title: Systemic hemodynamics affecting cardiac output during hypocapnic and hypercapnic hypoxia.
abstract: Systemic hemodynamic adjustments involved in the control of cardiac output (CO) were examined in chronically instrumented unanesthetized sheep inhaling gas mixtures resulting in hypocapnic hypoxia (H) [arterial pH (pHa) = 7.53, arterial partial pressure of O2 (Pao2) = 30 Torr, arterial partial pressure of CO2 (Paco2) = 29 Torr] or hypercapnic hypoxia (HCH) (pHa = 7.14, Pao2 = 34 Torr, Paco2 = 72 Torr) for 1 h. H (n = 7) and HCH (n = 6) resulted in 26% and 61% increases in CO, respectively, and mean systemic arterial pressure rose to a greater extent during HCH. Both H and HCH resulted in increased blood flow (microsphere method) to the peripheral systemic circulation including the brain, heart, diaphragm, and nonrespiratory skeletal muscle (the latter blood flow increased 120% during H and 380% during HCH). Gastrointestinal and renal blood flow remained unchanged during H and HCH. Transit time of green dye from the pulmonary artery to regional veins in the hindlimb and intestine was 5.0 and 8.2 s, respectively, during base-line conditions and remained unchanged with HCH. During HCH, regional O2 consumption increased 274% for the hindlimb and decreased 39% for the intestine. Total catecholamines rose 250% during H and 3,700% during HCH. During hypocapnic and hypercapnic hypoxia, CO is augmented in part by systemic hemodynamic adjustments that include a redistribution of blood flow and a translocation of blood volume to the fast transit time peripheral systemic circuit. The sympathetic nervous system may play an important role in mediating these systemic hemodynamic adjustments.
mesh_terms: D000136:Acid-Base Equilibrium; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output; D002395:Catecholamines / Q000097:blood; D006439:Hemodynamics; D006935:Hypercapnia / Q000150:complications / Q000503:physiopathology*; D000860:Hypoxia / Q000150:complications / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D012756:Sheep
chemical_list: D002395:Catecholamines; D002245:Carbon Dioxide; D010100:Oxygen