Intraocular pressure during handgrip exercise: The effect of posture and hypercapnia in young males

Abstract

Abstract Purpose As part of our investigations of intraocular pressure (IOP) as a potential contributing factor to the spaceflight‐associated neuro‐ocular syndrome using the 6° head‐down tilt (6°HDT) bed rest experimental model, we compared the effect of rest and isometric exercise in prone and supine 6°HDT positions on IOP with that observed in the seated position. Methods Ten male volunteers (age = 22.5 ± 3.1 yrs) participated in six interventions. All trials comprised a 10‐min rest period, a 3‐min isometric handgrip exercise at 30% of participant's maximum, and a 10‐min recovery period. The trials were conducted under normocapnic (NCAP) or hypercapnic (FICO2 = 0.01; HCAP) conditions, the latter mimicking the ambient conditions on the International Space Station. IOP, systolic and diastolic pressures, and heart rate (HR) were measured during the trials. Results Isometric exercise‐induced elevations in HR and mean arterial blood pressure. IOP in the prone 6°HDT position was significantly higher (p < 0.001) compared to IOP in supine 6°HDT position and seated trials at all time points. IOP increased with exercise only in a seated HCAP trial (p = 0.042). No difference was observed between trials in NCAP and HCAP. IOP in the prone 6°HDT position was constantly elevated above 21 mmHg, the lower limit for clinical ocular hypertension. Conclusions IOP in the prone 6°HDT position was similar to IOP reported in astronauts upon entering microgravity, potentially indicating that prone, rather than supine 6°HDT position might be a more suitable experimental analog for investigating the acute ocular changes that occur in microgravity.

Keywords

• head‐down tilt
• intraocular pressure
• spaceflight‐associated neuro‐ocular syndrome
• visual impairment