Mean Rate Of Rise Research Articles

Sea-Level Fingerprints Due to Present-Day Water Mass Redistribution in Observed Sea-Level Data

Satellite altimetry over the oceans shows that the rate of sea-level rise is far from uniform, with reported regional rates up to two to three times the global mean rate of rise of ~3.3 mm/year during the altimeter era. The mechanisms causing the regional variations in sea-level trends are dominated by ocean temperature and salinity changes, and other processes such as ocean mass redistribution as well as solid Earth’s deformations and gravitational changes in response to past and ongoing mass redistributions caused by land ice melt and terrestrial water storage changes (respectively known as Glacial Isostatic Adjustment (GIA) and sea-level fingerprints). Here, we attempt to detect the spatial trend patterns of the fingerprints associated with present-day land ice melt and terrestrial water mass changes, using satellite altimetry-based sea-level grids corrected for the steric component. Although the signal-to-noise ratio is still very low, a statistically significant correlation between altimetry-based sea-level and modelled fingerprints is detected in some ocean regions. We also examine spatial trend patterns in observed GRACE ocean mass corrected for atmospheric and oceanic loading and find that some oceanic regions are dominated by the fingerprints of present-day water mass redistribution.

Hydropeaking by Small Hydropower Facilities Affects Flow Regimes on Tributaries to the Pantanal Wetland of Brazil

Hydroelectric facilities often release water at variable rates over the day to match electricity demand, resulting in short-term variability in downstream discharge and water levels. This sub-daily variability, known as hydropeaking, has mostly been studied at large facilities. The ongoing global proliferation of small hydropower (SHP) facilities, which in Brazil are defined as having installed capacities between 5 and 30 MW, raises the question of how these facilities may alter downstream flow regimes by hydropeaking. This study examines the individual and cumulative effects of hydropower facilities on tributaries in the upland watershed of the Pantanal, a vast floodplain wetland system located on the upper Paraguay River, mostly in Brazil. Simultaneous hourly discharge measurements from publicly available reference and downstream gage stations were analyzed for 11 reaches containing 24 hydropower facilities. Most of the facilities are SHPs and half are run-of-river designs, often with diversion channels (headraces). Comparison of daily data over an annual period, summarized by indicators of hydrological alteration (HA) that describe the magnitude, frequency, rate of change, and duration of flows, revealed differences at sub-daily scales attributable to hydropeaking by the hydropower facilities. Results showed statistically significant sub-daily HA in all 11 reaches containing hydropower facilities in all months. Discharge indicators that showed the highest percentage of days with increased variability were the mean rates of rise and fall, amplitude, duration of high pulses, maximum discharge, and number of reversals. Those that showed higher percentages of decreased variability included minimum discharge, number of high pulses, duration of stability, and number of low pulses. There was no correlation between HA values and physical characteristics of rivers or hydropower facilities (including installed capacity), and reaches with multiple facilities did not differ in HA from those with single facilities. This study demonstrates that SHPs as well as larger hydropower facilities cause hydrological alterations attributable to hydropeaking. Considering the rapid expansion of SHPs in tropical river systems, there is an urgent need to understand whether the ecological impacts of hydropeaking documented in temperate biomes also apply to these systems.

Mathematical form of the Waldmeier effect

The Waldmeier effect is considered for empirical parameters of the functions that approximate solar activity cycles nos. 8–23 according to the Zurich numbering system. The cycle amplitude is found to linearly depend on the mean rate of rise in solar activity during its rising phase. This relationship seems to be a fundamental property of 11-year cycles and may be a reason for differences in solar cycles.

Can stormwater harvesting restore pre-development flows in urban catchments in South East Queensland?

Increases in the impervious area due to urbanisation have been shown to have negative impacts on the physical and ecological condition of streams, primarily through increased volume and frequency of runoff. The harvesting and detention of runoff has a potential to decrease this impact. This paper describes the effects of urbanisation on catchment flow and of stormwater harvesting on reducing those adverse impacts on a stream in South East Queensland (SEQ), Australia. A largely undeveloped catchment located southeast of Brisbane city was calibrated and validated using the Stormwater Management Model (SWMM). This model was used to investigate the effect of a range of future increases in urbanisation (represented by impervious area) on stream hydrology as well as the potential of stormwater harvesting to return the catchments to predevelopment flow conditions. Stormwater harvesting was modelled according to flow frequency measures specified in current SEQ development guidelines. These guidelines stipulate the capture of the first 10 mm of runoff from impervious areas of 0-40% and the first 15 mm from impervious areas of 40% or greater for urban developments. We found that increases in the impervious area resulted in increases in the mean, frequency and duration of high flows, and an increase in the mean rate of rise and fall for storm events in the catchment. However, the predevelopment (non-urbanised) flow distribution was very flashy in comparison with all urbanised scenarios; i.e. it had the quickest response to rainfall indicated by a high rate of rise to and fall from peak flow volume, followed by a return to zero flow conditions. Capturing the runoff according to the development guidelines resulted in a reduction in flow towards the flow distribution of a lower impervious area, however this was insufficient to meet predevelopment conditions. This suggests a stronger influence of impervious areas in this catchment on the volume of runoff than flow frequency measures are able to ameliorate.

Statistical Computer Model Analysis of the Reciprocal and Recurrent Inhibitions of the Ia-EPSP in α-Motoneurons

We simulate the inhibition of Ia-glutamatergic excitatory postsynaptic potential (EPSP) by preceding it with glycinergic recurrent (REN) and reciprocal (REC) inhibitory postsynaptic potentials (IPSPs). The inhibition is evaluated in the presence of voltage-dependent conductances of sodium, delayed rectifier potassium, and slow potassium in five α-motoneurons (MNs). We distribute the channels along the neuronal dendrites using, alternatively, a density function of exponential rise (ER), exponential decay (ED), or a step function (ST). We examine the change in EPSP amplitude, the rate of rise (RR), and the time integral (TI) due to inhibition. The results yield six major conclusions. First, the EPSP peak and the kinetics depending on the time interval are either amplified or depressed by the REC and REN shunting inhibitions. Second, the mean EPSP peak, its TI, and RR inhibition of ST, ER, and ED distributions turn out to be similar for analogous ranges of G. Third, for identical G, the large variations in the parameters' values can be attributed to the sodium conductance step (g(Na_step)) and the active dendritic area. We find that small g(Na_step) on a few dendrites maintains the EPSP peak, its TI, and RR inhibition similar to the passive state, but high g(Na_step) on many dendrites decrease the inhibition and sometimes generates even an excitatory effect. Fourth, the MN's input resistance does not alter the efficacy of EPSP inhibition. Fifth, the REC and REN inhibitions slightly change the EPSP peak and its RR. However, EPSP TI is depressed by the REN inhibition more than the REC inhibition. Finally, only an inhibitory effect shows up during the EPSP TI inhibition, while there are both inhibitory and excitatory impacts on the EPSP peak and its RR.

Physiological Assessment of Firefighters during a High Rise Scenario

1703 In the UK, buildings up to 18 metres high do not have to have firefighting lifts, requiring firefighters to climb stairs before reaching the fire floor. PURPOSE: to assess the physiological demands of a scenario involving simulated Firefighting and Search & Rescue tasks in the dark, in moderate temperatures (∼27°C) on the 5th floor of a high-rise building, under 4 task conditions. METHODS: Sixteen firefighters from London Fire Brigade participated. The four task conditions involved Standard (SDBA) (C1&C3) and Extended Duration Breathing Apparatus (EDBA) (C2&C4), and either 45 (C1&C2) or 70 mm (C3&C4) diameter hose. All participants underwent each condition in teams of two in a randomised fashion. Core temperature, skin temperature, heart rate and air use were monitored throughout; nude mass was measured pre- and post-trial. Mean (sd) age, height and mass of participants were 31.6 ± 4.8 years, 179 ± 5.0 cm and 84.9 ± 8.4 kg. Mean VO2max was 48.0 ± 4.1 ml.kg.−1min−1 and 4.07 ± 0.54 l.min−1. RESULTS: The primary reason for termination in SDBA conditions was shortage of air; and in EDBA conditions was achieving the withdrawal core temperature (39.5°C). Final core temperature reached higher values in EDBA compared to SDBA conditions (p<0.01), as they involved significantly longer work durations. The rise in temperature was also greater under EDBA (p<0.01), though mean rate of rise (0.05°C/min) did not differ. Firefighters in 10 of 32 teams reached 39.5°C, when the trials were terminated; 8 of 10 involved EDBA. The mean rise in skin temperature was 2.7°C and rate of rise 0.1°C/min, with no differences between conditions. Mean %HRR for all conditions was 68–72%, corresponding to a ‘hard’ intensity. In SDBA and EDBA, participants lost ∼0.75 l of sweat in ∼25 min, and 1.02 l in ∼34 min, respectively (p<0.01). The rate of sweat loss (0.03 l/min) was not different. Estimated mean air use in SDBA was 58 l.min−1 and in EDBA of 69 l.min−1. CONCLUSION: SDBA provided inadequate air to achieve the objectives, while EDBA provided ample air which sometimes led to high core temperatures and/or suspected exertional heat stress. Identifying the limiting factors to performance in these tasks will enable methods for extending the performance envelope in comparative safety to be explored. Funded by the Fire Research Division, Office of the Deputy Prime Minister, UK

Physiological Assessment of Firefighters during a High Rise Scenario

1703 In the UK, buildings up to 18 metres high do not have to have firefighting lifts, requiring firefighters to climb stairs before reaching the fire floor. PURPOSE: to assess the physiological demands of a scenario involving simulated Firefighting and Search & Rescue tasks in the dark, in moderate temperatures (∼27°C) on the 5th floor of a high-rise building, under 4 task conditions. METHODS: Sixteen firefighters from London Fire Brigade participated. The four task conditions involved Standard (SDBA) (C1&C3) and Extended Duration Breathing Apparatus (EDBA) (C2&C4), and either 45 (C1&C2) or 70 mm (C3&C4) diameter hose. All participants underwent each condition in teams of two in a randomised fashion. Core temperature, skin temperature, heart rate and air use were monitored throughout; nude mass was measured pre- and post-trial. Mean (sd) age, height and mass of participants were 31.6 ± 4.8 years, 179 ± 5.0 cm and 84.9 ± 8.4 kg. Mean VO2max was 48.0 ± 4.1 ml.kg.−1min−1 and 4.07 ± 0.54 l.min−1. RESULTS: The primary reason for termination in SDBA conditions was shortage of air; and in EDBA conditions was achieving the withdrawal core temperature (39.5°C). Final core temperature reached higher values in EDBA compared to SDBA conditions (p<0.01), as they involved significantly longer work durations. The rise in temperature was also greater under EDBA (p<0.01), though mean rate of rise (0.05°C/min) did not differ. Firefighters in 10 of 32 teams reached 39.5°C, when the trials were terminated; 8 of 10 involved EDBA. The mean rise in skin temperature was 2.7°C and rate of rise 0.1°C/min, with no differences between conditions. Mean %HRR for all conditions was 68–72%, corresponding to a ‘hard’ intensity. In SDBA and EDBA, participants lost ∼0.75 l of sweat in ∼25 min, and 1.02 l in ∼34 min, respectively (p<0.01). The rate of sweat loss (0.03 l/min) was not different. Estimated mean air use in SDBA was 58 l.min−1 and in EDBA of 69 l.min−1. CONCLUSION: SDBA provided inadequate air to achieve the objectives, while EDBA provided ample air which sometimes led to high core temperatures and/or suspected exertional heat stress. Identifying the limiting factors to performance in these tasks will enable methods for extending the performance envelope in comparative safety to be explored. Funded by the Fire Research Division, Office of the Deputy Prime Minister, UK

Measuring myoelectric fatigue of the serratus anterior in healthy subjects and patients with long thoracic nerve palsy

Proper function of serratus anterior plays a vital role in the movement and stability of the scapula, and thus of the glenohumeral joint and the upper limb. The unique anatomy of this muscle makes direct measurements of its fatigue properties impossible. Here we describe for the first time indirect measurements of the myoelectric manifestations of fatigue in the serratus anterior. Eight healthy volunteers (29–35 years) were tested, four of them on two different occasions, using two exercise protocols (60 s isometric maximum upward force in 120° arm flexion, and 60 s maximum forward force at 90° arm flexion) with simultaneous recording by surface and wire electrodes applied according to established methods. Signals were analysed to obtain the rate of fall of median EMG frequency and the rate of rise of amplitude. Both exercise protocols gave similar results. Frequency-slope measurements (mean rate of fall 0.6 ± 0.1% initial value per second (% s −1) with both surface and wire electrodes) were more precise than those of amplitude (mean rate of rise 2.6 ± 0.3% s −1 with surface electrodes, only 1.3 ± 0.2% s −1 with wire electrodes). Surface electrodes gave much lower variation than fine wires, the coefficient of variation of slopes for surface electrodes being approximately 20–40% both between studies in a single subject and between subjects. In 5 patients (aged 22–59 years) recovering from long thoracic nerve palsy studied using surface electrodes the frequency slopes was normal (0.6 ± 0.1% s −1), while the amplitude slope was reduced (0.9 ± 0.4% s −1, P=0.01). This shows abnormal fatigue properties of the reinnervated muscle and a dissociation between the frequency and amplitude manifestations of fatigue.

Low systemic blood flow and hyperkalemia in preterm infants

Objective: Early low systemic blood flow is common in preterm infants. This study examines the relationship among low flow, renal function, and early changes in blood potassium (K+). Methods: Preterm infants (n = 119) born before 30 weeks’ gestational age underwent serial Doppler echocardiographic studies. Superior vena cava flow (SVC flow) was assessed as a measure of upper body systemic blood flow uncorrupted by systemic to pulmonary shunts. Serial whole blood K+ concentrations on each arterial blood gas sample and urinary output in the first 48 hours were recorded. Results: Most infants had a variable degree of rise in K+ during the first 24 hours of life. The mean rate of rise was 0.17 mmol/L/h, the mean peak K+ was 5.54 mmol/L, and the mean time of peak K+ was 20 hours. The peak K+ occurred after the lowest measured SVC flow in 84% of infants. A significant positive relationship was found between the lowest measured SVC flow and the mean (r = 0.31, P =.001) and peak (r = 0.31, P =.001) K+ in the first 24 hours. Low SVC flow at 5 hours best predicted the rate of K+ rise (r = 0.28, P =.002) and at 12 hours best predicted the peak K+ concentration (r = 0.47, P <.001). The mean minimum SVC flow in the 17 babies who became hyperkalemic was 29.5 mL/kg/min versus 46.2 mL/kg/min in the 102 infants with normokalemia. Urine output in the first 24 hours was significantly lower in the hyperkalemic infants. A K+ rate rise exceeding 0.12 mmol/L/h in the first 12 hours predicted low SVC flow with 93% accuracy. Conclusions: The data are consistent with a role for low systemic blood flow leading to reduced urinary output and subsequent hyperkalemia in preterm infants. (J Pediatr 2001;139:227-32)

Relative sea-level rise during the Main Postglacial Transgression in NE Scotland, U.K.

AbstractFlandrian (Holocene) relative sea level changes in the lower Ythan valley, NE Scotland, U.K., are inferred from detailed stratigraphical evidence including microfossil analysis and radiocarbon assay. The principal event recorded is the Main Postglacial Transgression, which was under way in the area byc.8300 and had culminated beforec.4000 radiocarbon years BP. It is concluded that the rise in relative sea levels during the transgression in the area exceeded 12 m; that the mean rate of rise there was 8·05 mm a−1betweenc.8300 andc.7100 radiocarbon years BP, or 7·09 mm a−1based upon calibrated dates for the same period, before declining markedly to 1·75 mm a−1(radiocarbon) or 1·86 mm a−1(calibrated) to the culmination of the event. By comparison with other sites, the culmination appears to have been time-transgressive in eastern Scotland. Deposits of the Second Storegga Slide tsunami, which occurred during the Main Postglacial Transgression, are present in the Ythan valley, where the sediment run-up of the event at the sites studied is estimated to have been within the range 2·99–5·19 m.

Immediate response to inspiratory resistive loading in anesthetized patients with kyphoscoliosis: spirometric and neural effects.

In kyphoscoliosis (KS), lung volumes are reduced, respiratory elastance and resistance are increased, and breathing pattern is rapid and shallow, attributes that may contribute to defense of tidal volume (VT) in the face of inspiratory resistive loading. The control of ventilation of 12 anesthetized patients about to undergo corrective spinal surgery was compared to that of 11 anesthetized patients free of cardiothoracic disease during quiet breathing and the first breath through one of three linear resistors. Mean forced vital capacity (FVC) of the KS group was 48% that of the controls (C). Passive elastance (Ers) and active elastance and resistance (E'rs and R'rs, respectively) were computed according to previously described techniques (Behrakis PK, Higgs BD, Baydur A, Zin WA, Milic-Emili J (1983) Active inspiratory impedance in halothane-anesthetized humans. J Appl Physiol 54: 1477-1481). Baseline tidal volume VT, inspiratory duration Tl, expiratory duration TE, duration of total breathing cycle TT, and inspiratory duty cycle TI/TT were significantly reduced, while VE was slightly decreased in the KS. Ers, E'rs, and R'rs, were, respectively, 72, 69, and 89% greater in the KS. Driving pressure (Pmus) was derived from the equation of motion, using active values of respiratory elastance. With resistive loading, there was greater prolongation of TI in the C, while percent reduction in VT and minute ventilation VE was less in KS. Compensation in both groups was achieved through three changes in the Pmus waveform. (1) Peak amplitude increased. (2) The duration of the rising phase increased. (3) The rising Pmus curve became more concave to the time axis. These changes were most marked with application of the highest resistance in both groups. Peak driving pressure and mean rate of rise of Pmus were greater in the KS. Increased intrinsic impedance, Pmus, and differences in changes in neural timing in anesthetized kyphoscoliotics contribute to modestly greater VT defense, compared to that of anesthetized subjects free of cardiorespiratory disease.

Controlled reperfusion of the regionally ischemic myocardium with leukocyte-depleted blood reduces stunning, the no-reflow phenomenon, and infarct size

Open-chest sheep underwent 90 minutes' occlusion of the diagonal branch of the left anterior descending coronary artery, followed by vented cardiopulmonary bypass. After 30 minutes of cardioplegic arrest, simulating distal anastomoses, the occlusion on the coronary artery branch was released. Controlled reperfusion (40 to 50 mm Hg, 135 to 150 ml/min) for the first 20 minutes was delivered at the aortic root with either unmodified whole blood (control, n = 7) or blood passed through leukocyte filters (filters, n = 7). Serial measurements were made during 3 additional hours reperfusion off cardiopulmonary bypass. During ischemia, the major determinants of infarct size, which include area at risk, collateral myocardial blood flow, and rate-pressure product were not significantly different between groups. Overall, during reperfusion, mean left ventricular stroke work index in the filter group was greater than in the control group (28.7 +/- 5.8 versus 12.6 +/- 6.4 x 10(3) erg/gm, p less than 0.05), as was mean rate of rise of left ventricular pressure (1900 +/- 260 versus 1348 +/- 279 mm Hg/sec, p less than 0.05). Myocardial blood flow to the area at risk at 3 1/2 hours of reperfusion in the filter group was also significantly better than in the control group (0.57 +/- 0.15 versus 0.27 +/- 0.05 ml/min/gm, p less than 0.05), as was necrotic area as a percentage of area at risk (40% +/- 6% versus 70% +/- 5%, p less than 0.05). These results demonstrate amelioration of myocardial stunning and the no-reflow phenomenon, as well as decreased infarct size. We conclude that controlled reperfusion with leukocyte-depleted blood is superior to whole-blood reperfusion for the surgical treatment of acute regional ischemia.

Effects of the calcium antagonist gallopamil on the increase of myocardial extracellular potassium activity during LAD occlusion in dogs

It has been implied that the increase of myocardial extracellular potassium activity [( K+]e) in the early stage of acute myocardial ischemia is a major cause of the increased likelihood of arrhythmia after acute coronary artery occlusion. There is also experimental evidence that some calcium antagonists reduce the occurrence of ischemia-induced early ventricular arrhythmias. In order to clarify the antiarrhythmic effect of gallopamil during the early phase of acute LAD occlusion, the influence of this calcium antagonist on the time course of [K+]e during acute ischemia was measured in open-chest anesthetized dogs using a K+-selective surface multielectrode. The regional myocardial blood flow was determined with 9 micron radioactive tracer microspheres. After application of gallopamil (bolus 25 micrograms/kg and infusion 2.5 micrograms/kg.min for 30 min) the maximal and mean rate of rise of [K+]e as well as the plateau of [K+]e reached during ischemia were significantly diminished compared with the control occlusions. 90 min after gallopamil, the rate of rise of [K+]e as well as the plateau of [K+]e reached were still significantly reduced, but 180 min after the gallopamil application, no significant differences between the time course of [K+]e and that of the two control occlusions could be found. Gallopamil significantly elevated myocardial blood flow in the non-ischemic area, but did not influence blood flow in the ischemic region. While collateral perfusion remains unchanged, the slowed and reduced increase of myocardial [K+]e during acute coronary artery occlusion may be an important component of the antiarrhythmic effect of gallopamil during early ischemia.

Effects of extrapulmonary airway distension on breathing in anesthetized dogs.

Anesthetized dogs with open chests were perfused with a pump-oxygenator. We first observed the effects of intermittent periods of sustained inflation of both lungs, of only one lobe, and of an intra-airway balloon on the diaphragm electromyogram (EMG). Lung or lobe inflation with low pressures depressed respiratory frequency (fr) by prolonging expiratory time (TE) in proportion to inflating pressure, but balloon inflation was without effect. We next intermittently inflated one or two lobes after all others were ligated and thereafter inflated all the extrapulmonary airways following total lung excision. Lobe inflation, by varying TE, decreased fr at low pressures and often increased fr at higher pressures. Extrapulmonary airway distension slightly increased fr and the mean rate of rise of the integrated EMG, but decreased inspiratory time and peak EMG amplitude. TE was slightly prolonged by low pressures when using sustained airway pressurization but was shortened by higher pressures when distending cyclically. In comparison to lobe inflation, the effects from isolated airways were small, and the inhibitory effect of lung inflation could not be attributed to them.

Effect of SO2 on control of breathing in anesthetized cats.

In seven anesthetized tracheotomized cats we studied the acute respiratory effects of SO2 inhalation at different steady-state levels of arterial CO2 tension (Paco2). During room air breathing, SO2 (0.05%) addition caused a progressive reduction in tidal volume (VT) and increases in both respiratory frequency (f) and pulmonary resistance (RL). Atropine sulfate abolished the bronchoconstriction response to SO2 and thus permitted the study of the influence of SO2 on VT and f in the absence of constricted airways. Despite marked reductions in the VT VS. PaCO2 relationships with SO2 exposure after atropine, the relationship between pulmonary ventilation (VE) and PaCO2 was not signifcantly altered. This was the case since SO2 caused solely a reduction in inspiratory duration (Ti), affecting neither the mean rate of rise of inspiratory activity (i.e., VT/Ti) nor the relationship between Ti and breath duration. Thus, airways irritation with SO2 produced rapid, shallow breathing characterized by a shortening of inspiratory and total respiratory cycle times with no change in the rate of development of inspiratory activity. The findings suggest an influence exclusively concerned with the timing of inspiration. Perhaps premature onset of inspiratory activity accounts for the observed effects.

ELECTROPHYSIOLOGICAL AND ANTIARRHYTHMIC EFFECTS OF 4- (2-HYDROXY-3-ISOPROPYLAMINOPROPOXY) -INDOLE (LB-46) ON THE CANINE CARDIAC CELLS

The electrophysiological and antiarrhythmic effects of LB-46 on the membrane potentials of Purkinje fibers and ventricular muscle fibers of the dog were studied by means of the microelectrode technique in comparison with those of propranolol. The effects of LB-46 on the membrane potential of Purkinje fibers consisted of a reduction in amplitude of the action potential due to a diminution or loss of overshoot and unchanged resting potential, an acceleration of repolarization, a prolongation of latency, and a decrease in mean rate of rise. Nearly the same electrophysiological effects were produced by propranolol at a lower concentration. LB-46, as well as propranolol, prevented the isoproterenol-induced arrhythmia by blocking the increase in diastolic depolarization. The antiarrhythmic action of LB-46 may be due considerably to direct action on the cardiac cell membrane and partly to a beta-receptor blockade. It is very probable that LB-46 is more specific in beta-receptor blocking and little weaker in antiarrhythmic activity than propranolol.

Electrophysiological and antiarrhythmic effects of 4-(2-hydroxy-3-isopropylaminopropoxy)-indole (LB-46) on the canine cardiac cells.

Abstract The electrophysiological and antiarrhythmic effects of LB-46 on the membrane potentials of Purkinje fibers and ventricular muscle fibers of the dog were studied by means of the microelectrode technique in comparison with those of propranolol. The effects of LB-46 on the membrane potential of Purkinje fibers consisted of a reduction in amplitude of the action potential due to a diminution or loss of overshoot and unchanged resting potential, an acceleration of repolarization, a prolongation of latency, and a decrease in mean rate of rise. Nearly the same electrophysiological effects were produced by propranolol at a lower concentration. LB-46, as well as propranolol, prevented the isoproterenol-induced arrhythmia by blocking the increase in diastolic depolarization. The antiarrhythmic action of LB-46 may be due considerably to direct action on the cardiac cell membrane and partly to a beta-receptor blockade. It is very probable that LB-46 is more specific in beta-receptor blocking and little weaker in antiarrhythmic activity than propranolol.

Correlation of slow rates of rise of current with times to pinch in transient mercury-vapour plasma

Measurements of time of maximum pinch in a mercury-vapour-plasma discharge over a range of voltages up to 5kV are not, at first sight, in agreement with values calculated by using the Leontovich-Osovets theory, which has been shown to apply in similar experiments with noble gases. The influence of the external circuit involving the ignitron switch, measuring shunt and associated stripline connecting links, is deduccd from the oscillographic records of instantaneous v and i for the plasma discharge. The ratios v/i for both the external circuit and the plasma discharge are plotted against time to show the times at which the minima and the pinch maximum are reached. A graph showing measured times to pinch is compared with values calculated using the Leontovich-Osovets formula, using the initial rate of rise of current, and shown to be in poor agreement. A further plot of calculated values, obtained by using the mean rate of rise of current up to the pinch point as a fixed value, is shown to be in good agreement with the experimental results.

The relation between respiratory rate and heart rate in the calf subjected to severe heat stress

1. In experiments on three calves it was shown that, under severe heat stress, the respiratory rate at first rapidly rose from 88 to a maximum of 218 respirations/min. and then fell to 167 respirations/min., while breathing at first became shallower and then deeper.2. During the phase in which breathing became faster and shallower (panting), the heart rate rose at a mean rate of 13 beats/min. for each degree centigrade increase in rectal temperature. During the phase in which breathing became slower and deeper (‘second-phase breathing’) the mean rate of rise in heart rate was 50 beats/min. for each degree increase in rectal temperature.3. The changes in respiratory rate and in heart rate occurred at mean rectal temperatures of 40·6 and 41·0° C., respectively, and, on average, the change in respiratory rate preceded that in heart rate by 8 min.4. It is concluded that second-phase breathing was the cause of the steep increase in heart rate.5. The steep increase in heart rate is discussed in relation to heat production of the respiratory muscles.