Effect of high ambient pressure and oxygen tension on organ blood flow in conscious trained rats

Cardiac output and blood flow to different organs and tissues were investigated in conscious trained rats using radiolabeled microspheres (MS) injected into the left ventricle. Two subsequent MS injections were administered to each rat at normal gas atmosphere and pressure (control) and in one of the following experimental situations: at normal ambient pressure and high partial pressure of O₂ (PO₂ = 1.0 ATA) (Group 1); an ambient pressure of 5 ATA and high partial pressure of O₂ (PO₂ = 1.0 ATA) (Group 2); and at ambient pressure of 5 ATA and normal partial pressure of O₂ (PO₂ = 0.2 ATA). The inert gas was nitrogen. Cardiac output fell in Groups 1 and 2 with high PO₂ (P < 0.05), and was unchanged in Group 3 with normal PO₂. Heart rate decreased in Groups 1 (NS) and 2 (P < 0.01), and was unchanged in Group 3. The arterial pressure remained unchanged while the renal blood flow decreased (P < 0.05) in all groups. The myocardial blood flow fell (P < 0.05) in both groups with decreased cardiac output, and was increased by 25% (P < 0.05) in normoxia (Group 3) with maintained cardiac output. The blood flow to the adrenal glands fell (P < 0.05) in both groups with high PO₂, and increased in the normotoxic Group 3 (NS). The blood flow to the splanchnic area fell in all groups. The cerebral blood flow and blood flow to the eyes fell in both groups with high PO₂ (P < 0.05), and were constant in normoxia.