Exertion Responses

     In this study, the subject was a healthy male athlete performing a 3-interval exercise routine on a stationary bicycle. CEi, heart rate, and SpO2 were monitored throughout the exercise period and during about 10 minutes of no exertion at the end. His resting heart rate is typically in the 48-55 beats per minute range. A 5-minute, low-intensity "warm-up" period is followed by three intervals of about 2 minutes of heavy exertion interspersed by 4 to 5 minutes of relaxed pedaling. The third exertion interval was an "all-out" effort and achieved his highest heart rate of about 180 beats per minute.

     As with several other exercise studies with healthy athletes comparing CEi with SpO2, we have found little or no variation of SpO2. It is apparent from this that the healthy, mature human body is capable of homeostatically adapting to a wide range of metabolic demand. Increased rate and depth of breathing, increased heart rate and cardiac output increases intake of oxygen. It is apparent from the above recording that reflex vasoconstriction in the skin, resulting in increased detected intensity of the Infrared light, is a primary response to hypoxic stress at the onset of exertion. Absorption of the red light is also decreased, but to a lesser degree, indicating that the decreased blood flow also results in cellular hypoxia in the skin despite no change in SpO2. We conclude that this vasoconstriction in the skin helps to conserve the oxygen supply for vital organ tissues and to support muscular work.

     Also seen in this recording is progressively decreased signal responses in the Raw Data and in the calculated CEi trend with each successive exertion interval. We propose that this observed trend is evidence of cellular adaptation in the skin to the hypoxic stress imposed by vasoconstriction during the exercise session. Supporting this conclusion is the rebound cellular hyperoxia that was recorded upon abrupt discontinuation of the exertion as normal blood flow was restored to the skin; again, with no indication of change in SpO2.