Frequency Fb Research Articles

DIAPHRAGM METABOREFLEX INCREASES RESTING LEG VASCULAR RESISTANCE AND DECREASES LEG BLOOD FLOW

Fatiguing diaphragm contractions cause a time-dependent increase in muscle efferent sympathetic nerve activity recorded from the peroneal nerve (St Croix et al, J Physiol, in press). We tested the hypothesis that a metaboreflex arising from fatiguing diaphragmatic contractions can elicit an increase in resting leg vascular resistance (LVR) and a decrease in leg blood flow (QLEG). Healthy male subjects (n = 6, 25–36 yrs) performed two diaphragmfatiguing trials. Subjects inspired with their diaphragm to task failure (3–9 min) against resistance equal to 60% max inspiratory mouth pressure (PM), a prolonged duty cycle (TI/TTOT = 0.7), breathing frequency (fb) of 15/min, and tidal volume (VT) equal to twice eupnea; and 60% PM max, TI/TTOT = 0.4, fb = 20/min. In response to bilateral phrenic nerve stimulation, diaphragm force production was reduced (25–40%, P < 0.05) at the termination of both fatiguing trials. Mean arterial pressure (MAP) was determined with an automated blood pressure cuff. QLEG was measured in the femoral artery with pulsed Doppler ultrasound methods and leg vascular resistance (LVR = MAP/QLEG) was calculated. Vessel diameter was imaged and was unchanged during all trials. Compared to control conditions, the fatiguing trials increased LVR 25–80%, MAP increased 10–35 mmHg, and QLEG fell 10–30%. The time course of the effect was present by 2 min in all subjects and as early as 1 min in some subjects. During recovery, the observed changes were quickly dissipated (< 30 sec). QLEG and LVR were unchanged during (i) 3-min trials replicating the breathing pattern used in the fatiguing trials with no inspiratory resistance, (ii) 3-min non-fatiguing hyperoxic trials of increased central motor output (PM = 95% max, TI/TTOT = 0.35, fb = 12/min; and PM = 2% max, TI/TTOT = 0.4, fb = 45/min), and (iii) three non-fatiguing trials where inspiratory effort was gradually increased (30, 40, 50% PM max) and breathing pattern (TI/TTOT = 0.4, fb = 20/min) was constant. In summary, voluntary alterations to inspiratory effort, in the absence of fatigue, had no effect on LVR and QLEG whereas the two fatiguing trials elicited increases in LVR and decreases in QLEG. We attribute these changes to a metaboreflex originating in the diaphragm, which reaches its threshold for activation during fatiguing contractions. Supported by NHLBI

Fatiguing inspiratory muscle work causes reflex sympathetic activation in humans.

We tested the hypothesis that reflexes arising from working respiratory muscle can elicit increases in sympathetic vasoconstrictor outflow to limb skeletal muscle, in seven healthy human subjects at rest. We measured muscle sympathetic nerve activity (MSNA) with intraneural electrodes in the peroneal nerve while the subject inspired (primarily with the diaphragm) against resistance, with mouth pressure (PM) equal to 60 % of maximal, a prolonged duty cycle (TI/TTot) of 0.70, breathing frequency (fb) of 15 breaths min-1 and tidal volume (VT) equivalent to twice eupnoea. This protocol was known to reduce diaphragm blood flow and cause fatigue. MSNA was unchanged during the first 1-2 min but then increased over time, to 77 +/- 51 % (s.d.) greater than control at exhaustion (mean time, 7 +/- 3 min). Mean arterial blood pressure (+12 mmHg) and heart rate (+27 beats min-1) also increased. When the VT, fb and TI/TTot of these trials were mimicked with no added resistance, neither MSNA nor arterial blood pressure increased. MSNA and arterial blood pressure also did not change in response to two types of increased central respiratory motor output that did not produce fatigue: (a) high inspiratory flow rate and fb without added resistance; or (b) high inspiratory effort against resistance with PM of 95 % maximal, TI/TTot of 0.35 and fb of 12 breaths min-1. The heart rate increased by 5-16 beats min-1 during these trials. Thus, in the absence of any effect of increased central respiratory motor output per se on limb MSNA, we attributed the time-dependent increase in MSNA during high resistance, prolonged duty cycle breathing to a reflex arising from a diaphragm that was accumulating metabolic end products in the face of high force output plus compromised blood flow.

Cardiovascular effects of hyperbaric oxygen with and without addition of carbon dioxide.

It is commonly believed that during hyperbaric oxygen (HBO) treatment, in spite of the vasoconstriction induced by the increased O2 content in the breathing gas, the elevated carrying capacity of O2 in the arterial blood results in augmented O2 delivery to tissues. The experiments described here tested the hypothesis that HBO treatment would be more efficient in delivering O2 to poorly perfused tissues if the vasoconstriction induced by elevated O2 could be abolished or attenuated by adding CO2 to the breathing gas. Organ blood flow (QOBF), systemic hemodynamics, and arterial blood gases were measured before, during and after exposure to either 300 kPa O2 (group 1) or 300 kPa O2 with 2 kPa CO2 (group 2), in awake, instrumented rats. During the HBO exposure the respiratory frequency (fb) fell (4 breaths x min(-1) x 100 kPa O2(-1)), with no changes in arterial CO2 tension (PaCO2), but when CO2 was added, fb and PaCO2 increased. The left ventricular pressure (LVP) and the systolic arterial pressure (SBP) increased. The maximum velocity of LVP (+dP/dt) rose linearly with LVP whether CO2 was added or not (r2 = 0.72 and 0.75 respectively). Similarly, the cardiac output (Qc) and heart rate (fc) fell, while the stroke volume (SV) was unaltered, independent of PaCO2. There was a general vasoconstriction in most organs in both groups, with the exception of the central nervous system (CNS), eyes, and respiratory muscles. HBO reduced the blood flow to the CNS by 30%, but this vasoconstriction was diminished or eliminated when CO2 was added. In group 2, the blood flow to the CNS rose linearly with increased PaCO2 and decreased pH. After decompression fc and SBP stayed high, while Qc returned to control values by reducing the SV; CNS blood flow remained markedly elevated in group 2, while in group 1, it returned to control levels. We conclude that the changes in fc, Qc, LVP, dP/dt, SBP and most QOBF values induced by HBO were not changed by hypercapnia. Blood flow to the CNS decreased during HBO treatment at a constant PaCO2. Hypercapnia prevented this decline. Elevated PaCO2 augmented O2 delivery to the CNS and eyes, but increased the susceptibility to O2 poisoning. A prolonged suppression of O2 supply to the CNS occurred during the HBO exposure and in air following the decompression in the absence of CO2. This suppression was offset by the addition of CO2 to the breathing gas.

Cardiopulmonary Responses of Middle-Aged Men Without Cardiopulmonary Disease to Steady-Rate Positive and Negative Work Performed on a Cycle Ergometer

Understanding physiological responses to negative work allows therapists to be more knowledgeable when they prescribe this form of exercise. The physiological responses of 12 men without cardiopulmonary disease, aged 39 to 65 years (X=49.7, SD=9.3), to negative work (eccentric muscle contractions) and to positive work (concentric muscle contractions) were compared. Subjects performed the 2 types of work on a motorized cycle ergometer at pedaling frequencies of 35, 55, and 75 rpm with a constant power output of 60 W. Steady-rate values of oxygen consumption (VO2), heart rate (HR), minute ventilation (VE), tidal volume (VT), and breathing frequency (fb) were obtained during 6 test conditions (positive and negative work at each of the 3 pedaling frequencies). Values for all measures were greater during positive work than during negative work, except for fb. During positive work, values for all variables were greatest at 75 rpm, except for fb. During negative work, VO2 and HR were greater at 75 and 35 rpm than at 55 rpm, and VE and VT were greater at 75 rpm than at 55 rpm. Breathing frequency was not different among pedaling frequencies. The results confirmed that negative work performed on a cycle ergometer is associated with low metabolic cost in older men without cardiopulmonary disease. Although VE was determined primarily by changes in VT during negative work, a comparable disproportionate increase in fb was observed at the start of negative work. Such changes in breathing patterns have implications for the prescription of negative work for patients with lung disease.

Breathing pattern in highly competitive cyclists during incremental exercise.

The purpose of our investigation was to analyse the breathing patterns of professional cyclists during incremental exercise from submaximal to maximal intensities. A group of 11 elite amateur male road cyclists [E, mean age 23 (SD 2) years, peak oxygen uptake (VO2peak) 73.8 (SD 5.0) ml kg(-1) min(-1)] and 14 professional male road cyclists [P, mean age 26 (SD 2) years, (VO2peak) 73.2 (SD 6.6) ml kg(-1) min(-1)] participated in this study. Each of the subjects performed an exercise test on a cycle ergometer following a ramp protocol (exercise intensity increases of 25 W x min(-1)) until the subject was exhausted. For each subject, the following parameters were recorded during the tests: oxygen consumption (VO2), carbon dioxide output (VCO2), pulmonary ventilation (VE), tidal volume (VT), breathing frequency (fb), ventilatory equivalents for oxygen (VE x VO2(-1)) and carbon dioxide (VE x VCO2(-1)), end-tidal partial pressure of oxygen and partial pressure of carbon dioxide, inspiratory (tI) and expiratory (tE) times, inspiratory duty cycle (tI/tTOT, where tTOT is the time for one respiratory cycle), and mean inspiratory flow rate (VT/tI). Mean values of VE were significantly higher in E at 300, 350 and 400 W (P < 0.05, P < 0.05 and P < 0.01, respectively); fb was also higher in E in most moderate-to-maximal intensities. On the other hand, VT showed a different pattern in both groups at near-to maximal intensities, since no plateau was observed in P. The response of tI and tE was also different. Finally, VT/tI and tI/tTOT showed a similar response in both P and E. It was concluded that the breathing pattern of the two groups differed mainly in two aspects: in the professional cyclists, VE increased at any exercise intensity as a result of increases in both VT and fb, with no evidence of tachypnoeic shift, and tE was prolonged in this group at high exercise intensities. In contrast, neither the central drive nor the timing component of respiration seem to have been significantly altered by the training demands of professional cycling.

Influences of various factors upon parameters of the command–response model for fundamental frequency contour generation

The command–response model by Fujisaki and his co-workers formulates the generation process of the fundamental frequency contour (henceforth F0 contour) in terms of a set of input commands carrying linguistic and paralinguistic information and the mechanisms that respond to these commands. The parameters of the mechanisms are time constant of the phrase control mechanism (α), that of the accent control mechanism (β), and the baseline frequency (Fb). The present study investigates the influences of speech rate, speaking style, and individual difference on these parameters as well as their variability. The speech material consisted of recordings of a short story by six native speakers of Japanese at three speech rates (slow, normal, and fast) and in two speaking styles (reading and conversational). The parameters were extracted by the method of analysis-by-synthesis, and the results were analyzed statistically. The analysis indicated that utterance-to-utterance variations are quite small in all three parameters for a given rate, style, and speaker. Among the three parameters, only α showed a small but systematic tendency to increase with the speech rate, while differences in speaking style did not affect these parameters. Individual differences were quite small in α and β, while Fb varied from speaker to speaker.

Breathing patterns during slow and fast ramp exercise in man.

Breathing frequency (fb), tidal volume (VT), and respiratory timing during slow (SR, 8 W min-1) and fast (FR, 65 W min-1) ramp exercise to exhaustion on a cycle ergometer was examined in seven healthy male subjects. Expiratory ventilation (VE), pulmonary gas exchange (VO2 and VCO2) and end-tidal gas tensions (PET,O2 and PET,CO2) were determined using breath-by-breath techniques. Arterialized venous blood was sampled from a dorsal hand vein at 2 min intervals during SR and 30 s intervals during FR and analysed for arterial plasma PCO2 (PaCO2). PET,CO2 increased with increasing work rates (WRs) below the ventilatory threshold (VT); at WRs > or = 90% VO2,max, PET,CO2 was reduced (P < 0.05) below 0 W values in SR but not in FR.fb and VT were similar for SR and FR at all submaximal WRs, resulting in a similar VE. At exhaustion VE was similar but fb was higher (P < 0.05) and VT was lower (P < 0.05) in SR (fb, 51 +/- 10 breaths min-1; VT, 2590 +/- 590 ml) than in FR (fb, 42 +/- 8 breaths min-1; VT, 3050 +/- 470 ml). The time of expiration (TE) decreased with increasing WR, but there was no difference between SR and FR. The time of inspiration (TI) decreased at exercise intensities > or = VT; at exhaustion, TI was shorter (P < 0.05) during SR (0.512 +/- 0.097 s) than during FR (0.753 +/- 0.100 s). The TI to total breath duration (TI/TTot) and the inspiratory flow (VT/TI) were similar during SR and FR at all submaximal exercise intensities; at VO2,max, TI/TTot was lower (P < 0.05) and VT/TI was higher (P < 0.05) during SR (TI/TTot, 0.473 +/- 0.030; VT/TI, 5.092 +/- 0.377 l s-1) than during FR (TI/TTot, 0.567 +/- 0.050; VT/TI, 4.117 +/- 0.635 l s-1). These results suggest that during progressive exercise, breathing pattern and respiratory timing may be determined, at least at submaximal work rates, independently of alveolar and arterial PCO2.

Ventilatory response at the onset of voluntary exercise and passive movement in endurance runners.

The present study was performed to examine whether or not the ventilatory response at the onset of voluntary exercise and passive movement in endurance runners is the same as in untrained subjects. Twelve long-distance runners belonging to the varsity athletic club and 13 untrained subjects of our university participated as subjects in this study. Maximum oxygen uptake was significantly higher in the endurance runner group [mean (SD) 70.8 (4.7) ml.kg-1.min-1] than in the untrained group [49.8 (6.3) ml.kg-1.min-1]. Cardiorespiratory responses during voluntary exercise and passive movement of alternate flexion-extension of the right and left legs for about 15 s at a frequency of about 60 rpm, were determined by means of breath-by-breath techniques. Minute inspiratory ventilation (VI), tidal volume (VT), respiratory frequency (fb), cardiac output (Qc), stroke volume (SV) and heart rate (HR) increased significantly immediately at the onset of voluntary exercise and passive movement. The incremental rate for VI was greater than that for Qc. Average values and standard deviations of changes in VI were calculated as the difference between the mean of the first and second breath and the mean of five breaths preceding the exercise or movement. The rates obtained in voluntary exercise and passive movement in the endurance runner group [2.34 (0.82) and 1.72 (0.71 l.min-1), respectively] were significantly (P < 0.05) lower than those in the untrained group [4.16 (2.66) and 2.71 (1.56 l.min-1), respectively]. Also changes in VT and HR were significantly lower in the endurance group than in the untrained group with regard to both voluntary exercise and passive movement. The results suggest that the magnitude of cardiorespiratory responses at the onset of voluntary exercise and passive movement in humans is influenced by chronic endurance training for long periods.

The Frequency Dependence of the Noise Resistance for Polymer‐Coated Metals

Electrochemical noise and impedance data for polymer‐coated steel exposed to seawater have been analyzed in the time and frequency domains. Good agreement between spectral noise plots and impedance spectra was observed provided that accurate collection of current noise data was not affected by instrument limitations. The frequency range in which valid spectral noise plots for polymer‐coated steel can be obtained is quite limited compared to impedance plots. The noise resistance equals the polarization resistance only if both the potential and current power spectral density plots have the same slope resulting in frequency independent spectral noise plots. This means that the impedance spectra have to display a dc limit in the frequency region in which noise data are collected, i.e., the sampling frequency fs for collection of noise data must be less than the breakpoint frequency fb related to the dc limit of the impedance spectrum. In general, it has to be concluded that for protective coatings for which impedance spectra are capacitive between 1 Hz and 1 mHz, the frequency region in which meaningful noise data can be collected, is a function of the measurement bandwidth. Therefore interpretation of in terms of a single coating property is not possible.

VENTILATORY DYNAMICS DURING PROLONGED CYCLING IN NORMOCONVECTIVE AND HYPERCONVECTIVE ENVIRONMENTS 1194

To investigate the influence of convection on ventilatory dynamics, 12 subjects (25.7 ±3.4 yr, 182.6±8.0 cm, 73.38±6.97 kg, 1.0797 ±.009 g*mL-1) performed 90 min cycling trials at 70% VO2max in normoconvective (NC) (wind speed, <.20 m*s-1) and hyperconvective (HC) (wind speed, 4.05 m*s-1) environments. Ventilation rate (VE) remained higher(p≤.001) and had a progressively greater rate of increase (p≤.001) during the NC trial (min 90 M = 99.51 ± 15.19 L*min-1) as compared to the HC trial (min 90 M = 83.26 ± 12.82 L*min-1). The upward drift in VE, especially evident during the NC trial, was accomplished mainly by an increase in breath frequency (Fb) (min 90 NC trial M = 39.5±9.1 br*min-1; min 90 HC trial M = 34.2±9.8 br*min-1), also a significant interaction(p≤.033). Tidal volume (Vt) decreased slightly during both trials with the increase in Fb and remained higher (p≤.029) throughout the NC trial (M = 2.72 ± 3.7 L*br-1) than the HC trial (M = 2.54 ±.42 L*br-1). Rectal temperature was higher (p≤.037) and increased more rapidly (p≤.005) during the NC trial (min 90 M = 39.25 ±.50 °C) as compared to the HC trial (min 90 M = 38.61 ± 30 °C). Mean skin temperature was higher (p≤.001) during the NC trial(35.09±.81 °C) than the HC trial (32.52 ±.72 °C). Heat loss through the ventilatory track was greater (p≤.009) during the NC trial(47.54±3.06 W*m-2) than during the HC trial(45.43±2.53 W*m-2). These data indicate that fan-driven air circulation enhances thermoregulation and blunts the increases in VE, Fb, and Vt that are stimulated during exercise in a still-air environment to dissipate excess metabolic heat. When thermal equilibrium is maintained by convection, ventilatory volumes are correspondingly reduced.

System parameter analysis of NIR-TRS spectra from homogeneous media with and without an absorbing boundary and from heterogeneous media with a single absorber.

Traditional near infrared-time resolved spectroscopy (NIR-TRS) analysis includes fitting a spectrum with a known analytical solution to obtain the media absorption and scattering coefficients or computing mean time-of-flight for heterogeneity localization. The benefit of applying frequency response analysis to NIR-TRS data reduction is that magnitude ratio (MR) and phase shift (φ) information in a wide frequency range can be obtained from a single TRS spectrum. The sharper the input pulse is the wider the frequency range values one can obtain. This analysis has been applied to NIR-TRS spectra to obtain optical parameters from homogeneous systems (Kang et al., in press) and for localizing absorbers in heterogeneous systems (Kang et al., 1994). MR and φ can also be obtained from phase modulation spectroscopy (PMS). PMS, however, provides these values at a fixed modulation frequency unless the instrument is sophisticated enough to change the modulation frequency in a wide range. Another benefit is that multiple system parameters can be obtained from a single TRS spectrum, i.e., MR, φ, steady state gain (K), break frequency (fb)/time constant (τ), and system order (n). Steady state gain (K) is a valuable parameter that can be used to check system linearity. Other new parameters (fb/τ, n) are still to be studied in an optical sense.

Bubble Characteristics in Molten Copper Bath with Gas Injection.

Bubble characteristics in a molten copper bath at 1250°C agitated by Ar gas injection were measured using a newly developed electroresistivity probe. The bubble characteristics are specified by gas holdup (void fraction) α, bubble frequency fB, mean bubble rising velocity uB^- and mean bubble diameter dB^-. Ar gas was injected through a centered single-hole bottom nozzle or an L-type lance at the same temperature as the bath. The Ar gas flow rate was 50 or 100 cm3/s (at 1250°C), which was adjusted using a mass flow controller. Measured values of α, fB, uB^- and dB^- were compared with their respective empirical correlations for these quantities proposed previously on the basis of the cold model experiments. Good agreement between the measured values and empirical correlations was seen in the bath, except near the nozzle exit.

Effect of exposure to oxygen at 101 and 150 kPa on the cerebral circulation and oxygen supply in conscious rats.

Hyperbaric oxygen at pressures of 300 to 500 kPa has been shown to induce changed distribution of cerebral blood flow (QCBF) in rats, in places reducing the supply of the supplementary O2. Thus, in the present study, the effect of hyperoxia at 101 (group 1, n = 9) and 150 (group 2, n = 9) kPa O2 on cerebral blood flow distribution and central haemodynamics was tested in conscious, habituated rats. During the control period the systolic arterial pressure (BPs), heart rate (fc), breathing frequency (fb), cardiac output (Qc), arterial acid-base chemistry and glucose, as well as QCBF distribution (rQCBF) were similar in the two groups of animals. During O2 exposure, the acid-base chemistry remained unchanged. The haemoglobin decreased in group 2, but remained unchanged in group 1. The fc decreased rapidly in both groups during the change in gas composition, after which fc remained constant both in group 1 and in group 2, for whom pressure was increased. The Qc and fb decreased and BPs increased similarly in the two groups. Total QCBF and rQCBF decreased to the same extent in both groups, and the rQCBF changes were equally scattered. In group 1, breathing of pure O2 did not increase the O2 supply to any cerebral region except to the thalamus and colliculi after 60 min, whereas the O2 supply to the hypothalamus decreased and remained low. In group 2, the O2 supply was unchanged compared to the control period in all regions. These findings agree with previous observations during exposures to higher O2 pressures. In air after O2 exposure the acid-base chemistry remained normal. The fc and fb increased to higher levels than during the control period. The BPs remained high. The brain blood flows were increased, inducing elevated O2 supply to several brain regions compared to the control period. In conclusion, O2 supply to the central nervous system was found to be in the main unchanged during breathing of O2 at 101 kPa and 150 kPa.

Lung and respiratory impedance at low frequency during mechanical ventilation in rabbits

We have tested in eight rabbits the feasibility of measuring respiratory (Zrs) and lung (ZL) impedances in the low-frequency domain, including below the breathing frequency (fb), during conventional mechanical ventilation (CMV). The animals were tracheotomized and ventilated with a tidal volume (VT) of 20 ml at a fb of 1 Hz. The excitation signal was provided by a flow generator connected in parallel with the ventilator; it included six components ranging from 0.45 to 14.8 Hz, which met the neither-sum-nor-difference criterion of B. Suki and K. Lutchen (IEEE Trans. Biomed. Eng. 39: 1142-1151, 1992) to minimize the influence of nonlinearities. Zrs and ZL were also measured at the same mean lung volume and with the same excitation signal both during apnea and when the ventilator signal was replaced by a sine wave with the same VT and fb (SMV). The real parts (Re) of both Zrs and ZL, as well as the effective elastances, were significantly larger during apnea than during CMV and SMV over the whole frequency range. Re(Zrs) and Re(ZL) were similar during CMV and SMV above fb but they were lower during CMV at 0.45 Hz. The latter difference seems to be related to the presence of harmonics of fb and of additional frequency components due to pulse amplitude modulation. We conclude that, because of nonlinearities, it is feasible to measure Zrs and ZL during CMV only at and above fb.

Validity of Breathing Frequency to Monitor Exercise Intensity in Trained Cyclists

This study compared breathing frequency (fB) during a ventilation threshold (VT) test with fB during a simulated 40 km time trial (40TT) to assess whether fB can be used to monitor exercise intensity. Twenty-six male cyclists (mean +/- SD VO2max = 4.42 +/- 0274 l.min-1) performed an incremental VT ergometer test and a simulated 40TT on a set of wind-loaded rollers. During the 40TT, expired gas was collected for 3 min using open circuit spirometry at 10 km intervals. A significant correlation (r = 0.89; p < or = 0.05) was found between the fB threshold (VTf) and the gas exchange VT (VTg) (3.42 +/- 0.08 and 3.31 +/- 0.09 l.min-1, respectively). No differences were found in VO2 at the VTf vs. X VO2 (3.48 +/- 0.08 l.min-1) during the simulated 40TT. However, when fB in br.min-1 calculated from the VT test (32.5 br.min-1), was compared with fB during the 40TT (45.6 br.min-1), there was a significant difference. Ventilation, heart rate and the respiratory exchange ratio were all significantly higher during the 40TT. Although a significant relationship was found between the VT test and the 40TT for VTf measured in l.min-1 of VO2 (r = 0.66; p < or = 0.05), fB in br.min-1 obtained from the incremental test should not be used to identify exercise training intensity. These data suggest that during competition, trained athletes exercise at a higher fB than that determined when being tested, implying that fB in br.min-1 may not be a valid measurement of exercise intensity.

Plasma total CO2 and electrolytes: diurnal changes and effects of adrenaline, doxapram, rebreathing and transport

SummaryPre‐race testing for plasma bicarbonate is used in Australia to detect administration of large doses of bicarbonate or other alkalising agents. The rules specify upper limits for plasma TCO2 from 35 to 37 mmol/l, depending on State. There has been considerable speculation about physiological factors that may increase plasma total CO2 and lead to infringements of this rule. In order to address these purported influences, we measured body temperature (BT), heart rate (HR), haemoglobin concentration (Hb), packed cell volume (PCV), TCO2, potassium [K], sodium [Na], chloride [Cl] and breathing frequency (Fb) in 6 horses under the following conditions: rebreathing into a 3 litre bag for 90 s following respiratory stimulation with doxapram (0.5 mg/kg bwt i.v.); following excitement and during sweating induced by adrenaline (2.5 mg/kg bwt i.v.).We also evaluated whether significant diurnal variation existed in plasma electrolytes. There was no diurnal variation in sodium but potassium and chloride peaked in the evening and were lowest at early morning. TCO2 changes were also significant with peak values occurring before noon. Rebreathing produced transient marginal increases in TCO2 and potassium, declines in chloride and no change in sodium. The rise in TCO2 was from 29.6 ± 0.8 to 30.9 ± 1.4 mmol/l. Animals became markedly agitated by 90 s of rebreathing. Doxapram caused a 2‐fold increase in Fb, a small (&lt;1 mmol/l) increase in TCO2, marginal increases in sodium and potassium, but no change in chloride. Adrenaline caused marked sweating and anxiety in all horses and led to increased HR, sodium, chloride, PCV and Hb, caused decreased TCO2 (&lt;2 mmol/l), decreased chloride and had no consistent effect on BT.From these studies, we conclude that rebreathing, hyperpnoea induced by doxapram and sweating and excitement induced by adrenaline, in otherwise healthy horses, exerts only marginal effects on TCO2. Differences were significant for all measured electrolytes between horses, with magnitudes exceeding changes induced by experimental protocols. Mean TCO2 for individual horses ranged from 26.5 ± 0.3 to 33.8 ± 0.2 mmol/l in the adrenaline trial with similar ranges in other studies.

Ventilatory responses of horses to prolonged submaximal exercise

SummaryWhile prolonged submaximal exercise is associated with an increase in core body temperature, the role of ventilation in the dissipation of this heat load is unclear. We examined airway mechanics in 5 horses exercising on a treadmill at 40% V̇O2maxfor 60 min or until fatigued, in order to study the ventilatory response to prolonged low intensity exercise. Respiratory tract mechanics, pH and arterial blood gases were recorded at rest and at regular intervals during exercise. Mean ± s.d. run time was 51.7 ± 5.9 min. No changes in ventilatory mechanics were seen in the first 12–15 min of exercise. Mean breathing frequency (fb) did not change during the test (109 ± 11), however, tidal volume (VT) and fbvaried considerably in individual horses over the course of the run. Some animals freely interchanged their breathing pattern between shallow tachypnoea and regular tidal breathing with fbranging from 76 to 171. Minute ventilation was not affected by breathing pattern but increased from 935 ± 119 l/min after 12–15 min to 1365 ± 343 l/min at the end of exercise. This was associated with a rise in pulmonary arterial blood temperature (BT) from 39.2 ± 0.2°C to 41.8 ± 0.4°C and an increase in work of breathing (Wrm) from 214 ± 30 to 475 ± 122 kg/cm. Wrm/min/l and kg·min increased 1.98‐, 1.28‐ and 1.87‐fold, respectively, in the same period. VTand each expression of Wrmwere logarithmically correlated with BT. PCO2decreased from 41.2 ± 1.7 Torr after 12–15 min to 30.6 ± 1.3 Torr after 57–60 min, while pH increased from 7.43 ± 0.03 to 7.56 ± 0.03 in the same period. We conclude that while the thermoregulatory role of the equine respiratory system may be unclear, horses mount a concerted hyperventilatory response during prolonged submaximal exercise. This response may be associated with rises in core temperature and intermittent tachypnoea, is characterised by increases in Wrmand may be physiologically costly and inefficient.

Use of electrochemical impedance spectroscopy for the study of corrosion protection by polymer coatings

A discussion of the requirements for hardware and software necessary for collection and analysis of electrochemical impedance spectroscopy data for polymer coated metals is presented. Most authors agree that a simple model can describe the frequency dependence of impedance spectra for polymer coated metals exposed to corrosive environments. The water uptake of the coating can be estimated from the time dependence of the coating capacitance C c, The pore resistance R po depends both on the resistivity ρ of the coating and the disbonded area A d. The polarization resistance R P of the corroding area under the coating and the corresponding capacitance C dl both depend on A d. The breakpoint frequency method is discussed in detail and the dependence of the breakpoint frequency f b on ρ and A d is derived. In addition to f b other parameters can be obtained which depend on the ratio A d/ρ or only on A d or ρ. Since these parameters can be obtained at frequencies exceeding 1 Hz without the need for an analysis of the impedance spectra in the entire frequency region, this approach is considered especially useful for corrosion monitoring. The concepts proposed for the analysis and interpretation of EIS data for polymer coated metals are illustrated using data for Al alloys, Mg and steel exposed to NaCl. For an alkyd coating on cold rolled steel the time dependence of A d and ρ during exposure to 0.5 m NaCl has been determined qualitatively using the modified breakpoint frequency method.

Composition dependence of discontinuous magnetization in Ni1-xMgxFe2O4

The mean potential difference VB and the frequency FB of Bakhausen jumps were investigated for polycrystalline Ni1-xMgxFe2O4 where x=0, 0.2, 0.4, 0.8, 1.0. NiFe2O4 shows the lowest values of VB. The addition of Mg enhances the irreversible motion giving rise to higher values of VB and FB. When Mg content exceeds 0.4, the number of jumps begins to decrease. Mg addition affects the energetic situation of the domain walls.

Comparison of the reliability of two respiratory valves during maximal exercise testing

The change in respiratory volume during exercise because of the use of different types of respiratory apparatus has previously been reported in the literature. However, to our knowledge, there has been no report of the reliability of measurement for commonly used apparatuses. The purpose of this study was to compare the reliability of the Hans Rudolph 2700 NRB valve with the Vacumed Speak‐Easy Mask II during maximal exercise testing. Eight moderately trained college‐aged women performed two maximal graded exercise tests using each apparatus. Breath‐by‐breath measurements of pulmonary variables were collected and a moving point average displayed, every 15 seconds. A MANOVA (valve × trial × subject) revealed no significant difference (p > 0.05) in oxygen consumption, respiratory exchange ratio, rating of perceived exercise, minute ventilation (VE), tidal volume (Vt), or breathing frequency (fB) between the two pieces of equipment. Intraclass reliability of breath‐by‐breath measurements of VE, Vt, and fB was...