Simulation of oxygen delivery to tissues : the role of the hemoglobin oxygen equilibrium curve at altitude

A simplified model is described to estimate the oxygen delivery to tissues as a function of oxygen uptake, gas exchange ratio, 2,3-DPG/Hb concentration ratio, arterial and venous PO2, PCO2 and pH. Due to the complexity of the oxygen delivery system, the aim of this model is to predict relative changes of the oxygen delivery to tissues induced by changes of the other variables, rather than to yield absolute values. In this work, the importance of the observed shifts of the hemoglobin oxygen equilibrium curve at altitude is evaluated in terms of the efficiency of the oxygen transport system. It will be shown that a rightward shift of the oxygen equilibrium curve is beneficial up to 5400 m.a.s.l., while for higher altitudes such shifts lead to less efficient oxygen delivery to tissues

HUMAN RED-CELL AGE, OXYGEN-AFFINITY AND OXYGEN-TRANSPORT

The [2,3-DPG]/[Hb] ratio and the P50 were found to be lower in the 10% denser (old) than in the 10% lighter (young) red blood cell (RBC) fractions (0.57 \ub1 0.13 vs 0.96 \ub1 0.13 and 23.02 \ub1 0.85 vs 27.47 \ub1 1.05 Torr, respectively, mean \ub1 SD, P < 0.0005 for both, n = 6). The RBC aging processes appear thus to affect the RBC oxygen affinity. However, the [2,3-DPG] changes do not fully explain the drop of P50 as measured at constant [H+], [CO2] and [HbCO]. It is therefore postulated that an additional factor is involved in the regulation of the oxygen affinity in the ageing RBC. The RBC density in 59 normal individuals mathced for age (infants, adult, and aged) and for sex was found to be younger in adult females than in all other groups (P < 0.0005), including an age-matched group of pregnant women. Correspondingly, the [2,3-DPG]/[Hb] ratio and the P50 are higher in adult females than in adult males (0.92 \ub1 0.10 vs 0.82 \ub1 0.09, P < 0.009, and 29.03 \ub1 1.07 vs 27.72 \ub1 0.82 Torr, P < 0.002, respectively). These data are evaluated in terms of the efficiency of the oxygen transport calculating the circulatory load required to transport a given amout of oxygen to the tissues. The results indicate that the lower oxygen affinity (due to the younger RBC population) in adult female partially compensates for their lower [Hb]

Positive energy balance accelerates muscle atrophy and increases erythrocyte glutathione turnover rate during 35 days of bed rest

Background: Physical inactivity is often associated with positive energy balance and fat gain. Objective: We aimed to assess whether energy intake in excess of requirement activates systemic inflammation and antioxidant defenses and accelerates muscle atrophy induced by inactivity. Design: Nineteen healthy male volunteers were studied before and at the end of 5 wk of bed rest. Subjects were allowed to spontaneously adapt to decreased energy requirement (study A, n = 10) or were provided with an activity-matched diet (study B, n = 9). Groups with higher (HEB) or lower (LEB) energy balance were identified according to median values of inactivity-induced changes in fat mass (\u394FM, assessed by bioelectrical impedance analysis). Results: In pooled subjects (n = 19; median \u394FM: 1.4 kg), bed rest-mediated decreases in fat-free mass (bioelectrical impedance analysis) and vastus lateralis thickness (ultrasound imaging) were significantly greater (P < 0.03) in HEBAB (-3.8 \ub1 0.4kg and -0.32 \ub1 0.04 cm, respectively) than in LEBab (-2.3 \ub1 0.5 kg and -0.09 \ub1 0.04 cm, respectively) subjects. In study A (median \u394FM: 1.8 kg), bed rest-mediated increases in plasma leptin, C-reactive protein, and myeloperoxidase were greater (P < 0.04) in HEBA than in LEBA subjects. Bed rest-mediated changes of glutathione synthesis rate in eythrocytes (L-[3,3-2H2]cysteine incorporation) were greater (P = 0.03) in HEBA (from 70 \ub1 19 to 164 \ub1 29%/d) than in LEBA (from 103 \ub1 23 to 84 \ub1 27%/d) subjects. Conclusions: Positive energy balance during inactivity is associated with greater muscle atrophy and with activation of systemic inflammation and of antioxidant defenses. Optimizing caloric intake may be a useful strategy for mitigating muscle loss during period of chronic inactivity