Airway level at which edema liquid enters the air space of isolated dog lungs

To identify lung units associated with liquid leakage into the air space in high-pressure pulmonary edema, we perfused air-inflated dog lung lobes with albumin solution to fill the loose peribronchovascular interstitium. Next, we perfused the lobes for 90 s with fluorescent albumin solution then froze the lobes in liquid nitrogen. This procedure confined the fluorescent perfusate to the liquid flux pathway between the circulation and the air space and eliminated the previously filled peribronchovascular cuffs as a source of the fluorescence that entered the air space. We divided each frozen lobe into three horizontal layers and prepared fluorescence-microscopic sections of each layer. In the most apical layers where alveolar flooding was minimal, 10.6 +/- 21.0% (SD) of alveolar ducts were either fluorescence filled or air filled and continuous with fluorescence-filled alveoli. In the same layers, 11.0 +/- 19.0% of respiratory bronchioles were similarly labeled. No terminal bronchioles in these layers were fluorescence labeled. This suggested that the fluorescent albumin entered the air space across the epithelium of respiratory bronchioles, alveolar ducts, or their associated alveoli. To simulate an alternative explanation, i.e., that fluorescence first entered central airways then flowed into peripheral air spaces, we prepared two additional lobes that we first partially inflated with fluorescent albumin then filled to capacity with air. This pushed the fluorescent solution along the airways into the lung periphery. In these lobes the ciliary lining of bronchi and terminal bronchioles was fluorescence coated. By comparison, cilia in fluorescence-perfused lobes were not coated. We conclude that alveolar flooding in hydrostatic pulmonary edema occurs across the epithelium of alveolar ducts, respiratory bronchioles, or their associated alveoli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stochastic Modeling Predictions for the Clearance of Insoluble Particles from the Tracheobronchial Tree of the Human Lung

Bronchial clearance of deposited particles was simulated using a stochastic model of the tracheobronchial tree. The clearance model introduced in this study considers (1) a continuous decrease of the mucus thickness from the trachea to the terminal bronchioles according to a linear or an exponential function, (2) the possibility of mucus discontinuities, which are mainly found in intermediate and distal airways of the tracheobronchial compartment, (3) mucus production in proximal airways, (4) a slow bronchial clearance phase due to the capture of a defined particle fraction f _s in the periciliary sol phase, and (5) an eventual delay of the mucociliary transport at carinal ridges of airway bifurcations. Based on the concept of mucus volume conservation in single bifurcations, a reduction of the thickness of the mucus blanket from proximal to distal airways causes a significant increase of the mucus velocities in small ciliated airways compared to other stochastic modeling predictions assuming a constant thickness of the mucus layer throughout the conducting airways. This effect is further enhanced by the consideration of mucus discontinuities. In contrast, the ability of bronchial airways to produce a certain volume of mucus has a decreasing effect on the mucus velocities. In all generated clearance velocity models, mucociliary clearance is completely terminated within 24 h after exposure, consistent with the experimental evidence. Implementation of a slow bronchial clearance phase predicts a long-term retention fraction, which is fully cleared from the lung after several weeks. For 1-μm MMAD particles, 24-h retention varies between 0.42 and 0.52, in line with the suggestions of the ICRP. Mucus delay at carinal ridges only affects short-term clearance by increasing the retained particle fraction at a given time, while long-term retention is not influenced.     

Retention and clearance of 0.9-micron particles inhaled by hamsters during rest or exercise

We assessed the retention and clearance of inhaled particles in six anatomic compartments of the respiratory tract. Hamsters were exposed for 45 min to 0.9-micron fluorescent latex particles either at rest (n = 9) or while running on a laddermill (n = 9). Oxygen consumption, which was used to estimate minute ventilation, was continuously monitored. Three animals from each group, rest and exercise, were killed at 10 min, 24 h, or 7 days after the exposure. Morphometric techniques were used to determine the number of particles retained in nose and oropharynx (NOSE), trachea and extrapulmonary airways, intrapulmonary conducting airways, respiratory bronchioles, alveolar ducts (AD), and alveoli (ALV). At 10 min, total particle retention increased linearly as a function of O2 consumption (slope = 1.4 +/- 0.3 x 10(6) particles.ml-1.g-1.h-1, P less than 0.015). Exercised hamsters retained 4.4 times more total particles in their NOSE than rested hamsters, but parenchymal retention (AD + ALV) was unaffected. After 7 days, 95% of the particles were cleared from the NOSE, 80% from the trachea and extrapulmonary airways, 44% from intrapulmonary conducting airways and respiratory bronchioles, and 16% from AD and ALV. There was evidence of particle redistribution from AD to ALV during the 1st day. We conclude that exercise enhances the deposition of 0.9-micron particles in the upper respiratory tract but not in the parenchyma. Subsequently, the deposited particles are cleared at varying rates depending on the lung compartment.     

A method for the approximation of the relative humidity in the upper human airways

In order to determine the growth of inhaled aerosol particles in the human respiratory tract the relative humidity in a lung model has been calculated using a numerical method. The computations take into account different types of airflows, enhanced transport mechanisms and an optimized wall temperature profile in the upper airways. These parameters are varied to fit experimental temperature data. Under certain conditions the corresponding relative humidity shows a maximum near the first bifurcation, which exceeds the final humidity in the alveoli. This high humidity forces dry NaC1 particles with diameters less than 0.5 μm to grow to their maximum size in the first bronchi. Thereafter the droplets loose water and reach their final size in the terminal bronchioles.     

Tracheobronchial epithelium in the adult rhesus monkey: a quantitative histochemical and ultrastructural study

Previous studies of the intrapulmonary conducting airways of sheep and rabbit have demonstrated marked diversity in the epithelial populations lining them. Because studies of trachea and centriacinar regions of macaque monkeys suggested that primates may be even more diverse, the present study was designed to characterize the epithelial population throughout the airway tree of one primate species, the rhesus monkey. Trachea and intrapulmonary airways of the right cranial and middle lobes of glutaraldehyde/paraformaldehyde-infused lungs of five adult rhesus monkeys were microdissected following the axial pathway. Each branch was assigned a binary number indicating its specific location within the tree. The trachea and six generations of intrapulmonary airway from the right cranial lobe were evaluated for ultrastructure and quantitative histology as were those of the right middle lobe for quantitative carbohydrate histochemistry. Four cell types were identified throughout the tree: ciliated, mucous goblet, small mucous granule, and basal. The tallest epithelium lined the trachea; the shortest, the respiratory bronchiole. The most cells per unit length of basement membrane were in proximal intrapulmonary bronchi; the least, in the respiratory bronchiole. The nonciliated bronchiolar epithelial or Clara cell was restricted to respiratory bronchioles. Sulfomucins were present in the vast majority of surface goblet cells in the trachea and proximal bronchi. In proximal bronchi, neutral glycoconjugates predominated in glands and acidic glycoconjugates in surface epithelium. In terminal and respiratory bronchioles the ratio of acidic glycoconjugate to neutral glycoconjugate equaled that in proximal bronchi, although glands were not present. Sulfomucins were minimal in terminal airways. We conclude that the characteristics of the epithelial lining of the mammalian tracheobronchial airway tree are very species-specific. The lining of the rhesus monkey does not have the diversity in cell types in different airway generations observed in sheep and rabbit. Also, the populations lining these airways in the rhesus are very different from either the sheep or rabbit in number, proportions of different cell types, glycoconjugate content, and distribution of specific cell types.     

Distribution of ion transport mRNAs throughout murine nose and lung

Evidence of absorptive or secretory ion transport in different respiratory regions of the mouse was sought by assessing the regional distribution of alpha-, beta-, and gamma-epithelial sodium channel (ENaC; Na(+) absorptive), cystic fibrosis transmembrane conductor regulator (CFTR), and Na(+)-K(+)-2Cl(-) cotransporter mRNAs. High levels of ENaC subunit expression were found in nasal surface epithelium and gland ducts. CFTR was expressed in both superficial nasal respiratory epithelium and glands. These results are consistent with basal amiloride-sensitive Na(+) absorption and cAMP-dependent Cl(-) secretion in murine nasal epithelia. Expression of all three ENaC subunits increased progressively from trachea to terminal bronchioles. Intermediate levels of CFTR and cotransporter expression in bronchial epithelium diminished in bronchioles. The low abundance of CFTR mRNA throughout murine pulmonary epithelium is consistent with functional data that attributes Cl(-) secretion predominantly to an alternative Cl(-) channel. alpha-ENaC as the only mRNA found in all regions of airway epithelia is consistent with the alpha-subunit as requisite for Na(+) absorption, and the increased expression of alpha-, beta-, and gamma-ENaC in distal airways suggests a greater absorptive capability in this region.     

Flow field analysis in a compliant acinus replica model using particle image velocimetry (PIV)

Inhaled particles reaching the alveolar walls have the potential to cross the blood–gas barrier and enter the blood stream. Experimental evidence of pulmonary dosimetry, however, cannot be explained by current whole lung dosimetry models. Numerical and experimental studies shed some light on the mechanisms of particle transport, but realistic geometries have not been investigated. In this study, a three dimensional expanding model including two generations of respiratory bronchioles and five terminal alveolar sacs was created from a replica human lung cast. Flow visualization techniques were employed to quantify the fluid flow while utilizing streamlines to evaluate recirculation. Pathlines were plotted to track the fluid motion and estimate penetration depth of inhaled air. This study provides evidence that the two generations immediately proximal to the terminal alveolar sacs do not have recirculating eddies, even for intense breathing. Results of Peclet number calculations indicate that substantial convective motion is present in vivo for the case of deep breathing, which significantly increases particle penetration into the alveoli. However, particle diffusion remains the dominant mechanism of particle transport over convection, even for intense breathing because inhaled particles do not reach the alveolar wall in a single breath by convection alone. Examination of the velocity fields revealed significant uneven ventilation of the alveoli during a single breath, likely due to variations in size and location. This flow field data, obtained from replica model geometry with realistic breathing conditions, provides information to better understand fluid and particle behavior in the acinus region of the lung.     

Effect of C-fiber-mediated, ozone-induced rapid shallow breathing on airway epithelial injury in rats.

We examined the relationship between C-fiber-mediated, ozone-induced rapid shallow breathing and airway epithelial cell injury at different airway sites within the lower respiratory tract of conscious Wistar rats (n = 24). We combined an acute 8-h ozone inhalation with vagal perineural capsaicin treatment, a selective C-fiber conduction block, and 5-bromo-2'-deoxyuridine (BrdU) labeling as an index of epithelial injury. Vehicle-treated rats that inhaled ozone developed a rapid shallow breathing pattern during ozone inhalation, whereas the capsaicin-treated rats that inhaled ozone showed no changes in respiratory frequency. In vehicle-treated, ozone-exposed rats that developed rapid shallow breathing, a progressive increase in BrdU-labeling density (no. of BrdU-labeled cells/mm(2) airway) was observed starting at the bifurcation of the left main stem bronchi (central airway) and going down either a short or long airway path. In vehicle-treated, ozone-exposed rats, terminal bronchioles supplied by short and long airway paths had a similar degree of BrdU-labeling density that was significantly (P < 0.05) greater than the BrdU-labeling density of the proximal airways that supply them. In contrast, the attenuation of rapid shallow breathing produced by capsaicin treatment resulted in a significantly reduced BrdU-labeling density in the terminal bronchioles supplied by short airway paths compared with the terminal bronchioles supplied by long airway paths. Our data indicate that ozone-induced rapid shallow breathing protects large conducting airways while producing a more even distribution of injury to terminal bronchioles.     

Smooth muscle development during postnatal growth of distal bronchioles in infant rhesus monkeys.

Development of smooth muscle in conducting airways begins early in fetal life. Whereas the pattern and regulation of smooth muscle differentiation are well-defined, the impact of airway growth on the process is not. To evaluate the transformations in organization during postnatal growth, smooth muscle bundle organization (size, abundance, and orientation) was mapped in five generations of distal airways of infant rhesus monkeys (5 days and 1, 2, 3, and 6 mo old). On the basis of direct measurement of the bronchiole proximal to the terminal bronchiole, length increased by 2-fold, diameter by 1.35-fold, and surface area by 2.8-fold between 5 days and 6 mo of age. Smooth muscle bundle size was greater in proximal bronchioles than in respiratory bronchioles and did not change with age. However, relative bundle size decreased in proportion to airway size as the airways grew. Relative bundle abundance was constant regardless of airway generation or age. The distribution of smooth muscle bundle orientation changed with age in each airway generation, and there were significant changes in the terminal and respiratory bronchioles. We conclude that smooth muscle undergoes marked organizational changes as airways grow during postnatal development.     

Deposition of micrometer particles in pulmonary airways during inhalation and breath holding

We investigated how breath holding increases the deposition of micrometer particles in pulmonary airways, compared with the deposition during inhalation period. A subject-specific airway model with up to thirteenth generation airways was constructed from multi-slice CT images. Airflow and particle transport were simulated by using GPU computing. Results indicate that breath holding effectively increases the deposition of 5μm particles for third to sixth generation (G3-G6) airways. After 10s of breath holding, the particle deposition fraction increased more than 5 times for 5μm particles. Due to a small terminal velocity, 1μm particles only showed a 50% increase in the most efficient case. On the other hand, 10μm particles showed almost complete deposition due to high inertia and high terminal velocity, leading to an increase of 2 times for G3-G6 airways. An effective breath holding time for 5μm particle deposition in G3-G6 airways was estimated to be 4-6s, for which the deposition amount reached 75% of the final deposition amount after 10s of breath holding.     

Distribution of Clara cell secretory protein expression in the tracheobronchial airways of rhesus monkeys

Clara cell secretory protein (CCSP) is a protective lung protein that is believed to have antioxidant, immunomodulatory, and anticarcinogenic properties; to be present in all adult mammals; and to be well conserved in rodents, humans, and nonhuman primates. The rationale for this study is to define the distribution and abundance of CCSP in the airway epithelium and lavage fluid of the adult rhesus monkey and to provide information for evaluating CCSP as a marker of Clara cells and as a biomarker of lung health. Lung tissue and lavage fluid from 3-yr-old rhesus monkeys were examined using histopathology and immunohistochemistry. Proximal bronchi, midlevel bronchi, and terminal/respiratory bronchioles were compared for immunohistochemical localization of CCSP in three-dimensional whole mounts as well as in paraffin and Araldite sections. Immunoreactive CCSP was found in nonciliated cells throughout the airway epithelium. Proximal and midlevel airways had the highest labeling. CCSP decreased in distal airways, and respiratory bronchioles had little to no CCSP. CCSP in the most distal airways was in tall cuboidal cells adjacent to the pulmonary artery. Although a large number of cells were present in the terminal bronchioles that would be classified as Clara cells based on morphology (nonciliated cells with apical protrusions), only a small number stained positively for immunoreactive CCSP. Semiquantitative analysis of Western blots indicated that changes in lavage CCSP are consistent with, and may be predictive of, overall CCSP levels in the airway epithelium in this primate species that is phylogenetically similar to humans.     

Reaction of various experimental animals to exposure to acetylcholine or histamine, and morphological observations of bronchial smooth muscle

We investigated the sensitivity of the airway of various experimental animals to acetylcholine (ACh) and histamine (Hist). The experimental animals were exposed to 0.1% ACh or 0.05% Hist. Guinea pigs and rabbits exhibited an asthmatic reaction to both chemicals, but rabbits seemed to have a milder reaction than guinea pigs to both chemicals. Mice, rats and hamsters showed no reaction. We then performed a morphological study of the airways of 5 species in order to clarify the reason for their different reactivities to ACh and Hist. In the morphological study, abundant smooth muscle could be seen in the terminal bronchioles and respiratory bronchioles of guinea pigs and rabbits. In contrast, animals of other species had little smooth muscle in either site. Mice had no respiratory bronchioles. Consequently, we concluded that there is a high correlation between sensitivity to ACh and Hist and the extent of smooth muscle distribution around the airway.     

Adenosine 5'-monophosphate challenge elicits a more peripheral airway response than methacholine challenge

Adenosine 5'-monophosphate (AMP) and methacholine are commonly used to assess airway hyperreactivity. However, it is not fully known whether the site of airway constriction primarily involved during challenges with either agent is similar. Using a ventilation distribution test, we investigated whether the constriction induced by each agent involves the lung periphery in a similar fashion. Ventilation distribution was evaluated by the phase III slope (S) of the single-breath washout, using gases with different diffusivities like helium (He) and hexafluorosulfur (SF(6)). A greater postchallenge increase in S(He) reflects alterations at the level of terminal and respiratory bronchioles, while a greater increase in S(SF6) reflects alterations in alveolar ducts, increases to an equal extent reflecting alterations in more proximal airways where gas transport is still convective for both gases. S(SF6) and S(He) were measured in 15 asthma patients before and after airway challenges (20% forced expired volume in 1-s fall) with AMP and methacholine. S(He) increased to a greater extent than S(SF6) after AMP challenge (5.7 vs. 3.7%/l; P = 0.002), with both slopes increasing to an equal extent after methacholine challenge (3.1%/l; P = 0.959). The larger increase in S(He) following AMP challenge suggests distal ventilation impairment up to the level of terminal and respiratory bronchioles. With methacholine, the similar increases in S(He) and S(SF6) suggest a less distal impairment. AMP, therefore, seems to affect more extensively the very peripheral airways, whereas methacholine seems to have an effect on less distal airways.     

An immunosuppressed rat model of respiratory cryptosporidiosis.

A rat model is described in which animals develop respiratory cryptosporidiosis, a disease which is well documented in immunocompromised patients, especially those with AIDS. Our present lack of knowledge of the pathophysiology and immunology of Cryptosporidium parvum respiratory infections warrants the development of a laboratory animal model. Lewis rats immunosuppressed by subcutaneous injection of methylprednisolone acetate and inoculated intratracheally with 10(6) C. parvum oocysts developed a reproducible infection consisting of all known developmental stages in the epithelium lining airways from the trachea to the terminal bronchioles. Developmental stages were morphologically indistinguishable from those seen in gut epithelium. Infections were apparent at 4 days post-inoculation, and at 10-14 days post-inoculation, rats exhibited respiratory distress and severe weight loss and had enlarged, elastic lungs. Increased mucus production and exfoliative necrosis of the epithelium resulted in accumulation of large amounts of mucocellular exudate throughout the airways and patchy alveolitis involving alveoli emerging from respiratory bronchioles.     

Effects of oral airway geometry characteristics on the diffusional deposition of inhaled nanoparticles

The deposition of ultrafine aerosols in the respiratory tract presents a significant health risk due to the increased cellular-level response that these particles may invoke. However, the effects of geometric simplifications on local and regional nanoparticle depositions remain unknown for the oral airway and throughout the respiratory tract. The objective of this study is to assess the effects of geometric simplifications on diffusional transport and deposition characteristics of inhaled ultrafine aerosols in models of the extrathoracic oral airway. A realistic model of the oral airway with the nasopharynx (NP) included has been constructed based on computed tomography scans of a healthy adult in conjunction with measurements reported in the literature. Three other geometries with descending degrees of physical realism were then constructed with successive geometric simplifications of the realistic model. A validated low Reynolds number k-omega turbulence model was employed to simulate laminar, transitional, and fully turbulent flow regimes for the transport of 1-200 nm particles. Results of this study indicate that the geometric simplifications considered did not significantly affect the total deposition efficiency or maximum local deposition enhancement of nanoparticles. However, particle transport dynamics and the underlying flow characteristics such as separation, turbulence intensity, and secondary motions did show an observable sensitivity to the geometric complexity. The orientation of the upper trachea was shown to be a major factor determining local deposition downstream of the glottis and should be retained in future models of the respiratory tract. In contrast, retaining the NP produced negligible variations in airway dynamics and could be excluded for predominantly oral breathing conditions. Results of this study corroborate the use of existing diffusion correlations based on a circular oral airway model. In comparison to previous studies, an improved correlation for the deposition of nanoparticles was developed based on a wider range of particle sizes and flow rates, which captures the dependence of the Sherwood number on both Reynolds and Schmidt numbers.     

Morphology of the terminal bronchiolar region of common laboratory mammals

The histomorphology of the terminal bronchiolar region of the mouse, rat, hamster, guinea pig, gerbil and rabbit was studied. Although some general structural similarities existed in the progressive intrapulmonary branching pattern of the airway tree between species, there were conflicting accounts in the literature about the presence of the respiratory bronchioles in common laboratory mammals. In our light microscopy study we failed to detect the existence of typical respiratory bronchioles with characteristic interruptions on their walls projecting into the alveoli. Frequently in these species the terminal bronchioles were short and abrupt, opening directly into several alveolar ductules.     

A technique for quantitating airway size from bronchial casts

To develop a technique for quantitating the size of airways at various positions in the bronchial tree, we analyzed casts of formalin-fixed excised lungs of five mature male ferrets. The left lower lobe of each cast was dissected, the diameter and position of each terminal bronchiole were entered into a computer programmed to reconstruct the airway system, and the cross-sectional areas of 120 conducting airways were measured. The fraction of the lobe served by each measured airway was estimated by dividing the sum of the squared diameters of the terminal bronchioles subtended by that airway by the summed squared diameters of all terminal bronchioles in the lobe. In each cast the relationship between an airway's cross-sectional area (Y) and the fraction of the lobe it was estimated to subtend (X) was described (0.91 less than R2 less than 0.95) by the expression ln(Y) = A + B ln(X) + C [ln(X)]2. Linear regression of ln(Y) on ln(X) for 30-50 airways estimated to serve fractions of the lobe around each of three arbitrarily selected levels (airways serving 0.7, 2.2, and 9.5% of the lobe) was adequate to characterize the area of airways at each level in each of the five animals with 95% confidence intervals narrower than 8% of the estimated area. Variability of airway size at each level among the five casts was modest, suggesting that this technique identified analagous airways in the various animals. Interindividual variability did not increase when the data were reanalyzed with terminal units defined on the basis of airway diameters rather than on the morphological identification of terminal bronchioles.     

Methacholine responsiveness of proximal and distal airways of monkeys and rats using videomicrometry.

Rat and monkey are species that are used in models of human airway hyperresponsiveness. However, the wall structures of rat and monkey airways are different from each other, with that of the monkey more closely resembling that of humans. We hypothesized that differences in wall structure would explain differences in airway responsiveness. Using videomicrometry, we measured airway luminal area in lung slices to compare proximal and distal airway responsiveness to methacholine in the rat and monkey. The airway type was then histologically identified. Proximal airways of the young rat and monkey were equally responsive to methacholine. In contrast, respiratory bronchioles of monkeys were less responsive than were their proximal bronchi, whereas the distal bronchioles of rats were more responsive than their proximal bronchioles. Both proximal and distal airways of younger monkeys were more responsive than those of older monkeys. Airway heterogeneity in young monkeys was greatest with regard to degree of airway closure of respiratory bronchioles. We conclude that responsiveness to methacholine varies with airway wall structure and location.     

Convective and diffusive gas transport in canine intrapulmonary airways.

The significance of convective and diffusive gas transport in the respiratory system was assessed from the response of combined inert gas and particle boluses inhaled into the conducting airways. Particles, considered as "nondiffusing gas," served as tracers for convection and two inert gases with widely different diffusive characteristics (He and SF6) as tracers for convection and diffusion. Six-milliliter boluses labeled with monodisperse di-2-ethylhexyl sebacate droplets of 0.86-microns aerodynamic diameter, 2% He, and 2% SF6 were inspired by three anesthetized mechanically ventilated beagle dogs to volumetric lung depths up to 170 ml. Mixing between inspired and residual air caused dispersion of the inspired bolus, which was quantified in terms of the bolus half-width. Dispersion of particles increased with increasing lung depth to which the boluses were inhaled. The increase followed a power law with exponents less than 0.5 (mean 0.39), indicating that the effect of convective mixing per unit volume was reduced with depth. Within the pulmonary dead space, the behavior of the inert gases He and SF6 was similar to that of the particles, suggesting that gas transport was almost solely due to convection. Beyond the dead space, dispersion of He and SF6 increased more rapidly than dispersion of particles, indicating that diffusion became significant. The gas and particle bolus technique offers a suitable approach to differential analysis of gas transport in intrapulmonary airways of lungs.     

Respiratory deposition model of an inhaled aerosol bolus

The bolus delivery method is designed to deliver a dose to the desired location in the lung, and it has the advantage of fewer side effects and a more efficient way of delivery. Based upon the lung deposition model developed for continuously inhaling aerosols of constant concentration, a mathematical model of aerosol bolus deposition is proposed. The calculated results show that the recovery depends on the bolus penetration depth, flow rate, particle size, breath holding time and bolus volume. Three sets of published experimental data with different controlling factors (particle size, flow rate and breath holding time) are adopted to make the quantitative comparisons with the calculated results. The predictions and data for the low intrinsic motion particles (～1 μm) have good agreement, as do the coarse particles in the shallow airways region. For females, the recovery was found to be consistently lower than that for males.