Chest
Volume 103, Issue 5, May 1993, Pages 1470-1476
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Clinical Investigations
Effects of Obesity on Respiratory Resistance

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To assess the effects of obesity on pulmonary function, 46 healthy subjects exhibiting various degrees of obesity underwent lung function tests. Subjects were divided into three groups according to body mass index (BMI): 13 had minimal obesity (BMI, 25 to 29 kg/m2, group 1); 24 had a BMI in the 30 to 40. range (group 2); and 9 displayed to morbid obesity (BMI >40, group 3). Respiratory resistance was estimated by the forced random noise oscillation technique and airway resistance was determined by body plethysmography. Lung volumes and expiratory flows were also determined and significant negative correlations with BMI were found. Expiratory flows diminished in proportion to lung volumes, and the ratio of forced expiratory volume in 1 s to forced vital capacity was within normal limits. Although expiratory flows did not suggest bronchial obstruction, both respiratory resistance and airway resistance rose significantly with the level of obesity (p<0.005 and p<0.025, respectively), from 3.2 (±0.02) and 3.2 (±0.02) cm H2O·s·L-1, respectively, in group 1, to 5.5 (±0.06) and 5.0 (±0.05), respectively, in group 3. Evaluation of the factors responsible for this increased resistance disclosed a significant linear correlation between airway conductance and functional residual capacity (r=0.70, p<10-4), but specific airway conductance was found to be independent of the degree of obesity. The difference between respiratory resistance and airway resistance did not widen significantly according to the level of obesity, suggesting that chest wall resistance was not a factor enhancing these resistances. Taken together, these findings suggest that in addition to the elastic load, obese subjects have to overcome increased respiratory resistance resulting from the reduction in lung volumes related to being overweight.

Section snippets

Patients

Quetelet's index (or body mass index [BMI]), wt/ht2, in which wt is weight (kg) and ht is height (m), was the inclusion criterion for the subjects participating in this study. Obesity was defined by a BMI larger than 25.4

Forty-six patients were selected. They comprised 31 women and 15 men, aged from 16 to 63 years (38.7 ±14.4 years; mean ± SD), with a height of 165 ± 6 cm (range, 154 to 186 cm). All these subjects were healthy, with no cardiac or major metabolic disorders. They did not complain

RESULTS

The general characteristics of the patients are given in Table 1. Patients in all three groups were comparable for age and height (ANOVA, ns), and constituted a representative group of middle-aged obese subjects.

DISCUSSION

Although lung volumes are known to decrease in obesity,11 the resistive properties of the respiratory system have seldom been investigated in subjects with this disorder.12, 13 In the present study, we demonstrated that Rrs increases in obese subjects and showed that this increase was mainly due to the decrease in lung volumes.

ACKNOWLEDGMENTS

This study was supported by a grant from Caisse Nationale d'Assurance Maladie.

REFERENCES (29)

  • J Luce

    Respiratory complications of obesity

    Chest

    (1980)
  • A Lorino et al.

    On line determination of airway resistance by plethysmography and microcomputer

    Comput Biol Med

    (1985)
  • C Ray et al.

    Effects of obesity on respiratory function

    Am Rev Respir Dis

    (1983)
  • A Naimark et al.

    Compliance of the respiratory system and its components in health and obesity

    J Appl Physiol

    (1960)
  • E Jequier

    Energy, obesity, and body weight standards

    Am J Clin Nutr

    (1987)
  • P Quanjer

    Standardized lung function testing

    Bull Eur Physiopathol Respir

    (1983)
  • G Pelle et al.

    A microcomputer-based system to calculate respiratory impedance from forced random noise data

    Med Biol Eng Comput

    (1986)
  • L Brochard et al.

    Density and frequency dependence of resistance in early airway obstruction

    Am Rev Respir Dis

    (1987)
  • A Dubois et al.

    A new method for measuring airway resistance in man using a body plethysmograph: values in normal subjects and in patients with respiratory disease

    J Clin Invest

    (1956)
  • D Nolte et al.

    Comparing measurements of nasal resistance by body plethysmography and by rhinomanometry

    Respiration

    (1973)
  • E Bergofsky

    Respiratory failure in disorders of the thoracic cage

    Am Rev Respir Dis

    (1979)
  • J Sharp et al.

    The total work of breathing in normal and obese men

    J Clin Invest

    (1964)
  • C Emirgil et al.

    The effects of weight reduction on pulmonary function and the sensitivity of the respiratory center in obesity

    Am Rev Respir Dis

    (1973)
  • W Briscoe et al.

    The relationship between airway resistance, airway conductance and lung volume in subjects of different ages and body size

    J Clin Invest

    (1958)
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    Manuscript received June 15; revision accepted September 23.

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