Document Detail

Respiratory muscle work compromises leg blood flow during maximal exercise.
MedLine Citation:
PMID:  9134907     Owner:  NLM     Status:  MEDLINE    
We hypothesized that during exercise at maximal O2 consumption (VO2max), high demand for respiratory muscle blood flow (Q) would elicit locomotor muscle vasoconstriction and compromise limb Q. Seven male cyclists (VO2max 64 +/- 6 each completed 14 exercise bouts of 2.5-min duration at VO2max on a cycle ergometer during two testing sessions. Inspiratory muscle work was either 1) reduced via a proportional-assist ventilator, 2) increased via graded resistive loads, or 3) was not manipulated (control). Arterial (brachial) and venous (femoral) blood samples, arterial blood pressure, leg Q (Qlegs; thermodilution), esophageal pressure, and O2 consumption (VO2) were measured. Within each subject and across all subjects, at constant maximal work rate, significant correlations existed (r = 0.74-0.90; P < 0.05) between work of breathing (Wb) and Qlegs (inverse), leg vascular resistance (LVR), and leg VO2 (VO2legs; inverse), and between LVR and norepinephrine spillover. Mean arterial pressure did not change with changes in Wb nor did tidal volume or minute ventilation. For a +/-50% change from control in Wb, Qlegs changed 2 l/min or 11% of control, LVR changed 13% of control, and O2 extraction did not change; thus VO2legs changed 0.4 l/min or 10% of control. Total VO2max was unchanged with loading but fell 9.3% with unloading; thus VO2legs as a percentage of total VO2max was 81% in control, increased to 89% with respiratory muscle unloading, and decreased to 71% with respiratory muscle loading. We conclude that Wb normally incurred during maximal exercise causes vasoconstriction in locomotor muscles and compromises locomotor muscle perfusion and VO2.
C A Harms; M A Babcock; S R McClaran; D F Pegelow; G A Nickele; W B Nelson; J A Dempsey
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  82     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  1997 May 
Date Detail:
Created Date:  1997-07-21     Completed Date:  1997-07-21     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1573-83     Citation Subset:  IM; S    
John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin, Madison 53705, USA.
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MeSH Terms
Blood Pressure
Epinephrine / blood
Heart Rate
Leg / blood supply
Muscle, Skeletal / blood supply*,  innervation,  physiology
Norepinephrine / blood
Oxygen / blood
Oxygen Consumption / physiology
Physical Exertion / physiology*
Regional Blood Flow / physiology
Reproducibility of Results
Respiration / physiology
Respiratory Muscles / physiology*
Sympathetic Nervous System / physiology
Vascular Resistance / physiology
Vasoconstrictor Agents / metabolism
Work of Breathing / physiology
Grant Support
Reg. No./Substance:
0/Vasoconstrictor Agents; 51-41-2/Norepinephrine; 51-43-4/Epinephrine; 7782-44-7/Oxygen

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