PMC8478670_01
Average blood velocity in right radial artery (A) and heart rate (B) vs time of a test person during steady state ergometer cycling. Arrows indicate start and stop of a period of apnea and facial immersion (AFI) in ice-cold water.
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During ergometer cycling with constant workload, the radial artery ABV presented with respiration-synchronous changes, as shown during the first half a minute in Figure 1A. When steady state was obtained, as judged by HR of 150-160 beats/min, the test person began AFI (arrows indicate start and end), whereupon radial artery ABV signaling fell by 85%, in parallel with a 58% decline in HR (Figure 1B), as compared with the preceding period when he breathed freely. Of note, we observed sudden bursts in HR during the bradycardia periods both in Figures 1B and 2B.
Average blood velocity in right radial artery (A) and heart rate (B) vs time of a test person during steady state ergometer cycling. Arrows indicate start and stop of an apnea period without face immersion in ice-cold water.
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This resulted in similar patterns of decreased ABV (Figure 2A) and HR (Figure 2B), although developing at a slower pace. Of note, we observed sudden bursts in HR during the bradycardia periods both in Figures 1B and 2B.
Average blood velocity in the right radial artery (A) and heart rate (B) vs time of a test person during steady state ergometer cycling. Arrows indicate start and stop of a period of facial immersion in ice-cold water during which the test person breathed via a snorkel.
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However, this time radial artery ABV fell only transiently and returned to the preceding level before he had withdrawn his face from water (Figure 3A). We observed no concomitant drop in HR (Figure 3B).
Average blood velocity in the right vertebral artery vs time of a test person during steady state ergometer cycling. Arrows indicate start and stop of a period of apnea and face immersion (AFI) in ice-cold water.
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Finally, we investigated right vertebral artery ABV at the same workload as used above (Figure 4).