Operating Lung Volume Responses To Metronome-paced Incremental Hyperventilation In Obese Adults

Obstructive pulmonary disease and Obese individuals often show dynamic lung hyperinflation and increase dyspnea during exertion. Metronome-paced incremental hyperventilation (MPIH) has been reported to help predict dynamic lung hyperinflation during exercise in patients with chronic obstructive pulmonary disease; however, it has not been studied in obese adults. We hypothesized that intentional incremental hyperventilation may detect a decrease in expiratory reserve volume (ERV) at rest and a decrease in maximal inspiratory capacity at a higher ventilation in obese adults. PURPOSE: To compare changes in operating lung volume during MPIH in underweight, normal-weight, and obese adults. METHODS: Fifteen underweight adults (BMI <18.5), 73 normal-weight adults (BMI ≥18.5 and < 25), and 25 obese adults (BMI ≥25) underwent pulmonary function testing, operating lung volume measurements using MPIH, and obesity-related assessments (computed tomography, Supria, Hitachi). All participants breathed relaxedly and then breathed for 30 sec at 20, 30, and 40 metronome beats per minute in the MPIH. At least one min of rest was allowed between each set of hyperventilation tests. RESULTS: Obese adults had higher visceral fat than participants in the other groups (P < 0.05). Vital capacity was higher in obese adults than in underweight adults (P = 0.039); however, no significant differences existed in forced vital capacity (FVC; P = 0.097), forced expiratory volume in one sec (FEV1; P = 0.185), and FEV1/FVC (P = 0.268) among groups. Results of linear mixed model analysis (group×respiratory rate) showed no significant interactions in ERV, inspiratory reserve volume, and tidal volume corrected for vital capacity, whereas mean ERV in obese adults was lower than the other groups at all respiratory rate in MPIH (at rest: underweight, 40%; normal, 40%; obese, 33%; at 20 bpm: underweight, 38%; normal, 38%; obese, 31%; at 30 bpm: underweight, 41%; normal, 40%; obese, 36%; at 40 rpm: underweight, 42%; normal, 42%; obese, 34%; main effect P = 0.004). CONCLUSIONS: Although MPIH could not detect dynamic lung hyperinflation in the obese adults, fat accumulation in thoracic area and abdominal fat accumulation may have persisted in the lower ERV during hyperventilation.