[Guidelines for methacholine provocation testing]

Bronchial challenge with the direct bronchoconstrictor agent methacholine is commonly used for the diagnosis of asthma. The "Lung Function" thematic group of the French Pulmonology Society (SPLF) elaborated a series of guidelines for the performance and the interpretation of methacholine challenge testing, based on French clinical guideline methodology. Specifically, guidelines are provided with regard to the choice of judgment criteria, the management of deep inspirations, and the role of methacholine bronchial challenge in the care of asthma, exercise-induced asthma, and professional asthma.

A functional tool to differentiate nasal valve collapse from other causes of nasal obstruction: the FRIED test

Nasal valve collapse is a dynamic abnormality that is currently diagnosed purely on the basis of clinical features and thus subject to certain interpretation. The aim of this study was to develop a new and reliable functional test to objectively characterize nasal valve collapse. This was an observational prospective study including consecutive patients referred to our center for exploration of chronic nasal congestion. The patients were classified into two groups according to their symptoms and clinical abnormalities: the nasal valve collapse (NV+) group when nasal valve collapse was clinically detected during moderate forced inspiration and/or when the feeling of nasal congestion improved during passive nasal lateral cartilage abduction (n = 32); and the no-nasal valve collapse (NV-) group for the others (n = 23). All patients underwent nasal functional tests (posterior rhinomanometry and acoustic rhinometry) before and after topical nasal decongestion. We compared the difference between the pressure flow of the inspiratory and expiratory phases during posterior rhinomanometry [flow rate inspiratory-expiratory difference (FRIED) test] between the two groups. The difference between the absolute value of inspiratory and expiratory flow was significantly higher in the NV+ group than in the NV- group both before and after topical decongestion. The cutoff value for the FRIED test was -0.008 l/s with a good sensitivity (82%) and a specificity of 59%. We suggest that the FRIED test constitutes an objective and easy-to-apply technique to diagnose nasal valve collapse in daily practice.

Sinus fungal balls: characteristics and management in patients with host factors for invasive infection

BACKGROUND

The characteristics of sinus fungal ball (SFB), classically considered being a non-invasive form of fungal infection, in patients with host factors for invasive fungal infection (IFI) are unknown.

OBJECTIVE

To characterize SFB and their management in patients with host factors for IFI.

METHODOLOGY

Retrospective single-centre study of the clinical, radiology, histology and mycology records of patients treated for SFB between 1997 and 2007. Patients with and without host factors for IFI were compared.

RESULTS

One hundred eighty one patients were classified into two groups: 19 (group 1) with and 162 (group 2) without host fac- tors for IFI. In group 1, SFB were asymptomatic in 26.3% of the cases, ethmoido-sphenoidal sinuses were more frequently involved than in group 2 and fungal culture was positive in 37.5% of the cases. The main species was Aspergillus sp. in both groups. Four cases of complicated SFB were observed, only in patients of group 1. Cure without recurrence was obtained in both groups by endonasal surgery, combined with triazole therapy in complicated forms with osteolysis.

CONCLUSION

In patients with host factors for IFI, SFB more frequently involves deep sinuses and can be complicated by clinical signs suggestive of invasion and radiological signs of osteolysis, with no histological evidence of fungal invasion.

Airway responsiveness measured by forced oscillation technique in severely obese patients, before and after bariatric surgery

BACKGROUND

The influence of obesity on airway responsiveness remains controversial.

OBJECTIVE

This study was designed to investigate airway responsiveness, airway inflammation, and the influence of sleep apnea syndrome (SAS), in severely obese subjects, before and after bariatric surgery.

METHODS

A total of 120 non-asthmatic obese patients were referred consecutively for pre-bariatric surgery evaluation. Lung function, airway responsiveness to methacholine, exhaled nitric oxide measurement, and sleep studies were performed. Airway hyperresponsiveness (AHR) was defined as a 50% or greater increase in respiratory resistance measured using the forced oscillation technique in response to a methacholine dose ≤ 2000 μg. Forced expiratory volume in 1 second (FEV₁) was measured after the last methacholine dose. Airway responsiveness was reevaluated after weight loss in patients with a pre-surgery AHR.

RESULTS

AHR was found in 16 patients. The percent FEV₁ decrease or percent respiratory resistance increase in response to methacholine was related to baseline expiratory airflow (forced expiratory flow at 50%) (r = 0.26, p < .006 and r = 0.315, p = .0005, respectively) but not to body mass index (BMI) or exhaled nitric oxide. Both airway responsiveness parameters were significantly related to forced expiratory flow at 25-75%/forced vital capacity, a measure of airway size relative to lung size (r = 0.27, p < .005 and r = 0.25, p < .007, respectively). Sleep apnea was not significantly associated with AHR or airway inflammation. About 11 patients with AHR were reevaluated 18 months to 2 years after surgery, with no change in AHR associated with weight loss.

CONCLUSION

Airway responsiveness is not related to BMI or to SAS. AHR in severely obese patients might be related to distal airway obstruction or low relative airway size.

Validity criteria and comparison of analytical methods of flow-independent exhaled NO parameters

The objective was to assess both validity and comparability of multiple constant (MCF, mainly performed) and dynamically changing (DCF, new method) flow analyses calculating alveolar concentration (Calv(NO)), maximum conducting airway flux (J'aw(NO)) and airway diffusing capacity (Daw(NO)) of exhaled NO (FE(NO)). (Calv(NO), J'aw(NO))(R) where R is the correlation coefficient of the linear regression between NO output and expiratory flow rate (MCF) and (Calv(NO), J'aw(NO), Daw(NO))(Delta100) where Delta100 is the ratio ([observed-predicted FE(NO)]/observed FE(NO)) at 100 ml/s (DCF) were assessed in 18 healthy subjects (10 atopic). MCF demonstrated a linear relationship (R > or = 0.80) between NO output and expiratory flow in 15/18 subjects. DCF was valid (Delta100 < or = 30%) in 12/18 subjects. A good agreement between MCF and DCF was evidenced in the nine subjects with R > or = 0.80 and Delta100 < or = 30%. Failure of validity criteria was mainly observed in atopic subjects. In conclusion, when validity criteria are satisfied, the new DCF method similarly characterizes NO exchange parameters than MCF approach.

Impairment of nitric oxide output of conducting airways in primary ciliary dyskinesia

Nasal nitric oxide (NO) concentration is dramatically reduced in primary ciliary dyskinesia (PCD). The aims of this study were to apply a multiple-flow NO analysis to investigate whether NO output from the bronchial tree was affected in a similar way to nasal NO output, and to search for a relationship between flow-independent exchange parameters and airflow limitation. Multiple flow rate analysis of exhaled NO, allowing the calculation of maximum airway wall flux and alveolar NO concentration, was performed in 17 PCD patients (median age, 25-75th percentiles: 13.5, 12.1-17.6) with documented ultrastructural cilia abnormalities and 28 healthy subjects (16.0, 11.0-21.0). Median maximum airway wall flux and median alveolar NO concentration were significantly reduced in PCD patients compared to healthy subjects: 16.0, 7.5-29.5, vs. 25.0, 15.0-32.5 nl/min (P<0.05) and 2.5, 1.6-3.3, vs. 5.0, 3.6-6.5 ppb (P<0.01), respectively. Significant correlations between maximum airway wall flux and airflow limitation were found, i.e., resistance of respiratory system (rho=0.74, P<0.005), forced expiratory volume in one second (FEV(1))/VC (rho= -0.61, P<0.05), FEV(1) (rho=-0.52, P< 0.05), mid expiratory flow between 25 and 75% of forced vital capacity (MEF(25-75)) (rho=-0.54, P<0.05), and maximal instantaneous expiratory flow at 50% of the vital capacity (MEF(50)) (rho=-0.55, P<0.05). In conclusion, the impairment of NO output is less pronounced in the lower than in the upper (nasal) respiratory tract in PCD. A decrease in maximal NO output from conducting airways is associated with limited airflow impairment.

Factors associated with dyspnea in adult patients with sickle cell disease

OBJECTIVE

The aim of this prospective study was to determine the cardiorespiratory factors associated with dyspnea in patients with sickle cell SS-hemoglobin disease, with a specific interest in lung vascular involvement.

MEASUREMENTS

Forty-nine patients (29 women and 20 men; mean [+/- SD] age: women, 29 +/- 6 years; men, 31 +/- 11 years) underwent direct evaluations (Borg scale evaluation during a 6-min walk test) and indirect evaluations (modified Medical Research Council [MRC]score) of their dyspnea, pulmonary function tests (PFTs) [spirometry, volumes, diffusing capacity of the lung for carbon monoxide (Dlco), diffusing capacity of the alveolar-capillary membrane, and pulmonary capillary blood volume measurements], echocardiography, and biological evaluation.

RESULTS

Thirty-four patients complained of significant breathlessness (MRC score, > 1). Indirect and direct evaluations of dyspnea were correlated. PFT results depicted a very mild restrictive pattern (mean total pulmonary capacity, 86 +/- 11% predicted) and an impairment of Dlco (mean Dlco corrected for the degree of anemia, 69 +/- 13% predicted). The statistical analysis demonstrated that dyspnea and exercise performance were closely linked to indexes of Dlco but not with any echocardiographic or biological measure including anemia. Nevertheless, only approximately 25% of the variability was explained by these associations. Despite having a similar history of vasoocclusive crisis events, women had more severe anemia, dyspnea, decreases in Dlco (corrected for the degree of anemia), and a higher capillary blood volume (corrected for alveolar volume) than men.

CONCLUSION

Lung vascular disease contributes to dyspnea and the exercise limitation of patients with sickle cell disease. A sequential assessment of Dlco would therefore constitute one of the objective functional end points for follow-up studies of these patients.

Nasal wall compliance in vasomotor rhinitis

Nasal compliance is a measure related to the blood volume in the nasal mucosa. The objective of this study was to better understand the vascular response in vasomotor rhinitis by measuring nasal cross-sectional area and nasal compliance before and after mucosal decongestion in 10 patients with vasomotor rhinitis compared with 10 healthy subjects. Nasal compliance was inferred by measuring nasal area by acoustic rhinometry at pressures ranging from atmospheric pressure to a negative pressure of -10 cmH2O. Mucosal decongestion was obtained with one puff per nostril of 0.05% oxymetazoline. At atmospheric pressure, nasal cross-sectional areas were similar in the vasomotor rhinitis group and the healthy subject group. Mucosal decongestion did not induce any decrease of nasal compliance in patients with vasomotor rhinitis in contrast with healthy subjects. Our results support the hypothesis, already proposed, of an autonomic dysfunction based on a paradoxical response of the nasal mucosa in vasomotor rhinitis. Moreover, the clearly different behavior between healthy subjects and vasomotor rhinitis subjects suggests that nasal compliance measurement may therefore represent a potential line of research to develop a diagnostic tool for vasomotor rhinitis, which remains a diagnosis of exclusion.

Perceived inspiratory difficulty in neuromuscular patients with primary muscle disorders

Intensity of perceived inspiratory difficulty was investigated in 17 patients with severe respiratory insufficiency due to muscle disease, compared with healthy matched controls. Subjects breathed through a threshold valve generating a constant inspiratory negative pressure proportional to their maximal inspiratory pressure. Four load levels ranging from 10 to 40% of the maximal inspiratory pressure were applied in random order. Patients had significantly less perceived inspiratory difficulty than controls at each load level expressed as a percentage of maximal inspiratory pressure P < 0.001. However, when the load was expressed as the absolute value, the slope of the Borg scale score versus mouth pressure was similar in the two groups (P = 0.11). The ventilatory pattern remained unchanged in each group as the load increased. We conclude that in patients with myopathy, loads leading to respiratory muscle fatigue (40% of maximal inspiratory pressure) may fail to produce perceived inspiratory difficulty.

Increase in alveolar nitric oxide in the presence of symptoms in childhood asthma

STUDY OBJECTIVES

To determine respective contributions of alveolar and proximal airway compartments in exhaled nitric oxide (NO) output (QNO) in pediatric patients with asthma and to correlate their variations with mild symptoms or bronchial obstruction.

PATIENTS AND DESIGN

In 15 asthmatic children with recent mild symptoms, 30 asymptomatic asthmatic children, and 15 healthy children, exhaled NO concentration was measured at multiple expiratory flow (V) rates allowing the calculation of alveolar and proximal airway contributions in QNO, using two approaches, ie, linear and nonlinear models.

MEASUREMENTS AND RESULTS

Asymptomatic and recently symptomatic patients were not significantly different regarding FEV(1) and maximum V between 25% and 75% of FVC (MEF(25-75)): FEV(1), 93.3 +/- 13.4% vs 90 +/- 7.5%; MEF(25-75), 70 +/- 22% vs 68 +/- 28% of predicted values, respectively (mean +/- SD). Maximal airway QNO output was significantly higher in recently symptomatic vs asymptomatic patients (p < 0.0001), and in asymptomatic patients vs healthy children (p < 0.02): 134 +/- 7 nl/min, 55 +/- 43 nl/min, and 19 +/- 8 nl/min, respectively. In a multiple regression analysis, variables that influenced airway QNO output were symptoms (p < 0.0001) and distal airway obstruction as assessed by MEF(25-75) (p < 0.05). Alveolar NO concentration (FANO) was significantly (p < 0.03) higher in recently symptomatic than in patients without symptoms, whereas it was not significantly different between asymptomatic patients and healthy children: 7.2 +/- 2.4 parts per billion (ppb), 5.5 +/- 2.7 ppb, and 4.2 +/- 2.0 ppb, respectively.

CONCLUSIONS

An increase in FANO was observed in the presence of symptoms, and proximal airway NO output was correlated with distal obstruction during asthma.

Both inflammation and remodeling influence nitric oxide output in children with refractory asthma

BACKGROUND

Exhaled nitric oxide can be used to monitor airway inflammation in asthma. We hypothesized that the strong link between nitric oxide and inflammation may obscure a weaker link with airway remodeling.

OBJECTIVE

The aim of this study was to determine whether airway remodeling influenced exhaled nitric oxide in 28 asthmatic children (median age [25th-75th], 11 [10-14] years old) with refractory asthma defined as airflow limitation and/or exacerbations despite high-dose inhaled steroids.

METHODS

Multiple-flow analysis of exhaled nitric oxide was used to correlate alveolar nitric oxide concentration and maximal conducting airway nitric oxide output to pulmonary function tests, bronchoalveolar lavage, and bronchial biopsy findings.

RESULTS

Nitric oxide measurements were related to inflammation and T(H)1/T(H)2 balance, that is, subepithelial eosinophilic infiltration and eosinophilic cationic protein and IFN-gamma/IL-4 ratio in bronchoalveolar lavage fluids. Nitric oxide measurements were also correlated with several parameters of airway remodeling: alveolar nitric oxide concentration with TGF-beta in bronchoalveolar lavage fluid (r = 0.42, P =.03) and maximal conducting airway nitric oxide output with reticular basement membrane thickness (r = 0.61, P =.0007) and tissue inhibitor of matrix metalloproteinases 1/matrix metalloproteinase 9 ratio in bronchoalveolar lavage fluid (r = 0.43, P =.04). Moreover, alveolar nitric oxide concentration was correlated with MEF(25-75) (r = 0.60, P =.02).

CONCLUSIONS

These findings suggest that both subacute inflammation and remodeling influence nitric oxide output in refractory asthma.

Comparative effects of two ventilatory modes on speech in tracheostomized patients with neuromuscular disease

Many patients with respiratory failure related to neuromuscular disease receive chronic invasive ventilation through a tracheostomy. Improving quality of life, of which speech is an important component, is a major goal in these patients. We compared the effects on breathing and speech production of assist-control ventilation (ACV) and bilevel positive-pressure ventilation (BPPV) in nine patients with neuromuscular disease. Ventilator-delivered flow was measured using a pneumotachograph, and respiratory rate, inspiratory time, and ventilator-delivered volume were measured on this flow signal. Gas exchange was assessed using oxygen saturation and end-tidal carbon dioxide measurement. Microphone speech recordings were subjected to quantitative analysis. At rest, ventilatory parameters were similar with both modes. Speech induced an increase in inspiratory time during BPPV, with a greater increase in the volume released by the ventilator during speech as compared with ACV (172 +/- 194 versus 26 +/- 31 ml). Consequently, speech duration was longer during inspiration with BPPV. Moreover, BPPV allowed speech production to extend into expiration, and three patients could speak continuously during several respiratory cycles while receiving BPPV. Blood gas exchange was not modified by speech with BPPV or ACV. This study shows that BPPV provides better speech duration than ACV with no detectable short-term deleterious effects.

Increased nitric oxide output from alveolar origin during liver cirrhosis versus bronchial source during asthma

The aim of this study was to assess the usefulness of nitric oxide (NO) output measurement at multiple expiratory flow rates during diseases characterized by increased exhaled NO (FE(NO)) that could come from alveolar (liver cirrhosis) or bronchial (asthma) sources. It has been proposed that NO output measurements expressed as a function of expiratory flow allow alveolar NO concentration (FA(NO)) and maximal bronchial NO output (Qbr,max (NO)) to be computed. In 36 healthy nonsmoking subjects, we found that maximal bronchial NO output (37 +/- 3 nl/min) was correlated with the height of the subjects (p = 0.02). Alveolar NO concentration was 5.1 +/- 0.3 (SEM) ppb, which represented 31 +/- 2% and 61 +/- 3% of FE(NO) at 50 and 200 ml/s expiratory flow rate, respectively. Nonsmoking subjects with asthma (n = 28) were characterized by an increase in Qbr,max (NO) (133 +/- 14 nl/min) as compared with healthy nonsmoking subjects (p < 0.0001). FE(NO)50, FE(NO)200, and Qbr,max (NO) were equally efficient in differentiating subjects with asthma from healthy subjects. Patients with liver cirrhosis (n = 26, 14 smokers and 12 nonsmokers) had an increased FA(NO) compared with healthy subjects (cirrhosis: 8.3 +/- 0.9 ppb, healthy nonsmokers [n = 36] and smokers [n = 20], n = 56: 4.7 +/- 0.3 ppb, p < 0.05), which was correlated with the alveolar-arterial oxygen difference (p = 0.007). FA(NO) and FE(NO)200, but not FE(NO)50 values, allowed patients with liver cirrhosis to be differentiated from healthy subjects. These results suggest that a two-compartment model for NO output allows the increase in FE(NO) from alveolar sources to be differentiated from the increase from bronchial sources.

Increased nitric oxide output from alveolar origin during liver cirrhosis versus bronchial source during asthma

The aim of this study was to assess the usefulness of nitric oxide (NO) output measurement at multiple expiratory flow rates during diseases characterized by increased exhaled NO (FE(NO)) that could come from alveolar (liver cirrhosis) or bronchial (asthma) sources. It has been proposed that NO output measurements expressed as a function of expiratory flow allow alveolar NO concentration (FA(NO)) and maximal bronchial NO output (Qbr,max (NO)) to be computed. In 36 healthy nonsmoking subjects, we found that maximal bronchial NO output (37 +/- 3 nl/min) was correlated with the height of the subjects (p = 0.02). Alveolar NO concentration was 5.1 +/- 0.3 (SEM) ppb, which represented 31 +/- 2% and 61 +/- 3% of FE(NO) at 50 and 200 ml/s expiratory flow rate, respectively. Nonsmoking subjects with asthma (n = 28) were characterized by an increase in Qbr,max (NO) (133 +/- 14 nl/min) as compared with healthy nonsmoking subjects (p < 0.0001). FE(NO)50, FE(NO)200, and Qbr,max (NO) were equally efficient in differentiating subjects with asthma from healthy subjects. Patients with liver cirrhosis (n = 26, 14 smokers and 12 nonsmokers) had an increased FA(NO) compared with healthy subjects (cirrhosis: 8.3 +/- 0.9 ppb, healthy nonsmokers [n = 36] and smokers [n = 20], n = 56: 4.7 +/- 0.3 ppb, p < 0.05), which was correlated with the alveolar-arterial oxygen difference (p = 0.007). FA(NO) and FE(NO)200, but not FE(NO)50 values, allowed patients with liver cirrhosis to be differentiated from healthy subjects. These results suggest that a two-compartment model for NO output allows the increase in FE(NO) from alveolar sources to be differentiated from the increase from bronchial sources.

Predictive value of pulmonary function parameters for sleep apnea syndrome

Nocturnal polysomnography is the standard diagnostic test for sleep apnea syndrome (SAS) but is both expensive and time-consuming. We developed a predictive index for SAS based on pulmonary function data, including respiratory resistance determined by the forced oscillation technique, from 168 obese snorers with suspected SAS. Our model used logistic regression to obtain case-by-case predictions of the probability of SAS, defined as an apnea-hypopnea index (AHI) > or = 15 during overnight polysomnography. We then tested our model in a prospective group of 101 similar patients. Specific respiratory conductance and daytime oxygen saturation contributed significantly to the model. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the index computed from these parameters were 98%, 86%, 90%, and 97%, respectively. In the prospective group, the model proved repeatable, with 100% sensitivity, 84% specificity, 86% PPV, and 100% NPV. The high NPV may help to identify obese snorers with a SAS risk that is so low as to make polysomnography unnecessary. Based on the 50% prevalence of SAS in our study and on the fact that polysomnography is required in all patients with daytime somnolence, we calculated that using our model would have obviated the need for polysomnography in 38% of our patients.

Nasal obstruction as a risk factor for sleep apnoea syndrome

Nasal obstruction has frequently been mentioned as a possible risk factor in obstructive sleep apnoea syndrome (OSAS). Over a 2-yr period, 541 unselected consecutive snorers referred for suspected breathing disorders during sleep were included to undergo posterior rhinomanometry. In addition cephalometric landmarks and body mass index (BMI) were obtained. Polysomnography was used to determine the number of abnormal respiratory events that occurred during sleep. OSAS was defined as 15 episodes, or more, of apnoea or hypopnoea per hour of sleep (AHI). Of the 541 consecutive snorers 528 underwent nasal resistance measurement by posterior rhinomanometry (failure rate: 2.4%). Patients with OSAS (259 patients) had higher nasal resistance than patients without OSAS (2.6+/-1.6 hPa x L x s(-1) versus 2.2+/-1.0 hPa x L x s(-1), respectively, p<0.005). A stepwise multiple regression analysis showed that BMI, male sex, nasal resistance, and cephalometric parameters were contributing factors to the AHI. The r2-value of the multiple regression analysis was 0.183. Nasal resistance contributed 2.3% of the variance (p<0.0001), whereas mandibular plane-hyoid distance, BMI, male sex and age contributed 6.2%, 4.6%, 3% and 1.3% of the variance, respectively. To conclude, daytime nasal obstruction is an independent risk factor for OSAS.

Accuracy of the i-STAT bedside blood gas analyser

The performance of the i-STAT portable clinical analyser for measuring blood gases and pH was evaluated with reference to a conventional blood gas analyser (ABL520 Radiometer). Ninety-two samples from the routine blood gas analysis laboratory were chosen according to a wide distribution of partial pressure of carbon dioxide (Pa,CO2), partial pressure oxygen (Pa,O2) and pH and then analysed. All measurements were performed in duplicate by trained technicians from the central hospital laboratory. Differences between duplicate measurements were computed for Pa,CO2: (1.2 versus 0.4%), Pa,O2 (1.7 versus 1.1%) and pH (0.06 versus 0.02%), for the i-STAT and ABL520, respectively. pH and Pa,CO2 values measured with the i-STAT were very close to those obtained with the ABL520, the difference (mean+/-SD) being 0.006+/-0.018 and -0.13+/-0.17 kPa, respectively. Statistical analysis showed that the differences between analysers did not depend on values of pH or Pa,CO2. The performance of the analysers depended on the level of PO2. Below 15 kPa (n=48), the two systems gave nearly identical values, the mean difference was 0.01+/-0.37 kPa. Between 16 and 55 kPa (n=44), there was a systematic but small (-0.69+/-0.67 kPa) underestimation of Pa,O2 measured with the i-STAT (p<10(-8)). In conclusion, this study shows that blood gas analysis using the i-STAT portable device is comparable with that performed by a conventional laboratory blood gas analyser.

Pulmonary function in obese snorers with or without sleep apnea syndrome

We evaluated pulmonary function abnormalities associated with the sleep apnea syndrome (SAS) in 170 habitual snorers without SAS (n = 62, apnea-hypopnea index [AHI] < 10 per hour of sleep), with moderately severe SAS (n = 56, 10 < or = AHI < 30) or with severe SAS (n = 52, AHI > or = 30). The three groups were similar regarding obesity (BMI approximately 30 kg.m-2) and smoking history (approximately 20 pack-years). Pulmonary function was assessed by spirometry, forced oscillation mechanics, and gas exchange studies. Forced expiratory flows decreased as the SAS severity increased (p < 0.001, p < 0.02, and p < 0.05 for FEF50, FEV1, and FEV1/VC, respectively). Multiple regression analysis showed that the correlation between FEV50 and the AHI persisted when smoking history was taken into account (p < 0.05), suggesting that SAS may be an independent risk factor for small airway disease. A highly significant correlation was found between specific respiratory conductance (sGrs) and the AHI (p < 0.0001). In a multiple regression analysis (p < 0.0001), variables that influenced sGrs were distal airway obstruction as assessed by FEV50 (p < 0.05), morphological upper airway abnormalities as assessed by cephalometric parameters (p < 0.02), and the AHI (p < 0.0005). SAS appears to be highly correlated to lower and upper airway obstruction, as demonstrated by a reduction in specific respiratory conductance, which adds to the increase in breathing load due to obesity.