Effects of respiratory muscle work on blood flow distribution during exercise in heart failure

Heart failure (HF) patients have a reduced cardiac reserve and increased work of breathing. Increased locomotor muscle blood flow demand may result in competition between respiratory and locomotor vascular beds. We hypothesized that HF patients would demonstrate improved locomotor blood flow with re...

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Bibliographic Details
Published in:The Journal of physiology 2010-07, Vol.588 (13), p.2487-2501
Main Authors: Olson, Thomas P., Joyner, Michael J., Dietz, Niki M., Eisenach, John H., Curry, Timothy B., Johnson, Bruce D.
Format: Article
Language:English
Subjects:
Adult
Algorithms
Blood flow
Cardiac output
Cardiac Output - physiology
Exercise - physiology
Exercise Test
Failure
Female
Heart (exercise effects)
Heart Failure - physiopathology
Hemodynamics - physiology
Humans
Integrative
Leg - blood supply
Leg - physiology
Lung - physiology
Male
Middle Aged
Muscle, Skeletal - blood supply
Muscle, Skeletal - physiology
Muscles (activity)
Muscles (blood flow)
Muscles (exercise effects)
Patients
Pressure
Pulmonary Gas Exchange - physiology
Regional Blood Flow - physiology
Respiration
Respiration, Artificial
Respiratory Mechanics - physiology
Respiratory Muscles - physiopathology
Stress
Thermodilution
Work
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Summary:Heart failure (HF) patients have a reduced cardiac reserve and increased work of breathing. Increased locomotor muscle blood flow demand may result in competition between respiratory and locomotor vascular beds. We hypothesized that HF patients would demonstrate improved locomotor blood flow with respiratory muscle unloading during activity. Ten patients (ejection fraction = 31 ± 3%) and 10 controls (CTL) underwent two cycling sessions (60% peak work). Session 1 (S1): 5 min of normal breathing (NB), 5 min respiratory muscle unloading with a ventilator, and 5 min of NB. Session 2 (S2): 5 min NB, 5 min of respiratory muscle loading with inspiratory resistance, and 5 min of NB. Measurements included: leg blood flow (LBF, thermodilution), cardiac output , and oesophageal pressure (Ppl, index of pleural pressure). S1: Ppl was reduced in both groups (HF: 73 ± 8%; CTL: 60 ± 13%, P < 0.01). HF: increased (9.6 ± 0.4 vs. 11.3 ± 0.8 l min−1, P < 0.05) and LBF increased (4.8 ± 0.8 vs. 7.3 ± 1.1 l min−1, P < 0.01); CTL: no changes in (14.7 ± 1.0 vs. 14.8 ± 1.6 l min−1) or LBF (10.9 ± 1.8 vs. 10.3 ± 1.7 l min−1). S2: Ppl increased in both groups (HF: 172 ± 16%, CTL: 220 ± 40%, P < 0.01). HF: no change was observed in (10.0 ± 0.4 vs. 10.3 ± 0.8 l min−1) or LBF (5.0 ± 0.6 vs. 4.7 ± 0.5 l min−1); CTL: increased (15.4 ± 1.4 vs. 16.9 ± 1.5 l min−1, P < 0.01) and LBF remained unchanged (10.7 ± 1.5 vs. 10.3 ± 1.8 l min−1). These data suggest HF patients preferentially steal blood flow from locomotor muscles to accommodate the work of breathing during activity. Further, HF patients are unable to vasoconstrict locomotor vascular beds beyond NB when presented with a respiratory load. Heart failure patients tend to have stiff lungs and are less efficient when breathing. This requires extra work and more blood flow than healthy people. Since these patients have a reduced ability to increase blood flow to muscles because of limited cardiac output, they may redistribute blood away from other parts of the body such as the leg muscles. The results of our study in heart failure patients demonstrate that reducing the work of breathing during moderate intensity exercise results in increased blood flow to the leg muscles. This suggests that the respiratory muscles steal blood flow from the leg muscles. In contrast, during this same intensity of exercise, when the work of breathing is increased beyond that already observed, there is no further redistribution of blood flow away from leg musc
ISSN:0022-3751
1469-7793
DOI:10.1113/jphysiol.2009.186056