Respiratory modulation of left ventricular stroke volume in man measured using pulsed Doppler ultrasound.

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1. Beat-by-beat changes in left ventricular stroke volume (l.v.s.v.) with breathing were recorded in four normal subjects using pulsed Doppler ultrasound. The l.v.s.v. fell during inspiration and rose during expiration; these changes were exaggerated at high tidal volumes. 2. Respiratory changes in l.v.s.v. persisted when respiratory rate was increased to 25 breaths/min despite an associated reduction in the degree of sinus arrhythmia. 3. During relaxed breath-holding, respiratory variations in l.v.s.v. ceased immediately, and on resumption of breathing a significant fall in l.v.s.v. occurred with the first inspiratory effort. 4. Inspiratory efforts against an occluded mouthpiece were accompanied by significant variations in l.v.s.v., although the magnitude of these changes was smaller than during unoccluded breathing with similar pleural pressure changes. 5. A resistive inspiratory load increased the respiratory variations in l.v.s.v. in the three subjects studied. 6. In three patients with implanted dual-chamber pacemakers set to constant heart rates, breathing was associated with larger variations in l.v.s.v. 7. In two patients who had undergone pericardectomy, the magnitude of respiratory changes in l.v.s.v. was less than in the normal subjects. 8. We conclude that inspiration directly lowers l.v.s.v. in man by a direct mechanism which is largely independent of lung volume changes, is dependent on changes in pleural pressure, and persists in the absence of sinus arrhythmia. All these results, particularly those in pericardectomy patients, are compatible with previous animal work on the anatomical and functional interdependence of right and left ventricles during breathing.

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