Effect of Acute Increase in Blood Pressure on Intraocular Pressure in Pigs and Humans

To study the effect on intraocular pressure (IOP) of a sudden increase in blood pressure (BP) and of changes in partial pressure of CO(2) (pCO(2)). Two experimental studies were conducted: in pigs (n = 7), where BP was reduced by intravenous injection of sodium nitroprusside and increased by injection of angiotensin II; and in humans (n = 17 healthy subjects), where BP was increased by two types of isometric exercise (squatting and handgripping) performed for 2 minutes; IOP and pCO(2) were measured every 30 seconds during separate tests (rest, hyperventilation, isometric exercise) and then after 1, 3, 6, and 10 minutes of rest. In pigs, there is a linear relationship between BP and IOP variations: DeltaIOP = 1.21 DeltaBP - 0.14 (P < 0.001). In humans, this linear relationship is as follows: DeltaIOP = 0.40 DeltaBP + 0.85 (P < 0.001) for squatting and DeltaIOP = 0.54 DeltaBP + 0.55 (P = 0.02) for handgripping. BP and IOP increases are greater with squatting than with handgripping (53% vs. 46%, P = 0.05 and 46% vs. 35%, P = 0.03, respectively). Handgripping causes a greater fall in capnia than squatting does (P = 0.02). Capnia and IOP are positively correlated (P < 0.001). The pharmacological approach in animals and the study of isometric exercise in humans show that IOP rises significantly and rapidly with kinetics close to those of BP, and the two values are linearly related. The absence of variation in capnia and the greater increase in BP during squatting may explain the greater increase in IOP during this exercise compared to handgripping.