Effect of Inspiration of 12%O2 (Balance N2) on Cardiac Output, Respiration, Oxygen Saturation, and Oxygen Delivery
Low arterial oxygen saturation (SaO2) will result in a reduced rate of arterial oxygen delivery to the tissues (DO2), unless there is a compensatory increase in cardiac output (CO) or haemoglobin concentration (Hb). An adequate DO2 can therefore be maintained by increasing ventilation, CO, or both. Sustaining a tissue specific oxygen extraction is thought to play an important part in overall compensation. The present study has examined responses to acute hypoxic exposure in 8 volunteers (breathing 12% oxygen, balance nitrogen) and describes changes in CO, ventilation and the SaO2. Aims included: examination of the extent of intersubject variations and seeing whether DO2 was maintained. SaO2, PCO2, respiration (via stethograph) and Finapress (non-invasive) arterial blood pressure (BP) were recorded, firstly on air and then on 12% oxygen. CO was derived, off-line, from the BP record. CO was increased in 5 subjects (22%-45%) but was virtually unchanged in 3, and yet comparison for all 8 subjects showed that DO2 on 12% oxygen was not significantly different from DO2 on air (mean on air 1017 ml. min–1; hypoxia 1080 ml. min–1, p = 0.27). SaO2 on 12% oxygen ranged between 85% and 93%. In conclusion, exposure to the same hypoxic gas mixture resulted in differing individual ventilatory and CO responses. However, DO2 was well maintained.
KeywordsRespiration Cali Medex
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