440 



HANDBOOK OF PHYSIOLOGY ^-^ CIRCULATION I 



44 years in age. The mean value for cardiac output 

 in these subjects was 6.6 liters per min (range 4.4- 

 8.9). Since cardiac output varies directly with the 

 size of the subject, it is usually the practice to relate 

 the cardiac output to the body surface area. In these 

 subjects the mean cardiac output per square meter of 

 body surface area (cardiac index) was 3.5 liters per 

 min per m- (table i). These figures are comparable 

 to those given by others (71, 159). 



The "total" pulmonary resistance of 205 dynes 

 sec cm~^ was approximately one-sixth the total 

 systemic resistance of 1 1 30 dynes sec cm~^. The 

 pulmonary "arteriolar" resistance averaged 67 dynes 

 sec cm~^. The range of resistance values was wide 

 (table i). 



The average and range of pressures in the right side 

 of the heart and a systemic artery are shown in table 

 2. The point of reference for all pressures was taken 

 as the midanteroposterior chest level. The pressure 

 values for the pulmonary artery were approximately 

 one-sixth those for the systemic artery. 



No significant difference was found between the 

 right atrial and right ventricular diastolic pressures. 

 In this series of subjects the systolic pressure gradient 

 across the pulmonary valve averaged 2 mm of mercury 

 (range 0-7). 



The average and range of values for blood oxygen 

 saturation in various heart chambers and vessels in 

 the same subjects are shown in table 3 (19). Samples 

 of blood from the inferior vena cava were withdrawn 

 with the catheter tip at or just above the level of the 

 diaphragm, the catheter having been first advanced 

 to below the diaphragm to confirm its position in the 

 inferior vena cava and then withdrawn slightly. 

 Samples from this position showed an average oxygen 

 saturation of 83 per cent, whereas the oxygen satura- 

 tion of superior vena caval blood averaged 77 per 

 cent, a figure significantly less than that for inferior 

 vena caval saturation. The mean oxygen saturation of 

 right atrial blood equaled 80 per cent, a figure 



TABLE I. Means and Ranges of Cardiac Output and 

 Vascular Resistances in 26 Xormal Subjects 

 While Breathing Air 



T.^BLE 2. Afeans and Ranges of Pressures in J'arious 

 Heart Chambers and Vessels in 26 

 Normal Recumbent Subjects 



Cardiac index, liters/min/m- 



"Total" systemic vascular resistance, 

 dynes sec cm"' k** 



"Total" pulmonary vascular resist- 

 ance, dynes sec cm-'' 



Pulmonary "arteriolar" resistance, 

 dynes sec cm"' 



Mean 



3-5 

 1130 



205 

 67 



Range 

 (95'"r band) 



2.8-4.2 



952-1308 



'54-256 



44-90 



TABLE 3. Means and Ranges of Blood Oxygen Saturation 

 in J'arious Heart Chambers and Vessels in 

 26 Normal Subjects 



intermediate between the inferior and superior caval 

 saturations. 



There was a wide range of blood oxygen saturation 

 values from both the right atrium and the right 

 ventricle, apparently due to poor mixing of blood in 

 these chambers. For example, if the catheter tip is 

 adjacent to the orifice of the coronary sinus while 

 sampling from the right atrium, a very low value may 

 be obtained. 



