EFFECTS OF MUSCLE TRAUMA AND OF HEMORRHAGE UPON THE CARDIAC OUTPUT OF THE DOG

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Abstract
When the blood vol. of dogs is reduced to 30 to 40% following muscle trauma, shock occurs. The O2 consumption decreases to between 40 and 60% of the control values. The cardiac output (Fick method) is progressively reduced eventually reaching values only 10 to 25% of the control outputs. The high heart rates of severe shock are associated with extremely small outputs/beat (1-3 ml.). Arterial O2 saturation is relatively unchanged, but the mixed venous O2 content is low, being almost completely reduced in some instances. These changes in venous blood greatly increase the A-V O2 difference which sometimes approximates the O2 capacity of the blood. The pulmonary ventilation and the R.Q. increase. Calculated peripheral resistance increases. For the same reduction in blood vol., the respiratory and circulatory changes which occur in bled dogs are similar to those observed following muscle trauma. Certain differences are present, however, for the arterial blood pressure and the calculated peripheral resistances are higher in traumatized animals than in those in which the blood vol. has been decreased by hemorrhage. The relation of the peripheral venous O2 content to the cardiac output is discussed.