Original Article

International Journal of Obesity (2008) 32, 502–509; doi:10.1038/sj.ijo.0803752; published online 23 October 2007;

Effect of obesity on breathlessness and airway responsiveness to methacholine in non-asthmatic subjects

C M Salome1,2,3, P A Munoz1,2, N Berend1,2,3,4, C W Thorpe1,2,5, L M Schachter1,3 and G G King1,2,3,4

  1. 1Woolcock Institute of Medical Research, Camperdown, New South Wales, Australia
  2. 2Cooperative Research Centre for Asthma, Camperdown, New South Wales, Australia
  3. 3Department of Medicine, University of Sydney, Sydney, New South Wales, Australia
  4. 4Department of Respiratory Medicine, Royal North Shore Hospital, St Leonards, New South Wales, Australia
  5. 5Bioengineering Institute, University of Auckland, Auckland, New Zealand

Correspondence: Dr C Salome, Woolcock Institute of Medical Research, PO Box M77, Missenden Road, Camperdown, NSW 2050, Australia. E-mail: cms@woolcock.org.au

Received 12 April 2007; Revised 3 September 2007; Accepted 9 September 2007; Published online 23 October 2007.

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Abstract

Background:

 

Obesity is associated with increased prevalence and incidence of asthma, but the mechanism is unknown. Obesity reduces lung volumes, which can increase airway responsiveness, and increases resistive and elastic work of breathing, which can increase dyspnea.

Objective:

 

To determine if the intensity of dyspnea due to airway narrowing or if airway responsiveness is increased in obese, non-asthmatic subjects.

Subjects:

 

Twenty-three obese (BMI (body mass index) greater than or equal to30 kg m-2) and 26 non-obese (BMI <30 kg m-2) non-asthmatic subjects, aged between 18 and 70 years.

Methods:

 

High-dose methacholine challenge was used to determine the sensitivity and the maximal response to methacholine. Respiratory system resistance (Rrs) and reactance were measured, using the forced oscillation technique, as indicators of resistive and elastic loads during challenge. Perception of dyspnea was measured by the Borg score during challenge. Static lung volumes were measured by body plethysmography.

Results:

 

Static lung volumes were reduced in the obese subjects. There were no significant differences in the sensitivity or maximal response to methacholine between obese and non-obese subjects. The magnitude of change in Rrs was similar in both groups, but obese subjects had more negative reactance after challenge (P=0.002) indicating a greater elastic load. The intensity of dyspnea was greater in obese subjects (P=0.03).

Conclusions:

 

Obesity reduces lung volumes, but does not alter the sensitivity or maximal response to methacholine. However, obese subjects have enhanced perception of dyspnea, associated with greater apparent stiffness of the respiratory system, and may therefore be at greater risk of symptoms.

Keywords:

airway responsiveness, static lung volumes, elastance

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