Lactate, pyruvate and blood gases in the carotid artery, jugular vein and pulmonary artery during submaximal exercise

Research in exercise physiology in horses often involves the use of venous blood from the jugular vein to evaluate metabolic events. The advantage of sampling from the jugular vein is the ease and safety of collection. However, the use of jugular blood to evaluate exercise responses assumes that the venous blood returning from the head is representative of central circulation. These data were collected to determine whether differences exist between venous, mixed venous (pulmonary artery), and arterial blood for several parameters commonly measured during exercise. Four Quarter Horse mares with catheters placed in the carotid artery (CA), pulmonary artery (PA), and jugular vein were exercised for 15 minutes at 4.5 m/sec on a treadmill set at an 11% grade. The parameters measured were lactate, pyruvate, PO₂, PCO₂, and pH. As would be expected, time*location interactions (p<.005) occurred for pH, PO₂, and PCO₂. Blood pH and PO₂ were highest in the CA and lowest in the PA. During exercise, PCO₂ increased in the PA and decreased in the JV and CA. Interestingly, a time*location interaction occurred for pyruvate (P<.005) but not for lactate. Lactate was elevated by exercise but was not different between sources, suggesting that lactate concentrations in samples from the JV are representative of central circulation. However, the same does not appear to be true for pyruvate. Pyruvate was higher in the PA than in the JV or CA. Thus blood from the JV does not appear to give a representative value for pyruvate in central circulation. Also, lactate/pyruvate ratios calculated from jugular samples may not represent central circulation.