The Impact of Morbid Obesity on Oxygen Cost of Breathing (V˙o _2RESP) at Rest

Abstract

Oxygen consumption dedicated to respiratory work (V O(2RESP)) during quiet breathing is small in normal patients. In the morbidly obese, at high minute ventilations, VO(2RESP) is greater than in normal patients, but VO(2RESP) during quiet breathing in these patients is not known. We postulated that such patients have increased VO(2RESP) at rest which may predispose them to respiratory failure when additional respiratory workloads are imposed. We measured baseline VO(2) in morbidly obese patients immediately prior to gastric bypass surgery and again after intubation, mechanical ventilation, and paralysis, and compared their change in VO(2) to nonobese patients scheduled for elective abdominal surgery. Baseline VO(2) was higher in the obese patients compared with control patients (354.6 versus 221.4 ml/min; p = 0.0001) and the change in VO(2) from spontaneous breathing to mechanical ventilation was significant in the obese patients (354.6 versus 297.2 ml/min; p = 0.0002) but not the control patients (221.4 versus 219.8 ml/min; p = 0.86). We conclude that morbidly obese patients dedicate a disproportionately high percentage of total VO(2) to conduct respiratory work, even during quiet breathing. This relative inefficiency suggests a decreased ventilatory reserve and a predisposition to respiratory failure in the setting of even mild pulmonary or systemic insults.

Inspiratory muscle activity during incremental exercise in obese men

“…Regardless of the underlying cause, patients with obesity are likely to develop (i) a higher ventilatory requirement at a given exercise load, 2 (ii) a higher work of breathing at a given ventilation level and 27 (iii) a greater respiratory muscle oxygen consumption (VO 2resp ). 28 The energy cost of breathing (which reflects the oxygen consumed by the respiratory muscles) is particularly sensitive to the impact of mechanical impediments on breathing. It follows that energy demands (VO 2resp ) increase when the efficiency is reduced, for a given work output ( Figure 6).…”

Physiologic correlates of dyspnea in patients with morbid obesity

“…Finally, the oxygen cost of breathing at rest is increased in obese patients. 34 One hypothesis is that inspiratory muscle oxygen request during the ITL test could not be adequately satisfied, leading to diaphragmatic dysfunction. Dyspnea perception results from physiological as well as psychophysical sensory mechanisms.…”

Pulmonary function and aerobic capacity in asymptomatic bariatric candidates with very severe morbid obesity

“…These abnormalities have been confirmed by physiologic tests, during which a high metabolic cost for breathing, both at rest and after exercise, can be detected. 11,12 In spite of investigations concerning respiratory function in subjects with excessive adiposity, there is a scarcity of studies in advanced class III obesity or massive bariatric candidates including superobese subjects, and much controversy remains about their actual status.…”