Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0085383 (hypocapnia)
 1,697 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous reports suggest that isometric exercise (2-min handgrip at 50% maximal voluntary contraction [MVC]) substantially lowers intraocular pressure (IOP). The authors questioned whether the mechanism for lowered IOP in exercise is secondary to hyperventilation. Accordingly, in this study 11 subjects, with elevated IOP (greater than or equal to 18 mm Hg) and otherwise healthy, did 2 min of handgrip exercise at 50% MVC with and without carbon dioxide supplementation to maintain isocapnic conditions. Compared with a control experiment that involved neither exercise nor CO2 addition, exercise induced a fall in IOP from 18.3 to 15.6 mm Hg (P less than 0.001). This statistically significant decline in IOP persisted for 15 min after the exercise session. At the point of minimum IOP (1 min after the end of exercise), the minute ventilation was elevated from 6.5-8.1 l/min (P less than 0.05), and the end-tidal partial pressure of CO2 (PCO2) was reduced from 37.0 to 33.7 mm Hg (P less than 0.05) with respect to control values. By contrast, adding CO2 sufficient to maintain isocapnic conditions (experimental end-tidal PCO2 = 38.9 versus 38.5 mm Hg in the control study; P = not significant) abolished the exercise-induced ocular hypotension (experimental IOP = 17.8 versus 18.1 mm Hg in the control study; P = not significant). It was concluded that prevention of hypocapnia during isometric handgrip exercise blocks the subsequent fall in IOP, suggesting both that isometric exercise per se has no direct influence on IOP and that therapy for ocular hypertension could involve manipulation of blood gases.
 ...
PMID:Isocapnia blocks exercise-induced reductions in ocular tension. 160 33

Rats are increasingly used in ophthalmic research. However, little is known about the metabolic regulation of ocular blood flow. The purpose of this study was to examine the vasoreactivity in retina and choroid of the rat eye in response to experimentally altered partial arterial pressure of CO2 (PaCO2). The retinal and choroidal blood flows were measured sequentially in different PaCO2 with a modified microspheres method. The experiments were performed in two groups of adult male Brown-Norway rats. Under isofluorane anesthesia and mechanical ventilation, PaCO2 was monitored continuously by recording end tidal carbon dioxide level. Both femoral arteries and a femoral vein were cannulated for arterial blood pressure monitoring, blood sampling and drug administration, respectively. The intraocular pressure in both eyes was manometrically controlled at 20mmHg by anterior chamber cannulation. The retinal and choroidal blood flows were simultaneously measured by cardiac injection of a mixture containing 3.75 million of 8microm, and 0.5 million of 10microm microspheres; each size having a distinct color. In one experiment (n=10), blood flow was first measured during normocapnia (PaCO2=35mmHg) and then during hypocapnia (PaCO2=20-25mmHg). In another experiment (n=7), blood flow was measured during hypercapnia (PaCO2=45-50mmHg) and repeated one more time under the same experimental conditions to evaluate the repeatability of sequential measurements and the variances of the measurement between the two eyes. The results show that the mean blood flow in the retina measured during hypocapnia, normocapnia and hypercapnia were 8.1+/-4.8, 15.1+/-8.5 and 27.4+/-4.6microl/min per tissue, respectively. In the choroid, the corresponding blood flow rates were 120+/-38, 166+/-28 and 149+/-28microl/min per tissue, respectively. The difference of the mean blood flows across all the three different PaCO2 groups was highly significant for both retina and choroid (ANOVA: P<0.0001 and P=0.01, respectively). The mean blood flow during hypocapnia was significantly lower than normocapnia in both retina and choroid (P<0.02). The blood flow under hypercapnia was significantly higher than normocapnia in retina (P<0.01), but not in choroid (P=0.62). In conclusion, the study demonstrated that the dual-size and dual-dose microspheres mixture can be used as a reliable method to measure the retinal and choroidal blood flows simultaneously and sequentially in rats. The vasoreactivity to altered systemic PaCO2 in the retina in rats is similar to that of most other species studied. However, the choroidal vascular system exhibited complicated features that remain to be further clarified.
 ...
PMID:Retinal and choroidal vasoreactivity to altered PaCO2 in rat measured with a modified microsphere technique. 1842 Jan 96

Glaucoma is a disease characterized by progressive optic neuropathy resulting in retinal ganglion cell death, which affects approximately 68 million people worldwide. Risk factors include intraocular pressure (IOP), genetics, race, age, and vascular factors. Exercise is known to affect IOP and systemic cardiovascular factors and, therefore, may affect glaucoma pathophysiology. This review discusses the results of articles relevant to glaucoma, IOP, ocular blood flow (OBF), and exercise. Isometric and dynamic exercises have been studied with respect to effects on IOP and OBF. Isometric exercise results in an acute decrease in IOP, which correlates with hypocapnia. Dynamic exercise results in a more pronounced but also short duration decrease in IOP. Physical fitness is associated with lower baseline IOP but diminished acute IOP-lowering response to exercise. Upon cessation of exercise, values return to pretrained levels within 1 month. In glaucoma patients, these IOP-lowering effects are greater than in healthy subjects. In healthy subjects, OBF is unchanged during exercise due to vascular autoregulation. This autoregulation fails at ocular perfusion pressures greater than 70% above baseline. In conclusion exercise in glaucoma patients results in acutely lowered IOP and lower baseline IOP. The effects of exercise on the prevention of glaucoma and glaucomatous progression remain unknown. The role of exercise in glaucoma management should be investigated.
 ...
PMID:Effects of exercise on intraocular pressure and ocular blood flow: a review. 1968 49

Severe, short-term decreases in alveolar Pco2 acutely lower intraocular pressure (IOP). We wondered if less severe, physiologically relevant Pco2 reductions would also lower ocular tension and if this effect would persist in the longer term. To investigate the acute influence of small Pco2 changes on IOP, 11 healthy persons hyperventilated to reduce end-tidal Pco2 by first 10% (5 min) and then 20% (5 min). IOP fell when Pco2 fell 20% (14.5 +/- 2.1 mm Hg vs, 16.8 +/- 1.0 in a matched control series; p < 0.05) and remained depressed 20 min after Pco2 had returned to baseline levels. To investigate the persistence over time of this hypocapnia-associated IOP reduction, nine healthy persons hyperventilated to reduce end-tidal Pco2 by 15% for 1 h. IOP was substantially reduced by 30 min (11.7 +/- 0.5 vs. 14.8 +/- 0.6 mm Hg; p < 0.05) and at 60 min (11.2 +/- 0.7 vs. 14.2 +/- 0.6 mm Hg; p < 0.05) of sustained hypocapnia. In contrast, when the effects of acute hypocapnia were compared with standard nonselective beta-adrenergic blockade (levobunolol HC1, 1 drop 0.5% solution instilled 12 and 2 h before study; N = 7 normals), a 20% Pco2 reduction was less effective in lowering IOP than was drug treatment, and induction of hypocapnia failed to alter IOP after drug treatment [baseline IOP 14.4 +/- 1.3 mm Hg vs. 10.0 +/- 1.6 mm Hg after levobunolol (p < 0.05) and 10.7 +/- 1.9 mm Hg after hypocapnia and levobunolol were combined]. In addition, 3 days' treatment with the ventilatory stimulant drug medroxyprogesterone acetate (150 mg/day in 10 men, initial IOP </= 18 mm Hg) significantly elevated ventilation and lowered Pco2 but failed to change IOP. We conclude that although IOP is clearly linked to Pco2 in the short term, manipulation of Pco2, either alone or in combination with drug therapy, may not be an effective means for long-term IOP reduction.
 ...
PMID:Ocular hypotension during short- and long-term hypocapnia. 1992 Jun 1