Electronic Nose for Improved Environmental Methane Monitoring.

Reducing emissions of the key greenhouse gas methane (CH4) is increasingly highlighted as being important to mitigate climate change. Effective emission reductions require cost-effective ways to measure CH4 to detect sources and verify that mitigation efforts work. We present here a novel approach to measure methane at atmospheric concentrations by means of a low-cost electronic nose strategy where the readings of a few sensors are combined, leading to errors down to 33 ppb and coefficients of determination, R2, up to 0.91 for in situ measurements. Data from methane, temperature, humidity, and atmospheric pressure sensors were used in customized machine learning models to account for environmental cross-effects and quantify methane in the ppm-ppb range both in indoor and outdoor conditions. The electronic nose strategy was confirmed to be versatile with improved accuracy when more reference data were supplied to the quantification model. Our results pave the way toward the use of networks of low-cost sensor systems for the monitoring of greenhouse gases.

Timing resolution in double-sided silicon photon-counting computed tomography detectors.

Purpose: Our purpose is to investigate the timing resolution in edge-on silicon strip detectors for photon-counting spectral computed tomography. Today, the timing for detection of individual x-rays is not measured, but in the future, timing information can be valuable to accurately reconstruct the interactions caused by each primary photon. Approach: We assume a pixel size of 12 × 500 µ m 2 and a detector with double-sided readout with low-noise CMOS electronics for pulse processing for every pixel on each side. Due to the electrode width in relation to the wafer thickness, the induced current signals are largely dominated by charge movement close to the collecting electrodes. By employing double-sided readout electrodes, at least two signals are generated for each interaction. By comparing the timing of the induced current pulses, the time of the interaction can be determined and used to identify interactions that originate from the same incident photon. Using a Monte Carlo simulation of photon interactions in combination with a charge transport model, we evaluate the performance of estimating the time of the interaction for different interaction positions. Results: Our simulations indicate that a time resolution of 1 ns can be achieved with a noise level of 0.5 keV. In a detector with no electronic noise, the corresponding time resolution is ∼ 0.1 ns . Conclusions: Time resolution in edge-on silicon strip CT detectors can potentially be used to increase the signal-to-noise-ratio and energy resolution by helping in identifying Compton scattered photons in the detector.

Interprofessional simulation-based team-training and self-efficacy in emergency medicine situations.

Teamwork quality has been shown to influence patient safety, and simulation-based team-training (SBTT) is an effective means to increase this quality. However, long-term effects are rarely studied. This study aims to investigate the long-term effects of interprofessional SBTT in emergency medicine in terms of global confidence, self-efficacy in interprofessional communication and in emergency medicine situations. Newly graduated doctors, nurses, auxiliary nurses, and medical and nursing students participated. Four emergency medicine scenarios focused on teamwork according to the A-B-C-D-E-strategy. All participants increased their global confidence from 5.3 (CI 4.9-5.8) before to 6.8 (CI 6.4-7.2; p < .0001) after SBTT. Confidence in interprofessional communication increased from 5.3 (CI 4.9-5.8) to 7.0 (CI 6.6-7.4; p < .0001). Students had the greatest gain. The self-efficacy following the A-B-C-D-E strategy increased from 4.9 (CI 4.4-5.3) to 6.6 (CI 6.2-7.0). Again, students had the steepest increase. Newly graduated doctors achieved a superior increase in global confidence as compared to nurses and auxiliary nurses (p < .0001). Their propensity to recommend SBTT to colleagues was 9.9 (CI 9.8-10.0). The positive effects were sustained over a six-month period, indicating that interprofessional SBTT had a positive impact on competence development, and a potential to contribute to increased team quality in emergency medicine care.

1-µm spatial resolution in silicon photon-counting CT detectors.

Purpose: Spatial resolution for current scintillator-based computed tomography (CT) detectors is limited by the pixel size of about 1 mm. Direct conversion photon-counting detector prototypes with silicon- or cadmium-based detector materials have lately demonstrated spatial resolution equivalent to about 0.3 mm. We propose a development of the deep silicon photon-counting detector which will enable a resolution of 1 µ m , a substantial improvement compared to the state of the art. Approach: With the deep silicon sensor, it is possible to integrate CMOS electronics and reduce the pixel size at the same time as significant on-sensor data processing capability is introduced. A Gaussian curve can then be fitted to the charge cloud created in each interaction.We evaluate the feasibility of measuring the charge cloud shape of Compton interactions for deep silicon to increase the spatial resolution. By combining a Monte Carlo photon simulation with a charge transport model, we study the charge cloud distributions and induced currents as functions of the interaction position. For a simulated deep silicon detector with a pixel size of 12 µ m , we present a method for estimating the interaction position. Results: Using estimations for electronic noise and a lowest threshold of 0.88 keV, we obtain a spatial resolution equivalent to 1.37 µ m in the direction parallel to the silicon wafer and 78.28 µ m in the direction orthogonal to the wafer. Conclusions: We have presented a simulation study of a deep silicon detector with a pixel size of 12 × 500 µ m 2 and a method to estimate the x-ray interaction position with ultra-high resolution. Higher spatial resolution can in general be important to detect smaller details in the image. The very high spatial resolution in one dimension could be a path to a practical implementation of phase contrast imaging in CT.

A digital nervous system aiming toward personalized IoT healthcare.

Body area networks (BANs), cloud computing, and machine learning are platforms that can potentially enable advanced healthcare outside the hospital. By applying distributed sensors and drug delivery devices on/in our body and connecting to such communication and decision-making technology, a system for remote diagnostics and therapy is achieved with additional autoregulation capabilities. Challenges with such autarchic on-body healthcare schemes relate to integrity and safety, and interfacing and transduction of electronic signals into biochemical signals, and vice versa. Here, we report a BAN, comprising flexible on-body organic bioelectronic sensors and actuators utilizing two parallel pathways for communication and decision-making. Data, recorded from strain sensors detecting body motion, are both securely transferred to the cloud for machine learning and improved decision-making, and sent through the body using a secure body-coupled communication protocol to auto-actuate delivery of neurotransmitters, all within seconds. We conclude that both highly stable and accurate sensing-from multiple sensors-are needed to enable robust decision making and limit the frequency of retraining. The holistic platform resembles the self-regulatory properties of the nervous system, i.e., the ability to sense, communicate, decide, and react accordingly, thus operating as a digital nervous system.

Silicon photon-counting detector for full-field CT using an ASIC with adjustable shaping time.

Purpose: Photon-counting silicon strip detectors are attracting interest for use in next-generation CT scanners. For CT detectors in a clinical environment, it is desirable to have a low power consumption. However, decreasing the power consumption leads to higher noise. This is particularly detrimental for silicon detectors, which require a low noise floor to obtain a good dose efficiency. The increase in noise can be mitigated using a longer shaping time in the readout electronics. This also results in longer pulses, which requires an increased deadtime, thereby degrading the count-rate performance. However, as the photon flux varies greatly during a typical CT scan, not all projection lines require a high count-rate capability. We propose adjusting the shaping time to counteract the increased noise that results from decreasing the power consumption. Approach: To show the potential of increasing the shaping time to decrease the noise level, synchrotron measurements were performed using a detector prototype with two shaping time settings. From the measurements, a simulation model was developed and used to predict the performance of a future channel design. Results: Based on the synchrotron measurements, we show that increasing the shaping time from 28.1 to 39.4 ns decreases the noise and increases the signal-to-noise ratio with 6.5% at low count rates. With the developed simulation model, we predict that a 50% decrease in power can be attained in a proposed future detector design by increasing the shaping time with a factor of 1.875. Conclusion: Our results show that the shaping time can be an important tool to adapt the pulse length and noise level to the photon flux and thereby optimize the dose efficiency of photon-counting silicon detectors.

ASIC modelling of SENSE for parallel MRI.

Magnetic Resonance Imaging (MRI) is widely used in medical diagnostics and image reconstruction is a vital part of MRI systems. In Parallel MRI (pMRI), imaging process is accelerated by acquiring less data (undersampled) using multiple receiver coils and offline reconstruction algorithms are applied to reconstruct the fully sampled image. In this research, an Application Specific Integrated Circuits (ASIC) model of SENSE (a pMRI algorithm) is presented which reconstructs the image from the undersampled data right on the data acquisition module of the scanner. The proposed ASIC HDL architecture is compared with SENSE reconstruction model implemented on FPGAs, Multi-core CPU and Graphics Processing Units. The proposed architecture is validated using simulated brain data with 8-channel receiver coils and a human cardiac dataset with 20-channel receiver coils. The quality of the reconstructed images is analyzed using Artifact Power (0.0098), Peak Signal-to-Noise Ratio (53.4) and Structured Similarity Index (0.871) which validate the quality of the reconstructed images using the proposed design. The results show that the proposed ASIC HDL SENSE reconstruction model is ∼8000 times faster as compared to the multi-core CPU reconstruction, ∼700 times faster than the GPU implementation and ∼16 times faster as compared to the FPGA reconstruction model. The proposed architecture is suitable for image reconstruction right on the data acquisition system of the scanner and will open new ways for faster image reconstruction on portable MRI scanners.

NFC Powered Implantable Temperature Sensor.

Inductively powered 99% accurate implantable temperature sensor is designed, characterized and the findings are presented in this paper. The implantable sensors deliver a continuous temperature reading to external storage or readout devices via Near Field Communication interface. A 2.76µH rectangular inductive coil printed on a thin biocompatible plastic substrate is designed to establish the coupling link through NFC interface with external readout devices. A commercially available wide range temperature sensor chip is mounted along with the developed inductive coil on the same plastic substrate. For 50 samples, the received signal strength indicator, temperature accuracy and statistical distribution of measurement levels is investigated. Comparison of predetermined temperature in a controlled temperature and humidity chamber versus the temperature reading from the developed sensors proves a 99% accuracy.

Free flap surgery in Europe: an interdisciplinary survey.

Free flap surgery is essential for the aesthetic and functional reconstruction of various parts of the body. The aim of this study was to compare current concepts of perioperative flap management between ENT, craniomaxillofacial, and plastic surgeons. A European survey was conducted among 570 surgical departments, covering all aspects of free flap surgery. Focus was placed on antibiotic and antithrombotic drug use, aspects of osseous reconstruction, and flap monitoring strategies. One hundred and seventy-two medical units participated. A broad spectrum of anticoagulant regimens and a trend towards prolonged antibiotic prophylaxis were found. Fixation with (CAD/CAM) reconstruction plates was more popular than monocortical locking with miniplates in the mandible. Visual assessment and Doppler systems were reported to be the most common monitoring modalities. The flap loss rate was stated to be higher after osseous reconstruction. Only a few differences in perioperative flap management were identified between the different surgical fields, and osseous reconstruction appears to be the most challenging.

Browsing the Real World using Organic Electronics, Si-Chips, and a Human Touch.

Organic electronics have been developed according to an orthodox doctrine advocating "all-printed'', "all-organic'' and "ultra-low-cost'' primarily targeting various e-paper applications. In order to harvest from the great opportunities afforded with organic electronics potentially operating as communication and sensor outposts within existing and future complex communication infrastructures, high-quality computing and communication protocols must be integrated with the organic electronics. Here, we debate and scrutinize the twinning of the signal-processing capability of traditional integrated silicon chips with organic electronics and sensors, and to use our body as a natural local network with our bare hand as the browser of the physical world. The resulting platform provides a body network, i.e., a personalized web, composed of e-label sensors, bioelectronics, and mobile devices that together make it possible to monitor and record both our ambience and health-status parameters, supported by the ubiquitous mobile network and the resources of the "cloud".

Local full-thickness skin graft of the donor arm--a novel technique for the reduction of donor site morbidity in radial forearm free flap.

A novel technique to reduce donor site morbidity after radial forearm free flap (RFFF) harvest, using a local full-thickness skin graft (FTSG), is described. Thirty consecutive patients undergoing RFFF for head and neck reconstruction were enrolled in a prospective study. Donor site defect closure was performed with spindle-shaped FTSGs excised from the wavelike skin incision made for the vascular pedicle. Both the removal site of the FTSG on the volar forearm and the covered RFFF donor site healed uneventfully in 29 cases, with no impairment of function related to the skin graft. No skin graft failure and no exposure, tenting, or adherence of the flexor tendons occurred. All patients expressed satisfaction with postoperative pain, the functional outcome, and cosmetic appearance. Primary donor site defect closure could be achieved in all cases with the use of a local FTSG. This graft can be gained at the access incision for the vascular pedicle, avoids expansion of the incision for a local flap technique, and does not prolong wound healing, and thus reduces both donor site and graft site morbidity of the RFFF. This technique leads to an inconspicuous aesthetic result with no apparent relevant functional deficits and avoids the need for a second donor site.

Caffeine raises the serum melatonin level in healthy subjects: an indication of melatonin metabolism by cytochrome P450(CYP)1A2.

Caffeine is metabolized in the liver by cytochrome P450(CYP)1A2. Recent findings imply that this enzyme may also be of importance for the metabolism of human melatonin (MT). If caffeine and MT are metabolized by the same enzyme, one may expect to find different serum MT levels after ingestion of coffee compared with placebo. Although coffee is consumed by people all over the world, few studies have focused on whether caffeine actually affects serum MT levels in normal subjects. We decided to study that particular topic. For that purpose 12 healthy individuals were tested on two occasions, one week apart. On one of these occasions they were given a capsule containing 200 mg caffeine in the evening. On the other, they received placebo. The experimental order was randomized. Serum MT levels were determined every second hour between 22:00 h and 08:00 h, and the melatonin areas under the curve (MT-AUCs) were calculated. After caffeine the serum MT level rose from 0.09 +/- 0.03 nmol/l at 22:00 h to 0.48 +/- 0.07 nmol/l at 04:00 h. The corresponding rise after placebo was less prominent (from 0.06 +/- 0.01 to 0.35 +/- 0.06 nmol/l). This was reflected by the MT-AUC which was 32% larger after ingestion of caffeine compared with placebo (MT-AUC(caffeine) 3.16 +/- 0.44 nmol/l x h vs MT-AUC(placebo) 2.39 +/- 0.40 nmol/l x h; p < 0.02). These findings imply that caffeine, ingested in the evening at a dose corresponding to two ordinary cups of coffee, augments the nocturnal serum MT level, which in turn supports the notion that cytochrome P450(CYP)1A2 is involved in the hepatic metabolism of human MT.

The role of somatostatin (octreotide) in the regulation of melatonin secretion in healthy volunteers and in patients with primary hypothyroidism.

Somatostatin has been found in the pineal gland of several animal species, which suggests that it may be involved in the regulation of melatonin secretion. Whether somatostatin has regulatory influence on melatonin secretion in man has never been unequivocally shown. We studied the nocturnal melatonin secretion in 8 healthy volunteers, and 6 women with untreated primary hypothyroidism, a disease state that is associated with increased nocturnal secretion of melatonin. The participants were given subcutaneous injections at 18:00 h and 23:00 h of either saline or octreotide (Sandostatin; each injection 50 microg). During the nights when the healthy volunteers were given octreotide, melatonin secretion was similar to that recorded during administration of saline. Also the urinary excretion of melatonin was of similar magnitude at these two occasions. By contrast, the GH secretion was significantly lower the nights the healthy controls were given octreotide (GH AUC 22.6+/-5.4 mU/l x h during octreotide and 126.6+/-21.9 mU/l x h during saline; p<0.01). The patients with hypothyroidism also showed similar nocturnal melatonin secretion during octreotide and saline. Urinary excretion of melatonin also remained unchanged, as did GH secretion. The total nocturnal secretion of TSH was, however, significantly reduced by octreotide (TSH AUC 562+/-136 mU/l x h during octreotide and 851+/-185 mU/l x h during saline; p<0.05), thus suggesting that 100 microg of octreotide should be sufficient to inhibit also the pinealocytes if their function were regulated by somatostatin. Since exogenous somatostatin--in the form of octreotide--fails to influence nocturnal secretion and urinary excretion of melatonin in normal subjects and in patients with primary hypothyroidism, it is reasonable to assume that endogenous somatostatin may not be an important regulator of melatonin secretion in man.

Fibromyalgia--a syndrome associated with decreased nocturnal melatonin secretion.

OBJECTIVE: Most patients with fibromyalgic syndrome (FMS) complain of sleep disturbances, fatigue, and pain. These symptoms might be a consequence of changed melatonin (MT) secretion, since MT is known to have sleep promoting properties. Moreover, serum concentrations of two MT precursors (tryptophan and serotonin)--affecting both sleep and pain perception--appear to be low in patients with FMS. Therefore, the objective of this investigation was to study whether serum MT (s-MT) level is also low in these patients. DESIGN: Eight patients with FMS and 8 healthy sex-, BMI-, and age-matched controls were included in the study. s-MT concentrations were determined every second hour between 1800 and 0800 h. Urine was collected between 2200 and 0700 h for determination of urinary MT excretion. To evaluate total MT secretion between 1800 and 0800 h and MT secretion during the hours of darkness (between 23 and 07 h) individual MT areas under the curve (AUC) were calculated and expressed as group means. RESULTS: The FMS patients had a 31% lower MT secretion than healthy subjects during the hours of darkness (MT AUC 2300-0700 h (mean +/- SEM): 1.70 +/- 0.17 vs 2.48 +/- 0.38 nmol/l; P < 0.05). Also the s-MT peak value was significantly lower in the patient group: 0.28 +/- 0.03 vs 0.44 +/- 0.06 nmol/l; P < 0.05). CONCLUSION: Patients with fibromyalgic syndrome have a lower melatonin secretion during the hours of darkness than healthy subjects. This may contribute to impaired sleep at night, fatigue during the day, and changed pain perception.

Rapid determination of bacterial abundance, biovolume, morphology, and growth by neural network-based image analysis

Annual bacterial plankton dynamics at several depths and locations in the Baltic Sea were studied by image analysis. Individual bacteria were classified by using an artificial neural network which also effectively identified nonbacterial objects. Cell counts and frequencies of dividing cells were determined, and the data obtained agreed well with visual observations and previously published values. Cell volumes were measured accurately by comparison with bead standards. The survey included 690 images from a total of 138 samples. Each image contained approximately 200 bacteria. The images were analyzed automatically at a rate of 100 images per h. Bacterial abundance exhibited coherent patterns with time and depth, and there were distinct subsurface peaks in the summer months. Four distinct morphological classes were resolved by the image analyzer, and the dynamics of each could be visualized. The bacterial growth rates estimated from frequencies of dividing cells were different from the bacterial growth rates estimated by the thymidine incorporation method. With minor modifications, the image analysis technique described here can be used to analyze other planktonic classes.

Does hypercalcaemia or calcium antagonism affect human melatonin secretion or renal excretion?

Patients with primary hyperparathyroidism have higher serum melatonin concentrations during active disease than after surgical cure. Whether this is caused by hypercalcaemia per se, increased parathyroid hormone secretion or other mechanisms is unknown. We decided to elucidate whether exogenous hypercalcaemia influences melatonin secretion. For this purpose, eight healthy volunteers were infused with calcium and saline on separate days and in random order (experiment A). Hypercalcaemia inhibited nocturnal melatonin secretion by 20% but left urinary melatonin excretion unaffected. If exogenous hypercalcaemia inhibits melatonin secretion, it is reasonable to assume that calcium channel blockers such as verapamil might have the opposite effect. This was investigated in experiment B, in which eight healthy subjects were treated on separate occasions with oral verapamil and placebo. Verapamil did not affect nocturnal melatonin secretion but increased melatonin excretion by 145%. As 6-sulphatoxy-melatonin is the main melatonin metabolite excreted by the kidneys, it was considered important to find out whether verapamil would also influence the excretion of 6-sulphatoxy-melatonin. This was investigated in experiment C, in which eight healthy volunteers were treated, on separate occasions, with oral verapamil and placebo. In this experiment also, verapamil increased urinary melatonin excretion significantly (by 67%), but left excretion of 6-sulphatoxy-melatonin unaffected. These findings imply that verapamil influences the renal and/or hepatic handling of melatonin.

Melatonin secretion and excretion in patients with obstructive sleep apnea syndrome.

Melatonin (MT) secretion and excretion were investigated in patients with obstructive sleep apnea syndrome (OSAS). Nine men, mean age 55.1 years, mean body mass index 31.2, with a previously confirmed diagnosis of moderate to severe OSAS, were tested on two occasions: immediately before initiation of continuous positive airway pressure (CPAP) treatment and again after at least 4 weeks of continuous nocturnal use of CPAP. Serum MT concentrations were determined every second hour between 2000 and 0800 hours. Urine was collected between 2200 and 0700 hours for determination of urinary MT excretion. Sleep apnea recordings included ear oximetry, respiration and body movements, body position, and breathing sounds. Nine healthy male controls were tested on one occasion. We found that the MT secretion, as reflected by the area under the curve (AUC), among the OSAS patients did not differ from that found in healthy controls (MT AUC 1.68 vs. 1.92 nmol/l x h). Sleep apnea recordings were normalized during CPAP treatment. Moreover, the excessive daytime sleepiness disappeared in all patients. Neither MT secretion (MT AUC 1.68 vs. 1.56 nmol/l x h) nor urinary excretion of MT (0.122 vs. 0.108 nmol/9 h) changed significantly as a result of the CPAP treatment.

Impaired melatonin secretion in patients with Wernicke-Korsakoff syndrome.

OBJECTIVES: Melatonin (MT) undergoes circadian changes in response to external light conditions and has been implicated in the control of other circadian hormone variations. Alcohol inhibits MT secretion in healthy subjects. The purpose of the present investigation was to elucidate whether patients with Wernicke-Korsakoff syndrome (WKS) also have impaired MT secretion after a period of prolonged alcohol abstention. If so, it would be of interest to find out whether this affects cortisol rhythmicity. DESIGN: Seven patients with WKS and 8 healthy controls were included in the study. Venous blood was sampled every 2nd h between 18.00 and 08.00 hours, and urine collected between 22.00 and 07.00 hours. SETTING: Department of Internal Medicine, Endocrinology Section, Södersjukhuset, Stockholm. MAIN OUTCOME MEASURES: Peak serum MT values during the night, total nocturnal MT secretion (estimated by MT incremental areas), and urinary excretion of MT were determined in each participant. Serum cortisol levels were determined in the patients at 18.00, 02.00 and 08.00 hours. RESULTS: Patients with WKS had a markedly reduced nocturnal secretion of MT compared to healthy volunteers (MT incremental areas 0.33 +/- 0.21 vs. 1.60 +/- 0.29 nmol L-1 h-1, mean +/- SEM; P < 0.005). Amongst the patients, the serum cortisol level was higher in the morning than in the afternoon (331 +/- 46 vs. 240 +/- 52 nmol L-1; P < 0.01), and showed a nadir during the night (138 +/- 45 nmol L-1) as in normal individuals. CONCLUSION: Patients with WKS have markedly reduced nocturnal secretion of MT. The exact mechanism behind this finding has to be further elucidated. However, it is of interest to note that despite the lack of clearcut circadian MT changes. WKS patients retain normal cortisol secretion, thus suggesting that MT rhythm may not be obligatory for the proper control of circadian cortisol rhythmicity.

Inhibition of melatonin secretion by ethanol in man.

To determine whether ethanol inhibits nocturnal melatonin (MT) secretion, three experiments (A, B, and C) were performed in seven normal subjects. In A, ethanol at a dose of 0.34 g/kg was administered orally at 6:00, 8:00, and 10:00 PM. Each dose was increased to 0.52 g/kg in B. In C, water was substituted for ethanol. Blood samples for determination of serum MT levels were drawn every second hour between 6:00 PM and 8:00 AM. Urinary excretion of MT during the night was also determined. In A, serum ethanol reached a maximal level of 13 +/- 1 mmol/L at 12 midnight. In B, the corresponding maximum was 25 +/- 1 mmol/L. The higher alcohol dose inhibited nocturnal MT secretion by 20% +/- 5% (P < .01), whereas the lower dose lacked such effect. Urinary excretion of MT was left unaffected by alcohol at both doses. Five additional normal subjects were given alcohol as described above at a dose of 0.52 g/kg (experiment D). This induced mild nocturnal hypoglycemia as evidenced by a glucose decremental area (5.9 +/- 1.8 mmol/L.h) that differed significantly from zero (P < .05). To determine whether a reduced glucose delivery to pinealocytes might contribute to the decreased MT secretion in alcohol-intoxicated subjects, two experiments (E and F) were performed in eight healthy individuals. In E, ethanol was given orally as in B; three small oral doses of glucose were also given at 8:00 PM, 10:00 PM, and 12 midnight. In F, water was substituted for ethanol and glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise performance and beta-adrenergic blockade in patients with complete heart block treated with ventricular inhibited pacing.

The effect of beta-adrenergic blockade (propranolol) on exercise performance was studied in 15 patients (12 men and 3 women, mean age 70 years) with complete heart block treated with a ventricular-inhibited pacemaker (VVI). In a double-blind procedure, the patients were randomly given either 0.1 mg/kg of propranolol or saline solution i.v. before a first exercise test and vice versa before a second test. The interval between the tests was 24 hours. Nine patients were in sinus rhythm, 4 patients had atrial flutter, and 2 others had atrial fibrillation. The exercise capacity was on an average 11% lower with propranolol than with placebo (p less than 0.001). The most marked reductions (20 and 33%) were found in the two patients with atrial fibrillation. The atrial rate in patients with sinus rhythm was significantly lower with propranolol than placebo both at rest (68 vs. 83 beats/min, p less than 0.001) and at maximal work load (91 vs. 141 beats/min, p less than 0.001). The present findings show that beta blockade has negative effects on exercise capacity in patients with complete heart block treated with VVI pacemakers. This finding should be considered in the selection of drug treatment in patients with fixed rate pacing and concomitant hypertension and/or ischemic heart disease.