Low-flow Group Research Articles

INFLUENCE OF CHANGING THE WASH-OUT VOLUME AND REVOLUTION ROUND SETTINGS IN THE CELL SAVER

[Introduction] Blood concentration using the Cell Saver[C-S) is useful technique, but one concern is that after passing through this system the blood may have reduced hemostatic function. The purpose was to examine the effects of changing C-S wash-out volume and revolution round settings on blood hemostatic function following blood retransfusion. [Methods] 13 patients who had undergone surgery(open cardiac surgery n = 7 closed cardiac surgery n = 6) were assigned to groups treated for blood concentration using C-S with different settings for wash-out volumes, including different heparin doses and rounds of revolution. The study was performed on C-S blood sample, and included blood cell count, residual heparinemia and fibrinogen, and ACT. [Results] The platelet and fibrinogen of group A, for which C-S was set up with a priming flow of 150 ml/min and a wash flow of 100 ml/min, were higher than those of group B, which was set up with a priming flow of 300 ml/min and a wash flow of 300 ml/min. There was residual heparin in the low-flow group, which had 30,000 KIU/Kg added to the pump primer, and none in the high-flow group, which had 10,000 KIU/Kg added to the pump primer. [Conclusion] C-S program with low priming and wash flows was effective in enhancing the effect on hemostatic function. Although the instructions state that a heparin dose of 30,000–60,000 KIU/Kg should he added to the pump primer, we found that 10,000 KIU/Kg was sufficient.

Comparison between High Flow and Low Flow Anesthesia for Positive Pressure Ventilation in Pediatrics Using the Laryngeal Mask Airway

Background: Low flow anesthesia provides many advantages, including reduced cost, conservation of body heat and airway humidity. This study was performed to compare low flow anesthesia with high flow anesthesia and to investigate whether the advantages of low flow anesthesia during positive pressure ventilation can be combined with the laryngeal mask airway in paralyzed pediatric patients. Methods: Thirty-one pediatric patients of ASA physical status 1 or 2 were studied and divided into two groups according to the fresh gas flow (FGF) in the breathing system; low flow group (FGF 1 L/min, n = 17) or high flow group (FGF 4 L/min, n = 14). Each respiratory parameter was measured when a steady state was reached at 20 min after induction. Results: There were no significant differences of respiratory data between the two groups except that the inspired oxygen concentration was lower in the low flow group than in the high flow group. Hemodynamic changes with the laryngeal mask airway insertion were not statistically significant. Conclusions: A laryngeal mask airway is an effective airway device for low flow anesthesia as well as for high flow anesthesia in paralyzed pediatric patients.

Response of some biophysical properties of blood to changes in the perfusion flow rate during cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is a safe support system during major cardiac operations because it allows the distribution of adequately oxygenated blood to the entire body. The optimal perfusion flow to be used during hypothermic CPB remains a controversial issue. In the present study, the effect of different flows and pressures on oxygen delivery, extraction and consumption was compared. Such an effect was evaluated for 40 patients undergoing open-heart surgery using CPB (membrane oxygenator) and systemic hypothermia. The patients were randomized into two groups (20 each) according to the flow and pressure (low flow, low pressure and high flow, high pressure). The electrical impedance from 50 Hz to 10 MHz for blood samples and erythrocytes for both groups was also measured at different time intervals (before-, during and post-CPB). No significant change for low flow group was recorded (p > 0.05) while the dielectric properties of the high-flow group were greatly affected by the time of operation. Hence, low flow can be safely used in young patients without any organ impairment or carotid artery disease, while high flow should be used for patients with any organ dysfunction, at the initiation of CPB and during rewarming to compensate for the increase in oxygen consumption and the need for better perfusion pressure.

Optimizing dialysis dose by increasing blood flow rate in patients with reduced vascular-access flow rate

Dialysis efficacy indexed by Kt/V can generally be augmented by increasing the dialyzer blood flow rate. However, increasing the dialyzer blood flow rate may lead to vascular-access recirculation (AR) in patients with a compromised vascular-access flow rate. This can have an attenuating effect on dialysis efficacy. The aim of the present study is to investigate the effect of dialyzer blood flow rates of 200, 300, and 400 mL/min on AR and Kt/V in 8 patients with low (<600 mL/min) and 13 patients with normal (>600 mL/min) vascular-access flow rates. AR and vascular-access flow rate were determined using an ultrasound saline dilution technique, and session-delivered Kt/V was computed using an on-line dialysate urea monitor. AR was minor and only observed in 4 patients in the low vascular-access flow rate group (0.9% ± 0.6%) at dialyzer blood flow rates of 200 mL/min (1 patient), 300 mL/min (2 patients), and 400 mL/min (3 patients) and 4 patients in the normal vascular-access flow rate group (1.2% ± 1.1%) at dialyzer blood flow rates of 200 mL/min (3 patients) and 300 mL/min (1 patient). Kt/V increased with increasing dialyzer blood flow rates in both groups, and in individual cases, there was no decrease in Kt/V at greater dialyzer blood flow rates in either group. Also in those patients with minor AR, Kt/V increased at greater dialyzer blood flow rates, except in 1 patient in the low-flow group, in whom Kt/V remained unchanged at a change in dialyzer blood flow rate from 300 to 400 mL/min, whereas AR increased. From this study, it is concluded that even in patients with low access flow, increasing dialyzer blood flow rate in general leads to an increase in delivered Kt/V regardless of vascular access flow rate. © 2001 by the National Kidney Foundation, Inc.

Effects of flow and energy metabolism on injury and Rb(+) uptake in pig hearts: an (87)Rb and (31)P NMR study.

In this work the roles of coronary flow (CF) and metabolism in Rb(+) (K(+) congener) uptake were studied. In isolated pig hearts the left anterior descending artery (LAD) was cannulated to maintain adequate perfusion of the LAD bed. Rb(+) loading was initiated and the LAD flow was either completely stopped (no flow (NF)) or reduced to 12% (low flow (LF)), or buffer was deoxygenated without change in flow (hypoxic flow (HYP)) for 2 h. CF through the LAD was then restored to normal, or perfusion was switched to oxygenated buffer. Serial (87)Rb MR images or localized (31)P spectra were acquired to compare the Rb(+) uptake and energetics in the left ventricular (LV) anterior (ischemic/hypoxic) and posterior (normal) walls. End-ischemic/hypoxic (87)Rb signal intensities in the anterior wall were higher and the fluxes were greater in the HYP and LF groups than in the NF group. Phosphocreatine and ATP decreased less significantly and recovered better in the HYP and LF groups. Upon reperfusion/reoxygenation, the HYP and LF groups showed higher (87)Rb signal intensities and smaller or no infarctions in the anterior wall compared to those in the NF group. Ischemia reduces Rb(+) uptake due to both flow limitations and metabolic inhibition of cellular transport. (87)Rb MRI has a potential for distinguishing necrotic and reversibly damaged tissue.

Reduced tolerance of global ischemia in the hypertrophied heart

Reduced coronary reserve during reperfusion may cause postischemic diastolic dysfunction in pressure-overload-induced hypertrophy. We studied the effect of coronary flow regulation (simulated hyperemic or depressed flow) on postischemic cardiac function during reperfusion. Left ventricular pressure overload was induced in 4-week-old rats by abdominal aortic constriction. At 6 weeks of age, isolated Langendorff-perfused hearts (perfusion pressures: 75 mmHg in controls and 110 mmHg in the aortic constriction group) were subjected to hypothermic global ischemia (15 degrees C, 210 min), followed by 2 types of coronary flow regulation during the initial 20 min of reperfusion--manipulated high flow in control hearts (group I), manipulated low flow in control hearts (group II), manipulated high flow in aortic constriction hearts (group III), and manipulated low flow in aortic constriction hearts (group IV) (n = 6/group), and then constant pressure perfusion during the subsequent 45 min of reperfusion. Cardiac function was measured using an isovolumic balloon in the pre- and postischemic periods. Aortic constriction hearts exhibited greater left ventricular end-diastolic pressure than did control hearts. The increase in left ventricular end-diastolic pressure did not differ between group I (3 +/- 2 mmHg) and group II (-1 +/- 1 mmHg) or between group III (29 +/- 5 mmHg) and group IV (30 +/- 6 mmHg). No difference was seen in postischemic recovery of left ventricular systolic pressure between high and low flow groups in control and aortic constriction hearts. Manipulations in coronary flow during reperfusion did not affect postischemic cardiac function in control or aortic constriction hearts, suggesting that depressed coronary flow during early reperfusion is not a primary cause of postischemic diastolic dysfunction in the hypertrophied myocardium.

Effect of a leukocyte-depleting filter in an extracorporeal circuit used for low-flow ischemia and reperfusion of equine jejunum.

To determine effect of leukocyte depletion on hematologic, morphologic, and metabolic variables of equine jejunum after induction of arterial low-flow ischemia and reperfusion by use of an extracorporeal circuit. 14 healthy adult horses. A segment of jejunum was surgically removed and maintained in an isolated circuit for 3 hours (control group), arterial flow was reduced to 20% of baseline for 40 minutes followed by 1 hour of reperfusion (low-flow group), or leukocyte depletion was filter-induced, and low-flow ischemia and reperfusion were conducted as in the low-flow control group (filter-treated group). Various metabolic, hemodynamic, and histomorphologic variables were evaluated, including effects of electrical field stimulation and L-N-nitro-arginine-methyl-ester (L-NAME) on contractile activity. The extracorporeal circuit appeared to maintain the jejunum within physiologic limits for an extended period. Low-flow ischemia with reperfusion induced significant differences in various measurements, compared with control specimens. Significant differences were not detected between the low-flow and filter-treated groups. Myeloperoxidase activity was greater in the low-flow group than the control group, whereas a difference was not detected between control and filter-treated groups. The extracorporeal circuit maintained intestine for 3 hours in a physiologic state and may be used for simulation of tissue injury. Leukocyte depletion generally did not attenuate the effects of low-flow ischemia and reperfusion on equine small intestine.

Conversion of umbilical arterial doppler waveforms to cardiac cycle triggering signals: a preparatory study for online motion-gated three-dimensional fetal echocardiography

To remove motion artefacts, a device was built to convert “noisy” umbilical arterial Doppler waveforms (UADWs) from an ultrasound (US) system into sharp ECG R-wave-like cardiac cycle triggering signals (CCTSs). These CCTSs were then used to gate a simultaneous (online) 3-D acquisition of sectional fetal echocardiograms from another US system. To test the conversion performance, a study was carried out in sheep fetal twins. Pulmonary arterial flow waveforms (PAFWs) from implanted probes were traced, in the meantime, to determine the reference cardiac cycle. Interference caused by running the two nonsynchronised US systems was controlled to three degrees (not-noticeable, moderate, and severe), together with high (≥ 40 cm/s) and low (< 40) flow velocities on UADWs. The conversion efficiency, assessed by the percentage of UADWs converted into CCTSs, was in the range of 83% to 100% for not-noticeable and moderate interference, and 0% to 71% for severe interference. The triggering accuracy, assessed by [(time lag mean between the onsets of PAFWs and corresponding CCTSs) − (its 99% confidence level)] ÷ the mean, was 90% to 96% for the not-noticeable interference high- and low-flow groups and for the moderate interference high-flow group; 19% to 93% for the moderate interference low-flow group; and from not obtainable up to 90% for the severe interference groups. The results show that UADWs can be used as a satisfactory online motion-gating source even in the presence of moderate interference. The major problems are from severe interference or moderate interference with low-flow velocity, which can be minimised/eliminated by the integration of the individual systems involved. (E-mail: jdeng@medphys.ucl.ac.uk)

Temporal variability of macroinvertebrate assemblages in a neotropical intermittent stream in Northwestern Venezuela.

Changes in macroinvertebrate assemblages were identified among different flow phases during the dry and rainy seasons in a neotropical intermittent stream in Northwestern Venezuela. Invertebrates and physicochemical parameters were sampled during 9 months to assess temporal changes in biotic and abiotic variables. Macroinvertebrate densities decreased following either a high-flow or a stream drought. Three invertebrate assemblages were identified via PCA and cluster analysis. PCA ordination showed a temporal sequence between the sampling dates. A low flow association occurred in August, a period of rewetting after the stream drought in late July. A high-flow association was established by sampling dates (September and November) with the highest flows registered during the study, and an intermediate-flow association occurred during the longer dry period after the rainy season. The low-flow group was dominated by the Philopotamidae (65 %). The intermediate-flow group showed a more even distribution of macroinvertebrate abundances. The high-flow group was dominated by Philopotamidae, Leptophlebiidae, Chironomidae and Baetidae. The lowest richness and highest density values were observed for the low-flow group. Average physicochemical parameters also were different between the PCA groups. A gradient of physicochemical parameters was observed from the low-flow group to the high-flow group. Temporal flow changes probably structure macroinvertebrate communities during extreme episodes of drought or spates, but during intermediate flow periods some biotic processes may determine community structure.

Minimum cerebral blood flow in selective cerebral perfusion for brain protection within a limited period of time

We experimentally evaluated the minimum cerebral bral blood flow required for brain protection during 90 min of selective cerebral perfusion (SCP) at moderate hypothermia ranging from 24° to 28°C, using short-latency somatosensory evoked potentials (SSEPs) as a monitor for cerebral electrical activity. Twenty mongrel dogs were divided into two groups of 10. In group A the brain temperature was lowered to 26°–28°C by core cooling using cardiopulmonary bypass (CPB), and in group B the brain was cooled to 24°C. Each group was subdivided into high-flow (H) and low-flow (L) groups according to the flow rate of SCP. In the high-flow subgroups of group A (group AH,n=5) and group B (group BH,n=5), the flow rate of SCP was maintained at 5 ml/kg/min. In the low-flow subgroups of group A (group AL,n=5) and group B (group BL,n=5), the SCP flow was 3 ml/kg/min. After systemic hypothermia and circulatory arrest, SCP was performed for 90 min via the innominate artery. In the high-flow subgroups (AH + BH), all SSEP wave components from P1 to N2 were completely preserved in 9 of the 10 dogs after 90 min of SCP, with 90% recovery rate of SSEPs. In the low-flow subgroups (AL+BL), the recovery rate of SSEPs was 30%. In four dogs without full recovery of SSEPs in group AL, all components of SSEPs were abolished; however, P1N1 waves, which are regarded as an electrical activity originating from the subcortical pathway, were restored in two of the three in group BL. Therefore, it might be suggested that more than 5 ml/kg/min of SCP is needed as a minimum cerebral blood flow for 90 min at hypothermia of 24° to 28°C, but 3 ml/kg/min is insufficient to protect the whole brain.

Effect of blood flow rate on thrombogenesis in a rabbit extracorporeal circulation model.

Blood flow is believed to affect the thrombogenicity of extracorporeal circulation (ECC). The purpose of this study was to look at the relationship between blood flow and thrombogenicity in a rabbit model of ECC. Rabbits were anesthetized and systematically heparinized. Bilateral jugular cannulation was performed, and the animals were placed on venovenous ECC. The circuits were composed of 1 m of 1/4 inch size surgical grade polyvinylchloride (PVC) tubing. ECC was maintained for 4 hours. Three experimental groups were studied: a high flow group (n=7; flow rate: 30 ml/min/Kg), low flow group (n=7; flow rate: 10 ml/mg/Kg), and no ECC group (n=7). Platelet count, fibrinogen concentration, PaO2/FiO2, and postmortem findings were evaluated. Platelet consumption was higher with high flow, and fibrinogen consumption was higher with low flow.

Water flow requirements in the intensive production of Atlantic salmon ( Salmo salar L.) fry: growth and oxygen consumption

Atlantic salmon ( Salmo salar L.) fry (1–10 g) were exposed to three water flow rates: 1.4 (control), 1.0 (medium) and 0.7 l kg −1 min −1 (low). There were four replicate tanks in each group. Alkalinity was low (0.03–0.04 mM). Oxygen was added to the inlet water to maintain discharge water oxygen concentration higher than 7 mg l −1, at 16°C. The mean weight of fish in the low water flow group was significantly lower than in the control flow group after 2 months. No significant differences in mean fish length and condition factor between groups were found. There was no significant difference in the frequency of occurrence of gill lesions among the groups. Mortality was low in all groups (0.3–0.4%). In the majority of tanks (nine of 12), oxygen consumption rates decreased significantly as the mean fish size increased. An overall range of 5–12 mg O 2 kg −1 min −1 was observed. There were no significant differences between the b-values (weight exponent: log oxygen consumption versus log body weight) of the three groups. The range of the weight exponents for the combined groups (between −0.19 and −0.23) was narrower than that of the individual tanks (between −0.12 and −0.27). The wide range in the individual tanks may be a result of relatively few oxygen measurements. No significant differences were found in the oxygen consumption levels of the three groups. The oxygen consumption rate was however higher than predicted by earlier oxygen consumption models. The mathematical corrections of oxygen consumption rates due to reaeration of oxygen were generally within ±3% of the measured oxygen consumption rates (in all tanks). Further studies are needed both to quantify water flow requirements and oxygen consumption rates for Atlantic salmon fry.

Adrenomedullin in patients at high risk for pulmonary hypertension

Background. Adrenomedullin is a newly identified peptide with profound hypotensive effects. We investigated perioperative adrenomedullin levels among patients with congenital heart disease with and without pulmonary hypertension. Methods. Levels of plasma adrenomedullin, endothelin-1, and nitric oxide metabolites were measured in three groups: (1) low pulmonary flow (n = 11); (2) high flow/low pulmonary arterial pressure (less than 60% systemic pressure) (n = 9); and (3) high flow/high pressure (n = 10). Samples were obtained preoperatively, on and off pump, and 3, 6, and 12 hours after bypass. Results. Adrenomedullin levels were highest in the low pulmonary flow group (189.7 ± 15 pg/mL low flow versus 103.1 ± 9.5 pg/mL high flow/low pulmonary and 139 ± 17.5 pg/mL high flow/high pressure at 12 hours; p ≤ 0.05). The arterial pressure/systemic pressure re-mained significantly lower in the high flow/low pulmonary pressure compared with the high flow/high pressure group (0.37 ± 0.08 versus 0.62 ± 0.11; p < 0.005). Perioperative endothelin-1 and nitric oxide levels remained low in the low pulmonary flow group but increased progressively in both high flow groups. Conclusions. Circulating plasma adrenomedullin appears to affect baseline vascular tone in patients with intact endothelial function. It may interact with nitric oxide and endothelin-1 to help regulate blood pressure perioperatively in patients with congenital heart disease.

Low flow enhances platelet activation after acute experimental arterial injury

Purpose: Vascular smooth muscle cell (VSMC) proliferation and migration to the subintima or intimal hyperplasia (IH) occur after arterial injury and are thought to be induced by mitogenic factors released from activated platelets. Because low flow (LF) and shear have been attributed to the localization and progression of IH, we postulated that hemodynamic factors may regulate the degree of platelet activation, as measured by plasma thromboxane B 2 (TXB 2) and platelet-derived growth factor-AB (PDGF-AB) release at regions of experimental arterial injury. Methods: The right common carotid artery (CCA) was subjected to balloon injury in 18 New Zealand White male rabbits. Flow in the injured CCA was reduced by out-flow ligation (LF group, n = 6) or increased by ligation of the left CCA (high flow [HF] group, n = 6). In six other animals, flow was preserved (normal flow [NF] group). Mean blood flow and pressure in the right CCA were measured thereafter at 10 and 30 minutes. Plasma TXB 2 and PDGF-AB levels were determined with the enzyme-linked immunosorbent assay method in each animal with blood samples taken systematically before injury (baseline) and in the distal CCA at similar time points. Results: At 10 minutes, mean blood flow was reduced from 20 ± 2 ml/min in the NF group to 7 ± 1 ml/min in the LF group animals ( p < 0.01) and increased to 32 ± 2 ml/min in the HF group animals ( p < 0.05). Mean arterial blood pressure did not differ among the groups. Hemodynamic parameters were similar at 10 and 30 minutes. TXB 2 levels were more than fourfold greater in the LF group than in the HF and NF groups at both time points ( p < 0.05). In addition, there was a twofold increase in plasma PDGF-AB level at 10 minutes in the LF group compared with baseline levels ( p < 0.05). Conclusion: Platelet activation at regions of acute vascular injury was determined to be flow dependent. Upregulated platelet activity in low flow conditions may be due to increased platelet exposure time to subendothelial collagen and is greatly attenuated if normal or increased flow is present.(J Vasc Surg 1998;27:910-8.)

Effects of low flow and hypoxia on myocardial retention of technetium-99m BMS181321

The purpose of the present study was to determine whether graded levels of low-flow ischemia would lead to graded differences in uptake and clearance of BMS181321. Using a perfused rat heart model, 7.4 MBq (200 microCi) of BMS181321 was infused over 20 min, followed by a 60-min clearance phase. Activity was monitored using an NaI detector. Four groups were studied using Krebs-Henseleit buffer perfusion using low flow or hypoxia: group 1=12 ml/min, group 2=3 ml/min, and group 3=1 ml/min during uptake and clearance phases, and group 4=12 ml/min with hypoxia during clearance. Control and low-flow groups were also perfused using red blood cells and albumin. There was a stepwise increase in peak myocardial uptake (% injected dose) as flow progressively decreased (group 1=2.4%+/-0.2% SEM, group 2=13.1%+/-0.7%, group 3=28.6%+/-2.4%, P <0.05). Group 3/group 1 mean peak activity ratio was 12:1. Mean 1-h fractional retention significantly increased in a stepwise manner as flow decreased (group 1=0.32+/-0.02, group 2=0.43+/-0.03, group 3=0.59+/-0.05, P <0.05). Group 3/group 1 mean 1-h clearance activity ratio was 30:1. Groups 5 and 6 perfused with red blood cells and albumin demonstrated similar increases in peak uptake and 1-h retention in the low-flow hearts. This study demonstrates a stepwise increase in uptake and a stepwise increase in retention rate of BMS181321 with progressive reduction in flow.

Cerebral blood flow velocity in pediatric patients is reduced after cardiopulmonary bypass with profound hypothermia

Transcranial Doppler sonography of the middle cerebral artery was used to determine whether cerebral perfusion was detectable in low flow states during operations with cardiopulmonary bypass in pediatric patients. Quantitative and qualitative differences in cerebral blood flow velocity after rewarming in patients treated with continuous low-flow bypass or deep hypothermic circulatory arrest were assessed. To determine whether the alterations in cerebrovascular resistance pattern observed in our patients undergoing profound hypothermia was more a function of perfusion technique than of minimum temperature during operation, a third group of patients treated with moderate hypothermia was studied. The three patient groups were the arrest group (N = 16), comprised of patients undergoing circulatory arrest at 18 degrees to 20 degrees C; the low-flow group (N = 16), patients treated with continuous low-flow (cardiac index 0.5 L/min per square meter) bypass at 18 degrees to 20 degrees C; and the moderate group (N = 5), patients treated with moderate hypothermia at 24 degrees to 28 degrees C. Flow velocity was detectable in all patients in the low-flow group, with mean arterial pressures as low as 15 mm Hg. Mean flow velocity was reduced after bypass as compared with prebypass values in both the arrest and low-flow groups (p = 0.0001). Mean flow velocity increased after bypass in the moderate group (p = 0.0001). A Doppler waveform pattern consistent with high cerebrovascular resistance was found in 67% of patients in the arrest group and 44% of those in the low-flow group. None of the patients in the moderate group exhibited such a pattern. Patients treated with profound hypothermia who underwent a period of cold full-flow reperfusion before rewarming did not exhibit this high resistance pattern after rewarming. The present findings indicate that profound hypothermia may evoke changes in the cerebral vasculature that result in decreased mean cerebral blood flow velocity after cardiopulmonary bypass rewarming. A period of cold full-flow reperfusion before rewarming may prevent these alterations and improve cerebral perfusion during rewarming.

Pressure-flow specificity of inspiratory muscle training

The inspiratory muscles (IM) can be trained by having a subject breathe through inspiratory resistive loads or by use of unloaded hyperpnea. These disparate training protocols are characterized by high inspiratory pressure (force) or high inspiratory flow (velocity), respectively. We tested the hypothesis that the posttraining improvements in IM pressure or flow performance are specific to training protocols in a way that is similar to force-velocity specificity of skeletal muscle training. IM training was accomplished in 15 normal subjects by use of three protocols: high inspiratory pressure-no flow (group A, n = 5), low inspiratory pressure-high flow (group B, n = 5), and intermediate inspiratory pressure and flow (group C, n = 5). A control group (n = 4) did no training. Before and after training, we measured esophageal pressure (Pes) and inspiratory flow (VI) during single maximal inspiratory efforts against a range of external resistances including an occluded airway. Efforts originated below relaxation volume (Vrel), and peak Pes and VI were measured at Vrel. Isovolume maximal Pes-VI plots were constructed to assess maximal inspiratory pressure-flow performance. Group A (pressure training) performed 30 maximal static inspiratory maneuvers at Vrel daily, group B (flow training) performed 30 sets of three maximal inspiratory maneuvers with no added external resistance daily, and group C (intermediate training) performed 30 maximal inspiratory efforts on a midrange external resistance (7 mm ID) daily. Subjects trained 5 days/wk for 6 wk. Data analysis included comparison of posttraining Pes-VI slopes among training groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimal flow rates for retrograde warm cardioplegia

Retrograde delivery of warm blood cardioplegia may improve nutrient cardioplegic flow beyond coronary obstructions, but may not adequately perfuse the right ventricle and the posterior left ventricle. To determine the optimal flow rate for warm retrograde cardioplegia, we assessed 62 patients undergoing elective coronary artery bypass in two studies. In the low flow study, administration of 50 ml/min (n = 9), 75 ml/min (n = 11), or 100 ml/min (n = 7) was associated with high lactate production and oxygen extraction during cardioplegic administration. At 50 minutes of cardioplegic arrest, the coronary venous effluent pH was low in all groups. In the high flow study, 30 patients all received flow rates of 100, 200, and 300 ml/min in randomized order during the crossclamp period. In addition, five patients received cardioplegia at a rate of 500 ml/min for the duration of the crossclamp period. Administration of 200 ml/min or higher minimized lactate production and maintained coronary venous pH within the physiologic range, but flows of 300 ml/min or higher did not increase oxygen use or reduce lactate or acid production. Patients in the low flow groups had significantly greater myocardial lactate release during cardioplegic infusion and after removal of the crossclamp than the high flow group. Warm retrograde cardioplegia should be delivered at flow rates of at least 200 ml/min during elective coronary artery bypass operations.

Fetal cardiac bypass: Improved placental function with moderately high flow rates

Prenatal correction of certain cardiac lesions with a poor prognosis may have advantages over postnatal repair. For this to be done, safe and effective support of the fetal circulation must be devised. Studies involving fetal cardiac bypass have demonstrated progressive fetal hypoxemia, hypercapnia, and acidosis, indicating placental dysfunction. We performed fetal cardiac bypass in 18 fetal lambs (126 to 140 days' gestation) to assess the effect of flow rate on fetal oxygenation and metabolism and function of the placenta as an in vivo oxygenator. Fetal cardiac bypass was done for a 30-minute study period at normothermia in all fetuses. During the study period the fetal aorta was cross-clamped and cold cardioplegia was administered to the heart so there was no fetal cardiac contribution to systemic output. Nine fetuses underwent studies at low flow rates (109 ± 20 mL · kg −1 · min −1) and 9 at higher flow rates (324 ± 93 mL · kg −1 · min −1). At the lower flow rate, mean aortic pressure, arterial pH, and oxygen tension decreased whereas carbon dioxide tension and lactate levels increased when compared with prebypass levels. At the higher flow rate mean aortic pressure, pH, oxygen tension, carbon dioxide tension, and lactate levels remained similar to prebypass levels during the 30-minute study period. When the animals were weaned from the bypass circuit after studies at high flow rates, arterial oxygen tension and pH decreased whereas carbon dioxide tension increased to levels similar to those in the low-flow group. We conclude that low fetal cardiac bypass flow rates (100 to 125 mL · kg −1 · min −1) are inadequate to maintain hemodynamics, oxygenation, CO 2 removal, and normal lactate levels when the placenta is used as an in vivo oxygenator. Higher flow rates 1300 to 400 mL · kg −1 · min −1) may limit these changes by improving placental perfusion and function during bypass. Despite high flow rates, placental dysfunction and fetal blood gas abnormalities still occur after fetal cardiac bypass.

Cerebral lactate release after circulatory arrest but not after low flow in pediatric heart operations

Arteriovenous (jugular bulb) differences in blood lactate were followed throughout the procedure and until 18 hours postoperatively in 17 children undergoing congenital heart operations during profound hypothermia. Transcranial Doppler sonography was used to monitor changes in blood flow velocity in the middle cerebral artery. Ten children had a period of total circulatory arrest (39 ± 6 minutes) during profound hypothermia (arrest group). Another 7 children had continuous but reduced pump flow (0.6 to 1.2 L/m 2) throughout hypothermic cardiopulmonary bypass (low-flow group). The mean age was 7.3 ± 1.3 months in the arrest group and 7.9 ± 2.2 months in the low-flow group. The mean time on bypass was 90 ± 10 minutes in the arrest group and 75 ± 9 minutes in the low-flow group. The velocity of blood flow in the middle cerebral artery decreased significantly ( p < 0.05) in both groups to less than 50% of the preoperative level during hypothermia and increased during and after rewarming. Differences in blood lactate level were significantly less than zero ( p < 0.05) from the start of rewarming until 3 hours after the end of cardiopulmonary bypass in the arrest group, whereas differences in blood lactate level remained close to zero in the tow-flow group. We conclude that circulatory arrest during profound hypothermia is followed by a period with release of lactate from the brain, indicating anaerobic cerebral metabolism and possibly disturbed cerebral aerobic metabolism. This study argues for the avoidance of circulatory arrest whenever possible.