Measurement of the retinal venous pressure with a new instrument in healthy subjects

Background The retinal venous pressure (RVP) is a determining factor for the blood supply of the retina as well as the optic nerve head and until recently has been measured by contact lens dynamometry (CLD). A new method has been developed, potentially offering better acceptance. The applicability and the results of both methods were compared. Methods The type of this study is cross sectional. The subjects were 36 healthy volunteers, age 26 ± 5 years (mean ± s). Tonometry: rebound tonometer (RT) (iCare). The measurements were performed during an increase in airway pressure of 20 mmHg (Valsalva manoeuvre). Principle of RVP measurement: the central retinal vein (CRV) is observed during an increase of intraocular pressure (IOP) and at the start of pulsation, which corresponds with the RVP. Two different instruments for the IOP enhancement where used: contact lens dynamometry and the new instrument, IOPstim. Principle: a deflated balloon of 8 mm diameter—placed on the sclera laterally of the cornea—is filled with air. As soon as a venous pulsation occurs, filling is stopped and the IOP is measured, equalling the RVP. Examination procedure: randomization of the sequence: CLD or IOPstim, IOP, mydriasis, IOP three single measurements (SM) of the IOP with RT or of the pressure increase with CLD at an airway pressure of 20 mmHg, 5 min break, IOP, and three SM using the second method at equal pressure (20 mmHg). Results Spontaneous pulsation of the CRV was present in all 36 subjects. Pressures are given in mmHg. IOP in mydriasis 15.6 ± 3.3 (m ± s). Median RVP (MRVP)) of the three SM: CLD/IOPstim, 37.7 ± 5.2/24.7 ± 4.8 (t test: p < 0.001). Range of SM: 3.2 ± 1.8/2.9 ± 1.3 (t test: p = 0.36). Intraclass correlation coefficient (ICC) of SM: 0.88/0.83. ANOVA in SM: p = 0.48/0.08. MRVP CLD minus MRVP IOPstim: 13.0 ± 5.6. Ratio MRVP CLD/MRVP IOPstim: 1.56 ± 3.1. Cooperation and agreeability were slightly better with the IOPstim. Conclusion This first study with the IOPstim in humans was deliberately performed in healthy volunteers using Valsalva conditions. As demonstrated by ICC and ANOVA, reproducible SM can be obtained by both methods and the range of the SM does not differ greatly. The higher MRVP in CLD could be explained by the different directions of the force vectors.

Thyroid Storm: A Diagnostic Conundrum

Thyroid storm is a life threatening complication of hyperthyroidism which comes with multi-system involvement and is associated with a mortality of 8-25% despite modern advancements in treatment and supportive measures. A 47 year old woman with past medical history of hypertension and morbid obesity presented to the emergency room with 3 week history of shortness of breath and chest pain associated with productive cough, bilateral leg swelling, orthopnea and palpitations. Upon evaluation, she was in moderate respiratory distress, restless, tachypneic and tachycardic. She had bilateral proptosis and visible jugular venous pulsation along-with bibasilar crackles and pitting edema bilaterally. Lab tests revealed BNP 539 pg/ml and D-Dimer 6401 ng/ml. ECG showed atrial flutter, Chest X-Ray showed bilateral pleural effusions, and CT Chest was negative for pulmonary embolism but revealed anterior mediastinal mass, differential of which included thymoma or teratoma. She was admitted to CCU for aggressive diuresis, control of heart rate and was started on anticoagulation. A review of medical records from outside hospital revealed patient was hyperthyroid 8 months ago, however, was not on any medications. Given a Burch-Wartofsky score &gt;70, she was started on IV hydrocortisone and cholestyramine for severe thyrotoxicosis. Endocrinology was consulted and added PTU to management. TFTs revealed a TSH 0.006 IU/ml, FT4 4 ng/dL and T3 2.5 ng/ml. Bedside ECHO showed LVEF of 14% with global hypokinesis and thyroid ultrasound revealed an enlarged, heterogenous thyroid with a solid, isoechoic, calcified left lobe nodule measuring 0.8 x 0.4 x 0.5 cm. Her serum TSI and thyrotropin receptor antibodies were elevated at 17.20 IU/L and 20.20 IU/L, respectively. She responded to treatment and was discharged on metoprolol, losartan, spironolactone, and furosemide for new-onset heart failure, apixaban for atrial flutter, and PTU and cholestyramine for hyperthyroidism, with Cardiology and Endocrinology follow-ups. Thyroid disease is a common illness affecting 9 to 15 percent of the adults. Thyrotoxicosis refers to the clinical syndrome of hyper-metabolism due to excessive amount of circulating thyroid hormones. The incidence of thyroid storm is 0.57 to 0.76 per 100,000 people per year in the US. It most commonly occurs in women and is more common in patients with underlying Grave’s Disease. The exact underlying mechanism that leads to thyroid storm is not well understood but adrenergic activation seems to have a major role. Our patient had long standing untreated hyperthyroidism with a solid nodule which led to the crisis. The most common cause of death is cardiopulmonary failure and hence treatment should be initiated as soon as diagnosis is suspected owing to high mortality. Awareness of thyroid pathology affecting the heart is important to remember in evaluating the etiology of heart failure in patients.

Evaluation of spontaneous retinal venous pulsation in primary open-angle and primary angle-closure glaucoma patients

Introduction: Spontaneous retinal venous pulsation (SRVP) is a rhythmic variation in the calibre of one or more retinal veins. The incidence of SRVP was reduced in glaucoma patients. It was also reduced in people with raised intracranial pressure compared to a healthy population. Purpose: The main objective was to report the frequency and rate of SRVP in primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG) patients and to associate these with the severity of glaucoma in Malay patients. Design of study: A comparative cross-sectional study. Materials and methods: A comparative cross-sectional study involving primary glaucoma patients attending the eye clinic at Hospital Universiti Sains Malaysia (HUSM), Kelantan, Malaysia, was performed between December 2015 and June 2017. The main outcomes measured were the presence and rate of SRVP using a confocalscanning laser ophthalmoscope (Spectralis High-Resolution Optical Coherence Tomography Angiography, Heidelberg Engineering GmbH, Heidelberg, Germany). In the presence of SRVP, the rate of SRVP in one minute was counted manually based on the real-time fundus movie recorded using the confocal scanning laser ophthalmoscope. Results: Thirty-eight POAG, 14 PACG, and 51 control group subjects were included. There was a significantly lower incidence of SRVP in primary glaucoma patients than in the control group (p = 0.003). The presence of SRVP was significantly lower in POAG than PACG (p = 0.04). There was no significant difference in the rate ofSRVP between primary glaucoma patients and the control group (p = 0.873) or between the POAG group and PACG group (p = 0.511). There was no association of incidence (p = 0.574) and rate (p = 0.167) of SRVP according to the severity of glaucoma. Systolic blood pressure (95% CI: 0.95–1.00, p = 0.038) and retinal nervefibre layer thickness (95% CI: 1.01–1.09, p = 0.008) showed a significant association with the presence of SRVP. Conclusions: SRVP is a potential predictive factor for detection of primary glaucoma. The role of SRVP in the severity of glaucoma is still unclear. The role of SRVP in PACG patients warrants further studies in the future.

Analysis of Retinal Vessel Pulsations with Electrocardiographic Gating

Purpose The origin of retinal venous pulsations has been a matter of debate for some time. One classical explanation to the origin of these pulsations has been that the cardiac cycle induces systolic peaks in the intraocular pressure (IOP) which leads to decreases in retinal vein diameters. Recently, theoretical concepts have been published which postulate that IOP changes during the pulse cycle is not the primary driving force for venous pulsation, and hence, predict that the retinal vein diameter is indeed reduced during IOP diastole. The aim of the study was to test this hypothesis in a clinical trial. Subjects and Methods Continuous IOP and retinal vessel analyser (RVA) measurements were taken from 21 subjects, ages 20 to 30 years, with no known ophthalmologic diseases, while connected to a standard electrocardiograph (ECG). With this methodology, average and synchronised curves for the pulse cycle of IOP and retinal vessel pulsations were calculated for each subject. Each pulse cycle was standardised to 50 timepoints, which enabled direct phase shift comparisons. Results All subjects showed comparable results. Close to the optic disc (within 0 to 1.5 optic disc diameters away from the disc), retinal arteries led with the first peak at the 16/50 pulse cycle position, followed by IOP peak at the 23/50 cycle position, and then by veins at the 26/50 cycle position. Conclusion The present method indeed shows that retinal veins do not collapse when the IOP is highest, on the contrary, IOP and retinal vein diameters seem to be in phase, which lends support to the hypothesis that IOP is not the major driving force of the retinal vein pulsations.

Self-excited oscillations in a collapsible channel with applications to retinal venous pulsation

We consider a theoretical model for the flow of Newtonian fluid through a long flexible-walled channel which is formed from four compliant and rigid compartments arranged alternately in series. We drive the flow using a fixed upstream flux and derive a spatially one-dimensional model using a flow profile assumption. The compliant compartments of the channel are assumed subject to a large external pressure, so the system admits a highly collapsed steady state. Using both a global (linear) stability eigensolver and fully nonlinear simulations, we show that these highly collapsed steady states admit a primary global oscillatory instability similar to observations in a single channel. We also show that in some regions of the parameter space the system admits a secondary mode of instability which can interact with the primary mode and lead to significant changes in the structure of the neutral stability curves. Finally, we apply the predictions of this model to the flow of blood through the central retinal vein and examine the conditions required for the onset of self-excited oscillation. We show that the neutral stability curve of the primary mode of instability discussed above agrees well with canine experimental measurements of the onset of retinal venous pulsation, although there is a large discrepancy in the oscillation frequency. doi:10.1017/S1446181119000117

SELF-EXCITED OSCILLATIONS IN A COLLAPSIBLE CHANNEL WITH APPLICATIONS TO RETINAL VENOUS PULSATION

We consider a theoretical model for the flow of Newtonian fluid through a long flexible-walled channel which is formed from four compliant and rigid compartments arranged alternately in series. We drive the flow using a fixed upstream flux and derive a spatially one-dimensional model using a flow profile assumption. The compliant compartments of the channel are assumed subject to a large external pressure, so the system admits a highly collapsed steady state. Using both a global (linear) stability eigensolver and fully nonlinear simulations, we show that these highly collapsed steady states admit a primary global oscillatory instability similar to observations in a single channel. We also show that in some regions of the parameter space the system admits a secondary mode of instability which can interact with the primary mode and lead to significant changes in the structure of the neutral stability curves. Finally, we apply the predictions of this model to the flow of blood through the central retinal vein and examine the conditions required for the onset of self-excited oscillation. We show that the neutral stability curve of the primary mode of instability discussed above agrees well with canine experimental measurements of the onset of retinal venous pulsation, although there is a large discrepancy in the oscillation frequency.

Ventricular interaction in the jugular venous pulse in aortic regurgitation

A patient with severe aortic regurgitation due to rapidly progressive staphylococcal endocarditis demonstrated an unusual physical sign of prominent diastolic venous pulsation. We suggest that this venous pulse is the result of diastolic ventricular interaction in which inflow of blood into the right ventricle is arrested in the latter part of diastole due to extreme left ventricular distension. We wish to highlight this sign so that others can look for it with the aim of improving our understanding and treatment of ventricular interaction associated with heart failure.