Work of breathing and respiratory drive in obesity.
Obesity, particularly severe central obesity, affects respiratory physiology both at rest and during exercise. Reductions in expiratory reserve volume, functional residual capacity, respiratory system compliance and impaired respiratory system mechanics produce a restrictive ventilatory defect. Low functional residual capacity and reductions in expiratory reserve volume increase the risk of expiratory flow limitation and airway closure during quiet breathing. Consequently, obesity may cause expiratory flow limitation and the development of intrinsic positive end expiratory pressure, especially in the supine position. This increases the work of breathing by imposing a threshold load on the respiratory muscles leading to dyspnoea. Marked reductions in expiratory reserve volume may lead to ventilation distribution abnormalities, with closure of airways in the dependent zones of the lungs, inducing ventilation perfusion mismatch and gas exchange abnormalities. Obesity may also impair upper airway mechanical function and neuromuscular strength, and increase oxygen consumption, which in turn, increase the work of breathing and impair ventilatory drive. The combination of ventilatory impairment, excess CO(2)  production and reduced ventilatory drive predisposes obese individuals to obesity hypoventilation syndrome.
Division of Chest and Critical Care Medicine, Department of Internal Medicine, National Taiwan University Hospital, Hsin-Chu branch, Hsin-Chu, Taiwan.
Ching-Kai
CK
Lin
Ching-Chi
CC
Lin
D000403:Airway Resistance / Q000502:physiology; D000818:Animals; D004417:Dyspnea / Q000209:etiology / Q000503:physiopathology; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D018377:Neurotransmitter Agents / Q000502:physiology; D009765:Obesity / Q000150:complications* / Q000503:physiopathology*; D010101:Oxygen Consumption / Q000502:physiology; D051381:Rats; D012119:Respiration; D012120:Respiration Disorders / Q000209:etiology* / Q000503:physiopathology; D012132:Respiratory Muscles / Q000503:physiopathology; D012137:Respiratory System / Q000503:physiopathology; D012891:Sleep Apnea Syndromes / Q000209:etiology / Q000503:physiopathology; D014939:Work of Breathing / Q000502:physiology
D018377:Neurotransmitter Agents