RELATIONSHIP BETWEEN CAPILLARY AND SYSTEMIC VENOUS PO2 DURING NONHYPOXIC AND HYPOXIC VENTILATION

We evaluated the relationship between end-capillary and systemic venous PO2 values in the retractor muscle of 14 anesthetized hamsters during both nonhypoxic and hypoxic ventilation to ascertain whether the level of tissue oxygenation could be reliably estimated from the systemic parameter. End-capillary PO2 was estimated from measurements of oxygen saturation in capillaries at the venular end of the network obtained using in vivo video microscopy and computer-aided image-analysis techniques at three different levels of inspired oxygen (0.3, 0.21, and 0.1). Measurements of systemic arterial and venous blood gases were made in conjunction with these capillary determinations. In addition, in a portion of the study we utilized an oxygen microelectrode to determine the PO2 in the first-order venule draining the portion of the muscle containing the capillaries under study. We found that only when the animals were made acutely hypoxic was there any correspondence between the systemic venous and end-capillary PO2 values. In addition, these data provide support for the presence of arteriovenous shunting of oxygen during nonhypoxic ventilation.