasal resistance was 4.9 +/- 0.8 cm H2O/L/s, and the patients experienced 1.7 +/- 0.3 obstructive apneas per hour of sleep. In contrast, at the time of the control study, nasal resistance had decreased to 2.5 +/- 0.3 cm H2O/L/s (p less than 0.01); and the rate of obstructive apneas had decreased to 0.7 +/- 0.4 per hour of sleep (p less than 0.005). The duration of these apneas had also decreased from 15.5 +/- 0.8 s to 6.1 +/- 2.9 s (p less than 0.01). Apneas were rarely associated with significant O2 desaturation and were fewer in number than typically seen in a clinically significant sleep apnea syndrome. In male patients there was a direct relationship (r = 0.9) between the change in nasal resistance from symptomatic to control studies and the corresponding change in frequency of obstructive sleep apneas. Coincident with these respiratory changes at the time of the control study was an increase in the amount of slow-wave sleep (p = 0.05) and a small reduction in the frequency of arousals during sleep (p = NS). We conclude that in patients with allergic rhinitis, obstructive sleep apneas are longer and more frequent during a period of symptomatic nasal obstruction than when symptoms are absent. The results support the concept that a high nasal resistance may be a contributing factor in the pathogenesis of obstructive sleep apneas in general.

Adult↗
PubMed1981

Tonic inspiratory muscle activity as a cause of hyperinflation in asthma.

We studied tonic activity of the inspiratory muscles during exacerbation of asthma in five female and two male patients. Exacerbation was provoked by withholding bronchodilatory medication for 12 h prior to the study. Thoracic gas volume (TGV) at the end of resting expiration was determined before and after albuterol (salbutamol) inhalation with a body plethysmograph. Intercostal muscle electromyogram (EMG) was recorded with surface electrodes and diaphragmatic EMG with esophageal electrodes. Tonic activity was defined as electrical activity in the EMG present throughout expiration. After salbutamol the TGV decreased 13.4 +/- 2.9% (mean +/- SE) (P less than 0.01). This decrease in TGV was accompanied by a proportional reduction in tonic intercostal (r = 0.78, P less than 0.05) and diaphragmatic activity (r = 0.84, P less than 0.05). These findings suggest that the hyperinflation present during exacerbation of asthma is at least in part due to active inspiratory muscle activity present throughout expiration.

Adult↗
PubMed1981

Pneumotachograph calibration for inspiratory and expiratory flows during HeO2 breathing.

Maximum expiratory flows during breathing of a 80% helium-20% oxygen mixture (HeO2) are commonly used to determine the site of airflow limitation. To do this test the flowmeter is usually calibrated with the inspired gases, and the airflows are measured during expiration. We tested the adequacy of such calibration maneuvers by using two identical flowmeters in series through a bag-in-box system. Different gases were flowed though the test pneumotachograph into a bag contained in a closed box connected to the second pneumotachograph. Distension of the bag caused air to flow from the box through this second pneumotachograph. Our results indicate that when breathing HeO2, the flowmeter correction for different gas viscosity, compared with air, should be 20% for inspired HeO2 and 12% for expired gases. Inspired gases therefore cannot be used to calibrate the flowmeters when assessing expiratory flows.

Helium↗
PubMed1981

Upper airway occlusion induced by diaphragm pacing for primary alveolar hypoventilation: implications for the pathogenesis of obstructive sleep apnea.

This report describes a patient with primary alveolar hypoventilation who, after 2 yr of successful treatment with nocturnal oxygen, developed severe hypoxemia and hypercapnia during sleep, morning headaches, and daytime fatigue. Sleep studies demonstrated prolonged periods of hypoventilation and apnea without evidence of upper airway occlusion. Therefore, a phrenic nerve stimulator was implanted to allow pacing of the diaphragm during sleep. However, diaphragm pacing was accompanied by paradoxical movement of the rib cage and upper airway occlusion during sleep, and was unsuccessful in maintaining adequate ventilation. Therefore, the patient underwent a tracheostomy after which diaphragm pacing maintained adequate nocturnal ventilation; however, paradoxical movement of the rib cage persisted. The induction of upper airway occlusion as a result of diaphragm pacing, in contrast to the absence of occlusion during spontaneous breathing, highlights the importance of the normal temporal coordination of inspiratory activation of the upper airway muscles and diaphragm. The findings have important implications for the pathogenesis of obstructive sleep apneas in general.

Adult↗
PubMed1981

Predominant site of airway resistance in chronic obstructive pulmonary disease.

The purpose of the present clinical research was to establish the major site of resistance and obstruction in patients with severe, symptomatic chronic obstructive pulmonary disease. We used a noninvasive technique by measuring airflow in a plethysmograph after patients breathed air and after breathing a mixture of 80 percent helium and 20 percent oxygen. In group 1 were 14 patients (mean age, 63 +/- 7 years [+/- 1 SD]) with bronchitis. The ratio of their forced expiratory volume in one second over the vital capacity (FEV1/VC) was 43 +/- 10 percent (mean +/- 1 SD), and their single-breath carbon monoxide diffusing capacity (Dsb) was normal (125 +/- 41 percent of the predicted value). In group 2 were 13 patients with emphysema (mean age, 60 +/- 10 years), whose FEV1/VC was 33 +/- 11 percent and Dsb was 55 +/- 14 percent of predicted. All patients had abnormally low increases in the maximum expiratory flow at midvital capacity after breathing the helium-oxygen mixture. The range in group 1 was -11 percent to +14 percent and in group 2 was -10 percent to +15 percent. Normal subjects in our laboratory show increases of at least +24 percent. This indicates that the limitation of airflow occurs primarily in the small (less than 2 mm in internal diameter) and not the large airways.

Aged↗