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Biomedical subjects

O F Pedersen

Publications and source records attributed to O F Pedersen.

106 records · Page 6Linked to original sources
PubMed1976

The critical transmural pressure of the abirway.

The critical transmural pressure (Ptm) is defined as the transmural pressure of the airway at the site where and when flow is limited during a forced expiration. According to the presented theory, the maximal expiratory flow (Vmax) can be calculated from the relation between Ptm and the corresponding cross-sectional area of the airway (A). By means of a pitot-static tube, Ptm-A curves were constructed for several locations in the elastic airway of a mechanical model. From these curves local Vmax was calculated at different values of Ptm and compared with actual flow, i.e. measured Vmax for the entire airway. In the downstream part of the airway, the actual flow equalled calculated Vmax at most Ptm values. The site of flow limitation, being the most upstream point where actual flow equals calculated local Vmax could therefore be located. Theory and experiments showed positive as well as negative Ptm not influenced by change in upstream or downstream resistance. Flow limitation could therefore be initiated at distending as well as compressing pressures across the wall of the airway. V was regarded as a function of Ptm and the elastic recoil pressure of the lung (Pel). Measured and calculated iso-Pel, Ptm-V curves agreed well with one major exception: when Ptm less than Ptm measured curves were distorted due to a concomitant downstrean compression of the collapsible airway.

Airway Resistance↗
PubMed1976

A method to correct for the influence of gas density on maximal expiratory flow rate.

Maximal expiratory flow rate (Vmax) was measured at 20, 35, 50, 65, and 80% vital capacity in 4 young healthy subjects breathing air, SF6/O2, and He/O2 mixtures. The flows of SF6/O2 and He/O2 were corrected to normal alveolar gasflow by means of only the density of the gases. The values for normal alveolar gasflow and corrected SF6/O2 flow were identical at 35% VC and larger volumes while the values for normal alveolar gasflow and corrected He/O2 flow were not. The results indicate that in young healthy subjects it is possible to correct Vmax at lung volumes above 35% VC for the changes induced by an increase in density of the gas breathed, provided viscosity is not much changed. Without correction, Vmax after O2-breathing will be underestimated by about 6%, compared with Vmax for normal alveolar gas, whereas a change in alveolar CO2 concentrations between 3 and 9% only causes a 1% decrease of Vmax.

Adolescent↗
PubMed1976

The effect of CO2 on peripheral airways.

In each of ten healthy young subjects breathing different concentrations of CO2 in O2, four alveolar CO2-tension levels were obtained, ranging from about 20 mmHg when hyperventilating in O2 to 50 mmHg. Maximum expiratory flows at 60% total lung capacity were measured at each level and corrected for the influence of the expired gas on the flow. The corrected maximum flow decreased significantly when the alveolar CO2 tension was below 30-35 mmHg, while there was only slight or no influence of CO2 on the maximal flow when the tension was above 35 mmHg. The decrease is taken as evidence of a constrictor effect on peripheral bronchi of hypocapnia.

Adult↗
PubMedDate not supplied

Respiratory disease and lung function in a tobacco industry.

In a field study, 75 workers from a cheroot factory were compared with 50 reference workers from a large telephone company. Questionnaire responses revealed higher prevalences of cough and shortness of breath on exercise among the tobacco workers than controls. Cigarette smoking was the same in the two groups, but tobacco workers also smoked cheroots. Significantly decreased values (p less than .01) of forced expiratory volume in 1 sec (FEV1.0) and forced vital capacity (FVC) were found among tobacco workers compared to referents. After adjusting for number of cigarettes and cheroots smoked, there remained no significant differences. There was a suggestion (p less than .10) of decreased FEV1.0 among light or nonsmoking tobacco workers. When cigarette consumption only was considered, this difference was significant (p less than .01). Lung function values were not associated with the very low measured dust exposures. Bronchial reactivity to inhaled histamine, diurnal and weekly changes in FEV1.0, skin-prick tests with tobacco extracts, and precipitating serum antibodies to tobacco extracts and extracts of microorganisms were similar to that expected in a nonexposed population. Differences in lung function between the two groups may result from excess cheroot consumption and higher previous exposure to tobacco dust among the tobacco workers.

Adult↗
PubMedDate not supplied

Sensitivity of the eyes to airborne irritant stimuli: influence of individual characteristics.

The purpose of this study was to measure trigeminal sensitivity of the eyes to irritative exposures and to examine the influence of individual characteristics, e.g., gender, age, and smoking, on this sensitivity. During an experimental study, 158 of 2,025 randomly selected volunteers were examined for sensory irritation threshold in the eyes to carbon dioxide (CO2). Eyes were exposed to progressive concentrations of CO2 (10, 20, 40, 80, and 160 ml/l), until the subject claimed a distinct irritation. Each exposure level lasted 2 min. A special exposure mask system was used for eyes-only exposure. No significant dependence of gender or smoking was found, but subjects who were less than 40 y of age were more sensitive than were the elderly subjects. Subjects who reported frequent "sick building syndrome" irritation symptoms had lower thresholds (i.e., higher sensitivity). The CO2 threshold was related to skin irritation sensitivity, i.e., response to lactic acid smeared on the cheek, and there were indications that occupational stress was associated with low thresholds. Studies of irritation to n-decane indicate that the CO2 threshold may be an important factor in the prediction of individual sensitivity to irritation from airborne pollutants. The CO2 threshold of the eyes may be of value in the evaluation of hypersensitivity to indoor air pollution. Furthermore, the threshold may be used to assess important relationships between the different trigeminal innervated areas, e.g., skin and eyes. Finally, the method has the advantage of avoiding interference from olfactory stimulation.

Adolescent↗
PubMedDate not supplied

Comparative oral and topical decongestant effects of phenylpropanolamine and d-pseudoephedrine.

Nonselective adrenergic alpha-agonists such as phenylpropanolamine and d-pseudoephedrine are widely used as decongestants to treat nasal congestion associated with a variety of nasal diseases. Although the activity of these drugs is well established in clinical studies, a direct comparison of their nasal decongestant effect as determined by changes in nasal cavity dimensions and nasal architecture has not been studied. Using acoustic rhinometry, we evaluated the effects of these drugs on nasal cavity volume, minimum cross-sectional area (Amin), and the distance from the nosepiece to the Amin (Dmin) in a feline, pharmacological model of nasal congestion. Administration of topical compound 48/80 (1%), a mast cell histamine liberator, into the left nasal passageway decreased nasal volume by 66%, reduced Amin by 51%, and increased Dmin by 116%. The congestive responses to compound 48/80 (1%) were reproducible through six weeks. In a subset of cats, the nasal cavity volume effect of repetitive exposure to compound 48/80, given once every two weeks for six weeks, was not different from the nasal responses after the initial exposure to compound 48/80. Pretreatment with oral phenylpropanolamine (10 mg/kg) or oral d-pseudoephedrine (10 mg/kg) attenuated the nasal effects of compound 48/80, but were associated with a pronounced increase in systolic blood pressure of +51 and +82 mmHg, respectively. A similar decongestant profile was observed with phenylpropanolamine (1%) and d-pseudoephedrine (1%) when given topically. Topical phenylpropanolamine (1%) and d-pseudoephedrine (1%) 45 minutes after dosing increased blood pressure +44 and +17 mmHg, respectively, over control animals. We conclude that oral and topical phenylpropanolamine and d-pseudoephedrine display equieffective nasal decongestant activity and produce similar cardiovascular profiles characterized by significant increases in blood pressure.

Administration, Oral↗
PubMedDate not supplied

Evaluation of nasal passage patency after antigen and histamine challenge in guinea pigs by acoustic rhinometry.

We investigated the effects of antigen and histamine on the nasal passage patency in guinea pigs with or without nasal allergy. The change of nasal patency was measured by acoustic rhinometry and nasal airway resistance. Acoustic reflections have been used in adult humans to determine nasal cavity dimensions in terms of cross-sectional areas as a function of the distance from the nostril. In order to measure nasal cavity dimensions in guinea pigs, we modified equipment for use in humans by decreasing sound tube dimensions, increasing sampling frequency, and applying a special nosepiece. The percent change of volume, minimum cross-sectional area, and nasal airway resistance showed the largest changes at 10 minutes after antigen challenge in sensitized guinea pigs. There was a significant correlation between the individual percent change of nasal airway resistance and volume or minimum cross-sectional area. Histamine, 10(2) to 10(5) micrograms/mL, caused a dose-dependent reduction in percent change of volume in the challenged side of nonsensitized guinea pigs, but not in the opposite side. These results indicate that the noninvasive acoustic reflections technique is useful in small experimental animals, especially to assess the effect of nasal cavity dimensions after the challenge of antigen or nonspecific stimuli.

Adult↗
PubMedDate not supplied

Accuracy of measurement of acoustic rhinometry applied to small experimental animals.

Nasal obstruction is one of the major symptoms of allergic rhinitis. In the study of the mechanism of nasal obstruction, experiments on animal are useful. In adult humans, acoustic rhinometry has been used to evaluate nasal obstruction by determining nasal cavity dimensions in terms of cross-sectional areas as a function of the distance from the nostril. We modified the equipment used on humans to assess dimensions of nasal airway geometry of small experimental animals. The purpose of this study was to investigate the accuracy of measurement of the modified acoustic rhinometry applied to small experimental animals using nasal cavity models and guinea pigs. Measurement of the nasal cavity models (made of cylindrical silicone tubes) showed that the acoustic rhinometry estimated 85.5% of actual area and 79.0% of actual volume. In guinea pigs, nasal cavity volume determined by the acoustic rhinometry was 73.7 +/- 20.0% of actual volume. The actual volume was estimated by impression material instilled into the nasal cavity of the animals (IM volume), and volume determined by acoustic rhinometry significantly correlated with IM volume. Furthermore, there was a significant negative correlation between the volume and nasal airway resistance in guinea pigs. Measurement of the nasal airway resistance is the method frequently used in the evaluation of the nasal obstruction in guinea pigs. These results suggest that acoustic rhinometry is useful in evaluating nasal obstruction in small experimental animals.

Acoustics↗
PubMedDate not supplied

A device for evaluation of flow recording equipment.

We have constructed a calibration device which simulates a maximum expiratory flow, and which can also be used to determine quantitatively the frequency response and linearity of flow recording equipment. It consists of a pressure chamber full of copper chips serving as a heat exchanger. When inflated to twice the atmospheric pressure, it delivers 8.2 l of air during deflation. Deflation is released by a falling weight. The time tS between 10% and 90% of the peak expiratory flow out of the chamber (PEFR) can be varied between 10 ms and 90 ms. PEFR up to 19 l X s-1 can be obtained by changing the size of an orifice in the outlet line. The calibrator was tested with a Fleisch no 4 pneumotachograph linear up to 15 l X s-1. The coefficient of variation of PEFR (12.2 l X s-1) and FVC (8.2 l) was 2% and 1% respectively for 10 consecutive deflations. The frequency response in terms of tS of the tested equipment can be evaluated from the flow-volume curve produced by the calibrator. Examination of tS in 50 medical students shows that tS of the equipment should be less than about 20 ms in order to correctly measure PEFR. By means of a single deflation, the linearity of the total recording system can be tested over a range of flows because the flow signal of the calibrator is declining almost linearly with time.

Forced Expiratory Flow Rates↗