Relationship between dynamic expiratory time constant tau(edyn) and parameters of breathing cycle in pressure support ventilation mode.

Study of the relationship between ventilation parameters: monitored expiratory time constant - tau(edyn) and breathing - trigger frequency (f(trig)) and time of breathing cycle (T(cy)) are main goals of this article. Parameters were analyzed during last 4+/-2 h before weaning from ventilation in 66 patients ventilated in pressure support mode (PSV). We have found out, that there exist mathematical relationships, observed during adequate gas exchange, yet not described. Monitored parameters are represented by tau(edyn), f(trig) and T(cy). The analysis showed close negative correlation between T(cy) and f(trig) (R(2)=0.903). This implies that each increasing of tau(edyn) causes decreasing of f(trig) and vice versa. The calculation of regression equation between tau(edyn) and T(cy) outlined that T(cy) = 5.2625 * tau(edyn) + 0.1242 (R(2)=0.85). Regulation of respiratory cycles by the respiratory center in the brain is probably based on evaluation of tau(edyn) as the tau(edyn) probably represents a regulatory element and T(cy) regulated element. It can be assumed, that respiratory center can optimize the work of breathing in order to minimize energy in system patient + ventilator. The unique relationship, described above could be useful in clinical practice for development of new ventilation modes.

The optimal timing for magnetic resonance imaging in long-term follow-up of patients after a complete correction of the Tetralogy of Fallot.

OBJECTIVES: Long-term pulmonary regurgitation (PR) leads to right ventricular (RV) dilatation and dysfunction. In patients after a complete correction of the tetralogy of Fallot (TOF) it represents the most frequent and high risk late complication. Magnetic resonance imaging (MRI) is an objective possibility for RV measurements; on the other hand MRI is complicated and not always accessible method. BACKGROUND: We analyzed echocardiography (ECHO) and MRI parameters regarding RV dilatation and function and the correlation between these two methods with the aim to define optimal ECHO parameters indicating a necessity for further investigations. PATIENTS AND METHODS: In 50 patients with TOF > 10 years, after a complete surgical correction, ECHO and MRI were performed. RESULTS: ECHO finding of end-diastolic diameter (EDD) of RV > 30mm was detected in 13 patients (26%) and in 30 patients (60%) RV EDD above 4 standard deviations (SD) their normal values was present. MRI finding of end-diastolic volume (EDV) > 160 ml/m2 was present in 14 patients (28%) and end-systolic volume (ESV) > 85 ml/m2 in 17 patients (34%). Significant correlations between ECHO and MRI RV diastolic measurements were found (p=0.0001, r=0.34, resp. p=0.001, r=0.39). PR was significantly affecting diastolic RV dilatation (p=0.0001), on the other hand. RV dysfunction resulted in systolic RV dilatation (p=0.007). PR did not correlate with RV function (p=0.56). CONCLUSIONS: MRI is a golden standard for exact RV measurements and for the indication of pulmonary valve replacement, but ECHO still can be used during long-term follow-up, defining the point for further and more exact RV measurements (Tab. 2, Fig. 11, Ref. 17). Full Text in free PDF www.bmj.sk.

Factors influencing the intermediate outcome in patients with single-ventricle physiology after Fontan operation.

OBJECTIVE: This study was conducted to analyze the factors affecting the intermediate outcome following the Fontan procedure in the current era. METHODS: Between January 1992 and December 2008, 189 patients underwent Fontan procedure at a median age of 3.4 years (0.4-37 years). Single left ventricle was present in 77 (40%) patients, right ventricle in 70 (37%), in 7 (3.7%) patients, the ventricular morphology was indetermined and in 35 (18.5%) a dominant systemic ventricle with smaller second ventricle was present. The Fontan procedure was performed using an atriopulmonary connection (n=5, 5.6%), lateral atrial tunnel (n=99, 52%) or extracardiac conduit (n=85, 45%). 97.4% of patients recieved fenestration. RESULTS: The hospital survival was 95% and five patients required a takedown of Fontan circulation. The survival at 1.5 and 10 years was 94%, 93% and 92%, respectively. Multivariate analysis identified that the outcome was influenced by the diagnosis of a complete common AV canal (p = 0.015), duration of ventilation (p < 0.0001) and duration of pleural effusions (p = 0.003). Failure-free survival at 1.5 and 10 years was 95%, 92% and 89%, respectively. The overall freedom from reoperation was 73%. Risk factors for reoperation were preoperative pulmonary artery pressure and duration of ventilation. CONCLUSIONS: The Fontan procedure is associated with excellent operative and intermediate survival. Common atrioventricular canal, duration of pleural effusions and ventilation have an adverse influence on the intermediate outcome. Reintervention is associated with pulmonary artery pressure and duration of ventilation (Tab. 7, Fig. 3, Ref. 16).

Long-term results of surgical treatment of total anomalous pulmonary venous drainage in children.

AIM OF STUDY: Retrospective analysis of surgical correction of TAPVD performed between January 1992 and March 2008. METHODS: Review of patients' medical records. Patients' preoperative, operative as well as postoperative data were collated and analyzed using JMP statistical program version 5. RESULTS: A total of 51 patients with total anomalous pulmonary venous drainage underwent surgery at our center during a period of over seventeen years. Actuarial survival was 90.2%. Early postoperative death was recorded in 4 patients (7.8%) as against one late postoperative death. The only statistically significant risk factor for death was the time of surgical repair. Patients undergoing the repair before 1997 were more likely to die than those operated on after this period, p=0.006. Patients' survival following the surgical correction prior to the year 1997 was 63.63% as opposed to 97.5% for the period between 1997 and 2008. Freedom from surgical re-intervention over the period of follow-up was 92%. The obstructive type of TAPVD was associated with longer ICU stay and higher postoperative complications, p=0.003. CONCLUSION: We have recorded a significant improvement in patients' survival following surgery for total anomalous pulmonary venous drainage in the last decade. This can be attributed to a number of new measures both surgical and medical employed in the treatment of our patients (Tab. 3, Fig. 7, Ref. 17). Full Text (Free, PDF) www.bmj.sk.

Arrhythmias in congenital heart defects.

AIM OF THE STUDY: Evaluation of the incidence and severity of late arrhythmias in patients with predisposing congenital heart defects--either due to the anatomy of the defect itself or as a result of a particular type of surgical intervention. PATIENTS AND METHODS: In a retrospective long-term study authors analyzed 158 patients (divided into 5 groups) with congenital heart defects after surgical correction. Evaluated were: the incidence of rhythm disturbances, the type of arrhythmia and the need for medication or intervention. RESULTS: The most rhythm disturbances occurred in patients after physiological correction of D-transposition of the great arteries (68.5%) and these patients also mostly needed medication or pacemaker implantation; followed were by patients with hypoplastic left heart syndrome after Fontan procedure (40%), then were patients after long-term correction of tetralogy of Fallot (31.1%), atrial septal defect sinus venosus type with partial anomalous pulmonary venous return after Warden correction (25.7%) and congenitally corrected L-transposition of the great arteries (25 %). Most of these arrhythmias were asymptomatic and there was no need to treat them. There was an increased incidence of arrhythmias with time (p < 0.05). DISCUSSION: During childhood in patients after surgical correction late arrhythmias mostly do not represent a severe problem, but with time, when reaching adulthood, this may be an issue. It is therefore very important to understand the anatomy, physiology and the arrhythmogenic substrate of every high risk congenital heart defect (Tab. 2, Fig. 6, Ref. 10).

Interactive effects of ozone and climate on tree growth and water use in a southern Appalachian forest in the USA.

* A lack of data on responses of mature tree growth and water use to ambient ozone (O(3)) concentrations has been a major limitation in efforts to understand and model responses of forests to current and future changes in climate. * Here, hourly to seasonal patterns of stem growth and sap flow velocity were examined in mature trees from a mixed deciduous forest in eastern Tennessee (USA) to evaluate the effects of variations in ambient O(3) exposure and climate on patterns of stem growth and water use. * Ambient O(3) caused a periodic slowdown in seasonal growth patterns that was attributable in part to amplification of diurnal patterns of water loss in tree stems. This response was mediated by statistically significant increases in O(3)-induced daily sap flow and led to seasonal losses in stem growth of 30-50% for most species in a high-O(3) year. * Decreased growth and increased water use of mature forest trees under episodically high ambient O(3) concentrations suggest that O(3) will amplify the adverse effects of increasing temperatures on forest growth and forest hydrology.

Interactive effects of ozone and climate on water use, soil moisture content and streamflow in a southern Appalachian forest in the USA.

* Documentation of the degree and direction of effects of ozone on transpiration of canopies of mature forest trees is critically needed to model ozone effects on forest water use and growth in a warmer future climate. * Patterns of sap flow in stems and soil moisture in the rooting zones of mature trees, coupled with late-season streamflow in three forested watersheds in east Tennessee, USA, were analyzed to determine relative influences of ozone and other climatic variables on canopy physiology and streamflow patterns. * Statistically significant increases in whole-tree canopy conductance, depletion of soil moisture in the rooting zone, and reduced late-season streamflow in forested watersheds were detected in response to increasing ambient ozone levels. * Short-term changes in canopy water use and empirically modeled streamflow patterns over a 23-yr observation period suggest that current ambient ozone exposures may exacerbate the frequency and level of negative effects of drought on forest growth and stream health.

Alfalfa nutritive quality for ruminant livestock as influenced by ambient air quality in west-central Alberta.

Alfalfa (Medicago sativa) nutritive quality response to ambient ozone (O(3)), sulfur dioxide (SO(2)) and oxides of nitrogen (NO(x)) were assessed at three locations in west-central Alberta, Canada (1998-2002). Yield data were segregated into high and low relative to overall median yield. Ozone concentrations (hourly median and 95th-percentile) and precipitation (P) contributed 69 and 29%, respectively, to the variability in crude protein (CP) concentration in low-yielding alfalfa, whereas mean temperature (T) and relative humidity (RH) collectively influenced 98% of the variation in CP in high-yielding alfalfa. Three-fourths of the accounted variation in relative feed value (RFV) of low-yielding alfalfa was attributable to P, T and RH, whereas median and 95th-percentile hourly O(3) concentrations and SO(2) and NO(x) exposure integrals contributed 25%. In contrast, air quality, (mainly O(3)) influenced 86% of the accounted variation in RFV of high-yielding alfalfa, and T and P collectively contributed 14%.

New exposure-based metric approach for evaluating O(3) risk to North American aspen forests.

The United States and Canada currently use exposure-based metrics to protect vegetation from O(3). Using 5 years (1999-2003) of co-measured O(3), meteorology and growth response, we have developed exposure-based regression models that predict Populus tremuloides growth change within the North American ambient air quality context. The models comprised growing season fourth-highest daily maximum 8-h average O(3) concentration, growing degree days, and wind speed. They had high statistical significance, high goodness of fit, include 95% confidence intervals for tree growth change, and are simple to use. Averaged across a wide range of clonal sensitivity, historical 2001-2003 growth change over most of the 26 Mha P. tremuloides distribution was estimated to have ranged from no impact (0%) to strong negative impacts (-31%). With four aspen clones responding negatively (one responded positively) to O(3), the growing season fourth-highest daily maximum 8-h average O(3) concentration performed much better than growing season SUM06, AOT40 or maximum 1h average O(3) concentration metrics as a single indicator of aspen stem cross-sectional area growth.

Sildenafil as a pulmonary vasodilator after repair of congenital heart disease.

We describe successful use of enteral sildenafil following surgery for congenital heart disease in three cases. One infant after repair of ventricular septal defect and aortic coarctation had pulmonary hypertension non-responsive to nitric oxide, another infant and 3.5 year child following palliative surgery for congenital heart disease with univentricular physiology were treated with inhaled nitric oxide and had severe systemic desaturations associated with endotracheal suctioning. Therapy with sildenafil reduced pulmonary arterial pressure, prevented episodes of arterial desaturations and allowed weaning from nitric oxide (Ref. 7). Full Text (Free, PDF) www.bmj.sk

Surgical closure of patent ductus arteriosus in pre-term babies.

OBJECTIVES: To present by illustration the surgical options in neonatal PDA closure with emphasis on clip application. METHODS: Photo/video-documentation of surgical closure of PDA in a neonate by clip application coupled with free-hand drawings showing PDA closure by ligation and division. Review of 38 neonates undergoing surgical PDA closure in our institution between 1998 and 2006. RESULTS: Overall survival following surgery was 100%. There was one case of residual PDA and three postoperative complications - 2 cases of pneumothorax and one chylothorax. CONCLUSION: The outcome of surgical closure of PDA in neonates is very good with zero mortality in our series and only few postoperative complications.

Surgical treatment of aortic coarctation.

Coarctation of the aorta accounts for about 8% of all congenital heart diseases. Since the first successful case of surgical treatment in 1944 by Crafoord and Nylin1 in Sweden, several surgical techniques have been employed in the treatment of this anomaly. Here, we review by illustration the various surgical options in coarctation of the aorta with emphasis on our preferred technique - the extended resection and end-to-end anastomosis. Why the extended resection technique? Our experience - and that of other institutions - has shown that this is a better option in childhood as it is associated with a lesser degree of recoarctation and subsequent need for re-intervention.2.

Functional outcome of surgery for coarctation of the aorta.

AIM OF STUDY: Coarctation of the aorta (CoA) accounts for about 8% of all congenital heart diseases. This represents about 30 new cases of coarctation every year in Slovakia, of which more than half will require surgical treatment. Over the past years, many children with this diagnosis have been successfully operated on at the Department of Cardiac Surgery of the Children's University Hospital, Bratislava. Thus, the need for a comprehensive follow-up and analysis of the postoperative well being of these young patients arises. Our study is therefore aimed at: 1) identifying factors affecting the incidence and persistence of postoperative systemic hypertension, as well as the need for heart failure and hypertension treatment, 2) assessing patients' psychomotor development following surgery for coarctation of the aorta. METHODS AND DATA: Between January 1992 and December 2001, a total of 201 patients with aortic co-arctation were operated on at our institution. The three classes of aortic coarctation namely: isolated coarctation, coarctation with ventricular septal defect and coarctation with complex cardiac anomalies were represented. Patients' medical records were retrospectively reviewed, with attention paid to such variables as the type of lesion, gradient across the site of coarctation, type of surgical technique employed and surgery-related complications. Subsequently, these patients were followed for a time period ranging between six months and ten years during which their psychomotor development and overall clinical state were evaluated. RESULTS: Of the 201 operated patients, 64 (33%) had early postoperative hypertension, so-called paradoxical hypertension. There was a significant correlation between the incidence of early postoperative hypertension and patients' age at operation (p < 0.0001). Age at operation was also a significant risk factor for late hypertension (p = 0.005). In both cases we noticed a higher incidence of high blood pressure in patients operated on after the age of six years. The need for antihypertensive treatment of patients with early postoperative hypertension decreases with a younger age at operation. At five years of follow-up, the need for antihypertensive treatment was 15%. Clinical psychological evaluation of 64 patients showed a normal distribution of patients' intelligence quotients. No surgery-related variable correlated with the incidence of delayed mental development. There was, however, a certain correlation between the presence of complex anomalies and low verbal IQ in examined patients (p = 0.04) CONCLUSIONS: Early surgical treatment of aortic coarctation reduces the likelihood of early, as well as late postoperative hypertension. The preferred protocol in our institution is early surgical treatment of patients at about the age of two years. The need for antihypertensive treatment of patients at five years of follow-up is 15%. Patients' psychomotor development following surgery for aortic coarctation is not affected by type of surgical procedure. On the whole, we can conclude that patients' psychomo-whole, we can conclude that patients' psychomotor development does not differ from the rest of population. There is however, a certain correlation between complex cardiac anomalies and a tal, Bratislava delay in some components of patients' psychomotor development. (Tab. 3, Fig. 4, Ref. 17.)

Recoarctation and patients' freedom from re-intervention--a study of patients undergoing surgery for coarctation of the aorta at the Department of Cardiac Surgery of the Children's University Hospital, Bratislava.

BACKGROUND: Many children and young adults have undergone surgery for coarctation of the aorta. Individual surgical techniques employed in the treatment of patients and their effects on incidence of recoarctation were reviewed. METHODS AND DATA: Over the last ten years, a total of 201 cases of aortic coarctation were surgically treated at our department. The three forms of coarctation of the aorta recognized by the Society for Cardiothoracic Surgeons namely: isolated coarctation, coarctation with ventricular septal defects and coarctation with complex cardiac anomalies, were represented. RESULTS: 19 cases of recoarctation were recorded over the period of follow-up, representing 10% of all operated patients. On univariate analysis, the risk of recoarctation was closely linked with the following variables: use of resection and end-to-end anastomosis (p=0.01), age at operation less than one month (p=0.0002) and weight at operation less than 3 kg (p=0.01). The risk of recoarctation was found to be highest when resection and end-to-end anastomosis was employed in neonates (p<0.0001). Most cases of recoarctation as shown by the Kaplan-Meier plot occurred within the first year after surgery. CONCLUSION: The use of simple resection and end-to-end anastomosis in neonates is associated with a high risk of recoarctation. Hence, our preferred surgical technique in neonates is the extended resection and end-to-end anastomosis, which is associated with a considerably lower risk of recoarctation in this age group. (Tab. 4, Fig. 5, Re. 7)

Improved patient survival following surgery for coarctation of the aorta.

BACKGROUND: We conducted a retrospective review of children undergoing surgery for coarctation of the aorta in our institution over the last ten years with the aim of evaluating overall patient survival as well as detecting factors affecting it. We tried to identify the risk factors for mortality. METHODS AND DATA: Between January 1992 and December 2001, 201 patients with aortic coarctation were operated on at the Department of Cardiac Surgery of the Children's University Hospital, Bratislava. The three classes of aortic coarctation were represented: isolated coarctation, coarctation with ventricular septal defect (VSD) and coarctation with complex cardiac anomalies. Patients' preoperative, operative and immediate postoperative medical records were carefully studied with special attention paid to the type of lesion, patients' preoperative state, type of surgical technique employed, as well as the period of operation. For comparison, two equal time periods of follow-up were reviewed--1992 to 1996 and 1997 to 2001. The overall postoperative conditions of patients were also regularly monitored. Patient data were statistically analyzed using the JMP program version 4.04. RESULTS: An overall survival of 90% was recorded over the period of follow-up, ranging between one and ten years. A further break down showed a statistically significant difference between the various types of aortic coarctation, p=0.0001. Patients with simple or isolated coarctation had a survival rate of 100%, those with ventricular septal defect (VSD) in addition to coarctation had a survival rate of 80% while patients with associated complex cardiac anomalies had a survival rate of 65%. An improvement on overall patient survival was recorded in the period between 1997 and 2001--96% as against 86% for the period between 1992 and 1996. On univariate statistical analysis, the following variables were identified as significant risk factors for death: 1) Complex cardiac anomalies (p<0.0001), 2) Age at operation less than one month (p<0.0001) and 3) Treatment prior to the year 1997 (p=0.02). CONCLUSION: A considerable improvement on patient survival following surgery for coarctation of the aorta was recorded over the last five years. This could be attributed to new measures in preoperative, operative and postoperative care for patients with aortic coarctation. (Tab. 4, Fig. 5, Ref. 8.).

A multi-variate statistical model integrating passive sampler and meteorology data to predict the frequency distributions of hourly ambient ozone (O3) concentrations.

A multi-variate, non-linear statistical model is described to simulate passive O3 sampler data to mimic the hourly frequency distributions of continuous measurements using climatologic O3 indicators and passive sampler measurements. The main meteorological parameters identified by the model were, air temperature, relative humidity, solar radiation and wind speed, although other parameters were also considered. Together, air temperature, relative humidity and passive sampler data by themselves could explain 62.5-67.5% (R(2)) of the corresponding variability of the continuously measured O3 data. The final correlation coefficients (r) between the predicted hourly O3 concentrations from the passive sampler data and the true, continuous measurements were 0.819-0.854, with an accuracy of 92-94% for the predictive capability. With the addition of soil moisture data, the model can lead to the first order approximation of atmospheric O3 flux and plant stomatal uptake. Additionally, if such data are coupled to multi-point plant response measurements, meaningful cause-effect relationships can be derived in the future.

Use of passive ambient ozone (O3) samplers in vegetation effects assessment.

A stochastistic, Weibull probability model was developed and verified to simulate the underlying frequency distributions of hourly ozone (O3) concentrations (exposure dynamics) using the single, weekly mean values obtained from a passive (sodium nitrite absorbent) sampler. The simulation was based on the data derived from a co-located continuous monitor. Although at the moment the model output may be considered as being specific to the elevation and location of the study site, the results were extremely good. This effort for the approximation of the O3 exposure dynamics can be extended to other sites with similar data sets and in developing a generalized understanding of the stochastic O3 exposure-plant response relationships, conferring measurable benefits to the future use of passive O3 samplers, in the absence of continuous monitoring.

Relationships between passive sampler and continuous ozone (O3 ) measurement data in ecological effects research.

In ecological effects research, there is a rapid increase in the application of passive sampling techniques for measuring ambient ozone (O3) concentrations. Passive samplers provide data on cumulative exposures of a plant to a pollutant. However, O3 is not an accumulative contaminant within the plant tissue, and use of prolonged passive sampling durations cannot account for the dynamics of the occurrences of O3 that have a significant influence on the plant response. Therefore, a stochastic Weibull probability model was previously developed and applied to a site in Washington State (1650 m MSL) to simulate the cumulative exposure data from a passive sampler, to mimic the corresponding frequency distributions of hourly O3 concentrations that would otherwise have been obtained by continuous monitoring. At that site the correlation between the actual passive sampler and the continuous monitor data was R2 = 0.74. The simulation of the hourly O3 data was based on and compared with the results obtained from a colocated continuous monitor. In this paper we report the results of the model application to data from an unrelated monitoring site (New Hampshire, 476 m MSL) with poor correlation between the passive sampling and continuous monitoring (R2 = 0.24). In addition, as opposed to the previous work, we provide comparisons of the frequency distributions of the hourly O3 concentrations obtained by the simulation and the actual continuous monitoring. In spite of the major difference in the R2 values, at both sites the simulation provided very satisfactory results within the 95% confidence interval, suggesting its broad applicability. The final objective of this overall approach is to develop a generic model that can simulate reasonably well the occurrences of ambient O3 concentrations that are dependent upon the elevation of the measurement site and the synoptic and local meteorology. Such an effort would extend the relative utility of the passive sampling data in explaining stochastic plant responses.