title: Interaction between physical activity and continuous-flow left ventricular assist device function in outpatients.
abstract: OBJECTIVE
  Studies have shown that pump output by continuous-flow left ventricular assist devices (LVADs) increases with graded exercise testing. However, data on pump behavior during activities of daily living and sleep, where cardiac output requirements vary markedly, are lacking. We sought to determine pump parameters and activity levels in stable patients receiving outpatient LVAD therapy.
  
  
  RESULTS
  Eleven outpatients (mean age 51 ± 14 years, 9 male) with centrifugal continuous-flow LVADs underwent monitoring of LVAD flow, heart rate (HR), energy expenditure, and physical activity over 1 week in an outpatient setting. Physical activity was recorded with the use of a combined pedometer, accelerometer, and calorimeter Sensewear armband. Pump, HR, and physical activity parameters were time matched for correlation analysis. Outpatients had an average pump flow of 5.67 ± 1.27 L/min and engaged predominately in low levels of physical activity (mean daily step count 3,249/day). Across the entire cohort, pump flow exhibited strong univariate relationships with patients' energy expenditure (r = 0.73), step count (r = 0.69), HR (r = 0.73), sleep (r = -0.89), and skin temperature (r = -0.85; P < .0001 for all). Multivariate analysis suggested that pump output was predominantly affected by recumbent position, energy expenditure and skin temperature (r(2) = 0.84; P < .0001). Pump flow and power consumption were significantly lower during sleep than during wake periods (5.48 ± 1.31 L/min vs 5.80 ± 1.26 L/min; P < .001).
  
  
  CONCLUSIONS
  Pump output from continuous-flow LVADs is adaptive to changes in activities of daily living. Circadian variation in pump flow is mostly explained by recumbency and activity levels. Despite adequate pump flow, many LVAD patients continue to live sedentary lifestyles.
authors.affiliation: Heart Failure and Transplant Unit, St Vincent's Hospital, Sydney, Australia.
authors.forename: Sharon X H
authors.initials: SX
authors.lastname: Hu
authors.forename: Anne M
authors.initials: AM
authors.lastname: Keogh
authors.forename: Peter S
authors.initials: PS
authors.lastname: Macdonald
authors.forename: Eugene
authors.initials: E
authors.lastname: Kotlyar
authors.forename: Desiree
authors.initials: D
authors.lastname: Robson
authors.forename: Michelle
authors.initials: M
authors.lastname: Harkess
authors.forename: Emily
authors.initials: E
authors.lastname: Granger
authors.forename: Kumud
authors.initials: K
authors.lastname: Dhital
authors.forename: Paul
authors.initials: P
authors.lastname: Jansz
authors.forename: Phillip
authors.initials: P
authors.lastname: Spratt
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Hayward
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D000553:Ambulatory Care / Q000379:methods*; D005260:Female; D006353:Heart-Assist Devices; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D010045:Outpatients; D016277:Ventricular Function, Left / Q000502:physiology*