Effects of mass loading the respiratory system in man

Mass loading of the thorax in four normal conscious subjects and in six anesthetized paralyzed subjects transposed the thoracic volume-pressure curve to higher levels on the pressure axis without greatly affecting the slope of its linear portion. This effect is similar to that produced by forward acceleration and snorkel breathing. Mass loading the lower thorax produced a greater effect than mass loading the upper thorax. Mass loading the abdomen flattened the slope of the linear portion of the thoracic-volume pressure curve both in conscious subjects and in anesthetized paralyzed subjects, the effect resembling that of elastic loading which also flattened the thoracic volume-pressure curve. The shape of the total respiratory static volume-pressure curves in six of ten excessively obese subjects resembled that produced by thoracic mass loading in normal subjects. Five patients with the obesity-hypoventilation syndrome had curves suggesting a combination of elastic and mass loading or alternatively, abdominal mass loading. At any lung volume, the total transrespiratory static pressure is made up of a volume-dependent elastic component and a volume-independent gravitational component. The latter is approximately 5 cm H 2 O in the supine adult male of normal weight. thoracic compliance; total respiratory compliance; gravitational effects on thorax; respiratory compliances in obesity Submitted on January 6, 1964