Continuous measurement of internal left ventricular diameter.

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Abstract
Continuous recordings of instantaneous internal left ventricular transverse diameters were obtained on conscious dogs with a sonomicrometer and transducers implanted inside the heart. The instrumented animals showed no cardiac embarrassment and gave reliable recordings for as long as 7 weeks. Measurements of internal ventricular diameter are preferable to those made with transducers affixed to the external surface of the heart because the interposition of the ventricular walls between external transducers precludes accurate determination of internal chamber dimensions. During isovolumic contraction internal diameter decreases, whereas external diameter reportedly increase. Differences between internal and external diameter measurements are probably due to thickening of the ventricular wall during systole.