American Journal of Physiology. Heart and Circulatory Physiology vol:306 issue:6 pages:816-824
Background: Breathing-induced changes in intrathoracic pressures influence left and right ventricular (LV and RV) volumes, the exact nature and extent of which has not previously been evaluated in humans. We sought to examine this 'respiratory pump' using novel real-time cardiac magnetic resonance (CMR) imaging. Methods: Eight healthy subjects underwent serial multislice real-time CMR during normal breathing, breath-holding and the Valsalva maneuver. Subsequently, a separate cohort of 9 subjects underwent real-time CMR at rest and during incremental exercise. LV and RV end-diastolic and end-systolic volumes (EDV and ESV) and diastolic and systolic eccentricity indices were determined at peak inspiration and expiration. Results: During normal breathing, inspiration resulted in an increase in RV volumes [RVEDV +18±8%, RVESV +14±12% and RV stroke volume (SV) +21±10%; p<0.01] and an opposing decrease in LV volumes (P<0.0001 for interaction). During end-inspiratory breath-holding, RVSV decreased by 9±10% (p=0.046), whereas LVSV did not change. During Valsalva, volumes decreased in both ventricles (RVEDV -29±11%, RVESV -16±14%, RVSV -36±14% and LVEDV -22±17%, LVSV -25±17%; P<0.01). The reciprocal effect of respiration on LV and RV volumes was maintained throughout exercise. The diastolic and systolic eccentricity indices were greater during inspiration than during expiration, both at rest and during exercise (P<0.0001 for both). Conclusion: Ventricular volumes oscillate with respiratory phase such that RV and LV volumes are maximal at peak inspiration and expiration, respectively. Thus, interpretation of RV versus LV volumes requires careful definition of the exact respiratory time point for proper interpretation, both at rest and during exercise.