Improved Ventilatory Efficiency with Locomotor Muscle Afferent Inhibition is Strongly Associated with Leg Composition in Heart Failure

Abstract

Background Skeletal muscle atrophy contributes to increased afferent feedback (group III and IV) and may influence ventilatory control (high VE/VCO2 slope) in heart failure (HF). Objective This study examined the influence of muscle mass on the change in VE/VCO2 with afferent neural block during exercise in HF. Methods 17 participants [9 HF (60±6 yrs) and 8 controls (CTL) (63±7 yrs, mean±SD)] completed 3 sessions. Session 1: dual energy x-ray absorptiometry and graded cycle exercise to volitional fatigue. Sessions 2 and 3: 5 min of constant-work cycle exercise (65% of peak power) randomized to lumbar intrathecal injection of fentanyl (afferent blockade) or placebo. Ventilation (VE) and gas exchange (oxygen consumption, VO2; carbon dioxide production, VCO2) were measured. Results Peak work and VO2 were lower in HF (p<0.05). Leg fat was greater in HF (34.4±3.0 and 26.3±1.8%) and leg muscle mass was lower in HF (63.0±2.8 and 70.4±1.8%, respectively, p<0.05). VE/VCO2 slope was reduced in HF during afferent blockade compared with CTL (−18.8±2.7 and −1.4±2.0%, respectively, p=0.02) and was positively associated with leg muscle mass (r2=0.58, p<0.01) and negatively associated with leg fat mass (r2=0.73, p<0.01) in HF only. Conclusions HF patients with the highest fat mass and the least leg muscle mass had the greatest improvement in VE/VCO2 with afferent blockade with leg fat mass being the only predictor for the improvement in VE/VCO2 slope. Both leg muscle mass and fat mass are important contributors to ventilatory abnormalities and strongly associated to improvements in VE/VCO2 slope with locomotor afferent inhibition in HF.

VE/VCO2 slope in lean and overweight women and its relationship to lean leg mass

“…The OWTR group trended similarly to the OWS group, (r = −0.64), although this was not statistically significant. Therefore, similar to what was previously seen in HF [ 13 ], lean leg mass is associated with V E /VCO 2slope , but only in overweight/obese (BMI > 30 kg/m 2 ) individuals, such that greater lean leg mass may be beneficial and contribute to a lower V E /VCO 2slope in overweight/obese women.…”

“…The link between skeletal muscle mass and ventilatory efficiency has been demonstrated in other studies [ 13 , 23 ]. As such, after an 8-week aerobic training in a pediatric obesity cohort, V E /VCO 2 was improved [ 23 ].…”

“…V E /VCO 2slope measures are also independent of subject effort and BMI [ 12 ]. Recently, we have demonstrated that a higher V E /VCO 2slope , or reduced ventilatory efficiency, is associated with lower lean leg mass in HF [ 13 ]. This association is important, particularly because inhibiting afferent feedback from the skeletal muscle by fentanyl injections abolished this relationship in patients with HF [ 13 ].…”

“…Recently, we have demonstrated that a higher V E /VCO 2slope , or reduced ventilatory efficiency, is associated with lower lean leg mass in HF [ 13 ]. This association is important, particularly because inhibiting afferent feedback from the skeletal muscle by fentanyl injections abolished this relationship in patients with HF [ 13 ]. This previous work demonstrates a close link exists between leg lean mass skeletal muscle afferent feedback and ventilatory efficiency in HF.…”

Supervised, Vigorous Intensity Exercise Intervention for Depressed Female Smokers: A Pilot Study

“…Oxygen consumed (VO 2 ), carbon dioxide produced (VCO 2 ), and minute ventilation (VE) were measured by mouth piece and pneumotachograph (MedGraphics, St. Paul, MN) throughout exercise. 69,70 The respiratory exchange ratio was calculated as VCO 2 /VO 2 . Manual volume calibration was performed with a 3 L syringe, and gas calibration was performed with manufacturer-recommended gases of known concentration.…”