Optimal Pressure Waveforms for Pressure-Limited Ventilation

In this paper, we find the pressure waveform that minimizesthe work of distending the alveoli in the lungs while achievingthe desired mean airway pressure and alveolar tidal volume.The model used takes into account the compliance of the airway.The main result is a formula for the pressure waveform at themouth as a function of time and lung parameters.     

Assessment of mechanical ventilation parameters on respiratory mechanics

Better understanding of airway mechanics is very important in order to avoid lung injuries for patients undergoing mechanical ventilation for treatment of respiratory problems in intensive-care medicine, as well as pulmonary medicine. Mechanical ventilation depends on several parameters, all of which affect the patient outcome. As there are no systematic numerical investigations of the role of mechanical ventilation parameters on airway mechanics, the objective of this study was to investigate the role of mechanical ventilation parameters on airway mechanics using coupled fluid-solid computational analysis. For the airway geometry of 3 to 5 generations considered, the simulation results showed that airflow velocity increased with increasing airflow rate. Airway pressure increased with increasing airflow rate, tidal volume and positive end-expiratory pressure (PEEP). Airway displacement and airway strains increased with increasing airflow rate, tidal volume and PEEP form mechanical ventilation. Among various waveforms considered, sine waveform provided the highest airflow velocity and airway pressure while descending waveform provided the lowest airway pressure, airway displacement and airway strains. These results combined with optimization suggest that it is possible to obtain a set of mechanical ventilation strategies to avoid lung injuries in patients.     

输尿管软镜术中应用喉罩同步间歇指令通气的通气效果观察

目的评价输尿管软镜术中应用喉罩同步间歇指令通气（SIMV）的通气效果。方法选择2013年6月至9月广州医科大学附属第一医院泌尿外科收治的拟在输尿管软镜下行钬激光碎石术的肾结石患者30例,美国麻醉医师协会（ASA）分级I～Ⅱ级。使用丙泊芬、舒芬太尼麻醉诱导,手控辅助呼吸至患者自主呼吸消失,置入喉罩,连接麻醉机行SIMV。手术结束继续应用SIMV至患者呼吸恢复良好。记录麻醉前（T1）、喉罩置入后通气5min（T2）、手术结束（T3）和拔除喉罩患者自主呼吸5min（T4）4个时点的脉搏血氧饱和度（SpO2）、动脉血氧分压（PaO2）、动脉血二氧化碳分压（PaC02）和pH值,记录T2和T3时点气道峰压（P_peak）、分钟通气量（MV）、动态顺应性（C_dyn）、呼气末二氧化碳分压（PETC02）和压力一容量环（P-V环）、P_ETCO2波形。结果4个时点的PaO2、PaCO2、pH值和SpO2均在正常范围。他和,13时点的PaO2明显高于T1和T4时点（均P〈0．05）。术中行喉罩SIMV时,T2和T3时点的P_peak、MV、C_dyn、PETCO2差异无统计学意义（均P〉0．05）,P-V环和P_ETCO2波形无改变。结论全身麻醉下输尿管软镜术中应用喉罩SIMV能保持良好的通气效果。     

Further exploration of the Penh parameter

Unrestrained plethysmography (UP) has been widely used to measure airway reactivity in conscious mice. It is non-invasive, easy to use, suitable for longitudinal studies, and allows a large throughput of animals for screening purposes. A non-dimensional parameter based on a characteristic change in the expiratory waveshape of the UP box signal, Penh, has been used as an indicator of bronchconstriction. Hamelmann et al. [Non-invasive measurement of airway responsiveness in allergen mice using barometric plethysmography. Am J Respir Crit Care Med 1997;156:766–77] presented experimental data showing a correlation between Penh and intrapleural pressure, as well as lung resistance; and Dohi et al. [Non-invasive system for evaluating the allergen-specific airway response in a murine model of asthma. Lab Invest 1999;79:1559–71] showed that Penh tracked the bronchial response to allergen challenge. More recently, papers and letters to the editor have argued against the use of UP and Penh in resistance applications, presenting mathematical and theoretical arguments that the UP waveform, and parameters derived from it (Penh) are dominated by conditioning, and are essentially unrelated to resistance [Lundblad et al. A reevaluation of the validity of UP in mice. J Appl Physiol 2002;93:1198–207; Mitzner and Tankersley. Interpreting Penh in mice. J Appl Physiol 2003;94:828–32].This paper discusses the mathematics of UP as applied to two types of whole body plethysmographs (WBPs): a sealed chamber (pressure plethysmograph, PWBP); and a chamber with a pneumotachograph in its wall (flow plethysmograph, FWBP). We show that the PWBP waveform is largely dominated by conditioning, and exhibits little effect due to resistance; thus supporting the claim that UP and Penh are unrelated to resistance, when applied to measurements at typical room temperatures. By contrast, the effects of resistance or specific airway resistance (sRaw) are evident in the FWBP waveform, even at room temperature. Penh is derived from the FWBP waveform. We show that the changes in the FWBP waveform which occur in response to methacholine challenge cannot be due to conditioning, and are not simply due to changes in respiratory timing. Finally, we describe how Penh quantifies those changes.     

Impedance cardiographic measurement of the physiological response to the Valsalva manoeuvre

The Valsalva manoeuvre was performed, with airway pressures of 10, 20, 30, 40 and 50 mmHg, on 11 healthy male subjects in both the standing and supine positions, and was evaluated with impedance cardiography using the Minnesota impedance cardiograph. Along with the impedance waveform, the output of a finger photoplethysmograph was recorded. The ratios of the amplitude of the finger and impedance pulses at the end of a 10s strain phase during the Valsalva manoeuvre were compared with those of the control period. The results in the standing position showed the impedance ratio changed from 0.81 to 0.61 as the airway pressure increased from 10 to 50 mmHg, whereas, over the same pressure range, the finger pulse ratio changed from 0.44 to 0.21. In the supine position, the response was similar to that for standing for most pressures. Upon release of the pressure, the impedance showed an immediate, large decrease, which suggests a significant rightheart and vena cava component in the impedance cardiographic signal. The results show that the impedance signals responded similarly to those of previous studies of central arterial pressure during the Valsalva manoeuvre, whereas the finger pulse decrease was approximately twice as much.     

Reduced nocturnal cardiac output associated with preeclampsia is minimized with the use of nocturnal nasal CPAP

STUDY OBJECTIVES: Recent studies suggest a specific association between intrauterine growth restriction that commonly occurs in preeclampsia and decreased maternal cardiac output. Sleep is associated with marked hypertension in preeclampsia. We therefore aimed to determine how sleep influences other hemodynamic parameters in preeclampsia, specifically to determine if sleep-induced exacerbation of hypertension was associated with reductions in cardiac output. STUDY DESIGN: Randomized controlled trial of nasal continuous positive airway pressure. SETTING: King George V, Royal Prince Alfred Hospital. PATIENTS: Twenty-four women with severe preeclampsia and 15 control nulliparous subjects. INTERVENTION: Full polysomnography including beat-to-beat blood-pressure recording. Stroke volume, heart rate, cardiac output, total peripheral resistance, and ejection duration were derived from the blood pressure waveform. Half of the 24 preeclamptic subjects were randomly assigned to receive treatment with nasal continuous positive airway pressure and the other half to receive no treatment. MEASUREMENTS AND RESULTS: Heart rate, stroke volume, and cardiac output were similar in controls and patients with preeclampsia during wakefulness, while total peripheral resistance was significantly elevated. Sleep induced marked decrements in heart rate, stroke volume, and cardiac output in preeclamptic subjects and resulted in further increments in total peripheral resistance. Cardiac output during sleep was correlated with fetal birth weight (r2 = 0.64, P < .001). When preeclamptic subjects were treated with continuous positive airway pressure, reductions in cardiac output were minimized, while increments in total peripheral resistance were also reduced. CONCLUSIONS: These data indicate that sleep is associated with adverse hemodynamic changes in women with preeclampsia. These changes are minimized with the use of continuous positive airway pressure. Reduced cardiac output during sleep may have an adverse effect on fetal development.     

The CobraPLA during anesthesia with controlled ventilation: a clinical trial of efficacy

The CobraPLA (CPLA) is a relatively new supraglottic airway device that has not been sufficiently investigated. Here, we performed a prospective observational study to evaluate the efficacy of the CPLA during controlled ventilation. In 50 anesthetized and paralyzed patients undergoing elective surgery a CPLA was inserted and inflated to an intracuff pressure of 60 cm H2O. The success rate of insertion upon the first attempt was 82% (41/50), with a mean insertion time of 16.3 +/- 4.5 seconds. The adequacy of ventilation was assessed by observing the end tidal CO2 waveform, movement of the chest wall, peak airway pressure (13.5 cm H2O), and leak fraction (4%). We documented the airway sealing pressure (22.5 cm H2O) and noted that the the site of gas leaks at that pressure were either at the neck (52%), the abdomen (46%), or both (2%). In 44 (88%) patients, the vocal cords were visible in the fiberoptic view through the CPLA. There was no gastric insufflation during the anesthesia. Respiratory and hemodynamic parameters remained stable during CPLA insertion. Postoperative blood staining of CPLA was minimal, occurring in 22% (11/50) of patients. Mild and moderate throat soreness was reported in 44% (22/50) and 4% (2/50) of patients, respectively. Lastly, mild dysphonia was observed in 6% (3/50) of patients and mild dysphagia in 10% (5/50) of patients. Our results indicated that the CPLA is both easy to place and allows adequate ventilation during controlled ventilation.     

Arterial reservoir-excess pressure and ventricular work

This study is based on the hypothesis that the pressure within the arterial network can be usefully decomposed as the sum of a reservoir pressure and an excess pressure. The reservoir pressure waveform is defined to be the same in each vessel but delayed by the wave travel time from the root of the aorta. Using calculus of variations and mass conservation, which relates the flow and rates of change of pressure in the vessels, we show that the reservoir pressure waveform minimises the ventricular hydraulic work for any physiologically or clinically reasonable ejection waveform and arterial properties, i.e. vessel compliances and terminal resistances. We conclude that the excess pressure determines the excess work done by the ventricle, which may have clinically important implications.     

Blood pressure waveform analysis by means of wavelet transform

The assessment of cardiovascular function by means of arterial pulse wave analysis (PWA) is well established in clinical practice. PWA is applied to study risk stratification in hypertension, with emphasis on the measurement of the augmentation index as a measure of aortic pressure wave reflections. Despite the fact that the prognostic power of PWA, in its current form, still remains to be demonstrated in the general population, there is general agreement that analysis and interpretation of the waveform might provide a deeper insight in cardiovascular pathophysiology. We propose here the use of wavelet analysis (WA) as a tool to quantify arterial pressure waveform features, with a twofold aim. First, we discuss a specific use of wavelet transform in the study of pressure waveform morphology, and its potential role in ascertaining the dynamics of temporal properties of arterial pressure waveforms. Second, we apply WA to evaluate a database of carotid artery pressure waveforms of healthy middle-aged women and men. Wavelet analysis has the potential to extract specific features (wavelet details), related to wave reflection and aortic valve closure, from a measured waveform. Analysis showed that the fifth detail, one of the waveform features extracted applying the wavelet decomposition, appeared to be the most appropriate for the analysis of carotid artery pressure waveforms. What remains to be assessed is how the information embedded in this detail can be further processed and transformed into quantitative data, and how it can be rendered useful for automated waveform classification and arterial function parameters with potential clinical applications.     

容积型指脉波图监测及评价体外反搏效果的对照研究

对２０ 名男性健康志愿者采用经桡动脉穿刺置管主动脉根部测压的方法,分别研究不同反搏工作参数对主动脉压力和指脉波的影响。结果反搏时主动脉舒张压随储气罐压力的增加升高（最高可达１６８．５６ ｍ ｍ Ｈｇ）;主动脉舒张波的ｄｐ／ｄｔ值均逐渐上升,但收缩波的ｄｐ／ｄｔ值则呈下降趋势;指脉舒张波起点与主动脉舒张波起点比较平均滞后（１０８．２０±２５．７０） ｍ ｓ,而指脉收缩波起点则平均滞后（９６．６９±３８．７０） ｍ ｓ;指脉波的Ｄ／Ｓ比值与主动脉压力波的Ｄ／Ｓ比值随反搏储气罐压力的增加而同步增加,并由直线回归分析得出动脉Ｄ／Ｓ比值（Ｙ）与指脉Ｄ／Ｓ比值（Ｘ）的回归方程式Ｙ＝ ０．３７６＋ ０．４５７Ｘ。本研究指示体外反搏对动脉压力波的Ｄ／Ｓ比值、舒张压及其ｄｐ／ｄｔ值均有显著影响,指脉波仍然是目前调节反搏工作参数及监测反搏效果的较为安全、可靠的方法     

Technique to Determine Inspiratory Impedance during Mechanical Ventilation: Implications for Flow Limited Patients

We present the design of an enhanced ventilator waveform (EVW) for routine measurement of inspiratory resistance (R) and elastance (E) spectra in ventilator-dependent and/or severely obstructed flow-limited patients. The EVW delivers an inspiratory tidal volume of fresh gas with a flow pattern consisting of multiple sinusoids from 0.156 to 8.1 Hz and permits a patient-driven exhalation to the atmosphere or positive end-expiratory pressure. Weighted least-squares estimates of the coefficients in a sinusoidal series approximation of the EVW inspirations yielded inspiratory R and E spectra. We first validated the EVW approach using simulated pressure and flow data under different physiological conditions, noise levels, and harmonic distortions. We then applied the EVW in four intubated patients during anesthesia and paralysis: two with mild airway obstruction and two with severe emphysema and flow limitation. While the level of inspiratory R was similar in both groups of patients, the inspiratory E of the emphysematous patients demonstrated a pronounced frequency-dependent increase consistent with severe peripheral airway obstruction. We conclude that the EVW offers a potentially practical and efficient approach to monitor lung function in ventilator-dependent patients, especially those with expiratory flow limitation. © 1999 Biomedical Engineering Society. PAC99: 8719Uv, 8780-y     

动脉压力波形分析在麻醉诱导期的应用

为探索动脉波形分析方法的临床意义，使用波形分离法与储存压力波模型对采集到的25例进行全麻手术的高龄患者的动脉压力波形进行波形分析，在获得[Pf]、[Pb]以及[Pe]、[Pr]等波形形态参数后，将诱导前后的参数变化量与临床生命指标变化量进行相关性分析。在本文的研究群体中，波形分离法与储存压力波模型的参数均与诱导中的血压和心率变化量有相关性，其中△[Pe]与临床指标△PP相关系数最高（r=0.926）。从生理病理学的角度对波形参数的变化进行解读，旨在探索波形分析在诱导期对全麻患者麻醉水平的应用价值，可为动脉压力波形分析及其应用提供新的理论基础和技术方案。     

Effects of continuous positive airway pressure on blood pressure in obstructive sleep apnea patients: The Apnea Positive Pressure Long‐term Efficacy Study (APPLES)

Obstructive sleep apnea is associated with hypertension, and short‐term studies have demonstrated a modest reduction in blood pressure with continuous positive airway pressure therapy. We evaluated the effects of continuous positive airway pressure versus sham continuous positive airway pressure on blood pressure in 1,101 participants with obstructive sleep apnea from the Apnea Positive Pressure Long‐term Efficacy Study, a randomized, sham‐controlled double‐blinded study designed to assess the impact of continuous positive airway pressure on neurocognition. Participants with apnea?hypopnea index ≥ 10 were randomly assigned to continuous positive airway pressure or sham continuous positive airway pressure. Blood pressures measured in the morning and evening at baseline, 2 months and 6 months were analysed post hoc using a mixed‐model repeated‐measures analysis of variance. The largest magnitude reduction was approximately 2.4 mmHg in morning systolic pressure that occurred at 2 months in the continuous positive airway pressure arm as compared with an approximate 0.5 mmHg reduction in the sham group (continuous positive airway pressure effect ?1.9 mmHg, p = .008). At 6 months, the difference between groups was diminished and no longer statistically significant (continuous positive airway pressure effect ?0.9 mmHg, p = .12). Sensitivity analysis with use of multiple imputation approaches to account for missing data did not change the results. Treatment with continuous positive airway pressure for obstructive sleep apnea reduces morning but not evening blood pressure in a population with well‐controlled blood pressure. The effect was greater after 2 than after 6 months of treatment.     

Quantitative Comparison of Korotkoff Sound Waveform Characteristics: Effects of Static Cuff Pressures and Stethoscope Positions

The underlying principles of Korotkoff sound (KorS) during blood pressure measurement and its waveform characteristic changes with cuff pressure and stethoscope position have not been fully understood. This study aimed to quantify the effects of cuff pressure and stethoscope position on the measured KorS waveform characteristics. Thirty healthy subjects were recruited in this study. Four stethoscopes were placed on the circumferential direction around the arm (m1, m2, m3 and m4; m1 was above the artery, and equal distance between each other), and then sequentially at three different longitudinal positions (‘upper’, ‘middle’ and ‘low’ part under the cuff). At each longitudinal position, three levels of static cuff pressure (high: SBP?+?10 mmHg, low: DBP-10 mmHg, and medium: DBP?+?(SBP-DBP)/3) were applied during the recording of KorS waveform. The averaged KorS waveform was firstly computed by using an interpolation method, separately for measurements from different stethoscope locations and cuff pressures. Two quantitative indices were derived to characterize the recorded KorS waveform: intensity amplitude and high-level duration of KorS waveform. Post-hoc pairwise comparisons after analysis of variance were used to compare the waveform characteristic differences between different stethoscope locations and between cuff pressures. Variance analysis demonstrated that the effects of stethoscope circumferential and longitudinal positions and cuff pressure on the two KorS waveform indices were significant (all p?<?0.001). In detail, KorS waveform recorded at cuff pressure P_MEDIUM had larger intensity amplitude and shorter high-level duration than those recorded at cuff pressure P_HIGH or P_LOW. In most conditions, the stethoscope above the artery (m1) produced the largest RMS intensity amplitude and shortest high-level duration, while the stethoscope at the opposite location of m1 generated the smallest RMS intensity amplitude and longest high-level duration. In terms of the effect of longitudinal position, the stethoscopes below the middle of the cuff always produced KorS recordings with larger intensity amplitude and shorter high-level duration. This study has quantified and provided scientific evidence that cuff pressure, stethoscope longitudinal and circumferential positions are important factors influencing KorS waveform characteristics.     

Dose‐dependent effects of continuous positive airway pressure for sleep apnea on weight or metabolic function: Individual patient‐level clinical trial meta‐analysis

Therapeutic‐continuous positive airway pressure seems to increase weight compared with placebo‐continuous positive airway pressure. It is not known whether weight gain with therapeutic‐continuous positive airway pressure dose is dependent or whether it causes metabolic dysfunction. Data synthesis of three randomised placebo‐continuous positive airway pressure‐controlled trials (2–3 months) was performed to test whether there is a dose‐dependent effect of continuous positive airway pressure on weight. Fasting glucose, insulin, insulin resistance (homeostatic model assessment), lipids and visceral abdominal fat were also tested to determine any effect on metabolic function. Mixed‐model analysis of variance was used to quantify these effects. One‐hundred and twenty‐eight patients were analysed. Overall there was a small increase in weight with therapeutic‐continuous positive airway pressure use compared with placebo‐continuous positive airway pressure (difference: 1.17 kg; 0.37–1.97, p = 0.005), which was greater with high‐use therapeutic‐continuous positive airway pressure compared with high‐use placebo‐continuous positive airway pressure (1.45 kg; 0.10–2.80, p = 0.04). Continuous positive airway pressure use as a continuous variable was also significantly associated with weight change in continuous positive airway pressure users (0.30 kg hr^?1 night^?1; 0.04–0.56, p = 0.001), but not in placebo users (0.04 kg hr^?1 night^?1; ?0.22 to 0.26, p = 0.76). Neither therapeutic‐continuous positive airway pressure nor the dose of therapeutic‐continuous positive airway pressure caused any changes to metabolic outcomes. The weight gain effects of medium‐term therapeutic‐continuous positive airway pressure appear modest and are not accompanied by any adverse metabolic effects.     

Heterogeneous Airway Versus Tissue Mechanics and Their Relation to Gas Exchange Function During Mechanical Ventilation

We have advanced a commercially available ventilator (NPB840, Puritan Bennett/Tyco Healthcare, Pleasanton, CA) to deliver an Enhanced Ventilation Waveform (EVW). This EVW delivers a broadband waveform that contains discrete frequencies blended to provide a tidal breath, followed by passive exhalation. The EVW allows breath-by-breath estimates of frequency dependence of lung and total respiratory resistance (R) and elastance (E) from 0.2 to 8 Hz. We hypothesized that the EVW approach could provide continuous ventilation simultaneously with an advanced evaluation of mechanical heterogeneities under heterogeneous airway and tissue disease conditions. We applied the EVW in five sheep before and after a bronchial challenge and an oleic acid (OA) acute lung injury model. In all sheep, the EVW maintained gas exchange during and after bronchoconstriction, as well as during OA injury. Data revealed a range of disease conditions from mild to severe with heterogeneities and airway closures. Correlations were found between the arterial partial pressure of oxygen (P_aO2) and the levels and frequency-dependent features of R and E that are indicative of mechanical heterogeneity and tissue disease. Lumped parameter models provided additional insight on heterogeneous airway and tissue disease. In summary, information obtained from EVW analysis can provide enhanced guidance on the efficiency of ventilator settings and on patient status during mechanical ventilation.     

Development and testing of a PC-based system with menu-driven software for evaluating lung function in ICU patients

This paper describes a portable PC-based system for measuring respiratory system resistance (Rrs) and dynamic lung compliance (Cdyn) in intubated and mechanically ventilated patients. A pneumotachometer placed immediately proximal to the endotracheal tube measures flow, and a pressure catheter with its tip at the distal end of the endotracheal tube measures lateral airway pressure. The software is menu driven and allows the user to select from options including patient information display and entry, data collection, data editing, and waveform display. Up to ten consecutive breaths can be analyzed per run. Rrs and Cdyn are calculated on a breath by breath basis. Results are displayed to the screen, output to the system printer, and written to a user-specified ACSII data file. The system was tested by measuring resistance and compliance in a model of the lung, and results compared with those calculated from analog signals. It was then used to make measurements in intubated post-operative patients. Results were comparable to those previously reported in intubated ICU patients without primary lung disease. We conclude that our system provides reliable measurements of lung mechanics in the intubated patient, and represents an inexpensive and more versatile alternative to microprocessor-based ventilator systems currently being marketed.     

Good long‐term adherence to continuous positive airway pressure therapy in patients with resistant hypertension and sleep apnea

Although adequate adherence is paramount in achieving the beneficial effects of continuous positive airway pressure therapy in patients with obstructive sleep apnea, long‐term adherence and the variables involved in continuous positive airway pressure compliance in patients with resistant hypertension and obstructive sleep apnea are yet unknown. We conducted a prospective, multicentre, observational study in 177 patients recruited from hypertensive units with resistant hypertension confirmed by means of 24‐hr blood pressure monitoring (blood pressure ≥ 130 and/or ≥ 80 mmHg, despite taking at least three antihypertensive drugs or < 130/80 mmHg with > 3 drugs) and obstructive sleep apnea (apnea–hypopnea index ≥ 5 in a respiratory polygraph) who were prescribed continuous positive airway pressure treatment. Good adherence was defined as an average cumulative continuous positive airway pressure use of ≥ 4 hr per night at the end of the follow‐up. A multivariate Cox regression analysis was performed to identify independent predictors of continuous positive airway pressure adherence. Patients were followed for a median of 57.6 (42–72) months after initiating continuous positive airway pressure therapy. At the end of the follow‐up, the median continuous positive airway pressure use was 5.7 (inter‐quartile range 3.9–6.6) hr per night, and 132 patients (74.5%) showed good continuous positive airway pressure adherence. The only baseline variable associated with poor adherence was the presence of previous stroke (hazard ratio 4.00, 95% confidence interval 1.92–8.31). Adequate adherence at 1 month also predicted good adherence at the end of the follow‐up (hazard ratio 14.4, 95% confidence interval 4.94–56). Both variables also predicted adherence at a threshold of 6 hr per night. Our results show that good continuous positive airway pressure adherence is an achievable and feasible goal in patients with resistant hypertension and obstructive sleep apnea. Previous stroke and short‐term adherence predicted long‐term adherence.     

Acoustic analysis of infantile stridor: A review

The review compares five methods that utilise electronic/computer acoustic processing techniques for the analysis of infantile stridor sounds. The first method uses traditional spectrographic techniques to produce time/frequency/intensity three-dimensional representation of the waveform. The second method is computer-based and uses the fast Fourier transformation (FFT) to show the frequency composition of the waveform. The third uses linear prediction coefficients (LPCs) to produce a power spectrum and inverse filtering to estimate the cross-sectional area of the human upper airway. The fourth technique employs a proprietary digital filterbank to analyse normal infant vocalisations, which may be used as a control by subsequent researchers. In the fifth method, a physiologically based digital filterbank, designed to closely model the human ear response, is proposed. It is envisaged that this approach will offer the flexibility of all the previous techniques and also closely model the analysis procedure carried out using subjective auscultation. It is concluded that none of the above techniques are sufficiently robust to provide unambiguous diagnosis of stridor type and that a reappraisal is required in terms of feature extraction so that relevant features can be identified. To this end, the authors propose that a physiologically based model of the human airway, including the vocal cords, be developed as an aid to the assessment of acoustic features.     

脉动流模拟系统血压波形相似度算法研究

目的研究表征血压波形间相似程度的量化指标,并应用到脉动流模拟系统中血压波形的分析。方法在对已有相似度算法进行研究的基础上,结合血压波形自身的特点,提出加权平均算法。该算法将相关系数法和特征参数法相结合,分别从整体和局部特征对波形进行相似性度量,兼具全局匹配和局部比较的优点。结果与夹角余弦法、平均绝对差法和数值型相似系数法相比,加权平均算法更适用于血压波形相似度的分析。结论加权平均算法可以表征不同血压波形之间的差异,比较不同脉动流装置之间的模拟性能,进一步完善后还可以用于其他生理波形的分析。