Open-circuit Method Research Articles

Alterations in cerebral blood flow and cerebrovascular reactivity during 14 days at 5050 m

Upon ascent to high altitude, cerebral blood flow (CBF) rises substantially before returning to sea-level values. The underlying mechanisms for these changes are unclear. We examined three hypotheses: (1) the balance of arterial blood gases upon arrival at and across 2 weeks of living at 5050 m will closely relate to changes in CBF; (2) CBF reactivity to steady-state changes in CO2 will be reduced following this 2 week acclimatisation period, and (3) reductions in CBF reactivity to CO2 will be reflected in an augmented ventilatory sensitivity to CO2. We measured arterial blood gases, middle cerebral artery blood flow velocity (MCAv, index of CBF) and ventilation () at rest and during steady-state hyperoxic hypercapnia (7% CO2) and voluntary hyperventilation (hypocapnia) at sea level and then again following 2–4, 7–9 and 12–15 days of living at 5050 m. Upon arrival at high altitude, resting MCAv was elevated (up 31 ± 31%; P < 0.01; vs. sea level), but returned to sea-level values within 7–9 days. Elevations in MCAv were strongly correlated (R2= 0.40) with the change in ratio (i.e. the collective tendency of arterial blood gases to cause CBF vasodilatation or constriction). Upon initial arrival and after 2 weeks at high altitude, cerebrovascular reactivity to hypercapnia was reduced (P < 0.05), whereas hypocapnic reactivity was enhanced (P < 0.05 vs. sea level). Ventilatory response to hypercapnia was elevated at days 2–4 (P < 0.05 vs. sea level, 4.01 ± 2.98 vs. 2.09 ± 1.32 l min−1 mmHg−1). These findings indicate that: (1) the balance of arterial blood gases accounts for a large part of the observed variability (∼40%) leading to changes in CBF at high altitude; (2) cerebrovascular reactivity to hypercapnia and hypocapnia is differentially affected by high-altitude exposure and remains distorted during partial acclimatisation, and (3) alterations in cerebrovascular reactivity to CO2 may also affect ventilatory sensitivity.

High Basal Metabolic Rate Is a Risk Factor for Mortality: The Baltimore Longitudinal Study of Aging

Despite longstanding controversies from animal studies on the relationship between basal metabolic rate (BMR) and longevity, whether BMR is a risk factor for mortality has never been tested in humans. We evaluate the longitudinal changes in BMR and the relationship between BMR and mortality in the Baltimore Longitudinal Study of Aging (BLSA) participants. BMR and medical information were collected at the study entry and approximately every 2 years in 1227 participants (972 men) over a 40-year follow-up. BMR, expressed as kcal/m(2)/h, was estimated from the basal O(2) consumption and CO(2) production measured by open-circuit method. Data on all-cause and specific-cause mortality were also obtained. BMR declined with age at a rate that accelerated at older ages. Independent of age, participants who died had a higher BMR compared to those who survived. BMR was a significant risk factor for mortality independent of secular trends in mortality and other well-recognized risk factors for mortality, such as age, body mass index, smoking, white blood cell count, and diabetes. BMR was nonlinearly associated with mortality. The lowest mortality rate was found in the BMR range 31.3-33.9 kcal/m(2)/h. Participants with BMR in the range 33.9-36.4 kcal/m(2)/h and above the threshold of 36.4 kcal/m(2)/h experienced 28% (hazard ratio: 1.28; 95% confidence interval, 1.02-1.61) and 53% (hazard ratio: 1.53; 95% confidence interval, 1.19-1.96) higher mortality risk compared to participants with BMR 31.3-33.9 kcal/m(2)/h. We confirm previous findings of an age-related decline of BMR. In our study, a blunted age-related decline in BMR was associated with higher mortality, suggesting that such condition reflects poor health status.

A Simple Mutual Coupling Compensation Technique in Array of Single-Mode Elements by a Weighted Mutual Coupling Matrix Based on the Impedance Matrix

High-resolution Direction-of-Arrival (DOA) estimation techniques for antenna arrays have been widely desired in many applications such as smart antennas, RF position location, and RFID system. To realize high-resolution capability of the techniques, precise array calibration is necessary. For an array of single-mode elements, a calibration matrix derived by the open-circuit method is the simplest one. Unfortunately, calibration performance of the method is not enough for the high-reslution DOA estimation techniques. In this paper, we consider problems of the calibration matrix derived by the method, and show that errors in the matrix can be effectively removed by an optimal diagonal weight coefficient. In the proposed compensation technique, the number of newly introduced parameters, or unknowns, is only one for an array of the identical elements. Performance of the simple compensation technique is verified numerically and experimentally.

Indirect calorimetry: methodology, instruments and clinical application

This review aims to identify the basic methods for accurately measuring a patient's energy expenditure in clinical nutrition practice by indirect calorimetry, and the impact upon a disease state of applying the results obtained. The open-circuit method is the most widely used in the majority of classical instruments for measuring energy consumption. Advances in gas exchange measurement have made this technique readily and precisely available at the bedside. Nevertheless, it is important to understand its intricate primary methodology for safe and correct application. The stress and activity factors should be carefully and specifically applied, and the respiratory quotient abandoned, for tailoring a patient's daily nutrition regimens. Caloric expenditure measured by indirect calorimetry coupled with the doubly labeled water technique introduced the concept of physical activity energy expenditure, which added to resting energy expenditure results in total daily energy expenditure. Compact modular and handheld devices have been introduced into the market, together with similar technology for evaluating exercise energy expenditure, making utilization easier, safer and precise. In the critically ill population, which is exposed to medical and surgical interventions, indirect calorimetry has greatly changed the practice of caloric administration, significantly reducing the total daily amount. In conclusion, one has to be careful when choosing devices, and understanding and clinically applying the results obtained by indirect calorimetry, bearing in mind that measured resting energy expenditure should be the daily caloric goal in order to diminish clinical morbidity.

Multiple-breath washout in preschool children – FRC and ventilation inhomogeneity

The open-circuit multiple-breath inert gas washout method is used to measure functional residual capacity and also to quantify ventilation distribution. The technique is readily applicable in preschool children as it requires quiet tidal breathing. Guidelines for data collection and interpretation in this age group will shortly be published by the European Respiratory Society and the American Thoracic Society.

Non-invasive measurement of cardiac output: Evaluation of new infrared absorption spectrometer

The mass spectrometer (MS) traditionally has been the instrument of choice for measuring cardiac output (Q (T)) non-invasively using the foreign gas uptake method. However, the size and cost of the MS has hampered widespread adoption of this technique outside of the laboratory. Here, we present results, from six normal human subjects at rest and during exercise, of simultaneous Q (T) measurements by an MS and a new, portable infrared (IR) device developed in our laboratories. These measurements are made using on the open-circuit acetylene uptake method. The IR device measures inspired and end-tidal concentrations of acetylene, sulfur hexafluoride, and carbon dioxide by IR absorption spectroscopy with a 10-90% response time of 43 ms; accurate measurements were made down to sample flow rates of 50 mL min(-1). Excellent correlation [Q (T)(IR)=0.98 Q (T)(MS), R(2)=0.94] was observed between instruments across the range from rest to heavy exercise. These results suggest that the IR device, which is small, light-weight, and rugged may enable the foreign gas uptake method to be used in clinical, field, and point-of-care settings for Q (T) measurement.

An open-circuit method for determining lung diffusing capacity during exercise: comparison to rebreathe

To avoid limitations associated with the use of single-breath and rebreathe methods for assessing the lung diffusing capacity for carbon monoxide (D(L)CO) during exercise, we developed an open-circuit technique. This method does not require rebreathing or alterations in breathing pattern and can be performed with little cognition on the part of the patient. To determine how this technique compared with the traditional rebreathe (D(L)CO,RB) method, we performed both the open-circuit (D(L)CO,OC) and the D(L)CO,RB methods at rest and during exercise (25, 50, and 75% of peak work) in 11 healthy subjects [mean age = 34 yr (SD 11)]. Both D(L)CO,OC and D(L)CO,RB increased linearly with cardiac output and external work. There was a good correlation between D(L)CO,OC and D(L)CO,RB for rest and exercise (mean of individual r2 = 0.88, overall r2 = 0.69, slope = 0.97). D(L)CO,OC and D(L)CO,RB were similar at rest and during exercise [e.g., rest = 27.2 (SD 5.8) vs. 29.3 (SD 5.2), and 75% peak work = 44.0 (SD 7.0) vs. 41.2 ml.min(-1).mmHg(-1) (SD 6.7) for D(L)CO,OC vs. D(L)CO,RB]. The coefficient of variation for repeat measurements of D(L)CO,OC was 7.9% at rest and averaged 3.9% during exercise. These data suggest that the D(L)CO,OC method is a reproducible, well-tolerated alternative for determining D(L)CO, particularly during exercise. The method is linearly associated with cardiac output, suggesting increased alveolar-capillary recruitment, and values were similar to the traditional rebreathe method.

Energy Expenditure Of Professional Soccer Players During Official Games

The existing information concerning the metabolic demands imposed upon Soccer players is sparse but this sport is usually considered an activity of high intensity. PURPOSE The purpose of the present study was to estimate the caloric expenditure of top level Brazilian professional Soccer players during official games of a regional championship. METHODS Nineteen professional Soccer players (24.2 ± 3.8yrs, 178.6 ± 6,0cm 74.5 ± 5.9kg and 10.2 ± 1.9% Fat) volunteered for the study. Individual energy expenditure (indirect calorimetry, open circuit method) versus heart rate (EE × HR) curves were developed while the subjects performed a graded run on a motor driven treadmill, starting at speeds of 7 ± 8 km/h with 2 km/h increments at every other three minutes of exercise. During five games, three to nine athletes wore heart rate recorder/transmitter belts. Later the recorded HR files were transferred into a computer. The total recording time was 1970 minutes. The player's average HR was then used to estimate his energy expenditure during the game, according to his EE × HR curve. RESULTS The individual EE values of the players averaged 11.34 kcal/min, ranging from 6.49 kcal/min to 16.87 kcal/min. The mean EE values for the five games were 11.28 ± 2.90, 11.38 ± 3.27, 10.92 ± 1,79, 11,82 ± 2.07, 11.48 ± 3.56 kcal/min. CONCLUSIONS Even though a very high inter-individual variability existed, the mean values during all games were similar. Research supported by: CNPq./CAPES

Energy Expenditure Of Professional Soccer Players During Official Games

The existing information concerning the metabolic demands imposed upon Soccer players is sparse but this sport is usually considered an activity of high intensity. PURPOSE The purpose of the present study was to estimate the caloric expenditure of top level Brazilian professional Soccer players during official games of a regional championship. METHODS Nineteen professional Soccer players (24.2 ± 3.8yrs, 178.6 ± 6,0cm 74.5 ± 5.9kg and 10.2 ± 1.9% Fat) volunteered for the study. Individual energy expenditure (indirect calorimetry, open circuit method) versus heart rate (EE × HR) curves were developed while the subjects performed a graded run on a motor driven treadmill, starting at speeds of 7 ± 8 km/h with 2 km/h increments at every other three minutes of exercise. During five games, three to nine athletes wore heart rate recorder/transmitter belts. Later the recorded HR files were transferred into a computer. The total recording time was 1970 minutes. The player's average HR was then used to estimate his energy expenditure during the game, according to his EE × HR curve. RESULTS The individual EE values of the players averaged 11.34 kcal/min, ranging from 6.49 kcal/min to 16.87 kcal/min. The mean EE values for the five games were 11.28 ± 2.90, 11.38 ± 3.27, 10.92 ± 1,79, 11,82 ± 2.07, 11.48 ± 3.56 kcal/min. CONCLUSIONS Even though a very high inter-individual variability existed, the mean values during all games were similar. Research supported by: CNPq./CAPES

Minimum norm mutual coupling compensation with applications in direction of arrival estimation

This paper introduces a new mutual coupling compensation method based on the minimum norm solution to an underdetermined system of equations. The crucial advantage over previous techniques is that the formulation is valid independent of the type of antenna element and provides good results in situations where signal strengths vary considerably. In using the matrix pencil algorithm to estimate the directions of arrival, the examples show that the proposed method results in significantly lower bias than the traditional open circuit method. The analysis of mutual coupling is also applied in the context of a code division multiple access communication system.

Solubility of eflucimibe in supercritical carbon dioxide with or without a co-solvent

Eflucimibe is a drug, which displays hypocholesterolemic and anti-atherosclerotic properties in animal models. The solubility of eflucimibe in supercritical carbon dioxide has been investigated with an apparatus based on an analytical open circuit method. Solubility values have been measured at 308.15 and 318.15 K in the pressure range 8–30 MPa. Solubility appears to be an increasing function of both temperature and pressure. The two co-solvents investigated, ethanol and dimethylsulphoxide, are found to significantly enhance the solubility. Solubility data are reported for the 308.15 K isotherm at different total pressures and different solvent/co-solvent ratios. The observed co-solvent effects can be explained not only by density effects, but by the effect of molecular interactions on the basis of compound solubility parameters.

Circadian patterns of breathing.

In the rat, a mostly nocturnal animal, activity, body temperature and metabolic rate increase during the dark hours of the day. Since all these variables are known to influence breathing, it is expected that also pulmonary ventilation (VE) will present a circadian pattern. In rats chronically instrumented for measurements of body temperature and activity by telemetry, carbon dioxide production and oxygen consumption (V(O(2))) were measured continuously for several days by an open-circuit method, while VE was monitored by a modification of the barometric technique. Tidal volume, frequency, and VE increased in the dark (D) compared to the light (L) hours, with minor L-D differences in VE/V(O(2)). L-D differences in activity were not responsible for the circadian pattern of VE. Both in hypoxia and in hypercapnia the degree of hyperventilation (percent increase in VE/V(O(2))) was essentially independent of the time of the day, despite the fact that in hypoxia, differently from hypercapnia, the amplitude of the circadian pattern of all variables decreased, activity being the least affected, and body temperature the most. These effects of hypoxia, which occurred before and after sino-aortic denervation and did not compromise the period of the biological clock, may be mediated by the hypothalamic thermoregulatory centers. The data of these experiments and of others reviewed in this article indicate that (1) breathing and its control mechanisms accompany the daily oscillations of numerous physiological variables, and (2) the advantages of a biological clock do not compromise the adequacy of the hyperventilatory responses to chemical challenges.

EFFECTS OF AEROBIC EXERCISE ON CARDIOVASCULAR RESPONSES DURING THE COLD PRESSOR TEST IN AFRICAN AMERICANS

Previous studies have shown that during the cold pressor test (CPT) an increase in systolic blood pressure (SBP) ≥ 25 mm Hg above baseline is associated with an increased risk of developing hypertension(HT). We investigated the effects of aerobic exercise training on cardiovascular reactivity (CR) during the CPT in normotensive college-aged African American (AA) males. Ten aerobically-trained males and ten similar non-trained males served as subjects. The CPT consisted of immersing the foot in ice water (5°C) for two minues. The exercise training protocol consisted of eight weeks of cycling at 70% peak oxygen uptake (VO2peak), three days/week for 30 minutes/session. Oxygen uptake was determined using the open-circuit method. Blood pressure (BP) was assessed noninvasively using the continuous method of tonometry. Cardiac output(CO) and stroke volume (SV) were measured using impedance cardiography. Total peripheral vascular resistance (TPR) was calculated using the mean arterial BP (MABP) and CO values. Cardiac neural activity (CNA) was assessed by time domain and frequency domain analysis of heart rate variability. CR was determined by contrasting differences in resting measures and those recorded during the CPT. After training, VO2peak in the trained group increased 16% (pre-trained = 33.6 ± 2 vs. post-trained = 40.1 ± 1 ml kg−1 min−1) (P < 0.05). No significant change in VO2peak was found in the control group. In the exercise-trained group SBP, diastolic BP, MABP, heart rate, SV, CO, and TPR differences tended to be lower than before training (p > 0.05). We observed that in the exercise-trained group pre and post-trained SBP difference values were 27.4 ± 4 and 21.7 ± 6 mm Hg respectively. This magnitude of decrease in the post-trained SBP difference score is of clinical significance since it is indicative of a reduction in the risk for developing HT. In the control group there were no changes in the measured CR difference scores. Analysis of difference scores for CNA determined by assessing R-R interval (SDNN) and spectral analysis illustrated no difference in the exercise-trained and non-trained groups. In this study exercise training had no significant effect on the CR to behavioral stress. However, our data are of clinical significance since the training program used in this study produced a difference in the SBP response to stress. A change such as this may reduce the risk of HT in AA. Supported by NIH GM-08016.

Single-layer type microwave absorber made of magnetic-dielectric composite material

It has been shown experimentally in a single-layer microwave absorber that a matching frequency can be adjusted in the frequency range from 7.7GHz to 9.4GHz. A reflection loss above -40dB or more in maintained by changing the mixing ratio of magnetic and dielectric material in the composite. Complex relative permeability and permittivity coefficients were measured using a terminative short and open circuit method. Theoretical calculations clarified the relations among these constants, matching frequency and the reflection loss.

Ventilatory behavior and metabolism in two strains of obese rats

This study examined differences in metabolism and ventilatory responsiveness in the Zucker (Z) and Koletsky (K) rat which each carry a different recessive mutation of the leptin receptor gene. The Null hypothesis was that the obese (homozygous) rats from the strains would not differ among the variables assessed. Male and female rats of obese and lean phenotypes were studied, with 5–6 animals in each group. Animals of the same age were assessed for ventilation and metabolism by whole-body plethysmography and the open circuit method. During quiet wakefulness, each animal was exposed to 5 min presentations of: room air; 10% O2/bal N2; 100% O2; room air, and 7% O2/93% O2. Differences in metabolism, independent of phenotype included: K<Z for RQ in both lean and obese rats; oxygen consumption in obese K>Z females and Z>K for males; CO2 production in obese K<Z. Some differences in breathing were independent of obese phenotype, with K<Z in frequency (f) for air (P<0.02), and persisting with each chemical challenge: for hypoxia (P<0.01); hyperoxia (P<0.002); and hypercapnia (P<0.001). Factors dependent on obesity were K<Z for minute ventilation (P<0.01), and minute ventilation/CO2 production (P<0.001). Ventilatory chemoresponses were independent of phenotype, with Z>K often for every challenge (P<0.001). A higher f and Ve in Z compared with K rats was present in both genders, and persisted with each challenge. In conclusion, obese rats from these two strains do not breathe the same, even when age, weight, body mass index, and diet are alike. We conclude that that factors other than fat accumulation contribute to the expression of respiratory control and ventilation in obesity in the rat.

Circadian patterns of breathing

Life has evolved on a planet with rotation around itself and the Sun. A fundamental mechanism of adaptation is the capacity of time-keeping, such that daily and seasonal events can be anticipated and prepared for. Many physiological variables have a circadian pattern, which in mammals is controlled by a biological clock with its own period of 24 h, placed in the suprachiasmatic nucleus of the hypothalamus. Among the most studied are the patterns of activity (Act), body temperature (Tb) and metabolic rate (oxygen consumption, VO2, and carbon dioxide production, VCO2). In the rat, a mostly nocturnal animal, all these variables increase during the dark hours of the night. Since all of them are known to influence pulmonary ventilation (VE), it is expected that also the breathing pattern, and possibly its controlling mechanisms, will present circadian oscillations. In rats chronically instrumented for measurements of Tb and Act by telemetry, VO2 and VCO2 were measured continuously for several days by an open-circuit method, while VE was monitored by a modification of the barometric technique [1]. All variables of the breathing pattern (tidal volume VT, frequency f, and VE) increased in the dark (D) compared to the light (L) hours, with minor L-D differences in VE/VO2. The L-D differences in VE, and in all other parameters, persisted when comparisons between the L-D phases were made for the same level of either very low or very high Act, indicating that the oscillations in breathing pattern do not depend on Act. Indeed, ongoing experiments on rats in which circadian patterns are disturbed by sudden phase shifts between D and L, indicate a very poor correlation between levels of Act and breathing, which is much better correlated with Tb. Sustained hypoxia (10% O2) blunted the amplitude of the circadian oscillations of all variables, Act being the least affected, and Tb the most [2,3]. In constant L ('free running' conditions), in which the natural period of the clock is unmasked, the effects of hypoxia on the Tb oscillations were not accompanied by a change in the clock period [2], and were not abolished by sino-aortic denervation [4], suggesting that hypoxia does not affect the clock itself but acts elsewhere centrally to affect the circadian patterns, possibly at the level of the hypothalamic thermoregulatory centers. Alterations in Tb patterns were also observed in men living intermittently at high altitude [5]. Preliminary observations in adult rats seem to indicate that the hypoxic effects on the oscillations of Tb are less marked in females than males. Sustained hypercapnia had minimal effects on Tb, activity, VO2 and VCO2, and, as observed during sustained hypoxia [3], the degree of hyperventilation (percent increase in VE/VO2) was essentially independent of the time of the day. In conclusion, the existence of a biological clock implies the oscillations of numerous variables known to affect the breathing pattern; indeed, VT, f, and VE present daily oscillations. The hyperventila-tory responses to hypoxia and hypercapnia, however, remain constant, despite the fact that hypoxia and hypercapnia can have major and differential effects on numerous physiological variables and their circadian patterns.

Lack of integrative control of body temperature after capsaicin administration.

BackgroundBody temperature is usually regulated by opposing controls of heat production and heat loss. However, systemic administration of capsaicin, the pungent ingredient of hot peppers, facilitated heat production and heat loss simultaneously in rats. We recently found that the capsaicin-induced heat loss and heat production occur simultaneously and that the biphasic change in body temperature is a sum of transient heat loss and long-lasting heat production. Moreover, suppression of the heat loss response did not affect capsaicin-induced heat production and suppression of heat production did not affect capsaicin-induced heat loss. These observations suggest the independent peripheral mechanisms of capsaicin-induced thermal responses. Thus, the capsaicin-induced thermal responses apparently lack an integrated control.MethodsMale Wistar rats were maintained at an ambient temperature of 24 ± 1°C on a 12 h on-off lighting schedule at least for two weeks before the experiments. They were anesthetized with urethane (1.5 g/kg, i.p.) and placed on a heating pad, which was kept between 29 and 30 °C. Skin temperature(Ts) was measured with a small thermistor, which was taped to the dorsal surface of the rat’s tail, to assess vasoactive changes indirectly. Colonic temperature(Tc) was measured with another thermistor inserted about 60 mm into the anus. O2 consumption was measured by the open-circuit method, and values were corrected for metabolic body size (kg0.75). Capsaicin (Sigma) was dissolved in a solution comprising 80% saline, 10% Tween 80, and 10% ethanol, and injected subcutaneously at a dose of 5 mg/kg. Each rat received a single injection of capsaicin because repeated administration of capsaicin renders an animal insensitive to the subsequent administration of capsaicin. Laminectomy was performed at the level of the first and second cervical vertebrae to expose the cervical spinal cord for sectioning. The brain was transected at 4-mm rostral from the interaural line with an L-shaped knife.ResultsAfter administration of capsaicin, O2 consumption increased from 13.5 ± 0.4 mL/min/kg0.75 at 0 min to a peak of 15.9 ± 0.4 mL/min/kg0.75 at 71 min and gradually declined but remained higher than the basal value until the end of the 4-h observation period. Ts also immediately increased from 27.7 ± 0.2 °C to 31.9 ± 0.3 °C at 39 min, and it returned to the baseline level within 90 min after the capsaicin administration. Tc initially decreased from 37.1±0.1 °C to 36.8 ± 0.2 °C at 43 min and then gradually increased over the baseline level and remained at 37.6 ± 0.2 °C until the end of the experiment, in spinalized rats, the capsaicin-induced increase in O2 consumption was largely attenuated, while the basal O2 consumption was similar to that of control rats. The basal Ts of spinalized rats was 32.4 ± 0.3 °C, which was higher than that of control rats. Capsaicin increased Ts by less than 1 °C, and Tc did not change after the capsaicin administration. O2 consumption of decerebrated rats was statistically higher than that of control rats after the injection of capsaicin. However, capsaicin did not increase Ts, showing a lack of a vasodilatory response. Decerebration between the hypothalamus and midbrain prevented the capsaicin-induced heat loss but not the heat production response.ConclusionThese results show that the capsaicin-induced heat production and heat loss are controlled separately by the brainstem and by the forebrain, respectively, and suggest that the body temperature regulation is performed without an integrative center.

A study on measuring the electromagnetic parameters of chiral materials

In this paper, a new method for simultaneously measuring the complex permittivity, complex permeability and complex chirality parameter of chiral materials in free space is presented. One has to measure the rotation angle, the axial ratio and the complex reflection coefficients of short-circuit (sample is backed with metal) and open-circuit (sample is not backed with metal) samples. Here, this method is named the free space short-circuit and open-circuit method.

Effects of prolonged bed rest on cardiovascular oxygen transport during submaximal exercise in humans.

The hypothesis was tested that prolonged bed rest impairs O2 transport during exercise, which implies a lowering of cardiac output Qc and O2 delivery (QaO2). The following parameters were determined in five males at rest and at the steady-state of the 100-W exercise before (B) and after (A) 42-day bed rest with head-down tilt at -6 degrees: O2 consumption (VO2), by a standard open-circuit method; Qc, by the pressure pulse contour method, heart rate (fc), stroke volume (Qh), arterial O2 saturation, blood haemoglobin concentration ([Hb]), arterial O2 concentration (CaO2), and QaO2. The VO2 was the same in A and in B, as was the resting fc. The fc at 100 W was higher in A than in B (+17.5%). The Qh was markedly reduced (-27.7% and -22.2% at rest and 100 W, respectively). The Qc was lower in A than in B [-27.6% and -7.8% (NS) at rest and 100 W, respectively]. The CaO2 was lower in A than in B because of the reduction in [Hb]. Thus also QaO2 was lower in A than in B (-32.0% and -11.9% at rest and at 100 W, respectively). The present results would suggest a down-regulation of the O2 transport system after bed rest.

NUMERICAL CALCULATION OF DEMAGNETIZING FACTOR FOR PERMANENT MAGNET

Recently, rare earth magnets with high coercive force such as Nd‐Fe‐B magnets have been developed. When the magnetic characteristic (M‐H curve) of such a strong magnet is measured, the conventional closed magnetic circuit method using an electromagnet cannot be applicable due to the magnetic saturation of the yoke. Therefore, the open magnetic circuit method has been proposed in which high magnetic fields are generated by using a superconducting or a pulsed magnet. In this method, the correction for demagnetizing field is required. The correction can be done using the demagnetizing factor which is a function of the shape and M‐H curve. The conventional studies take into account only the shape.