Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Jamova 39, Ljubljana, SI-1000, Slovenia.
Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, V51 1S6, Canada.
Exp Physiol. 2020 Apr;105(4):641-651. doi: 10.1113/EP088236. Epub 2020 Mar 17.
What is the central question of this study? Astronauts on-board the International Space Station (ISS) perform daily exercises designed to prevent muscle atrophy and bone demineralization: what is the effect of resistive exercise performed by subjects while exposed to the same level of hypercapnia as on the ISS on intraocular pressure (IOP)? What is the main finding and its importance? The static exercise-induced elevation in IOP during 6° prone head-down tilt (simulating the headward shift of body fluids in microgravity) is augmented by hypercapnia and exceeds the ocular hypertension threshold.
The present study assessed the effect of 6° head-down (establishing the cephalad fluid displacement noted in astronauts in microgravity) prone (simulating the effect on the eye) tilt during rest and exercise (simulating exercise performed by astronauts to mitigate the sarcopenia induced by unloading of weight-bearing limbs), in normocapnic and hypercapnic conditions (the latter simulating conditions on the International Space Station) on intraocular pressure (IOP). Volunteers (mean age = 57.8 ± 6 years, n = 10) participated in two experimental sessions, each comprising: (i) 10 min rest, (ii) 3 min static handgrip exercise (30% max), and (iii) 2 min recovery, inspiring either room air (NCAP) or a hypercapnic mixture (1% CO , HCAP). We measured IOP in the right eye, cardiac output (CO), stroke volume (SV), heart rate (HR) and mean arterial pressure (MAP) at regular intervals. Baseline IOP in the upright seated position while breathing room air was 14.1 ± 2.9 mmHg. Prone 6° head-down tilt significantly (P < 0.01) elevated IOP in all three phases of the NCAP (rest: 27.0 ± 3.7 mmHg; exercise: 32.2 ± 4.8 mmHg; recovery: 27.4 ± 4.0 mmHg) and HCAP (rest: 27.3 ± 4.3 mmHg; exercise: 34.2 ± 6.0 mmHg; recovery: 29.1 ± 5.8 mmHg) trials, with hypercapnia augmenting the exercise-induced elevation in IOP (P < 0.01). CO, SV, HR and MAP were significantly increased during handgrip dynamometry, but there was no effect of hypercapnia. The observed IOP measured during prone 6° HDT in all phases of the NCAP and HCAP trials exceeded the threshold pressure defining ocular hypertension. The exercise-induced increase in IOP is exacerbated by hypercapnia.
本研究的核心问题是什么？国际空间站（ISS）上的宇航员进行日常锻炼，旨在预防肌肉萎缩和骨质流失：在与 ISS 上相同的高碳酸血症水平下，进行抗阻运动对眼内压（IOP）有什么影响？主要发现及其重要性是什么？在 6°头低位（模拟微重力下体液的头向转移）下进行的静态运动引起的 IOP 升高，在高碳酸血症的情况下会加剧，并超过了眼高压阈值。
本研究评估了在常氧和高碳酸血症条件下（后者模拟国际空间站的条件），6°头低位（建立微重力状态下宇航员的头向液体移位）仰卧位（模拟对眼睛的影响）倾斜，在休息和运动（模拟宇航员进行的运动以减轻非负重肢体卸载引起的肌肉减少症）期间，对IOP 的影响。志愿者（平均年龄= 57.8 ± 6 岁，n= 10）参加了两个实验阶段，每个阶段包括：（i）10 分钟休息，（ii）3 分钟静态握力运动（30%最大），和（iii）2 分钟恢复，分别呼吸室内空气（NCAP）或高碳酸混合气体（1%CO2，HCAP）。我们定期测量右眼的眼压（IOP）、心输出量（CO）、每搏输出量（SV）、心率（HR）和平均动脉压（MAP）。在呼吸室内空气的直立坐姿下，基础 IOP 为 14.1 ± 2.9mmHg。在 NCAP 的所有三个阶段（休息：27.0 ± 3.7mmHg；运动：32.2 ± 4.8mmHg；恢复：27.4 ± 4.0mmHg）和 HCAP（休息：27.3 ± 4.3mmHg；运动：34.2 ± 6.0mmHg；恢复：29.1 ± 5.8mmHg）中，6°头低位仰卧位显著（P<0.01）升高了 IOP，高碳酸血症增强了运动引起的 IOP 升高（P<0.01）。在握力测力时，CO、SV、HR 和 MAP 显著增加，但高碳酸血症没有影响。在 NCAP 和 HCAP 试验的所有阶段，观察到的 6°头低位仰卧位 IOP 均超过定义眼高压的阈值压力。运动引起的 IOP 升高会因高碳酸血症而加剧。
