Determination of end groups of synthetic polymers by matrix-assisted laser desorption/ionization: high-energy collision-induced dissociation.

Matrix-assisted laser desorption/ionization has been combined with high-energy collision-induced dissociation for the analysis of poly(ethylene glycols) with butanoyl, benzoyl and acetyl end groups, using novel technology comprising a magnetic-sector mass spectrometer and ion buncher with an in-line quadratic-field ion mirror. High-energy (>8 keV) collision-induced dissociation facilitated unambiguous end-group determination of these polymers, providing masses of end groups and structural information. The high-energy collision-induced dissociation also provided information regarding repeat units.

Passive optical interconnection network employing a shuffle-exchange topology.

The design of the optical interconnection network (OIN) system is presented. The network is implemented by the use of only passive optical elements and is based on a shuffle-exchange interconnection pattern. Each passive optical shuffle-exchange stage is designed for cascadability. The OIN switch nodes are capable of broadcast and combine operations in addition to bypass and exchange. The OIN is designed to be controlled by an electronic address computer in a circuit-switched manner. Although the OIN is designed to be used as a subsystem on the shared-memory optical/electronic computer, it may be used as a complete subsystem in other communication or computing architectures.

Shared-memory optical/electronic computer: architecture and control.

The design of a parallel digital computer architecture, the shared-memory optical/electronic computer (SMOEG), and its associated control algorithms are presented. The design is based on the shared-memory model of computation and incorporates an optical interconnection network as an essential element. The arthitecture consists of a novel passive optical shuffle-exchange network, which is detailed in another paper [Appl. Opt. 33, (1994)],.that interconnects electronic processing elements with electronic memory modules and incorporates network control. Improved capability of this optical-electronic multiple-instruction multiple-data (MIMD) architecture over fully electronic implementations stems from the reduced complexity inherent in the optical interconnection network and the resulting memory access capability. In this system the simultaneous development of three main design facets, architecture, hardware, and control algorithms, is crucial in designing an efficient high-performance system.

Effect of alterations in frequency, inspiratory time, and airway pressure on gas exchange during high frequency jet ventilation in dogs with normal lungs.

High frequency jet ventilation (HFJV) is becoming increasingly useful for providing respiratory support in patients with normal lungs during operative procedures, and also has been advocated as a technique for ventilating patients during cardiopulmonary resuscitation. We studied the effect of frequency, percent inspiratory time (I/E ratio), peak airway pressure, and airway pressure difference (peak-PEEP) during HFJV as operational variables on the efficacy of gas exchange in dogs with normal lungs. We observed that at a constant peak airway pressure and percent inspiratory time, PaCO2 generally increases as frequency rises above 100/min. In contrast, PaCO2 generally decreases as percent inspiratory time is reduced at a constant frequency and peak airway pressure. In addition, increasing peak airway pressure and airway pressure difference are associated with lower levels of PaCO2. Arterial oxygenation was adversely affected by frequencies above 300/min, but was otherwise not influenced by alterations in frequency, percent inspiratory time, or airway pressure.

Cardiac output measurements. A review of current techniques and research.

Cardiac output is the volume of blood ejected by the heart per unit time. It is a useful measurement in that it can be used to evaluate overall cardiac status in both critically ill patients and patients with suspected cardiovascular disease. An ideal cardiac output measurement system would have automated continuous output capability, be minimally invasive, accurate, fast, small, low cost and clinically adaptable. This paper presents a theoretical and practical description of the variety of clinical techniques in use today and lists their advantages and shortcomings with respect to the ideal system. Included are the Fick method, indicator dilution techniques, velocity measurements and transthoracic impedance and combined Doppler ultrasound as noninvasive techniques. In addition, several experimental methods are described along with their desirable features and possible constraints. These include intravascular heating/recording, thermistor tracking of cardiac output, ejection fraction measurements and magnetic susceptibility plethysmography.

Clinical factors influencing the selection of high-frequency jet ventilators.

Criteria for selection of high-frequency ventilators, and in particular high-frequency jet ventilators are not significantly different from those for conventional mechanical ventilators. Selection is based upon the design principles and performance characteristics of the ventilator and successful clinical applications that establish clearly its safety and efficacy. The final choice is also influenced by the physical status of the patient, potential physiologic advantages and disadvantages, the necessary requirements of the clinical situation, and the capability of providing adequate oxygenation and ventilation.

Airway pressure as a measure of gas exchange during high-frequency jet ventilation.

Airway pressure during high-frequency jet ventilation (HFJV) reflects safety, ventilator performance, and gas exchange. The value of airway pressure as a monitoring and control variable for predicting the effectiveness of gas exchange was examined in 2 studies using healthy dogs. In the first study, HFJV was delivered to the airway via an extra lumen in the wall of an endotracheal tube, at a frequency of 150 cycle/min and 30% inspiratory time. Airway pressures (peak, mean, trough) were measured at various locations, from 5 cm below to 30 cm above the jet port. Pressures measured above the jet were misleading, but the proper measurement distance below the jet remains uncertain. The second study used the same ventilator settings but varied the airway pressure difference between peak and end-expiratory pressures (2, 4, or 6 cm H2O), and either the mean airway pressure (6 or 10 cm H2O) or the positive end-expiratory pressure (0, 5, 10, or 15 cm H2O). The airway pressure difference correlated strongly with efficiency of gas exchange for both CO2 elimination and oxygenation. Mean and end-expiratory pressures showed little influence over moderate ranges, but use of 15 cm H2O of PEEP decreased efficiency of both CO2 elimination and oxygenation, presumably due to increased dead space because of lung overdistension. We conclude that the airway pressure difference, measured as far distal in the airway as is safe and practical, can be useful for monitoring and controlling HFJV.

Comparison of high-frequency jet ventilation with conventional mechanical ventilation in saline-lavaged rabbits.

A surfactant-depletion lung-injury model was produced in 37 New Zealand white rabbits by saline lavage. During the next 2 to 3 h, rabbits were ventilated with conventional mechanical ventilation (CMV, group 1), high-frequency jet ventilation (HFJV, group 2), or CMV for 1 h followed by HFJV for 2 h (CMV/HFJV, group 3). Survival until planned termination of the protocol was 56%, 77%, and 63% in groups 1, 2 and 3, respectively. Causes of early demise were usually pneumothorax or metabolic acidosis. There were no statistically significant differences among the groups with respect to survival, incidence of pneumothorax or metabolic acidosis. Arterial oxygenation was more efficient with HFJV (group 2) (P[A-a]O2 = 372 +/- 51 torr [mean +/- SE] at 2 h) than with CMV (group 1) (P[A-a]O2 = 512 +/- 18 torr at 2 h, p less than .01). Furthermore, oxygen gas exchange in 3 of 5 group 3 rabbits improved after institution of HFJV. In contrast to previous findings with high-frequency oscillation (HFO), there were no qualitative histologic differences between lungs ventilated with HFJV vs. CMV. Thus, although HFJV produced more efficient gas exchange in this model, it did not improve pulmonary pathology. HFO may be preferable to HFJV in infant respiratory distress syndrome.

Airway movement in dogs during high-frequency jet ventilation.

Cine tantalum bronchograms were recorded from 7 pentobarbital-anesthetized dogs during spontaneous ventilation (SV), high-frequency jet ventilation (HFJV) at 3 frequencies, and intermittent positive-pressure ventilation (IPPV) at 3 combinations of tidal volume (VT) and rate. During SV and the 3 IPPV conditions, the percent inspiratory increase in the diameter of airways greater than 3 mm was the same as in airways less than 3 mm. With HFJV, the percent increase in the diameter of airways greater than 3 mm was twice that of smaller airways. Increases in airway diameter are proportional to transmural, and hence intraluminal airway pressure. These data, therefore, indicate that the contribution of intraluminal pressure changes to intrapulmonary gas transport in small airways during HFJV is less than with either SV or IPPV, and that mechanisms responsible for intrapulmonary gas transport in small conducting airways during HFJV are different than those associated with either SV or IPPV.

Gas and vapor delivery.

Technology for gas and vapor delivery has not changed substantively in decades. Technology possessing greater precision and reliability has been in use by nonmedical industries to regulate gas flows and to vaporize liquids. Adaptation of existing technology to the needs of anesthesia delivery systems requires stimulus from the anesthesia community and commitment from the anesthesia device industry. No insurmountable problems are evident, but the perennial problem of inertia has prevented progress consistent with that seen in other fields of biomedical technology.

Recovery of waste anesthetic gases.

The problem of waste anesthetic gases must be addressed because of potential health hazards. However, solutions must be considered within a larger context than that of the operating room or dental suite. The impact of shifting wastes from the hospital into the atmosphere must be examined for both ecologic and ethical implications. A hypothetic situation has been proposed in which the waste anesthetics are dealt with by recovery and reuse. Although potential costs and benefits can be discussed, overall feasibility and desirability cannot be assessed until certain questions are addressed. Are waste anesthetic gases an atmospheric pollutant with impact sufficient to cause concern? If not, do the economic considerations of recycling exhausted anesthetic and respiratory gases warrant implementation? Anesthesiologists need to consider these issues within the constraints of the environments in which they practice. The problem will exist as long as inhalation anesthesia is in use. Solution should not create new problems.

High frequency ventilation applications in the OR.

High frequency ventilation provides effective gas exchange at frequencies between 60 and 2,400 min-1. It can be potentially useful in the operating room for bronchoscopy, laryngoscopy, airway surgery, general surgery, and microscopic neurosurgery.

The anesthesia machine: current design and alternatives.

The anesthesia machine is a major component in an integrated anesthesia care system. It can be considered in terms of the functional subsystems responsible for gas proportioning, anesthetic vapor delivery, patient ventilation, and waste gas scavenging. Alternative technologies for these functional units should be examined in light of the disadvantages inherent in present machines. Safety features, often added on an ad hoc basis, should instead be designed into the machine itself. The anesthesia delivery system should include feedback about the patient status and device performance, as well as provide for the delivery of anesthetic and pharmacologic agents. Improvements in performance and provisions for automation of some functions should be considered as future design criteria.

Hemodynamic effects of high-frequency jet ventilation.

The hemodynamic effects of high-frequency jet ventilation (HFJV) and conventional ventilation were compared in normovolemic and functionally hypovolemic dogs. In normovolemic animals, no differences in hemodynamic function were found among spontaneous ventilation, conventional ventilation, and HFJV. When venous return was impaired by 15 cm H2O PEEP, cardiac index and stroke index were 25% higher with HFJV than with conventional ventilation (P less than 0.05). In another study with PEEP, conventional ventilation was compared to spontaneous ventilation, HFJV synchronized to five different parts of the cardiac cycle, and asynchronous HFJV. Heart rate was 15% lower and mean arterial pressure was 26% lower with conventional ventilation than with HFJV modes (P less than 0.05). There were no differences between synchronous and asynchronous HFJV. These results indicate that hemodynamic dysfunction may be less likely with HFJV than conventional ventilation. No advantage of synchronizing jet pulsations to a specific part of the cardiac cycle could be demonstrated.