Effects of various acute hypoxic conditions on the hemorheological response during exercise and recovery ¹

Even though exercise hemorheology at hypoxic condition has been considered as a good tool to understand clinical hemorheology, there have been limited studies reported. Previous researches showed that hemorheological variables are closely correlated with oxygen delivery capacity during exercise. The present study investigated hypoxic responses including RBC deformability and aggregation, metabolic parameters and complete blood cell counts at various hypoxic conditions during cycling exercise and recovery. Eleven Korean healthy male subjects performed submaximal bike exercise at sea level (20.9 O₂) and under various hypoxic conditions (16.5 O₂, 14.5 O₂, 12.8 O₂, and 11.2 O₂) in a random order. The submaximal bike exercise intensity of the subjects was 70 maximum heart rate at sea level. All variables were measured at rest, during exercise and recovery 30-minute, respectively. As oxygen partial pressure decreased, arterial blood oxygen saturation decreased but oxygen uptake did not change much. Heart rate and lactate concentration during exercise increased when oxygen partial pressure is less than or equal to 14.5 O₂ condition. Red blood cell (RBC) counts, hemoglobin counts, and hematocrit level were not apparently altered with hypoxic conditions. RBC deformability showed significant alterations at 11.2 O₂ conditions compared with other hypoxic conditions during exercise or recovery, except at 10 minutes recovery. However, decreases in oxygen partial pressure did not affect red blood cell aggregation. Therefore, we conclude that alterations in RBC deformability may reduce aerobic capabilities at hypoxic condition.