Spontaneous respiration and inspiratory obstruction in dogs caused significant noncongruent shape changes in left ventricular dimensions, independent of pleural pressure changes.
How do different modes of respiration affect regional left ventricular dimensions and shortening in a canine model?
Lung volume changes during respiration can affect left ventricular geometry independently of pleural pressure changes, causing noncongruent shape changes that may confound volume estimates based on only one or two axes.
To clarify the effects of respiration on left ventricular (LV) dimensions and shortening, we studied chronically instrumented dogs with endocardial sonomicrometer crystals in the anterior-posterior (AP), septal to lateral (SL), and long axes (LA) following pericardiectomy. Ten anesthetized dogs were examined during spontaneous unobstructed respiration, partial inspiratory obstruction (PIO), and Mueller maneuvers (MM). During unobstructed inspiration, end-diastolic dimensions (EDD) demonstrated a significant increase in the AP and a similar decrease in the SL axis (i.e., noncongruent shape changes). During PIO only the SL EDD diminished significantly, while no significant changes occurred in any EDD during MM. Individual dogs also demonstrated noncongruent shape changes at end systole during inspiration. However, the end-systolic dimensions for the entire group demonstrated a significant increase in one dimension during each inspiratory mode with no significant changes in the other two axes suggesting an increased ventricular volume. Regional shortening declined only in the SL axis during both unobstructed respiration and PIO. Spontaneous sighs with large tidal volumes, yet smaller changes in pleural pressure than during the MM, were associated with marked noncongruent shape changes in both diastole and systole. We conclude that 1) estimates of LV volumes during respiration based on only one or two axes and assuming regional congruent shape changes may be misleading; and 2) lung volume changes can affect LV geometry independently of changes in pleural pressure.
Robotham et al. (1983) studied this question. Spontaneous unobstructed respiration, partial inspiratory obstruction, and Mueller maneuvers was evaluated on Left ventricular dimensions and shortening. Spontaneous respiration and inspiratory obstruction in dogs caused significant noncongruent shape changes in left ventricular dimensions, independent of pleural pressure changes.