Pulsed Ecosystem Research Articles

A case study of sequential colonization: intra- and interspecific patterns of recovery in a hydrologically pulsed ecosystem

A case study of sequential colonization: intra- and interspecific patterns of recovery in a hydrologically pulsed ecosystem

Hemodynamic Advantages of Right Heart Decompression during Off-Pump Surgery

Cardiac maneuvering during off-pump coronary artery bypass surgery can compress the right ventricle, causing temporary dysfunction and hemodynamic instability. The hemodynamic impact of a decompression technique comprising right pleurotomy and pericardial release was investigated during cardiac elevation. Intraoperative continuous real-time monitoring of cardiac index and stroke volume index was carried out using the PulseCO system in 12 consecutive patients with normal ventricular function who underwent off-pump coronary artery bypass by a single surgeon. A pulmonary artery catheter was used to monitor pulmonary artery pressure and systemic venous O(2) saturation. Hemodynamic changes during vertical displacement of the heart were measured before and after performing a right pleurotomy and pericardial release. Following right heart decompression, stroke volume index, cardiac index, mean arterial pressure, and systemic venous O(2) saturation were significantly better preserved during cardiac elevation. This demonstrates that right heart decompression via pleurotomy and pericardial release significantly improves hemodynamic stability during cardiac manipulation. We recommend the use of this procedure in off-pump coronary artery bypass when cardiac tilting is required.

Acute normovolemic hemodilution, intraoperative cell salvage and PulseCO hemodynamic monitoring in a Jehovah’s Witness with placenta percreta

A Jehovah's Witness who had had four previous cesarean deliveries was referred to our institution for management of a complete placenta previa at 34 weeks of gestation. A subsequent ultrasound scan was suggestive of placenta percreta with bladder involvement. After erythropoietin and iron supplementation, cesarean hysterectomy was performed. Using PulseCO technology for continuous hemodynamic monitoring, preoperative acute normovolemic hemodilution and intraoperative cell salvage were used resulting in a successful cesarean hysterectomy with a 5500-mL estimated blood loss. The PulseCO system provides continuous, real-time hemodynamic data by applying pulse power analysis to the arterial pressure waveform. A bolus of oxytocin given after delivery produced profound hypotension, the hemodynamics of which were elucidated with the PulseCO system. To our knowledge, the combined use of acute normovolemic hemodilution, intraoperative cell salvage and PulseCO hemodynamic monitoring for cesarean hysterectomy has not been reported previously. These techniques may be particularly useful in managing patients who refuse blood products and/or in whom the baseline hemoglobin is suboptimal.

Accuracy of cardiac output measurements with pulse contour analysis (PulseCOTM) and Doppler echocardiography during off-pump coronary artery bypass grafting

During off-pump coronary bypass grafting, surgical manipulation and dislocation of the heart may cause cardiovascular instability. Monitoring of cardiac output facilitates intraoperative haemodynamic management but pulmonary artery catheters are often considered too invasive. Pulse contour analysis and transoesophageal echocardiography could serve as alternatives, but there is controversy about their accuracies. We validated pulse contour analysis using a standard radial arterial catheter (PulseCO) and aortic Doppler flowmetry with transoesophageal echocardiography in patients undergoing off-pump coronary bypass surgery. Pulmonary arterial thermodilution served as the reference technique. In 20 patients undergoing off-pump coronary bypass, cardiac output was measured with bolus thermodilution (COTD), pulse contour analysis (COPC), and transoesophageal echocardiography (COecho) at fixed time intervals during the procedure. Data were compared using linear regression and Bland-Altman analysis. At the end of the procedure, dobutamine was infused at a rate of 2.5 microg kg(-1) min(-1) in six patients to study the agreement between methods in quantifying changes in cardiac output. Comparison between COPC and COTD showed a bias +/- limits of agreement of -0.03 +/- 1.30 L min(-1) (mean error 29%). Doppler echocardiography was not always feasible when the heart was displaced from the oesophagus and had lower accuracy: bias +/- limits of agreement vs. COTD was 0.45 +/- 1.93 (mean error 43%). Increases in cardiac output induced by dobutamine were well quantified both by pulse contour analysis (COPC = 0.76 x COTD + 0.58; r(2) = 0.65) and Doppler, although the latter tended to overestimate these changes (COecho = 1.58 x COTD - 0.13; r(2) = 0.53). Calibrated pulse contour analysis using the PulseCO system is an acceptable technique to measure cardiac output non-invasively in off-pump coronary bypass patients. Doppler echocardiography performs less well and is not always feasible with transoesophageal echocardiography when the heart is displaced.

Arterial pulse wave analysis: An accurate means of determining cardiac output in children*

Cardiac output is a useful measure of myocardial performance. Standard methods of determining cardiac output are not without risk and can be problematic in children. Arterial pulse wave analysis (PulseCO), a novel, minimally invasive cardiac output determination technique, offers the advantage of continuous monitoring, convenience, and low risk. This technique has not been validated in children. The purpose of this study was to validate PulseCO as an accurate means of noninvasively determining real-time cardiac output in children. Prospective, single-center evaluation. Children's hospital. Any child with a structurally normal heart, undergoing hemodynamic evaluation in the cardiac catheterization laboratory, was included. A prograde right heart catheterization was performed, and cardiac output was determined using the thermodilution technique, via placement of a pulmonary arterial catheter. Thermodilution results were compared with continuous real-time cardiac output measurements obtained with the PulseCO system, and they were then analyzed by standard correlation techniques and Bland-Altman analysis. Twenty patients were evaluated with a median age of 10.5 yrs and a median weight of 25 kg. The mean thermodilution cardiac index was 3.3 +/- 0.9 L/min/m, whereas the mean PulseCO cardiac index was 3.1 +/- 0.9 L/min/m. Standard Pearson correlation tests revealed a correlation coefficient of .94 (p < .001). Bland-Altman analysis revealed excellent clinical agreement with a mean difference of 0.19 L/min/m and a precision of 0.28 L/min/m at 2 sd. Arterial pulse wave analysis by the PulseCO system provides a novel, minimally invasive method of determining real-time cardiac output in children.

Validation Study of PulseCO System for Continuous Cardiac Output Measurement

Ultrasonic flow probes have been used to optimize biventricular pacing immediately after cardiopulmonary bypass, improving cardiac output (CO) by 10%; however, flow probes must be removed with chest closure. The PulseCO system (LiDCO Limited, Cambridge, UK) may extend optimization into the postoperative period, but controlled validations have not been reported. Six anesthetized pigs were instrumented for right heart bypass. Flow was varied from 3 to 1 L/min and then back to 3 in 0.5 L/min increments for 60 second intervals. CO was measured by ultrasonic flow probe on the aorta and by PulseCO using a femoral arterial line. PulseCO and flow probe accurately measured CO (PulseCO R2: 0.79-0.95; flow probe R2: 0.96-0.99). At flow of 2 L/min, when the heart was paced 30 bpm over the sinus rate, PulseCO falsely indicated an increase in CO (2.13 vs. 2.30 L/min, p = 0.014). When mean arterial pressure was increased by 20% using a phenylephrine infusion, PulseCO falsely indicated an increase in CO (2.13 vs. 2.47 L/min, p = 0.014). When mean arterial pressure was decreased by 20% using a nitroprusside infusion, PulseCO falsely indicated a decrease in CO (2.13 vs. 1.79 L/min, p = 0.003). PulseCO appears to be useful for assessing acute changes in CO if its limitations are recognized.

Room C, 10/16/2000 2: 00 PM - 4: 00 PM (PS) Hemodynamic Monitoring during Cardiac Surgery: Improved Arterial Pressure Waveform Analysis - The PulseCO System

<b>Room C, 10/16/2000 2: 00 PM - 4: 00 PM (PS) Hemodynamic Monitoring during Cardiac Surgery: Improved Arterial Pressure Waveform Analysis - The PulseCO System</b>

Modeling fish dynamics and effects of stress in a hydrologically pulsed ecosystem

Many wetlands undergo seasonal cycles in precipitation and water depth.This environmental seasonality is echoed in patterns of production of fishbiomass, which, in turn, influence the phenology of other components of thefood web, including wading birds. Human activities, such as drainage orother alterations of the hydrology, can exacerbate these natural cycles andresult in detrimental stresses on fish production and the higher trophic levels dependent on this production. In this paper we model theseasonal pattern of fish production in a freshwater marsh, with specialreference to the Everglades/Big Cypress region of southern Florida.The model illustrates the temporal pattern of production through theyear, which can result in very high densities of fish at the end of ahydroperiod (period of flooding), aswell as the importance of ponds and other deep depressions, both as refugia and sinks during dry periods. The model predicts that: (1) there is an effective threshold in the length of the hydroperiod that must beexceeded for high fish-population densities to be produced, (2) large,piscivorous fishes do not appear tohave a major impact on smaller fishes in the marsh habitat, and (3) therecovery of small-fish populations in the marsh following a major droughtmay require up to a year. The last of these results is relevant toassessing anthropogenic impacts on marsh production, as these effectsmay increase the severity and frequency of droughts.