How is maximal expiratory flow reduced in canine postpneumonectomy lung growth?

Six dogs underwent left pneumonectomy (P) at 10 wk of age, while four littermates had a sham operation (C). All dogs were studied at 26 wk of age. Pressure capsules were placed on the right lung to measure lobar alveolar pressures and flows, and a Pitot-static tube was used to measure dynamic intrabronchial pressures. Vital capacity and lung elastic recoil did not differ between P and C. At all lung volumes studied, maximum expiratory flows (Vmax) in P were substantially lower than in C. Choke points in P were located more peripherally than in C. In central airways subjected to the same distending pressure, calculated cross-sectional area was significantly lower in P than in C, indicating different bronchial area-pressure behavior. In P, frictional resistances of the right lower, middle, and cardiac lobes were significantly higher than those in C. These results indicate that the reduction in Vmax in P was greater than would have been expected on the basis of reductions in central airway diameter alone. We calculated that, in the middle vital capacity range, approximately 60% of the decrease in Vmax was due to changes in dynamic central airways properties, and approximately 40% was due to increased lobar frictional resistance related to compensatory growth.     

Effects of corticosteroids on postnatal lung and airway growth in the ferret

To investigate the influence of corticosteroids on postnatal lung and airway growth, young male ferrets were given cortisone acetate (20 mg/kg im daily) beginning at 8 wk of age. At 19 wk of age pulmonary function was measured. The lungs were excised for measurements of recoil pressures and wet and dry weights. The dimensions of central and peripheral airways were estimated from analysis of bronchial casts. Corticosteroid-treated animals were shorter and tended to be lighter than control animals but were heavier in relation to length. Total lung capacity was reduced in proportion to the reduction in body size. Lung recoil and wet-to-dry weight ratios were nearly identical. Maximal expiratory flows were reduced in proportion to the reduction in body size. Size-corrected airway conductance was reduced, suggesting a sensitivity of central airways to growth suppression by corticosteroids. Peripheral airways, on the other hand, were not smaller in treated animals and were larger in proportion to body size. In the ferret corticosteroid administration is associated with a suppression of lung parenchymal growth similar to that of overall body growth. The peripheral airways may be less sensitive and the central airways more sensitive to the effect of corticosteroids on growth.     

Genetic influence on normal variability of maximum expiratory flow-volume curves.

To determine the importance of genetic influence on the variability of maximum expiratory flow-volume (MEFV) curves in normal individuals, MEFV curves breathing air and a mixture of 80% helium and 20% oxygen (He-O2), lung volumes, specific airway conductance, and closing capacity (CC) were obtained in 10 pairs of identical and 6 pairs of nonidentical twins, all nonsmokers and asymptomatic. For a given pair of identical twins, MEFV curves on air were more similar than those of a pair of nonidentical twins (P less than 0.02). The intrapair differences of identical twins were smaller than nonidentical twins of maximum expiratory flow (Vmax) at 60% of total lung capacity (TLC) on air (P less than 0.001) and on He-O2 (P less than 0.01). However, intrapair differences of Vmax at 40% TLC and CC were not significantly different in the two groups. Since Vmax at 60% TLC on air and He-O2 are dependent on the geometry of large airways these findings are suggestive that the geometry of large airways may be related to genetic factors. The relationship of the geometry of the peripheral airways and genetic factors has not been defined.     

Relationship between maximal expiratory flows and lung volumes in growing humans

We examined airway vs. lung parenchymal growth, as inferred from maximal expiratory flows (MEF) and lung volumes (V), respectively, to determine whether the interindividual variability of airway size (inferred from MEF) changes during lung growth and whether a young child with large (or small) airways for his parenchymal size (inferred from V) maintains relatively large (or small) airways for his lung size as he grows to adulthood. Serial measurements of MEF and V were obtained from a cohort of healthy 6- to 27-yr-old males (n = 26) and females (n = 21) over a period of 18 yr. Data were analyzed using logarithmic transformation of the power law equation, MEF = aVb, to fit a regression line to each subject's data points. These growth trajectories were satisfactorily modeled as parallel lines with 20-30% variability of their y-intercepts, indicating that substantial intersubject variability of MEF relative to V is present in early childhood and remains constant during growth. The results further indicate that MEF does track V during lung growth. We conclude that dysanapsis originates in early childhood.     

Effect of intensive swimming training on lung volumes, airway resistances and on the maximal expiratory flow-volume relationship in prepubertal girls

The aim of the present study was to analyse the effect of 1 year of intensive swimming training on lung volumes, airway resistance and on the flow-volume relationship in prepubertal girls. Five girls [9.3 (0.5) years old] performing vigorous swimming training for 12 h a week were compared with a control group of 11 girls [9.3 (0.5) years old] who participated in various sport activities for 2 h per week. Static lung volumes, maximal expiratory flows (MEF) at 75, 50 and 25% of vital capacity, 1-s forced expiratory volume (FEV_1.0) and airway resistance (R _aw) were measured by means of conventional body plethysmograph techniques. Prior to the training period there were no significant differences between the two groups for any of the parameters studied. Moreover, for both groups, all parameters were within the normal range for children of the corresponding age. After 1 year of training, vital capacity (VC), total lung capacity (TLC) and functional residual capacity (FRC) were larger (P<0.05) in the girl swimmers than in the control group, while physical development in terms of height and weight was similar. FEV_1.0 (P<0.01), MEF₂₅, MEF₅₀ (P<0.05) and MEF₇₅ as well as the ratio MEF₅₀ / TLC (P<0.05) had increased in the girl swimmers but were unchanged in the control group. R _aw tended to be lower in the girl swimmers and higher in the control group. The results indicate that intensive swimming training prepuberty enhances static and dynamic lung volumes and improves the conductive properties of both the large and the small airways. As to the causative mechanism, it can be speculated that at prepuberty intensive swimming training promotes isotropic lung growth by harmonizing the development of the airways and of alveolar lung spaces. Accepted: 5 March 1997     

Trachea and lung dimensions in nonsmoking twins: morphological and functional studies

To compare genetic and environmental factors that determine lung function and dimensions, chest radiographs and pulmonary function were measured in 17 pairs of nonsmoking twin adolescent boys (12 monozygotic pairs and 5 dizygotic pairs). Genetic factors dominated in tracheal width and lung dimensions (height, width, and apicofissural and fissurodiaphragmatic distances) at residual volume. Genetic factors also affected forced vital capacity, functional residual capacity, forced expiratory volume in 1 s, maximum expiratory flow at 25% vital capacity, and maximum flow at 50% vital capacity-to-forced vital capacity ratio. Peak expiratory flow correlated with tracheal width at residual volume. Age correlated with lung dimensions (width and depth) but not with tracheal width. These results indicate that genetic factors determine the dimensions and function of central airways, peripheral airways, and lung parenchyma in adolescent males. The effects of genetic factors on some functional measurements (airway resistance, closing volume-to-vital capacity ratio, and phase III in single-breath N2 washout) may be masked because of poor reproducibility of the tests.     

Circulatory and respiratory responses to muscular exercise in Czech and Norwegian children

This paper presents a comparison between Czech and Norwegian rural healthy children with regard to the functional characteristics of the circulatory and respiratory system based upon work physiological variables and measurements of some pulmonary volumes. The study included randomised samples of boys and girls at the age of 8, 12 and 16 years, 66 Czech boys and 63 girls, 54 Norwegian boys and 57 girls. At the age of 8 years the maximal aerobic power was closely similar in both countries, but in the older age groups the Norwegian children exhibited lower physical fitness. The maximal heart rate was close to 200 min-1 on the average without any sex, age or ethnic differences. In agreement with the higher maximal aerobic power the 12 and 16 year old Czech children had lower submaximal heart rates for the same oxygen uptake than the Norwegian children. The forced vital capacity and forced expiratory volume in one second was significantly higher on the average in Czech than in Norwegian children but the latter, expressed in percent age of the former, averaged 87 to 91% without any sex, age or ethnic differences. The maximal ventilation volumes during muscular exercise reached higher values in Czech than in Norwegian children of the same age, but the mean maximal respiratory rate was close to 60 min-1, being independent of age, sex and cultural differences. During heavy exercise only 40 to 50% of the vital capacity and 45 to 55% of the forced expiratory volume were taken into account and this index of pulmonary function did not differ with sex, age or ethnic differences.     

Effect of chest strapping on regional lung function.

We studied lung mechanics and regional lung function in five young men during restrictive chest strapping. The effects on lung mechanics were similar to those noted by others in that lung elastic recoil increased as did maximum expiratory flow at low lung volumes. Chest strapping reduced the maximum expiratory flow observed at a given elastic recoil pressure. Breathing helium increased maximum expiratory flow less when subjects were strapped than when they were not. These findings indicated that strapping decreased the caliber of airways upstream from the equal pressure point. Regional lung volumes from apex to base were measured with xenon 133 while subjects were seated. The distribution of regional volumes was measured at RV, and at volumes equal to strapped FRC and strapped TLC; no change due to chest strapping was observed. Similarly, the regional distribution of 133Xe boluses inhaled at RV and strapped TLC was unaffected by chest strapping. Closing capacity decreased with chest strapping. We concluded that airway closure decreased during chest strapping and that airway closure was not the cause of the observed increase in elastic recoil of the lung. The combination of decreased slope of the static pressure-volume curve and unchanged regional volumes suggested that strapping increased the apex-to-base pleural pressure gradient.     

Pulmonary physiology of the ferret and its potential as a model for inhalation toxicology

Physiological measurements were made from anesthetized, tracheotomized, supine male ferrets. Six animals weighing 576 +/- 12 g, had tidal volumes (Vt) of 6.06 +/- 0.30 ml, respiratory frequencies (f) of 26.7 +/- 3.9 min(-1), dynamic lung compliance (CDYN) of 2.48 +/- 0.21 ml cmH2O(-1), pulmonary resistance (RL) of 22.56 +/- 1.61 cmH2O L(-1) sec. Pressure-volume curves from nine ferrets (including the above six) revealed almost infinitely compliant chest walls so that lung and total respiratory system curves were essentially the same. Total lung capacity (TLC) (89 +/- 5 ml) and functional residual capacity (FRC) (17.8 +/- 2.0 ml) were determined by gas freeing the lungs in vivo. The TLC of these ferrets was about the same as in 2.5 kg rabbits. Maximum expiratory flow-volume curves showed peak flows of 10.1 vital capacities (VC) sec(-1) at 75% VC and flows of 8.4 and 5.4 VC sec(-1) at 50% and 25% VC. No particular problems were encountered in making these measurements using conventional techniques available in laboratories capable of making pulmonary function measurements on rats and guinea pigs. Preliminary studies of airways reactivity showed equal increases in pulmonary resistance in response to equivalent challenges of aerosolized carbachol and histamine. Light and electron microscopic studies showed that the airways of ferrets are even more like those of humans than are the dog's. The ease with which physiological measurements can be made and the favorable aspects of the lung anatomy indicate the ferret may be more useful, as well as less expensive, than the dog for use in studies of pulmonary physiology and inhalation toxicology.     

Respiratory dynamics during laughter.

Lung and chest wall mechanics were studied during fits of laughter in 11 normal subjects. Laughing was naturally induced by showing clips of the funniest scenes from a movie by Roberto Benigni. Chest wall volume was measured by using a three-dimensional optoelectronic plethysmography and was partitioned into upper thorax, lower thorax, and abdominal compartments. Esophageal (Pes) and gastric (Pga) pressures were measured in seven subjects. All fits of laughter were characterized by a sudden occurrence of repetitive expiratory efforts at an average frequency of 4.6 +/- 1.1 Hz, which led to a final drop in functional residual capacity (FRC) by 1.55 +/- 0.40 liter (P < 0.001). All compartments similarly contributed to the decrease of lung volumes. The average duration of the fits of laughter was 3.7 +/- 2.2 s. Most of the events were associated with sudden increase in Pes well beyond the critical pressure necessary to generate maximum expiratory flow at a given lung volume. Pga increased more than Pes at the end of the expiratory efforts by an average of 27 +/- 7 cmH2O. Transdiaphragmatic pressure (Pdi) at FRC and at 10% and 20% control forced vital capacity below FRC was significantly higher than Pdi at the same absolute lung volumes during a relaxed maneuver at rest (P < 0.001). We conclude that fits of laughter consistently lead to sudden and substantial decrease in lung volume in all respiratory compartments and remarkable dynamic compression of the airways. Further mechanical stress would have applied to all the organs located in the thoracic cavity if the diaphragm had not actively prevented part of the increase in abdominal pressure from being transmitted to the chest wall cavity.     

Heterogeneity of maximal lobar emptying rates in dogs with compensatory lung growth

Five dogs underwent left pneumonectomy at 10 wk of age, whereas four littermates underwent a sham operation. At 26 wk of age the postpneumonectomy dogs had total lung vital capacity (VC) and lung weight similar to controls, but maximum expiratory flow was reduced. Pressure capsules were glued to right lower (RLL) and right cardiac (RCL) lobes, and alveolar pressures (PA) were measured during forced expiration. In postpneumonectomy dogs RLL and RCL both emptied more slowly than in control dogs, and emptying was especially delayed in RCL, which underwent the most growth. When both lobes deflated together, PA in RCL and RLL were similar in control dogs, but in postpneumonectomy dogs PA in RCL exceeded that in RLL by approximately 3 cmH2O from 80 to 20% VC. Because the higher driving pressure in RCL compensated for the relatively high resistance of RCL, the pattern of lobar emptying was relatively uniform over these lung volumes. This result was compatible with interdependence of lobar maximum expiratory flows. In addition, at PA of 6-10 cmH2O in postpneumonectomy dogs, maximum emptying rates of RCL were less when RCL deflated alone than when RCL and RLL emptied together, again demonstrating interdependence of lobar maximum expiratory flow.     

Interdependence of regional expiratory flow

Flows from different lung regions interact at the junctions of the bronchial tree, and flow from each region depends on the driving pressures for other regions. At each junction, flow from the region with the higher driving pressure is favored. As a result there is a limit on the difference in alveolar pressures that can develop during expiratory flow from a lung with regional differences in lung compliance and airway resistance. The limiting pressure difference is smaller for lower flow. A nonuniform lung therefore empties more uniformly if it empties slowly, and maximum flow at low lung volume may be greater than it would be at the same lung volume during a maximal expiratory vital capacity maneuver.     

Inflation of antishock trousers increases bronchial response to methacholine in healthy subjects

We studied changes in lung volumes and in bronchial response to methacholine chloride (MC) challenge when antishock trousers (AST) were inflated at venous occlusion pressure in healthy subjects in the standing posture, a maneuver known to shift blood toward lung vessels. On inflation of bladders isolated to lower limbs, lung volumes did not change but bronchial response to MC increased, as evidenced by a greater fall in the forced expiratory volume in 1 s (FEV1) at the highest dose of MC used compared with control without AST inflation (delta FEV1 = 0.94 +/- 0.40 vs. 0.66 +/- 0.46 liter, P less than 0.001). Full inflation of AST, i.e., lower limb and abdominal bladder inflated, significantly reduced vital capacity (P less than 0.001), functional residual capacity (P less than 0.01), and FEV1 (P less than 0.01) and enhanced the bronchial response to MC challenge compared with partial AST inflation (delta FEV1 = 1.28 +/- 0.47 liter, P less than 0.05). Because there was no significant reduction of lung volumes on partial AST inflation, the enhanced bronchial response to MC cannot be explained solely by changes in base-line lung volumes. An alternative explanation might be a congestion and/or edema of the airway wall on AST inflation. Therefore, to investigate further the mechanism of the increased bronchial response to MC, we pretreated the subjects with the inhaled alpha 1-adrenergic agonist methoxamine, which has both direct bronchoconstrictor and bronchial vasoconstrictor effects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Partial forced expiratory flow-volume curves in young children during ketamine anesthesia

Maximal flows at functional residual capacity (VmaxFRC) from partial forced expiratory flow-volume (PEFV) curves were obtained in 14 normal preschool children (8 boys, 6 girls) of average age 44 mo, under general anesthesia before elective surgery. PEFV curves were generated from end inspiration by rapid compression of the chest wall with an inflatable jacket. VmaxFRC, expressed in milliliter per second, correlated linearly with height, weight, age, and FRC in milliliter and milliliters per kilogram. The best correlation of VmaxFRC (ml/s) was to height to the power of 2.47, which agrees with the results predicted by wave-speed theory. Mean FRC-corrected VmaxFRC was 2.42 +/- 0.50 (SD) FRC's/s with no significant difference between boys (2.35 FRC's/s) and girls (2.51 FRC's/s). There was no correlation between lung-size corrected VmaxFRC and height, weight, or age, but it tended to decrease with increasing FRC. The intersubject variability for VmaxFRC was reduced by normalizing for FRC, and was significantly better than that reported for awake children. This can be attributed to the greater control over volume history and more reliable maximal flow generation during anesthesia. The intrasubject coefficient of variation (CV) for VmaxFRC was 12.2%, and the intersubject CV was 20.0%. The difference may represent the variability due to dysanapsis. It is concluded that dysanapsis is not a prominent factor in children of this age group. In addition, the similarity of the regression equation for VmaxFRC vs. height to that of FRC vs. height supports the concept of equidimensional growth of the airways and lung parenchyma.     

Analysis of bronchial mechanics and density dependence of maximal expiratory flow

The computational model for expiratory flow in humans of Lambert and associates (J. Appl. Physiol. Respirat. Environ. Exercise Physiol. 52: 44-56, 1982) was used to investigate the effect of bronchial constrictions in three airway zones on the density dependence of maximal expiratory flow. It was found that constriction of the peripheral airways (less than 2 mm diam) reduced density dependence and increased the volume of isoflow. Constriction of the larger intraparenchymal airways resulted in increased density dependence at low lung volumes and essentially normal values at other volumes. The volume of isoflow was reduced. Extraparenchymal (but intrathoracic) airway constriction caused no change in the volume of isoflow but caused increased density dependence at the higher lung volumes. It was shown that in these model simulations the addition of extraparenchymal constriction to intraparenchymal constriction causes essentially no changes in density dependence. An increased volume of isoflow and significantly decreased density dependence at 50 and 25% vital capacity were produced by simulated constrictions only in the peripheral airways.     

Effects of rapid saline infusion on lung mechanics and airway responsiveness in humans.

Lung mechanics and airway responsiveness to methacholine (MCh) were studied in seven volunteers before and after a 20-min intravenous infusion of saline. Data were compared with those of a time point-matched control study. The following parameters were measured: 1-s forced expiratory volume, forced vital capacity, flows at 40% of control forced vital capacity on maximal (Vm(40)) and partial (Vp(40)) forced expiratory maneuvers, lung volumes, lung elastic recoil, lung resistance (Rl), dynamic elastance (Edyn), and within-breath resistance of respiratory system (Rrs). Rl and Edyn were measured during tidal breathing before and for 2 min after a deep inhalation and also at different lung volumes above and below functional residual capacity. Rrs was measured at functional residual capacity and at total lung capacity. Before MCh, saline infusion caused significant decrements of forced expiratory volume in 1 s, Vm(40), and Vp(40), but insignificantly affected lung volumes, elastic recoil, Rl, Edyn, and Rrs at any lung volume. Furthermore, saline infusion was associated with an increased response to MCh, which was not associated with significant changes in the ratio of Vm(40) to Vp(40). In conclusion, mild airflow obstruction and enhanced airway responsiveness were observed after saline, but this was not apparently due to altered elastic properties of the lung or inability of the airways to dilate with deep inhalation. It is speculated that it was likely the result of airway wall edema encroaching on the bronchial lumen.     

Effect of airway closure on ventilation distribution

We examined the effect of airway closure on ventilation distribution during tidal breathing in six normal subjects. Each subject performed multiple-breath N2 washouts (MBNW) at tidal volumes of 1 liter over a range of preinspiratory lung volumes (PILV) from functional residual capacity (FRC) to just above residual volume. All subjects performed washouts at PILV below their measured closing capacity. In addition five of the subjects performed MBNW at PILV below closing capacity with end-inspiratory breath holds of 2 or 5 s. We measured the following two independent indexes of ventilation maldistribution: 1) the normalized phase III slope of the final breaths of the washout (Snf) and 2) the alveolar mixing efficiency of those breaths of the washout where 80-90% of the initial N2 had been cleared. Between a mean PILV of 0.28 liter above closing capacity and that 0.31 liter below closing capacity, mean Snf increased by 132% (P less than 0.005). Over the same volume range, mean alveolar mixing efficiency decreased by 3.3% (P less than 0.05). Breath holding at PILV below closing capacity resulted in marked and consistent decreases in Snf and increases in alveolar mixing efficiency. Whereas inhomogeneity of ventilation decreases with lung volume when all airways are patent (J. Appl. Physiol. 66: 2502-2510, 1989), airway closure increases ventilation inequality, and this is substantially reduced by short end-inspiratory breath holds. These findings suggest that the predominant determinant of ventilation distribution below closing capacity is the inhomogeneous closure of airways subtending regions in the lung periphery that are close together.     

Why Are Girls Less Physically Active than Boys? Findings from the LOOK Longitudinal Study

Background

A gender-based disparity in physical activity (PA) among youth, whereby girls are less active than boys is a persistent finding in the literature. A greater understanding of the mechanisms underlying this difference has potential to guide PA intervention strategies.

Methods

Data were collected at age 8 and 12 years (276 boys, 279 girls) from 29 schools as part of the LOOK study. Multilevel linear models were fitted separately for boys and girls to examine effects of individual, family and environmental level correlates on pedometer measured PA. Cardio-respiratory fitness (multi-stage run), percent fat (DEXA), eye-hand coordination (throw and catch test) and perceived competence in physical education (questionnaire) were used as individual level correlates. At the family level, parent’s support and education (questionnaire) were used. School attended and extracurricular sport participation were included as environmental level correlates.

Results

Girls were 19% less active than boys (9420 vs 11360 steps/day, p<0.001, 95%CI [1844, 2626]). Lower PA among girls was associated with weaker influences at the school and family levels and through lower participation in extracurricular sport. School attended explained some of the variation in boys PA (8.4%) but not girls. Girls compared to boys had less favourable individual attributes associated with PA at age 8 years, including 18% lower cardio-respiratory fitness (3.5 vs 4.2, p<0.001, CI [0.5,0.9]), 44% lower eye-hand coordination (11.0 vs 17.3, p<0.001, CI [5.1,9.0]), higher percent body fat (28% vs 23%, p<0.001, CI [3.5,5.7]) and 9% lower perceived competence in physical education (7.7 vs 8.4, p<0.001, CI [0.2,0.9]). Participation in extracurricular sport at either age 8 or 12 years was protective against declines in PA over time among boys but not girls.

Conclusion

Girls PA was less favourably influenced by socio-ecological factors at the individual, family, school and environmental levels. These factors are potentially modifiable suggesting the gap in PA between boys and girls can be reduced. Strategies aiming to increase PA should be multicomponent and take into consideration that pathways to increasing PA are likely to differ among boys and girls.     

The growth of lung volumes affected by physical performance capacity in boys and girls during childhood and adolescence

The paper concerns a longitudinal study of the relationship between growth in lung functions in terms of forced vital capacity and forced expiratory volume in 1 s, and the development of maximal aerobic power during the age span from 8-18 years of age. The growth curves of anatomical dimensions for boys and girls were similar to those previously established for Northern European children. The growth in lung volume ended later than the growth in body height. It was found that the growth in lung volume was entirely due to growth in body dimensions, with no additional effect of changes in the development of physical performance capacity.