Nested ring Mach-Zehnder interferometer.

We propose a new device configuration that incorporates a nested ring with a Mach-Zehnder interferometer. The nested ring is analogous to a dual-bus coupled ring resonator, with the ends of the two buses connected to form a semi-closed loop. With proper design of the length of the U-shaped loop, as well as the coupling coefficient between the ring and the waveguide, the device is capable of generating a box-shaped spectral response. This is shown to be mainly due to the double-Fano resonances that arise from constructive interference between the nested ring and the outer loop. The device is simple in that it requires only one ring, and unique in that it harnesses a pair of Fano resonances to generate a reasonably box-like filter response. The analysis is based on the transfer matrix formalism, and compared and verified with the FDTD simulations.

Shivering during regional anaesthesia and its control with pethidine.

Ninety-seven consecutive patients who underwent four different types of regional anaesthesia such as lumbar epidural, spinal, caudal and brachial blocks were studied for their incidence of shivering. Fifty percent of patients who received epidural anaesthesia shivered compared to 19% of patients who received either spinal or caudal anaesthesia. None of the patients who had brachial block shivered. Intravenous injection of 25 mg pethidine would stop shivering in almost all patients who shivered during regional blocks.

Intravenous sedation for upper gastrointestinal endoscopy: Midazolam versus propofol.

Propofol was compared with Midazolam for sedation during upper gastrointestinal endoscopy in a randomised, double blind study. Both drugs were equally acceptable to endoscopists and patients. There was significant oxygen desaturation after sedation and during endoscopy (p < 10(-6)). Significantly more patients in the propofol group could remember the diagnosis which was revealed to them immediately after the gastroscopy (p < 0.001).

The effects of diet and supplements on a male world champion lightweight rower.

A world-class lightweight rower who came to the Hong Kong Sports Institute was evaluated over a two-month period of training. He was preparing for the 1995 World Rowing Championships. The subjects trained for approximately 70 minutes per day at different levels of intensity, to simulate race conditions. Caloric expenditures (based upon heart rate response and estimation from specific activity) were estimated to be approximately 4125 kcal/day. A three day dietary survey revealed that the subject was able to maintain caloric balance (caloric intake = 4088 kcal/day). Body weight was maintained at a constant level, another indication that the subject was able to meet energy needs. A breakdown of his food intake revealed protein, carbohydrate, and fat, made up 19%, 51%, and 30% of his caloric intake, respectively. This was somewhat surprising since recommendations for endurance athletes are for higher carbohydrate contribution. During and after the training bouts the subject consumed two separate carbohydrate supplements. A total of 218 g of carbohydrate were consumed daily. This level of supplementation was able to maintain the subject's blood glucose concentration at normal levels following recovery from exercise. Comparisons of recovery heart rates when either water or carbohydrate was consumed indicate a beneficial effect of the supplement. Despite consuming carbohydrates at lower than recommended levels, this athlete went on to win this third gold medal in rowing.

Cardiorespiratory fitness and isokinetic muscle strength of elite Asian junior soccer players.

There is a scarcity of descriptive data on the physiological characteristics of elite Asian junior soccer players. The purpose of this study was to evaluate the cardiorespiratory fitness and isokinetic muscle strength of elite junior soccer players in Hong Kong. It was conducted in conjunction with the selection of the Hong Kong team to the 1989 Gothia Cup held in Sweden. Twenty-one top junior soccer players were selected as subjects for the study. The following means (+/- SD) were observed: age 17.3 +/- 1.1 years; height 172.5 +/- 6.2 cm; weight 62.8 +/- 7.0 kg; body fat 5.2 +/- 1.8%; forced vital capacity (FVC) 4.6 +/- 0.6 L; maximum oxygen uptake (VO2max) 58.6 +/- 2.9 ml.kg-1.min-1; anaerobic threshold (AT) 76.7 +/- 10.2% of VO2max; peak isokinetic dominant knee extensor and flexor strengths 3.28 +/- 0.37 Nm.kg-1 and 1.84 +/- 0.24 Nm.kg-1; hamstring to quadriceps peak torque ratio (H/Q) 56 +/- 0.6% measured at 60 degrees s-1. Hong Kong players appeared to have comparable aerobic power, light body weight, poor flexibility and above average isokinetic muscle strength compared to other international junior soccer players. Training programs to improve the contralateral knee muscle imbalance and to increase the fast speed movement capability of the non-dominant knee flexors are recommended.

Sedation for gastroscopy: a comparison between midazolam and midazolam with nalbuphine.

Forty patients received either midazolam or midazolam with nalbuphine in a double-blind randomised study of sedation for upper gastrointestinal endoscopy. There were less retching, gagging and salivation in the combination group compared to midazolam alone. They were also more cooperative. These resulted in greater ease of insertion of the gastroscope. There was no significant difference in the degree of amnesia in both groups. A significant decrease in oxygen saturation was noted in both groups during the procedure. Monitoring with a pulse oximeter is recommended when sedation is administered during gastroscopy.

Spread of spinal anaesthesia with 0.5% bupivacaine: influence of the vertebral interspace and speed of injection.

Three millilitres of plain 0.5% bupivacaine were injected intrathecally at two different spinal interspaces (L2/3 and L4/5) and at two different speeds (15 and 30 sec) in four groups of ten patients. Injection at L2/3 over 15 sec produced a significantly higher mean maximum spread of analgesia (T6.4) when compared to injection at L4-5 over 15 sec (T10.3) (P < 0.05). Over the same interspace L2/3, injection over 15 sec also produced a higher level of spread as compared to the 30 sec group (p < 0.05). At 15 min there was a greater fall in blood pressure in the L2/3 15 sec group when compared to the other groups (p < 0.01). There was a further decrease in the blood pressure in L2/3 15 sec and L4/5 30 sec groups after 30 minutes of blockade (p < 0.01). Therefore close monitoring of cardiovascular parameters must be continued for at least 30 min in spinal anaesthesia with bupivacaine.

Phenylephrine eye drops in ophthalmic surgery--a clinical study on cardiovascular effects.

Phenylephrine in concentrations of either 2.5% or 10% is widely used as a mydriatic agent in ophthalmic surgery. Its potential cardiovascular effects are seldom recorded as ophthalmic surgery is not usually monitored by an anaesthetist. A prospective randomised double blind study was carried out in 89 consecutive cases of uncomplicated cataract surgery in the presence of an anaesthesiologist ensuring the continuous monitoring of blood pressure, heart rate, electrocardiography and pulse oximetry. All these patients were given a drop of either normal saline, 2.5% or 10% phenylephrine in addition to mydriacyl prior to surgery. Blood pressure readings were found to be significantly higher in non-hypertensive patients receiving phenylephrine at the start of the operation and at five, 10, 15 and 20 minutes intra-operatively and the first three hours post-operatively. Blood pressure readings in hypertensive patients, on the other hand, were also found to increase after phenylephrine administration, though not statistically significant. 10.3% of the 10% phenylephrine group and 3% of the 2.5% phenylephrine group required intraoperative intravenous hypotensive agent to control the blood pressure. There were no arrhythmias or ischaemic changes observed intraoperatively. None of the patients complained of palpitation, headache or chest discomfort. There was no oxygen desaturation observed. We concluded that significant hypertensive effects can arise after phenylephrine eye drop administration. Hence, it should be used cautiously with intraoperative monitoring of the cardiovascular status during cataract surgery.

Simple electrical biasing for minimizing the nonlinearities of quantum-well Mach-Zehnder modulators.

The quadratic nature of the electro-optic effect in semiconductor Mach-Zehnder modulators based on the quantum-confined Stark effect allows simple electrical biasing to eliminate either the second-order or the third-order distortions in the optical output, improving the device linearity for single-octave bandwidth multicarrier analog modulation applications.

InGaAs/InAlAs quantum-well electroabsorption waveguide modulators with large-core waveguide structure: design and characterization.

The design and the systematic characterization of the waveguide and the material properties of a modulator based on InGaAs/InAlAs quantum-well material for 1.5-µm operation are described. Following our previously developed theoretical design algorithm for optimizing the total performance of waveguide electroabsorption modulators [IEEE J. Quantum Electron, 29, 2476 (1993)], we designed an unconventional waveguide structure with a large passive core to yield better coupling efficiency for standard optical fibers and a thin active layer that yields a small optical-confinement factor. To evaluate the performance of this waveguide modulator, experimental methods for measuring the coupling efficiency, the optical-filling factor, and the absorption coefficient of the waveguide modulator and for characterizing the material properties were developed. The limitations of the material and the waveguide design, and the generalization of the limited set of experimental results based on a specific modulator to the design of more-general waveguide modulators are discussed.

Echocardiographic left ventricular hypertrophy in Chinese endurance athletes.

Most echocardiographic data on the athletic heart syndrome originate from the United States and Western Europe. There are no published data on echocardiographically documented left ventricular hypertrophy in Asian athletes. We investigated the echocardiographic changes which take place with endurance training by studying eight Hong Kong national cyclists. This study confirms that left ventricular hypertrophy and increased left ventricular end-diastolic dimensions are common findings in Chinese endurance athletes as in their Caucasian counterparts. Calculated left ventricular muscle mass exceeded the 95th percentile in seven of eight subjects.

Delivery of constant air-oxygen mixtures using a closed circle absorber system.

The aim of this study was to devise and validate a technique to deliver constant air-oxygen mixtures from a standard anaesthetic machine using only oxygen as the compressed gas source. The common gas outlet was modified to allow measured quantities of ambient air to be insufflated via a three-way attachment into a closed circle absorber system with a double-circuit collapsible bellows ventilator. During positive pressure ventilation, leakages of between 50-150 ml.min-1 occur from the circuit and nomograms of the minimal air and oxygen flow rates needed to maintain constant oxygen concentrations in the presence of the leaks were then mathematically derived. The accuracy of the nomograms was tested on three different anaesthetic machines using test lung models. There were no differences observed among the mean oxygen concentrations using the three machines. Pooled mean values (SD) of 30.65% (0.77), 51.07% (1.04) and 70.4% (0.73) were obtained for predicted inspired concentrations of 30, 50 and 70% respectively. Next, the technique was studied on 18 patients who underwent isoflurane or propofol anaesthesia (duration 40-210 min) for various surgical procedures. Pooled mean values (SD) obtained were 29.3% (1.86), 40.95% (1.65) and 50.06% (1.41) respectively for predicted oxygen concentrations of 30, 40 and 50% respectively. We conclude that this technique can be used to deliver constant air-oxygen mixtures accurately during inhalational or total intravenous anaesthesia when N2O is contraindicated but a source of compressed air is not readily available.

Physiological profiles of Hong Kong élite soccer players.

Most physiological profiles of élite soccer players originate from Western Europe and North America. Unfortunately, there is a scarcity of descriptive data on the physical characteristics of Asian soccer players. Therefore, the purpose of this study was to evaluate the physiological profiles of élite soccer players in Hong Kong. It was conducted in conjunction with the selection of the Hong Kong team before the 1990 Beijing Asian Games. In all, 24 professional soccer players were selected from a pool of 180 players as subjects for the study. The following means(s.d.) were observed: height 173.4(4.6) cm; weight 67.7(5.0) kg; body fat 7.3(3.0)%; forced vital capacity (FVC) 5.1(0.6) l; maximum oxygen uptake (VO2max) 59.1(4.9) ml kg-1 min-1; anaerobic threshold (AT 80.0(7.2)% of VO2max; alactic power index 13.5(2.4) W kg-1; lactic work index 298(27) J kg-1; peak isokinetic dominant knee extensor and flexor strengths 2.72(0.36) Nm kg-1 and 1.65(0.20) Nm kg-1. On average the physique of Hong Kong soccer players appeared to be smaller and lighter than those found in Europe, which may be one of the key factors that contribute to the lack of success of Hong Kong soccer teams in international competition.

Bilateral isokinetic variables of the shoulder: a prediction model for young men.

Clinicians frequently want to know the pre-injury strength of an uninjured limb. The purpose of this study was to delineate the differences in bilateral isokinetic peak torque (PT) at 60 degrees and 240 degrees, and torque acceleration energy (TAE), average power (AP) and total work (TW) at 240 degrees during shoulder extension and flexion movements, and to develop a method to determine the expected maximal isokinetic variables of the dominant shoulder based upon isokinetic measurements from the non-dominant shoulder. Shoulder isokinetic measurements were obtained from 30 normal young male adults. While bilateral correlation was significant (P < 0.01), results also suggest significant bilateral differences P < 0.01). Thus, it is inappropriate to use the uninjured extremity to predict the pre-injured strength of the injured side without adjustment. In this investigation models were developed relating the expected maximal isokinetic measurement of the dominant shoulder to the non-dominant shoulder measurements.

Physiological profiles and sport specific fitness of Asian elite squash players.

There is a scarcity of descriptive data on the physiological characteristics of elite Asian squash players. The purpose of this study was to evaluate the physiological profile and sports specific fitness of Hong Kong elite squash players. It was conducted before the selection of the Hong Kong national squash team for the 1992 Asian Squash Championship. Ten elite squash players were selected as subjects for the study. Maximum oxygen uptake was measured using a continuous treadmill running test. A sports specific field test was performed in a squash court. The following means (s.d.) were observed: height 172.6(4.3) cm; weight 67.7(6.9) kg; body fat 7.4(3.4)%; forced vital capacity (FVC) 5.13(0.26) litres; maximum oxygen uptake (VO2max) 61.7(3.4) ml.kg-1.min-1; anaerobic threshold (AT) 80.2(3.3)% of VO2max; alactic power index 15.5(1.8) W.kg-1; lactic work index 323.5(29.4) J.kg-1, peak isokinetic dominant knee extensor and flexor strengths 3.11(0.29) Nm.kg-1 and 1.87(0.18) Nm.kg-1. The results show that the Hong Kong squash players have relatively high cardiorespiratory sports specific fitness and muscle strength which may be one of the key factors that contributed to the success of the Hong Kong team in the Asian Championship.

Low-loss measurement in partially buried opticalwaveguideson glass with a plastic prism.

Surface and buried planar waveguides have been fabricated in glass microscope slides with purely thermal potassium and sodium ion-exchange techniques. We measured propagation loss as low as 0.08 dB/cm in the partially buried waveguides using an improved two-prism coupling method. The method includes a plastic prism and involves applying heat to soften the base of the outcoupling plastic prism so that the prism is temporarily in extremely close contact with the waveguide surface.

Isokinetic profile of dorsiflexors and plantar flexors of the ankle--a comparative study of élite versus untrained subjects.

A comparative study was made of the isokinetic characteristics of the ankle (plantar-flexion and dorsiflexion) in young men. Six cyclists, seven gymnasts, 10 soccer players and 25 non-athletic young men were tested on the Cybex II+ dynamometer. Peak torque, torque acceleration energy (TAE), total work and average power were measured. Cyclists had slightly higher (5%) mean plantar flexion than the others, but this was not significant. The situation was reversed for dorsiflexion. Moreover, the average dorsiflexion per unit of plantar flexion was significantly higher in the gymnasts than it was in the cyclists for both torque and work. This suggests that at a specific level of plantar flexion, the gymnasts had stronger dorsiflexion compared with the cyclists and that in sports involving jumping and running, increased attention should be given to strengthening the antagonist muscle groups (dorsiflexors) in order to achieve greater agonist-to-antagonist muscle balance thus preventing injury. The non-athletic subjects had substantially lower endurance capability in both flexors as measured by the endurance ratio. This implies that identifiable specialization in particular muscles results from training or participating in specialized sports.

Sport specific fitness testing of elite badminton players.

There is a scarcity of descriptive data on the performance capacity of elite badminton players, whose fitness requirements are quite specific. The purpose of this paper is to investigate the physiological response of elite badminton players in a sport-specific fitness test. Twelve Hong Kong national badminton team players performed a field test on a badminton court. Six light bulbs were connected to a programming device causing individual bulbs to light up in a given sequence. The players were instructed to react to the flashes by running towards them, and striking shuttles mounted in the vicinity of the bulbs. Exercise intensity was controlled by altering the interval between successive lightings. A low correlation (r = 0.65) was found between the results of the field test and the rank-order list of subjects, based on an objective on-field physiological assessment and subjective ranking. This may be explained by the requirements of other factors besides physical fitness which contribute to success in elite level badminton competition. These factors may include, for example, technical skill, mental power, and aesthetic judgements on the court. Maximum mean (s.d.) heart rate data (187(8) beats.min-1) and blood lactate values (10.4(2.9) mmol.l-1) in this study showed that players were under maximal load during the field test. From the testing data, it seems reasonable to speculate that the intensity of level 3 (20 light pulses.min-1; 3.0 s.pulse-1) and level 4 (22 light pulses.min-1; 2.7 s.pulse-1) simulates the requirement of actual games energy expenditure of the Hong Kong badminton players exercising at close to their anaerobic threshold. The results also show that an estimate of fitness can be derived from measurements involving exercise closely resembling that which is specific for the sports activity in question. Improved training advice and guidance may result from such studies.