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The Booth (1951) multiplier represents an efficient and simple way to multiply signed binary numbers. This paper describes an improvement to the standard implementation of a Booth multiplier at any radix. More specifically, it compares VHDL implementations of conventional radix 2, 4, 8, 16, and 32 Booth multipliers against multipliers with the product select circuitry added. VHDL models of the multipliers are analyzed and conclusions are drawn. Estimates of area gain and speedup indicate that this multiplier scheme has significant advantages at lower radices and, at higher radices, still maintains a relative advantage over the radix 2 implementation. >

This paper presents the results of comparative testing of standard encapsulants versus inorganic hermetic-equivalent protective coatings in a full factorial study that also compares wire-bond assembly versus flip-chip assembly and supplemental encapsulant/underfill die protections versus no encapsulant/underfill protection. The demonstration multichip modules (MCMs) included two design versions, flip-chip and wire-bond, of a general aviation data accumulator MCM. Full wafer probe testing was performed both before and after the supplemental ChipSeal/sup TM/ processing and flip-chip wafer bump processing steps. ChipSeal/sup TM/ and flip-chip wafer processing steps were shown to cause no yield degradation of the the two different wafer types used in the MCMs. Known good die (KGD) screening of all ICs in the modules was used to keep infant mortality failures out of the reliability test results. Preliminary substrate reliability investigations determined that BT and polyimide laminate materials are suitable for robust MCM-L applications. Reliability testing includes vibration in step-stress exposures from 2 to 44 g(RMS), thermal cycling for 2000 cycles from -55 to +125/spl deg/C, 85/spl deg/C/85% RH high humidity testing accelerated by pre-conditioning and power cycling, and 130/spl deg/C bias highly accelerated stress testing (HAST). Comparative reliability results are presented for identical circuit designs in flip-chip versus wire-bonded assemblies, with and without the protective inorganic coatings, and with and without organic encapsulant/underfill protection.

Expressions have been derived to show the dependence of alveolar oxygen and anaesthetic concentrations on fresh gas flow to a circle system, the composition of fresh gas, ventilation and gas uptake. The form of these expressions is influenced by the degree of mixing of fresh and expired gases within the circle system. These expressions assume an equilibrium state within the circle system and the rate at which equilibrium will be approached has been quantified in terms of the time-constants of change of composition of gas within the system. Time-constants approach infinity as fresh gas flow approaches values which just satisfy gas uptake. Whilst simplifying assumptions made in the derivation of the various alveolar gas equations limits their accuracy, the expression can serve as a guide to the likely behaviour of circle systems under any given conditions of use.

Three electronic respirometers, two of which have been recently introduced (the Birchover respiratory flowmeter and the Wright respiration monitor), and one a prototype model (Spiroflo) have been laboratory tested in conditions designed to simulate possible modes of clinical use. It was found that the accuracy of the Spiroflo and Wright instruments were acceptable, but the Birchover was limited in its application and became less accurate in the variations of use described.

A paramagnetic oxygen analyser which has a response time allowing oxygen concentration to be followed within a breath is described. Noise generated by the differential pressure transducer precludes the achievement of accuracy comparable with other paramagnetic analysers (e.g., Servomex OA150). The performance of the analyser is not disturbed by the presence of other gases or water vapour. It cannot be used during IPPV as pressure changes produce false deflections in the transducer system for which there is no simple method of compensation.

SUMMARY Gas concentrations and ventilation levels have been measured within a conventional Magill circuit when conscious volunteers breathed a non-narcotic gas mixture at varying fresh gas flows. When evidence of rebreathing of alveolar gas was detected, the fresh gas flow was kept constant until a steady state developed. All subjects showed evidence of rebreathing when the fresh gas flow approached the predicted alveolar ventilation levels. A variety of subject-circuit interactions was seen and shown to be precipitated by naturally occurring breath-to-breath variations in ventilation. A single large breath could perturb the system. This could have a temporary effect, when the fresh gas flow was sufficient to wash the increased aliquot of expired carbon dioxide from the circuit. At other times a progressive response occurred as ventilatory stimulation as a result of the increased inspired carbon dioxide concentrations caused alveolar gas to reach the reservoir bag and converted the system behaviour from that of a simple added deadspace to that of a total mixing device. Whilst marked changes occurred commonly in both ventilation and inspired gas concentrations, only slight changes in end-tidal gas concentrations occurred.

An experimental lung model was used, with controlled ventilation, to determine the effect of different circle arrangements and varying ventilatory frequencies on the efficiency of carbon dioxide removal from a circle system without carbon dioxide absorption. Greater efficiency was found when fresh gas entered the system between the unidirectional inspiratory valve and the subject that when the fresh gas inlet was on the ventilator side of this valve. At any fresh gas flow and minute volume, efficiency was greater at low respiratory frequencies. Good correlations existed between carbon dioxide concentration in the model lung, fresh gas flow and minute ventilation when respiratory frequency was constant. Paradoxical results were obtained when minute volume was varied by changes in frequency at a constant tidal volume. The major cause of the various differences in performance has been ascribed to variations in the degree of mixing of fresh and expired gas within the system.

A mathematical model of a subject breathing from a circle system has been used to follow the course of anaesthetic uptake during the simulated administration of 60% nitrous oxide, 2% halo-thane and 2% methoxyflurane, under non-re-breathing conditions and with fresh gas flows to the circle system of between 8 and 0.25 litre min−. Compared with the non-rebreathing state, the use of a circle system reduced the initial rate of increase of alveolar towards fresh gas anaesthetic concentration, and the rate of increase in body anaesthetic content. The degree of reduction became more marked as fresh gas flow was reduced, and as agents of increasing blood solubility were used. These effects of a circle system were influenced by the volume of the circle system and the composition of gas initially present within the system. When the circle system was in use there were increases in the magnitude of both the concentration effect and the second gas effect which were related to the magnitude of fresh gas flow. The use of a circle system augmented the effects of changes in cardiac output and reduced the effects of changes in ventilation on the alveolar concentrations of the anaesthetic. These influences of a circle system were also dependent on the magnitude of fresh gas flow. The degree of augmentation of the effects of cardiac output decreased with increasing blood solubility of the agent in use, whilst the limitation of the effects of ventilation was greatest with the agent of highest blood solubility. Both under non-rebreathing conditions and with the circle system in use, the effects of cardiac output and ventilation were greater with 2% nitrous oxide than with 60% nitrous oxide, and were also greater when gases were given separately than when administered in combination.

Passive Valsalva manoeuvres were performed on young healthy patients about to undergo elective plastic surgery requiring induction of hypotension. This challenge was applied both in the supine and 30-degree head-up postures, during light anaesthesia, and after administration of beta-adrenergic blocking and ganglion blocking drugs, halothane and methoxyflurane. The resulting changes in blood pressure, pulse rate and systolic time intervals were recorded. During light anaesthesia more than half the responses were found to be unblocked, despite administration of beta-adrenergic blocking and ganglion blocking agents. Deepening the level of anaesthesia with either halothane or methoxyflurane usually resulted in a blocked response. The response to the manoeuvre could be influenced by posture. Marked alterations in the pre-ejection period occurred during every manoeuvre and were the same whether the manoeuvre was blocked or unblocked.

summary The interrelationship between Fio2, true gas exchange ratio (R) and the mathematical slope of the gas R line (RS) is not at all obvious. This paper shows the derivation of an equation relating these quantities and offers both a graphical presentation and an example of a table enabling R to be measured from knowledge of RS and Fio2.

SUMMARY Equations have been derived to determine the alveolar gas concentrations which occur when the Magill (Mapleson A) circuit is used with a low fresh gas flow. Alveolar oxygen and carbon dioxide concentrations are determined by the fresh gas flow and composition, carbon dioxide output and oxygen uptake. Gas mixing within the circuit and alterations in the inspired gas concentrations do not affect the final equilibrium. If oxygen uptake and carbon dioxide output are constant, the alveolar gas concentrations are unaffected by alterations in ventilation.

A black box and a geometrical approach have been used to deduce the relationships between alveolar oxygen and carbon dioxide concentrations when rebreathing occurs during the use of semi-closed anaesthetic rebreathing systems.

The squared reciprocal of the pre-ejection period (1/PEP2) is an inotropic index which may be measured without catheterization of the left ventricle. Changes in 1/PEP2 in response to changes in arterial carbon dioxide tension have been studied. The character of the Paco2/myocardial inotropy response

Summary Twenty-five patients were anaesthetized with chloroform. In 2 instances a partial rebreathing method using nitrous oxide and oxygen as the carrier gases was used. In 6 patients a non-rebreathing technique with oxygen alone as the carrier gas was substituted; the inspired concentration varied between 1.5 and 2.5 per cent. In the remainder a closed circle system was used giving inspired concentrations of up to 4 per cent. Cardiac irregularities were seen in 7 patients before recovery of consciousness. Hypotension below 90 mm Hg occurred in 3 patients. Of 26 cardiac output determinations in 8 patients 18 fell within the range 5 to 7 l./min. A four- to tenfold increase in finger blood flow was observed as well as a less marked increase in forearm blood flow. In 87 determinations of arterial carbon dioxide tension in 18 patients 38 per cent were less than 40 mm Hg and only 20 per cent were above 60 mm Hg. Metabolic acidosis was observed in only 3 of 18 patients investigated. In the closed circle system oxygen consumption in 9 patients ranged from 159 to 261 ml/min. Blood chloroform levels derived from 29 samples from 7 patients gave a mean value of 17.9 ±4.7 mg percent.

A special purpose analogue computer for beat by beat determination of the pre-ejection period of cardiac systole is described.

Duplicate determinations of arterial oxygen and carbon dioxide tensions were made in seventy adult patients of both sexes awaiting elective surgery. No difference in arterial oxygen tension was noted between the sexes but a marked inverse correlation between age and arterial oxygen tension was demonstrated. When this relationship was evaluated from the duplicate estimations the resultant regression equation was such that Pao2 = 102.5–0.22 (age). No statistically significant differences were noted between the Paco2 values of patients of different sexes and age groups.

An investigation was made of the pharmacological properties of a commercial heart extract (Recosen), said to be of value in the treatment of angina pectoris. This extract increased coronary flow but decreased force of beat in isolated perfused mammalian hearts. It potentiated the pressor effects of adrenaline in the spinal cat whilst not affecting those of noradrenaline, and it antagonised the actions of adrenaline and noradrenaline upon intestinal muscle. A mild anticholinesterase activity was demonstrated on striped muscle. The significance of these findings is discussed.

THE convenience of the interpolation techniques1,2 for the assessment of acid-base imbalance in patients has been widely recognized, and in clinical surgery the ability to differentiate rapidly between the metabolic and respiratory components of such a disturbance has special value. In particular, the standard bicarbonate value, defined as the bicarbonate content of oxygenated blood at 38° C. equilibrated at a P co2 of 40 mm. mercury provides a quantitative assessment of metabolic disorder. It was therefore disconcerting that when 63 arterial blood samples from a group of 22 patients anaesthetized with halothane were analysed, the standard bicarbonate values obtained (18.14 ± 1.94 m.equiv.) were significantly lower than those quoted by Astrup et al.3 (22.9 ± 1.5 m.equiv.). Because there was no other evidence of metabolic acidosis in these patients and because the bicarbonate value of plasma (23.28 ± 2.82 m.equiv.) in a similar group under the same conditions fell within the range of Astrup's figures it was decided to establish our own standards.