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Biomedical subjects

R Peslin

Publications and source records attributed to R Peslin.

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

Influence of panting frequency on thoracic gas volume measurements in chronic obstructive pulmonary disease.

Frequency dependence of thoracic gas volume (Vtg) and phase angles between volume and mouth pressure signals were evaluated in 10 normal subjects and in 31 patients with bronchitis, who panted sequentially at 0.8 Hz and 2.5 Hz during the same occlusion. A slight negative frequency dependence of Vtg (-1.2 +/- 0.9%/Hz, -m +/- SD), accompanied by a very small phase lag of volume with respect to pressure variations (-1.5 +/- 0.9 degrees at 2.5 Hz) was found in normal subjects. In contrast, patients with bronchitis exhibited a mild positive frequency dependence of Vtg (+ 0.5 +/- 1.7%/Hz and + 0.8 +/- 2.3%/Hz in subjects with normal and increased airway resistance, respectively), whereas the volume signal slightly led the pressure signal at 2.5 Hz. Both the frequency dependence and the phase difference increased when the subjects with the largest airway resistance did not support their cheeks during the panting maneuvers. The data confirm previous indirect evidence that Vtg is, in most instances, accurately measured by Boyle's law in mild and moderate chronic airway obstruction.

Adult↗
PubMed1984

Respiratory mechanical impedances. Methodology and interpretation.

A synthetic approach to lung and chest mechanics is to apply pressure variations to the respiratory system over a range of frequencies and to study the amplitude and phase relationships between applied pressure and resulting gas or tissue flow. Such impedance measurements may be performed in different ways, which are not equivalent: the most usual are to measure gas flow at the mouth while pressure is varied either at the same place (input impedance) or around the chest (transfer impedance). Transfer impedance measurements were performed in healthy subjects from 3 to 70 Hz and tentatively interpreted with a model featuring tissue elasticity, resistance and inertance, gas compressibility, and airway gas resistance and inertance. The pressure-flow ratio was minimum at 5-10 Hz and increased very fast above 50 Hz. The phase angle was nil around 7 Hz, of + 90 degrees at 30-40 Hz and close to 180 degrees at 70 Hz. The validity of the model is supported by the quality of the fit to the data up to 50 Hz, the values of the coefficients and the results of experiments where the subject's mechanical properties were varied.

Biomechanical Phenomena↗
PubMed1984

[Study of maximal expiratory flows with light gases. Theoretical aspects].

The modification of maximum expiratory flows with low gas density breathing was proposed a decade ago as a test of small airway obstruction. This short review discusses the theoretical bases of the method. Three kinds of approaches have been proposed to interpret the findings: the "equal pressure point" concept of Mead et al. has stressed the role of the resistance upstream and of elastic recoil; the "flow limiting segment" concept of Pride et al. has underlined the role of central airways compliance (the compressed segment acting as a resistor); recently, the "choke point theory" proposed by Dawson and Eliott discusses the role of wave speed propagation in the walls of elastic tubes. All these three interpretations take into account the influence of the density of the gas breathed--a factor governing the drop in transmural pressure between the alveoli and the central airways, and a determinant of the speed of pressure wave propagation. In principle, every reduction in gas density should lead to an increase in maximal flow; this modification would be less marked if the flow in the upstream segment is essentially laminar due to obstruction in the peripheral airways. Several points complicating the interpretation are discussed: a) the flow in the small airways is never strictly laminar; b) the change in gas density (usually-breathing a He-O2 mixture) also influences the length of the upstream segment and the pressure wave speed; c) the influence of the cross sectional area and compliance of central airways cannot be neglected.(ABSTRACT TRUNCATED AT 250 WORDS)

Forced Expiratory Flow Rates↗
PubMed1983

Effects of induced hypotension on breathing pattern in halothane-anaesthetized man.

The effects of hypotension induced by trimetaphan on ventilatory control were assessed in sixteen normal subjects under halothane anaesthesia. The breathing pattern, mouth occlusion pressures, lung mechanics, acid-base balance, and arterial blood gases were analysed before and during trimetaphan infusion. During induced hypotension, the only significant change in the ventilatory variables was an increase in the ratio of inspiratory duration to total cycle duration from 0.39 +/- 0.05 (SD) to 0.42 +/- 0.03; P less than 0.01. The average minute ventilation remained unchanged. No modification in lung mechanics was observed, but all subjects developed a slight but significant hypocapnic alkalosis: PaCO2 was reduced from 5.5 +/- 0.4 to 5.2 +/- 0.4 kPa (P less than 0.001) and pH increased from 7.34 to 7.36 (P less than 0.05), without change in standard bicarbonate concentration. Our data indicate that the reduction in sympathetic nervous system activity induced by trimetaphan infusion in spontaneously breathing man causes only a minor alveolar hyperventilation. The weak respiratory response to hypotension suggests that changing peripheral afferent activity has little influence on the typically rapid breathing pattern induced by halothane.

Acid-Base Equilibrium↗
PubMed1983

Influence of second-order data filtering on common forced expiration indices.

Forced expiratory manoeuvres are extensively recorded using flow meters coupled to pressure transducers, which usually behave like second-order filters. To assess what should be the dynamic characteristics of such equipment for accurate determination of common forced expiration indices, 125 curves were obtained from 25 healthy subjects in the best technical conditions. The flow-time curves were then submitted to various degrees of second-order filtering, and the indices derived from filtered and unfiltered curves were compared. Considering that experimental error is acceptable if it does not exceed 20% of the normal interindividual variability for 95% of the curves, the following conclusion was drawn; with an optimal damping ratio (r) of 0.7, forced expiratory volume in one second, maximum midexpiratory flow rate and maximal expiratory flow at 25% of the forced vital capacity (MEF25) are still correctly measured when the resonant frequency (fn) is as low as 3 Hz. The corresponding figures are 5 Hz for MEF50, 20 Hz for peak expiratory flow rate and above 20 Hz for MEF75. Higher values of fn are usually required when r is higher or lower than 0.7.

Adult↗
PubMed1983

Influence of increased alveolar PCO2 on thoracic gas volume measurements.

We examined the possibility that cyclic gas exchange between alveolar space and the surrounding tissue, induced by alveolar pressure variations, could interfere with plethysmographic measurements of thoracic gas volume (TGV). A model study suggested that TGV could be overestimated by up to 100 ml and that the phenomenon could account for some of its previously reported negative frequency dependence (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 52: 739-747, 1982). As the error would be mainly due to CO2 exchange and be proportional to its partial pressure (PCO2), we studied in nine normal subjects the influence of increasing alveolar PCO2 from 30 to 50 Torr on TGV measurements at panting frequencies (f) of 0.5 and 2-2.5 Hz. Contrary to model predictions, CO2 tended to decrease TGV estimates at low frequency and to increase them at high frequency. As a consequence, frequency dependence of TGV (delta TGV/delta f) was less at high than at low PCO2 (-39 +/- 32 vs. -84 +/- 49 ml x Hz-1, P less than 0.001). The data are not satisfactorily explained but suggest that gas exchange is not an important factor in TGV measurements.

Adult↗
PubMed1983

1-second forced expiratory volume and density dependence in early airflow limitation.

Density dependence variables (helium-to-air difference in forced expiratory flows at 50 and 25% vital capacity and volume of isoflow) were compared with spirographic performance (vital capacity, FEV 1.0) in 76 men aged 33-56 years. The group included nonsmokers, asymptomatic smokers, subjects with chronic expectoration, but normal ventilatory function and subjects with chronic expectoration and minimal obstructive ventilatory impairment. Low-level correlations were found (coefficients of less than 0.3) between delta He25% or volume of isoflow on one side and FEV1.0 or FEV1.0/VC. Some possibly confounding factors for these correlations are discussed. We conclude that density dependence variables are not consistently related to the FEV1.0 in subjects 'at risk' or with minimal airflow limitation.

Adult↗
PubMed1982

Variability, reproducibility and observer difference of body plethysmographic measurements.

The variability (coefficient of variation of five consecutive measurements), reproducibility (difference of results at 1 h and 24 h), and interobserver difference (independent reading of the tracings by two observers) of airways resistance (Raw) and static lung volumes (residual volume, functional residual capacity, total lung capacity) using a body plethysmograph were assessed in 14 healthy subjects and in 25 patients with various respiratory disorders. The variability was low for TLC (4-5%), moderate for FRC (7-8%) and high for Raw (28%). No significant changes of Raw or lung volumes were found for the groups at 1 h and 24 h. Between observers, a slight difference existed for FRC and Raw in normal subjects; the difference was higher (4.5% for FRC and 11% for Raw) and became significant in patients. The overestimation of Raw by observer 2 as compared to observer 1 was more important at larger values. The present findings call for caution when pooling results obtained by several observers in large-scale studies, or when comparing figures obtained by different technicians in the pulmonary function laboratory.

Adult↗
PubMed1982

Density dependence of maximal expiratory flows in normal subjects: influence of sex, age, body build and spirographic variables.

We studied the correlation between density-dependence parameters (delta He, volume of isoflow) and age, body build, spirography and forced expiratory fows in 69 healthy non-smokers (16 females) aged 18 to 51 years. Density dependence variables showed no significant differences between young (less than 35 years) males and females. Volume of isoflow per cent of forced vital capacity (Viso V % FVC) was poorly significantly related to age (r = +0.25 P less than 0.05) and weight (r = +0.27 P less than 0.05). Significant correlations were found between density dependence at low lung volume and the FEV1/VC ratio (r = 0.31, P = 0.01 for delta He 25%; r = -0.40, P less than 0.001 for Viso V% FVC) or the forced expiratory flows with air (Viso V% FVC vs. FEF 25% r = -0.42, P less than 0.001). These correlations were closer in females as compared to males. Volume of isoflow was well related to delta He 25% (r = -0.64, P less than 0.001), but the relationship with delta He 50% was weaker (r = -0.38; P less than 0.01).

Adolescent↗
PubMed1982

Influence of panting frequency on plethysmographic measurements of thoracic gas volume.

Using an integrated flow pressure-corrected body plethysmograph we obtained total lung capacities (TLC) derived from thoracic gas volumes measured at low, medium, and high panting frequencies in 10 healthy men and in 13 patients with chronic airflow obstruction before and after an aerosol of albuterol. Using a gastric balloon we also assessed gastric-to-mouth pressure ratios (delta Pga/delta Pm). In patients before albuterol, estimated TLC remained unchanged from low to medium and increased (not significantly) from medium to high frequency. Healthy subjects and patients after albuterol showed a significant decrease in TLC from low to medium panting frequencies, which persisted after correcting the data for abdominal gas compression using observed delta Pga/delta Pm. In patients after albuterol the results may be explained, at least in part, by intrathoracic airway compliance and mechanical inhomogeneity of the lung. In healthy subjects a remote possibility is the association of mechanical inhomogeneity and nonuniform pleural pressure.

Adult↗
PubMed1982

Mechanical properties of the lungs during acclimatization to altitude.

Mechanical properties of the lung were studied in nine healthy lowlanders during a 6-day sojourn at an altitude of 3,457 m. In comparison to sea-level values, it was found at altitude that 1) lung volumes measured by plethysmography including total lung capacity, vital capacity, and functional residual capacity (FRC) presented small changes not exceeding 300 ml; 2) static and dynamic lung compliances were not modified but static pressure-volume curves of lungs were shifted progressively to the left (the decrease in lung elastic recoil averaged about 2 cmH2O on days 4-6); and 3) maximal midexpiratory flow, forced expiratory volume in 1 s, and maximal expiratory and inspiratory flows were increased and, conversely, airways and pulmonary flow resistances were decreased on most days at altitude. The unchanged FRC in the face of a decreased lung recoil may be explained by an increase in thoracic blood volume at altitude, but other possible mechanisms are discussed. The decrease in resistances and increase in maximal flows may be partly explained by the decreased air density at altitude, but another contributing factor such as a bronchodilatation is also suggested. It is proposed that changes in lung mechanics at altitude may account for some of the changes in the pattern of breathing and mouth occlusion pressure (P0.1) observed during acclimatization of lowlanders to altitude.

Acclimatization↗
PubMed1981

Sensitivity of forced expiration indices to induced changes in peripheral airway resistance.

To assess the actual sensitivity of forced expiration indices to changes in the resistance of peripheral airways, maximal expiratory flow-volume curves were obtained in 30 normal subjects breathing air and breathing an O2-Ne-SF6 gas mixture having the same density as air but a 45% larger viscosity. The measurements were made using a bag-in-box system to circumvent calibration problems, and the data were processed digitally. Besides the usual forced expiration indices, slope ratios, as described by Mead (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44: 156-165, 1978), and transit time indices were also computed. Breathing the viscous mixture, the largest changes were seen with the slope ratio measured at 60% forced vital capacity, followed by other slope ratios, the standard deviation of transit times, and maximal flows at low lung volumes. However, when the data were compared using the t test for paired measurements, the most significant changes were found with the forced expiratory volumes at 1 and 2 s, due to their low within-subject variability. These indices may therefore by considered as the most suitable for detecting changes in individuals.

Adult↗
PubMed1981

Phrenic activity, respiratory pressures, and volume changes in cats.

In eight anesthetized cats we measured the integrated ("moving time average") phrenic activity [using phrenic electroneurogram (EPHR)] and the active transdiaphragmatic pressure [Pdi(mus)] during room air breathing, hypoxia, and hypercapnia. The relationship between Pdi(mus) and EPHR was unaffected by either hypoxic or hypercapnic stimulation of breathing, suggesting that in spontaneously breathing cats the pressure losses are negligible. In all cats, however, there was a substantial volume-related decrease in Pdi(mus), indicating that with increasing lung volume the effectiveness of the diaphragm as a pressure generator decreases. In addition, we have developed a model that allows prediction of the time course changes in lung volume for different morphology of inspiratory driving pressure. This model explains many of the features of control of breathing found experimentally in our cats.

Animals↗
PubMed1980

Usefulness of forced expiration slope ratios for detecting mild airway abnormalities.

To assess their value for early recognition of airway abnormalities, forced expiration slope ratios as recently defined by Mead, were measured at 5 lung volumes in 114 healthy nonsmokers and in 76 cigarette smokers. In healthy nonsmokers, slope ratios were independent of sex and body height, but were significantly correlated with age. They tended to be higher at low lung volume, particularly in older subjects. In male smokers with a tobacco consumption of less than 5 pack-years, slope ratios were increased at both ends of the volume range, suggesting nonhomogeneous lung emptying and peripheral airway obstruction. With increasing tobacco consumption, slope ratios tended to return to normal values at low lung volume, perhaps because of airway closure. In female smokers, slope ratios were decreased at high lung volume and increased at low lung volume, suggesting that both central and peripheral airways were abnormal. Mead's analysis appeared to be a useful tool for discussing the data in terms of functional abnormalities. However, because of their large variability, slope ratios were not as successful as transit time indices for recognizing abnormal subjects.

Adult↗
PubMed1979

[Pulmonary function and clinical pattern in homozygous (PiZ) alpha1-antitrypsin deficiency (author's transl)].

A group of 6 males with severe alpha1-antitrypsin deficiency, underwent clinical and pulmonary function evaluation. Findings were compared to those in a group of males with different degrees of airflow obstruction, comparable ages and tobacco consumption, but with normal serum levels of alpha1-antitrypsin. The deficient group was characterized by: (1) a relatively early appearance of symptoms; (2) disturbed lung scans, mostly in the basal zones; (3) radiological evidence, in most cases, of pulmonary emphysema with, in particular, bullae in the lower lung zones; (4) hypoxemia without hypercapnia and a decreased TCO/VA, and (5) a more or less severe reduction of maximal expiratory flows largely, but not exclusively due to a decrease in lung elastic recoil. Clinical and functional parameters did not permit a clear distinction between the deficient and non-deficient groups.

Adult↗