Despite advances in medical and cardiac resynchronization therapy (CRT), individuals with chronic congestive heart failure (CHF) have persistent symptoms, including exercise intolerance. Optimizing ...cardio-locomotor coupling may increase stroke volume and skeletal muscle perfusion as previously shown in healthy runners. Therefore, we tested the hypothesis that exercise stroke volume and cardiac output would be higher during fixed-paced walking when steps were synchronized with the diastolic compared with systolic portion of the cardiac cycle in patients with CHF and CRT.
Ten participants (58±17 years of age; 40% female) with CHF and previously implanted CRT pacemakers completed 5-minute bouts of walking on a treadmill (range, 1.5-3 mph). Participants were randomly assigned to first walking to an auditory tone to synchronize their foot strike to either the systolic (0% or 100±15% of the R-R interval) or diastolic phase (45±15% of the R-R interval) of their cardiac cycle and underwent assessments of oxygen uptake (V̇o
; indirect calorimetry) and cardiac output (acetylene rebreathing). Data were compared through paired-samples
tests.
V̇o
was similar between conditions (diastolic 1.02±0.44 versus systolic 1.05±0.42 L/min;
=0.299). Compared with systolic walking, stroke volume (diastolic 80±28 versus systolic 74±26 mL;
=0.003) and cardiac output (8.3±3.5 versus 7.9±3.4 L/min;
=0.004) were higher during diastolic walking; heart rate (paced) was not different between conditions. Mean arterial pressure was significantly lower during diastolic walking (85±12 versus 98±20 mm Hg;
=0.007).
In patients with CHF who have received CRT, diastolic stepping increases stroke volume and oxygen delivery and decreases afterload. We speculate that, if added to pacemakers, this cardio-locomotor coupling technology may maximize CRT efficiency and increase exercise participation and quality of life in patients with CHF.
Timing foot strike to occur in synchrony with cardiac diastole may reduce left ventricular afterload and promote coronary and skeletal muscle perfusion.
PURPOSEThis study aimed to assess heart rate ...(HR) and metabolic responses to running when foot strikes are timed to occur exclusively during 1) the systolic phase of the cardiac cycle or 2) the diastolic phase.
METHODSTen elite male distance runners performed a testing session on a treadmill at 4.72 m·s while matching their steps to an auditory tone and wearing a chest strap that transmitted accelerometer and ECG signals. Testing comprised eight prompted 3-min stages, where a real-time adaptive auditory tone guided subjects to step with each ECG R-wave (systolic stepping) or alternatively, at 45% of each R-R interval (diastolic stepping), followed by a 3-min unprompted control stage. Metabolic variables were measured continuously.
RESULTSHR (P < 0.001) and minute ventilation (P < 0.001) were significantly lower during diastolic stepping compared with systolic stepping, whereas O2 pulse (P < 0.001) was correspondingly significantly higher during diastolic stepping.
CONCLUSIONSynchronizing foot strikes when running to the diastolic portion of the cardiac cycle results in a significantly reduced HR and minute ventilation compared with stepping during systole. This cardiac and ventilatory response to diastolic stepping may be beneficial to distance running performance.
Grouse—an ecologically important group of birds that include capercaillie, prairie chickens, and ptarmigan—are distributed throughout the forests, grasslands, and tundra of Europe, Asia, and North ...America. Today, many grouse populations are in decline, and the conservation and management of these charismatic birds is becoming a global concern. This volume summarizes current knowledge of grouse biology in 25 chapters contributed by 80 researchers from field studies around the world. Organized in four sections—Spatial Ecology, Habitat Relationships, Population Biology, and Conservation and Management—the chapters offer important insights into spatial requirements, movements, and demography of grouse. Much of the research employs emerging tools in ecology that span biogeochemistry, molecular genetics, endocrinology, radio-telemetry, and remote sensing. The chapters explore topics including the impacts of climate change, energy development, and harvest, and give new evidence for life-history changes in response to human activities.
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