ISSN:
1439-6327
Keywords:
Moderate exercise
;
Hypoxia
;
CO2
;
Leg oxygen consumption
;
Leg blood flow
;
Leg vascular resistance
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The effect of acute hypoxia and CO2 inhalation on leg blood flow (LBF), on leg vascular resistance (LVR) and on oxygen supply to and oxygen consumption in the exercising leg was studied in nine healthy male subjects during moderate one-leg exercise. Each subject exercised for 20 min on a cycle ergometer in four different conditions: normoxia, normoxia +2% CO2, hypoxia corresponding to an altitude of 4000 m above sea level, and hypoxia +1.2% CO2. Gas exchange, heart rate (HR), arterial blood pressure, and LBF were measured, and arterial and venous blood samples were analysed for $$P_{{\text{CO}}_{\text{2}} } $$ , $$P_{{\text{O}}_{\text{2}} } $$ , oxygen saturation, haematocrit and haemoglobin concentration. Systemic oxygen consumption was 1.83 l · min−1 (1.48–2.59) and was not affected by hypoxia or CO2 inhalation in hypoxia. HR was unaffected by CO2, but increased from 136 beat · min−1 (111–141) in normoxia to 155 (139–169) in hypoxia. LBF was 6.5 l · min−1 (5.4–7.6) in normoxia and increased significantly in hypoxia to 8.4 (5.9–10.1). LVR decreased significantly from 2.23 kPa · l−1 · min (1.89–2.99) in normoxia to 1.89 (1.53–2.52) in hypoxia. The increase in LBF from normoxia to hypoxia correlated significantly with the decrease in LVR. When CO2 was added in hypoxia a significant correlation was also found between the decrease in LBF and the increase in LVR. In normoxia, the addition of CO2 caused a significant increase in mean blood pressure. Oxygen consumption in the exercising leg (leg $$\dot V_{{\text{O}}_{\text{2}} } $$ ) in normoxia was 0.97 l · min−1 (0.72–1.10), and was unaffected by hypoxia and CO2. It is concluded that the O2 supply to the exercising leg and its $$\dot V_{{\text{O}}_{\text{2}} } $$ are unaffected by hypoxia and CO2. The increase in LBF in hypoxia is caused by a decrease in LVR. These changes can be counteracted by CO2 inhalation. It is proposed that the regulatory mechanism behind these changes is that change in brain $$P_{{\text{CO}}_{\text{2}} } $$ causes change in the central regulation of vascular tonus in the muscles.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00418456
Permalink
