Threshold Research Articles

TOD Performance Model for Staring Thermal Imager with Machine Vision

A triangle orientation discrimination threshold(TOD) performance theoretical model is derived for the staring thermal imager based on machine vision. Specifically, how to obtain the TOD curve based on machine vision is briefly described. The spatial frequency distribution of the triangle test pattern is first determined. The transform and response characteristics of the non-periodic triangle pattern and its background clutter through machine vision-based thermal imager are analyzed. The three-dimensional matched filter is adopted to characterize quantitatively the spatial and temporal integration of image enhancement algorithms to the output triangle pattern signal, various noise components and background clutter, and the signal-to-interference ratio (SIR) of the triangle pattern output image is derived for the staring thermal imager based on machine vision. Then, the TOD performance theoretical model is established by assuming that the output SIR is equal to the threshold SIR75% determined by the discrimination criteria of machine vision. Preliminary simulation and experimental results show that this theoretical model can give reasonable prediction of the TOD performance curve for staring thermal imagers based on machine vision.

Change in characteristics of human vagal sigmoidal baroreflex curve during conscious state and general anesthesia.

Volatile anesthetics have been shown to decrease baroreflex. In humans, cardiovagal baroreflex curve is best described to be sigmoidal and analysis of sigmoid model can provide more information, such as threshold (THR), saturation (SAT), maximal gain (Gmax), operating range (OR, difference between THR and SAT), operational point (OP, relative position of resting set point within the OR) in addition to the linear gain. We compared the changes in the sigmoid model of the systolic blood pressure (SBP)-RR interval relation between awake state and general anesthesia. Sigmoid curve was obtained using the 'modified Oxford technique' (bolus sodium nitroprusside followed by bolus phenylephrine) to perturb SBP in awake group and 2 vol% sevoflurane anesthesia group. Radial arterial beat-by-beat SBP and raw RR interval data points were plotted and then binned in 2 mmHg SBP increments. Curve fittings were performed using symmetric four-parameter sigmoid model and asymmetric five-parameter sigmoid model. Gmax was calculated from the first derivative of the logistic function. Compared with awake control, general anesthesia caused decreases of linear gain, Gmax and OR. RR interval THR and SBP THR were unaffected, whereas SBP SAT increased and RR interval SAT decreased, resulting from reduced linear gain and curvature parameter. Resting set point fell and OP shifted significantly to THR region. Sigmoidal baroreflex curve revealed diminished gains, OR and OP during general anesthesia. Moreover, our results demonstrate that the analysis of sigmoid baroreflex arc across the entire baroreflex range provide more unique information beyond that of linear gain.

Comparison of atrial fibrillation inducibility by electrical stimulation of either the extrinsic or the intrinsic autonomic nervous systems

To study the effects of bilateral vagosympathetic nerve stimulation (VNS) and ganglionated plexi stimulation (GPS) on atrial refractoriness and inducibility of atrial fibrillation (AF). Studies were performed in fourteen adult mongrel dogs anesthetized with Na-pentobarbital, 30 mg/kg. VNS was achieved by insertion of wires into the left and right VN trunks. An octapolar catheter was attached to contact the right superior pulmonary vein (RSPV) and other octapolar catheter electrodes were sutured to the right atrial (RA) free wall and appendage (RAA). GPS was performed via a plaque electrode sutured to the fat pad containing the anterior right (AR) GP. VNS and GPS were matched to decrease heart rate by approximately 50%. Programmed stimulation delivered from the RSPV or RAA at 2x, 4x and 10x threshold (TH) allowed the determination of atrial refractory period (ARP) and the AF inducibility. The latter was quantitated by the cumulative window of vulnerability (WOV), i.e., the longest minus the shortest coupling interval during which AF was induced at 2x, 4x, 10x, TH combined. Programmed electrical stimulation at the RSPV showed that the ARP was significantly shorter for both VNS and GPS than baseline (baseline, 113 +/- 22 ms; VNS, 94 +/- 26 ms; GPS, 85 +/- 31 ms) but there was no significant difference in ARP between VNS and GPS. In contrast, the cumulative WOV was significantly wider with GPS (39 +/- 36 ms) than either the baseline state (1 +/- 1 ms) or with VNS (14 +/- 26 ms), p < 0.05. Moreover, pacing from RAA showed a significantly greater cumulative WOV for VNS (33 +/- 36 ms) vs both baseline and GPS (1 +/- 4 ms and 15 +/- 26 ms, respectively, p < 0.05). The heart rate slowing caused by GPS and VNS was not significantly different, 82 +/- 11/min vs 82 +/- 7/min. These data indicate a distinct functional separation of autonomic nerve innervation to the atria from the extrinsic and intrinsic nervous systems. AF is more liable to occur due to intrinsic nerve stimulation at the PVs whereas peripheral atrial sites are more readily inducible for AF due to the extrinsic neural input.

Analysis of clinical usefulness of the heat flux technique: predictability of the recovery from neurosensory disturbances in the chin undergoing mandibular sagittal split ramus osteotomy

To examine the prognosis of the neurosensory disturbance (NSD) in the chin after bilateral sagittal split ramus osteotomy (BSSRO), using the heat flux technique. Twenty-nine patients (total 58 sides) undergoing BSSRO were examined. The warm sensory threshold (WHF) and cold sensory threshold (CHF) in the chins of these patients were measured by the heat flux technique. Touch sensory threshold (TS) was measured by an Semmes-Weinstein esthesiometer. Touch sensory disturbance was subjectively evaluated by visual analog scale. At all of the postoperative time points, there were no significant differences in the incidence rate among all tests (chi-squared test; P > .05). WHF, CHF, and TS were significantly correlated with the subjective evaluation. Recovery from NSD was delayed in cases that the postoperative variation of 2 weeks was >400 W/m(2) in WHF and CHF and the filament marking at 2 weeks after surgery was >3.5 in TS. The heat flux technique appears to be a useful method for the prediction of the recovery from NSD in the chin.

Uncertainty Analysis in Triangle Orientation Discrimination Threshold Measurement

The Triangle Orientation Discrimination Threshold (TOD) is a new figure of merit for characterizing the performance of an infrared imager. In this paper, focusing on a reflective infrared target projector, the TOD curve is measured utilizing four alternative forced choice (4AFC) test method. Furthermore, the dominant sources affecting uncertainties in the TOD measure values, are analyzed in detail, the effective temperature difference, sensor, and observer. And, the variation of the TOD measurement is described quantitatively utilizing the uncertainty analysis theory. Simulation results show that the TOD measurement values vary in a small range, which show a higher stability than minimum resolvable temperature difference (MRTD) measure values.

The analgesic effects of intrathecal xylazine and detomidine in sheep and their antagonism with systemic atipamezole

ObjectiveTo evaluate the analgesic and adverse side effects of intrathecal (IT) xylazine (XYL) and detomidine (DET) and the subsequent effects of two doses of intravenous (IV) atipamezole (ATI). Study designProspective, randomized, cross-over. AnimalsFive adult healthy female sheep with mean body mass of 55 ± 2.3 kg. Material and methodsEach sheep underwent four treatments: 1) 50 μg kg−1 XYL IT and 5 μg kg−1 ATI IV, 2) 50 μg kg−1 XYL IT and 2.5 μg kg−1 ATI IV, 3) 10 μg kg−1 DET IT and 5 μg kg−1 ATI IV, 4) 10 μg kg−1 DET IT and 2.5 μg kg−1 ATI IV. Pain threshold (TH) was tested by applying pulsed and stepwise incremental direct current to the skin overlying the pastern. The current at the point of foot lift was recorded as the TH. Heart rate (HR), mean arterial pressure, arterial oxygen (PO2) and carbon dioxide (PCO2) tensions were monitored. Outcomes were derived as differences between baseline assessment and measurements after treatment. Two-way anova was used to analyse drug effects, treatment differences between groups were examined with an F-test or Wilcoxon's rank sum test in case of non-parametric data distribution. p was set at 0.05. ResultsBoth drugs increased the pain TH, caused small increases in PCO2, and small decreases in HR, the latter was only significant for XYL recipients. Xylazine produced a significantly higher TH, more rapidly and for longer than DET. Atipamezole only significantly affected PaCO2 in the XYL group 2. The pain TH was not affected in either group after IV ATI. ConclusionsAt the doses used, IT XYL, and to a lesser extent DET, induced pastern analgesia. Atipamezole 5 μg kg−1 IV antagonized some side effects without affecting analgesia. Clinical relevanceIntrathecal XYL may be useful as an analgesic in sheep. Its safety is increased because IV ATI antagonizes side effects, but not analgesia.

TOD performance theoretical model for scanning infrared imagers

Since the triangle orientation discrimination threshold (TOD) measure was proposed, good progress has been made in some aspects, such as experimental validation, field performance, and TOD sensor performance model. However, what is still missing is a TOD curve prediction model similar to the minimum resolvable temperature difference (MRTD) equation. In this paper, an equation-based TOD performance model was first developed for scanning thermal imagers. Specifically, the spatial distribution of the triangle standard test pattern is described quantitatively. The resolution transfer characteristic of the scanning infrared imagers is modeled with linear system theory, and system noise is characterized by introducing a three-dimensional noise model. The modulation effect of overall subsystems of scanning thermal imager on the non-periodic standard triangle pattern is analyzed. The matched filter idea is adopted to characterize quantitatively the spatial–temporal integration of the human visual system to signal and various noise components over the triangle pattern area, and the perceived signal-to-noise ratio for the scanning infrared imager is derived. From this, a TOD performance theoretical model is established. Comparisons with experimental results show that this theoretical model gives reasonable prediction of the TOD performance curve for scanning thermal imagers. Although more tests and modifications are required, these preliminary results suggest that this model can be developed into a model that predicts the TOD for all kinds of sensors.

An electrophysiological study of the initial step of face perception

We studied the initial step of face perception examining the visual evoked potentials (VEPs) elicited by mosaic pictures. Ten healthy right-handed adult volunteers served as subjects. The threshold level of perception was determined psychophysically, and three different mosaic levels (subthreshold (SUB), threshold (THR) and suprathreshold (SUP)) for a familiar face (FF), an unfamiliar face (UF) and an object (OB) were used as the visual stimuli, which were presented for 250 ms in a random order. VEPs were recorded from 15 electrodes according to the international 10–20 system, referring to an electrode at nose tip. An epoch of 700 ms including a 200-ms prestimulus baseline was collected. The peak amplitudes and latencies of major components (N100 at O1 and O2 and N170 at T5 and T6) were analyzed. The peak latencies of N100 and N170 were shortened by decreasing the mosaic levels for FF and UF, but there were no significant changes for OB. The latency difference between N100 and N170 for FF and UF was shortened by decreasing mosaic levels especially that of FF was significantly shorter at THR. The N100 amplitude was unchanged for all pictures, while the N170 amplitude was increased at THR and SUP for FF and UF. Therefore, our findings suggest that the first step of face perception is already set in the primary visual cortex and familiarity can facilitate the cortico-cortical processing of facial information.

Effect of Short Pulse Width Programming in AutoCapture Devices

Pacing chronaxie can increase over time. The impact of a short pulse duration on threshold (THR) variations, frequency of noncapture episodes, and overall patient safety has not been fully studied. AutoCapture (AC) pacemakers are capable of memorizing THR trends and loss of capture (LOC) episodes. The study included 20 recipients of AC pacemakers (mean age = 76 +/- 9 years, 15 men) followed for 6 months. They were randomly assigned to pulse durations of 0.2 versus 1.0 ms at 1 month, and crossed over to the alternate programming at 3 months. Evoked response (ER) and AC tests were performed at follow-up. At 0.2 ms and 1.0 ms, the mean number of LOC/day was 2.37 +/- 5.81 and 0.91 +/- 0.49, respectively (ns). LOC trends between follow-up were significantly different with 0.2 versus 1.0 ms pulse duration (P < 0.01). AC THR at 1.0 ms was significantly lower (0.44 +/- 0.77) than at 2.0 ms (0.97 +/- 0.26, P < 0.05). No patient reported symptoms related to LOC during the study. Pulse duration programmed near the strength-duration curve is associated with greater variations in THR and LOC. AC responds to these changes by delivering 4.5 V pulses and keeping the capture THR at low, though safe values.

TOD Performance Theoretical Model for Staring Thermal Imagers

The TOD (triangle orientation discrimination threshold) metric, as a promising sensor performance measure, is suitable for all types of thermal imaging systems and corresponds to the field performance very well. Since this method was proposed, a great progress has been made in some aspects, such as experimental validation, field performance, and TOD sensor performance model. However, what is still missing is a TOD curve prediction model similar to MRTD (minimum resolvable temperature difference) equation. Here, an equation-based TOD performance model was first developed focusing on staring thermal imagers. Specifically, spatial distribution of the triangle standard test pattern is described quantitatively. Resolution transfer characteristic of the staring infrared imagers is modeled with linear system theory, and system noise is characterized with the introduction of three-dimensional noise model. The modulation effect of overall subsystem of staring thermal imager on the non-periodic triangle standard pattern is analyzed. The matched filter idea is adopted to characterize quantitatively the spatial integration of the eye to signal and various noise components over the triangle pattern area, and the perceived signal-to-noise ratio of the staring thermal imager is derived. Then, the TOD performance theoretical model is established. Comparing with experimental results, this theoretical model gives reasonable prediction of the TOD performance curve of staring thermal imagers. Although more tests and modifications are required, these preliminary results suggest that this model can be developed into a model that predicts the TOD for all kinds of sensors.

Dynamic range and intensity discrimination with high-rate pulse-train carriers: predictions from a stochastic model and comparison with performance for noise-modulated pulse-train stimuli

This work investigates the properties of the neural response to a low frequency sinusoidal signal with a high-rate pulse-train carrier using a stochastic auditory nerve model. The agreement between the theoretical predictions, model simulations, and psychophysical data is demonstrated. Theoretical prediction of threshold (THL) and the most uncomfortable level (UCl), thus dynamic range, is considered as a function of various stimulus parameters, including carrier rate. Performance of dynamic range and intensity discrimination are compared for sinusoidal amplitude-modulated stimuli with high-rate pulse-train carriers and noise-modulated pulse-train stimuli.

Recovery of nerve injury after mandibular sagittal split osteotomy. Diagnostic value of clinical and electrophysiologic tests in the follow-up

The diagnostic value of several clinical, quantitative sensory tests (brush-stroke directional discrimination (BSD), touch detection threshold (TD), warm/cold (W/C) and sharp/blunt discrimination (S/B)), and electrophysiologic tests (mental nerve blink reflex (BR), nerve conduction study (NCS), cold (CDT), and warm (WDT) detection thresholds) in the recovery of inferior alveolar nerve (IAN) injury was evaluated in a prospective 1-year follow-up study of 20 patients after bilateral sagittal split osteotomy (BSSO). The subjective sensory alteration was assessed from patients' drawings. The predictive values of different tests at 2 weeks were determined in relation to the subjective sensory recovery at 12 months.The most pronounced recovery of the nerve damage occurred during the first 3 months according to all measures used. After 3 months, the electrophysiologic tests, especially the NCS, indicated significant further improvement. Except for the TD test, all other clinical test results were normal already at 3 months postoperatively. At early and late controls, the NCS and the thermal quantitative sensory testing could best verify the subjective sensory alteration, and most accurately assess the degree of thick and thin fibre dysfunction. At 1 year, the nerve dysfunction, as revealed by the NCS, corresponded with the figures of sensory alteration reported by the patients (35% R, 40% L). The W/C, BSD, S/B and WDT tests had the best early positive predictive values. Electrophysiologic tests had higher negative predictive values compared to clinical tests.

Antinociceptive effect of intrathecally applied alpha2 agonists (xylazine and detomidine) in sheep and the response to atipamezole

This study evaluated the antinociceptive and physiologic effects of xylazine (X) and detomidine (D) administered intrathecally (IT) at the lumbosacral space, before and after the injection of atipamezole (A) IV. The study was approved by the National Animal Protection Authorities. Five adult healthy female sheep were anaesthetized with propofol on four occasions to inject the following treatments IT: groups 1 and 2, 0.05 mg kg−1 X (2 mg mL−1 saline) IT; groups 3 and 4, 0.01 mg kg−1 D (0.5 mg mL−1 saline) IT (Waterman et al. 1988). Nociceptive threshold (TH) was tested by applying pulsed and stepwise enhanced direct current (Ludbrook et al. 1995) at one hind leg pastern and noting the current at the moment of foot lift. Maximum current applied was 40 mA. Baseline TH was measured twice before anaesthesia and every 10 minutes when the sheep regained consciousness. Atipamezole was given IV immediately after reaching maximum analgesic action of X and D as defined by two equal or decreasing TH values and measurements were continued for 90 minutes. The dose of A for groups 1 and 3 was 0.005 mg kg−1 (0.25 mg mL−1 saline) IV, and for groups 2 and 4 was 0.0025 mg kg−1 A (0.25 mg mL−1 saline) IV. Heart rate (HR), mean direct arterial pressure (MAP), PaO2 and PaCO2 were measured. The differences between measurements recorded before and after treatment were analysed using a paired t-test for the drug effects and a nonparametric Wilcoxon's rank sum test for the comparison between groups. A p-value < 0.05 was considered significant. All sheep were able to stand before A IV. Threshold baseline value was 4.5 ± 1.7 (mean ± SD) mA for all animals. Xylazine caused a significantly higher TH rise (35.2 ± 1.8 mA), faster onset (21.1 ± 16.0 minutes) and longer duration of the TH enhancement (104.1 ± 8.6 minutes) than D (TH: 16.3 ± 7.8 mA, onset: 49.5 ± 28.4 minutes, duration: 59.3 ± 27.3 minutes). A significant increase in PaCO2 was observed in the X and D treated animals, 0.39 ± 0.21 kPa (2.9 ± 1.6 mm Hg) and 0.39 ± 0.29 kPa (2.9 ± 2.2 mm Hg), respectively. Heart rate was significantly decreased by −21 ± 17 beats minute−1 for X animals and −13 ± 13 beats minute−1 for D. Mean arterial pressure (−9 ± 13 mm Hg for X and −1 ± 11 mm Hg for D animals) and PaO2 0.65 ± 1.32 kPa (4.9 ± 9.9 mm Hg) for X and 1.45 ± 4.19 kPa (10.9 ± 31.4 mm Hg) for D animals) did not change significantly. The nociceptive threshold was not affected by A in any group. Threshold values of all X treated animals before A was 39.3 ± 1.4 mA and after was 37.2 ± 6.3 (group 1) and 40 ± 0 (group 2). Threshold values of all D treated animals before A was 21.0 ± 8.3 and after was 19.4 ± 7.3 (group 3) and 24.8 ± 8.0 (group 4). At the dosages administered intrathecally in this study, X and to a lower degree D induce antinociception without major physiologic changes. Atipamezole up to 0.005 mg kg−1 IV does not affect the resulting antinociception as assessed by electrical stimulation.

An evaluation of clinical and electrophysiologic tests in nerve injury diagnosis after mandibular sagittal split osteotomy

The yield of clinical sensory tests and electrophysiologic tests in the diagnostics of inferior alveolar nerve (IAN) damage after bilateral sagittal split osteotomy (BSSO) was studied. The diagnostic value of these tests was evaluated by comparing the test results to the degree of nerve damage at the end of the operation as documented by means of the intraoperative nerve conduction recording of the IAN. Twenty patients undergoing BSSO were analysed preoperatively and 2 weeks postoperatively. The frequency of the IAN disturbance ranged from 10% to 94% depending on the test method and the test site used. Of the clinical sensory tests, the touch detection threshold (TD) test was the most sensitive and clinically useful test. It also correlated best with the electrophysiologically verified intraoperative nerve damage (R=−0.603,P =0.017 on the right, R=−0.626, P=0.01 on the left). The blink reflex and quantitative cold detection threshold tests were almost as often abnormal as the TD-test, but nerve conduction study (NCS) was the most sensitive (88%) of all clinical and electrophysiologic tests. The frequency of abnormal findings in the electrophysiologic tests indicating IAN injury, 75% on the right side and 90% on the left side, corresponded exactly with the figures of subjective sensory alteration. Almost all electrophysiologic tests showed obvious associations with the objectively verified IAN damage. All tests, except the NCS, showed only moderate sensitivity. Specificity of the tests was generally high, the only exceptions being the TD test and the NCS. To increase the diagnostic accuracy of the testing and to detect different types of damage in different nerve fibre populations, a combination of different sensory and electrophysiologic tests is recommended.

Long-term frequency tuning of local field potentials in the auditory cortex of the waking guinea pig.

The goal of our study was to determine the extent of changes in frequency tuning in the auditory cortex over weeks. The subjects were awake adult male guinea pigs (n = 8) bearing electrodes chronically implanted in layers IV-VI of primary auditory cortex. Tuning was determined by presenting sequences of pure tone bursts (approximately 0.97-41.97 kHz, -20 to 80 dB, 100-ms tone duration, 5-ms rise-fall, 800-ms intertone intervals, 1.5-s intersequence interval) either in 0.5-octave steps (n = 5, 14 probes) or 0.25-octave steps (n = 3, 9 probes) delivered to the ear contralateral to recording sites. Tuning curves were determined for local field potentials (LFPs), which were tuned to frequency (negative potential, latency to peak 15-20 ms), repeatedly for up to 27 days (0.5 octave) or 12 days (0.25 octave). Characteristic frequency (CF), best frequency at 10 and 30 dB above absolute threshold (BF10, BF30), threshold (TH), and bandwidth (10 dB above threshold; BW) were measured. Absolute amplitude often decreased across weeks, necessitating normalization of amplitude. However, there were no significant trends in tuning over days for CF, BF10, or BF30 for either the half- or the quarter-octave group. Both groups exhibited random daily variations in frequency tuning, the quarter-octave group revealing larger variations averaging 0.228, 0.211, and 0.250 octave for CF, BF10, and BF30, respectively. Therefore, frequency tuning in waking animals does not exhibit directional drift over very long periods of time. However, daily tuning variations on the order of 0.20-0.25 octave indicate that the peaks of tuning curves (CF, BF) represent a preferred frequency range rather than a fixed frequency.

Transcranial magnetic stimulation reveals an interhemispheric asymmetry of cortical inhibition in focal epilepsy.

Transcranial magnetic stimulation (TCS) was applied to both hemispheres of 16 patients affected by criptogenic focal epilepsy to evaluate the interhemispheric symmetry of the motor cortex excitability. The amplitude of the motor evoked potentials (MEPs) and the duration of the post-MEP silent period (SP) were measured at threshold (THR) and at increasing TCS stimulation intensities. The THR was significantly higher in patients than in 16 age-matched control subjects (p < 0.01). No interhemispheric differences were found in MEP amplitude. In controls, the correlation between SP duration and increasing TCS stimulus intensity was linear with a symmetrical progression of the SP duration over the two hemispheres. In patients this linear SP progression was lacking on the 'epileptic' hemisphere: the SP duration did not increase following TCS > 40% above THR, indicating abnormal interhemispheric asymmetry. This finding suggests a selective dysfunction of inhibition in the epileptic hemisphere as signaled by an abnormal SP duration in response to progressively higher TCS intensities.

Bias-free procedure for the measurement of the minimum resolvable temperature difference and minimum resolvable contrast

MRTD (Minimum Resolvable Temperature Difference) The characterization of electro-optical system performance by means of the standard minimum resolvable temperature difference (MRTD) or the minimum resolvable contrast (MRC) has a number of serious disadvantages. One of the problems is that they depend on the subjective decision criterion of the observer. We present an improved measurement procedure in which the results are free from observer bias. In an adaptive two-alternative forced-choice (2AFC) procedure, both the standard four-bar pattern and a five-bar reference pattern of the same size and contrast are presented consecutively in random order. The observer decides which of the two presentations contains the four-bar pattern. Misjudgments are made if the bars cannot be resolved or are distorted by sampling. The procedure converges to the contrast at which 75% of the observer responses are correct. The reliability of the responses is tested statistically. Curves cut off near the Nyquist frequency, so that it is not necessary to artificially set a frequency limit for sampling array cameras. The procedure enables better and easier measurement, yields more stable results than the standard procedure, and avoids disputes between different measuring teams. The presented procedure is a 'quick fix' solution for some of the problems with the MRTD and MRC, and is recommended as long as bar patterns are used as the stimulus. A new and fundamentally better method to characterize electro-optical system performance, called the triangle orientation discrimination threshold (TOD) was recently proposed by Bijl and Valeton (1998).

EFFECTS OF PARTIAL NEUROMUSCULAR BLOCKADE ON CAROTID BAROREFLEX FUNCTION DURING DYNAMIC EXERCISE IN HUMANS

1068 We evaluated the influence of central command on carotid-cardiac baroreflex function during steady state dynamic exercise. Five subjects (26±2 yrs) performed dynamic exercise at 20% V̇O2max for seven minutes. Each subject performed the exercise bout under two conditions: control and partial neuromuscular blockade using Norcuron (curare). Heart rate (HR; beats/min) and mean arterial pressure (MAP; mmHg) were measured throughout. Carotid baroreflex function (CBR) was recorded using a pulsed neck pressure/neck suction technique. Cardiac responses were used to model CBR curves. Threshold (TH), saturation (SAT), gain, range (RR) and minimum response (HRmin) were defined. Increased central command with curare significantly elevated MAP (117.6±5) and HR (112.8±6) from control MAP (92.3±5) and HR (98.5±6) during dynamic exercise (P<0.05). (Table)TableThe results indicate that the feed-forward efferent neural input from central command actively regulates the carotid baroreflex during low intensity dynamic exercise. Supported by Copenhagen Muscle Research Center

MODEL OF AORTIC BAROREFLEX FUNCTION IN HUMANS

1208 The purpose of this investigation was to model isolated aortic cardiac baroreflex function (ABR) in humans. Pharmacologically-induced increases(phenylephrine) and decreases (nitroprusside) in aortic distending pressure were implemented in five healthy young normotensive subjects in order to determine the maximal gain (Gmax) of the reflex heart rate (HR) response in i) an intact ABR and carotid baroreflex (CBR) and ii) an isolated ABR. Mean arterial blood pressure (MAP) was monitored by an intra-radial arterial catheter. The threshold (THR), saturation point (SAT), response range(RES), centering point (CP) and minimum HR response (HRmin) were calculated using the Kent Logistical Model. The ABR was functionally isolated from the CBR by application of neck pressure during the hypertensive response and neck suction during the hypotensive response. Mean ± SE calculations presented in table below:TableThe Gmax of the ABR was 56% and the response range of the ABR was 81% of the arterial baroreflex (ABR+CBR). We conclude the ABR is the predominant reflex regulator of MAP.

UPPER BODY POWER RELATES TO SKI SKATING ECONOMY OF ELITE BIATHLON SKIERS796

Biathlon racing involves the exclusive use of the ski skating technique. Since economy has been determined to be important in running performance, the purpose of this study was to evaluate gross economy during treadmill roller ski skating of elite biathletes. 17 male biathletes (4 Olympic medalists) performed incremental treadmill roller ski skating to volitional exhaustion, and a double poling upper body power (UBP) test. In addition, athletes performed a submaximal roller ski test to evaluate skiing economy (EC). Respiratory gas and blood lactate(LA) values were collected during roller skiing. Performance rank did not relate to peak VO2, but did relate to, lactate threshold (TH) VO2, UBP (w & w/kg), ECVO2, and ECLA (respective r's = -0.08, -0.75, -0.72, -0.82, 0.65, 0.59). Table Lower ECLA was coincident with higher UBP (w & w/kg; r=-0.82 &-0.75) and THVO2 (r=-0.64). ECVO2 was also significantly related to THVO2, absolute & relative UBP (respective r's = -0.59, -0.57, -0.55). The results of this study indicate that upper body power is highly related to skiing economy and in turn ski performance.