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1 John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States
* To whom correspondence should be addressed. E-mail: jordan-miller{at}uiowa.edu.
We sought to determine if the normal inspiratory intrathoracic pressures (PITP) produced during exercise contribute to the blunted cardiac output and locomotor limb blood flow responses observed in chronic heart failure (CHF). We observed several key differences in the cardiovascular responses to changes in the inspiratory (PITP) excursion between health and CHF, namely: 1) Removing ~70% of the normally produced inspiratory intrathoracic pressure excursion during exercise (with 15 cm H2O IPPV) significantly reduced stroke volume (SV) in healthy animals by 5 ± 2% (p < 0.05), but significantly increased SV and cardiac output (QTOT) in animals with CHF by 5 ± 1% (p < 0.05), 2) Doubling the magnitude of the inspiratory PITP excursion had no effect on SV or QTOT in healthy animals, but significantly reduced steady-state QTOT and SV in animals with CHF by -4 ± 3% and -10 ± 3%, respectively, 3) Removing the majority of the normally produced inspiratory intrathoracic pressure excursion had no effect on blood flow distribution in healthy animals, but increased hindlimb blood flow (9 ± 3%, p < 0.05) out of proportion to the increases in QTOT. 4) The only similarity between healthy and CHF animals was that increasing the inspiratory intrathoracic pressure excursion significantly reduced steady-state locomotor limb blood flow by 5 ± 2% and 6 ± 3%, respectively (p < 0.05 for both) . We conclude that: 1) the normally produced inspiratory PITP excursions are required for a for a maximal stroke volume response to submaximal exercise in healthy animals, but detrimental to the stroke volume and cardiac output responses to submaximal exercise in CHF, 2) the respiratory muscle ergoreflex tonically restrains locomotor limb blood flow during submaximal exercise in CHF, and 3) excessive inspiratory muscle work further compromises cardiac function and blood flow distribution in both health and CHF.
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