Transaortic inflow and outflow cannula for centrifugal mechanical assistance

A specific cannula allowing single site transaortic inflow and outflow cannulation for centrifugal assist devices is described. The cannula is inserted through a straight 18 mm collagen coated Dacron tube anastomosed to the anterior aspect of the ascending aorta. The inflow conduit of the cannula is positioned into the left ventricle through the aortic valve, and the end hole of the outflow conduit is positioned in the ascending aorta. The cannula was evaluated in vivo in 3 adult pigs by the institution of a centrifugal pump for left ventricular support. Optimal flow varied between 5 and 6 L/min and mean aortic pressure between 55 and 70 mm Hg throughout the 3 days of left ventricular support. Recently, we employed this cannula in a patient who was not able to be weaned from cardiopulmonary bypass for the institution of left ventricular support using a centrifugal pump. The cannula provided effective inflow and outflow drainage with an optimal flow of 5.2 L/min throughout the 72 h of support. The patient was successfully weaned from support on the fourth postoperative day. This rational transaortic approach of cannulation using this specific cannula is a refined implantation technique which allows direct left ventricular inflow drainage, reduces the time of implantation, spares left ventricular myocardium, avoids bleeding that is sometimes encountered at other cannulation sites, and avoids compression of the heart by cannulas.     

Morphine blood concentrations in elderly postoperative patients following administration via an indwelling subcutaneous cannula

The pharmacokinetics of morphine in venous blood after a 5 mg bolus dose via an indwelling subcutaneous cannula were characterised in 22 elderly patients undergoing elective major surgery. In a subgroup of seven patients, the kinetics were also characterised after a second 5 mg dose of morphine administered 180 min after the first dose. Blood morphine concentrations following the single dose were highly variable — the coefficients of variation of C _max, T _max and the AUC up to 180 min ( AUC ₁₈₀) were 54, 37 and 39%, respectively, with mean values of 86.6 ng.ml⁻¹, 15.9 min and 3954 ng.ml⁻¹, respectively. These mean values for the second dose were not statistically different to those of the first dose but were more variable. It was concluded that the injection of morphine via an indwelling subcutaneous cannula results in blood concentrations that are comparable to, and as variable as, those arising from intramuscular injection.     

Hemodynamic Evaluation of Avalon Elite Bi‐Caval Dual Lumen Cannulas and Femoral Arterial Cannulas

Translational research is a useful tool to provide scientific evidence for cannula selection during extracorporeal life support (ECLS). The objective of this study was to evaluate four Avalon Elite bi‐caval dual lumen cannulas and nine femoral arterial cannulas in terms of flow range, circuit pressure, pressure drop, and hemodynamic energy transmission in a simulated adult ECLS model. A veno‐venous ECLS circuit was used to evaluate four Avalon Elite bi‐caval dual lumen cannulas (20, 23, 27, and 31 Fr), and a veno‐arterial ECLS circuit was used to evaluate nine femoral arterial cannulas (15, 17, 19, 21, and 23 Fr). The two circuits included a Rotaflow centrifugal pump, a Quadrox‐D adult oxygenator, and 3/8 in ID tubing for arterial and venous lines. The circuits were primed with lactated Ringer’s solution and packed human red blood cells (hematocrit 40%). Trials were conducted at rotational speeds from 1000 to 5000 RPM (250 rpm increments) for each Avalon cannula, and at different flow rates (0.5–7 L/min) for each femoral arterial cannula. Real‐time pressure and flow data were recorded for analysis. Small caliber cannulas created higher circuit pressures, higher pressure drops and higher M‐numbers compared with large ones. The inflow side of Avalon dual lumen cannula had a significantly higher pressure drop than the outflow side (inflow vs. outflow: 20 Fr‐100.2 vs. 49.2 mm Hg at 1.1 L/min, 23 Fr‐93.7 vs. 41.4 mm Hg at 1.6 L/min, 27 Fr‐102.3 vs. 42.8 mm Hg at 2.6 L/min, 31 Fr‐98.1 vs. 44.7 mm Hg at 3.8 L/min). There was more hemodynamic energy lost in the veno‐arterial ECLS circuit using small cannulas compared to larger ones (17 Fr vs. 19 Fr vs. 21 Fr at 4 L/min—Medtronic: 71.0 vs. 64.8 vs. 60.9%; Maquet: 71.4 vs. 65.6 vs. 62.0%). Medtronic femoral arterial cannulas had lower pressure drops (Medtronic vs. Maquet at 4 L/min: 17 Fr‐121.7 vs. 125.0 mm Hg, 19 Fr‐71.2 vs. 73.7 mm Hg, 21 Fr‐42.9 vs. 47.4 mm Hg) and hemodynamic energy losses (Medtronic vs. Maquet at 4 L/min: 17 Fr‐43.6 vs. 44.4%, 19 Fr‐31.0 vs. 31.4%, 21 Fr‐20.8 vs. 22.4%) at high flow rates when compared with the Maquet cannulae. The results for this study provided valuable hemodynamic characteristics of all evaluated adult cannulas with human blood in order to guide ECLS cannula selection in clinical practice. Use of larger cannulas are suggested for VV‐ and VA‐ECLS.     

Cardiovascular depression by isoflurane and concomitant thoracic epidural anesthesia is reversed by dopamine

Interactive effects between exogenous dopamine (DA) and isoflurane (I) combined with thoracic epidural blockade (TEA) were studied in dogs during chloralose anesthesia. The I–TEA intervention per se decreased heart rate (HR; 28%), mean arterial pressure (MAP; 63%), cardiac output (CO; 54%), left ventricular dP/ dt (LVdP/dt; 75%) and LVdP/dt/systolic arterial pressure (SAP; 42%). Prior to the I–TEA intervention , dopamine increased MAP, CO, LVdP/dt, LVdP/dt/SAP and stroke volume (SV) already at the dose 10 μg–kg^-1. min^-1 and, additionally, increased mean pulmonary artery pressure (MPAP) at the dose 20 μg–kg^-1. min^-1. During the I–TEA intervention , the DA–induced increases in MAP and systemic vascular resistance (SVR) were significantly higher than prior to I–TEA, as indicated by significant ANOVA interactive effects. At the dose 10 μg–kg^-1 min^-1, DA restored MAP, CO, LVdP/dt, LVdP/dt/SAP and SV to levels found before the I–TEA intervention, while HR was restored first at the dose 20 μg–kg^-1 –min^-1. At the dose 20 μg–kg^-1–min^-1, DA also increased MAP (39%), LVdP/dt (119%), LVdP/dt/SAP (73%), SVR (28%) and MPAP (70%) above levels prior to I–TEA. To conclude, exogenous dopamine effectively and dose–dependently counters cardiovascular depression induced by the anesthetic technique of combining I and TEA. The pressor and systemic vasoconstrictor actions of dopamine are potentiated by conjoint administration of I and TEA.     

α1-adrenoceptor stimulation is able to reverse halothaneinduced cardiac depression in isolated rat hearts

Background: Stimulation of myocardial α₁-adrenoceptors has been shown to exert positive inotropic effects through a cyclic AMP-independent mechanism. The purpose of this study was to examine if α₁-adrenoceptor stimulation is able to attenuate myocardial depression produced by exposure to halothane, and to test if α₁-adrenoceptor stimulation alters myocardial oxygen supply-demand balance in hearts exposed to halothane.
Methods: The effects of phenylephrine were examined in 7 isolated perfused rat hearts. Variables measured were: heart rate, isovolumetric peak left ventricular pressure (LVP), LV dP/dt, coronary arterial flow, myocardial O₂ delivery (DO₂), myocardial O₂ consumption (MVO₂) and the ratio of DO₂/MVO₂. Each heart was exposed to phenylephrine cumulatively 0.1 μM, 0.3 μM, 1 μM and 3 μM under the administration of 1% halothane in the presence of propranolol 1μM.
Results: Halothane 1% decreased the heart rate by 9±3%, LVP by 37±3%, and LV dP/dt by 35±2%. Phenylephrine restored these decreases to the baseline levels. Phenylephrine maintained or further enhanced the reductions in coronary flow and DO₂ produced by halothane, resulting in a decrease in the DO₂/ MVO₂ ratio.
Conclusion: α₁adrenoceptor stimulation is capable of restoring direct cardiac depressant effects of halothane with a possible impairment of the oxygen supply-demand balance.     

The Effect of Valve Type and Drive Line dP/dt on Hemolysis in the Pneumatic Ventricular Assist Device

Abstract: The objective of this experiment was to investigate the relationship between blood damage and drive line dP/dt and valve type in the pneumatic ventricular assist device. Two mock circulatory loops were assembled using 70–ml Penn State pneumatic ventricular assist devices, one fitted with convexoconcave (CC) valves and one fitted with monostrut (MS) valves. Use of a compliance chamber established three ranges of drive line dP/dt values. Using bovine blood and the methods of generalized estimating equations, it was found that drive line dP/dt was significantly associated with the index of hemolysis (p = 0.00): the lower drive line dP/dt values yielded lower indices of hemolysis. In addition, this association differed between MS and CC valves (p = 0.01); the MS valves consistently yielded a higher index of hemolysis than the CC valves across all drive line dP/dt ranges. However, the relative hemolytic potential of each valve type became much closer at low drive line dP/dt values (2,000–3,000 mm Hg).     

Enhanced functional recovery with venting during cardioplegic arrest in chronically damaged hearts

Thirty dogs with experimental myocardial infarction underwent cardiopulmonary bypass, hypothermic asanguineous K+ cardioplegia (1 hour), and reperfusion (30 minutes). Ten hearts were vented throughout, 5 only during arrest, and 5 only during reperfusion; 10 were not vented. Left ventricular (LV) performance and compliance were assessed by isovolumic (LV balloon) indexes before bypass and after reperfusion. Vented hearts recovered 116 +/- 8.3% of prearrest developed LV systolic pressure (DLVSP) and 131 +/- 13.6% of prearrest rate of rise of LV pressure (dP/dt). Nonvented hearts allowed to develop pressure during arrest (11.6 +/- 1.6 mm Hg) and reperfusion (65 +/- 4 mm Hg) recovered 50 +/- 3.9% of prearrest DLVSP and 55 +/- 5% of prearrest dP/dt (p less than 0.05). Reduction in LV compliance was comparable in both groups. Mitochondrial architecture (electron microscopy) was preserved in vented hearts, but was modestly disrupted in nonvented hearts, thus suggesting slight metabolic impairment. Functional recovery was nearly complete in hearts vented only during reperfusion (DLVSP, 94 +/- 10.4%; dP/dt, 89 +/- 12.6%), but venting only during arrest led to functional depression (DLVSP, 50 +/- 6.6%; dP/dt, 51 +/- 8%; p = 0.01). We conclude that venting chronically infarcted hearts during cardiac operations affords better myocardial protection by avoiding the damage that occurs during nonvented reperfusion.     

Helium/Oxygen Breathing Improves Hypoxemia after Cardiac Surgery

Abstract: The effects of helium/oxygen (He/O₂) on oxygen-ation (respiratory index [Pao₂,/Fio₂] and inuapulmonary shunt [Qs/Qt]) and on lung parameters (dynamic compliance [Cdyn] and peak inspiratory pressure [PIP]) were studied in 12 patients. After cardiac surgery, they had impairment of oxygen-ation without physiological findings and with normal chest radiographs despite having a positive end expiratory pressure of up to 10 cm H₂O. After 90 min of inhalation of He/O₂., oxy-genation had improved significantly; that is, Pao₂/Fio₂, in creased significantly (from 113 to 174 mm Hg; mean values are given; p < 0.01), and there was a significant fall in Qs/Qt (from 29 to 19%; p < 0.01) together with an increase in Cdyn (from 60 ml/cm H₂O to 64 mVcm H₂O; p < 0.05). These results suggest that HeiO₂ may have improved oxygenation by recruiting previously obstructed small airways and alveoli.     

Life–Saving Effect of Pyridoxalated Hemoglobin–Polyoxyethylene Conjugate on Carbon Monoxide Intoxication of Rabbits

Abstract: We examined whether pyridoxalated hemoglo–bin–polyoxyethylene conjugate (PHP) could be life–relievable for carbon monoxide (CO) intoxication. Toxic gas (O₂, 5. 0%; CO₂, 16. 0%; CO, 1. 8%; and N₂, 77. 2%) was inhaled by rabbits anesthetized with urethane and the following parameters were measured: blood pressure, arterial and venous PO₂, PCO₂, pH, and carboxyhemoglobin (COHb). When mean blood pressure reached 0 or 20 mm Hg as an index after inhalation of the toxic gas, the toxic gas was switched to air; intravenous infusion of physiological saline or PHP (1. 2 g/20 ml/kg/30 min) was simultaneously initiated. In the experiment using 0 mm Hg blood pressure, PHP prolonged the survival time and exhibited significant temporary recovery of PO₂ and PCO₂ in comparison with saline. In the experiment using the 20 mm Hg blood pressure, a significant difference in each parameter was observed between the saline and PHP groups. Two of 8 animals in the saline group died without any recovery of each parameter. All 6 animals in the PHP group survived and each parameter recovered. PHP accelerated recovery from high COHb concentrations, low arterial and venous PO₂, reduction of arterial and venous PCO₂, and elevations of pH and blood pressure. These results suggest that PHP treatment during the early stage of CO intoxication is life–saving and effective in facilitating the recovery of various functions.     

Cleveland Clinic PediPump lamb cadaver fitting studies

We are developing the PediPump, a magnetically suspended, mixed-flow pump, as an implantable pediatric ventricular assist device (VAD). Lamb cadaver fitting studies were performed to determine the optimal pump location and optimal design of the inflow and outflow conduits for chronic in vivo studies. A prototype of the PediPump right and left ventricular assist devices (RVAD and LVAD, respectively) were implanted via a sternotomy or left thoracotomy in four lamb cadavers (3.7-34.2 kg). Via a sternotomy, the RVAD and LVAD required long inflow cannulas when placed into the right or left thoracic cavities, respectively. Via a left thoracotomy, with both pumps implanted in the left thoracic cavity, the RVAD required a 70 degrees inflow cannula and a bent outflow graft while the LVAD required a 130 degrees inflow cannula and a straight outflow graft. In conclusion, left thoracotomy provided optimal fitting for both LVAD and RVAD for the small lamb model.     

Blood Density Monitoring During Dialysis

Abstract Continuous monitoring of blood density (BD) was preformed in 4 stable dialysis patients in 20 sessions using a density meter based on a mechanical oscillator technique. Mean predialysis and postdialysis BDs were 1.0427 ± 0.0031 g/cm³ and 1.0502 ± 0.0055 g/cm respectively. For similar predialysis to postdialysis total body water reduction, significant difference in the mean BD increase was found between hypotensive and nonhy-potensive groups (1.29 ± 0.07%, 0.47 ± 0.12%, respectively; p < 0.001). Eight hypotensive episodes occurred during 6 sessions. The mean value of the blood density changes slope (dBD/dt) during the 5 min preceding a hypotensive episode increased about 2.5 times more than did the mean of the predialysis to postdialysis blood density slope (27.6 ± 2.2 g/cm³ min 10^-5, 10.5 ± 0.4 g/cm³ min 10^-5 respectively; p < 0.001) under the condition of a constant ultrafiltration rate of 18.9 ± 0.6 ml/min. Continuous monitoring of blood density allows abrupt change in plasma volume to be identified and seems to have a potential utility to the prevention of symptomatic hypotension episodes in patients receiving hemodialysis.     

Influence of Changes in Arterial PCO2 on Cerebral Blood Flow and Cerebral Energy State during Hypothermia in the Rat

In order to study the relationship between arterial P_CO2 and cerebral blood flow (CBF) in hypothermia, the body temperature of artificially ventilated rats was decreased to 22C, and changes in CBF were evaluated from arteriovenous differences in oxygen content (AVD_O2) at Pa_CO2 values of 15, 30, 40 and 60 mm Hg. The results were compared to those obtained at normal body temperature (37C) over the Pa_CO2 range 15–60 mm Hg. Separate experiments were performed to evaluate CBF and CMR_O2 at 22C and a Pa_CO2 of 15 mm Hg, using an inert gas technique for CBF. The tissue contents of phosphocreatine, ATP, ADP, AMP and lactate were measured in hypothermic animals at Pa_co2values of 15, 30 and 60 mm Hg.
The results showed that changes in CBF were of the same relative magnitude in hypothermia and normothermia when Pa co2 was increased from about 35 to about 60 mm Hg. However, with a decrease in Pa_CO2 the reduction in CBF was much more pronounced in hypothermia, and at Pa_CO2 15 mm Hg CBF was less than 20 % of the value measured in normothermic and normocapnic animals. The results of the metabolite measurements gave no evidence of tissue hypoxia in spite of the pronounced reduction in CBF. Although the results demonstrate that the brain of a hypothermic animal is protected against the harmful effects of a lowered CBF, it may not warrant recommending hyperventilation in clinical cases of hypothermia, especially not in patients with arteriosclerosis or cerebrovascular diseases.     

Survival of Densely Packed Follicular Unit Grafts Using the Lateral Slit Technique

BACKGROUND The use of densely packed follicular unit grafts (>30 grafts/cm²) is a highly debated issue, with some claiming decreased survival rates. Those who perform dense packing routinely do not believe they have seen any impaired survival. However, no prior study has rigorously analyzed densely packed areas to assess survival rates.
OBJECTIVE In this study, the authors assessed the survivability of densely packed (>70 grafts/cm²) follicular unit grafts using the lateral slit technique.
METHODS This study was a strictly observational study in one patient. Several 1-cm² areas tattooed on the mid scalp were grafted at densities ranging from 23 to 72 grafts/cm² using the lateral slit technique. The area surrounding the observation sites was transplanted at a density of 30 to 40 grafts/cm².
RESULTS Examination of the most densely packed area (72 grafts/cm²) at 8 months posttransplant revealed that the number of implanted grafts showing growth was 98.6% whereas the least densely transplanted area (23 grafts/cm²) revealed a growth rate of 95.6%.
CONCLUSION This is the first study that demonstrates high growth rates in densely packed follicular units using the lateral slit technique, even at densities of 72 grafts/cm². These data are in contradistinction to previously performed studies using older methodologies.     

A Volume-Controlled Liquid Ventilator with Pressure-Limit Mode: Imperative Expiratory Control

Abstract Liquid ventilation with perfluorocarbon (PFC) has been considered to offer advantages over gas ventilation to respiratory distress syndrome patients. We developed a volume-controlled liquid ventilator with pressure-limit mode; inspiration is performed mechanically with an actuator under the preset limit of the intratracheal pressure (Paw); expiration is performed by gravity assistance. Oxygenation and C0₂ removal of PFC are done with a membrane oxygenator. An endotracheal tube with a Paw monitor line was placed in 5 rabbits weighing 2.7 ± 0.6 kg, and liquid ventilation was conducted with the condition that the upper and lower limits of Paw were 20 and – 20 mm Hg, respectively. The best arterial pH and gas tension were examined. The averaged arterial pH, Pao₂, Paco₂, and Sao₂ were 7.45 mm Hg, 369 mm Hg, 46.2 mm Hg, and 100% at the best values, respectively. Ventilatory conditions at the best values were as follows: ventilation rates, tidal volume peak Paw, average Paw, and trough Paw were 5–15 (11 ± 4) times/min, 13.3–17.3(15.6 ± 1.4) ml/kg, 5–18(12 ± 5) mm Hg, -7-4 (-1 ± 4) mm Hg, and -20–6 (-13 ± 5) mm Hg, respectively. Pressure-limit control of the system worked well, but in the initial 3 animals, fluorothrax, that is the leakage of PFC into thoracic cavity, was recognized at the Paw from 20 to 25 mm Hg after the upper pressure limit was raised to 25 mm Hg to improve Paco,. The fluorothrax seemed to be caused by excess end-expiratory residual volume. An expiratory control mechanism appears to be imperative for further improvement of our liquid ventilator.     

Role of zatebradine and propranolol in attenuation of tachycardia produced by dobutamine in pigs

Background: Zatebradine is a new specific bradycardic agent that selectively slows the depolarization in the pacemaker cells of the sinoatrial node. The purpose of our investigation was to determine whether the tachycardia induced by dobutamine can be attenuated by the administration of zatebradine. The results were compared with those produced by propranolol, which is used in the treatment of sinus tachycardia.
Methods: Twelve pigs were anesthetized with sodium pentobarbital, intubated, and ventilated. After baseline hemodynamic measurements were obtained, dobutamine was administered until the heart rate reached 25% above baseline. Animals were randomized to one of two groups. Group I received zatebradine, 0.5 mg/kg IV, and Group II received propranolol, 0.5 mg/kg IV.
Results: Dobutamine 10 μg kg^-1 min^-1 increased the heart rate (HR) by 25%, and increased mean arterial blood pressure (MAP), left ventricular (LV) dP/dt, and cardiac output (CO) ( P < 0.05). Zatebradine decreased the HR to baseline ( P < 0.05) without affecting left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), LV dP/dt, or CO. Stroke volume (SV) increased significantly ( P < 0.05). Propranolol also reduced HR to baseline, but decreased LV dP/dt, LVSP, CO, and SV ( P < 0.05).
Conclusion: Zatebradine effectively attenuates the tachycardia caused by dobutamine in anesthetized pigs, without reducing cardiac performance.     

Improved right heart function with a compliant inflow artificial lung in series with the pulmonary circulation

BACKGROUND: We previously reported a 50% incidence of immediate right heart failure using a rigidly housed, noncompliant inflow artificial lung in series with the pulmonary circulation in a healthy ovine survival model. Three device modifications resulted: (1) an inflow cannula compliance chamber, (2) an inlet blood flow separator, and (3) modification of the artificial lung outlet geometry, all to reduce resistance and mimic the compliance of the pulmonary vascular bed. METHODS: In 7 sheep, arterial grafts were anastomosed end-to-side to the proximal and distal main pulmonary artery, with the paracorporeal artificial lung interposed. A pulmonary artery snare between anastomoses diverted full pulmonary blood flow through the artificial lung for up to 72 hours. RESULTS: Six of 7 sheep exhibited good cardiac function throughout the test period: mean central venous pressure was 6.8 mm Hg (range, 4 to 11 mm Hg), mean cardiac output, 4.17 +/- 0.12 L/min (range, 2.4 to 6.3 L/min); before and after device mean pulmonary arterial pressure, 21.8 and 18.5 mm Hg, and left atrial pressure, 10.8 mm Hg. CONCLUSIONS: This modified artificial lung prototype with an inflow compliance chamber, blood flow separator, and modified outlet geometry has greatly improved cardiac function and initial survival in our healthy ovine model.     

Cutaneous Monitoring of Systemic Pco2 on Patients in the Respiratory Intensive Care Unit being Weaned from the Ventilator

A procedure for measuring the partial pressure of CO₂ in equilibrium with the epidermis was developed at Hewlett-Packard Laboratories. It consists of determining by infra-red absorption techniques the concentration of CO₂ inside a small (50 μl) chamber applied hermetically over and around an epidermal window (2.25 cm²) stripped of its stratum corneum or horny layer. We have applied the procedure to 25 patients in the Respiratory Intensive Care Unit at Stanford Hospital. Only patients scheduled for weaning from the ventilator were selected for the study. The epidermal windows were on the medial aspect of the forearm and were monitored for 3–6 h. Arterial blood samples were periodically withdrawn from the catheterized radial artery and were analysed by conventional means for subsequent comparison with the cutaneous measurements which were recorded in real time at the rate of one a minute. The range of arterial P_co2 values that were measured varied from 3.33 to 9.30 kPa (25 to 70 mmHg) and correlated well with the corresponding cutaneous P_co2 values that were typically higher than the arterial values by 0.7 kPa (5.2 mmHg) with a standard deviation of 0.2 kPa (1.5 mmHg). Some typical recordings of cutaneous P_co2 are shown and discussed.     

Development of a Hemodynamically Optimized Outflow Cannula for Cardiopulmonary Bypass

The jet of the outflow cannula is a potential risk for patients undergoing cardiopulmonary bypass (CPB), because increased jet velocities lead to altered flow conditions and might furthermore mobilize atherosclerotic plaques from calcified aortas. The cannula jet is therefore among the main reasons for cerebral hypoxia and stroke in CPB patients. In the past, we developed a validated computational fluid dynamics (CFD) model to analyze flow conditions during CPB as dependent on cannulation and support modalities. This model is now applied to develop a novel CPB outflow cannula to reduce the jet effect and increase cerebral blood flow. The Multi‐Module Cannula (MMC) is based on a generic elbow cannula that was iteratively improved. It features an inner wall to smoothly guide the blood as well as an elliptically shaped outlet diffuser. During standard CPB conditions of 5 L/min, the pressure drop over the MMC is 61 mm Hg, compared with 68 mm Hg with a standard cannula. The maximum velocities are decreased from 3.7 m/s to 3.3 m/s. In the cannula jet of the MMC, the velocities are reduced further, down to 1.6 m/s. The cerebral blood flow is typically reduced during CPB. Using the MMC, however, it reaches almost physiological values at 715 mL/min. These results suggest that the MMC outperforms standard CPB cannulas. Further design improvements and improved insertion techniques are under consideration.     

The combination of external high-frequency oscillation and pressure support ventilation in acute respiratory failure

Background: Effective gas exchange can be maintained in animals by using external high-frequency oscillation (EHFO). The present study evaluates the effect of relatively long-term duration EHFO combined with pressure support ventilation (PSV) in patients with acute respiratory failure.
Methods: Twelve patients were ventilated with EHFO combined with PSV for 8 h at 60 oscillations min^-1, with a cuirass pressure of 36 cm H₂O: -26 to +10 cm H₂O (27 mm Hg: -19.5 to +7.5 mm Hg) and an inspiratory-to-expiratory ratio of 1: 1. Blood gas values and hemodynamic parameters were measured. Results: Significant increases were noted in cardiac index (3.0±0.7 to 3.2±0.7 1 min^-1 m^-2, P < 0.05) and stroke volume index (32±14 to 35±13 ml m^-2, P < 0.05) without changes in pulmonary artery wedge pressure at 1 h after EHFO. PaO₂(kPa)/FiO₂ and PaCO₂ improved from 21.9±7.5 to 26.8±8.0 ( P < 0.05) at 2 h and from 6.9±1.7 to 6.1±0.9 kPa ( P < 0.01) at 30 min after EHFO, respectively. Breath sounds could be heard well throughout the lung fields after institution of EHFO. The mucous rales also decreased.
Conclusions: As a method of ventilation for patients with acute respiratory failure, EHFO combined with PSV may have potential advantages over conventional mechanical ventilation when drainage of secretions is facilitated. Beneficial effects of EHFO may appear after several hours.