Responses to constant work exercise in patients with chronic heart failure.
OBJECTIVE
To describe the kinetics of metabolic gas exchange at the onset and offset of low level, constant work exercise in patients with chronic heart failure.


METHODS
Tertiary referral centre for cardiology.


METHODS
10 patients with chronic heart failure and 10 age matched controls.


METHODS
Each subject undertook maximum incremental exercise testing with metabolic gas exchange measurements, and a fixed load exercise test at 25 watts with metabolic gas exchange measurements before, during, and after the test. A monoexponential curve was fitted to the data to describe the kinetics of gas exchange at onset and offset of fixed load exercise.


METHODS
Peak oxygen consumption; time constants of onset and offset for metabolic gas exchange variables during constant load exercise.


RESULTS
Peak oxygen consumption (mean (SD)) was higher in controls (26.1 (4.3) v 15.3 (5.3) ml/kg/min; p < 0.001) than in heart failure patients. Oxygen consumption during steady state was the same in both groups (9.2 (1.8) ml/kg/min in controls v 8.6 (1.6) in patients). The time constant of onset was the same in each group, but the time constant of offset was longer in patients (1.29 (0.14) v 0.82 (0.07); p < 0.005). There was a relation between peak oxygen consumption and time constant of offset (R = 0.56; p < 0.001).


CONCLUSIONS
The dynamics of gas exchange at the onset of low level exercise are normal in heart failure, but the recovery is delayed. The delay is related to the reduction in exercise capacity. A patient may spend a greater portion of the day recovering from exercise, and may not begin the next bout from a position of true recovery, perhaps contributing to the sensation of fatigue.
Picozzi
N M
NM
Department of Medicine and Therapeutics, Glasgow University, Western Infirmary, Dumbarton Road, Glasgow G11 6NT, UK.
Clark
A L
AL
Lindsay
K A
KA
McCann
G P
GP
Hillis
W S
WS
D000368:Aged; D000704:Analysis of Variance; D016022:Case-Control Studies; D002908:Chronic Disease; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006321:Heart / Q000503:physiopathology*; D006333:Heart Failure / Q000503:physiopathology*; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D005082:Physical Exertion