Tonometric Parameters Research Articles

The choice of IOP measurement method for assessing the effectiveness of glaucoma surgery

Purpose of this study — to compare the results of different tonometry methods before surgical treatment of glaucoma and in the early postoperative period.The study was conducted on a group of 50 patients (50 eyes) aged 55 to 80 years with uncompensated primary open-angle glaucoma, who were admitted to in-patient department for glaucoma surgery. Patients were examined using bidirectional applanation tonometry of the cornea performed on Ocular Response Analyzer, pneumotonometry on Canon TX-20P device, and with Icare tonometer. These studies were carried out on the day before the surgery, the next day, and 2 weeks after the operation.Significant differences in tonometry readings were revealed between all tested devices at high intraocular pressure (IOP) levels (before glaucoma surgery). Significant differences were also found in IOP values obtained with Icare tonometer in the central zone of the cornea and in the middle periphery in the nasal and temporal sectors. A significant difference between the indicators remained on the next day after surgery, except for the Icare readings. After two weeks, the tonometric parameters did not differ significantly from each other.Corneal compensated IOP (IOPcc) is the most important tonometric indicator in clinical practice because it takes into account the individual biomechanical characteristics of the patient’s cornea. When examining patients with glaucoma, the IOPcc indicator significantly differed in uncompensated IOP, which is important for determining the correct treatment tactics. When assessing the level of IOP after surgery this trend persisted, indicating a systematic underestimation of IOP level (overestimation of the effect of glaucoma surgery). The reliability of the study is confirmed by the results of measurements on unoperated fellow eyes (control).

Pathophysiological characteristics of the development of arterial hypertension in Yorkshire Terriers with alimentary obesity

Relevance.The study of the pathogenesis of obesity in domestic animals is an urgent problem in veterinary medicine, which is associated with the high prevalence of this pathological condition and a significant risk of complications from the cardiovascular system. The aim of the study was to present the pathophysiological characteristics of the development of arterial hypertension syndrome in obesity in Yorkshire Terrier dogs.Methods.In a comparative aspect, clinical, tonometric, electrocardiographic, echocardiographic and biochemical parameters were studied in obese patients (n = 13) and clinically healthy dogs (n = 7).Results.Our study shows the negative role of obesity in the development of arterial hypertension syndrome in Yorkshire Terrier dogs. It was also found that obesity in dogs is accompanied by impaired lipid metabolism, oxidative stress, the development of arterial hypertension and a tendency to the development of concentric hypertrophy of the left ventricular myocardium and hepatopathy.

Performance Investigation of a Wearable Distributed-Deflection Sensor in Arterial Pulse Waveform Measurement

This paper presents a performance investigation of a wearable distributed-deflection sensor in arterial pulse waveform measurement. Built on a flexible substrate, the sensor entails a polymer microstructure embedded with an electrolyte-enabled resistive transducer array. By pressing the sensor against an artery with hold-down pressure exerted by two fingers, the pulse signal from the artery deflects the microstructure and registers as a resistance change by the transducer at the artery site. The radial and carotid pulse signals of five subjects are recorded via the sensor. Related signal-processing algorithms are written in Matlab to remove motion artifacts from a recorded pulse signal, extract its key tonometric parameters, and calculate the Pulse Wave Velocity (PWV) and radial and carotid Augmentation Index (AI). Whereas the tonometric parameters of the measured radial and carotid pulse waveforms on each subject are consistent with the related findings in the literature, the difference in tonometric parameters among the subjects also reveals physiological significance. The measured PWV and radial and carotid AI of the subjects show good agreement with how they should vary with age, gender and hypertension. Finally, the effect of the hold-down pressure on a measured pulse signal and the repeatability of the sensor are examined.

Prediction of poor graft function by means of gastric tonometry in patients undergoing liver transplantation

Introduction. Splanchnic hypoperfusion appears to play a key role in the failure of functional recovery of the graft after orthotopic liver transplantation (LT). The aim of this study was to determine if alterations of tonometric parameters, which are related to splanchnic perfusion, could predict poor graft function in patients undergoing LT.Materials and methods: After Ethics Committee approval, 68 patients undergoing LT were enrolled. In all the patients, regional-arterial CO2 gradient (Pr-aCO2) was recorded; in addition, the difference between Pr-aCO2 recorded at anhepatic phase (T1) and at the end of surgery (T2) (T2- T1 = ΔPr-aCO2) was calculated. Poor graft function was determined on the basis of Toronto’s classification 72 hours after LT. Student t-test and logistic regression analysis were used for statistical purpose.Results. ΔPr-aCO2 was significantly greater in patients with poor graft function (3.5 ± 13.2) compared to patients with good graft function (−5.8 ± 12.3) (p = 0.014). The logistic regression analysis showed that the ΔPr-aCO2 was able to predict the onset of poor graft function (p = 0.037). A value of ΔPr-aCO2 ≥ −4 was associated with poor graft function with a sensibility of 93.3% and a specificity of 42.3%.Conclusion. Our study suggests that the change of Pr-aCO2 may be a valuable index of graft dysfunction. Gastric tonometry might give early prognostic information on the graft outcome, and it may aid clinicians in planning a more strict follow-up and proper interventions in order to improve graft survival.

Effect of intraoperative dobutamine on splanchnic tissue perfusion and outcome after Whipple surgery

PurposeSplanchnic hypoperfusion during abdominal surgery contributes to postoperative gut sepsis and mortality. Dobutamine is an inotrope with vasodilator properties that improve hepatosplanchnic perfusion. The aim of this study was to examine the effect of intraoperative dobutamine infusion during Whipple surgery on splanchnic perfusion, hemodynamic, and overall postoperative outcome. MethodsSixty patients were randomly allocated to receive intraoperatively (3 μg/kg per minute or 5 μg/kg per minute) doses of dobutamine or saline. Baseline measurements included hemodynamic parameters, gastric tonometric parameters, and arterial and mixed venous gases. These patients had a follow-up for development for in-hospital morbidity and mortality. ResultsIntraoperative use of dobutamine increased oxygen-derived parameters as evidenced by increased mixed venous oxygen saturation. Tonometered gastric mucosal pH, a surrogate for splanchnic perfusion, increased in patients who received intraoperative dobutamine. Patients in the dobutamine groups demonstrated significant higher heart rates, premature ventricular contraction arrhythmias, and electrocardiographic signs of ischemia. Mean arterial blood pressure demonstrated no significant difference among groups. The overall incidence of postoperative complications was higher in control group 70 % vs 20% to 40% in dobutamine groups. ConclusionIntraoperative use of dobutamine improved global oxygen delivery, splanchnic perfusion, and postoperative outcome after Whipple surgery. These findings may be of clinical importance when the therapeutic goal is to improve gut perfusion.

The Relationship between Resistant Hypertension and Arterial Stiffness

Objectives: With growing awareness of arterial stiffness (AS) in the past 10 years, it was realized that resistant hypertension (RH) and AS share the same associated conditions such as older age, isolated systolic hypertension (HT), obesity, chronic kidney disease (CKD), and so on. Until now, there is no study investigating the role of AS in RH. In our study we aimed to determine whether there is an association between RH and AS. Methods: Among 87 patients enrolled in this study, 30 were resistant hypertensives (Group 1), 29 were controlled hypertensives (Group 2), and 28 were normotensives (Group 3). Arterial stiffness was measured by both applanation tonometry and echocardiography; augmentation index, pulse wave velocity (PWV), aortic strain, and aortic distensibility were recorded in each patient. Diastolic function parameters were also assessed. Results: In resistant hypertensive group, augmentation index and PWV were significantly higher than Group 2 and Group 3 (P = .03 and P < .01). Aortic strain and aortic distensibility parameters were significantly lower in RH group (P < .01 and P < .01). Arterial stiffness parameters were similar among Group 2 and Group 3. Among diastolic function parameters, left atrial volume index and left ventricular mass index significantly differ between groups. These two parameters were significantly lower in control group (P < .01 and P = .02) whereas similar in Group 1 and Group 2. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels were significantly different between groups as expected. When the correlation between two methods of AS was analyzed, a significant strong inverse correlation was found between echocardiographic and tonometric parameters. Conclusion: Arterial stiffness was found to be associated with RH. The inconsistency of this association in controlled hypertensives suggests a possible role of AS in RH pathogenesis. This study also showed that aortic strain and distensibility correlate well with the PWV which is the gold standard in the assessment of AS. This finding is important for the evaluation of AS more commonly in daily practice as echocardiography is a more feasible device than applanation tonometry.

Bench-to-bedside review: Is there a place for epinephrine in septic shock?

The use of epinephrine in septic shock remains controversial. Nevertheless, epinephrine is widely used around the world and the reported morbidity and mortality rates with it are no different from those observed with other vasopressors. In volunteers, epinephrine increases heart rate, mean arterial pressure and cardiac output. Epinephrine also induces hyperglycemia and hyperlactatemia. In hyperkinetic septic shock, epinephrine consistently increases arterial pressure and cardiac output in a dose dependent manner. Epinephrine transiently increases lactate levels through an increase in aerobic glycolysis. Epinephrine has no effect on splanchnic circulation in dopamine-sensitive septic shock. On the other hand, in dopamine-resistant septic shock, epinephrine has no effect on tonometric parameters but decreases fractional splanchnic blood flow with an increase in the gradient of mixed venous oxygen saturation (SVO2) and hepatic venous oxygen saturation (SHO2). In conclusion, epinephrine has predictable effects on systemic hemodynamics and is as efficient as norepinephrine in correcting hemodynamic disturbances of septic shock. Moreover, epinephrine is cheaper than other commonly used catecholamine regimens in septic shock. The clinical impact of the transient hyperlactatemia and of the splanchnic effects are not established.

Characterization of the pupil light reflex, electroretinogram and tonometric parameters in healthy mouse eyes

Purpose. To characterize the pupil light reflex (PLR), electroretinographic (ERG) and tonometric parameters which might be of importance for the in vivo characterization of mouse models of chronic ocular hypertension. Methods. C57/BL6 mice were used for experiments. The PLR was evaluated with a computerized pupillometer (n = 14), ERGs were recorded simultaneously from both eyes (n = 23) and IOP was measured with a modified Goldmann tonometer (n = 23). Results. The analysis of the PLR parameters confirmed the consensual PLR did not have significantly different amplitude (p > 0.1) and latency time (p > 0.1) compared to the direct PLR. However, PLR velocity (p = 0.004) was significantly smaller in the consensual PLR. Electroretinography revealed a-wave amplitude of 168.3 ± 9.6µV with latency of 27.5 ± 0.6 ms and b-wave 403 ± 28.8µV with latency of 22.7 ± 0.6 ms. The flicker ERG recording revealed amplitudes of 20.6 ± 2.4µV. Tonometry experiments revealed that modified Goldmann tonometer measurements correlated well with invasive manometry (r 2 = 0.89). The mean IOP of the mouse was 15.3 ± 0.6mmHg. Conclusions. Consensual PLR in mice is relatively slower than the direct PLR, but retains the same degree of constriction comparing to the direct PLR. A modified Goldmann tonometer seems to be a reliable non-invasive tool for IOP measurements in mice.

Dobutamine and gastric-to-arterial carbon dioxide gap in severe sepsis without shock

To evaluate the effect of an early dobutamine infusion on gastrointestinal perfusion in patients with severe sepsis. Prospective, randomized, controlled, multicenter clinical study. Six medical and/or surgical intensive care units (ICU) of teaching hospitals. Forty-two patients with severe sepsis. Patients were divided into two groups according to gastric-to-arterial CO2 gap (DeltaCO2) [normal DeltaCO2 group ( n=17): DeltaCO2 < or = 8 mmHg; increased DeltaCO2 group ( n=25): DeltaCO2 > 8 mmHg]. Patients within each group were then randomized to receive either dobutamine (5 microg/kg per min) or saline for 72 h. SAPS II was similar in both groups [group 1: 44.0 (33.0-56.5); group 2: 48.5 (40.5-59.0), p=0.27]. At ICU admission, mean arterial pressure was lower in the high DeltaCO2 group [73.0 (67.0-79.5) mmHg, p=0.03] than in the normal DeltaCO2 group [84.0 (73.7-104.0) mmHg] while blood lactate [normal DeltaCO2 group: 1.6 (0.8-2.3); high DeltaCO2 group: 1.6 (1.1-1.9) mmol/l] was similar for the two groups. DeltaCO2 was significantly lower in the normal DeltaCO2 group [5.0 (2.0-6.0) mmHg)] than in the high DeltaCO2 group [11.0 (10.0-19.0) mmHg]. Dobutamine infusion did not significantly change hemodynamics, blood lactate concentration or tonometric parameters in any group within the first 72 h and had no particular beneficial effect in this population. An early infusion of dobutamine at a fixed dose of 5 microg/kg per min during the first 72 h of severe sepsis does not influence gastric DeltaCO2.

Characterization of the pupil light reflex, electroretinogram and tonometric parameters in healthy rat eyes

Purpose. To characterize the pupil light reflex (PLR), electroretinographic (ERG) and tonometric parameters in healthy rat eyes. Methods. Brown Norway rats were used for experiments. The PLR was evaluated with a computerized pupillometer (n = 27), ERGs were recorded simultaneously from both eyes (n = 27) and IOP was measured with a Tonopen (n = 15). Results. The analysis of the PLR parameters confirmed that the consensual PLR had a significantly smaller amplitude (0.1-0.2mm; p = 0.03) and an increased latency time (p = 0.001) compared to the direct PLR. Electroretinography revealed an a-wave amplitude of 207.2 ± 13 µV with a latency of 25.6 ± 0.7 ms, and a b-wave 554.3 ± 24.5 µV with a latency of 21.4 + 1.8 ms. The flicker ERG recording revealed amplitudes of 40.6 ± 2.4 µV. Tonometry measurements revealed that isoflurane, but not halothane, anesthesia suppressed the IOP (non-anesthetized: 25.3 ± 1.0 mmHg; 1 % halothane + 30% NO: 26.2 ± 1.1 (p > 0.1); 1 % isoflurane + 30 % NO: 20.1 + 1.6 (p < 0.05)). Conclusions. Consensual PLR in rats has a relative deficit compared to the direct PLR. Isoflurane anesthesia has a suppressive effect on the IOP in healthy rat eyes.

Directly measured tissue pH is an earlier indicator of splanchnic acidosis than tonometric parameters during hemorrhagic shock in swine

To compare tissue pH in the stomach, bowel, and abdominal wall muscle during hemorrhagic shock and recovery using tissue electrodes; also, to compare tissue electrode pH measurements to gastric intramucosal pH (pHi), gastric luminal PCO2, and PCO2 gap (gastric luminal CO2--arterial CO2) measured with an air-equilibrated tonometer. Prospective animal study. University animal research laboratory. Eight anesthetized, mechanically ventilated Yorkshire swine. Hemorrhagic shock was initiated by withdrawing blood over a 15-min period to lower systolic blood pressure to 45 mm Hg. Shock was maintained for 45 mins and was followed by a 5-min resuscitation to normal blood pressure with a blood/lactated Ringer's (1:2) mixture. Recovery was monitored for 60 mins. pH was measured with electrodes in the submucosa of the stomach, the submucosa of the small bowel, and the abdominal wall muscle. Gastric luminal PCO2 was measured with an air-equilibrated tonometer and pHi and PCO2 gap were calculated. Each organ showed a different sensitivity to shock and resuscitation. The bowel pH responded most rapidly to the onset of hemorrhagic shock and had the largest change in tissue pH. The bowel also showed the most rapid recovery during resuscitation. The submucosal pH of the stomach responded more slowly than the bowel, but faster than the abdominal wall muscle pH, gastric PCO2 gap, or pHi. The smallest changes in organ pH as a result of hemorrhagic shock were seen in the abdominal wall muscle and the stomach as assessed by gastric tonometry. Direct measurement of tissue pH indicates that intra-abdominal organ pH varies during hemorrhagic shock. The small bowel pH changes the most in magnitude and rapidity compared with stomach pH or abdominal wall muscle pH. Tonometrically derived parameters were not as sensitive in the detection of tissue acidosis during shock and resuscitation as pH measured directly in the submucosa of the stomach or small bowel.

Comparison of norepinephrine and dobutamine to epinephrine for hemodynamics, lactate metabolism, and gastric tonometric variables in septic shock: a prospective, randomized study

To compare the effects of norepinephrine and dobutamine to epinephrine on hemodynamics, lactate metabolism, and gastric tonometric variables in hyperdynamic dopamine-resistant septic shock. A prospective, intervention, randomized clinical trial. Adult medical/surgical intensive care unit in a university hospital. 30 patients with a cardiac index (CI) > 3.51 x min(-1) x m(-2) and a mean arterial pressure (MAP) < or = 60 mmHg after volume loading and dopamine 20 microg/kg per min and either oliguria or hyperlactatemia. Patients were randomized to receive an infusion of either norepinephrine-dobutamine or epinephrine titrated to obtain an MAP greater than 80 mmHg with a stable or increased CI. Baseline measurements included: hemodynamic and tonometric parameters, arterial and mixed venous gases, and lactate and pyruvate blood levels. These measurements were repeated after 1, 6, 12, and 24 h. All the patients fulfilled the therapeutic goals. No statistical difference was found between epinephrine and norepinephrine-dobutamine for systemic hemodynamic measurements. Considering metabolic and tonometric measurements and compared to baseline values, after 6 h, epinephrine infusion was associated with an increase in lactate levels (from 3.1 +/- 1.5 to 5.9 +/- 1.0 mmol/l;p < 0.01), while lactate levels decreased in the norepinephrine-dobutamine group (from 3.1 +/- 1.5 to 2.7 +/- 1.0 mmol/l). The lactate/pyruvate ratio increased in the epinephrine group (from 15.5 +/- 5.4 to 21 +/- 5.8; p < 0.01) and did not change in the norepinephrine-dobutamine group (13.8 +/- 5 to 14 +/- 5.0). Gastric mucosal pH (pHi) decreased (from 7.29 +/- 0.11 to 7.16 +/- 0.07; p < 0.01) and the partial pressure of carbon dioxide (PCO2) gap (tonometer PCO2-arterial PCO2) increased (from 10 +/- 2.7 to 14 +/- 2.7 mmHg; p < 0.01) in the epinephrine group. In the norepinephrine-dobutamine group pHi (from 7.30 +/- 0.11 to 7.35 +/- 0.07) and the PCO2 gap (from 10 +/- 3.0 to 4 +/- 2.0 mmHg) were normalized within 6 h (p < 0.01). The decrease in pHi and the increase in the lactate/pyruvate ratio in the epinephrine group was transient, since it returned to normal within 24 h. Considering the global hemodynamic effects, epinephrine is as effective as norepinephrine-dobutamine. Nevertheless, gastric mucosal acidosis and global metabolic changes observed in epinephrine-treated patients are consistent with a markedly inadequate, although transient, splanchnic oxygen utilization. The metabolic and splanchnic effects of the combination of norepinephrine and dobutamine in hyperdynamic dopamine-resistant septic shock appeared to be more predictable and more appropriate to the current goals of septic shock therapy than those of epinephrine alone.

Optic disc interpretation in glaucoma: is confidence misplaced?

A photographic questionnaire has been used to investigate whether or not clinicians have realistic expectations of their ability to distinguish optic discs associated with glaucomatous visual field loss from discs of healthy eyes. The questionnaire consisting of 30 non-stereoscopic fundus photographs from 15 patients was administered to 40 ophthalmologists of varying experience and 10 optometrists. Each group displayed large discrepancies between their expected and achieved scores suggesting that clinicians may overestimate their ability to recognize the glaucomatous optic disc. This could lead to diagnostic errors especially in cases where tonometric and visual field parameters are considered equivocal. An over-reliance on the cup/disc ratio appeared to be the most likely cause of error.