Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of isoflurane and halothane on intraocular pressure (IOP) were studied in 28 children. Measurements were made during spontaneous ventilation and at a various levels of reduced PaCO2 achieved by controlled ventilation. Control IOP values were determined prior to anesthesia following premedication with chloral hydrate, pentobarbital, pentobarbital with meperidine. At roughly equivalent levels of anesthesia, mean IOP values during spontaneous ventilation ranged frm 16.3 to 17.6 torr for each anesthetic. These values were significantly less (P less than 0.01) than control values only in those patients receiving chloral hydrate who did not cooperate. In contrast, no significant change in IOP was found in more sedated and cooperative patients who received pentobarbital and meperidine. Moderate hypocarbia and hypercarbia over a range of PaCO2 greater than 42 torr had little influence on IOP. We conclude that IOP's during isoflurane and halothane anesthesia do not differ significantly from IOP in the sedated, cooperative, healthy pediatric patient.
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PMID:Intraocular pressures in children during isoflurane and halothane anesthesia. 111 65

There appear to be 3 factors in the development of papilloedema - an arterial shunt to the prelaminar tissue and a raised venous pressure in the absence of a raised intraocular pressure, which are passive effects, and an overspill of pial autoregulative vasodilatation which is not passive. In addition the arterial shunt may lead to excessive local autoregulative effects. The engorgement of the fine vessels of the prelaminar tissue, the loss of the spontaneous venous pulse on the disc and the venous overfilling are thought to indicate increased supply and blood flow rather than the reverse. The other general causes of papilloedema can also be explained by the autoregulative mechanism or its breakdown as they involve hypercapnia, tissue anoxia or severe hypertension.
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PMID:Pathogenesis of papilloedema. 126 65

The ocular hypertension caused by the mu agonist alfentanil (10 micrograms/kg, i.v.) in spontaneously breathing rabbits was reversed to ocular hypotension by pretreatment with the kappa agonist-mu antagonist, nalbuphine (0.6 mg/kg, i.v.). This is probably due to nalbuphine's mu antagonistic action which prevents the respiratory-depressant effect of alfentanil that elevates the blood pCO2 with a drop in blood pH. It is known that hypoxia and hypercarbia lead to uveal vasodilation and increase in aqueous production which cause elevation of intraocular pressure. Both alfentanil and nalbuphine have miotic effects when used individually. However, no further reduction in the pupil size was noted by their combined use. These results indicate that using nalbuphine and alfentanil together may be considered a safe combination for eye surgery because it preserves the analgesic effect of either drug while prevents the undesirable respiratory-center depression and the ocular hypertension observed with alfentanil alone.
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PMID:Interaction between nalbuphine and alfentanil on intraocular pressure and pupil size of conscious rabbits. 249 54

This study summarizes our results with various ataralgesic combinations and their effects on circulation and respiration. Together with the new water-soluble 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine midazolam, Ro 21-3981, Dormicum), 7-chloro-1,3-dihydro-1-methyl-5-phenyl-(2H)1,4-benzodiazepin-2-one (diazepam) and 5-(o-fluorophenyl)-1,3-dihydro-1-methyl-7-nitro-2H-1,4-benzodiazepin-2-one (flunitrazepam) are also considered, for the purpose of comparison. Pharmacokinetic studies confirm the clearly shorter duration of action of midazolam. The poor respiratory depressant action of the benzodiazepines can be easily and rapidly increased by premedication, ataralgesic combinations and substances for the prolongation of anaesthesia. Adequate spontaneous respiration is possible only in exceptional cases. The threshold doses for 100% suppression of cardiac stimulation due to 2-(o-chlorophenyl)-2-methylaminocyclohexanone (ketamine) were determined for all three benzodiazepines. These doses are also valid for hypertension. The effect of intubation is not suppressed by the ataralgesic combination alone, whereas it does suppress the increase in pressure in the pulmonary circulation which is synchronous with the systemic blood pressure. The rise in intracranial pressure following ketamine alone is also prevented by premedication with benzodiazepines, which on the other hand offer no protection against certain other effects (hypoxia, hypercapnia, intubation), The same is true for increases in intraocular pressure. According to the results of investigations carried out, the new benzodiazepine midazolam justifies our hope for a substance with a similar basic effect, but with a clearly improved pharmacokinetic profile.
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PMID:[Cardiocirculatory and respiratory effects of the combination of midazolam and ketamine]. 719 33

Thick, 0.34 mm, 38% water hydrogel lenses were fitted, under a pressure patch, to one eye of 18 type I diabetic patients (aged 18-40 years) to assess the acute response to hypoxia and hypercapnia; the response was compared with that in 18 healthy, aged-matched non-diabetic subjects; the closed-eye lens wear was started mid-morning. Pre-lens wear assessments were made of acuity, intraocular pressure (IOP), central corneal thickness (CCT) and corneal appearance by biomicroscopy. The mean duration of the diabetes was 13 +/- 7 years and the average fasting blood glucose was 8.7 +/- 3.3 mMl-1. Baseline CCT values were marginally greater in diabetic patients (600 +/- 33 microns) compared with a group of non-diabetic control subjects (584 +/- 26 microns; P > 0.5). A 7.7 +/- 2.1% increase in CCT was measured after 3 h lens wear in the diabetic patients while an average 10.6 +/- 2.4% increase in CCT was measured in the control subjects (P < 0.05). The recovery of corneal thickness to baseline values in diabetic patients was slower (at 44.8 +/- 2.0% per hour) than the control subjects (53.9 +/- 2.1 per hour; P < 0.05) although recovery of corneal thickness occurred in both groups within 2.5-3h. IOP values (non-contact tonometry) were higher in the diabetic patients than in the controls (14.5 +/- 2.9 vs 12.4 +/- 1.7 mmHg; P < 0.01). Overall, those corneas with greater baseline CCT values tended to swell less than those with lower baseline CCT values (r = 0.582). Positive correlations were also found between corneal thickness and IOP and blood glucose. The diabetic patients thus tended to have slightly thicker corneas (but this could be related to blood glucose or IOP rather than true corneal disease) and also had corneas that tended to swell less with a contact lens stress test (but this could be constitutively due to the slight oedema already present). The different corneal response in diabetic patients may thus be the result of physical determinants such as initial oedema and IOP and not the result of a disease of the cornea itself.
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PMID:Corneal swelling and recovery following wear of thick hydrogel contact lenses in insulin-dependent diabetics. 766 21

Fenoldopam (FE), a dopamine DA1-receptor agonist, has been introduced for treatment of arterial hypertension and heart failure and for preservation of renal function. Vasodilators are generally assumed to affect all vascular beds including the cerebral circulation. We have evaluated effects of FE-induced (4 micrograms.kg-1.min-1) arterial hypotension on intracranial pressure (ICP) and intraocular pressure (IOP) under conditions of normal and increased intracranial elastance. ICP and IOP responses to hypertension were tested by infusion of angiotensin II (15 micrograms.kg-1.min-1), and the response to hypercapnia was tested by elimination and reintegration of soda lime canisters in the breathing circuit. Intracranial elastance was increased by infusing mock cerebrospinal fluid (CSF) into the lateral ventricle (20 +/- 3 ml.h-1). Arterial hypotension induced with FE did not increase ICP. With increased intracranial elastance, the infusion rate of mock CSF had to be reduced while administering FE to avoid a rise in ICP (p < 0.05 compared with preinfusion value); this indicates a shift on the volume-pressure curve to the right. There were no indicators that cerebral autoregulation or CO2 reactivity of the cerebral vasculature were affected by FE in this anesthetized porcine model, as speculated from analysis of the time course of delta ICP. There are, however, indicators of increased intracranial elastance, most likely caused by vasodilation. Caution should hence be exercised when FE is administered to patients with increased intracranial elastance.
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PMID:Effects of fenoldopam on intracranial pressure and hemodynamic variables at normal and elevated intracranial pressure in anesthetized pigs. 791 22

The aim of the study was to evaluate whether the Heidelberg retina flowmeter (HRF), a new device for retinal and anterior optic nerve blood flow assessment, can gauge, at least semiquantitatively, a known effect such as an increase in optic nerve blood flow by hypercapnia or a decrease in optic nerve blood flow by hyperoxia or high intraocular pressure (IOP). Measurements with the HRF were obtained at the papilla of three groups of 5 young healthy subjects (1) at baseline and after breathing 5% carbogen, (2) at baseline and after breathing 100% oxygen and (3) at baseline and after increasing IOP to 20 and 50 mm Hg. The changes in the value of the HRF parameter 'flow' were analyzed by means of a paired Student's t test. Breathing 100% oxygen for 7 min resulted in a statistically significant decrease of 34.7+/-2.5% (mean+/-SEM) in HR parameter 'flow' (p < 0.01) at the papilla. Breathing 5% carbogen for 7 min resulted in a statistically significant increase of 18.3+/-2.6% in HRF parameter 'flow' (p = 0.024). Increasing IOP to 20 mm Hg did not result in a statistically significant change in HRF parameter 'flow' (-9.6+/-7.4%; p = 0.13). Increasing IOP from 20 to 50 mm Hg, however, resulted in a statistically significant decrease of 40.1+/-6.6% in HRF parameter 'flow' (p = 0.003). With the applied stimuli, the HRF parameter 'flow' changed in the expected direction, i.e. an increase with hypercapnia and a decrease with hyperoxia or high IOP. The simplicity of use of the HRF instrument suggests that it might be well suited for a non-invasive, at least semiquantitative, assessment of changes in blood flow at the papilla.
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PMID:Effect of carbogen, oxygen and intraocular pressure on Heidelberg retina flowmeter parameter 'flow' measured at the papilla. 956 85

We evaluated the retrobulbar response to a selective versus nonselective beta blocker in a subgroup of primary open-angle glaucoma patients (POAG) characterized by ocular vasospasm. Eleven patients who exhibited ocular vasospasm (i.e. a significant increase in ophthalmic artery blood flow velocity or a significant decrease in ophthalmic artery resistance index during hypercapnia) underwent medication washout for 4 weeks and were enrolled in a double-masked cross-over study (betaxolol versus timolol). Patients were evaluated for blood flow velocity of the retrobulbar vessels using color Doppler imaging, intraocular pressure, visual field sensitivity and contrast sensitivity at the beginning and end of each 4 week treatment period. Timolol treatment caused a significant reduction in IOP (p = .007), but no change in retrobulbar hemodynamics or visual function. After betaxolol treatment, resistance index fell significantly (p = .040) in the ophthalmic artery and increased significantly in both the central retinal (p = .003) and temporal posterior ciliary arteries (p = .030). Also following betaxolol treatment, contrast sensitivity improved significantly (p = .006), and a significant positive correlation was shown between change in contrast sensitivity and change in resistance index (r = .70; p = .015) of the ciliary arteries. POAG patients characterized by ocular vasospasm display a significant hemodynamic response to betaxolol, but not to timolol.
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PMID:Primary open-angle glaucoma patients characterized by ocular vasospasm demonstrate a different ocular vascular response to timolol versus betaxolol. 1060 70

The autoregulatory capacity of the human retina is well documented, but the pressure-flow relationship of the human choroid is still a matter of controversy. Recent data, using laser Doppler flowmetry to measure choroidal blood flow, indicate that the choroid has some autoregulatory potential, whereas most data using other techniques for the assessment of choroidal hemodynamics indicate that the choroidal pressure-flow curve is linear. We used a new laser interferometric technique to characterize choroidal blood flow during isometric exercise. Twenty healthy subjects performed squatting for 6 min during normocapnia and during inhalation of 5% CO2 and 95% air. Ocular fundus pulsation amplitude, flow velocities in the ophthalmic artery, intraocular pressure, and systemic hemodynamics were measured in 2-min intervals. To gain information on choroidal blood flow fundus pulsation amplitude was corrected for changes in flow pulsatility using data from the ophthalmic artery and for changes in pulse rate. Ocular perfusion pressure was calculated from mean arterial pressure and intraocular pressure. The ocular pressure-flow relationship was calculated by sorting data according to ascending ocular perfusion pressure values. In a pilot study in 6 healthy subjects comparable ocular pressure flow relationships were obtained when choroidal blood flow was assessed with the method described above and with laser Doppler flowmetry. In the main study isometric exercise caused a significant increase in mean arterial pressure (56%, P < 0.001), pulse rate (84%, P < 0.001), and intraocular pressure (37%, P 0.004), but decreased fundus pulsation amplitude (-36%, P < 0.001). Significant deviations from baseline choroidal blood flow were observed only at ocular perfusion pressures >69% during normocapnia and 70% during hypercapnia. Our data indicate that during isometric exercise the choroid has a high capacity to keep blood flow constant despite changes in perfusion pressure and that this pressure-flow relationship is not altered by moderate changes in arterial carbon dioxide levels.
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PMID:Ocular hemodynamics during isometric exercise. 1116 91

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.
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PMID:Retinal and choroidal vasoreactivity to altered PaCO2 in rat measured with a modified microsphere technique. 1842 Jan 96


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