Sackett James R, Schlader Zachary J, O'Leary Morgan C, Chapman Christopher L, Johnson Blair D
Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, 14214, USA.
Exp Physiol. 2018 May 1;103(5):714-727. doi: 10.1113/EP086870.
What is the central question of the study? Is central chemosensitivity blunted during thermoneutral head-out water immersion in healthy humans? What is the main finding and its importance? Central chemosensitivity is augmented during thermoneutral head-out water immersion in healthy men and women. Thus, we suggest that the central chemoreceptors do not contribute to CO retention during head-out water immersion.
Carbon dioxide retention occurs during water immersion. Therefore, we tested the hypothesis that central chemosensitivity to hypercapnia is blunted during 2 h of thermoneutral head-out water immersion (HOWI) in healthy young adults. Twenty-six participants (age 22 ± 2 years; body mass index 24 ± 3 kg m ; 14 women) participated in two experimental visits: a HOWI visit (HOWI) and a dry time-control visit (Control). Central chemosensitivity was assessed via a rebreathing test at baseline, 10, 60, 90 and 120 min and after HOWI and Control. End-tidal CO tension (P ET ,CO2), minute ventilation, blood pressure and heart rate were recorded continuously. The P ET ,CO2 increased from baseline throughout HOWI (peak increase at 120 min 2 ± 2 mmHg; P < 0.001), and the change in P ET ,CO2 was greater throughout HOWI than Control (P < 0.001). The change in minute and alveolar ventilation was not different throughout time (P ≥ 0.173) or between conditions (P ≥ 0.052). Central chemosensitivity was greater than at baseline throughout HOWI (peak increase 0.74 ± 1.01 l min mmHg at 120 min; P < 0.001), and the change in central chemosensitivity was greater throughout HOWI than Control (P ≤ 0.006). We also divided the cohort into tertiles based on baseline central chemosensitivity (i.e. Low, Intermediate and High) and compared Low versus High during HOWI. Low demonstrated an increase in P ET ,CO2 starting at 10 min (2 ± 3 mmHg; P < 0.001), whereas High did not exhibit an increase in P ET ,CO2 until 60 min (2 ± 2 mmHg; P = 0.018). These data indicate that CO retention occurs throughout HOWI despite augmented central chemosensitivity and that having a high baseline central chemosensitivity might delay the onset of CO retention.
该研究的核心问题是什么？在健康人体处于热中性头露出水面的浸水中时，中枢化学敏感性是否会减弱？主要发现及其重要性是什么？在健康男性和女性处于热中性头露出水面的浸水中时，中枢化学敏感性增强。因此，我们认为在头露出水面的浸水中，中枢化学感受器对二氧化碳潴留没有影响。
在水浸过程中会发生二氧化碳潴留。因此，我们测试了这样一个假设：在健康的年轻成年人进行2小时热中性头露出水面的水浸（HOWI）过程中，对高碳酸血症的中枢化学敏感性会减弱。26名参与者（年龄22±2岁；体重指数24±3kg/m²；14名女性）参加了两次实验性访视：一次HOWI访视（HOWI）和一次干燥时间对照访视（对照）。在基线、10、60、90和120分钟以及HOWI和对照之后，通过重复呼吸测试评估中枢化学敏感性。持续记录呼气末二氧化碳分压（PET,CO2）、分钟通气量、血压和心率。在整个HOWI过程中，PET,CO2从基线开始升高（在120分钟时峰值升高2±2mmHg；P<0.001），并且在整个HOWI过程中PET,CO2的变化大于对照（P<0.001）。分钟通气量和肺泡通气量的变化在整个时间段内（P≥0.173）或不同条件之间（P≥0.052）没有差异。在整个HOWI过程中，中枢化学敏感性高于基线（在120分钟时峰值升高0.74±1.01l/min/mmHg；P<0.001），并且在整个HOWI过程中中枢化学敏感性的变化大于对照（P≤0.006）。我们还根据基线中枢化学敏感性将队列分为三分位数（即低、中、高），并比较了HOWI期间低与高的情况。低三分位数在10分钟时开始出现PET,CO2升高（2±3mmHg；P<0.001），而高三分位数直到60分钟才出现PET,CO2升高（2±2mmHg；P=0.018）。这些数据表明，尽管中枢化学敏感性增强，但在整个HOWI过程中仍会发生二氧化碳潴留，并且具有高基线中枢化学敏感性可能会延迟二氧化碳潴留的发生。
