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CFD has emerged as a promising diagnostic tool for clinical trials, with tremendous potential. However, for real clinical applications to be useful, overall statistical findings from large population samples (e.g., multiple cases and models) are needed. Fully resolved solutions are not a priority, but rather rapid solutions with fast turn-around times are desired. This leads to the issue of what are the minimum modelling criteria for achieving adequate accuracy in respiratory flows for large-scale clinical applications, with a view to rapid turnaround times. This study simulated a highly-resolved solution using the large eddy simulation (LES) method as a reference case for comparison with lower resolution models that included larger time steps and no turbulence modelling. Differences in solutions were quantified by pressure loss, flow resistance, unsteadiness, turbulence intensity, and hysteresis effects from multiple cycles. The results demonstrated that sufficient accuracy could be achieved with lower resolution models if the mean flow was considered. Furthermore, to achieve an established transient result unaffected by the initial start-up quiescent effects, the results need to be taken from at least the second respiration cycle. It was also found that the exhalation phase exhibited strong turbulence. The results are expected to provide guidance for future modelling efforts for clinical and engineering applications requiring large numbers of cases using simplified modelling approaches.

Paediatric Asthma contributes in paediatric global burden of diseases, as the most common chronic disease in children. Children are exposed to many environmental risk-factors, able to determine or worsen respiratory diseases, and contributing to asthma and asthma-like symptoms increases, especially in metropolitan areas. In urban settings, surrounding vegetation (greenness) may provide important benefits to health, including the promotion of physical activity and the mitigation of air and noise pollution. The aim of this study was to investigate the association between greenness and respiratory health. A total of 187 children (10&ndash, 13 yrs old) were recruited in Turin, the north-western part of Italy. The prevalence of asthma and asthma-like symptoms was calculated from self-reported data collected by SIDRIA questionnaire. Spirometry test was performed to obtain respiratory flow measurements. Greenness was measured at individual level through the Normalised Difference Vegetation Index (NDVI) estimations from remote-sensing images. Higher exposure (3rd tertile vs. 1st tertile) to NDVI was associated to significantly lower ORs for asthma [0.13 CI 95% 0.02&ndash, 0.7, p = 0.019], bronchitis [0.14 CI 95% 0.05&ndash, 0.45, p = 0.001], and current wheezing [0.25 CI 95% 0.09&ndash, 0.70, p = 0.008]. A significative positive association was found between greenness and FEF25&ndash, 75, since children exposed to the 2nd tertile of NDVI reported a significantly decreased FEF25&ndash, 75 compared to those in the 3rd tertile [B: &minus, 2.40, C.I.95%: &minus, 0.48&ndash, 0.01, p = 0.049]. This cross-sectional study provided additional data on still inconsistent literature referring to respiratory health in children and green spaces, attesting a positive effect of greenness in a specific area of Italy. Further research is still needed.

Respiratory inductive plethysmography (RIP) is recommended as an alternative respiratory sensor for the identification of each apnea and hypopnea event in polysomnography. Using this sensor, the cumulative RIP results from the chest and abdomen (RIP sum) and time-derived results of the RIP sum (RIP flow) are calculated to track respiratory flow. However, the effectiveness of this sensor and the calculated respiratory results is still unclear, and validation studies for the scoring of respiratory events in polysomnography are rare. Two hundred subjects were selected according to the severity of obstructive sleep apnea. A sleep specialist re-evaluated the respiratory events based on RIP flow data in a single-blind study. Statistical analysis was conducted with paired respiratory events scored in each of the RIP flow and polysomnography datasets. All respiratory events scored from the RIP flow were strongly correlated with those identified with standard sensors of polysomnography, regardless of disease severity. Most of the respiratory parameters from RIP flow trended toward underestimation. The RIP flow obtained from the alternative RIP sensor was appropriate for the diagnosis of obstructive sleep apnea based on a receiver operating characteristic curve. Scored respiratory events from RIP flow data effectively reflected the respiratory flow and statistically correlated with the results from standard polysomnography sensors. Therefore, analyzing RIP flow utilizing an RIP sensor is considered a reliable method for respiratory event scoring.

The objective of this pilot study was to determine the minimum operational flow for loose-fitting powered air-purifying respirators (PAPR) used in healthcare cleaning services. An innovative respiratory flow recording device was worn by nine healthcare workers to obtain the minute volume (MV, L/min), mean inhalation flow (MIF, L/min), and peak inhalation flow (PIF, L/min) while performing “isolation unit work” (cleaning and disinfecting) of a patient room within 30 min. The MV and PIF were compared with the theoretical values obtained from an empirical formula. The correlations of MV, MIF, and PIF with subjects’ age, weight, height, body surface area (A(Du)), and body mass index (BMI) were analyzed. The average MV, MIF, and PIF were 33, 74, and 107 L/min, with maximal airflow rates of 41, 97, and 145 L/min, respectively, which are all below the current 170 L/min minimum operational flow for NIOSH certified loose-fitting PAPRs.

OBJECTIVES Using a method developed for this study, the objective was to perform a quantitative analysis of glottic aperture during the respiratory cycle in subjects suspected of having inducible laryngeal obstruction (ILO) and to compare results to healthy individuals. Correlations between glottic aperture and spirometric parameters were assessed. METHODS Subjects with high clinical suspicion of ILO and atypical inspiratory findings in spirometry had the images of their laryngoscopy displayed alongside a respiratory flow chart and both were recorded simultaneously. This method allowed detailed analysis of the glottic aperture by measuring the angle of the anterior commissure during inspiration and expiration. Healthy volunteers who performed the same tests and agreed to provide data to this study were used as a control group. RESULTS All 15 subjects with ILO and 16 healthy participants were evaluated successfully using the proposed method. Measures of the anterior commissure angle in the ILO versus control group were significantly different in all observed parameters and just three ILO subjects had an anterior commissure closure greater than 50% during the respiratory cycle. Inspired volume (FIF50 ) and mid-vital capacity ratio (FEF50 /FIF50 ) had a significant correlation with glottic aperture parameters when considering the evaluation of the subjects all together. CONCLUSION The proposed method provided precise and quantitative analysis of glottic aperture during the respiratory cycle thus indicating that the usage of equipment that allows for such assessment should be encouraged. Also, the threshold of vocal cords closure accepted as indicative of ILO should be reconsidered, especially during the intercritical period of the disease. LEVEL OF EVIDENCE 4 Laryngoscope, 130:E349-E356, 2020.

Objective: The aim of this research was to develop a swallowing assessment method to help prevent aspiration pneumonia. The method uses simple sensors to monitor swallowing function during an individual's daily life. Methods: The key characteristics of our proposed method are as follows. First, we assess swallowing function by using respiratory flow, laryngeal motion, and swallowing sound signals recorded by simple sensors. Second, we classify whether the recorded signals correspond to healthy subjects or patients with dysphagia. Finally, we analyze the recorded signals using both a feature extraction method (linear predictive coding) and a machine learning method (support vector machine). Results: Based on our experimental results for 140 healthy subjects (54.5 $ \pm $ 32.5 years old) and 52 patients with dysphagia (75.5 $ \pm $ 20.5 years old), our proposed method could achieve 82.4% sensitivity and 86.0% specificity. Conclusion: Although 20% of testing sample sets were erroneously classified, we conclude that our proposed method may facilitate screening examinations of swallowing function. Significance: In combination with the portable sensors, our proposed method is worth utilizing for noninvasive swallowing assessment.

BACKGROUND Nasal septal deviation is one of the major causes of nasal respiratory flow disorders. During the rhinoseptoplasty, the septum can be treated through a closed traditional access or through an open access. To date, there are still no objective functional indications of the best access to use in rhinoseptoplasty. For this reason, we evaluated, objectively and subjectively, the functional efficiency of open access and compared it with that of closed access. The aim is to highlight any functional outcome differences between the 2 types of access. METHODS The study involved up to 50 patients, from January 2006 to June 2017; 20 patients underwent modified extracorporeal rhinoseptoplasty with open access, and 30 patients underwent modified extracorporeal rhinoseptoplasty with closed access. We evaluated the nasal obstruction by using the validated questionnaire Nasal Obstruction Symptoms Evaluation (subjective method) and by performing the anterior active rhinomanometry (objective method). Both evaluations were performed in 3 different times: preoperative period, 3 months, and 6 months after surgery. RESULTS In the open cohort, the rhinomanometric analysis showed a statistically significant increase between preoperative period and sixth month after surgery; however, the nose score had a statistically significant increase in both 3 and 6 months after surgery. At 3 months after surgery, the rhinomanometric score was higher in patients with closed access than patients with open access; this difference has disappeared at 6 months after surgery. At 3 and 6 months after surgery, the improvement in the Nasal Obstruction Symptoms Evaluation average score was greater in patients with open access compared with patients with closed access. No complications were observed. CONCLUSIONS Based on the results obtained from our work, we can declare that open access is a functionally valid procedure. At 6 months after surgery, the 2 accesses have a comparable functional efficacy.

Sleep-related breathing disorders (SRBD) are commonly present in patients with Prader-Willi syndrome (PWS). Recombinant human growth hormone (rhGH) treatment is reported to improve breathing function in PWS, but the findings are not explicit.Screening polysomnography- polygraphy (PSG), assessing nasal respiratory flow, respiratory effort, and blood oxygen saturation, was used. Group 1 - before rhGH therapy (n = 11, mean age 3.0 years); PSG was repeated after the start of rhGH therapy in a mean time of 0.9 years in six patients (Group 1a). Group 2 - on rhGH treatment, for a mean time of four years (n = 17, mean age 8.8 years). Group 3 - without rhGH therapy due to severe obesity (n = 8, mean age 13.1 years).Group 1 - mean apnoea-hypopnoea index (AHI) was 10.2, oxygen desaturation index (ODI)- 36.3, Group 1a- AHI 12.0, ODI 60.9, Group 2-AHI 9.0, ODI 25.1, Group 3- AHI 8.2, ODI 22.0. ODI was significantly higher in Group 1a than in the other groups (p0.005), but not strictly related to SRBD. The results in Group 2 did not differ significantly from those of Group 1.Our study proves the high frequency of SRBD among PWS patients, with worsening of ODI after short-term rhGH therapy.

This work presents a detailed framework to detect the location of heart sound within the respiratory sound based on temporal fuzzy c-means (TFCM) algorithm. In the proposed method, respiratory sound is first divided into frames and for each frame, the logarithmic energy features are calculated. Then, these features are used to classify the respiratory sound as heart sound (HS containing lung sound) and non-HS (only lung sound) by the TFCM algorithm. The TFCM is the modified version fuzzy c-means (FCM) algorithm. While the FCM algorithm uses only the local information about the current frame, the TFCM algorithm uses the temporal information from both the current and the neighboring frames in decision making. To measure the detection performance of the proposed method, several experiments have been conducted on a database of 24 healthy subjects. The experimental results show that the average false-negative rate values are 0.8 ± 1.1 and 1.5 ± 1.4 %, and the normalized area under detection error curves are $$0.0145$$ and $$0.0269$$ for the TFCM method in the low and medium respiratory flow rates, respectively. These average values are significantly lower than those obtained by FCM algorithm and by the other compared methods in the literature, which demonstrates the efficiency of the proposed TFCM algorithm. On the other hand, the average elapsed time of the TFCM for a data with length of $$20$$ s is 0.2 ± 0.05 s, which is slightly higher than that of the FCM and lower than those of the other compared methods.

In this paper, an innovative method for estimating the respiratory flow and efforts is proposed and evaluated in various postures and flow rates. Three micro electro-mechanical system accelerometers were mounted on the suprasternal notch, thorax and abdomen of subjects in supine, prone and lateral positions to record the upper airway acceleration and the movements of the chest and abdomen wall. The respiratory flow and efforts were estimated from the recorded acceleration signals by applying machine learning methods. To assess the agreement of the estimated signals with the well-established measurement methods, standard error of measurement (SEM) was calculated and $$\rho = 1-{\rm SEM}$$ was estimated for every condition. A significant agreement between the estimated and reference signals was found ( $$\rho = 0.83, 0.82$$ and 0.89 for the estimated flow, thorax and abdomen efforts respectively). Additionally, the agreement of the estimated and reference flows was assessed by calculating the ratio of time at the tidal peak inspiration flow to the inspiration time ( $$t_{\rm PTIF}/t_{\rm I}$$ ) and the ratio of time at the tidal peak expiration flow to the expiration time ( $$t_{\rm PTEF}/t_{\rm E}$$ ). Overall mean and standard deviation of absolute value of differences between $${t}_{{\rm PTIF}}/{t}_{{\rm I}}$$ and $${t}_{{\rm PTEF}}/{t}_{{\rm E}}$$ ratios calculated for every breathing cycle of reference and estimated flow were 0.0035 (0.06) and 0.051 (0.032), respectively. The presented results demonstrate the feasibility of using the upper-body acceleration as a simple solution for long-term monitoring of respiratory features.

Tracheal respiratory sound analysis is a simple and non-invasive way to study the pathophysiology of the upper airway and has recently been used for acoustic estimation of respiratory flow and sleep apnea diagnosis. However in none of the previous studies was the respiratory flow-sound relationship studied in people with obstructive sleep apnea (OSA), nor during sleep. In this study, we recorded tracheal sound, respiratory flow, and head position from eight non-OSA and 10 OSA individuals during sleep and wakefulness. We compared the flow-sound relationship and variations in model parameters from wakefulness to sleep within and between the two groups. The results show that during both wakefulness and sleep, flow-sound relationship follows a power law but with different parameters. Furthermore, the variations in model parameters may be representative of the OSA pathology. The other objective of this study was to examine the accuracy of respiratory flow estimation algorithms during sleep: we investigated two approaches for calibrating the model parameters using the known data recorded during either wakefulness or sleep. The results show that the acoustical respiratory flow estimation parameters change from wakefulness to sleep. Therefore, if the model is calibrated using wakefulness data, although the estimated respiratory flow follows the relative variations of the real flow, the quantitative flow estimation error would be high during sleep. On the other hand, when the calibration parameters are extracted from tracheal sound and respiratory flow recordings during sleep, the respiratory flow estimation error is less than 10%.

Background Nasal obstruction is one of the most frequent symptoms in the ear, nose, and throat (ENT) setting. It can be evaluated either subjectively or objectively. In a subjective way, a visual analog scale (VAS) and the Sino-Nasal Outcome Test 20 (SNOT 20) can rapidly quantify the degree of obstruction, whereas the most commonly used objective methods are nasal endoscopy and active anterior rhinomanometry (AAR). It is still a matter of controversy to what extent the sense of nasal obstruction is associated with objective measures for nasal space and airflow. The aim of the study was to evaluate nasal breathing before and after functional nasal surgery by video-rhino-hygrometer (VRH) comparing the results with widely accepted methods. Methods Twenty patient candidates for septoplasty and inferior turbinate reduction were included in the study. SNOT-20, VAS, nasal endoscopy, and AAR were analyzed and compared with VRH values. Results Before surgery VRH showed variability of nasal respiratory flow between individuals and between nostrils. After surgery we had an increase (p < 0.05) of airflow in both nostrils. VRH data were found to be correlated with VAS and SNOT-20 values (p < 0.05) both pre- and postoperatively. Despite the statistically significant correlation of AAR with SNOT-20 and VAS, no statistically significant correlation between AAR and VRH was found. Conclusion VRH provides an immediate, easy, and noninvasive assessment of nasal respiration. For these reasons it can be used, in association with rhinoscopic data and other instrumental tests, to evaluate nasal breathing in daily ENT practice.

Clear evidence links voluntary breath control, intra-abdominal pressure and lumbar stability. However, little is known regarding optimal breath control during manual materials handling. No studies have examined natural breath control while lifting a maximal load. Fourteen healthy subjects lifted a loaded crate from the floor to a table while respiratory flow data were collected. The loads lifted began at 10% of body weight and increased up to 50% (if tolerated) by 5% increments. Data from the minimum, moderate and maximum loads were analysed. Uniform and consistent breath holding during lifting of a maximally tolerated load did not occur. Across all three loads, frequency of inspiration was highest immediately prior to lift-off and significantly higher inspired volume occurred at lift-off of the load compared with preparation for lifting. Holding the breath does not appear to be related to lifting of a maximally tolerated load from floor to table. STATEMENT OF RELEVANCE: The findings demonstrate that consistent patterns of naturally occurring breath control during lifting of a maximal load can be identified and do not include uniform breath holding. The findings may assist in creating models for optimal breath control, which will minimise risk of injury during manual material handling tasks.

The assessment of swallowing function is important for the prevention of aspiration pneumonia. We developed a new swallowing monitoring system that uses respiratory flow, swallowing sound, and laryngeal motion. We applied this device to 11 healthy volunteers and 10 patients with dysphagia. Videofluoroscopy (VF) was conducted simultaneously with swallowing monitoring using our device. We measured laryngeal rising time (LRT), the time required for the larynx to elevate to the highest position, and laryngeal activation duration (LAD), the duration between the onset of rapid laryngeal elevation and the time when the larynx returned to the lowest position. In addition, we evaluated the coordination between swallowing and breathing. We found that LAD was correlated with a VF-derived parameter, pharyngeal response duration (PRD) in healthy subjects (LAD: 959 ± 259 ms vs. PRD: 1062 ± 149 ms, r = 0.60); however, this correlation was not found in the dysphagia patients. LRT was significantly prolonged in patients (healthy subjects: 320 ± 175 ms vs. patients: 465 ± 295 ms, P

Weaning from mechanical ventilation is still one of the most challenging problems in intensive care. Unnecessary delays in discontinuation and weaning trials that are undertaken too early are both undesirable. This study investigated the contribution of spectral signals of heart rate variability (HRV) and respiratory flow, and their coherence to classifying patients on weaning process from mechanical ventilation. A total of 121 candidates for weaning, undergoing spontaneous breathing tests, were analyzed: 73 were successfully weaned (GSucc), 33 failed to maintain spontaneous breathing so were reconnected (GFail), and 15 were extubated after the test but reintubated within 48 h (GRein). The power spectral density and magnitude squared coherence (MSC) of HRV and respiratory flow signals were estimated. Dimensionality reduction was performed using principal component analysis (PCA) and sequential floating feature selection. The patients were classified using a fuzzy K-nearest neighbour method. PCA of the MSC gave the best classification with the highest accuracy of 92% classifying GSucc versus GFail patients, and 86% classifying GSucc versus GRein patients. PCA of the respiratory flow signal gave the best classification between GFail and GRein patients (79% accuracy). These classifiers showed a good balance between sensitivity and specificity. Besides, the spectral coherence between HRV and the respiratory flow signal, in patients on weaning trial process, can contribute to the extubation decision.

The physiological mechanisms by which vibration and other physiotherapy interventions may clear secretions in subjects with cystic fibrosis are unknown. The main aim of this study was to compare the expiratory flow rates and frequencies of airflow oscillation of vibration to those of Acapella(R), Flutter(R), positive expiratory pressure and percussion. Respiratory flow rates were measured during interventions, the order of which was randomised. The oscillation of the airflow of the interventions was determined by frequency spectral analysis. In 18 young adult subjects with cystic fibrosis, the mean peak expiratory flow rate of vibration was greater than Flutter(R), percussion, Acapella(R) and positive expiratory pressure. The mean+/-sd of the oscillation of the airflow of vibration (8.4+/-0.4 Hz) was lower than Acapella(R) (13.5+/-1.7 Hz) and Flutter(R) (11.3+/-1.5 Hz) but similar to percussion (7.3+/-0.3 Hz). Theoretically, the higher peak expiratory flow rate of vibration compared to the other physiotherapy interventions may promote secretion clearance. In addition, the frequency of oscillation of vibration was within the range demonstrated to increase mucus transport. This study has provided some evidence for the physiological rationale for the use of vibration to aid secretion clearance.

The functional residual capacity (FRC) and airway resistance (R(aw)) of the rat were measured, using a newly designed body plethysmograph (BPG), the inner environment of which was maintained at body temperature and was water-vapor saturated. The subjects were anesthetized and tracheally intubated male Wistar rats (n = 15). After measuring the FRC and R(aw), we analyzed the effects of inhaled methacholine (Mch, 0-8 mg/ml) on R(aw).The determined FRC was 5.37 +/- 0.22 ml (mean +/- SE). An almost linear relationship between box pressure and respiratory flow was obtained when the difference between box-gas temperature and the rectal temperature of the rat was less than 1.0 degrees C. The R(aw) at FRC was 0.230 +/- 0.017 cm H(2)O/ml/s. It increased proportionally with increases in the Mch concentration. When the dynamic changes in R(aw) were analyzed, the R(aw) was found to progressively increase during expiration; this increase continued throughout inspiration. Thus in the rat, R(aw) is not simply a function of changes in lung volume. In conclusion, the humidity- and temperature-adjusted BPG provided an absolute and possibly dynamic value of R(aw).

Studying the inspiratory recruitment of the scalenes is clinically relevant, but the interpretation of surface electromyographic (EMG) recordings is difficult. The aim of this study was to optimize an averaging method to analyze the surface EMG activity of the scalenes. Ten healthy subjects were studied. Nasal flow and surface EMG of the right scalene were recorded during 15 min epochs of quiet breathing. In four subjects, needle scalene EMG was also recorded. The flow signal was used to trigger the ensemble averaging of the ventilatory wave forms from 80 consecutive breaths. In eight cases, this evidenced a phasic inspiratory activation of the scalenes and permitted the determination of the electromechanical inspiratory delay (134+/-55 ms) and post-inspiratory activity (811+/-233 ms). When simultaneously available, surface and intramuscular recordings provided identical results. An averaging method triggered from a respiratory flow signal can identify and characterize a low phasic inspiratory activity of the scalenes within a noisy surface signal.

A partial-body plethysmograph was developed for measuring the respiratory flow of anesthetized mice during routine microimaging experiments performed in the close confines of an 89-mm-diameter, vertical-bore magnet. Respiratory flow patterns were used for synchronizing conventional T2-weighted spin-echo imaging with the respiratory cycle, thereby, significantly reducing motion-induced artifacts and increasing observed liver lesion contrast.

We previously published a method for measuring several physiological traits causing obstructive sleep apnea (OSA). The method, however, had a relatively low success rate (76%) and required mathematical modeling, potentially limiting its application. This paper presents a substantial revision of that technique. To make the measurements, continuous positive airway pressure (CPAP) was manipulated during sleep to quantify 1) eupneic ventilatory demand, 2) the level of ventilation at which arousals begin to occur, 3) ventilation off CPAP (nasal pressure = 0 cmH2O) when the pharyngeal muscles are activated during sleep, and 4) ventilation off CPAP when the pharyngeal muscles are relatively passive. These traits could be determined in all 13 participants (100% success rate). There was substantial intersubject variability in the reduction in ventilation that individuals could tolerate before having arousals (difference between ventilations #1 and #2 ranged from 0.7 to 2.9 liters/min) and in the amount of ventilatory compensation that individuals could generate (difference between ventilations #3 and #4 ranged from −0.5 to 5.5 liters/min). Importantly, the measurements accurately reflected clinical metrics; the difference between ventilations #2 and #3, a measure of the gap that must be overcome to achieve stable breathing during sleep, correlated with the apnea-hypopnea index (r = 0.9, P < 0.001). An additional procedure was added to the technique to measure loop gain (sensitivity of the ventilatory control system), which allowed arousal threshold and upper airway gain (response of the upper airway to increasing ventilatory drive) to be quantified as well. Of note, the traits were generally repeatable when measured on a second night in 5 individuals. This technique is a relatively simple way of defining mechanisms underlying OSA and could potentially be used in a clinical setting to individualize therapy.

One objective of mechanical ventilation is the recovery of spontaneous breathing as soon as possible. Remove the mechanical ventilation is sometimes more difficult that maintain it. This paper proposes the study of respiratory flow signal of patients on weaning trials process by autoregressive moving average model (ARMA), through the location of poles and zeros of the model. A total of 151 patients under extubation process (T-tube test) were analyzed: 91 patients with successful weaning (GS), 39 patients that failed to maintain spontaneous breathing and were reconnected (GF), and 21 patients extubated after the test but before 48 hours were reintubated (GR). The optimal model was obtained with order 8, and statistical significant differences were obtained considering the values of angles of the first four poles and the first zero. The best classification was obtained between GF and GR, with an accuracy of 75.3% on the mean value of the angle of the first pole.

To study the efficacy of peak nasal inspiration flow (PNIF) as a means of recording change in nasal patency 20 subjects were given increasing doses of intranasal 5tometazo1ine. Nasal resistance (NR) and peak nasal inspiratory flow (PNIF) were measured in the resting stateand after each xylometazoline administration. Successive increases in dose caused a progressive decrease in nasal resistance and an increase in PNIF but the change in peak nasal inspiratory flow (PNIF) was much less. Peak nasal inspiratory flow shows a plateau effect as nasal resistance decreases. The reasons for this plateau are discussed in terms of respiratory flow mechanics

Auto-CPAP devices (APAP) are controlled, e.g.,by the respiratory flow and pressure to adjust the treatment pressure to the variable obstruction in sleep apnea syndromes.By obstruction of the upper airway during inspiration,a pressure difference between the lower airways and the mask can be measured. In case of an opening of the pharynx at the end of the obstruction, the pressure decreases immediately. This brief negative pressure, the so-called obstructive pressure peak (OPP) can be used to identify obstruction or open airways with the algorithm of an APAP device. Useless pressure increases, e.g., after central apneas without obstruction may be avoided. We therefore investigated the association of the OPP signal with respiratory events during APAP therapy.In this pilot study, 13 patients with obstructive sleep apnea syndrome were evaluated. Attended automatic CPAP titration (SOMNO balance, Fa Weinmann Hamburg/Germany)was performed. The OPP signal was recorded synchronous lyin parallel with the polysomnographic data. If the OPP signal was within a time range of ± 5 s of the resumption of normal breathing, it was assigned to the event.A total of 480 sleep-related breathing disorders events were studied. The most common were the mixed apneas associated with more than 90% of all cases with an OPP signal, followed by obstructive sleep apneas (66.7%)and central apneas (38%). The difference in OPP frequency distribution between central apneas and obstructive apneas was significant with p0.001.The analysis of the pressure characteristics of APAP treatment with the registration of OPP allows a further differentiation in obstructed and not obstructed upper airways.

Background and Objectives : Obstructive sleep apnea syndrome (OSAS) is a common disorder characterized by numerous episodes of absence of respiratory flow during sleep, which can be followed by a decrease in SaO2 , which is rapidly normalized when ventilation resumes. We hypothesize that this hypoxia-reoxygenation phenomena may affect the generation of vascular endothelial growth factor (VEGF), erythropoietin (EPO), endothelin-1 (ENDO-1), and inducible nitric oxide synthase (iNOS). Design and Setting : Prospective, patients referred to sleep disorders center. Patients and Methods : The presence and severity of OSAS were determined using the standard overnight polysomnography. Diagnosis of OSAS was made when the apnea-hypopnea index (AHI) was ≥15, independent of the appearance of symptoms. Serum levels of VEGF, EPO, ENDO-1, and nitrite-nitrate were measured after overnight fasting in 69 patients with OSAS and in 17 healthy control subjects. Serum levels of VEGF and nitrite-nitrate were measured again after 12 weeks of treatment with continuous positive airway pressure (CPAP) in OSAS patients. Results : Serum VEGF levels were found to be significantly higher and nitrite-nitrate levels were found to be significantly lower in OSAS patients than in controls (P=.003, .008, respectively), but no differences in EPO and ENDO-1 levels were found between the groups. We demonstrated that in OSAS patients, the serum VEGF levels were decreased and nitrate levels were increased after 12 weeks of CPAP treatment (P=.001, .002, respectively). Conclusion : According to our data, it is likely that hypoxia-reoxygenation phenomena affect the VEGF and nitrite-nitrate levels, which may be pathogenic factors in generating cardiovascular complications in OSAS.

Statistical analysis, power spectral density, and Lempel Ziv complexity, are used in a multi-parameter approach to analyze four temporal series obtained from the Electrocardiographic and Respiratory Flow signals of 126 patients on weaning trials. In which, 88 patients belong to successful group (SG), and 38 patients belong to failure group (FG), i.e. failed to maintain spontaneous breathing during trial. It was found that mean values of cardiac inter-beat and breath durations give higher values for SG than for FG; Kurtosis coefficient of the spectrum of the rapid shallow breathing index is higher for FG; also Lempel Ziv complexity mean values associated with the respiratory flow signal are bigger for FG. Patients were then classified with a pattern recognition neural network, obtaining 80% of correct classifications (81.6% for FG and 79.5% for SG).

Respiratory drives folow various afferent pathways to the respiratory centres; nevertheless, steady-state breathing patterns described in terms of tidal volumes and phase durations are largely independent of the nature of the respiratory stimulus. Flow has now been recorded during steady states from six subjects in rest and hyperpnoea induced by exercise, and hypercapnia in euoxia and in hypoxia (asphyxia). Flow patterns from different stimuli were compared isopnoeically. Quantitative methods allowed the patterns to be described in terms of several variables. The consistent small differences in isopnoeic flow patterns were: In asphyzia, the initial inspiratory acceleration was greater than in hypercapnia, and the peak flow was reached earlier. In exercise the peak flow occured later in inspiration, and the expiratory flow was maintained high until nearer the end of the phase than with the chemical drives so that the flow pattern was less angular in shape. Stimulus-dependent effects, obvious during transient changes, are greatly attenuated rather than absent in steady states.

Background Although inspiratory assist of spontaneous breathing in intubated patients is common, expiratory assist functions have rarely been reported. Effective expiratory support (ES) could be used to compensate for endotracheal tube (ETT) resistance during spontaneous breathing. In this study, we examined the performance of a new system designed to provide both inspiratory support (IS) and ES during spontaneous breathing with the goal of reducing the effective resistance of the ETT. Methods The ES system consisted of a ventilator demand valve and a computer-controlled piston cylinder, which aspirated gas from the respiratory circuit during the expiratory phase. The movement of the piston was synchronized with spontaneous breathing. We compared the pressures at the tip of the ETT and in the breathing circuit during spontaneous breathing through an ETT of internal diameter (ID) 5 mm with that of an ETT with ID 8 mm in nine healthy adult male volunteers. The ventilatory mode was set to maintain a continuous airway pressure of 0 cm H(2)O. Three ventilator settings (no support, IS only, and IS plus ES) were compared using ID 5 mm ETT. Results We monitored pressure in the breathing circuit (P(aw)), ETT tip pressure (P(tip)), and respiratory flow. The P(tip) of the ID 5 mm ETT showed a large negative deflection during inspiration and a positive deflection during expiration without support. IS alone did not improve the respiratory pattern through the small ETT. However, IS plus ES resulted in negative P(aw) during expiration in addition to positive deflection of P(aw) during inspiration, making the pressure characteristics of P(tip) similar to those of ID 8 mm ETT. Moreover, IS plus ES produced a respiratory pattern through the ID 5 mm ETT that was similar to that through the ID 8 mm ETT. Conclusions In this study of healthy volunteers, IS plus ES compensated for the airway resistance imposed by a ID 5.0 mm ETT to create pressure changes at the tip of the ETT similar to those of an ID 8.0 mm ETT.

Capnography waveforms and capnometry are useful perioperative monitoring tools. The paramagnetic oxygen analyzers incorporated in many clinical monitoring systems estimate oxygen concentration in the breathing circuit during various phases of ventilation. The oxygen concentration is plotted as a real-time waveform and displayed as an oxygraph. However, the clinical utility of oxygraphy is under evaluated. We are reporting four different clinical scenarios in neurosurgical patients, wherein the information yielded by oxygraphy were either not available on the capnograph or were revealed in a more promising way on the oxygraph than on the capnograph. A real-time oxygraphy waveform has four phases similar to a capnograph, although displayed in a reverse manner. Oxygraphy was useful in our patient to determine the adequacy of preoxygenation. Airway complications and unwanted neuromuscular recovery can be detected earlier by oxygraphy compared to capnography. The oxygraphy peak-to-baseline scale difference can be compressed to as low as to 6% of oxygen concentration. When the peak-to-baseline scale difference is 6 mmHg, the oxygraph becomes sensitive to even minute changes in respiratory flow characteristics. Oxygraphy may have a potential role in clinical monitoring.

1. Resonant frequency of the chest-lung system in six tracheotomized, spontaneously breathing dogs was determined by analyzing the shape of the respiratory flow curve. 2. The resonant frequency was calculated from the periodic deviations from a sinusoidal flow pattern observed in the inspiratory phase of the breathing cycle. 3. Mean (+/- S.D.) resonant frequency was 6.1 +/- 0.9 Hz which was very close to the panting frequency (5.7 Hz) of the same dogs. 4. Resonant frequencies of the respiratory system in various species are compared.

Brachycephalic obstructive airway syndrome (BOAS) is an important health and welfare problem in several popular dog breeds. Whole-body barometric plethysmography (WBBP) is a non-invasive method that allows safe and repeated quantitative measurements of respiratory cycles on unsedated dogs. Here respiratory flow traces in French bulldogs from the pet population were characterised using WBBP, and a computational application was developed to recognise affected animals. Eighty-nine French bulldogs and twenty non-brachycephalic controls underwent WBBP testing. A respiratory functional grading system was used on each dog based on respiratory signs (i.e. respiratory noise, effort, etc.) before and after exercise. For development of an objective BOAS classifier, functional Grades 0 and I were considered to have insignificant clinical signs (termed here BOAS-) and Grades II and III to have significant signs (termed here BOAS+). A comparison between owner-perception of BOAS and functional grading revealed that 60 % of owners failed to recognise BOAS in dogs that graded BOAS+ in this study.WBBP flow traces were found to be significantly different between non-brachycephalic controls and Grade 0 French bulldogs; BOAS- and BOAS+ French bulldogs. A classifier was developed using quadratic discriminant analysis of the respiratory parameters to distinguish BOAS- and BOAS + French bulldogs, and a BOAS Index was calculated for each dog. A cut-off value of the BOAS Index was selected based on a receiver operating characteristic (ROC) curve. Sensitivity, specificity, positive predictive value, and negative predictive value of the classifier on the training group (n=69) were 0.97, 0.93, 0.95, and 0.97, respectively. The classifier was validated using a test group of French bulldogs (n=20) with an accuracy of 0.95. WBBP offers objective screening for the diagnosis of BOAS in French Bulldogs. The technique may be applied to other brachycephalic breeds affected by BOAS, and possibly to other respiratory disease in dogs.

Background Maximum pressures developed by the respiratory muscles can indicate the health of the respiratory system, help to determine maximum respiratory flow rates, and contribute to respiratory power development. Past measurements of maximum pressures have been found to be inadequate for inclusion in some exercise models involving respiration. Methods Maximum inspiratory and expiratory airway pressures were measured over a range of lung volumes in 29 female and 19 male adults. A commercial bell spirometry system was programmed to occlude airflow at nine target lung volumes ranging from 10% to 90% of vital capacity. Results In women, maximum expiratory pressure increased with volume from 39 to 61 cmH2O and maximum inspiratory pressure decreased with volume from 66 to 28 cmH2O. In men, maximum expiratory pressure increased with volume from 63 to 97 cmH2O and maximum inspiratory pressure decreased with volume from 97 to 39 cmH2O. Equations describing pressures for both sexes are: Pe/Pmax = 0.1426 Ln( %VC) + 0.3402 R2 = 0.95 Pi/Pmax = 0.234 Ln(100 - %VC) - 0.0828 R2 = 0.96 Conclusion These results were found to be consistent with values and trends obtained by other authors. Regression equations may be suitable for respiratory mechanics models.

Summary The effects of training on ventilation and blood gases during exercise were investigated in 6 clinically normal, detrained Thoroughbred horses. They underwent a 16 week training programme similar to the type frequently used for Thoroughbred racehorses in Great Britain. Standardised treadmill exercise tests (2 min canter at 8 and 10 m/s [C8 and C10] and 2 min gallop at 12 m/s [G12], on a level surface) were performed prior to and after 16 weeks of training. Respiratory flow rates were measured using ultrasound flow transducers. Blood samples were drawn from a transverse facial artery and the right atrium. Minute ventilation, respiratory frequency and tidal volume were not significantly altered by training. Peak inspiratory flow rate was lower following training at 8 and 10 m/s, but not at 12 m/s. Arterial oxygen tension was decreased during trot and canter following training. Blood lactate concentration post G12 decreased following training (10.5 ± 2.2 mmol/l vs. 7.7 ± 2.2 mmol/l; P

ResMed Autoset (AS) is a simplified diagnosis system for obstructive sleep apnoea/hypopnoea syndrome (OSAS) based on the respiratory flow/time relationship by pressure variation measured through simple nasal prongs. A multicentre prospective trial was used to compare AS and polysomnography (PSG) for diagnosing 95 patients, with suspected OSAS. Physicians gave a pretest probability of the patient having OSAS. The apnoea/hypopnoea index (AHI) was compared between the two methods of diagnosis for the whole population and for subgroups according to the pretest probability. Twenty-four patients had AHI < 15 events x h(-1) on PSG and 19 AHI 15-30, and 52 patients had AHI > or = 30. Correlation between AHI assessed by AS and PSG was r=0.87 for total sleep time (TST), p or = 15 events x h(-1) to diagnose OSAS, AS has a sensitivity of 92%, specificity of 79%, positive predictive value of 93% and negative predictive value of 76%. With a pretest probability > or = 80%, sensitivity and positive predictive value were 98 and 100% respectively. Of six false negative, four had a high pretest probability (> 80%) or Epworth score > or = 10. Using these parameters as a criterion for proceeding to PSG after a negative AS study would mean that two apnoeic patients (AHI 20 and 17 events x h(-1) by PSG) would escape detection. The Autoset is useful for the detection of obstructive sleep apnoea but with high pretest probability and a negative Autoset result polysomnography should be performed.

Employing a bolus inhalation system, we noninvasively measured the fraction of inhaled ozone (O3) that is absorbed during a single breath (lambda) as a function of bolus penetration volume into the respiratory tract (Vp). During nasal breathing at a constant respiratory flow of 250 ml/s, lambda increased smoothly as Vp increased with 80% of the inhaled O3 absorbed in the upper airways and 90% absorbed at the distal end of the trachea. Oral breathing caused a distal shift of the lambda-Vp distribution to the extent that absorption in the upper airways was reduced to 50% and inhaled O3 was 90% absorbed only after a bolus reached the 13th bronchial generation. Therefore, an exercise-induced change from nasal to oral breathing can render the distal lung more susceptible to O3 damage because of an elevation in O3 dose. We also found that changing the peak inhaled bolus concentration over a 10-fold range of 0.4–4 ppm O3 did not affect the lambda-Vp distribution. This finding implies that the diffusion and chemical reaction dynamics that dictate O3 absorption are linear processes.

In our previous work, we developed a bolus inhalation apparatus and measured the longitudinal distribution of ozone (O3) uptake in intact human lungs at a quiet respiratory flow of 250 ml/min. The objective of the present study was to determine the effect of alternative respiratory flows between 150 and 1,000 ml/s. Uptake was expressed as the O3 absorbed during a single breath relative to the amount of O3 in the inhaled bolus (lambda). Measurements of lambda were correlated with the penetration volume of the bolus into the respiratory tract (Vp). Vp in the range of 20–70 ml was considered to indicate upper airways (UA), the Vp interval of 70–180 ml was identified as lower conducting airways (CA), and Vp > 180 ml was associated with the respiratory air spaces (RA). During quiet oral breathing at 250 ml/s, lambda increased smoothly as Vp increased, with 50% of the inhaled O3 absorbed in the UAs and the remainder absorbed within the CAs such that no O3 reached the RAs. The effect of increasing the respiratory flow was to shift the lambda-Vp distribution distally such that significantly less O3 was absorbed in the UAs and CAs and some O3 reached the RAs. For example, at 1,000 ml/s, only 10% of the inhaled O3 was absorbed in UAs and 65% was absorbed in the CAs such that 25% reached the RAs.(ABSTRACT TRUNCATED AT 250 WORDS)

The additional work attributable to breathing through five Mapleson A anaesthetic breathing systems (Magill, Lack, Parallel Lack, Humphrey ADE and Enclosed Magill) was studied using a lung model. With all five systems, the additional work was found to be a function of fresh gas flow, respiratory flow as well as system geometry. Within the range of fresh gas flow and respiratory flow studied, the additional work ranged between 80 mJ.l-1 and 182 mJ.l-1. Expiratory work was always greater than the inspiratory workload. Increasing fresh gas inflow into the system increases expiratory work, both resistive and elastic components. The Magill system posed the least work expenditure. The values for the additional work obtained with the lung model were of the same order of magnitude when measurements were taken in volunteers.

This study investigates the effect of helium concentration in inspired gas on resistance to breathing during experimental upper airway obstruction. Obstruction was modeled by use of a series of four polyvinyl endotracheal tubes narrowed progressively in their midportions with C clamps. Percentage ratios of helium-oxygen gas mixtures were 0:100, 40:60, 60:40, and 80:20. Gas flow was provided by two methods: 1) nontidal flow from compressed gas tanks from which resistance was calculated from pressure and flow measurements, and 2) tidal respiratory flow from human volunteers from whom respiratory effort was evaluated by using airway pressure measurements integrated over 90-second trial periods. The results derived from both methods demonstrated that the effect of helium in reducing resistance and pressure in an obstructed airway is linear (p < .016) and inversely proportional to helium concentration. Reductions in resistance and pressure were larger for the tighter obstructions (p < .007). As helium was added to the gas mixture (from 0% to 80%), resistance and airway pressure measurements dropped 42% and 58%, respectively. The major conclusions are that 1) even low concentrations of helium may have therapeutic value and 2) helium is effective only for more severe obstructions.

We studied the effects of prostacyclin on pattern of breathing in six anaesthetized pigs with aortic obstruction. PGI 2 causes a rightward displacement of VT/T relationship (Hering-Breuer threshold curve) without a corresponding change I respiratory flow. With airways occluded at the end expiratory level, we analyzed how PGI affects the central respiratory rhythm in the absence of the phasic lung volumi-related vagal loop. Infusion of prostacyclin causes leftward displacement of the T /T relationship and an increase in T o correlated with the hypotensive action The change in the bulbo-pontine pacemaker is caused by a marked increase in T , and this suggests that PGI can modulate the central respiratory rhythm, inde$endently of the blood pressure level.

Vagal influence on inspiratory motor output was assessed in 20 normal subjects and in 12 patients with respiratory disorders under enflurane anethesia using the method of airway occlusion. The change in inspiratory duration during occlusion (delta TI) was measured from mechanical parameters (respiratory flow and tracheal pressure). In eight of the subjects, however, the effect of occlusion and augmentation of tidal volume was further evaluated from diaphragmatic electromyogram. In normal subjects delta TI (mechanical) averaged 0.15 s (range -0.1 to +0.77 s) and correlated with the duration of inspiration during occlusion. Electromyographic observations indicated that the change in neural TI exceeds the change in mechanical TI by approximately 0.2 s and that augmentation of tidal volume shortens TI with no apparent volume threshold. There was a tendency for vagal influence to be higher with restrictive lung disease and lower with obstructive airway disease. These observations indicate that a majority of humans display a significant vagal influence on TI in the spontaneous tidal volume range under anesthesia.

351 SPF OF1 non-immunized mice of both sexes were infected by aerosolized Pasteurella multocida. Female mice were significantly less susceptible to infection than were males of the same age (which were heavier). Males and females of equal bodyweight, but different age, showed no significant difference in susceptibility. The difference at equal ages can be explained by the lower respiratory flow of females. The consequences of these results for experimental studies on atmospheric pollutants are discussed.

When the whole body is exposed to sinusoidal variations of ambient pressure (delta Pam) at very low frequencies (f), the resulting compression and expansion of alveolar gas is almost entirely achieved by gas flow through the airways (Vaw). As a consequence thoracic gas volume (TGV) may be computed from the imaginary part (Im) of the delta Pam/Vaw relationship: TGV = PB/[2 pi f X Im(delta Pam/Vaw)], where PB is barometric minus alveolar water vapor pressure. The method was tested in 35 normal subjects and compared with body plethysmography. The subjects sat in a chamber connected to a large-stroke-volume reciprocating pump that brought about pressure swings of 40 cmH2O at 0.05 Hz. delta Pam and Vaw were digitally processed by fast Fourier transform to extract the low-frequency component from the much larger respiratory flow. Total lung capacities (TLC) obtained by ambient pressure changes and by plethylsmography were highly correlated (r = 0.959, p less than 0.001) and not significantly different (6.96 +/- 1.38 l vs. 6.99 +/- 1.38). TLC obtained by ambient pressure changes were not influenced by lowering the frequency to 0.03 Hz, adding an external resistance at the mouth, or increasing abdominal gas volume. We conclude that the method is practical and in agreement with body plethysmography in normal subjects.

A new oral bronchodilator, cp-12,521-1 was studied in 17 asthmatics. Respiratory flow-volume loops were obtained during an 8-week double-blind randomized crossover study. The usefulness and practicality of this technique in the evaluation of the response of patients to treatment were clearly indicated.

The method of forced oscillations was used to examine the effect of curare on respiratory flow resistance and to compare it to the effect of pancuronium. The results indicate that curare has a bronchoconstrictor effect that is significant in those with pre-existing airways obstructive disease. In contrast, pancuronium has no such effect. It is concluded that curare should be avoided in any patient with significant airways obstruction. The data suggests that pancuronium is the agent of choice.

Measurements of flow resistance of various components of the respiratory system were measured in adult male subjects in the sitting position. Nasal resistance is the largest single component being nearly one-half the total and two-thirds of the airway resistance during nose breathing. It is highly nonlinear, and shows much variability. During mouth breathing upper airway resistance (mouth, pharynx, glottis, larynx and upper trachea) is also markedly nonlinear, and accounts for one-third the total airway resistance. Lower airway resistance is approximately linear up to flows of 2 liters/sec. Pulmonary tissue resistance is low as reported in this study. Chest wall resistance is nearly linear up to flow rates of 2 liters/sec and accounts for slightly less than half the total respiratory resistance during mouth breathing and 10–19% during nasal breathing. larynx; airways; chest wall; nose Submitted on December 16, 1963

An adaptation of the method reported by Amdur and Mead (1958, Amer. J. Physiol.192, 364–368) was used to evaluate pulmonary mechanics in conscious rats, utilizing a flow plethysmograph and intraesophageal catheter to determine compliance, resistance, respiratory flow, thoracic pressure, tidal volume, frequency, and minute volume. The procedure did not require surgery, and repeat evaluations were made in conscious rats. Real time calculations of pulmonary parameters were accomplished with an analog computer interfaced with a digital computer for display and data storage. Multiple evaluations (1, 3, 6, 13, 18, 24, 30, and 36 weeks) in 40 rats are reported. The utility of the system in establishing a base line against which pulmonary impairment, related to the effects of known pulmonary toxicants, e.g., ANTU and NO2, could be measured, was evaluated.

To evaluate the regional ventilation using 133Xe under different conditions, the respiratory flow and the phase with image were measured simultaneously, and sequential frames were made breath by breath. The flow signal and phase signal were converted to pulse signals by a microcomputer and stored with image data in the same file. Thus, the tidal volume and duration of each breath were measured. From sequential frames compiled breath by breath, an activity breath-number curve was made in each pixel, and the half-clearance breath number (B1/2) was calculated. The changes in conventional half-clearance time (T1/2) and B1/2 were compared under different ventilatory conditions in normal subjects and in patients with chronic pulmonary emphysema. Values of B1/2 indicated the change of turnover rate more accurately than T1/2. It is considered that B1/2 is a better parameter than T1/2 for evaluating the change in regional ventilatory function under different conditions.

A previously developed transport analysis was used to simulate two sets of single-breath nitrogen washout data from each of four normal subjects. The analysis treats simultaneous gas flow and longitudinal diffusion and incorporates a modified form of Weibel's anatomical model “A” to describe the airway geometry. For each data set, four geometric parameters of the analysis were varied in a computer simulation until it matched the instantaneous expiratory concentration curve; particular emphasis was placed on matching the data in the concentration transition. Monitored values of functional residual capacity and instantaneous respiratory flow were supplied as inputs to each simulation. For each subject, a reasonable computer simulation could be obtained using a single set of lower airway geometric parameters, even though the average respiratory flow rate varied by as much as 53% from test to test; this result is due to the ability of the transport analysis to directly account for gas mixing during normal respiration. Under the same conditions the anatomic dead space varied by as much as 24%.

Inspiratory ramp activity, postramp activity (PRA) of diaphragm and respiratory flow were studied in anesthetized rabbits and conscious humans under inspiratory resistive load. Under load with chloralose-urethane anesthesia neural inspiration lasted 124 +/- 12 msec more than under control conditions and end of mechanical inspiration lagged behind that of neural inspiration by 114 +/- 4 msec. With pentobarbital-urethane anesthesia corresponding changes under load were 67 +/- 18 msec and 44 +/- 6 msec; after SO2 block of slowly adapting stretch receptors in bronchi corresponding changes under load were nil and 65 +/- 7 msec. In humans corresponding changes under load were about 192 and 127 msec. Both in rabbits and humans time course of PRA under load was essentially unchanged. Hence, under load a considerable part of PRA (or all of it under pentobarbital-urethane anesthesia without SO2 block) occurred during inspiration and that occurring during expiration was smaller than under control conditions. Consequently, under load braking of expiratory flow was smaller and peak expiratory flow occurred earlier than under control conditions.

Breathing pattern as periodic breathing (PB) in chronic heart failure (CHF) is associated with poor prognosis and high mortality risk. This work investigates the significance of a number of time domain parameters for characterizing respiratory flow cycle morphology in patients with CHF. Thus, our primary goal is to detect PB pattern and identify patients at higher risk. In addition, differences in respiratory flow cycle morphology between CHF patients (with and without PB) and healthy subjects are studied. Differences between these parameters are assessed by investigating the following three classification issues: CHF patients with PB versus with non-periodic breathing (nPB), CHF patients (both PB and nPB) versus healthy subjects, and nPB patients versus healthy subjects. Twenty-six CHF patients (8/18 with PB/nPB) and 35 healthy subjects are studied. The results show that the maximal expiratory flow interval is shorter and with lower dispersion in CHF patients than in healthy subjects. The flow slopes are much steeper in CHF patients, especially for PB. Both inspiration and expiration durations are reduced in CHF patients, mostly for PB. Using the classification and regression tree technique, the most discriminant parameters are selected. For signals shorter than 1 min, the time domain parameters produce better results than the spectral parameters, with accuracies for each classification of 82/78, 89/85, and 91/89 %, respectively. It is concluded that morphologic analysis in the time domain is useful, especially when short signals are analyzed.