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PubMed1986

Dependence of double-pulse facilitation on amplitude and duration of the depolarization pulses at frog's motor nerve terminals.

Motor nerve terminals of the frog were depolarized by pairs of pulses with 5 to 10 ms interval and the resulting quantal transmitter releases were determined. In 'fixed pulse facilitation', Fc, the second pulse was kept constant, and the effect of a varying pre-pulse was measured, comparing the thus facilitated release after the fixed pulse to control release after the fixed pulse alone. If depolarization in the pre-pulse was increased from threshold to almost saturation level of release, Fc had a maximum, Fc, at about 1/10 the saturation level of release, as reported before. In 'double-pulse facilitation', Fd, two identical pulses were applied, and the facilitated release after the second pulse was compared to control release after the first pulse. On increasing pulse duration from 0.4 to 2.5 ms, at fixed depolarization levels, Fd had a peak at short pulse duration and low release, and declined with increasing pulse duration and release. This dependence is expected if facilitation is caused by 'residual Ca'. Alternatively, if at fixed duration depolarization in the pulses was increased from threshold level, in most preparations Fd rose to a maximum at low depolarization and release, declined to a minimum at the depolarization level of Fc, and rose again for larger depolarizations. In some preparations, and for short pulses, the peak of Fd at low depolarizations was not observed, but always Fd increased with depolarization beyond Fc. The complicated dependence of Fd on depolarization can be explained by the residual Ca theory, if at depolarizations larger than that which produced Fc and the minimum of Fd, Ca-inflow decreases.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Increased aortic pulse and fractional pulse pressures in patients with cardiac syndrome X.

BACKGROUND: Angina with normal coronary arteries, cardiac syndrome X, is a diagnosis of exclusion. The exact mechanism of this clinical syndrome remains unclear. Although the prognosis is as good as equal to that of the normal population, symptoms related to the syndrome largely impair quality of life. Aortic pulse and fractional pulse pressures are strong and independent indicators of the risk of coronary heart disease. An increase in these hemodynamic parameters is significantly associated with the presence of coronary artery disease in men and women. METHODS AND RESULTS: We evaluated aortic pulse and fractional pulse pressures of patients with cardiac syndrome X and control subjects, and investigated the relation between the two groups. One hundred and twenty-six patients with cardiac syndrome X with a mean age of 53.1 +/- 9.5 years and 76 patients without the syndrome with a mean age of 53.1+/-11.2 years were studied consecutively from May 2004 to May 2005. Aortic systolic, diastolic, mean and pulse pressures were measured and the fractional pulse pressure was calculated (aortic pulse pressure/mean pressure). Aortic pulse and fractional pulse pressures were significantly higher in the cardiac syndrome X group than in the control group (51 +/- 13 mmHg and 43+/-9 mmHg, p < 0.001; 0.54 +/- 0.11 and 0.47 +/- 0.08, p < 0.001, respectively). All patients were classified into tertiles of aortic pulse pressure level to evaluate whether aortic pulse pressure was associated with the presence of cardiac syndrome X in the study. The multiple-adjusted odds ratio of the risk of cardiac syndrome X was 6.72 (95% CI 2.76-16.37) for tertile 2 and 29.94 (95% CI 5.59-160.44) for tertile 3 of aortic pulse pressure level compared with tertile 1. In addition, all patients were divided into two groups as lower and higher levels of aortic fractional pulse pressure. The multiple-adjusted OR of the risk of cardiac syndrome X was 4.09 (95% CI 2.05-8.15) for the higher group compared with the lower group of aortic fractional pulse pressure level. CONCLUSION: Ascending aorta pulse and fractional pulse pressures are significantly associated with the presence of cardiac syndrome X and these associations are independent of age and other cardiovascular risk factors.

Adult↗
PubMed1994

A prospective randomized comparison of defibrillation efficacy of truncated pulses and damped sine wave pulses in humans.

INTRODUCTION: Damped sine wave pulses have been used for nearly 50 years in transthoracic defibrillation systems. The purpose of this study was to determine whether damped sine wave pulses have a role in implantable defibrillators. METHODS AND RESULTS: In 21 survivors of cardiac arrest, we prospectively compared defibrillation efficacy of a standard truncated capacitor (RC) monophasic pulse with a damped sine wave inductor-capacitor (LRC) pulse using a right ventricular-left ventricular epicardial patch-patch electrode system. The RC pulse was a standard 65% tilt monophasic waveform generated from a 120 mu F capacitor. The LRC pulse was designed to simulate the waveform currently used in transthoracic defibrillators and was generated by passing the charge stored on a 40 mu F capacitor through a 37-mH inductor. Capacitor voltage, peak delivered voltage, peak delivered current, discharge pathway resistance, delivered energy, and stored energy were compared for the two waveforms at the defibrillation threshold. There was no difference in defibrillation efficacy for the two waveforms. Peak delivered voltage was similar at the defibrillation threshold: 313 +/- 101 V for the RC pulse and 342 +/- 119 V for the LRC pulse (P = 0.16). Similarly, no differences were found in defibrillation threshold peak delivered current: 8.6 +/- 2.5 (RC) versus 9.3 +/- 2.7 (LRC) amperes (A) (P = 0.20); discharge pathway resistance: 37 +/- 11 (RC) versus 38 +/- 13 (LRC) omega (P = 0.71); delivered energy: 7.0 +/- 4.5 (RC) versus 7.0 +/- 4.0 (LRC) joules (J) (P = 0.88); and stored energy: 8.7 +/- 5.7 (RC) versus 9.8 +/- 5.4 (LRC) J (P = 0.35). Although both waveforms performed the same, it was necessary to use substantially higher stored voltages with the damped sine wave delivery system than with the truncated waveform delivery system: 356 +/- 110 V for the RC pulse and 675 +/- 192 V for the LRC pulse (P < 0.0001). CONCLUSION: This study demonstrates that RC monophasic pulses provide equally effective epicardial defibrillation as LRC pulses with respect to delivered voltage and current and stored and delivered energy. However, in order for LRC pulses to provide comparable delivered voltage, current, and energy to that of RC pulses, nearly twice the voltage must be stored on the capacitor to accomplish the same task. These findings suggest that despite the nearly 50-year experience with damped sine wave pulses with transthoracic defibrillators, there is no need to begin using damped sine wave pulses for implantable defibrillators. Moreover, these data raise a question regarding the need for inductors in transthoracic defibrillators.

Aged↗
PubMedDate not supplied

Effect of simultaneous pulsed hyperthermia and pulsed radiation treatment on survival of SiHa cells.

Relatively mild temperatures (40-41.5 degrees C) can sensitize human cells to radiation without the development of thermal tolerance to radiosensitization. Therefore there may be a therapeutic benefit to adding mild hyperthermia to brachytherapy regimens for the treatment of cancer. However, the required heating times are long (approximately 48 h) which renders this approach somewhat impractical. A novel alternative is to combine pulsed brachytherapy with pulsed hyperthermia to enable the total radiation dose to be given at an elevated temperature while the total heating time is kept short. A treatment schedule in which 1 Gy radiation pulses were given once per hour during 5-min heating pulses also delivered once per hour, was investigated in vitro in the human cervical carcinoma line, SiHa. The degree of cytotoxicity and thermoradiosensitization of the cells were assessed by cell survival using the colony forming assay. Cells were exposed to pulsed hyperthermia alone (5 min at 45 degrees C, delivered once per hour), acute hyperthermia alone (45 degrees C), pulsed radiation alone (1 Gy per hour), acute radiation alone, and simultaneous pulsed hyperthermia and pulsed radiation. Pulsed heating alone caused little cytotoxicity. However when pulsed heating was added to pulsed radiation, the level of cytotoxicity was greater than for pulsed radiation alone or acute radiation alone. The effect was also greater than would be predicted from a simple additive effect of pulsed radiation and pulsed heating. In conclusion, pulsed heating at 45 degrees C sensitized cells to pulsed radiation without the development of thermal tolerance.

Cell Survival↗
PubMed1987

Intraoperative comparison of sequential-pulse and single-pulse defibrillation in candidates for automatic implantable defibrillators.

Sixteen survivors of cardiac arrest underwent intraoperative comparison of the effectiveness of sequential-pulse and single-pulse defibrillation. Defibrillation was tested alternately with the single-pulse or sequential-pulse technique 10 seconds into an episode of ventricular fibrillation that was induced with alternating current. The sequential-pulse defibrillation technique using truncated exponential pulses was performed with a right ventricular endocardial catheter and a left ventricular epicardial patch electrode. The first pulse was delivered between the right ventricular apical and the superior vena caval electrode on the right ventricular endocardial catheter. The second pulse was delivered between the right ventricular apical electrode and the left ventricular patch electrode 0.2 ms after termination of the first pulse. Single-pulse defibrillation was performed with a standard intracardiac defibrillation system in which a single truncated exponential pulse was delivered across 2 epicardial patch electrodes positioned over the anterolateral right ventricle and the posterolateral left ventricle. During defibrillation threshold determination, voltage and current waveforms were recorded and integrated to determine delivered energy. Average defibrillation threshold leading-edge voltage for the sequential pulse technique was 496 +/- 140 V, compared with 365 +/- 157 V for the single-pulse technique (p less than 0.005). Defibrillation threshold leading-edge current for the sequential-pulse technique was 6.0 +/- 2.3 A, compared with 10.6 +/- 5.1 A for the single-pulse method (p less than 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Prospective comparison of sequential pulse and single pulse defibrillation with use of two different clinically available systems.

Sixteen out-of-hospital survivors of ventricular fibrillation underwent a prospective, randomized, intraoperative comparison of sequential pulse and single pulse defibrillation with use of two distinct electrode systems and waveform shapes currently available for clinical use. Defibrillation was tested alternately with either the single pulse or the sequential pulse system 10 s into an episode of ventricular fibrillation. Sequential pulse defibrillation was performed with two 4 ms truncated exponential pulses of constant duration delivered to three equally spaced oval epicardial patch electrodes composed of concentric coils. The posterior left ventricular electrode served as the common cathode. The first anode was over the anterior right ventricle and the second anode was over the anterior left ventricle. Single pulse defibrillation was performed with the standard intracardiac defibrillation system with use of a single truncated exponential pulse with a fixed 65% tilt delivered across two rectangular, wire mesh epicardial patch electrodes positioned over the anterior right ventricle and posterolateral left ventricle. During defibrillation threshold determination, voltage and current waveforms were recorded and used to determine pulsing resistance and delivered and stored energy. Average defibrillation threshold leading edge voltage for the single pulse technique was 273 +/- 101 V compared with 246 +/- 67 V (11% less) for the sequential pulse technique (p = 0.136). Defibrillation threshold leading edge current for the single pulse technique was 6.7 +/- 2.5 A compared with 5.2 +/- 1.7 A (29% less) for the sequential pulse method (p = 0.005). The defibrillation threshold delivered energy was 5.6 +/- 4.0 J for the single pulse technique and 3.5 +/- 1.8 J (38% less) for the sequential pulse technique (p = 0.021).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2002

The reliable measurement of radial pulse: gender differences in pulse profiles.

This study was undertaken to determine whether healthy adults exhibited characteristic pulse profiles. Pulse characteristics measured for 83 women and 65 men included presence at the Traditional Chinese Medicine (TCM) locations (Cun, Guan, Chi); and depth (superficial, middle, deep), overall pulse force, relative pulse force, pulse width and pulse rhythm. Most subjects had similar values for many of the characteristics investigated including relative pulse force at the three traditional palpation locations (Cun, Guan and Chi), pulse width and pulse rhythm. There were some significant gender differences. The pulse was present beyond Chi in 90% of males compared with 56% of females. Female pulses tended to be less forceful compared with males. However, with the exception of overall force, there was little support for TCM assumptions of gender differences in pulse such as in left/right balance. There was some support for the use of the TCM palpation locations Cun, Guan and Chi to discriminate between pulses since there was significant differences in manifestations of some pulse characteristics among these locations.

Adult↗
PubMed1994

The retinal venous pulse. Its relation to optic disc characteristics and choroidal pulse.

PURPOSE: The presence or absence of the spontaneous retinal venous pulse is an important clinical sign, especially when one is evaluating a patient who may have increased intracranial pressure. The purpose of this study is to evaluate a large group of healthy patients, correlating optic disc characteristics, choroidal pulse, and brachial pulse pressure with the presence and intensity of the spontaneous retinal venous pulse. METHODS: Ninety-seven patients were studied correlating these parameters with their fundus photographs. Ocular pneumotonometry as a measure of the choroidal pulse and the brachial pulse pressure were correlated with the optic disc characteristics and the intensity of the retinal venous pulse statistically. RESULTS: The results showed a highly significant correlation with these parameters. The greater the pulse amplitude--especially the choroidal pulse the more likely the spontaneous retinal venous pulse would be present. More importantly, the anatomic variable of optic disc cup and vascular configuration had the greatest influence on whether the spontaneous retinal venous pulse is present or absent. CONCLUSION: The authors conclude that unless the clinician is aware of the importance of optic nerve characteristics and pulse amplitude in the choroid (indirectly measured in a normal clinical setting by the brachial pulse) the significance of the spontaneous retinal venous pulse cannot be properly determined.

Adolescent↗
PubMed1999

Depth of vaporization and the effect of pulse stacking with a high-energy, pulsed carbon dioxide laser.

BACKGROUND: Laser resurfacing of photodamaged skin has become popular, but questions regarding its safety with regard to the risks of scarring have arisen. OBJECTIVE: This study was designed to investigate the depth of vaporization and residual thermal necrosis of single-pulse vaporization and multiple passes versus pulse-stacking and multiple passes. The potential significance of operator technique and laser parameters is considered. METHODS: Skin samples from surgical excisions were treated by means of a Coherent Ultrapulse carbon dioxide laser at 250 mJ per pulse and 500 mJ per pulse with a 3 mm collimated beam and a repetition rate of 10 Hz. A total of 70 treatment areas were performed. Blinded analysis of the histologic effects of single-pulse, double-pulse, and triple-pulse vaporization after 1 through 10 passes was undertaken. RESULTS: A plateau of vaporization was observed after 3 passes at both 250 and 500 mJ whether single-, double-, or triple-pulse vaporization was used. This plateau occurs at approximately 100 to 250 microm from the skin surface. Thermal necrosis is well controlled only with single-pulse vaporization. There is a direct linear increase in the depth of thermal necrosis both with the number of pulses stacked and the number of passes. CONCLUSION: Pulsed carbon dioxide laser resurfacing is a safe and self-limited procedure if a pulse width of less than 1 msec is used with single-pulse vaporization and fluences of 3.5 J/cm2 and 7.0 J/cm2. There appears to be little justification for performing more than 3 or 4 passes. Pulse stacking may significantly increase residual thermal necrosis, thereby increasing the risk of scarring. Operator technique may be significant in avoidance of this occurrence.

Cicatrix↗
PubMed2005

Assessment of pulse rate variability by the method of pulse frequency demodulation.

BACKGROUND: Due to its easy applicability, pulse wave has been proposed as a surrogate of electrocardiogram (ECG) for the analysis of heart rate variability (HRV). However, its smoother waveform precludes accurate measurement of pulse-to-pulse interval by fiducial-point algorithms. Here we report a pulse frequency demodulation (PFDM) technique as a method for extracting instantaneous pulse rate function directly from pulse wave signal and its usefulness for assessing pulse rate variability (PRV). METHODS: Simulated pulse wave signals with known pulse interval functions and actual pulse wave signals obtained from 30 subjects with a trans-dermal pulse wave device were analyzed by PFDM. The results were compared with heart rate and HRV assessed from simultaneously recorded ECG. RESULTS: Analysis of simulated data revealed that the PFDM faithfully demodulates source interval function with preserving the frequency characteristics of the function, even when the intervals fluctuate rapidly over a wide range and when the signals include fluctuations in pulse height and baseline. Analysis of actual data revealed that individual means of low and high frequency components of PRV showed good agreement with those of HRV (intraclass correlation coefficient, 0.997 and 0.981, respectively). CONCLUSION: The PFDM of pulse wave signal provides a reliable assessment of PRV. Given the popularity of pulse wave equipments, PFDM may open new ways to the studies of long-term assessment of cardiovascular variability and dynamics.

Adult↗
PubMed1996

Checking the carotid pulse check: diagnostic accuracy of first responders in patients with and without a pulse.

International guidelines for cardiopulmonary resuscitation (CPR) in adults advocate that cardiac arrest be recognized within 5-10 s, by the absence of a pulse in the carotid arteries. However, validation of first responders' assessment of the carotid pulse has begun only recently. We aimed (1) to develop a methodology to study diagnostic accuracy in detecting the presence or absence of the carotid pulse in unresponsive patients, and (2) to evaluate diagnostic accuracy and time required by first responders to assess the carotid pulse. In 16 patients undergoing coronary artery bypass grafting, four groups of first responders (EMT-1: 107 laypersons with basic life support (BLS) training; EMT-2: 16 emergency medical technicians (EMTs) in training; PM-1: 74 paramedics in training; PM-2: 9 certified paramedics) performed, single-blinded and randomly allocated, carotid pulse assessment either during spontaneous circulation, or during non-pulsatile cardiopulmonary bypass. Time to diagnosis of carotid pulse status, concurrent haemodynamics and diagnostic accuracy were recorded. In 10% (6/59), an absent carotid pulse was not recognized as pulselessness. In 45% (66/147), a pulse was not identified despite a carotid pulse with a systolic pressure > or = 80 mmHg. Thus, although sensitivity of all participants for central pulselessness approached 90%, specificity was only 55%. Both sensitivity and, to a lesser degree, specificity improved with increasing training; blood pressure or heart rate had no significant effect. The median diagnostic delay was 24 s (minimum 3 s). When no carotid pulse was found, delays were significantly longer (30 s: minimum 13 s), than when a carotid pulse was identified (15 s; minimum 3 s) (P < 0.0001). Of all participants, only 15% (31/206) produced correct diagnoses within 10 s. Only 1/59 (2%) identified pulselessness correctly within 10 s. Our cardiopulmonary bypass model of carotid pulse assessment proved to be feasible and realistic. We conclude that recognition of pulselessness by rescuers with basic CPR training is time-consuming and inaccurate. Both intensive retraining of professional rescuers and reconsideration of guidelines about carotid pulse assessment are warranted.

Adult↗
PubMed1989

The arterial pulse analyzer as a potential replacement for manual pulse palpation in Oriental medicine.

Application of the arterial pulse analyzer now makes it possible to automatically diagnose such geriatric disorders as arteriosclerosis by using simple electrocardiograms and radial, carotid and posterior tibial artery pressure pulse wave charts. If the arterial pulse analyzer is adopted for use in Oriental medical clinics, there will no longer be a need for manual pulse palpation. In brief, applying the arterial pulse analyzer to the 8 key pulses of Oriental medicine yields the following results: 1) 'Slow' or 'rapid' pulses can be defined by the S-S interval (almost identical to the R-R interval of the ECG). 2) 'Slippery' or 'hesitant' pulses can be defined by the S-P time and the Dh/Ch% (P time & Incisura) ratio. 3) 'Floating' or 'submerged' pulses can be defined by the Ph/Ch% (pressure pulse wave to height) ratio. 4) 'Scattered' or 'moderate' pulses can be defined by the S-C- time (E time). Thus, by employing the arterial pulse analyzer, subjectivity problems inherent in the manual pulse palpation used by Oriental medicine for over 1500 years can be analyzed objectively.

Arteriosclerosis↗
PubMed2000

Noninvasive assessment of the digital volume pulse. Comparison with the peripheral pressure pulse.

The digital volume pulse can be recorded simply and noninvasively by photoplethysmography. The objective of the present study was to determine whether a generalized transfer function can be used to relate the digital volume pulse to the peripheral pressure pulse and, hence, to determine whether both volume and pressure pulse waveforms are influenced by the same mechanism. The digital volume pulse was recorded by photoplethysmography in 60 subjects (10 women, aged 24 to 80 years), including 20 subjects with previously diagnosed hypertension. Simultaneous recordings of the peripheral radial pulse and digital artery pulse were obtained by applanation tonometry and a servocontrolled pressure cuff (Finapres), respectively. In 20 normotensive subjects, measurements were obtained after the administration of nitroglycerin (NTG, 500 microgram sublingually). Transfer functions obtained by Fourier analysis of the waveforms were similar in normotensive and hypertensive subjects. In normotensive subjects, transfer functions were similar before and after NTG. By use of a single generalized transfer function for all subjects, the radial and digital artery pressure waveforms could be predicted from the volume pulse with an average root mean square error of 4.4+/-2.0 and 4.3+/-1.9 mm Hg (mean+/-SD) for radial and digital artery waveforms, respectively, similar to the error between the 2 pressure waveforms (4.4+/-1.4 mm Hg). The peripheral pressure pulse is related to the digital volume pulse by a transfer function, which is not influenced by effects of hypertension or NTG. Effects of NTG on the volume pulse and pressure pulse are likely to be determined by a similar mechanism.

Adult↗
PubMed2000

Piezoelectric pulse sensor device (Pulse Chek)-monitoring after the treatment of lower leg ischemia.

BACKGROUND: The aim of this study was to evaluate the usefulness of the piezoelectric pulse sensor device (Pulse Chek) as a continuous monitoring method in early surveillance after the treatment of lower leg ischemia with either surgical or interventional procedures. METHODS EXPERIMENTAL DESIGN: prospective study. SETTING: institutional practice. PATIENTS AND INTERVENTIONS: two patient groups with peripheral arterial occlusive disease were included; a surgical group undergoing femoropopliteal bypass grafting (22 patients) and a group undergoing PTA of the femoral or popliteal arteries (18 patients). MEASURES: the piezoelectric pulse sensor was applied on the skin over the dorsalis pedis artery. A baseline waveform was recorded preoperatively and continuous monitoring begun immediately after the surgical or interventional procedure. Hard copy recordings of the pulse wave were done in the immediate postoperative period, the postoperative evening, the following morning or at any time the alarm was triggered. A late follow-up waveform was recorded after an average of 34 days. Simultaneous ABI measurements were recorded. RESULTS: Preoperatively or pre-intervention, the pulse waveform was accurately recorded in 15/22 (68%) patients in the surgical group and 14/18 (78%) patients of the PTA group. In 20 (91%) surgical group patients and in 14 (78%) PTA group patients, postoperative monitoring was reliable, the pulse waveform confirmed patency of the vessel. Piezoelectric pulse sensor device monitoring did not detect graft occlusion in only one patient in the surgical group where interpretation of the pulse wave was complicated by a slow atrial fibrillation. There were 19 alarms in the pulse waveform during monitoring for 11 (55%) surgical group patients and 18 alarms for 9 (64%) PTA group patients. None of the alarms resulted from graft occlusion. Reliable pulse waveform recordings were obtained in 16/21 (76%) surgical group patients of the original 22 (one graft occluded) and for 15/18 (83%) PTA group patients in the follow-up assessment after the mean 34 days. One surgical patient was lost to follow-up. CONCLUSIONS: The piezoelectric pulse sensor device can be recommended as a method of continuous monitoring immediately after the revascularization procedure in those patients who have a pedal artery where a reliable pulse waveform can be recorded.

Aged↗
PubMed2004

Modifying the 'pulse-reserve' paradigm for deserts of North America: precipitation pulses, soil water, and plant responses.

The 'pulse-reserve' conceptual model--arguably one of the most-cited paradigms in aridland ecology--depicts a simple, direct relationship between rainfall, which triggers pulses of plant growth, and reserves of carbon and energy. While the heuristics of 'pulses', 'triggers' and 'reserves' are intuitive and thus appealing, the value of the paradigm is limited, both as a conceptual model of how pulsed water inputs are translated into primary production and as a framework for developing quantitative models. To overcome these limitations, we propose a revision of the pulse-reserve model that emphasizes the following: (1) what explicitly constitutes a biologically significant 'rainfall pulse', (2) how do rainfall pulses translate into usable 'soil moisture pulses', and (3) how are soil moisture pulses differentially utilized by various plant functional types (FTs) in terms of growth? We explore these questions using the patch arid lands simulation (PALS) model for sites in the Mojave, Sonoran, and Chihuahuan deserts of North America. Our analyses indicate that rainfall variability is best understood in terms of sequences of rainfall events that produce biologically-significant 'pulses' of soil moisture recharge, as opposed to individual rain events. In the desert regions investigated, biologically significant pulses of soil moisture occur in either winter (October-March) or summer (July-September), as determined by the period of activity of the plant FTs. Nevertheless, it is difficult to make generalizations regarding specific growth responses to moisture pulses, because of the strong effects of and interactions between precipitation, antecedent soil moisture, and plant FT responses, all of which vary among deserts and seasons. Our results further suggest that, in most soil types and in most seasons, there is little separation of soil water with depth. Thus, coexistence of plant FTs in a single patch as examined in this PALS study is likely to be fostered by factors that promote: (1) separation of water use over time (seasonal differences in growth), (2) relative differences in the utilization of water in the upper soil layers, or (3) separation in the responses of plant FTs as a function of preceding conditions, i.e., the physiological and morphological readiness of the plant for water-uptake and growth. Finally, the high seasonal and annual variability in soil water recharge and plant growth, which result from the complex interactions that occur as a result of rainfall variability, antecedent soil moisture conditions, nutrient availability, and plant FT composition and cover, call into question the use of simplified vegetation models in forecasting potential impacts of climate change in the arid zones in North America.

Biomass↗
PubMed2005

Precipitation pulse use by an invasive woody legume: the role of soil texture and pulse size.

Plant metabolic activity in arid and semi-arid environments is largely tied to episodic precipitation events or "pulses". The ability of plants to take up and utilize rain pulses during the growing season in these water-limited ecosystems is determined in part by pulse timing, intensity and amount, and by hydrological properties of the soil that translate precipitation into plant-available soil moisture. We assessed the sensitivity of an invasive woody plant, velvet mesquite (Prosopis velutina Woot.), to large (35 mm) and small (10 mm) isotopically labeled irrigation pulses on two contrasting soil textures (sandy-loam vs. loamy-clay) in semi-desert grassland in southeastern Arizona, USA. Predawn leaf water potential (psi(pd)), the isotopic abundance of deuterium in stem water (deltaD), the abundance of 13C in soluble leaf sugar (delta13C), and percent volumetric soil water content (theta(v)) were measured prior to irrigation and repeatedly for 2 weeks following irrigation. Plant water potential and the percent of pulse water present in the stem xylem indicated that although mesquite trees on both coarse- and fine-textured soils quickly responded to the large irrigation pulse, the magnitude and duration of this response substantially differed between soil textures. After reaching a maximum 4 days after the irrigation, the fraction of pulse water in stem xylem decreased more rapidly on the loamy-clay soil than the sandy-loam soil. Similarly, on both soil textures mesquite significantly responded to the 10-mm pulse. However, the magnitude of this response was substantially greater for mesquite on the sandy-loam soil compared to loamy-clay soil. The relationship between psi(pd) and delta13C of leaf-soluble carbohydrates over the pulse period did not differ between plants at the two sites, indicating that differences in photosynthetic response of mesquite trees to the moisture pulses was a function of soil water availability within the rooting zone rather than differences in plant biochemical or physiological constraints. Patterns of resource acquisition by mesquite during the dynamic wetting-drying cycle following rainfall pulses is controlled by a complex interaction between pulse size and soil hydraulic properties. A better understanding of how this interaction affects plant water availability and photosynthetic response is needed to predict how grassland structure and function will respond to climate change.

Carbohydrate Metabolism↗
PubMed2004

Azimuth-dependent recovery cycle affects directional selectivity of bat inferior collicular neurons determined with sound pulses within a pulse train.

In our previous study, we have shown that the recovery cycle of most neurons in the inferior colliculus (IC) of the big brown bat, Eptesicus fuscus, is typically longer at ipsilateral azimuth than at contralateral azimuth under free-field stimulation conditions. The present study is to test the hypothesis that this azimuth-dependent recovery cycle may contribute to the variation of directional selectivity of IC neurons with sequential presented sound pulses within a pulse train. A 300-ms pulse train containing nine sound pulses of 4-ms with an inter-pulse interval of 33.3 ms was delivered at several selected azimuthal angles between +/-80 degrees lateral in the frontal auditory space of a bat. A family of nine directional selectivity curves was plotted with a neuron's number of impulses in response to each individual pulse against the azimuthal angles. The type and sharpness of these directional selectivity curves were then compared in relation to pulse position within the pulse train. All 675 directional selectivity curves obtained from 75 IC neurons could be described as directionally selective (423, 63%), hemifield (220, 32%), or non-directional (32, 5%). The directional selectivity curves of 45 (60%) neurons did not vary with pulse position. However, those of the remaining neurons (30, 40%) changed from one type to another such that the number of neurons with directionally selective curves progressively increased and the number of neurons with hemifield and non-directional selectivity curves decreased with increasing pulse position within the pulse train. Among 68 IC neurons whose directional selectivity curves were compared quantitatively, directional selectivity determined with sequentially presented sound pulses significantly increased in 38 (56%) neurons; decreased in 18 (26%) neurons but did not change in 12 (18%) neurons. This change of directional selectivity was due to the variation in recovery cycle of these IC neurons with azimuthal angle as we hypothesized.

Acoustic Stimulation↗
PubMed1997

Interactions between pulse separation and pulse polarity order in cochlear implants.

Interactions between pulse separation and pulse polarity order were examined using psychophysical studies of electrical detection thresholds in nonhuman primates. Subjects were trained using acoustic stimuli, then deafened in one ear and implanted with an electrode array for electrical stimulation of the cochlea. Threshold vs pulse separation functions for trains of biphasic electrical pulses were compared for constant and alternating leading phase polarity. When leading phase polarity was held constant, threshold vs pulse separation functions were nonmonotonic (U-shaped). Small polarity-dependent (cathodic vs anodic leading phase) differences in absolute thresholds were observed at long pulse separations, but function shape was independent of leading phase. When leading phase polarity alternated, there was a pronounced reduction in thresholds at short pulse separations (below about 1 ms), resulting in monotonically increasing threshold vs pulse separation functions. At long pulse separations, functions for alternating and constant polarity stimuli were similar. Polarity effects were most apparent for longer duration trains (20 pulses) at long pulse durations (1-2 ms/phase). For stimuli consisting of only two biphasic pulses, alternating polarity effects depended on whether cathodic or anodic phases were adjacent. The neural mechanisms underlying these effects probably include refractory properties and/or residual potentials.

Acoustic Stimulation↗