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PubMed1993

Alveolar ventilation to perfusion heterogeneity and diffusion impairment in a mathematical model of gas exchange.

This study describes a two-compartment model of pulmonary gas exchange in which alveolar ventilation to perfusion (VA/Q) heterogeneity and impairment of pulmonary diffusing capacity (D) are simultaneously taken into account. The mathematical model uses as input data measurements usually obtained in the lung function laboratory. It consists of two compartments and an anatomical shunt. Each compartment receives fractions of alveolar ventilation and blood flow. Mass balance equations and integration of Fick's law of diffusion are used to compute alveolar and blood O2 and CO2 values compatible with input O2 uptake and CO2 elimination. Two applications are presented. The first is a method to partition O2 and CO2 alveolar-arterial gradients into VA/Q and D components. The technique is evaluated in data of patients with chronic obstructive pulmonary disease (COPD). The second is a theoretical analysis of the effects of blood flow variation in alveolar and blood O2 partial pressures. The results show the importance of simultaneous consideration of D to estimate VA/Q heterogeneity in patients with diffusion impairment. This factor plays an increasing role in gas alveolar-arterial gradients as severity of COPD increases. Association of VA/Q heterogeneity and D may produce an increase of O2 arterial pressure with decreasing QT which would not be observed if only D were considered. We conclude that the presented computer model is a useful tool for description and interpretation of data from COPD patients and for performing theoretical analysis of variables involved in the gas exchange process.

Blood Gas Monitoring, Transcutaneous↗
PubMed1977

Long-term physiologic consequences of the adult respiratory distress syndrome.

Six survivors of the adult respiratory distress syndrome were studied. Measurements were made of lung volumes, flow rates, single-breath diffusing capacity for carbon dioxide (Dsb), arterial blood gas levels at rest and during exercise, the ratio of physiologic dead space to tidal volume (VD/VT), alveolar-arterial oxygen pressure difference (P[A-a]O2) and percent shunt (using an assumed arteriovenous oxygen content difference). At the time of study, which varied from 3 to 16 months after recovery, we found minor and inconsistent abnormalities in the lung volumes (reduced vital capacity in one patient, elevated residual volume [RV] in two, and reduced RV in three) and in the flow rates (reduced instantaneous forced expiratory flow after 50 percent of the forced vital capacity had been exhaled in two patients). In those tests having to do with transfer of gas, there were more abnormalities, consisting of a decreased Dsb in three patients, an elevated P(A-a)O2 in four, a low resting arterial oxygen pressure (PaO2) in two, a decrease in exercise PaO2 in three, an elevated shunt fraction (Qsan/Qt) in three, and an elevated VD/VT in one patient. Clinically, at the time of study, the patients all had returned to their status before illness.

Adult↗
PubMed2007

Intense hypoxic cycle exercise does not alter lung density in competitive male cyclists.

We tested the hypothesis that intense short duration hypoxic exercise would result in an increase in extravascular lung water (EVLW), as evidenced by an increase in lung density. Using computed tomography (CT), baseline lung density was obtained in eight highly trained male cyclists (mean +/- SD: age = 28 +/- 8 years; height = 180 +/- 9 cm; mass = 71.6 +/- 8.2 kg; VO2max= 65.0 +/- 5.2 ml kg min(-1)). Subjects then completed an intense hypoxic exercise challenge on a cycle ergometer and metabolic data, HR and %S(p)O2 were recorded throughout. While breathing 15% O2, subjects performed five 3 km cycling intervals (mean power, 286 +/- 20 W; HR = 91 +/- 4% HRmax) separated by 5 min of recovery. From a resting hypoxic S(p)O2 of 92 +/- 4%, subjects further desaturated during exercise to 76 +/- 3%. CT scans were repeated 76 +/- 10 min (range 63-88 min) following the completion of exercise. There was no change in lung density from pre (0.18 +/- 0.02 g ml(-1)) to post-exercise (0.18 +/- 0.04 g ml(-1)). The substantial reduction in S(p)O2 may be explained by a number of potential mechanisms, including decreased pulmonary diffusion capacity, alveolar hypoventilation, reduced red cell transit time, ventilation/perfusion inequality or a temperature and pH induced rightward-shift in the oxyhaemoglobin dissociation curve. Alternatively, the integrity of the blood gas barrier may have been disrupted without any measurable increase in lung density.

Adult↗
PubMed1996

Improvement in pulmonary function and elastic recoil after lung-reduction surgery for diffuse emphysema.

BACKGROUND: Pulmonary function may improve after surgical resection of the most severely affected lung tissue (lung-reduction surgery) in patients with diffuse emphysema. The basic mechanisms responsible for the improvement, however, are not known. METHODS: We studied 20 patients with diffuse emphysema before and at least three months after either a unilateral or a bilateral lung-reduction procedure. Clinical benefit was assessed by measurement of the six-minute walking distance and the transitional-dyspnea index, which is a subjective rating of the change from base line in functional impairment and the threshold for effort- and task- dependent dyspnea. Pressure-volume relations in the lungs were measured with static expiratory esophageal-balloon techniques, and right ventricular systolic function was assessed by echocardiography. RESULTS: The patients had significant improvement in the transitional-dyspnea index after surgery (P<0.001). The mean (+/-SD) coefficient of retraction, an indicator of elastic recoil of the lung, improved (from 1.3+/-0.6 cm of water per liter before surgery to 1.8+/-0.8 after, P<0.001). Sixteen patients with increased elastic recoil had a greater increase in the distance walked in six minutes than the other four patients, in whom recoil did not increase (P=0.02). The improved lung recoil led to disproportionate decreases in residual volume as compared with total lung capacity (16 percent vs. 6 percent), but the decreases in both values were significant (P<0.001). Forced expiratory volume in one second increased (from 0.87+/-0.36 to 1.11+/-0.45 liters, P<0.001). End-expiratory esophageal pressure also decreased (P=0.002). These improvements in lung mechanics led to a decrease in arterial partial pressure of carbon dioxide form 42+/-6 to 38+/-5 mm Hg (P=0.006). Furthermore, the fractional change in right ventricular area, an indicator of systolic function, increased from 0.33+/-0.11 to 0.38+/-0.010 (P=0.02). CONCLUSIONS: Lung-reduction surgery can produce increases in the elastic recoil of the lung in patients with diffuse emphysema, leading to short-term improvement in dyspnea and exercise tolerance.

Adult↗
PubMed1984

Correlations between structure and function in the design of the bat lung: a morphometric study.

The lungs of five species of bat Pipistrellus pipistrellus, Miniopterus minor (Peters), Tadarida mops (De Blainville), Cynopterus brachyotis (Muller) and Cheiromeles torquatus (Horstield) have been analysed by morphometric techniques. The mean body weight (W) ranged from 5 g in Pipistrellus pipistrellus to 173 g in Cheiromeles torquatus; the lung volume (VL) ranged from 0.3 cm3 in Pipistrellus to 10 cm3 in Cheiromeles. The volume densities or the main components of the bat lung, namely the parenchyma [VV(p,L)] (the gas exchange region) and the non-parenchyma [VV(np,L)], were closely similar, the VV(p,L) constituting a mean value of 84.2% and the VV(np,L) 15.8% in the five species. The VL, the surface area of the blood--gas (tissue) barrier (St), the pulmonary capillary blood volume (Vc), and the total morphometric pulmonary diffusing capacity (DLO2) were all strongly correlated with body weight. The harmonic mean thickness of the blood--gas (tissue) barrier (tau ht) and the surface density of the blood--gas (tissue) barrier [SV(t,p)] were poorly correlated with W. The bats had a remarkably higher VL than either birds or terrestrial mammals. The Vc in the bat lung was similar to that in the bird lung but higher than that of the terrestrial mammals. The bats had a more extensive St than either the birds or the terrestrial mammals. In the bats the tau ht was thicker than in the birds but thinner than that of the terrestrial mammals. These pulmonary structural adaptations culminated in a higher DLO2 in the bat than either in the birds or in the terrestrial mammals. The superior morphometric properties of the bat lung coupled with the established physiological adaptations may help to explain how the bat lung is capable of providing the immense amount of oxygen demanded by flight.

Animals↗
PubMed1982

Diffusing capacity in idiopathic scoliosis and its interpretation regarding alveolar development.

We measured lung volumes, diffusing capacity by the single breath method (DL), membrane permeability (DM), and capillary blood volume (Vc) in 22 subjects with idiopathic scoliosis (mean angle of curvature, 66 degrees). Compared with an age-matched group, vital capacity, total lung capacity, and functional residual capacity were respectively, 21% (p less than 0.0001), 18% (p less than 0.01), and 15% (p less than 0.05) lower. The DL was 17% lower (p less than 0.01), but specific DL (DL divided by alveolar volume = DLVA) was the same. For both groups, DLVA was inversely correlated with VA. The same qualitative relationship existed between DM, Vc, their specific values, and VA except for a larger spread of Vc in the scoliotic group. The data show that DL and its components, DM and Vc, are normal in idiopathic scoliosis when reduced lung volumes are allowed for. These findings are consistent with partial failure of alveolar enlargement as a result of the thoracic deformity rather than any atrophy of the alveoli or pulmonary vasculature. Thus scoliosis results in a delay of lung development, such that in a group of symptomatic patients with moderate degrees of deformity (mean angle of curvature, 66 degrees), lung volumes and DL are about 80% of that of an age-matched control group; the alveolar characteristics of a 12-yr-old with scoliosis are therefore similar to those of a 9-yr-old normal child.

Adolescent↗
PubMed1976

Congenital lobar emphysema: long-term evaluation of surgically and conservatively treated children.

The clinical conditions, roentgenographic findings, and pulmonary function tests of 6 children (mean age, 10.9 years) with surgically treated congenital lobar emphysema (group 1) were compared with those of 5 children (mean age, 10.3 years) with congenital lobar emphysema who had been treated conservatively, i.e., nonsurgically (group 2). At the time of this study, patients in both groups were asymptomatic. Patients in group 1 were surgically treated because of severe respiratory distress in the newborn period, with the exception of one patient, who was eupneic as a newborn and was not operated on until the age of 9 years. Patients in group 2 were eupneic or mildly distressed in the neonatal period and received only conservative treatment. Two patients in group 1 had occasional wheezing and labored breathing, but no patient in group 2 had recurrent respiratory distress. Roentgenographically, at the time of the study, patients in group 1 had generalized overinflation, whereas those in group 2 had only localized overinflation of the involved lobe and minimal compression of remaining lung tissue. Pulmonary function studies in both groups were not significantly different (P greater than 0.05). Both groups had reduced forced vital capacities, large trapped gas volumes, and reduced forced expiratory flows at low lung volumes. Reductions in forced vital capacity were proportional to the unventilated volumes of lung either excised because of congenital lobar emphysema (group 1) or chronically obstructed by congenital lobar emphysema (group 2). These studies suggest that lung growth was not different in these 2 groups and that asymptomatic or midly symptomatic patients do not benefit from surgical treatment.

Adolescent↗
PubMed1988

A steady-state model of maximal oxygen and carbon dioxide transport in anuran amphibians.

A steady-state model, incorporating pulmonary ventilation, pulmonary diffusion capacity, cardiovascular transport capacity, and tissue diffusion capacity, was developed to describe the maximal O2 and CO2 transport capacity for an anuran amphibian (Bufo). Solution of the model by iterative calculation closely predicted 1) the empirical maximal O2 consumption (VO2max) for Bufo, 2) variation in empirical VO2max for three other genera (Rana, Xenopus, Scaphiopus), and the empirically observed effects on VO2max of 3) hypobaric hypoxia, 4) artificially induced anemia, and 5) beta-blockade of heart rate increment with activity. The model indicates that cardiovascular transport is the rate-limiting step to VO2max in amphibians and that an increase in circulatory O2 transport is a major physiological adaptation for increasing total aerobic capacity. CO2 transport and body fluid PCO2 values were primarily determined by pulmonary ventilatory capacity, and to a lesser extent by cardiovascular transport. The model should be generally applicable to other terrestrial vertebrates.

Animals↗
PubMed1979

Assessment of alpha-1-antitrypsin deficiency heterozygosity as a risk factor in the etiology of emphysema. Physiological comparison of adult normal and heterozygous protease inhibitor phenotype subjects from a random population.

For plethysmographic studies of lung mechanics and measurement of pulmonary diffusing capacity, 62 subjects were drawn from a randomly selected population sample. Data obtained from the 24 subjects of heterozygous phenotype for alpha-1-antitrypsin deficiency (PiMZ) were compared by age group with data from 38 normal (PiM) subjects matched for sex, age, and smoking history. Comparison of mean values by age group for lung volumes, diffusing capacity, lung elastic recoil, maximum expiratory flow, and the occurrence of frequency dependence of dynamic compliance revealed no differences between phenotype groups. There was no evidence of an accelerated effect of aging among PiMZ subjects when compared with normal counterparts nor was there evidence of an increased effect of smoking. From these data it appears that the PiMZ phenotype per se is not a risk factor in the development of emphysema.

Adult↗
PubMed1985

Perinatal age determines the severity of retarded lung development induced by starvation.

Susceptibility of the lung to caloric restriction is age-dependent, with more permanent damage occurring during the phases of growth and differentiation. Because the guinea pig is born with more well-developed alveoli than are other rodents, the postnatal lung of this species may better resist alveolar hypoplasia than the prenatal lung. Control animals were raised from sows provided food ad libitum during and after normal gestations (66 to 68 days). Starvation groups received 50% rations of control food intakes during 1 of three 21-day periods: prenatal starvation, with sows rationed during their last trimester (Day 45 to term); neonatal starvation, with nursing sows rationed during the 21 days postpartum before weaning; weanling starvation, with animals starved from 21 to 42 days postpartum. Lungs were fixed in situ with glutaraldehyde and analyzed for pulmonary morphometrics. At the end of starvation and before refeeding, lungs of prenatal and weanling starvation groups were significantly reduced for tissue volumes, alveolar and capillary surface areas, and pulmonary diffusing capacity. Recovery with feeding was complete for most parameters in the starved weanlings by maturity, but animals starved prenatally showed residual starvation effects as adults. The neonatally starved animals showed minimal effects of starvation on lung dimensions, both acutely and as adults. Morphologically, the lungs of some prenatally starved neonates were apparently retarded, at least to the saccular phase, and correlated with significant increases in the number of stillborn litters and in neonatal mortality within hours of parturition.

Age Factors↗
PubMed1984

Relative contribution of intrinsic lung dysfunction and hypoventilation to hypoxemia during hemodialysis.

Two mechanisms have been proposed to explain hemodialysis (HD)-induced hypoxemia: reversible lung damage due to intrapulmonary leukostasis as a consequence of the contact of blood with the dialyzer membrane, or alveolar hypoventilation due to the loss of carbon dioxide through the dialyzer. To assess the role of these factors, seven chronically uremic patients were studied before and during 4-hr HD sessions using a cuprophane membrane and either acetate (AHD) or bicarbonate (BHD) dialysate. In AHD only we observed, by comparison with predialysis values, a significant hypoxemia, and a decrease of alveolar ventilation (VA), lung carbon dioxide output, and respiratory exchange ratio. In both the AHD hypoxemic group and BHD nonhypoxemic group, there was a similar decrease in lung carbon dioxide diffusing capacity (DLCO) and of white blood cells (WBC), and a positive correlation between arterial oxygen pressure and VA without modification of alveolo arterial PO2 difference, an argument against the existence of ventilation-perfusion or ventilation-diffusion mismatching. We conclude that, although WBC sequestration induced a lung damage evidenced by DLCO impairment, the key factor of hypoxemia observed in AHD was the hypoventilation.

Acetates↗
PubMed2005

Real-time detection of nitric oxide isotopes in lung function tests.

In lung function tests, the determination of the pulmonary diffusing capacity (D) using the single-breath method is a commonly applied technique. The calculation of D is performed on the basis of accurate measurements of indicator gas concentrations. In this chapter, we demonstrate the appropriateness of the stable nitric oxide (NO) isotopes 14NO and 15NO in revealing reliable data of D. We performed studies on animals (14NO) by using respiratory mass spectrometry (M3) and on humans (15NO) by applying laser magnetic resonance spectroscopy (LMRS). The equipment was characterized by sufficient detection limits of 70 parts/billion at [14NO] = 0.001% (M3) and 40 parts/billion at [15NO] = 0.002 % (LMRS), respectively. Lastly, we were able to show that D-values for 14NO indeed reveal the entire diffusive properties of the alveolar-capillary membrane and that 15NO is a useful indicator gas for reflecting disturbances of pulmonary gas exchange.

Animals↗
PubMed1979

Pulmonary sarcoidosis: roentgenographic, functional, and pathologic correlations.

Discrepancies were observed between functional (PFT), chest roentgenographic, and open lung biopsy findings (granulomata, interstitial pneumonitis, angiitis, and fibrosis) in 81 patients with clinical diagnosis of sarcoidosis. A combination of normal PFT and Type 1 roentgenographic findings (hilar lymphadenopathy) was associated with minimal lung lesions without fibrosis. Type 1 findings alone did not preclude extensive lesions or fibrosis. Advanced roentgenographic and PFT abnormalities correlated with the presence of extensive lung lesions. The pulmonary diffusing capacity correlated best with specific and overall lung pathology, and roentgenographic types. Only this test differentiated the extent of granulomata and the roentgenographic types. Moderate degrees of other pathologic changes were not distinguished by any other PFT. Degrees of overall lung pathology correlated with an individual PFT and most significantly with overall PFT (p less than 0.001). Serial studies of PFT are a practical and valuable means for assessment of the disease process in sarcoidosis.

Adolescent↗
PubMed1985

[Steady-state carbon monoxide transfer during progressive muscular exercise in patients. Relation to PaO2. Value of specific VCO].

During muscular exercise, the alveolo-capillary gas exchange reaches its optimal capacity, but taking blood for arterial blood gases is associated with certain risks and the classical criteria of CO transfer in the steady state are difficult to interpret as they are influenced by age, sex, ventilatory regime. The "specific" CO uptake (VCO Sp) does not correspond to these criteria (6). When related to the ERCO2, it allows the DuCO to be determined (4). It has the same value at the 3rd minute and at the 10th minute of constant exercise (5). Like TCO, it is correlated with the PaO2 during effort (5). In this study, a triangular exercise was performed by men aged between 45 add 55 years, smokers and former smokers, classified into 4 A: 12 healthy subjects; B: 56 cases of chronic respiratory disease; C: 9 cases of chronic obstructive airways disease (COAD); D: 12 cases of diffuse pulmonary fibrosis (DPF). Groups C and D were derived from group B. The VCO SP, TCO and DuCO were measured at each plateau of the triangular exercise. In the patients, the PaO2 was measured at the same time as the FF (CO, CO2). In the last phase of exercise (Ex. Max.): VCO Sp was more frequently altered at rest and more strongly correlated to TCO; TCO/V had the same significance as DuCO. The results of TCO, VCO Sp and DuCO were compared between groups A, C and D.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1999

Rate of nitric oxide production by lower alveolar airways of human lungs.

This report describes methods for measuring nitric oxide production by the lungs' lower alveolar airways (VNO), defined as those alveoli and bronchioles well perfused by the pulmonary circulation. Breath holding or vigorous rebreathing for 15-20 s minimizes removal of NO from the lower airways and results in a constant partial pressure of NO in the lower airways (PL). Then the amount of NO diffusing into the perfusing blood will be the pulmonary diffusing capacity for NO (DNO) multiplied by PL and by mass balance equals VNO, or VNO = DNO(PL). To measure PL, 10 normal subjects breath held for 20 s followed by exhalation at a constant flow rate of 0.83 +/- 0.14 (SD) l/s or rebreathed at 59 +/- 15 l/min for 20 s while NO was continuously measured at the mouth. DNO was estimated to equal five times the single-breath carbon monoxide diffusing capacity. By using breath holding, PL equaled 2.9 +/- 0.8 mmHg x 10(-6) and VNO equaled 0.39 +/- 0.12 microl/min. During rebreathing PL equaled 2.3 +/- 0.6 mmHg x 10(-6) and VNO equaled 0.29 +/- 0.11 microl/min. Measurements of NO at the mouth during rapid, constant exhalation after breath holding for 20 s or during rebreathing provide reproducible methods for measuring VNO in humans.

Adult↗
PubMed2006

Measurement of single breath-hold carbon monoxide diffusing capacity in healthy infants and toddlers.

We describe a method for measuring carbon monoxide diffusing capacity (DL(CO)) and alveolar volume (V(A)) in sleeping infants, using a single 4-sec breath-hold technique. The breath-hold maneuver is obtained by inducing a respiratory pause of the respiratory system. Several inflations of the respiratory system with room air to a lung volume with an airway pressure of 30 cmH2O (V30) inhibit inspiratory effort. The respiratory system is then inflated with a test gas containing helium and a stable isotope of carbon monoxide (C18O), and a respiratory pause is maintained for 4 sec and followed by passive expiration to functional residual capacity. Concentrations of helium and C18O are continuously measured with a mass spectrometer. Twelve healthy infants between 6-22 months of age were evaluated. For 9 of 12 subjects, duplicate measurements of alveolar volume at 30 cmH2O (V(A30)) and DL(CO) were within 10%, which are the recommendations for older children and adults. Among these 9 subjects, values of V(A30) and DL(CO) increased with increasing body length (r2 = 0.82 and 0.79, respectively). The remaining 3 subjects had two values within 10-15%. Measurement of V(A) and DL(CO) with the single breath-hold technique at an elevated lung volume offers the potential to assess growth and development of the lung parenchyma early in life.

Body Height↗
PubMed1989

Gas transfer in isolated lungs perfused with red cell suspension or hemoglobin solution.

Rapid mixing experiments have shown that the reaction between oxygen and hemoglobin is faster in hemoglobin solutions than in red cell suspensions. In this study we tested whether this observation can also be made in the lung. Excised rabbit lungs were perfused either with washed human red cell suspensions or with hemoglobin solutions, each with 50 g hemoglobin/L, and steady-state diffusing capacities (DLO2) for oxygen elimination measured. Mean settings were a temperature of 29.5 degrees C of the inflowing and outflowing perfusate of the lung, a total ventilation of 1.7 L.min-1, and a perfusion rate of 116 ml.min-1. Under those conditions resulted a DLO2 with hemoglobin solution of 0.68 +/- 0.18 ml.min-1.mm Hg-1, and a significantly lower value of 0.50 +/- 0.06 ml.min-1.mm Hg-1 with red cell suspension (P less than 0.01). An extraerythrocytic diffusing resistance, formed by a plasma layer and/or arising from a dynamic diffusion boundary layer, which is also known as unstirred layer, could explain the lower value with red cell suspensions.

Animals↗
PubMed1994

Differing effects of airway obstruction on physical work capacity and ventilation in men and women with COPD.

BACKGROUND: Although the natural history of COPD is thought to be well known, studies assessing differences in the onset and course of the disease by gender are surprisingly lacking. This study is a cross-sectional analysis using progressive cycle ergometry exercise testing to assess male and female patients at specific levels of airway obstruction to see if they differ in their exercise capacity and decline in functional capacity. METHODS: The study group included 417 patients with COPD, 55 to 85 years of age, who were compared with 29 controls of similar age; all patients had COPD (FEV1/FVC < 75% predicted) without restrictive disease. Exercise testing in groups based on the level of pulmonary dysfunction defined by FEV1/FVC ratios (mild, 60.5 to 69.5%; moderate, 50.5 to 60.5%; severe < 50.5%) was analyzed. Data were evaluated using the Statistical Analysis System, analyzing gender and degree of airway obstruction and adjusting for any difference in age and peak exercise heart rate (covariate analysis of variance). RESULTS: Men demonstrated progressive reductions of body weight, exercise ability (assessed by the VO2), oxygen pulse (O2P, an indicator of stroke volume), and maximum exercise ventilation (VEmax) even with mild pulmonary dysfunction. Women did not lose weight, and maintained usual exercise ability (VO2, VEmax) and O2P until moderate or severe disease was present. Additional confirmation of a decrease in cardiac function for men with mild airway obstruction (p < 0.0001, controls), but not for women with mild airway disease, was obtained by estimation of cardiac output. Further, women presented with COPD at lower levels of tobacco smoke exposure than men for the entire group (43.8 vs 63.0 pack-years, p < 0.0001) and for each subgroup of disease severity. There were proportionally more life-time female nonsmokers than male nonsmokers with COPD (16 vs 5, p < 0.001). CONCLUSIONS: Male and female patients with COPD differed in their decline of functional aerobic capacity even at equivalent levels of pulmonary dysfunction. One reason for this appeared to be a decrease in the O2P occurring early in the natural history of the disease in the men and not in the women. Although general body de-conditioning may be the cause, heart disease may also be a contributing aspect. The relative delay in the loss of exercise capacity and body mass by the women may relate to predisease differences in physical activity. Women manifested significant lung disease with less cigarette smoking than men. This may be attributable to a different susceptibility to cigarette smoke between the sexes. These results suggest that there appear to be differences in the natural history of COPD in men and women.

Aged↗