Heart volume in relation to body posture and immersion in a thermo-neutral bath. A roentgenometric study.

Ten subjects, aged 24–32, were studied in a roentgenometric determination of heart volume during changes of posture and water immersion. Heart volume was determined under three conditions: Standing in air, standing in water and supine. Heart size in the supine posture, which is taken as standard, was 739.4±38.1 ml. This increased to 839.1±65.2 ml during immersion, and decreased to 658.8±46.7 ml in the subject standing in air. The increase in heart-volume when immersing a standing subject in a water bath amounted to 120 to 329 ml (mean 180 ml±61.8 ml). This increase represents 25–75% (mean 50%) of the blood volume contained in the four cavities of the heart (approximately 400 ml). The radius of curvature of the right atrium decreased considerably during the transition from standing in air (r=79 mm) to standing in water (r=62 mm). This is taken as an indication of preferential atrial, as opposed to ventricular, filling which should be expected from the different thickness of the atrial and ventricular walls.