Correction to: Electrocardiogram-based predictors for arrhythmia after spinal cord injury.

There is a typographical error in the formula presented for QTVI. While the formula was correctly applied to the data presented, the description of the formula has an incorrectly placed parenthesis. It should read.

Assessment of the reliability of intubation and ease of use of the Cook Staged Extubation Set-an observational study.

The Staged Extubation Set has recently been introduced by Cook Medical for the management of difficult airway patients who potentially require reintubation; however, its reliability for intubation and ease of use is not reported in the literature. The set contains a wire and reintubation catheter with a central lumen for the wire and oxygenation if required. Reintubation is by a two-stage Seldinger-like technique. After induction of general anaesthesia, 23 low-risk elective surgical patients had the Staged Extubation Wire from the Cook set inserted into their trachea under direct laryngoscopy. The intubation was subsequently completed using the rest of the Staged Extubation Set as designed. Difficult intubation was simulated by intentionally decreasing the laryngeal view. Simulated reintubation failed in 8.3% and significant technical difficulty in simulated reintubation was noted in another 17.3% of intubation sequences. The latter represent probable failures in a clinical difficult reintubation setting. The mean time taken to intubate was 109 seconds. Using the Cook Staged Extubation Set may be inferior to using an airway exchange catheter for reintubation.

Electrocardiogram-based predictors for arrhythmia after spinal cord injury.

PURPOSE: Individuals with spinal cord injury (SCI) have an increased risk of cardiac arrhythmias, particularly during autonomic dysreflexia (acute hypertensive episodes). This may be partly due to impaired autonomic control of the heart after SCI. The interval between the peak and end of the T-wave of the electrocardiograph (ECG) provides an index of transmural dispersion of repolarisation, a factor underlying the development of ventricular arrhythmias. Another ECG-based risk factor for ventricular arrhythmias is variability in the QT segment, the QT variability index (QTVI). Similarly, P-wave variability may be correlated with risk for atrial arrhythmias. We aimed to: (1) determine whether there are abnormalities in these parameters at rest in those with SCI; (2) determine correlations between these ECG parameters and severity of autonomic impairment after SCI. METHODS: ECG intervals were determined using customised software from a 15 min ECG recording (lead II) in 28 SCI subjects and 27 controls. Autonomic severity of SCI was determined from sympathetic skin responses, low frequency systolic blood pressure variability, and plasma noradrenaline levels. RESULTS: T(peak)-T(end) variability and QTVI were increased in those with autonomically complete SCI compared to controls. P-wave variability was increased in SCI individuals compared to controls, and was negatively correlated with plasma noradrenaline. CONCLUSION: The higher T(peak)-T(end) variability, QTVI and P-wave variability in individuals with SCI could be markers of severity of injury to cardiac autonomic (sympathetic) pathways after SCI, and may represent new risk assessment parameters for predisposition to cardiac arrhythmias in this population.

Delayed vasoconstrictor response to venous pooling in the calf is associated with high orthostatic tolerance to LBNP.

Central blood volume loss to venous pooling in the lower extremities and vasoconstrictor response are commonly viewed as key factors to distinguish between individuals with high and low tolerance to orthostatic stress. In this study, we analyzed calf vasoconstriction as a function of venous pooling during simulated orthostatic stress. We hypothesized that high orthostatic tolerance (OT) would be associated with greater vasoconstrictor responses to venous pooling compared with low OT. Nineteen participants underwent continuous stepped lower body negative pressure at -10, -20, -30, -40, -50, and -60 mmHg each for 5 min or until exhibiting signs of presyncope. Ten participants completed the lower body negative pressure procedure without presyncope and were categorized with high OT; the remaining nine were categorized as having low OT. Near-infrared spectroscopy measurements of vasoconstriction (Hachiya T, Blaber A, Saito M. Acta Physiologica 193: 117-127, 2008) in calf muscles, along with heart rate (HR) responses for each participant, were evaluated in relation to calf blood volume, estimated by plethysmography. The slopes of this relationship between vasoconstriction and blood volume were not different between the high- and low-tolerance groups. However, the onset of vasoconstriction in the high-tolerance group was delayed. Greater HR increments in the low-tolerance group were also observed as a function of lower limb blood pooling. The delayed vasoconstriction and slower HR increments in the high-tolerance group to similar venous pooling in the low group may suggest a greater vascular reserve and possible delayed reduction in venous return.

Survey of patients' experiences after nail surgery.

Nail surgery is performed to aid diagnosis and treatment of nail disease. A survey was conducted to determine whether patients understood the nature and consequences of nail surgery at the time of consent and to ascertain the most important aspects of morbidity after the procedure. The results identified that most patients understood the nature of their surgery and the immediate postoperative limitations they would face. Pain was short-lived, with no patients requiring analgesics after 6 weeks. The most important finding from this survey was that sensory disturbance was recorded by a large proportion (47%; 29/62) of patients. Of these, 35% (22/62) recorded either complete or partial resolution by 6-12 months after surgery, but 11% (7/62) noted no improvement. This is a point that is not made clear in standard surgical texts. The significance of dysaesthesia of a fingertip must be considered when counselling a patient before surgery.

Purpura and bleeding due to calcium-channel blockers: an underestimated problem? Case reports and a pilot study.

BACKGROUND: Surgical bleeding and occasionally purpura due to calcium-channel blockers have been described. AIM: To present cases in whom purpura or internal bleeding due to calcium-channel blockers was a presenting feature, including one subject with drug-induced haematuria and haematospermia due to amlodipine and one with the Rumpel-Leede sign. Further support for a true association was sought in a pilot study using Hess testing to provoke purpuric skin lesions. METHODS: Four representative cases presenting due to purpura or bleeding are described, all of whom had an abnormal Hess test. A further 19 patients taking calcium-channel blockers and 13 control subjects were also tested. RESULTS: Of 19 patients on calcium-channel blockers, 16 had either abnormal Hess results (n = 13) or marked acral purpura (n = 3) after a Hess test procedure. A similar abnormal response, of milder degree, occurred in only 2 of 13 control subjects. CONCLUSIONS: The high frequency of purpura shown in this study, whether spontaneous or provoked, suggests that this is a pharmacological class effect rather than idiosyncratic. Purpura in patients taking these drugs may be a clue to diagnosis of internal or postsurgical bleeding. We conclude that purpura related to calcium-channel antagonists is probably underestimated, but further studies are needed to identify the mechanism by which this occurs.

Control of the wrist joint in humans.

As one considers changes in motor activity from lower mammals to higher primates, one of the major changes one observes lies in the cortical control of forelimb muscles. There has been a shift from disynaptic control of spinal motoneurons in, for example, the cat, to a greater and greater percentage of monosynaptic control of hand and forelimb motoneurons in the primate. In spite of the species and evolutionary changes in the synaptic connections of the corticospinal tract, it appears that the interneurons identified in the cat are retained in the monkey and human. These interneurons, under the influence of descending pathways, modulate the output of motoneuron pools. Perhaps the control of these interneurons has also changed towards finer control of movement, as has been suggested by recent studies in the monkey. Whether in cat or human, the recruitment pattern for motor units is the same; the change from disynaptic to monosynaptic connections has not changed the recruitment pattern of muscles. Differences in the recruitment patterns of muscles may lie in the finer control of inputs to motoneurons in the primate. This review seeks to integrate the current knowledge of the mechanisms involved in the motor control of the wrist joint and especially in the recruitment patterns of the muscles. These motor control mechanisms include the biomechanics of the wrist joint, recruitment patterns of wrist muscles, interneurons and spinal cord circuits in the cervical regions mediating the output of spinal motoneurons, and the supraspinal control of these muscles.

Whole body fatigue and critical power: a physiological interpretation.

Critical power (CP) is a fundamental concept describing fatigue and exhaustion. The main physiological determinant of CP is the ability to utilise oxygen. This in turn is dependent primarily on diffusion distance. During exercise, many different tissue systems must increase their metabolic demand. It is argued that each tissue system, such as cardiac, respiratory and leg muscles, has their own CP. Cardiac muscle has the greatest CP relative to its maximum power because it has the shortest diffusion distances. Respiratory muscle also has a substantially higher relative CP than leg muscle. The higher relative CPs of cardiac and respiratory muscle are due in part to the homeostatic functions these tissues provide. This built in protective design can be disrupted in certain conditions such as hypoxia. During high intensity exercise, fatigue and ensuing exhaustion will occur if any contributing physiological system functions above its CP.

Effect of endurance training on blood lactate clearance after maximal exercise.

The aim of this study was to measure serial changes in the rate of blood lactate clearance (gamma2) in response to sequential periods of training and detraining in four male triathletes aged 22-44 years. There were two major phases of training and taper, each lasting 4-5 weeks (training 1 = 5 weeks, taper 1 = 2 weeks, training 2 = 4 weeks and taper 2 = 2 weeks), in preparation for a triathlon competition. The training stimulus absorbed by each subject was carefully quantified from the duration and intensity of the training exercise. A serial weekly measure of each trainee's physical response to training was evaluated as the peak power, termed a 'criterion performance', developed by a subject during a 30 W x min(-1) ramp cycle ergometer test to exhaustion each week. During 30 min of recovery after this test, 13 samples of venous blood were drawn sequentially from a subject to measure the blood lactate recovery curve. The rate constant of blood lactate clearance was estimated by a non-linear least-squares regression technique. In addition, the concurrent time to peak lactate concentration and the peak lactate concentration were also estimated to help define changing lactate kinetics. The criterion performance generally declined throughout each period of incremental training and improved during each taper period, rising iteratively in this way to be clearly above baseline by the end of the second taper. The blood lactate clearance rate increased transiently in early training before declining from the middle of the first training period to the middle of the first taper; thereafter, gamma2 increased above baseline in each trainee throughout the remaining first taper and the major portion of the second training period, decreasing only in the final criterion performance test. The time to peak lactate declined from baseline throughout all phases of training and taper. Peak blood lactate increased in all subjects to the end of the first taper before declining by the end of the second training period, rising again to baseline levels during the second taper. The change in gamma2 was examined relative to the work rate achieved in cycle ergometry above an initial baseline score (deltaCP) and against concurrent peak blood lactate. There was a clear upward shift in gamma2 above baseline throughout the first and second training and taper in two subjects; this was less clear in the remaining two subjects, each of whom had a lower deltaCP. We conclude that this indicates improved lactate clearance, manifest by the change in gamma2 induced by endurance training.

Aggression in the lactating female rat: the normal decline is not dependent on the physical development of the pups.

Female rats that had been assessed for aggression on two occasions during pregnancy were also assessed for aggressiveness toward an unfamiliar adult female on days 5, 12, and 19 of lactation. Each female had its litter of pups exchanged for another litter on days 10 and 17 following parturition. Half of the females received pups that were 2 days old. The other half received pups of the same age as those taken away. Aggression by females of the two groups declined at a similar rate during the period of lactation. Retrieval of a group of seven 6-day-old pups following the last aggression test was present in females whose litter had been replaced with 2-day-old pups but not in females whose litter had been replaced with same-age pups. Lactation was maintained in all females during the three weeks following parturition but declined to a level that was not sufficient to maintain growth following the normal 21 day lactation period. A single set of biological or stimulus variables does not maintain all aspects of maternal behavior. Physical and behavioral maturation of the pups does not appear responsible for the decline in maternal aggression during the final two weeks of lactation.

Motor unit activity during isometric and concentric-eccentric contractions of the human first dorsal interosseus muscle.

1. Motor unit activity was recorded with intramuscular fine wire electrodes during isometric, concentric, and eccentric activity in the human first dorsal interosseus muscle. Twenty-one units from 11 subjects were sampled. 2. During isotonic cycles of shortening and lengthening, 18 of 21 units were recruited during the concentric phase, increased their discharge rates as the concentric movement progressed, then decreased their discharge rate during the eccentric phase, and were derecruited. 3. A different pattern of recruitment was observed in recordings from three units. These units were recruited during the eccentric phase, at a time when other units were decreasing their discharge rate or being derecruited. In two of the units selectively recruited during the eccentric phase, it was possible to determine their isometric thresholds, which were higher than those of units exhibiting the more common pattern of recruitment. 4. For two of the three units exhibiting selective recruitment during eccentric contraction, the unit was recorded simultaneously with different pairs of recording wires separated by 5-10 mm. Each discharge of these units was detected by both electrodes, making it unlikely that movement artifact was responsible for the initiation or cessation of discharge. 5. The recruitment patterns observed suggest that changes in the type or distribution of synaptic inputs to motoneurons during movement can, in some instances, override pre- and postsynaptic factors that shape recruitment order in isometric conditions.

Aggression is attenuated by ovariectomy in pregnant female rats given progesterone and estradiol replacement to maintain pregnancy.

Female rats were tested for aggression toward an unfamiliar female conspecific 13 days following the beginning of cohabitation with a male. Forty-eight hours later, half of the females that displayed aggression were ovariectomized. To maintain pregnancy, they were also given Silastic implants of estradiol (1-mm tube) and progesterone (6 tubes, 30-mm long; Dow-Corning tubing #602-305) sufficient to maintain pregnancy but at lower levels than those normally present. Control females were given a sham ovariectomy and implanted with empty tubes. Each animal received a second aggression test at 48 h following surgery and a third test, 3 days following the second. Hormone implants successfully maintained pregnancy and supported the normal development of the pups. However, Ovariectomized females with hormone implants did not spontaneously give birth. Ovariectomized females displayed less aggression than their sham-ovariectomized counterparts at the second and third aggression tests. The difference was due to an increasing level of aggression by the control but not the experimental animals. These results are consistent with other evidence that circulating gonadal hormones influence the onset of maternal aggression in the female rat.

Task-dependent factors in fatigue of human voluntary contractions.

This chapter explores the hypothesis that fatigue is not caused uniquely by any common set of factors, but rather that the amount of stress placed on each site depends on the type of exercise from which fatigue develops. Evidence supporting this idea is presented by comparing results from various studies in which fatigue was caused by different exercise protocols. However, the way in which human endurance capacity changes with the type or intensity of the task performed suggest a unitary process. Thus, perhaps the neuromuscular system as a whole is so well adjusted that any task-related additional impairment at one site is compensated by corresponding functional improvements at others. We suggest that nature has had a long time in which to "get it right".

The influence of inspired oxygen on the oxygen uptake response to ramp exercise.

The relation between VO2 and work rate (WR) was examined in seven male subjects who performed ramp (1 W.3s-1) two-legged cycle ergometry to exhaustion while inspiring either hypoxic (12% O2), normoxic (21% O2), or hyperoxic (40% O2) air. The anaerobic threshold was estimated from respiratory gas exchange threshold (RGET). Prior to the RGET, the delta VO2/delta WR was greater under normoxic [mean (SD); 10.19(1.04) ml O2.min-1.W-1] and hyperoxic [10.44 (0.72)] conditions compared with hypoxia [9.34 (0.89)]. Above the RGET, the delta VO2/delta WR for hypoxia [8.91 (0.63)], normoxia [10.40 (0.77)], and hyperoxia [11.08 (0.48)] were all significantly different from each other. These data indicated that for two-legged, cycle, ramp ergometry in normoxia below the RGET, both the delta VO2/delta WR and response time was constant. Above the RGET, the normoxic VO2 response was the net result of a declining delta VO2/delta WR and a longer response time to the unsteady state character of a ramp exercise protocol.

Statistical evidence consistent with two lactate turnpoints during ramp exercise.

A number of studies have identified the existence of two ventilation thresholds during ramp or incremental exercise to exhaustion on the cycle ergometer. This study was undertaken to investigate whether two threshold turnpoints could be identified in blood lactate concentration data collected at such times. Five trained athletes provided serial blood samples on several occasions each during a 3-month period of training. Blood lactate concentration was analysed by fitting models with no, one or two turnpoints. Ordinary residuals from the first two models were often found to exhibit an oscillatory behaviour consistent with the existence of two turnpoints in lactate concentration. A comparative analysis of goodness of fit of these models revealed that the model with two turnpoints was significantly better than either of the simpler models. This suggests that two transitions exist, which divide the time domain for blood lactate concentration in ramp exercise into three regions. These two transitions may correspond to the two ventilation thresholds.

Influence of combined estradiol and testosterone implants on the aggressiveness of nonaggressive female rats.

Female rats that had been cohabiting with a sterile male or with another female for 6 weeks were tested for aggression toward an unfamiliar female once each week for 3 weeks. Females that were not aggressive as a result of cohabitation with a sterile male were ovariectomized. Half were implanted with a Silastic tube containing estradiol (1 mm long hormone-filled space) and a tube containing testosterone (5 mm long hormone-filled space). The other half were implanted with empty tubes. All females that had been cohabiting with another female were ovariectomized and implanted with an estradiol- and a testosterone-filled tube. Three additional weekly tests of aggression were given beginning 1 week postoperatively. Females given hormone replacement displayed only a slight increase in aggression postoperatively. Females not given hormone replacement declined in aggressiveness. These results indicate that hormone replacement levels sufficient to maintain aggression in highly aggressive females following ovariectomy are not sufficient to produce a high level of aggression in females that have not become aggressive following cohabitation with a sterile male or that have been cohabiting with another female.

Aggression by a female rat cohabiting with a sterile male declines within 27 h following ovariectomy.

Females that had become aggressive as a result of cohabiting with a sterile male were ovariectomized and implanted with empty Silastic tubes. Control groups were either sham ovariectomized or ovariectomized and implanted with Silastic tubes providing replacement levels of estradiol and testosterone. Twenty-seven hours following surgery, all animals were tested for aggressiveness toward an unfamiliar female rat. The aggression of ovariectomized females without hormone replacement declined to a minimal level postoperatively and was significantly lower than that of sham-ovariectomized females or ovariectomized females with estradiol and testosterone replacement. Both sham-ovariectomized females and ovariectomized females given hormone replacement displayed a level of aggression close to that observed preoperatively. The aggression of a female rat cohabiting with a sterile male appears to be highly sensitive to the removal of gonadal hormones. This corresponds with observations made on pregnant females and contrasts with those made on lactating females.