Neil E. Richardson

Near infra-red spectroscopy and arterial oxygen extraction at altitude.

The ratio of oxygenated to total haemoglobin (Hb), or rSO2, obtained by near infrared spectroscopy (NIRS), includes both arterial and venous blood of the region examined. The relationship of arterial oxygen extraction, E, and saturation, SaO2, to rSO2 can be expressed, for normally functioning tissue, as E = 1.39 (1 - rSO2/SaO2). Cerebral E, at rest, is constant at lower altitudes but is reduced at 5000 m. This corresponds to constant values of E for SaO2 values above 90% (approximately). E declines linearly for lower SaO2 values, either including measurement at high altitude or at sea level with a reduced inspiratory oxygen concentration. In addition to measurements of brain NIRS resting oxygen extraction of liver, muscle and kidney have also been calculated from NIRS measurements made, on normal inspired air, at sea level and after acute ascent to 2400 m and 5050 m. At 5050 m E was reduced for all four regions but at 2400 m was the same as at sea level for brain, liver and muscle; for the kidney E was elevated at 2400 m. Cerebral oxygen extraction was calculated for rest and the full range of exercise. It was constant at sea level for the lower levels of exercise and, if the calculated extraction value assumptions still hold at lower SaO2 values, reduced for the higher work rates at intermediate altitudes. The present study confirms constancy of oxygen extraction and hence the ratio of oxygen delivery to oxygen consumption (1/E), within physiological limits, and appears to show where those limits lay and, to some extent, show how matters change beyond ordinary physiological limits.

Human T Lymphocyte Activation

The T lymphocyte receptor for antigen and histocompatibility molecules is a molecular complex comprised of five polypeptide chains. Both the 49KD alpha and 43KD beta chains are immunoglobulin-like and thus contain variable domains responsible for ligand binding. In contrast, the 20-25KD T3 gamma, delta and epsilon chains are monomorphic structures presumably involved in transmembrane signalling. The alpha and beta subunits are disulfide bonded to each other and held in noncovalent association with the T3 chains. T3-Ti receptor crosslinking leads to conformational modification of a second T lineage specific molecule, termed the 50KD T11 structure and in turn, protein kinase C activation, elevation in intracytoplasmic free calcium and Na+/H+ antiport stimulation.