Cardiovascular responses to face immersion and apnea during steady state muscle exercise: A heart catheterization study on humans

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Abstract
The cardiovascular adjustments to face immersion and apnea (FIA) in human beings during steady‐state muscle exercise (163 and 98 watt) have been investigated. Using a triple lumen flow directed catheter inserted into the pulmonary artery we were able to measure cardiac output (CO) by thermodilution technique, pulmonary arterial pressure (PPA) right atrial pressure (PRA) and left ventricular filling pressure (PAD). Phasic arterial blood pressure (BP) was measured via a cannula in the radial artery. A 12 lead ECG was recorded continuously. FIA caused an immediate rise in BP (median 61 %), the highest level being 25.33 kPa. CO during the last half of FIA was reduced by 49% (range 46–59, n=7) systemic vascular resistance increased by median 200% (range 111–280). Myocardial oxygen demand determined by the heart rate pressure double product fell from median 33.6 to 16.8 (163 W) and 28.5 to 19.1 (98 W) given as beats/min · kPa ·4 102. Mean reduction was by 42%. PPA and PRA immediately increased and remained constant until a further pronounced increase was seen towards the end of FIA when pulmonary vascular resistance (PVR) went up. PACO2 and PAO2 at the end of 30 sec FIA (163 W) was 10.0 and 5.6 kPa, respectively, values which expectedly would cause pulmonary vasoconstriction. Our findings demonstrate that humans are able to make principally the same cardiovascular adjustments to diving as aquatic mammals, although the response patterns are slower and less efficient. The marked increase in systemic arterial blood pressure which we observed is in contrast to that in e.g. diving seals. In humans the rises in SVR and PVR is not so closely adjusted to the reduction in CO. This will reduce the oxygensaving potential by causing a rise in cardiac afterloads.

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