Rapid Pressure Changes Research Articles

Does Hemodialysis Hurt the Brain?

Dialysis patients have a high prevalence of both structural brain abnormalities and cognitive impairment. The pathogenesis of the structural brain abnormalities and cognitive impairment as well the relationship between the two is however less clear. In this editorial, we question whether the hemodialysis procedure itself may be partly responsible for the structural abnormalities noted on imaging studies as well as for the cognitive impairment. We invoke several mechanisms whereby the procedure itself may "hurt" the brain including rapid changes in blood pressure, microembolization, microbleeds, and cerebral edema. We then summarize research questions whose answers may help move the field forward.

Quantification of neurological and other contributors to continence in female rats

Smooth muscle, striated muscle, their central and peripheral innervations and control, and mucosal coaptation contribute to maintenance of continence. We used manual leak point pressure (mLPP) testing and electrical stimulation LPP (eLPP) testing in female rats to quantify the contribution of these factors to urethral resistance, a measure of continence. Abdominal muscles were electrically stimulated to induce leakage for eLPP. A Crede maneuver was applied for mLPP. These were repeated after complete T8 spinal cord injury (SCI) and/or bilateral pudendal nerve transection (PNT). After euthanasia, mLPP was repeated. MLPP was not significantly affected by opening the abdomen, suggesting that intra-abdominal pressure transmission contributes little to continence during slow pressure changes. ELPP was significantly higher than mLPP in intact rats, after PNT, and after SCI+PNT, suggesting that abdominal pressure transmission contributes to continence during rapid increases in intra-abdominal pressure. MLPP decreased significantly after PNT, indicating that urethral striated muscles contribute significantly to continence. ELPP decreased significantly after PNT with and without SCI, suggesting that supraspinal control significantly affects continence during rapid pressure changes, but not during slow pressure changes. MLPP after euthanasia was significantly decreased compared to mLPP after SCI+PNT, suggesting that urethral mucosal seal coaptation and tissue elasticity also contribute to continence. The urethra is a complex organ that maintains continence via a highly organized and hierarchical system involving both the central and peripheral nervous systems.

Temporal Processing in the Auditory System

Received July 2, 2011 Accepted September 5, 2011 Address for correspondence Min-Hyun Park, MD Department of Otorhinolaryngology, Boramae Medical Center, Seoul National University-Seoul Metropolitan Government, 20 Boramae-ro 5-gil, Dongjak-gu, Seoul 156-707, Korea Tel +82-2-870-2443 Fax +82-2-831-0714 E-mail drpark@snu.ac.kr The auditory system recognized sound waves. The sound waves are longitudinal waves in the air, where the pressure varies in time. It is distinguished as the rapid pressure changes, referred to as ‘fine structure’, and slower overall changes of amplitude fluctuations, as ‘envelope’. The auditory system has a limited ability to follow the time-varying envelope, and this ability is known as ‘temporal resolution’. Our auditory system analyzes sound waves in frequency, intensity, and time domain. The understanding about frequency and intensity domain is relatively easy compare to time domain. Hearing threshold is measured by sound intensity in frequency domain. However the speech discrimination and understanding of the sentence in quiet and noise are associated with temporal resolution. So for the comprehensive understanding about the auditory system and hearing ability, we must extend our knowledge to the temporal ability of the auditory system. Korean J Otorhinolaryngol-Head Neck Surg 2011;54:585-91

Effects of limb posture on reactive hyperemia

To examine the role of limb posture on vascular conductance during rapid changes in vascular transmural pressure, we determined brachial (n = 10) and femoral (n = 10) artery post-occlusive reactive hyperemic blood flow (RHBF, ultrasound/Doppler) and vascular conductance in healthy humans with each limb at three different positions-horizontal, up and down. Limb posture was varied by raising or lowering the arm or leg from the horizontal position by 45°. In both limbs, peak RHBF and vascular conductance were highest in the down or horizontal position and lowest in the up position (arm up 338 ± 38, supine 430 ± 52, down 415 ± 52 ml/min, P < 0.05; leg up 1,208 ± 88, supine 1,579 ± 130, down 1,767 ± 149 ml/min, P < 0.05). In contrast, the maximal dynamic fall in blood flow following peak RHBF (in ml/s/s) in both limbs was highest in the limb-down position and lowest with the limb elevated (P < 0.05). These data suggest that the magnitude and temporal pattern of limb reactive hyperemia is in part related to changes in vascular transmural pressure and independent of systemic blood pressure and sympathetic control.

Cardiac Baroreflex Sensitivity Is Not Correlated to Sympathetic Baroreflex Sensitivity Within Healthy, Young Humans

The purpose of this study was to evaluate the relationship between the cardiac and sympathetic baroreflex sensitivities within healthy, young humans. The sensitivities of the cardiac and sympathetic baroreflexes were compared in 53 normotensive individuals (28 men and 25 women; age: 24.0 ± 0.9 years; body mass index: 24.0 ± 0.3 cm/kg², mean ± SEM). Heart rate, arterial blood pressure, and peroneal muscle sympathetic nerve activity were recorded under resting conditions (heart rate: 58 ± 1 bpm; systolic blood pressure: 126 ± 2 mm Hg; diastolic blood pressure: 72 ± 1 mm Hg; mean arterial blood pressure: 89 ± 1 mm Hg; muscle sympathetic nerve activity: 18 ± 1 bursts per min) and during rapid changes in blood pressure induced by sequential boluses of nitroprusside and phenylephrine. Cardiac and sympathetic baroreflex sensitivities were analyzed using the slopes of the linear portions of the muscle sympathetic nerve activity-diastolic blood pressure and R-R interval-systolic blood pressure relationships, respectively. When individual cardiac baroreflex sensitivity was compared with sympathetic baroreflex sensitivity, no correlation (R-R interval: r = -0.13; heart rate: r = 0.21) was observed when studied as a group. Analysis by sex unveiled a correlation in women between the cardiac and sympathetic baroreflex sensitivities (R-R interval: r = -0.54; P = 0.01; no correlation with hazard ratio: r = 0.29). No relationship was found in men (R-R interval: r = 0.17; heart rate: r = 0.12). These results indicate that, although both cardiac and sympathetic efferents function in baroreflex control of arterial pressure, there is no correlation in their sensitivities within healthy normotensive humans. However, sex-stratified data indicate that sex-based differential correlations might exist.

Continuous non-invasive finger arterial pressure monitoring reflects intra-arterial pressure changes in children undergoing cardiac surgery

BackgroundContinuous non-invasive measurement of finger arterial pressure (FAP) is a reliable technology in adults. FAP is measured with an inflatable cuff around the finger and simultaneously converted to a reconstructed brachial artery pressure waveform (reBAP) by the Nexfin™ device. We assessed the adequacy of a prototype device (Nexfin-paediatric), designed for a paediatric population, for detecting rapid arterial pressure changes in children during cardiac surgery. MethodsThirteen anaesthetized children with a median age of 11 months (2 months–7 yr) undergoing congenital cardiac surgery were included in the study. reBAP and intra-arterial pressure (IAP) were recorded simultaneously during the surgical procedure. To assess the accuracy of reBAP in tracking arterial pressure changes, the four largest IAP variations within a 5 min time interval were identified from each procedure. These variations were compared offline with reBAP during a 10 s control period before and a 10 s period after an arterial pressure change had occurred. ResultsIn 10 out of 13 children, a non-invasive arterial pressure recording could be obtained. Therefore, recordings from these 10 children were eligible for further analysis, resulting in 40 data points. The correlation coefficient between reBAP and IAP in tracking mean arterial pressure (MAP) changes was 0.98. reBAP followed changes in IAP with a mean bias for systolic, diastolic arterial pressure, and MAP of 0.0 mm Hg (sd 5.8), 0.1 (sd 2.8), and 0.19 (sd 2.7), respectively. ConclusionsThe prototype device closely follows arterial pressure changes in children. However, in a considerable number of attempts, obtaining a signal was time-consuming or unsuccessful. This technique seems promising but requires further technical development.

Spontaneous fluctuations in cerebral blood flow regulation: contribution of PaCO2

To investigate the temporal variability of dynamic cerebral autoregulation (CA), the transient response of cerebral blood flow to rapid changes in arterial blood pressure, a new approach was introduced to improve the temporal resolution of dynamic CA assessment. Continuous bilateral recordings of cerebral blood flow velocity (transcranial Doppler, middle cerebral artery), end-tidal Pco(2) (Pet(CO(2)), infrared capnograph), and blood pressure (Finapres) were obtained at rest and during breath hold in 30 young subjects (25 ± 6 yr old) and 30 older subjects (64 ± 4 yr old). Time-varying estimates of the autoregulation index [ARI(t)] were obtained with an autoregressive-moving average model with coefficients expanded by orthogonal decomposition. The temporal pattern of ARI(t) varied inversely with Pet(CO(2)), decreasing with hypercapnia. At rest, ARI(t) showed spontaneous fluctuations that were significantly different from noise and significantly correlated with spontaneous fluctuations in Pet(CO(2)) in the majority of recordings (young: 72% and old: 65%). No significant differences were found in ARI(t) due to aging. This new approach to improve the temporal resolution of dynamic CA parameters allows the identification of physiologically meaningful fluctuations in dynamic CA efficiency at rest and in response to changes in arterial CO(2).

Nonlocal formulation of the Reynolds equation for rarefied gas flow with steep pressure variation

The current formulation of the Reynolds equation for lubrication problems in the rarefied gas flow regime breaks down when the pressure varies rapidly in the flow direction, which could often happen in the complicated modern hard-disk drive air bearings. In this paper the effect of rapid pressure change in a small distance is examined using a new nonlocal formulation of rarefied Poiseuille flow. The new formulation couples the pressure distribution and the velocity distributions via the Reynolds equation. Detailed numerical strategies required to solve the nonlocal pressure field are explained by analyzing a particular slider structure. Comparisons of the pressure field calculated using the proposed nonlocal formulation with the pressure predicted by the local formulation reveal significant differences between them in the region of large pressure variation. The nonlocal effect discussed in this paper could be significant for certain disk-drive air-bearing design that involves large pressure variations.

Computational study of pulsatile blood flow in prototype vessel geometries of coronary segments

The spatial and temporal distributions of wall shear stress (WSS) in prototype vessel geometries of coronary segments are investigated via numerical simulation, and the potential association with vascular disease and specifically atherosclerosis and plaque rupture is discussed. In particular, simulation results of WSS spatio-temporal distributions are presented for pulsatile, non-Newtonian blood flow conditions for: (a) curved pipes with different curvatures, and (b) bifurcating pipes with different branching angles and flow division. The effects of non-Newtonian flow on WSS (compared to Newtonian flow) are found to be small at Reynolds numbers representative of blood flow in coronary arteries. Specific preferential sites of average low WSS (and likely atherogenesis) were found at the outer regions of the bifurcating branches just after the bifurcation, and at the outer-entry and inner-exit flow regions of the curved vessel segment. The drop in WSS was more dramatic at the bifurcating vessel sites (less than 5% of the pre-bifurcation value). These sites were also near rapid gradients of WSS changes in space and time – a fact that increases the risk of rupture of plaque likely to develop at these sites. The time variation of the WSS spatial distributions was very rapid around the start and end of the systolic phase of the cardiac cycle, when strong fluctuations of intravascular pressure were also observed. These rapid and strong changes of WSS and pressure coincide temporally with the greatest flexion and mechanical stresses induced in the vessel wall by myocardial motion (ventricular contraction). The combination of these factors may increase the risk of plaque rupture and thrombus formation at these sites.

Cardiovagal baroreflex sensitivity is not correlated to sympathetic baroreceptor sensitivity within healthy, young individuals

The purpose of this study was to evaluate the relationship between the cardiac and sympathetic baroreflex sensitivities within healthy, young individuals. The gains in cardiac (as measured by changes in R‐R interval, RRI, and heart rate, HR) and sympathetic (as measured by changes in muscle sympathetic nerve activity, MSNA) baroreflex during rapid changes in arterial blood pressure were compared in 27 normotensive individuals (18 men and 9 women; age 24 yrs ±1.24; body mass index 24 ±0.51 cm/kg2, mean ±SEM). Heart rate, arterial blood pressure (brachial artery catheter), and peroneal MSNA were recorded under resting conditions (HR 58 ±1.6 bpm; SBP 124 ±2.7 mmHg; DBP 71 ±1.7 mmHg; MAP 87 ±1.7 mmHg; MSNA BF 17 ±1.6 bursts/min) as well as during rapid changes in arterial blood pressure induced by sequential boluses of nitroprusside and phenylephrine (Modified Oxford technique). Integrated baroreflex sensitivities for MSNA and HR were analyzed using the slopes of the linear portions of the MSNA‐diastolic blood pressure and RRI‐systolic blood pressure relationships, respectively. When individual cardiac baroreflex sensitivity was compared to sympathetic baroreflex sensitivity, no correlation (R2=0.0003) was found. These results indicate that although both cardiac and sympathetic efferents function in baroreflex control of the autonomic system, there does not appear to be a direct correlation in their function within healthy normotensive individuals.Research Support: NIH HL083947 and Swedish Medical Council grant 12170

An experimental verification of the compensation of length change of line scales caused by ambient air pressure

Line scales are used as a working standard of length for the calibration of optical measuring instruments such as profile projectors, measuring microscopes and video measuring systems. The authors have developed a one-dimensional calibration system for line scales to obtain a lower uncertainty of measurement. The scale calibration system, named Standard Scale Calibrator SSC-05, employs a vacuum interferometer system for length measurement, a 633 nm iodine-stabilized He–Ne laser to calibrate the oscillating frequency of the interferometer laser light source and an Abbe's error compensation structure. To reduce the uncertainty of measurement, the uncertainty factors of the line scale and ambient conditions should not be neglected. Using the length calibration system, the expansion and contraction of a line scale due to changes in ambient air pressure were observed and the measured scale length was corrected into the length under standard atmospheric pressure, 1013.25 hPa. Utilizing a natural rapid change in the air pressure caused by a tropical storm (typhoon), we carried out an experiment on the length measurement of a 1000 mm long line scale made of glass ceramic with a low coefficient of thermal expansion. Using a compensation formula for the length change caused by changes in ambient air pressure, the length change of the 1000 mm long line scale was compensated with a standard deviation of less than 1 nm.

Continuous estimates of dynamic cerebral autoregulation during transient hypocapnia and hypercapnia

Dynamic cerebral autoregulation (CA) is the transient response of cerebral blood flow (CBF) to rapid blood pressure changes: it improves in hypocapnia and becomes impaired during hypercapnia. Batch-processing techniques have mostly been used to measure CA, providing a single estimate for an entire recording. A new approach to increase the temporal resolution of dynamic CA parameters was applied to transient hypercapnia and hypocapnia to describe the time-varying properties of dynamic CA during these conditions. Thirty healthy subjects (mean +/- SD: 25 +/- 6 yr, 9 men) were recruited. CBF velocity was recorded in both middle cerebral arteries (MCAs) with transcranial Doppler ultrasound. Arterial blood pressure (Finapres), end-tidal CO(2) (ET(CO(2)); infrared capnograph), and a three-lead ECG were also measured at rest and during repeated breath hold and hyperventilation. A moving window autoregressive moving average model provided continuous values of the dynamic CA index [autoregulation index (ARI)] and unconstrained gain. Breath hold led to significant increase in ET(CO(2)) (+5.4 +/- 6.1 mmHg), with concomitant increase in CBF velocity in both MCAs. Continuous dynamic CA parameters showed highly significant changes (P < 0.001), with a temporal pattern reflecting a delayed dynamic response of CA to changes in arterial Pco(2) and a maximal reduction in ARI of -5.1 +/- 2.4 and -5.1 +/- 2.3 for the right and left MCA, respectively. Hyperventilation led to a marked decrease in ET(CO(2)) (-7.2 +/- 4.1 mmHg, P < 0.001). Unexpectedly, CA efficiency dropped significantly with the inception of the metronome-controlled hyperventilation, but, after approximately 30 s, the ARI increased gradually to show a maximum change of 5.7 +/- 2.9 and 5.3 +/- 3.0 for the right and left MCA, respectively (P < 0.001). These results confirm the potential of continuous estimates of dynamic CA to improve our understanding of human cerebrovascular physiology and represent a promising new approach to improve the sensitivity of clinical applications of dynamic CA modeling.

A Case of Post Spinal Headache with Symptoms of Meniere's Disease Caused by Rapid Change in Atmospheric Pressure

A Case of Post Spinal Headache with Symptoms of Meniere's Disease Caused by Rapid Change in Atmospheric Pressure

Existence of NO-triggered vagal afferent activation in the rat gastric mucosa

We previously reported the possible involvement of mucosal nitric oxide (NO)-triggered 5-HT release in luminal glutamate sensing by the gastric vagus nerve, and we proposed that the stomach, like the duodenum, could "taste" luminal nutrients. Nitric oxide synthase (NOS) is widely distributed in the gastric mucosa, but the physiological role of mucosal NO is not well understood. In this study, we investigated the functional coupling of NO and vagal nerve endings in the gastric mucosa. For electrophysiological recordings, male Sprague-Dawley rats were anesthetized with urethane, and afferent nerve responses of rat vagal gastric branches to a NO donor were monitored. Intravenous application of 100microg/kg sodium nitroprusside (SNP) transiently increased afferent nerve discharges of the rat ventral gastric vagus, which was followed by rapid changes in blood pressure. High doses of SNP (>300microg/kg, i.v.) showed a biphasic increase in afferent discharges. Secondary activation of the vagal afferent continued even after blood pressure returned to basal levels. SNP-evoked afferent responses were abolished by mucosal 5-HT depletion using p-cholorophenylalanine and were inhibited by pre- and post-treatment with the 5-HT(3) antagonist granisetron. These pharmacological results strongly indicate that NO-triggered 5-HT release is coupled to vagal afferent activation in the rat gastric mucosa.

Adaptive multiscale finite-volume method for nonlinear multiphase transport in heterogeneous formations

In the previous multiscale finite-volume (MSFV) method, an efficient and accurate multiscale approach was proposed to solve the elliptic flow equation. The reconstructed fine-scale velocity field was then used to solve the nonlinear hyperbolic transport equation for the fine-scale saturations using an overlapping Schwarz scheme. A coarse-scale system for the transport equations was not derived because of the hyperbolic character of the governing equations and intricate nonlinear interactions between the saturation field and the underlying heterogeneous permeability distribution. In this paper, we describe a sequential implicit multiscale finite-volume framework for coupled flow and transport with general prolongation and restriction operations for both pressure and saturation, in which three adaptive prolongation operators for the saturation are used. In regions with rapid pressure and saturation changes, the original approach, with full reconstruction of the velocity field and overlapping Schwarz, is used to compute the saturations. In regions where the temporal changes in velocity or saturation can be represented by asymptotic linear approximations, two additional approximate prolongation operators are proposed. The efficiency and accuracy are evaluated for two-phase incompressible flow in two- and three-dimensional domains. The new adaptive algorithm is tested using various models with homogeneous and heterogeneous permeabilities. It is demonstrated that the multiscale results with the adaptive transport calculation are in excellent agreement with the fine-scale solutions. Furthermore, the adaptive multiscale scheme of flow and transport is much more computationally efficient compared with the previous MSFV method and conventional fine-scale reservoir simulation methods.

Decreased renal perfusion rapidly increases plasma membrane Na-K-ATPase in rat cortex by an angiotensin II-dependent mechanism

To understand how rapid changes in blood pressure can regulate Na-K-ATPase in the kidney cortex, we tested the hypothesis that a short-term (5 min) decrease in renal perfusion pressure will increase the amount of Na-K-ATPase in the plasma membranes by an angiotensin II-dependent mechanism. The abdominal aorta of anesthetized Sprague-Dawley rats was constricted with a ligature between the renal arteries, and pressure was monitored on either side during acute constriction. Left renal perfusion pressure was reduced to 70 +/- 1 mmHg (n = 6), whereas right renal perfusion pressure was 112 +/- 4 mmHg. In control (nonconstricted) rats (n = 5), pressure to both kidneys was similar at 119 +/- 6 mmHg. After 5 min of reduced perfusion, femoral venous samples were taken for plasma renin activity (PRA) and the kidneys excised. The cortex was dissected, minced, sieved, and biotinylated. Lower perfusion left kidneys showed a 41% increase (P < 0.003) in the amount of Na-K-ATPase in the plasma membrane compared with right kidneys. In controls, there was no difference in cell surface Na-K-ATPase between left and right kidneys (P = 0.47). PRA was 57% higher in experimental animals compared with controls. To test the role of angiotensin II in mediating the increase in Na-K-ATPase, we repeated the experiments (n = 6) in rats treated with ramiprilat. When angiotensin-converting enzyme was inhibited, the cell surface Na-K-ATPase of the two kidneys was equal (P =0.46). These results confirm our hypothesis: rapid changes in blood pressure regulate trafficking of Na-K-ATPase in the kidney cortex.

Two-Dimensional Simulation of Nonlinear Acoustic Wave Propagation Using Constrained Interpolation Profile Method

In this study, a numerical simulation of the nonlinear sound wave propagation in the time domain is demonstrated by constrained interpolation profile/cubic-interpolated pseudoparticle (CIP) method. The CIP method is a novel numerical scheme which was proposed by Yabe et al. It is a method of characteristics (MOC) and is a low-dispersion and stable scheme. The CIP method is suitable for analysis of nonlinear wave propagation including weak shock formation because the rapid pressure change, such as that caused by a shock front, easily causes numerical dispersion error in a conventional numerical scheme. Some of the authors have reported application of the CIP method to a one-dimensional nonlinear sound wave propagation in air. Then, we demonstrate a numerical calculation of the nonlinear sound wave propagation for a two-dimensional acoustic field.

Maternal age and spine development in the rotiferBrachionus calyciflorus: increase of spine length with birth orders1

Summary1. Maternal effects have long been known to influence phenotypic plasticity in rotifers. Females inBrachionus calyciflorusand several other species produce long‐spined offspring when the predatory rotiferAsplanchnais present;B. calyciflorusalso develops short spines when food concentrations are low. These spines protect against predation and decrease food threshold concentrations.2. Some strains ofB. calyciflorusdevelop long spines even in the absence ofAsplanchnaand other environmental stimuli. We demonstrate in this study that spine length in such cases is dependent on the age of the mother.3. In strains from Florida and Georgia, offspring spine length increased significantly with birth order, sometimes to lengths formerly observed only in the presence ofAsplanchna. Significant variation in this trait was found among and within clones of a strain. Offspring body size also increased with maternal age. This is the first time maternal age has been shown to affect rotifer morphology.4. These birth‐order effects may have important ecological implications and explain phenotypic plasticity and polymorphism in body size and spine length in populations when predators are absent and food concentrations are high. They may be a bet‐hedging mechanism to assure adaptation to rapid changes in predation pressure or food conditions.

The improvement of middle ear ventilation by laser ablation of the epipharyngeal eustachian tube: a prospective study

A long-lasting dysfunction of the eustachian tube seems to be the etiologic origin for development of chronic otitis media (COM) with mesotympanic perforation, otitis media with effusion (OME), and chronic atelectasis of the middle ear. Surgical interventions in the middle ear generally treat the sequelae of the tube dysfunction but not the dysfunction itself. This prospective clinical study investigated how far fiber-guided laser ablation of the posterior half of the epipharyngeal tubal ostium led to better middle ear ventilation in the otologic disease patterns mentioned below. There were 38 adult patients included in the analysis. The patients in one group had a perforated tympanic membrane [COM before primary tympanoplasty (n = 14) or revision tympanoplasty (n = 5)]; the patients in a second group had an intact eardrum [OME resistant to therapy (n = 3), with an atelectasis of the middle ear (n = 2) or problems of pressure equalization with fast changes in ambient pressure (diving, flying) (n = 14)]. Laser ablation of the posterior half of the epipharyngeal tubal ostium was performed, generally with local anesthesia, if tubal function testing was pathologic (Valsalva maneuver, passive tube opening, tympanogram). In patients with COM the procedure was performed 8 weeks before the middle ear surgery. All patients were checked 8 weeks postoperatively and in the course of the following year. The intervention seemed to have had a positive effect on tube function in 68.4% of patients operated on (P = 0.001). In 26 of the 38 patients that had undergone operation, an improvement the results of tubal function tests could be seen in the postoperative follow-up. In the COM group the Valsalva maneuver improved in 14 of 19 patients (73.6%) (P = 0.001), and the passive tube opening improved in nine of 18 patients (50%). In the group with an intact eardrum the Valsalva maneuver improved in 13 of 18 patients (72.2%) (P = 0.001). The resulting condition remained stable after 1 year. None of the patients showed any complications as a result of the therapy. Minimally invasive shaping of the distal eustachian tube under topical anesthesia can be recommended for patients with the above-mentioned diagnoses who have pathologic middle ear ventilation. Especially prior to tympanoplasties, and especially in otologic revision procedures, where middle ear ventilation is a prerequisite for successful otologic surgery, the function of the eustachian tube can be optimized in 70% of the patients, particularly if there are pathological findings (tubal tonsil, narrow orifice of the tubal ostium, adenoids). The placement of permanent ear tubes in adults with recurrent OME can also be avoided by the procedure described. The resultant conditions remained stable for the next year. Patients with tympanic ventilation problems due to rapid pressure changes (flying, diving) can also benefit from this procedure.

Variations in arterial blood pressure are associated with parallel changes in FlowTrac/Vigileo®-derived cardiac output measurements: a prospective comparison study

IntroductionThe reliability of autocalibrated pressure waveform analysis by the FloTrac-Vigileo® (FTV) system for the determination of cardiac output in comparison with intermittent pulmonary arterial thermodilution (IPATD) is controversial. The present prospective comparison study was designed to determine the effects of variations in arterial blood pressure on the reliability of the FTV system in patients undergoing coronary artery bypass grafting (CABG).MethodsComparative measurements of cardiac output by FTV (derived from a femoral arterial line; software version 1.14) and IPATD were performed in 16 patients undergoing elective CABG in the period before institution of cardiopulmonary bypass. Measurements were performed after induction of anesthesia, after sternotomy, and during five time points during graft preparation. During graft preparation, arterial blood pressure was increased stepwise in intervals of 10 to 15 minutes by infusion of noradrenaline and lowered thereafter to baseline levels.ResultsMean arterial blood pressure was varied between 85 mmHg and 115 mmHg. IPATD cardiac output did not show significant changes during periods with increased arterial pressure either during sternotomy or after pharmacological manipulation. In contrast, FTV cardiac output paralleled changes in arterial blood pressure; i.e. increased significantly if blood pressure was raised and decreased upon return to baseline levels. Mean arterial blood pressure (MAP) and FTV cardiac output were closely correlated (r = 0.63 (95% confidence interval [CI]: 0.49 - 0.74), P < 0.0001) while no correlation between MAP and IPATD cardiac output was observed. Bland-Altman analyses for FTV versus IPATD cardiac output measurements revealed a bias of 0.4 l/min (8.5%) and limits of agreement from 2.1 to -1.3 l/min (42.2 to -25.3%).ConclusionsAcute variations in arterial blood pressure alter the reliability of the FlowTrac/Vigileo® device with the second-generation software. This finding may help to explain the variable results of studies comparing the FTV system with other cardiac output monitoring techniques, questions the usefulness of this device for hemodynamic monitoring of patients undergoing rapid changes in arterial blood pressure, and should be kept in mind when using vasopressors during FTV-guided hemodynamic optimization.