Technical pitfalls in middle ear gas studies: Errors introduced by the gas permeability of tubing and additional dead space

Conclusions We demonstrated errors introduced by the gas permeability of the tubing and additional dead space. Materials with practically no permeability, such as glass, must be used to overcome the loss or gain of gas through the walls of tubes used for studying ME gas variations. Experiments conducted at a constant volume (variable pressure) require the smallest possible tubing volume in order to obtain good sensitivity and improve the accuracy of the results.

Objectives Experimental studies that investigate middle ear (ME) gas exchanges, using either pressure measurements or volume changes, are conducted using various tubing connections between the ME and a measuring device. The aims of this study were to highlight experimental problems due to the errors introduced by (i) the gas permeability of the tubing used and (ii) additional dead space in experiments conducted at constant volume.

Material and methods The problem of the gas permeability of the tubing was addressed by comparing three types of tube (silicone, polyethylene, PVC) with a glass tube. Horizontally placed tubes were connected to a syringe filled with pure CO₂ via a gas-tight valve. The end of each tube tested was plunged into colored water (5% Coomassie Brilliant Blue R-250). The tube was washed out with CO₂ until gas bubbles were seen leaving it. The valve was then closed and the movement of water in the tube was observed. The same experiments were repeated for pure O₂. The problem of the error introduced by the additional dead space volume was addressed at a theoretical level using the well-known gas laws. Two conditions were studied: condition A, in which the experiment was conducted at constant pressure and the volume was measured; and condition B, in which the experiment was conducted at constant volume and the pressure was measured. The main outcome measure of each condition was the calculated variation in the final number of moles of gas involved.

Results No water movement was observed in glass tubes. In contrast, plastic tubes exhibited significant gas permeability effects for both CO₂ and O₂. The colored solution advanced at a faster rate with CO₂ than O₂ but differently for each type of tubing. For condition A, gas transfer was independent of the volume of the external tubing and was accurately measured by the displacement of the droplet in the lumen. In contrast, for condition B, the pressure variations were influenced by the volume of the tubing.     

不同药物对急性中毒性肾衰家兔作用效果的比较

目的观察10%葡萄糖、0.9%氯化钠溶液、肾上腺素对急性中毒性肾衰家兔的作用效果。方法制备家兔急性中毒性肾衰模型,观察急性中毒性肾衰状态下家兔动脉血压、心率、血尿素氮、血清肌酐的变化,以及注射10%葡萄糖、0.9%氯化钠溶液、肾上腺素对肾衰家兔动脉血压、心率、血尿素氮、血清肌酐的影响。对比肾衰前后以及肾衰后各药物注射后家兔的生命体征变化。结果肾衰家兔与正常家兔相比动脉血压下降,心率略下降,血清尿素氮、肌酐明显上升;肾衰家兔注射葡萄糖后动脉血压和心率都基本不变,血清尿素氮、肌酐略上升;注射0.9%氯化钠溶液后血压升高,心率略升高,血清尿素氮、肌酐略下降;注射肾上腺素后动脉血压上升,心率下降,血清尿素氮、肌酐明显下降。结论肾上腺素对急性中毒性肾衰家兔的治疗效果最佳。     

The Cardiovascular Response to Acoustic Stimuli

The purposes of this investigation were to determine whether adults display alterations of cardiac rate under acoustical stimulus conditions and whether such alterations are influenced by signal level. The stimulus consisted of a narrow band of noise centered at 1000 Hz and presented at 20, 40, 60 and 80 dB SPL. The stimulus was found to produce alterations of heart rate significantly different from variation under non-stimulus conditions, indicating that cardiovascular responses occurred. However, the responses themselves were unaffected by differences of sound pressure level.     

Type a Behavior and Cardiovascular Recovery from a Psychosocial Stressor

Abstract

The present study examined heart rate responses of Type A and Type B individuals during and after performance on the Stroop perceptual conflict task. The student version of the Jenkins Activity Survey was administered to thirty-two male Caucasians, who then performed the Stroop task for six minutes under conditions that emphasized time urgency and competition. Results showed that Type A's recovered significantly slower than Type B's after task completion. Type A's, compared to Type B's reported feeling more angry, time pressured, and impatient. The notion that Type A individuals may be at higher risk for coronary heart disease because of maladaptively prolonged cardiovascular arousal was discussed.     

Continuous Measurement of O2 Consumption and CO2 Elimination During a Wakeful Hypometabolic State

Abstract

A previous investigation has demonstrated that the practice of a meditational technique elicits a wakeful, hypometabolic state. Measurement of O₂ consumption and CO₂ elimination was made by sampling techniques; mean values of these parameters were calculated from 6–10 minute samples. The present study extends this investigation, using a recently developed method of continuous measurement of O₂ consumption and CO₂ elimination. Continuous measurement of these parameters permitted the determination of mean values for the entire experimental periods as well as for selected intervals and permitted the examination of the sequence of respiratory changes. The present study reports statistically significant decreases in O₂ consumption of 5 percent and CO₂ elimination of 6 percent for the entire 20 minutes of the meditation period. These are lower than the sample values of 16 percent and 15 percent reported in the previous study. However, when selected intervals of the meditation period are examined, decreases in O₂ consumption and CO₂ elimination are comparable to those previously reported. The results are consistent with the difference between the discontinuous sampling measurement method originally employed and the continuous measurement method of the present investigation.     

Significance of the SISI Test and Its Relation to Recruitment

Auditory brainstem responses (ABR) evoked by clicks allow a threshold evaluation for the high-frequency range (2-4 kHz) but not for middle and low frequencies (0.5-1 kHz). In 19 normally hearing subjects aged between 24 and 40 years, ABRs have been recorded using clicks and 0.5- and 1-kHz tone pips, with durations of 6 and 3 ms, respectively, and rise-decay times of 3 and 1.5 ms. The input signal was filtered by a passband filter of 20-5000 Hz. Parameters of tracings elicited by the different kinds of stimuli are compared. Tone-pip ABR morphology does not show the conventional seven peaks but a single large vertex-positive wave. On the ascending branch high-frequency potentials, probably corresponding to the I, II, III and IV-V click-evoked peaks, were visible in some cases, but they rapidly disappeared as the stimulus intensity was decreased. Their 2.3-3 ms greater mean latency values are presumably related to the rise times of the stimuli employed. In terms of bioelectric generators, this large vertex-positive peak probably corresponds to the Jewett V wave. It probably represents a generalized asynchronous dendritic activity. Thus it is possible to obtain ABRs to middle- and low-frequency stimuli. Mean amplitude values of the slow wave are considerably higher than those of the Jewett V wave, but standard deviations are also larger. The positive wave has been identified in response to 1-kHz tone pips in 100% of cases at 30 dB nHL and in 52% of cases at 20 dB, while for 0.5-kHz tone pips in 73.7% of cases at 30 dB and in 57% at 20 dB. On the whole the threshold is located between 15 and 30 dB nHL.

L'étude des potentiels auditifs du tronc cérébral évoqués par des clics permet une évaluation objective du seuil auditif dans le domaine des hautes fréquences (2-4 kHz), mais pas dans celui des fréquences moyennes et basses (0, 5-1 kHz).

Nous avons étudié, chez 19 sujets normo-entendants aˇgés de 24 à 40 ans, les potentiels auditifs du tronc cérébral évoqués par des clics et des pips tonaux de 0,5 et 1 kHz, la durée des pips tonaux étant respectivement de 6 et 3 ms, avec un temps de montee de 3 et 1,5 ms.

Le signal était filtré avec une bande passante de 20-5000 Hz. Nous avons ainsi comparé les paramètres des tracés obtenus avec ces différents types de stimulus et trouvé que les pips tonaux n'évoquaient pas l'apparition des sept pics conventionnels, mais seulement une onde assez ample, positive au vertex; parfois, il est possible de reconnaiˇtre sur sa branche ascendante la présence de potentiels à haute fréquence qui correspondent selon toute probabilité aux pics I, II, III et IV-V évoqués par des clics. Leur amplitude décroiˇt et ils disparaissent lorsqu'on diminue l'intensité de la stimulation. Les latences de cette onde ample, positive au vertex, supérieures de 2,3-3 ms à celles de l'onde V de Jewett, sont probablement liées au temps de montée du stimulus employé. En termes d'origine bioélectrique, cette onde correspond vraisemblablement à celle du pic V de Jewett. Elle semble représenter une activité dendritique, asynchrone. On peut done obtenir des potentiels auditifs du tronc cérébral avec des stimuli de basse et de moyenne fréquence. Les amplitudes moyennes de cette onde sont beaucoup plus importantes que celles du pic V de Jewett, mais les déviations standard sont aussi plus grandes. Cette onde est présente dans 100% des cas pour les pips tonaux de 1 kHz à 30 dB nHL et dans 52% à 20 dB, tandis qu'elle est présente dans 73,7% des cas à 30 dB et dans 57% à 20 dB lorsque on emploie des pips tonaux de 0,5 kHz. Les seuil objectif se situe ainsi entre 15 et 30 dB nHL.     

Cardiac Autonomic Function and Global Left Ventricular Performance in Autoimmune Eauthyroid Chronic Thyroiditis: Is Treatment Necessary at the Euthyroid Stage?

Objective: Autoimmune chronic thyroiditis (ACT) is characterized by lymphocyte infiltration in the thyroid gland and the presence of antithyroid antibodies in serum. Medical treatment does not affect antibody levels and treatment decision is not definite yet for the euthyroid patients. We aimed to evaluate cardiac autonomic function and global left ventricular performance in autoimmune euthyroid chronic thyroiditis and determine the need for medical treatment. Method: We studied 30 ACT patients and 25 healthy control subjects. Cardiac autonomic function is evaluated by heart rate recovery (HRR). Global left ventricular performance is evaluated by two‐dimensional echocardiography and pulsed‐wave tissue Doppler echocardiography. Results: There was no difference between patients and controls with respect to clinical and biochemical parameters except hemoglobin (13.67 ± 1.25 g/dL, 14.51 ± 1.35 g/dL, p:0.047) and low density lipoprotein (120.71 ± 24.91 mg/dL, 100.55 ± 14.73 mg/dL, p: 0.003). Tei index was significantly higher in ACT group (0.521 ± 0.074, 0.434 ± 0.034, P < 0.0001). E′/A′ was found to be significantly lower (1.234 ± 0.42, 1.750 ± 0.291, P < 0.0001) and E/E′ was found to be higher than the controls (8.482 ± 0.449, 6.039 ± 0.209, P < 0.0001). HRR was significantly lower than the controls (20 ± 4 BPM, 30 ± 8 BPM, P < 0.0001). Conclusion: Although left ventricular performance is found to be normal by conventional echocardiographic methods, it is found to be impaired when Tei index and tissue Doppler parameters are used. Cardiac autonomic function is also impaired in ACT patients. As a result of these cardiac changes, medical treatment may be considered earlier, even at the euthyroid stage. (Echocardiography 2011;28:15‐21)     

Ratiometric analysis in hyperpolarized NMR (I): test of the two‐site exchange model and the quantification of reaction rate constants

Conventional methods for the analysis of in vivo hyperpolarized ¹³C NMR data from the lactate dehydrogenase (LDH) reaction usually make assumptions on the stability of rate constants and/or the validity of the two‐site exchange model. In this study, we developed a framework to test the validity of the assumption of stable reaction rate constants and the two‐site exchange model in vivo via ratiometric fitting of the time courses of the signal ratio L(t)/P(t). Our analysis provided evidence that the LDH enzymatic kinetics observed by hyperpolarized NMR are in near‐equilibrium and satisfy the two‐site exchange model for only a specific time window. In addition, we quantified both the forward and reverse exchange rate constants of the LDH reaction for the transgenic and mouse xenograft models of breast cancer using the ratio fitting method developed, which includes only two modeling parameters and is less sensitive to the influence of instrument settings/protocols, such as flip angles, degree of polarization and tracer dosage. We further compared the ratio fitting method with a conventional two‐site exchange modeling method, i.e. the differential equation fitting method, using both the experimental and simulated hyperpolarized NMR data. The ratio fitting method appeared to fit better than the differential equation fitting method for the reverse rate constant on the mouse tumor data, with less relative errors on average, whereas the differential equation fitting method also resulted in a negative reverse rate constant for one tumor. The simulation results indicated that the accuracy of both methods depends on the width of the transport function, noise level and rate constant ratio; one method may be more accurate than the other based on the experimental/biological conditions aforementioned. We were able to categorize our tumor models into specific conditions of the computer simulation and to estimate the errors of rate quantification. We also discussed possible approaches to the development of more accurate rate quantification methods for hyperpolarized NMR. Copyright © 2013 John Wiley & Sons, Ltd.     

Total ankle replacement in patients under the age of 50. Should the indications be revised?

BackgroundHigh physical demand and young age are currently considered contraindications for total ankle replacement. This study aimed to compare its results between patients under the age of 50 and those aged 50 or older.Methods103 patients derived from an ongoing prospective multicentric study with a mean follow-up of 41 (range, 24–72) months were included in this study. Clinical status (AOFAS score), range of motion (ROM), complication and survivorship rates were compared between <50 and ≥50 patients.ResultsROM and AOFAS score were significantly higher, as were their increases relatively to pre-operative values in patients <50. Complication and survivorship rates were comparable between both groups.ConclusionsAt medium-term, ankle replacement is at least as effective in patients under the age of 50 as in those with aged 50 or older. Long-term results will allow to assess whether surgical indications for should be revised.