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Biomedical subjects

O F Pedersen

Publications and source records attributed to O F Pedersen.

At least 37 records · Page 2Linked to original sources
PubMed2000

Acoustic rhinometry: recommendations for technical specifications and standard operating procedures.

This document is the result of the work and discussion of the Standardization Committee on Acoustic Rhinometry and presents guidelines for quality control and optimal application of acoustic rhinometry at its present stage. It is suggested that: 1. A well-defined standard nose is used for testing and optimising the equipment (data for a standard nose is given in the paper). 2. Procedures for evaluation of accuracy and repeatability of the measurements in the standard nose are presented, and error limits are defined for the area-distance curve as a whole, for the minimum cross-sectional area and for the volume from 0-5 cm into the nose. 3. Publication of results should include the volume 0-5 cm into the nose (volume from 2-5 cm for mucosal changes) the minimum cross-sectional area or preferably the two first minima and the distances to those areas. 4. The operator should be trained, follow a standard operating procedure and the environmental conditions (temperature and noise) be controlled. 5. Attention should be given to the nosepiece and the coupling between the equipment and the nose to obtain correct position, and sufficient seal without disturbing the anatomy. 6. The manufacturer should give information about the performance of the equipment, calibration procedures and maintenance, hygiene, environmental and safety standards.

Acoustics↗
PubMed2000

Acoustic rhinometry in infants and children.

Acoustic rhinometry (AR), introduced a decade ago for assessment of the nasal airways of adults, has several attractive features relevant to application in a paediatric population. Its non-invasive nature, simplicity and rapidity are prime assets when examining infants and small children. Valid AR measurements can be obtained in a few seconds and require minimal co-operation. The striking consistency of AR studies of healthy subjects and the agreement with CT-derived and directly measured choanal dimensions are a strong indication of its reliability. Acoustic rhinometry optimised for infants and small children opens new perspectives and possibilities in the assessment of nasal airway dimensions and their relationship to pathological conditions in both the upper and the lower airways. The objective of this paper is to describe the advantages of AR in infants and children, but also point out its limitations and potential sources of error. Practical guidelines as to the measurement procedure and analysis and interpretation of AR-data are outlined.

Acoustics↗
PubMed1999

Characterization of heparin aerosols generated in jet and ultrasonic nebulizers.

Inhaled heparin has been used for asthma treatment, but results have been inconsistent, probably due to highly varying lung doses. We determined the output per unit time and the particle size distributions of sodium heparin, calcium heparin, and low molecular weight (LMW) heparin formulations in five concentrations from Sidestream jet nebulizers (Medic-Aid, Bognor Regis, England) and an Ultraneb 2000 ultrasonic nebulizer (DeVilbiss, Langen, Germany). We also determined the inhaled mass and the estimated respirable mass for some combinations. For the jet nebulizer, output per minute increased with increasing concentration and flow rate, and particle size decreased from 3.64 to 2.01 microns (mass median diameter [MMD]). The percentage of particles less than 3 microns ranged from 41% to 74%. For the ultrasonic nebulizer, maximum output per minute was achieved at a concentration of 7000 i.u./mL; this maximum depended upon the viscosity and temperature of the solution. MMD was independent of formulation, temperature, or concentration and ranged from 5.61 to 7.03 microns. Sodium heparin/calcium heparin in a concentration of 20,000 i.u./mL in the jet nebulizer driven at 10 L/min produced the highest dose of heparin capable of reaching the lower respiratory tract. Mass balance was determined for these combinations with the jet nebulizer run until visible aerosol generation ceased. Of a loading dose of 80,000 i.u. of heparin, 45,000 i.u. remained in the dead space of the nebulizer, 20,000 i.u. was deposited on the exhalation filter, and 15,000 i.u. was captured on the inhalation filter (inhaled mass). This corresponds to a respirable mass of 10,000 i.u. of heparin with a high probability of reaching the lower respiratory tract in normal healthy adults.

Adult↗
PubMed1999

Lung status in young Danish rurals: the effect of farming exposure on asthma-like symptoms and lung function.

The aim of this study was to assess the prevalence of asthma (self-reported) and relate this to lung function and factors associated with asthma in young farmers. Two hundred and ten female and 1,691 male farming students together with 407 males controls were studied. Each subject underwent a medical interview; forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were recorded using a dry wedge spirometer. Histamine bronchial reactivity was measured using the Yan method. Skin prick testing was performed using inhalant allergens. Nonsmokers had lower prevalence of asthma (5.4-10.8%) than smokers (11.3-21.0%) (p<0.05). Females reported symptoms of asthma nearly twice as often as males. Sex, smoking and a family history of asthma/allergy were significantly associated with asthma. Controls had higher standardized FEV1 and FVC residuals than male students, both nonsmokers (0.21 and 0.24) versus (-0.06 and -0.05) and smokers (0.29 and 0.33) versus (-0.11 and 0.13) (p<0.032). Bronchial hyperresponsiveness, asthma, siblings with allergy and working with cattle (controls only) were significantly associated with reduced lung function. In conclusion, the prevalence of asthma was significantly related to smoking, female sex, family history of asthma and allergy. Whilst bronchial hyperresponsiveness was associated with reduced lung function and lung function was slightly reduced in the male farming students, there was no association found between occupational farming exposure and either lung symptoms or lung function.

Adolescent↗
PubMed1998

Acoustic reflections during rhinometry: spatial resolution and sound loss.

The accuracy of the acoustic reflections method for the evaluation of human nasal airway geometry is determined by the physical limitations of the technique and also by the in vivo deviations from the assumptions of the technique. The present study 1) examines the sound loss caused by nonrigidity of the nasal mucosa and viscous loss caused by complex geometry and its influence on the estimation of the acoustic area-distance function; 2) examines the optimal relation between sampling frequency and low-pass filtering, and 3) evaluates advantages of breathing He-O2 during the measurements on accuracy. Measurements made in eight plastic models, with cavities exactly identical to the "living" nasal cavities, revealed only minor effects of nonrigidity of the nasal mucosa. This was confirmed by an electrical analog model, based on laser vibrometry admittance measurements of the nasal mucosa, which indicated that the error in the acoustic measurements caused by wall motion is insignificant. The complex geometry of the nasal cavity per se (i.e., departure from circular) showed no significant effects on the measurements. Low-pass filtering of the signal is necessary to cut off cross modes arising in the nasal cavity. Computer simulations and measurements in models showed that the sampling frequency should be approximately four times the low-pass filtering frequency (i.e., twice the Nyquist frequency) to avoid influence on the result. No advantage was found for the the use of He-O2 vs. air in the nasal cavity.

Acoustic Stimulation↗
PubMed1998

The rise and dwell time for peak expiratory flow in patients with and without airflow limitation.

The response of peak expiratory flow (PEF) meters may be affected by the magnitude of PEF, the time taken to get to PEF, and the duration that the peak is sustained. We undertook a retrospective study to define the 10 to 90% rise time (RT) and dwell time for flow above 90% (DT90) and 95% (DT95) of PEF. Blows were analyzed that had been recorded using a pneumotachograph from 912 patients older than 17 yr of age (556 men) who routinely attended a lung function laboratory. For each subject, that blow with the largest PEF was used to derive the PEF, FEV1, FVC, RT, DT90, and DT95. The values for RT, DT90, and DT95 were negatively skewed with the median values for men of 58, 29, and 19 ms, respectively, being significantly shorter than those for the women of 67, 49, and 31 ms. From the 912 subjects, there were 277 (153 men) who had all their spirometric indices within the normal range, and 305 (220 men) had both PEF and FEV1 more than 1. 645 SD below predicted, indicating airflow limitation. For subjects with airflow limitation the median RT was significantly smaller than in the normal subjects (men: 46 versus 72 ms, women: 50 versus 72 ms), and the same was found for DT90 (men: 22 versus 40 ms, women: 27 versus 56 ms) and DT95 (men: 15 versus 26 ms, women: 18 versus 34 ms). We conclude that the dwell times for PEF are shorter in men, and the rise and dwell times are shorter in patients with airflow limitation. Profiles used to test PEF meters should encompass the range of rise and dwell times found in subjects most likely to be using PEF meters, that is, those with airflow limitation.

Adult↗
PubMed1997

Spirometry with a Fleisch pneumotachograph: upstream heat exchanger replaces heating requirement.

The exact temperature of the head of an unheated Fleisch pneumotachograph (PT) during recording is not known, and variation in its temperature may lead to errors in measuring spirometric indexes. We measured PT head temperature during blows from five normal subjects, recorded by using a PT with and without an upstream heat exchanger to condition the air to the ambient temperature that was set in a climate chamber. Group mean (+/- SD) temperature of a thermocouple (TC) placed inside the PT head was 11.8 +/- 1.9 degrees C with 7 degrees C ambient, 25.4 +/- 1.3 degrees C at 23 degrees C, and was 37.2 +/- 0.3 degrees C at 37 degrees C. The between-subject range of temperature for this TC was 7.5 degrees at 7 degrees C, 5.5 degrees at 23 degrees C, and 1.1 degrees at 37 degrees C. The mean within-subject within-blow variation of temperature for this TC was 10.0 degrees and 3.3 degrees C for ambient of 7 degrees and 23 degrees C, respectively. At the usual ambient temperature in a laboratory, these differences in temperature lead to a 3.6% between-subject bias in recording, and the within-subject differences lead to 2.6% underreading of peak expiratory flow and a 0.5% overreading later in the blow, which makes ATPS-to-BTPS correction erroneous or difficult to perform. With the use of an upstream heat exchanger, the group mean temperature was 8.7 +/- 0.4 degrees, 23.2 +/- 0.2 degrees, and 37.1 +/- 0.2 degrees C at the three ambient temperatures, respectively, and the within-subject within-blow variation was reduced to < 1 degrees C. A heat exchanger placed upstream of the PT satisfactorily conditioned expired air to the ambient temperature and removed the error.

Adult↗
PubMed1997

Gas compression in lungs decreases peak expiratory flow depending on resistance of peak flowmeter.

It has recently been shown (O. F. Pedersen T. R. Rasmussen, O. Omland, T. Sigsgaard, P. H. Quanjer. and M. R. Miller. Eur. Respir. J. 9: 828-833, 1996) that the added resistance of a mini-Wright peak flowmeter decreases peak expiratory flow (PEF) by approximately 8% compared with PEF measured by a pneumotachograph. To explore the reason for this, 10 healthy men (mean age 43 yr, range 33-58 yr) were examined in a body plethysmograph with facilities to measure mouth flow vs. expired volume as well as the change in thoracic gas volume (Vb) and alveolar pressure (PA). The subjects performed forced vital capacity maneuvers through orifices of different sizes and also a mini-Wright peak flowmeter. PEF with the meter and other added resistances were achieved when flow reached the perimeter of the flow-Vb curves. The mini-Wright PEF meter decreased PEF from 11.4 +/- 1.5 to 10.3 +/- 1.4 (SD) l/s (P < 0.001), PA increased from 6.7 +/- 1.9 to 9.3 +/- 2.7 kPa (P < 0.001), an increase equal to the pressure drop across the meter, and caused Vb at PEF to decrease by 0.24 +/- 0.09 liter (P < 0.001). We conclude that PEF obtained with an added resistance like a mini-Wright PEF meter is a wave-speed-determined maximal flow, but the added resistance causes gas compression because of increased PA at PEF. Therefore, Vb at PEF and, accordingly, PEF decrease.

Adult↗
PubMed1997

Wave-speed-determined flow limitation at peak flow in normal and asthmatic subjects.

The purpose of this study was to examine whether peak expiratory flow is determined by the wave-speed flow-limiting mechanism. We examined 17 healthy subjects and 11 subjects with stable asthma, the latter treated with inhaled bronchodilators and corticosteroids. We used an esophageal balloon and a Pitot-static probe positioned at five locations between the right lower lobe and midtrachea to obtain dynamic area-transmural pressure (A-Ptm) curves as described (O. F. Pedersen, B. Thiessen, and S. Lyager. J. Appl. Physiol. 52: 357-369, 1982). From these curves we obtained cross-sectional area (A) and airway compliance (Caw = dA/dPtm) at PEF, calculated flow at wave speed (Vws = A[A/(Caw*rho)0.5], where rho is density) and speed index is (SI = V/Vws). In 13 of 15 healthy and in 4 of 10 asthmatic subjects, who could produce satisfactory curves, SI at PEF was > 0.9 at one or more measured positions. Alveolar pressure continued to increase after PEF was achieved, suggesting flow limitation somewhere in the airway in all of these subjects. We conclude that wave speed is reached in central airways at PEF in most subjects, but it cannot be excluded that wave speed is also reached in more peripheral airways.

Adult↗
PubMed1997

The Peak Flow Working Group: physiological determinants of peak expiratory flow.

Peak expiratory flow (PEF) can be defined as the maximum flow at the mouth achieved during an expiration, delivered with maximum force starting from the level of maximum lung inflation. There is evidence that PEF may be determined by the wave speed flow-limiting mechanism, in which case a high PEF is consistent with a low resistance upstream to the flow-limiting segment (the choke point), a large cross-sectional area here, and/or a small compliance of the airway wall. PEF is obtained when the expiration is initiated with maximal inflation of the lungs, because this will make the elastic recoil pressure maximal and the upstream frictional pressure loss minimal. PEF is obtained with maximum expiratory effort, because high acceleration of flow will cause wave speed limitation at a higher lung volume. If PEF is not flow-limited, the effort-dependence will be marked. Flow transients of PEF beyond the maximum flow-volume perimeter may be related to effort-dependent contribution of flow from the collapsing airway, but time-dependent factors, instability of the airway, and inhomogeneities of the lungs may contribute. For the purpose of standardization, it is recommended that forced expiration is initiated with open glottis and immediately after a maximal inspiration. The position of the head should be neutral, because hyperextension may increase PEF and flexion may decrease PEF by changing the stiffness of the larger airways.

Humans↗
PubMed1997

The Peak Flow Working Group: test of portable peak flow meters by explosive decompression.

In 1991, 50 new Vitalograph peak flow meters and 27 previously used mini-Wright peak flow meters were tested at three peak flows by use of a calibrator applying explosive decompression. The mini-Wright peak flow meters were also compared with eight new meters. For both makes of meter there was an excellent within-meter and between-meter variation. The accuracy, however, was poor, with a maximal overestimation of true flows of 50 and 70 L.min-1 in the interval from 200 to 400 L.min-1 for the Vitalograph and mini-Wright meters, respectively. The deviation is explained by the physical characteristics of the variable orifice peak flow meters. They have been supplied with equidistant scales, which give non-linear readings.

Calibration↗
PubMed1997

Prediction of nasal obstruction based on clinical examination and acoustic rhinometry.

The aim of this study was to find variables which characterize nasal obstruction. Scores from the clinical history, anterior rhinoscopy and objective values from acoustic rhinometry were found of importance. In a randomly-selected adult population of 230 individuals, 14% had the subjective feeling of nasal obstruction. The variables of significant value to predict nasal obstruction were: (1) symptoms of hypersensitivity/allergy and infection; (2) anterior septal deviations; and (3) small anterior dimensions of the nasal cavity. A minimum cross-sectional area (MCA) equal to 0.50 cm2, a cross-sectional area at the piriform aperture of 0.70 cm2 and a large effect of decongestion at MCA were found to be the best variables to separate obstructed from normal noses. Also, differences between each side of the nose were found of predictive value. In conclusion, a nose at risk for nasal obstruction is one with symptoms of allergy, frequent infections, small dimensions anteriorly, large difference between both sides, and a large degree of swelling of the mucosa.

Acoustics↗
PubMed1996

Long-term performance of a hand held spirometer.

BACKGROUND: A study was undertaken to test the long term performance of a small hand held spirometer for self-administered serial spirometric testing. METHODS: Thirty turbine pocket spirometers (MicroMedical DiaryCard) were used in a clinical trial on 22 emphysematous patients with severe alpha 1-antitrypsin deficiency. The spirometers were able to store the date, time, forced expiratory volume in one second (FEV1), forced vital capacity (FVC), peak expiratory flow (PEF), and flow-volume loop for each blow. Every four weeks when the patients came for alpha 1-antitrypsin infusions the performance of their spirometer was checked before and after retrieval of the data from the spirometer. Calibration checks were threefold and included volume calibration with a 1.0 litre and 3.0 litre syringe, and flow calibration with a decompression calibrator. RESULTS: After two years of study the mean number of spirometric recordings performed per spirometer was 693 (range 237-1178), and the mean number of calibration checks was 33 (range 2-57). The coefficient of variation of the calibration signal was 1-2% for syringes and 0.5-1% for the decompression calibrator. The bearings of one turbine exhibited excessive friction after 17 months. None of the other 29 instruments showed drift, and a general drift of all spirometers towards larger or smaller readings could not be shown. However, unforeseen problems in the stability of the calibrating devices were observed. CONCLUSIONS: The small hand held turbine spirometers are suitable for long term patient-administered serial spirometric testing. The two year durability is acceptable and the long term reproducibility excellent.

Calibration↗
PubMed1996

Acoustic rhinometry: influence of paranasal sinuses.

The influence of the maxillary sinuses in acoustic rhinometry (AR) has not been evaluated, and this is the aim of the present study. We examined six subjects with AR and magnetic resonance imaging (MRI) after nasal decongestion to compare the area-distance relationships determined by the two methods. From the MRI data we obtained copies of the nasal cavities with and without maxillary sinuses, which were made in plastic by a stereolithographic method. AR curves from models without maxillary sinuses differed from AR curves with sinuses included but were in agreement with MRI curves without inclusion of sinuses. A similar difference in AR was seen in two subjects before and after the nasal cavities were flushed with saline to fill up the maxillary sinuses. The measured volume in the first 50 mm of the nasal cavity models was unaffected by the sinuses, but the volume in the first 70 mm corresponding to the length of the nasal cavity septum was increased slightly but significantly (from 10.8 to 11.3 cm3; P = 0.05). The presence of maxillary sinuses increased the volume of the epipharynx (70-100 mm from the nostril) from 12.2 to 21.3 cm3 (P < 0.01), and this increase was not due to the influence from the contralateral nasal cavity. We conclude that the maxillary sinuses may significantly contribute to the acoustically determined areas in the posterior part of the nasal cavity and the epipharynx, especially during decongestion, and may explain a part of the difference between area-distance curves obtained by AR and MRI, whereas contribution from the contralateral nasal cavity does not.

Humans↗