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Biomedical subjects

D E Knudson

Publications and source records attributed to D E Knudson.

14 recordsLinked to original sources
PubMed1991

Expiratory computed tomography for assessment of suspected pulmonary emphysema.

Results of computed tomography of the lung performed at two levels in upper lung zones at full inspiration and full expiration were compared with results of tests of ventilatory function, lung mechanics, and single breath carbon monoxide diffusing capacity in 64 subjects, many of whom had some form of airflow obstruction. From the CT scans, the mean percentage of pixels in the range -900 to -1,024 Hounsfield units, or pixel index, was determined for each subject. The highest correlations of pixel index with physiologic variables consistent with a diagnosis of emphysema were observed for CT taken at full expiration. In some subjects, the inspiratory CT would give a "false positive" for emphysema when the hyperaeration observed at inspiration was not observed at expiration. We believe that the CT scan taken at full expiration can effectively reveal the abnormal permanent enlargement of airspaces which defines emphysema and provides a noninvasive method of assessing lung morphology in the living human subject.

Adult↗
PubMed1989

Subclinical effects of cigarette smoking. A five-year follow-up of physiologic comparisons of healthy middle-aged smokers and nonsmokers.

Measurements of ventilatory function, lung elastic recoil, diffusing capacity, and distribution of ventilation were obtained on healthy middle-aged cigarette smokers and nonsmokers on two occasions five years apart in order to assess the effects of smoking and the change which may occur over this five-year interval. Subjects were drawn from a randomly selected sample of the population of Tucson, AZ. Exactly the same protocol, methods, and equipment were employed in both studies. Although very few of these healthy subjects had abnormal function, there were significant differences in most indices of function between smokers and nonsmokers. However, we could discern no difference between smokers and nonsmokers in change in function over five years. It appears that, in smokers who remain free of serious respiratory trouble, there are subtle changes which accumulate over the years and which are too gradual to detect over a five-year interval.

Female↗
PubMed1987

Physiologic characteristics of subjects exhibiting accelerated deterioration of ventilatory function.

From a randomly selected community population sample followed with sequential surveys since 1972, 13 subjects who exhibited a mean annual decline in FEV1 greater than 60 ml/yr were drawn for detailed studies of lung function. These subjects had developed clinically significant airway obstruction during this period of follow-up. Clinical evaluation was not successful in characterizing the nature of the disorder. None of the subjects had alpha-1-antitrypsin deficiency. In a small proportion of subjects, elevated total serum immunoglobulin E may have played a role in the obstructive airway disorder. Some subjects exhibited loss of lung elastic recoil and diminished carbon monoxide diffusing capacity suggestive of developing emphysema. Others appeared to have intrinsic airway disease involving large and/or small airways, which may be fixed in some and responsive to bronchodilator in others. Thus, neither the site nor the nature of the disorder inferred from results of physiologic tests was uniform, illustrating the heterogeneous nature of chronic obstructive lung disease.

Adult↗
PubMed1987

The single-breath carbon monoxide diffusing capacity. Reference equations derived from a healthy nonsmoking population and effects of hematocrit.

Measurements of the single-breath carbon monoxide diffusing capacity (DL) were obtained on a randomly selected sample representative of the white non-Mexican-American population of Tucson, Arizona. Methods of measurement followed the guidelines set forth in the ATS-sponsored Epidemiology Standardization Project. There were 228 healthy nonsmokers who had duplicate tests that met the criteria for being acceptable. On the basis of data from these subjects, reference equations were derived for DL, alveolar volume (VA), and DL/VA. The data demonstrate the effects of growth and development, height, and age on these variables. Because a significant proportion of women, but not of men, had low hematocrit values, an effect of hematocrit on DL and DL/VA could be demonstrated only in females in this population sample.

Adult↗
PubMed1984

Subclinical effects of smoking. Physiologic comparison of healthy middle-aged smokers and nonsmokers and interrelationships of lung function measurements.

Measurements of ventilatory function, distribution of ventilation, diffusing capacity, and lung mechanics were made on healthy middle-aged smokers and nonsmokers drawn from a randomly selected population in order to assess the effects of cigarette smoking and the interrelationships of the several indices of lung function. Although very few subjects had abnormal function, there were significant differences in most indices of function between smokers and nonsmokers. For the total group studied, there were significant correlations between various indices of function. A significant proportion of the variance in diffusing capacity and in diffusing capacity per liter of lung volume can be accounted for by an index of lung recoil which may, in turn, be related to size of terminal air spaces.

Adult↗
PubMed1984

Frequency dependent phase and amplitude differences between simulated mouth and pleural pressures during panting. Demonstration with a mechanical model.

A mechanical model was employed to examine phase and amplitude relationships between simulated pleural and mouth pressures during panting at different frequencies with and without lower airway obstruction and with rigid or flaccid extrathoracic airways. Results confirm the hypothesis that, in the presence of lower airways obstruction, compliant extrathoracic airways act as a shunt impedance. Consequently, mouth pressure changes may be out of phase with and underestimate changes in pleural pressure, affecting the measurement of thoracic gas volume.

Humans↗
PubMed1983

Influence of airway geometry on expiratory flow limitation and density dependence.

In a study of individuals of the same sex and similar age and size, between subject variability was noted in lung recoil, lung size, density dependence of maximum expiratory flow, tracheal cross-sectional area, and anatomic dead space. No significance was observed in the relationships to one another of lung size or either estimate of airway size, nor did the magnitude of the change in flow with changes in gas density show a consistent relationship to any of the size variables. The results indicate that there is a dissociation between tracheal dimensions and anatomic dead space as well as between airway size and lung size, suggesting that dysanapsis is a general phenomenon. This introduces additional sources of interindividual variability of maximum expiratory flow and measurements of density dependence of flow.

Adult↗
PubMed1977

Effect of aging alone on mechanical properties of the normal adult human lung.

For plethysmographic studies of respiratory mechanics, we selected, from a general population, 51 subjects, aged 25-75 yr, who had never smoked, had no present or past cardiorespiratory symptoms or disease, were alpha1-antitrypsin MM phenotypes, and were normal by physical examination, vectorcardiography, and chest roentgenography. Approximately equal numbers of men and women were represented in each of three age groups; 25-35, 36-64, and 65-75. Both sexes demonstrated loss of lung elastic recoil with age, most significant at high lung volumes, but the rate of loss was less than previously reported. Males had higher lung recoil than females of comparable age, but if lung size was taken into account, there were no sex differences in bulk elastic properties. Maximum expiratory flow diminished with age only at low volumes, suggesting that equal pressure points are more centrally located at low lung volumes in the elderly.

Adult↗
PubMed1977

The closing volume test: evaluation of nitrogen and bolus methods in a random population.

The closing volume test, using helium bolus and nitrogen washout techniques simultaneously, was evaluated in more than 1,900 persons randomly selected as representative of the white population of Tucson, Arizona. Normal values were based on data obtained from those totally asymptomatic persons who had never smoked cigarettes. In the remaining population, the slope of Phase III appeared to be more sensitive than any other measurement in detecting abnormalities, but all measurements taken in conjunction were superior to any single parameter. Closing volumes measured by the bolus method were systematically greater than those obtained by resident nitrogen technique in normal subjects and were slightly more sensitive in detecting abnormalities in other population subgroups. Nevertheless, the single-breath test was of only limited value in distinguishing asymptomatic smokers from nonsmokers. Parameters used in conjunction revealed abnormalities in 36% of symptomatic subjects, many of whom already had physician-confirmed obstructive pulmonary disease. Our data suggest that, when applied to a randomly selected population, abnormalities in the closing volume test occur in only a very small proportion of persons in whom a respiratory disorder would not otherwise be suspected or already diagnosed.

Adolescent↗
PubMed1975

Effect of muscle constriction on flow-limiting collapse of isolated canine trachea.

Before and after trachealis muscle contraction, induced by application of acetylcholine, the relationship of changing pressures to flow through excised canine tracheas was examined in a mechanical model simulating isovolume pressure-flow relationships in vivo. At the same time, the change in cross-sectional lumen area at a point in the downstream third of the trachea was measured using slit-lamp transillumination and cinematographic measurements. Trachealis muscle contraction reduced the uncompressed lumen area but inhibited dynamic collapse as driving pressures increased. As a result, following contraction, the initial slope of the tracheal pressure-flow (TPF) curve changed, indicating increase in resistance at low flows, but higher flows were achieved at higher driving pressures. Results suggest that smooth muscle tone of large airways may affect maximum expiratory flow (Vmax) and explain apparent discrepancies between in vivo measurements of resistance and Vmax. The magnitude of the Bernoulli effect contributing to airway narrowing was demonstrated by measurements of lateral airway pressures well in excess of driving pressure.

Acetylcholine↗