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PubMed2000

A dosimetric model for inhaled radioactive gases.

Mathematical simulation models have been used to study transport of insoluble and nonreactive gases for more than twenty years. However, gas and vapor transport and uptake still are not well understood, and a mathematical model for slightly soluble and nonreactive gas transport and uptake still has not been developed. This paper describes the development of a mathematical model of diffusion, convection, lateral transport into the airway wall, and alveolar absorption for inhaled radioactive gases in human conductive and respiratory airways. The model is based on a single-path trumpet-bell model. Sensitivity studies were conducted to ascertain the influence on the final model of the functional residual capacity, the tidal volume and diffusivity and solubility. Results obtained with this model are presented for HT gas exposure and are compared with other findings. In general, the results obtained in this research are in good agreement with other mean experimental results.

Air Pollutants, Radioactive↗

PubMed1980

Effects of expiratory loading on respiration in humans.

We examined the effects of expiratory resistive loads of 10 and 18 cmH2O.l-1.s in healthy subjects on ventilation and occlusion pressure responses to CO2, respiratory muscle electromyogram, pattern of breathing, and thoracoabdominal movements. In addition, we compared ventilation and occlusion pressure responses to CO2 breathing elicited by breathing through an inspiratory resistive load of 10 cmH2O.l-1.s to those produced by an expiratory load of similar magnitude. Both inspiratory and expiratory loads decreased ventilatory responses to CO2 and increased the tidal volume achieved at any given level of ventilation. Depression of ventilatory responses to Co2 was greater with the larger than with the smaller expiratory load, but the decrease was in proportion to the difference in the severity of the loads. Occlusion pressure responses were increased significantly by the inspiratory resistive load but not by the smaller expiratory load. However, occlusion pressure responses to CO2 were significantly larger with the greater expiratory load than control. Increase in occlusion pressure observed could not be explained by changes in functional residual capacity or chemical drive. The larger expiratory load also produced significant increases in electrical activity measured during both inspiration and expiration. These results suggest that sufficiently severe impediments to breathing, even when they are exclusively expiratory, can enhance inspiratory muscle activity in conscious humans.

Adult↗

PubMed1979

Airway closure during anesthesia: a comparison between resident-gas and argon-bolus techniques.

Airway closure was measured in awake and then anesthetized supine healthy subjects with the argon-bolus and the resident-gas (nitrogen) techniques simultaneously. The preinspiratory lung volume for the closing volume maneuver was varied from residual volume to closing capacity (CC). Comparative measurements were also performed in the upright and supine positions in awake subjects. Closing volume (CV) was consistently larger with the bolus technique in supine subjects both when awake and when anesthetized (difference between methods 0.1--0.2 l, P less than 0.01), whereas no difference between the methods was noted in upright subjects. The lower "nitrogen CV" in supine subjects may be due to a shorter vertical lung height with a smaller range of nitrogen concentrations, resulting in a less abrupt onset of phase IV (taken to indicate CV). CV was not significantly affected by the preinspiratory lung volume with either technique, and CC was unchanged when anesthesia was instituted. Functional residual capacity (FRC) was reduced with anesthesia (mean reduction: 0.6 l, P less than 0.01) and FRC-CC became negative in all subjects with either technique. This implies intermittent or continuous airway closure during anesthesia and the possibility of increased venous admixture.

Adult↗

PubMed1985

Effects of paralysis with pancuronium on chest wall statics in awake humans.

The influence of tonic inspiratory muscle activity on the relaxation characteristics of the chest wall, rib cage (RC), and abdominal wall (ABW) has been investigated in four highly trained subjects. Chest wall shape and volume were estimated with magnetometers. Pleural pressure (Pes) and abdominal pressure were measured with esophageal and gastric balloons, respectively. Subjects were seated reclining 30 degrees from upright, and respiratory muscle weakness was produced by pancuronium bromide until RC inspiratory capacity was decreased to 60% of control. Only minor changes were observed for Konno-Mead relaxation characteristics (RC vs. ABW) between control and paralysis. Similarly, although RC relaxation curves (RC vs. Pes) during paralysis were significantly different from control (P less than 0.05), the changes were small and not consistent. The differences between paralysis-induced changes in resting end-expiratory position of the chest wall and helium-dilution functional residual capacity (FRC) suggested changes in volume of blood within the chest wall. We conclude that 1) although tonic inspiratory activity of chest wall muscles exists, it does not significantly affect the chest wall relaxation characteristics in trained subjects; 2) submaximal paralysis produced by pancuronium bromide is likely to modify either spinal attitude or the distribution of blood between extremities and the thorax; these effects may account for the changes in FRC in other studies.

Blood Volume↗

PubMed1978

Effect of tidal volume and positive end-expiratory pressure on compliance during mechanical ventilation.

In 12 patients requiring therapy with mechanical ventilation for acute respiratory failure, total static compliance (Cst) increased from 29 +/- 4 ml/cm H2O at a tidal volume (TV) of 5 ml/kg to 42 +/- 7 ml/cm H2O at a TV of 15 ml/kg. Similarly, Cst increased from 42 +/- 7 ml/cm H2O to 52 +/- 8 ml/cm H2O between 0 and 6 cm H2O of positive end-expiratory pressure (PEEP). At high levels of pulmonary inflation (ie, high PEEP and large TV) compliance decreased. The changes of total respiratory compliance with TV were mainly due to changes in pulmonary compliance. With PEEP, the functional residual capacity increased, and specific compliance did not change. Two mechanisms may be responsible for the changes in compliance. First, varying TV or PEEP will alter the position of tidal ventilation on the pressure-volume curve, resulting in an increase in compliance with increasing TV and PEEP up to a point, where overdistention occurs and compliance decreases. Secondly, the function of the surface-lowering substance may be altered in acute pulmonary parenchymal disease, thus disturbing the regulation of surface tension over the range of pulmonary inflation studied.

Adult↗

PubMed1975

Airway closure in pregnancy.

Closing capacity (CC; the lung volume at which dependent lung zones cease to ventilate, presumably as a result of airway closure) and standard lung volumes were measured in twenty-four normal women 21 to 29 years of age in the seated and supine positions. Measurements were made serially during pregnancy and once 6 to 8 weeks post partum (the control period). CC was unchanged during pregnancy, while functional residual capacity (FRC) fell by approximately 15%. The difference between FRC and CC (FRC-CC) was reduced during pregnancy, but in one of the subjects when seated, and in only two supine subjects did CC exceed FRC. FRC-CC was reduced in the supine position as compared to seated. The reduced FRC-CC during pregnancy offers a potential explanation for the observations of abnormally low arterial oxygen tensions (Pao2) during pregnancy in some women, and of reduced Pao2 in pregnant women in the supine as compared to upright position.

Adult↗

PubMed2001

Inspiratory flow reserve in boys with Duchenne muscular dystrophy.

Patients with advanced muscular dystrophy frequently develop ventilatory failure. Currently respiratory impairment usually is assessed by measuring vital capacity and the mouth pressure generated during a maximal inspiratory maneuver (PI,max), neither of which directly measures ventilatory capacity. We assessed inspiratory flow reserve in 26 boys [mean (SD) age 12.8 (3.8) years] with Duchenne muscular dystrophy (DMD) without ventilatory failure and in 28 normal boys [mean (SD) age 12.6 (1.9) years] by analyzing the ratio between the largest inspiratory flow during tidal breathing (V'I,max(t)) and during a forced vital capacity maneuver (V'I,max(FVC), (V'I,max(t)/V'I,maxFVC). We have compared this ratio with the forced vital capacity FVC and PI,max measured at functional residual capacity. Mean PI,max was -90(30)cmH2O, average 112% (range 57-179%) of predicted values in control boys and -31(11)cmH2O, average 40% predicted values in DMD boys (control vs DMD, P < 0.001). FVC was reduced in DMD boys [59(20)% predicted values vs 86(10)% predicted values in controls, P < 0.01]. Absolute V'I,max(FVC) was strongly related to FVC in both control and DMD boys; V'I,max(FVC) (expressed as FVC. s(-1)) was not related to PI,max in either group. The mean V'I,max(t)/V'I,max(FVC); ratio was higher in DMD 0.22 (0.08) than in controls 0.12 (0.03) (P < 0.001) indicating a reduction in inspiratory flow reserve in DMD. Inspiratory flow reserve was within the normal range in 8 of 19 DMD patients with PI,max less than 50% of predicted values. We conclude that measurement of inspiratory flow reserve (V'I,max(t)/V'I,maxFVC ratio) provides a simple and direct assessment of dynamic inspiratory muscle function which is not replicated by static measurement of PI,max or vital capacity and might be useful in assessment of respiratory impairment in boys with Duchenne muscular dystrophy. Follow-up studies are required to establish whether measures of inspiratory flow reserve are of clinical value in predicting subsequent ventilatory failure.

Adolescent↗

PubMed1978

A rationale for epidural analgesia in the treatment of multiple rib fractures.

Thoracic epidural analgesia (EA) is described as an alternative to controlled ventilation in patients presenting with multiple rib fractures. Lung mechanics were especially studied in 6 patients selected from a total of 49. The average ICU stay for this group was 4.5 days (2-11) and the mean age 55.7 years. The EA group was compared with 51 patients primarily ventilated who had an average stay in the ICU of 9.8 days and a mean age of 44.7 years. Mean number of rib fractures of the ventilated group at 6.5 was almost equal to the mean of 6.8 in the EA group. There was a difference in the number of associated fractures, 98 in the ventilated group compared to 35 in the EA group. Severe pulmonary and cerebral contusion were the two most important factors in enforcing the need to ventilate. The success of the method is evidenced by the increase in functional residual capacity (FRC), dynamic lung compliance (Cdyn), vital capacity (VC), the decrease of airway resistance (R) and a significantly increase of PaO2 (p less than 0,001) for the EA group with a balanced fluid therapy. All this accounts for the clinical observation of diminishing paradoxical movement of the flail segment.

Adult↗

PubMed1978

Physiologic effects of the position of the body in experimental unilateral emphysema.

The functional residual capacity (FRC), static compliance (Cst) of the respiratory system, minute ventilation, and arterial blood gas levels were studied in the prone, the suprine, and the right and left lateral decubitus positions in dogs with papain-induced emphysema of the right lung alone and were compared with control values. The FRC and Cst of the respiratory system were significantly increased in experimental animals in all four positions, as compared with controls. This was due entirely to increases in FRC and Cst for the right lung alone; for the unexposed left lung the FRC and Cst were significantly reduced, as compared to controls. The mean arterial oxygen tension (PaO2) was decreased in all positions, except the right lateral decubitus position, in which the mean PaO2 was not different from controls. This model demonstrates that in unilaterally distributed, experimentally induced emphysema, alterations alterations in the position of the body alone may significantly alter the FRC, Cst, and gas exchange either favorably or unfavorably, depending upon the position.

Animals↗

PubMed2001

Relevance of dyspnoea and respiratory function measurements in monitoring of asthma: a factor analysis.

Previous studies in patients with stable chronic obstructive pulmonary disease have demonstrated that objective measures (lung volumes and respiratory muscle force) and clinical or subjective measures (symptoms of breathlessness and exercise tolerance) are quantities that independently characterize the conditions of these patients. Such an evaluation has not been previously applied in patients with stable bronchial asthma. Sixty-nine patients with stable chronic asthma underwent evaluation of static (functional residual capacity, FRC) and dynamic [forced expiratory volume in 1 sec (FEV1) and forced vital capacity, FVC] lung volumes; respiratory muscle strength (RMS), by measuring maximal inspiratory and expiratory pressures, and exercise capacity by means of the 6-min walking distance (6MWD). Chronic exertional dyspnoea was assessed by the Baseline Dyspnoea Index (BDI) focal score and by the Medical Research Council (MRC) scale. Statistical evaluation was performed by applying factor analysis. Three factors accounted for 78% of the total variance in the data: FEV1, FVC loaded on a factor I; RMS, FRC and 6MWD loaded on a factor II; dyspnoea ratings loaded on a factor III. Post-hoc analysis by randomly dividing the patients into two subgroups gave the same results. In asthmatic patients, airway obstruction appeared as an independent dimension or factor. Dyspnoea independently characterized the condition of asthma. Submaximal exercise tolerance could not be associated with the symptom of breathlessness. Evidence of independent factors support the validity of routine, multi-factorial assessment and the primary goal of treatment to alleviate symptoms and improve functional capacity in stable asthmatics.

Adult↗

PubMed1979

Differential ventilation in unilateral lung disease: effects on respiratory mechanics and gas exchange.

Conventional PEEP ventilation has been recently reported to be deleterious in some cases of ARF with unilateral pneumonia. In such respect, two cases of unilateral bacterial pneumonia were intubated with a Carlens tracheal tube. Measurement of tidal volume, static compliance, and functional residual capacity of each lung showed marked inequality. Subsequently, both patients were ventilated with a selective distribution circuit, allowing the introduction of a PEEP valve in the expiratory line of the diseased lung. Evident improvement in blood gases was obtained within 24 hours, as tidal volume, static compliance, and FRC of the diseased lung were markedly improved. In one case equalisation of V/Q ratio was documented using the 81m Kr method. Final recovery was obtained in one case.

Adult↗

PubMed1981

Transient pulmonary impairment during attacks of Crohn's disease.

Lung function was studied in 10 patients with Crohn's disease during and after an attack of the disease. Pulmonary volumes and lung transfer factor were not impaired but functional residual capacity was greater during the attack than during remission; it was also greater than in normal subjects. FRC values and disease activity decreased concomitantly during remission as well as finger clubbing. The etiology of this impairment was unknown.

Adult↗

PubMed2007

Lung aeration during sleep.

BACKGROUND: During sleep, ventilation and functional residual capacity (FRC) decrease slightly. This study addresses regional lung aeration during wakefulness and sleep. METHODS: Ten healthy subjects underwent spirometry awake and with polysomnography, including pulse oximetry, and also CT when awake and during sleep. Lung aeration in different lung regions was analyzed. Another three subjects were studied awake to develop a protocol for dynamic CT scanning during breathing. RESULTS: Aeration in the dorsal, dependent lung region decreased from a mean of 1.14 +/- 0.34 mL (+/- SD) of gas per gram of lung tissue during wakefulness to 1.04 +/- 0.29 mL/g during non-rapid eye movement (NREM) sleep (- 9%) [p = 0.034]. In contrast, aeration increased in the most ventral, nondependent lung region, from 3.52 +/- 0.77 to 3.73 +/- 0.83 mL/g (+ 6%) [p = 0.007]. In one subject studied during rapid eye movement (REM) sleep, aeration decreased from 0.84 to 0.65 mL/g (- 23%). The fall in dorsal lung aeration during sleep correlated to awake FRC (R(2) = 0.60; p = 0.008). Airway closure, measured awake, occurred near and sometimes above the FRC level. Ventilation tended to be larger in dependent, dorsal lung regions, both awake and during sleep (upper region vs lower region, 3.8% vs 4.9% awake, p = 0.16, and 4.5% vs 5.5% asleep, p = 0.09, respectively). CONCLUSIONS: Aeration is reduced in dependent lung regions and increased in ventral regions during NREM and REM sleep. Ventilation was more uniformly distributed between upper and lower lung regions than has previously been reported in awake, upright subjects. Reduced respiratory muscle tone and airway closure are likely causative factors.

Adult↗

PubMed1995

Effect of preinspiratory maneuver on the single-breath DLCO.

We have observed in some patients with pulmonary disease and normal subjects that the difference between two successive measurements for single-breath DLCO amounted to 10%. By scrutinizing data from these subjects, we observed that they spontaneously changed their preinspiratory maneuver just before inhaling the test gas mixture. The purpose of the present work is to assess the influence of five different preinspiratory maneuvers on DLCO. Nine healthy males were investigated. They performed at random the five following maneuvers: (A) rapid exhalation from functional residual capacity (FRC) to residual volume (RV), (B) rapid exhalation from FRC to RV and long apnea at RV, (C) rapid exhalation from FRC to RV and short apnea at RV, (D) slow exhalation at a constant speed from FRC to RV, and (E) curvilinear exhalation from FRC to RV. The DLCO values after maneuver B were higher than those after the four other maneuvers; there was a significant relationship between DLCO and the duration of the preinspiratory maneuver. The data are best explained by an alteration in the distribution of the inspired gas mixture to areas with different diffusing capacities. In conclusion, the preinspiratory maneuvers must be standardized in order to improve the reproducibility of the single-breath DLCO measurements.

Adult↗

PubMed1996

Lower transversal laparotomy has no appreciable effect on respiratory mechanics in guinea pigs.

Respiratory system, lung, and chest wall resistances and dynamic elastances were determined in six anesthetized, paralyzed, and mechanically ventilated guinea pigs both before and after lower transversal abdominal opening performed at the level of the spina iliaca anterosuperior. Furthermore, the resistances were also split into their two components, one reflecting the Newtonian resistances and the other representing the viscoelastic/inhomogeneous pressure dissipations in the system. The method of end-inflation occlusion during constant inspiratory flow was used. Chest wall configuration was also evaluated by measurements of lateral and anteroposterior diameters and circumferences at the 4th intercostal space and xiphoid levels both at functional residual capacity and at the end of tidal inspiration before and after surgery. After abdominal incision no statistically significant changes could be detected in any of the measured variables. It may be concluded that lower transversal abdominal opening does not alter respiratory mechanics.

Abdomen↗

PubMed1978

Effects of arachidonic acid and prostaglandins on lung function in the intact dog.

The effects of the prostaglandin (PG) precursor, arachidonic acid (AA), and the primary PG's, PGF2alpha, and PGD2, on lung function were compared in 39 intact-chest, paralyzed, artificially ventilated dogs. Intravenous AA decreased dynamic compliance (Cdyn) and functional residual capacity and increased airway resistance (Rl) and transpulmonary pressure at end-passive expiration. The decrease in Cdyn correlated closely with a rise in pulmonary arterial pressure (Ppa). Indomethacin abolished airway and vascular responses to AA, but did not attenuate responses to the PG's. The effects of AA, PGD2, and PGF2alpha on lung function and Ppa were similar, whereas PGE2 had little effect. Vagotomy attentuated the RL increase in response to AA, PGE2alpha, and PGD2 and the Cdyn decrease in response to the PG's. The effects of the PG's on compliance were greater than those produced by mechanically increasing pulmonary venous pressure. The present studies suggest that the PG precursor is rapidly converted to agents that have marked effect on both pulmonary vessels and airways, particularly peripheral airways, in the dog.

Airway Resistance↗

PubMed1977

Airway closure and pregnancy.

During pregnancy there is a fall in functional residual capacity and expiratory reserve volume. The point of airway closure in relation to vital capacity and the expiratory reserve volume was determined in 11 post-partum patients who had previously been studied during pregnancy. The lung volume at which airway closure occurred in pregnancy and the post-partum period did not change in relation to the vital capacity whereas the expiratory reserve volume did, so that airway closure became imminent in the pregnant women during tidal ventilation, especially whilst in the suping position. The significance of this alteration in pulmonary function to obstetric anaesthesia is discussed.

Adult↗

PubMed1992

The effect of maternal smoking during pregnancy on early infant lung function.

We studied the effect of prenatal maternal cigarette smoking on the pulmonary function (PF) of 80 healthy infants tested shortly after birth (mean, 4.2 +/- 1.9 wk). Mothers' prenatal smoking was measured by: (1) questionnaire reports at each prenatal visit of the number of cigarettes smoked per day, and (2) urine cotinine concentrations (corrected for creatinine) obtained at each visit. Infant PF was assessed by partial expiratory flow-volume curves and helium-dilution measurement of FRC. Forced expiratory flow rates were significantly lower in infants born to smoking mothers, both when unadjusted and after controlling for infant size, age, sex, and passive exposure to environmental tobacco smoke (ETS) between birth and the time of PF testing. Flow at functional residual capacity (VFRC) in infants born to smoking mothers was lower than that found in infants whose mothers did not smoke during pregnancy (74.3 +/- 15.9 versus 150.4 +/- 8.9 ml/s; p = 0.0007). Differences remained significant when flow was corrected for lung size (VFRC/FRC: 0.87 +/- 0.26 versus 1.77 +/- 0.12 s-1; p = 0.013). No differences in pulmonary function were evident among infants exposed and unexposed to ETS in the home after stratifying by prenatal exposure status. We conclude that maternal smoking during pregnancy is associated with significant reductions in forced expiratory flow rates in young infants. The results suggest that maternal smoking during pregnancy may impair in utero airway development and/or alter lung elastic properties. We speculate that these effects of maternal prenatal smoking on early levels of forced expiratory flow may be an important factor predisposing infants to the occurrence of wheezing illness later in childhood.

Adult↗