Direct and indirect assessment of skeletal muscle blood flow in chronic congestive heart failure

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

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.

Muscle ubiquinone in male effort angina patients

Seven (7) males with effort angina and listed for coronary by-pass surgery had muscle biopsies taken from their vastus lateralis muscle for determination of muscle fiber types (%ST), ubiquinone (vitamin Q, UQ), oxidative and fermentative enzyme activities. Graded cycle ergometer exercise to determine intensities corresponding to onset of blood lactate accumulation set to 2.0 mmol x l-1 (WOBLA) and symptom limited exercise ('maximal', WSL) were also undertaken. WOBLA was positively related to %ST (r = 0.92, p < 0.001). %ST was on the other hand inversely related to UQ (r = -0.82, p < 0.05), the heart specific LD subunit LD-H (r = -0.96, p < 0.001), the isozyme LD3 as the fraction of LD (%LD3) (r = -0.93, p < 0.01), and the CK isozyme CKMB as the fraction of CK (%CKMB) (r = -0.88, p < 0.05). It was suggested that muscle UQ depletion in the patients was related to molecular oxygen and free oxygen radical formation. The lack of antioxidants then caused a radical trauma specifically to the ST fiber and their mitochondria. This could be a cause and-effect explanation for the selective ST fiber downregulation in effort angina and heart failure in general.

Muscle fibers, ubiquinone and exercise capacity in effort angina

Seventeen male patients with ischaemic heart disease (IHD) and effort angina performed OBLA exercise stress tests (set to 2.0 mmol x l-1). They had muscle biopsies from the vastus lateralis muscle the day before coronary by-pass grafting, and from the internal and external intercostal, diaphragm and gastrocnemius muscles during surgery. They had a low WOBLA (83 +/- 6 W, mean +/- 1 S.E.M), WOBLA corresponded to 79 +/- 4% (% WOBLA) of WSL (symptom limited or 'maximal' capacity = 111 +/- 11 W). Peak blood lactate concentration averaged 2.9 mmol x l-1. Muscle fibre composition disclosed a depressed percent slow twitch (ST or 'red') muscle fibres in the vastus lateralis and intercostal muscles (%ST). The diaphragm and gastrocnemius muscles had normal %ST. Intercostal muscles had elevated values for the fast twitch muscle fibre (FT) subgroup FTa indicative of endurance adaptation. The vastus lateralis, gastrocnemius and diaphragm muscles had normal muscle ubiquinone (UQ) contents, whereas the intercostals were depleted. Plasma contents of the antioxidants UQ and alpha-tocopherol were low as compared to healthy man.

Muscle fibre types, ubiquinone content and exercise capacity in hypertension and effort angina

The composition of skeletal muscle fibre expressed as a percentage of slow twitch (ST), type I or "red" and fast twitch (FT), type II or "white" were determined in patients with hypertension (HT) or with severe ischaemic heart disease (IHD) and compared to age matched controls. Similarly, exercise capacity expressed as the cycle intensity eliciting a blood lactate concentration corresponding to 2.0 mmol x 1-1 were compared with healthy controls. Both patient groups had a higher percentage of FT fibres with relatively lower exercise capacities than their controls. The exercise capacities were reduced even when the relationship of decreased capacity with the percentage of increased FT was considered. There was an increase IHD but not in HT in patients with fibre subgroup FTc, which most probably reflected fibre trauma. Both patient groups were low in the skeletal muscle mitochondrial electron carrier and unspecific antioxidant ubiquinone, coenzyme Q10 or CoQ10. Patients with IHD but not HT showed, however, a faster fall in the ratio CoQ10 over ST% the higher the percentage value of ST. The ratio reflects the antioxidant activity related to CoQ10 in the fibre hosting most of the oxidative metabolism. A low ratio indicates a risk of metabolic lesion and cell trauma. This could explain fibre plasticity and offer an alternative cause to heredity in elucidating in deviating muscle fibre composition in patients with HT and IHD.