Physiologic correlates of dyspnea in patients with morbid obesity

Objective: Mechanisms of dyspnea in obesity remain unclear. This study was undertaken to determine the relationships between dyspnea and pulmonary function including inspiratory muscle endurance (IME) in morbidly obese patients before bariatric surgery. Research methods and procedures: Fifty-five patients with a mean +/- s.d. body mass index (BMI) of 49.4 +/- 7.0 kg/m(2) were included. Dyspnea was evaluated by the Baseline Dyspnea Index (BDI; 0-12,0 maximal dyspnea). Pulmonary function tests included a plethysmography, maximal inspiratory pressure (PImax) and IME was assessed by the incremental threshold loading test, determining the maximal pressure sustained for 2 min (Plim(2)) and Plim(2)/PImax ratio. Patients were classified according to their BMI in two groups: BMI p49 (n = 27) and 449 kg/m(2) (n =28). Results: Breathlessness was higher in the BMI 449 kg/m(2) group compared to the BMI p49 kg/m(2) group ( BDI score at 6.9 +/- 2.2 in the BMI 449 kg/m(2) group vs 8.972.5 in the BMI p49 kg/m(2) group, P < 0.01). Patients with BMI 449 kg/m(2) had significantly higher PaCO2 level and significantly lower vital capacity, inspiratory capacity and PImax values compared with the BMI p49 kg/m2 group. Correlations between BDI and lung function were moderate: forced expiratory volume in 1 s (FEV1)% pred: Rho 0.27; P =0.05; vital capacity % pred: Rho=0.40; P =0.004; and Plim(2)/PImax: Rho=0.40; P=0.003. Higher correlations with dyspnea were found in the BMI p49 kg/m(2) group: FEV1% pred: Rho=0.38; P=0.05; and Plim(2)/PImax: Rho=0.49; P=0.01. Discussion: Inspiratory muscle performance is moderately reduced in morbid obesity. Dyspnea in these patients remains moderately related to lung function and inspiratory muscle performance. However, inspiratory muscles performance correlates more significantly with dyspnea in patients with a BMI p49 kg/m(2).