Abstract
Respiratory muscle (RM) performance has been theorized to contribute to exercise-induced dyspnea, exercise intolerance, and low exercise capacity in patients with obesity. However, the impact of acute impairments in RM performance on exercise intolerance and exercise capacity in patients with obesity remains uncertain. We hypothesized, that following peak aerobic exercise, impairments in RM performance would be observed in patients with obesity.
We prospectively recruited 7 participants (recruitment is ongoing; 1 male, 6 female, Age: 42 ± 9 yrs; BMI: 47.7 ± 5.9 kg/m
; Waist Circumference: 126 ± 12.04 cm; Body Fat [%]: 50.91 ± 3.6). Diaphragm Thickness at expiration and Thickening Ratio (thickness at end-inspiration - thickness at end-expiration)/thickness at end-expiration) were assessed via B-mode ultrasound at the right 8
intercostal space while patients were in a semi-recumbent position elevated 30 degrees from supine. Participants performed a cardiopulmonary exercise test (CPET) using a ramp treadmill protocol to peak exercise capacity. Measurements of RM performance were measured at baseline and repeated at 0-minutes and 5-minutes following CPET; which included Maximal Inspiratory Pressure (MIP), Sustained Maximal Inspiratory Pressure (SMIP), Inspiratory Duration (ID), Slope of the SMIP Plot (SMIP Slope), and Maximal Expiratory Pressure (MEP). Two-Sided Paired T-Tests were used to compare RM performance data before and after testing; statistical significance was set at p<0.05.
Mean CPET Results: VO2peak: 19.37 ± 2.4 mL/kg/min; RER: 1.01 ± 0.11; Age Predicted Heart Rate Max [%] 87.57 ± 0.14; Ventilatory Reserve [%] 25.25 ± 18.32; VE/VCO2 Slope: 28.84 ± 4.50. Diaphragm Thickness: 2.8 ± 0.24 mm and Thickening Ratio: [%]: 75.47 ± 25.97. When comparing Baseline to 0-minues following CPET significant reductions in MIP, SMIP, and MEP were observed: MIP (94.57 ± 25.01 cmH2O vs. 72.29 ± 22.09 cmH2O p = 0.02); SMIP (524.14 ± 198.85 PTU vs. 418.43 PTU p = 0.04); MEP (73.71 ± 17.10 cmH2O vs. 62.29 ± 12.83 cmH2O p= 0.02). A reduction in ID (10.6 ± 2.30 vs 8.99 sec p= 0.06) and an increase in SMIP Slope (9.2 ± 3.39 vs. 9.74 ± 3.30 p= 0.74) were observed at 0-minutes following CPET compared to baseline but were not significant. At 5-minutes following CPET, significant reductions in MIP (67.3 cmH2O ± 12.6 p= 0.01) and MEP (62.57 ± 14.47 cm H2O p= 0.01) were observed but not for other measures of RM performance.
Our results suggest that patients with obesity demonstrate significant reductions in RM performance following peak aerobic exercise which may persist even after recovery. Interestingly, at baseline, the patients with obesity in this study demonstrated relatively normal RM performance, diaphragm thickness and thickening ratio. Acute fatigue of the respiratory muscles may contribute to the exercise induced dyspnea, exercise intolerance and low exercise capacity observed in patients with obesity.