Key result
During the early phase of resting apnoea in air, baroreflex sensitivity significantly decreased to a median of 6.6 ms·mmHg-1 compared to 20.3 ms·mmHg-1 at pre-apnoea steady state.
Why the study?
The study was conducted to analyse the characteristics of arterial baroreflexes during the first phase of apnoea.
How do rest and exercise apnoeas in air and pure oxygen affect arterial baroreflex sensitivity and operating point in healthy divers?
How do rest and exercise apnoeas in air and pure oxygen affect arterial baroreflex sensitivity and operating point in healthy divers?
Absolute Event Rate: 6.6% vs 20.3%
p-value: p=<0.05
During the first phase of apnoea, a sudden fall in mean arterial pressure is corrected by baroreflex resetting, likely driven by parasympathetic withdrawal rather than central command.
Apnoea-phase baroreflex shifts remain hypothesis-generating; leaves open extension to clinical hypoxia or patient populations.
Purpose We analysed the characteristics of arterial baroreflexes during the first phase of apnoea (φ1). Methods 12 divers performed rest and exercise (30 W) apnoeas (air and oxygen). We measured beat-by-beat R-to-R interval (RRi) and mean arterial pressure (MAP). Mean RRi and MAP values defined the operating point (OP) before (PRE-ss) and in the second phase (φ2) of apnoea. Baroreflex sensitivity (BRS, ms·mmHg−1) was calculated with the sequence method. Results In PRE-ss, BRS was (median [IQR]): at rest, 20.3 [10.0–28.6] in air and 18.8 [13.8–25.2] in O2; at exercise 9.2[8.4–13.2] in air and 10.1[8.4–13.6] in O2. In φ1, during MAP decrease, BRS was lower than in PRE-ss at rest (6.6 [5.3–11.4] in air and 7.7 [4.9–14.3] in O2, p < 0.05). At exercise, BRS in φ1 was 6.4 [3.9–13.1] in air and 6.7 [4.1–9.5] in O2. After attainment of minimum MAP (MAPmin), baroreflex resetting started. After attainment of minimum RRi, baroreflex sequences reappeared. In φ2, BRS at rest was 12.1 [9.6–16.2] in air, 12.9 [9.2–15.8] in O2. At exercise (no φ2 in air), it was 7.9 [5.4–10.7] in O2. In φ2, OP acts at higher MAP values. Conclusion In apnoea φ1, there is a sudden correction of MAP fall via baroreflex. The lower BRS in the earliest φ1 suggests a possible parasympathetic mechanism underpinning this reduction. After MAPmin, baroreflex resets, displacing its OP at higher MAP level; thus, resetting may not be due to central command. After resetting, restoration of BRS suggests re-establishment of vagal drive.
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Taboni et al. (2020) studied Healthy divers (n=12). Dry resting and exercise apnoeas vs. Pre-apnoea steady state was evaluated on Baroreflex sensitivity (BRS) during early phase 1 of resting apnoea in air (ms·mmHg-1) (p=<0.05). During the early phase of resting apnoea in air, baroreflex sensitivity significantly decreased to a median of 6.6 ms·mmHg-1 compared to 20.3 ms·mmHg-1 at pre-apnoea steady state.
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