Respiratory control and work of breathing in obese subjects

Lung volumes, arterial blood gases, respiratory control system sensitivity, and oxygen cost of breathing were studied in obese but otherwise normal individuals and compared to similar studies in nonobese control subjects. Respiratory control system sensitivity as measured by the response to 5% carbon dioxide in air was normal in most obese subjects but reduced in certain obese individuals indistinguishable from the others on the basis of clinical evaluation or resting air studies. While breathing 5% carbon dioxide, the ventilation required to maintain any given alveolar carbon dioxide tension was directly dependent on weight. Oxygen cost of breathing in the ventilation range of 10–30 l/min. was elevated in 4 of 12 obese subjects, and in 6 of 9 obese subjects in the range of 20–40 l/min. There was no correlation between oxygen cost of breathing and respiratory control system sensitivity.

Submitted on April 29, 1960

THE EFFICIENCY OF THE RESPIRATORY MUSCLES IN OBESITY

The work done to overcome the elastic resistance and the efficiency of the respiratory muscles were determined in normal and obese subjects. The work done was no greater in the obese subjects, but the efficiency of the muscles was low. These findings suggest that the high oxygen cost of breathing in obesity is due to inefficient respiratory muscles rather than to an increased amount of work required to overcome elastic resistance. When an extrapulmonary elastic resistance was applied to the normal subjects, the compliance of the chest wall and the efficiency of the respiratory muscles fell to the level of that in the obese. This suggests that the inefficiency of the respiratory muscles of obese individuals may have been due to the reduced chest wall compliance or to the lower lung volume at which ventilation took place.

Estimation of body surface area of extremely obese human subjects

The body surface areas of one normal and four extremely obese human subjects have been estimated by three methods: a) direct measurement by a method similar to that which Du Bois described; b) calculation from the Du Bois height-weight formula; and c) calculation from the Du Bois linear formula. The values for the total body surface area of the obese subjects calculated from the height-weight formula varied up to 11% below those that were directly measured. The values for the total body surface area obtained with the linear formula ranged between 13% and 20% above the direct measurements, this being almost entirely due to discrepancies in the trunk and in the thigh estimations. It has been concluded that estimation of the body surface area oxf extremely obese subjects by the Du Bois height-weight formula is satisfactory when considered in relation to the accuracy of the physiologic measurements with which it is generally used. Because of the unusual body form the Du Bois linear formula has been found unsatisfactory for this group.

Submitted on March 1, 1960

Obesity, age and gastric hunger contractions

Gastric motility of a group of obese and nonobese women was measured in an effort to determine whether any correlation existed between patterns of gastric motility, obesity and age. Nineteen obese and 18 nonobese women were studied during a standardized 4-hour test, by means of an intragastric balloon. No difference was observed in the patterns of gastric motility in obese and nonobese groups, and there was no correlation between the degree of obesity (% overweight) and the total amount of gastric activity. There was an apparent diminution in gastric motility with increasing age (correlation coefficient 0.347, P < .05). There was thus no evidence to indicate that altered gastric motility was responsible for or expressive of difficulties in the regulation of food intake of obese persons.

Submitted on July 29, 1959

WATER RETENTION IN OBESITY

In 27 cases of obesity, renal function was examined by clearance methods with a constant plasma level. The results showed that, as compared with normal controls, renal blood flow, glomerular filtration and the filtration fraction were significantly reduced.

Therapy with L-tri-iodothyronine (TIT) covered 17 cases of obesity. The influence of the drug on renal function, total body fluids and extracellular fluids was examined. Statistical probability indicated that total body fluid and glomerular filtration were nearly normalised and renal blood flow was significantly increased while the extracellular fluids volume remained unchanged at a low level.

Blood Pressure and Obesity

Previous surveys have shown that height of observed blood pressure and degree of overweight are related. However, excess weight does not necessarily mean excess fat and the possibility of error in the measurement of blood pressure due to variations in the size of the arm has not been excluded. The present survey, taking these factors into account, shows that blood pressure is influenced by the total bulk of the body but not especially by fat except insofar as it contributes to total bulk. A possible explanation of the findings is offered.

Relation Between Body Fat and Glycogen Levels of Inbred Strains of Mice

Previous studies suggested that an inverse relation existed between concentrations of body fat and muscle glycogen among inbred strains of mice. Of six strains, one, the I strain, was resistant to obesity, and the levels of muscle glycogen were 3–6 times greater than those of the other five strains. Because the tentative proposal was based on data from only one lean strain, mice of the DBA strain were studied as another possible lean strain. Although small animals, sublines 1 and 2 of this strain became obese when fed a 50% fat diet, and the levels of muscle glycogen were in the range of the other five obese strains. It was also found that concentrations of body fat up to 25% could be induced in 4–5-month-old mice of the I strain, and by dietary means alone. The concentrations of muscle glucogen in these mice were not lower than those of I strain mice exhibiting concentrations of body fat of 11%. It was concluded, therefore, that an inverse relation between carbohydrate and fat stores does not exist among inbred strains of mice. The unusually high levels of muscle glycogen in the I strain appear to be unique, and are most likely genetically determined.