Postural changes in lung volumes and respiratory resistance in subjects with obesity

• Published in: Journal of applied physiology (1985) Vol. 98; no. 2; pp. 512 - 517
• Main Authors: Watson, R. A, Pride, N. B
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.02.2005; American Physiological Society
• Subjects: Adaptation, Physiological; Adult; Airway Resistance; Biological and medical sciences; Body fat; Female; Humans; Lung Volume Measurements - methods; Lungs; Male; Medical sciences; Metabolic diseases; Middle Aged; Obesity; Obesity - physiopathology; Posture; Respiratory diseases; Respiratory system; Supine Position; Tidal Volume; Human; Obesity; Nutrition disorder; Respiratory system; Functional residual capacity; Posture; Resistance; Respiratory tract; Lung volume; supine posture; nasal resistance; restrictive defect; total respiratory resistance; Nutritional status
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00430.2004

Respiratory Medicine National Heart and Lung Institute, Faculty of Medicine, Imperial College, London, United Kingdom Submitted 29 April 2004 ; accepted in final form 30 September 2004 Reduced functional residual capacity (FRC) is consistently found in obese subjects. In 10 obese subjects (mean ± SE age 49.0 ± 6 yr, weight 128.4 ± 8 kg, body mass index 44 ± 3 kg/m 2 ) without respiratory disease, we examined 1 ) supine changes in total lung capacity (TLC) and subdivisions, 2 ) whether values of total respiratory resistance (Rrs) are appropriate for mid-tidal lung volume (MTLV), and 3 ) estimated resistance of the nasopharyngeal airway (Rnp) in both sitting and supine postures. The results were compared with those of 13 control subjects with body mass indexes of <27kg/m 2 . Rrs at 6 Hz was measured by applying forced oscillation at the mouth (Rrs,mo) or the nose (Rrs,na); Rnp was estimated from the difference between sequential measurements of Rrs,mo and Rrs,na. All measurements were made when subjects were seated and when supine. Obese subjects when seated had a restrictive defect with low TLC and FRC-to-TLC ratio; when supine, TLC fell 80 ml and FRC fell only 70 ml compared with a mean supine fall of FRC of 730 ml in control subjects. Values of Rrs,mo and Rrs,na at resting MTLV in obese subjects were about twice those in control subjects in both postures. Relating total respiratory conductance (1/Rrs) to MTLV, the increase in Rrs,mo in obese subjects was only partly explained by their reduced MTLV. Rnp was increased in some obese subjects in both postures. Despite the increased extrapulmonary mass load in obese subjects, further falls in TLC and FRC when supine were negligible. Rrs,mo at isovolume was increased. Further studies are needed to examine the causes of reduced TLC and increases in Rrs,mo and sometimes in Rnp in obese subjects. nasal resistance; total respiratory resistance; restrictive defect; supine posture Address for reprint requests and other correspondence: N. B. Pride, Thoracic Medicine National Heart and Lung Institute, Faculty of Medicine, Imperial College, Dovehouse St., London SW3 6LY, UK (E-mail: n.pride{at}imperial.ac.uk )