Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, School of Public Health and Health Professions, University at Buffalo, Buffalo, NY, United States of America.
Department of Human Physiology, College of Arts and Sciences, University of Oregon, Eugene, OR, United States of America.
PLoS One. 2024 Mar 13;19(3):e0298587. doi: 10.1371/journal.pone.0298587. eCollection 2024.
Episodic increases in cerebral blood flow (CBF) are thought to contribute to improved cerebrovascular function and health. Head-out water immersion (HOWI) may be a useful modality to increase CBF secondary to the hydrostatic pressure placed on the body. However, it is unclear whether water temperatures common to the general public elicit similar cerebrovascular responses. We tested the hypothesis that mean middle cerebral artery blood velocity (MCAvmean) and cerebrovascular reactivity to CO2 (CVRCO2) would be higher during an acute bout of thermoneutral (TN; 35°C) vs. cool (COOL; 25°C) HOWI. Ten healthy participants (age: 23±3 y; 4 women) completed two randomized HOWI visits. Right MCAvmean, end-tidal CO2 (PETCO2) mean arterial pressure (MAP), and MCA conductance (MCAvmean/MAP) were continuously recorded. CVRCO2 was assessed using a stepped hypercapnia protocol before (PRE), at 30 minutes of HOWI (HOWI), immediately after HOWI (POST-1), and 45 minutes after HOWI (POST-2). Absolute values are reported as mean ± SD. MCAvmean, PETCO2, MAP, and CVRCO2 were not different between conditions at any timepoint (all P≥0.17). In COOL, MCAvmean increased from PRE (61±9 cm/s) during HOWI (68±11 cm/s), at POST-1 (69±11 cm/s), and POST-2 (72±8 cm/s) (all P<0.01), and in TN from PRE to POST-1 (66±13 vs. 71±14 cm/s; P = 0.05). PETCO2 did not change over time in either condition. In COOL, MAP increased from PRE (85±5 mmHg) during HOWI (101±4 mmHg), at POST-1 (97±7 mmHg), and POST-2 (96±9 mmHg), and in TN from PRE (88±5 mmHg) at HOWI (98±7 mmHg) and POST-1 (99±8 mmHg) (all P<0.01). In COOL, CVRCO2 increased from PRE to HOWI (1.66±0.55 vs. 1.92±0.52 cm/s/mmHg; P = 0.04). MCA conductance was not different between or within conditions. These data indicate that 30 minutes of cool HOWI augments MCAvmean and that the increase in MCAvmean persists beyond cool HOWI. However, cool HOWI does not alter CVRCO2 in healthy young adults.
episodic increases in cerebral blood flow (CBF) are thought to contribute to improved cerebrovascular function and health. Head-out water immersion (HOWI) may be a useful modality to increase CBF secondary to the hydrostatic pressure placed on the body. However, it is unclear whether water temperatures common to the general public elicit similar cerebrovascular responses. We tested the hypothesis that mean middle cerebral artery blood velocity (MCAvmean) and cerebrovascular reactivity to CO2 (CVRCO2) would be higher during an acute bout of thermoneutral (TN; 35°C) vs. cool (COOL; 25°C) HOWI. Ten healthy participants (age: 23±3 y; 4 women) completed two randomized HOWI visits. Right MCAvmean, end-tidal CO2 (PETCO2) mean arterial pressure (MAP), and MCA conductance (MCAvmean/MAP) were continuously recorded. CVRCO2 was assessed using a stepped hypercapnia protocol before (PRE), at 30 minutes of HOWI (HOWI), immediately after HOWI (POST-1), and 45 minutes after HOWI (POST-2). Absolute values are reported as mean ± SD. MCAvmean, PETCO2, MAP, and CVRCO2 were not different between conditions at any timepoint (all P≥0.17). In COOL, MCAvmean increased from PRE (61±9 cm/s) during HOWI (68±11 cm/s), at POST-1 (69±11 cm/s), and POST-2 (72±8 cm/s) (all P<0.01), and in TN from PRE to POST-1 (66±13 vs. 71±14 cm/s; P = 0.05). PETCO2 did not change over time in either condition. In COOL, MAP increased from PRE (85±5 mmHg) during HOWI (101±4 mmHg), at POST-1 (97±7 mmHg), and POST-2 (96±9 mmHg), and in TN from PRE (88±5 mmHg) at HOWI (98±7 mmHg) and POST-1 (99±8 mmHg) (all P<0.01). In COOL, CVRCO2 increased from PRE to HOWI (1.66±0.55 vs. 1.92±0.52 cm/s/mmHg; P = 0.04). MCA conductance was not different between or within conditions. These data indicate that 30 minutes of cool HOWI augments MCAvmean and that the increase in MCAvmean persists beyond cool HOWI. However, cool HOWI does not alter CVRCO2 in healthy young adults.
间歇性增加脑血流（CBF）被认为有助于改善脑血管功能和健康。头部浸水（HOWI）可能是一种有用的方法，通过身体上的静水压力增加 CBF。然而，目前尚不清楚公众常见的水温是否会引起类似的脑血管反应。我们假设在急性热中性（TN；35°C）与凉爽（COOL；25°C）的 HOWI 期间，平均大脑中动脉血流速度（MCAvmean）和对二氧化碳的脑血管反应性（CVRCO2）会更高。10 名健康参与者（年龄：23±3 岁；4 名女性）完成了两次随机 HOWI 访问。连续记录右侧 MCAvmean、呼气末二氧化碳（PETCO2）平均动脉压（MAP）和 MCA 传导性（MCAvmean/MAP）。使用逐步高碳酸血症方案在 PRE（之前）、HOWI 30 分钟时（HOWI）、HOWI 后立即（POST-1）和 HOWI 后 45 分钟时（POST-2）评估 CVRCO2。绝对值以平均值±标准差表示。在任何时间点，MCAvmean、PETCO2、MAP 和 CVRCO2 在条件之间均无差异（均 P≥0.17）。在 COOL 中，MCAvmean 在 HOWI 期间从 PRE（61±9 cm/s）增加（68±11 cm/s），在 POST-1（69±11 cm/s）和 POST-2（72±8 cm/s）（均 P<0.01），并且在 TN 中从 PRE 到 POST-1（66±13 与 71±14 cm/s；P = 0.05）。在两种情况下，PETCO2 均未随时间变化。在 COOL 中，MAP 在 HOWI 期间从 PRE（85±5 mmHg）增加（101±4 mmHg），在 POST-1（97±7 mmHg）和 POST-2（96±9 mmHg），在 TN 中从 PRE（88±5 mmHg）在 HOWI（98±7 mmHg）和 POST-1（99±8 mmHg）（均 P<0.01）。在 COOL 中，CVRCO2 从 PRE 增加到 HOWI（1.66±0.55 与 1.92±0.52 cm/s/mmHg；P = 0.04）。MCA 传导性在条件之间或内部没有差异。这些数据表明，30 分钟的凉爽 HOWI 可增加 MCAvmean，并且 MCAvmean 的增加在凉爽 HOWI 之后仍然存在。然而，凉爽的 HOWI 不会改变健康年轻成年人的 CVRCO2。
