bluuebunny/crossref_metadata_2025 huggingface dataset:
A noncontact method for three-dimensional analysis of vascular elasticity in vivo and in vitro
Authors: Fronek K. , Schmid-Schoenbein G. , Fung Y. C.
Published: December 2017

A new method is described to measure the deformation of the blood vessel wall simultaneously in longitudinal and circumferential directions. This information is of paramount importance for further characterization of the elastic properties of the arterial wall. The new method consists of a closed-circuit TV system in conjunction with a video dimension analyzer (VDA). The VDA utilizes the video signal from the TV camera and forms a DC voltage proportional to the distance between two selected points in the scene. The resulting analog voltage, calibrated in dimensional units, is recorded. Dimensional changes in two directions, due to intraluminal pressure oscillations, are tracked continuously. The measurement can be performed in vivo on exposed vessels as well as in vitro on excised specimens. Distortion caused by the end effects is completely eliminated. For further data analysis, the wall thickness of the artery is determined microscopically. Stress and strain relationship in longitudinal and circumferential directions is calculated for every intraluminal pressure change. This approach yields data on mechanical properties of the vessel wall in a far more physiological way than the hitherto used direct-contact techniques.
Measurement of brain oxygen utilization with radioactive oxygen-15: experimental verification
Authors: Raichle M. E. , Grubb R. L. , Eichling J. O. , Ter-Pogossian M. M.
Published: December 2017

This study was designed to provide direct experimental evidence in support of the method employing radioactive 15O-tagged hemoglobin for the in vivo and regional measurement of the cerebral oxygen utilization rate (CMRO2). This was accomplished by simultaneously measuring in vivo the mean CMRO2 in monkeys and human beings by the 15O method and a direct appeal to the Fick principle using measured arteriovenous oxygen differences of brain. The correlation between the 2 methods was excellent, with a correlation coefficient of 0.90 (P less than 0.001) in monkeys and 0.88 (P less than 0.001) in human beings.
Alveolar-capillary CO2 and O2 gradients due to uneven hematocrits
Authors: King T. K. , Mazal D.
Published: December 2017

The effect of uneven hematocrit of the blood perfusing the different pulmonary capillaries on gas exchange in the lung was studied in vitro. Venous blood was separated anaerobically into plasma and red cell fractions, arterialized in separate tonometers, and finally reconstituted anaerobically. This simulated the effect of complete separation of plasma and red cells on pulmonary gas exchange. The reconstituted blood had a significantly higher carbon dioxide tension and a lower oxygen tension compared with whole blood similarly arterialized. Experiments in which plasma and red cells were incompletely separated yielded qualitatively similar results; the changes in gas tensions were smaller but still significant. While the degree and extent of separation of plasma and red cells in the pulmonary capillary in vivo is uncertain, direct observation and hemodynamic consideration suggest it must occur to some extent. Thus unevenness in the hematocrit of the perfusing pulmonary capillary blood is a mechanism in the genesis of the alevolar-arterial gradients which should be considered in addition to the known mechanisms of uneven ventilation-perfusion ratios and diffusion defects.
Sweating responses to central and peripheral heating in spinal man
Authors: Downey J. A. , Huckaba C. E. , Kelley P. S. , Tam H. S. , Darling R. C. , Cheh H. Y.
Published: December 2017

Studies of central and peripheral heating of a resting spinal man (T6) were performed under various ambient temperatures (20–34 degrees C). It was found that at a constant core temperature, sweating could not be initiated by sentient skin heating alone, but skin cooling alone did produce a rapid decrease in sweating response. Central heating alone induced sweating responses and the central temperature thresholds of sweating were inversely related to the ambient (sentient skin) temperatures. The local and mean sweating rates were found to be linearly related to the core temperature. The slopes of local sweating rates versus the core temperature vary increasingly with the following locations: chest, forearm, and forehead; but the slopes of mean sweating rates versus core temperature were essentially constant.
Relationship of AaDO2 TO AIRWAY PCO2 in dog lungs
Authors: Ingram R. H. , Finlay G. D. , Bradford J. M.
Published: December 2017

We measured the arterial Po2 and AaDo2 in open-chest dogs respired with air and with 5% CO2 in air at various lung volumes using a constant hyperventilatory pattern. The AaDo2 was an inverse function of lung volume with both air and 5% CO2 and was also an inverse function of both alveolar and arterial Pco2 values except at quite high lung volumes. There were two series of closed-chest experiments. In the first series, ventilation was varied to produce alveolar Pco2 and Po2 changes. In the second series, the dogs were hyperventilated at a constant rate and Pco2 was varied by adding CO2 with alveolar Po2 levels kept relatively constant. In both series the AaDo2 was inversely related to Pco2. We conclude that, in dogs, the AaDo2 is independent upon the Pco2 and speculate that this may be related to the effect of CO2 on collateral ventilation, although the Bohr effect may account for some of the dependence.
Closing volumes in man immersed to the neck in water
Authors: Bondi K. R. , Young J. M. , Bennett R. M. , Bradley M. E.
Published: December 2017

Closing volumes (CV), along with residual volume (RV), vital capacity (VC), along with residual volume (RV), vital capacity (VC), and expiratory reserve volume (ERV) were determined in 10 subjects in the dry and while immersed to the neck in water. Closing volumes during immersion increased 41.3% (P less than 0.001) over dry values while RV decreased 9.35% (P less than 0.001) and VC decreased 9.94% (P less than 0.001). The large decrease of 71.3% (P less than 0.001) in ERV resulted in the impingement of closing capacity (CV + RV) on the tidal volume in 9 out of 10 subjects. We interpret this to mean that airway closure occurs during tidal ventilation in immersed subjects and may result in impaired gas exchange. When tourniquets were applied to all four limbs during immersion closing volumes increased only 32.1%, but increased to 64.3% when they were removed. If engorgement of peribronchial vessels predisposes airways to collapse, a reduction of plasma volume during an extended period of immersion might lessen this possibility. In a series of long term (2.5-h) immersion experiments where moderate reductions (-10 to -7%y in plasma volume were observed, we found, however, no correlative changes in closing volume.
Skeletal muscle enzyme alterations after sprint and endurance training
Authors: Hickson R. C. , Heusner W. W. , Van Huss W. D.
Published: December 2017

Specifically designed programs of sprint and endurance running were used to determine how different types of training affect enzyme activities in selected energy metabolism pathways. Three types of rat skeletal muscle were studied. After 8 wk of training, small but significant decreases in lactate dehydrogenase activity (15%) were found in the soleus and white vastus lateralis muscles of the sprint animals. Decreased levels of phosphoglucomutase and lactate dehydrogenase (approx. 20%) of the white vastus lateralis muscles of the endurance group were observed at the same time. By 16 wk of training, fumarase activity increased approximately twofold in the white vastus muscles and 45% in the soleus and plantaris muscles of the endurance group. Similarly, increased fumarase activity (42%) was seen in the soleus muscles of the sprint group. In all muscles, phosphoglucomutase and lactate dehydrogenase activities generally were lower in the endurance animals than in the control animals. No significant differences were found between the sprint and endurance groups at either or sixteen weeks of training. These results suggest that similar enzyme adaptations occur over time with both types of training.
Effect of indomethacin and atropine in experimental asthma in conscious guinea pigs
Authors: Michoud M. C. , Fraser R. S. , Pare P. D. , Hogg J. C.
Published: December 2017

Pulmonary mechanics were measured in unanesthetized guinea pigs sensitized to horseradish peroxidase (HRP) before and during two aerosolized challenges of this antigen. During the first challenge the pulmonary resistance increased in all animals. Prior to second challenge the animals received either atropine (0.2 mg/kg) or indomethacin (10 mg/kg) intraperitoneally. We found that during the second challenge the indomethacin group had an increase in pulmonary resistance slightly greater or similar to that during the first exposure to the antigen, while the animals treated with atropine had a significantly diminished response (P less than 0.05). In five guinea pigs sensitized to HRP but challenged with a nonspecific aerosal made up of rabbit albumin, we found that pulmonary resistance increased in some animals and that this increase could be partially blocked by atropine. These results show that indomethacin has no effect on this model of allergic airways disease. They also confirm the importance of the vagus nerves in allergic bronchoconstriction and in addition show that nonspecific hyperirritability can be induced in some animals by immunization.
Respiratory load compensation in awake and sleeping dogs
Authors: Phillipson E. A. , Kozar L. F. , Murphy E.
Published: December 2017

We have investigated immediate and progressive ventilatory responses to external elastic loads in five dogs with cervical vagal loops. Three dogs were studied while awake (W) and during non-REM sleep (S); the other two during barbiturate anesthesia (A). Elastic loads were applied at the end expiration for 1–6 breaths by having the dogs breathe from a rigid container (partial load) or against an occluded airway (infinite load). “Effective” elastance (EE) was determined from the tidal volume (VT)-tracheal pressure relationships of the unloaded, partially loaded, and infinitely loaded breaths. Passive thoracic elastance during W and S averaged 16.7 cmH2O/1. EE averaged 55.8 cmH2O/1 during W, 54.7 during S, and 59.5 during A. Vagal blockade (VB) induced large changes in VT but no change in EE in W or S; during A, EE decreased 37.5%. With sustained loading (partial) there was a progressive increase in VT but a corresponding increase in chemical (primarily hypoxic) respiratory drive, so that EE remained constant during five loaded breaths. VB augmented the progressive increase in VT during W or S but virtually abolished the increase in A. Thus the responses to elastic loads in W and S are similar and independent of conscious reactions or vagal influence; responses during A differ considerably. “Progressive load compensation” is a reflection of increasing of increasing chemical drive and not of progressive changes in EE.
Visceral blood flow distribution during exercise to exhaustion in conscious dogs
Authors: Sanders T. M. , Werner R. A. , Bloor C. M.
Published: December 2017

We measured changes in organ blood flow (OBF) distribution and systemic hemodynamics in 9 dogs running 5–13 km/h during steady-state (SS) and exhaustive (EE) exercise on a treadmill at 8–15% grade for an average of 35 min. SS was defined when a heart rate (HR) of 80% maximum was attained and when HR was constant for 5–8 min. EE was defined as when the dog collapsed, unable to run longer. We measured heart rate, mean aortic pressure, cardiac output, and stroke volume via implanted probes and catheters. All hemodynamic parameters rose significantly (P less than 0.05) with exercise. Stroke volume and aortic pressure did not rise above SS levels during EE. OBF, determined with microspheres, to the liver, stomach, and intestines declined during SS and returned to control levels during EE. OBF to the kidneys and pancreas was not significantly changed by either SS or EE. OBF to the spleen declined progressively with SS and EE. We concluded that 1) the effect of exercise on OBF depends on the severity of exercise, emphasizing the need to quantify work loads in exercise studies, and 2) the splanchnic organs do not respond homogeneously to exercise and that this response is not adequately described by % of CO assessments.
Gas transport in a model derived from Hansen-Ampaya anatomical data of the human lung
Authors: Paiva M. , Lacquet L. M. , van der Linden L. P.
Published: December 2017

The anatomical data of the human lung published by Hansen and Ampaya are used in a model of gas transport in the lung. The Bohr dead space is calculated from solutions of a transport equation where diffusivity is given by an empirical formula obtained by Sherer et al. A satisfactory agreement is found with experimental data obtained from simultaneous washouts of H2 and SF6 for respiratory frequencies ranging between 15 and 60 min-1 and tidal volumes between 200 and 1,800 ml. The results support the idea that molecular diffusion is the main but not the only physical phenomenom which intervenes in gas mixing during breathing.
Sex and age differences in pulmonary mechanics in normal nonsmoking subjects
Authors: Gibson G. J. , Pride N. B. , O'cain C. , Quagliato R.
Published: December 2017

Maximun flow-volume, static pressure-volume, and maximum flow static recoil curves of three groups of nonsmoking, normal subjects (young men, youngwomen, elderly women) were used to assess age and sex differences in pulmonary mechanics. No significant sex differences in maximum flow were seen butthe young men showed higher lung recoil pressures at full inflation. When the influence of the inspiratory muscles and chest wall was excluded by exponential extrapolation of the pressure-volume curves to a maximum volume thebulk elastic properties of the lungs of young men and women appeared identical. Loss of maximum expiratory flow at low lung volumes and of lung recoilpressure occurred with age in nonsmoking women in whom emphysema should be minimal and therefore indicate true physiological effects of aging. The changes in pulmonary mechanics with age are consistent with an increase in unstressed dimensions and loss of elastic recoil of both alveoli and airways.
Age and sex differences in lung elasticity, and in closing capacity in nonsmokers
Authors: Bode F. R. , Dosman J. , Martin R. R. , Ghezzo H. , Macklem P. T.
Published: December 2017

Static volume-pressure characteristics of the human lung, closing capacity (CC), closing pressure, and subdivisions of lung volumes were measured in 66 adult nonsmokers, aged 24–58 yr. There were systemic differences between the sexes as well as with age. Young females had less elastic recoil at any lung volume than young males. However, males lost elastic recoil with age faster than females so that in the older age groups the recoil was similar. There were no significant changes in compliance over the volume range containing most values of CC in either males or females. By comparing the age regression of CC and of elastic recoil pressures at 40 and 50% TLC we conclude that the increase in CC with age in males was attributable almost entirely to loss of recoil. In females none of the increase in closing capacity with age was attributable to loss of recoil. By exclusion, it is probably attributable to a change in the intrinsic properties of small airways or an increase in the pleural pressure gradient with age.
Cold-induced shivering in men with thermoneutral skin temperatures
Authors: Buguet A. G. , Livingstone S. D. , Reed L. D. , Limmer R. E.
Published: December 2017

Twenty-two male Caucasians, aged 20–47 yr, were exposed in a cold room to air temperatures of -33 degrees C while lying in sleeping bags for 2 h. Skin and rectal temperatures as well as electromyographic activity of the chin, forearm, and thigh, were recorded. Shivering occurred in all the subjects, even though skin temperatures were maintained between 31 and 33 degrees C. It is suggested that a counter-current heat exchange occurs whereby the warm blood of the common carotid artery is cooled by cool venous blood in the jugular veins. This cooled arterial blood, in irrigating the hypothalamus, causes shivering.
Respiratory adaptations in burrowing pocket gophers from sea level and high altitude
Authors: Lechner A. J.
Published: December 2017

To examine the adaptations to low O2 and high CO2 among fossorial and nonfossorial rodents, hematological parameters were determined for laboratory rats, the valley pocket gopher (Thomomys bottae) from 250 m, and the mountain pocket gopher (T. umbrinus melanotis) from 3150 m. Hematocrit, hemoglobin concentration, and O2 capacity were higher in pocket gophers than in rats. Blood PO2 at 50% saturation and pH 7.4 was 33 mmHg for both gophers and 39 mmHg for rats. Bohr factors for all three rodents were similar (-0.55 to -0.61) but buffer value, delta log PCO2/delta pH, was -2.54 for T. umbrinus, -1.97 for T. bottae, and -0.98 for Rattus. Concentrations of total acid-soluble phosphates were 50–75% higher in gophers than in rats, while bicarbonate values were within the normal mammalian range. All three rodents had similar myoglobin concentrations in cardiac muscle. Myoglobin concentrations were significantly higher in skeletal muscles (diaphragm, gastrocnemius) of T. umbrinus when compared to T. bottae, and significantly higher in both gophers when compared to rats. These differences may constitute important adaptations to the hypoxia and hypercapnia in burrows; certain of these factors in pocket gophers respond to the additional stress of high altitude hypoxia.
Maximal oxygen uptake during exercise with various combinations of arm and leg work
Authors: Bergh U. , Kanstrup I. L. , Ekblom B.
Published: December 2017

Oxygen uptake (VO2) was determined in 10 males during the following types of maximal exercise (work time: about 5 min): uphill running, bicycling, arm work (cranking), and combined arm work and bicycling (A + L). The A + L exercise was performed in four different ways, the arms doing 10%, 20%, 30%, or 40% of the same total rate of work; and also with the maximal bicycle work load plus either maximal or submaximal arm work. VO2 was the same in running as in all types of A + L exercise, except when the arm work load was 10% and 40% of the total rate of work, where VO2 was 2.5% (P less than 0.05) and 9.4% (P less than 0.001) lower, respectively. Bicycle VO2 was lower than VO2 in running but equal to A + L VO2 when arm work intensity was 40% of the total rate of work. It is concluded that VO2 during maximal exercise a) to a certain extent depends on the exercising muscle mass, b) is lower than the oxygen-consuming potential of the muscles involved in A + L exercise, and c) in A + L exercise is influenced by the ratio of arm work to total rate of work and the subject's fitness for arm work and bicycling.
Uteroplacental blood flow during hyperthermia with and without respiratory alkalosis
Authors: Oakes G. K. , Walker A. M. , Ehrenkranz R. A. , Cefalo R. C. , Chez R. A.
Published: December 2017

The effect of induced maternal hyperthermia (1.5 degrees C rise over 60 min) on the uterine and umbilical circulations was examined in two groups of chronically instrumented pregnant sheep. Hyperventilation occurred in both groups. In the group in which the resultant respiratory alkalosis was untreated (N = 5), uterine blood flow decreased to 53 +/- 3% (mean +/- SE; P less than 0.01) of control at maximal maternal temperature. Umbilical blood flow also decreased 30 +/- 6% (P less than 0.01) below control levels. In the other group, normocapnia was maintained (N = 4). Uterine blood flow decreased in this group to 75% +/- 2% (P less than 0.01) of control levels, butumbilical blood flow did not significantly change. There was no significantchange in maternal or fetal mean arterial pressure during hyperthermia ineither group. Thus, maternal hyperthermia per se results in a significant decrease in uterine blood flow primarily through an effect on uterine vascularresistance, but without a concomitant change in umbilical blood flow.
Influence of muscular development, obesity, and age on the fat-free mass of adults
Authors: Womersley J. , Durnin J. V. , Boddy K. , Mahaffy M.
Published: December 2017

Body fat and the fat-free mass (FFM) were estimated in 36 men and 43 women deliberately chosen to represent a variety of physical types; these were 1) young sedentary, 2) “muscular,” 3) younger obese, 4) older obese, and 5) older nonobese individuals of both sexes. The body fat and the FFM were estimated from measurements of body density (by total immersion in water, measurement being made of the residual volume of air present in the lungs at immersion) and from measurements of total body potassium (using a whole-body monitor to assess the natural 40K isotope present in the body). The muscular men and women and the younger obese men and women had a considerably greater FFM and thus had greater quantities of potassium than the corresponding sedentary groups. There were significantly different estimates of the FFM calculated from density and from total body K in three groups, the sedentary young men, the muscular, and the younger obese women. The density and the potassium content of the FFM appear to decline with obesity and aging. Muscular development is associated with a decrease in the density but an increase in the potassium content of the FFM.
Correction for cardiac output calculations by the nitrous oxide technique
Authors: Wagner J. A. , Bedi J. F. , Horvath S. M.
Published: December 2017

Calculations of cardiac output using the N2O technique as described by Becklake et. al. (J. Appl. Physiol. 17: 579, 1962) result in spurious valueswhen barometric pressure or body temperature deviates from 760 Torr or 37.0degrees C, respectively. Nitrous oxide (N2O) uptake (VN2O) must be corrected to standard pressure, dry at 37.0 degrees C.
Physiological and behavioral reactions to repeated tail cooling in the white rat
Authors: Eide R.
Published: December 2017

The purpose of the study was to examine a) the effect of local cooling on the metabolic rate, b) the effect of metabolic rate on the peripheral circulation, and c) acclimation to local cooling. After habituation to the experimental situation, 10 white rats had their tails exposed to ice water for 40 min/day for 37 days. Metabolic rate and tail temperature were measured. There was a conspicuous increase in oxygen consumption during the first 10 min of each cold exposure. This increase did not change significantly through the series. The metabolic rate during cooling was significantly reduced in the last half of the series. Tail temperature was significantly influenced by metabolic rate and increased significantly from the beginning of the series to the middle, and decreased from the middle to the end. Time of onset of the cold-induced vasodilatation decreased in the middle of the series and increased again at the end. These paradoxical findings are believed to be due to interplay between orienting reactions and habituation. It is pointed out that habituation may counteract acclimation.
Role of the carotid bodies in the heart rate response to breath holding in man
Authors: Gross P. M. , Whipp B. J. , Davidson J. T. , Koyal S. N. , Wasserman K.
Published: December 2017

To investigate the role of the carotid bodies in regulating the bradycardia of breath holding in man, we studied heart rate (HR) responses to prolonged breath holding (BH) in five asymptomatic asthmatic patients whose carotid bodies had been resected (CBR). Seven normal subjects served as controls. BH experiments were randomly initiated with single breaths of 100%, 21%,or 12% 92. During BH with 21% O2, normal subjects displayed the typical bradycardia; this response, however, was attenuated with the other O2 concentrations. In contrast, the CBR subjects manifested BH tachycardia which was inversely proportional to the O2 tension. HR increased in be CBR group by 5%, 31%, and 45% during BH with 100%, 21%, and 12% O2, respectively. These results demonstrate that the bradycardia of BH in normal man is under the influence of the carotid bodies. During BH and in the absence of carotid bodies, an O2 tension-dependent tachycardia is unveiled.
Depressed myocardial function in the goat at high altitude
Authors: Tucker C. E. , James W. E. , Berry M. A. , Johnstone C. J. , Grover R. F.
Published: December 2017

To determine if depressed myocardial function contributes to the reported decrease in cardiac performance at high altitude, six chronically instrumented, unsedated goats were studied before, during, and after 2-wk exposureto hypobaric hypoxia (PaO2 44 mmHg). Undistorted ventricular pressure wave form was obtained from a miniature transducer implanted in the left ventricular cavity. The relationship between (dP/dt)/28P and P was extrapolated toobtain Vmax as an index of myocardial function. With beta sympathetic blockade (practolol) and pacing to reproduce heart rates, Vmax was uniformly andsignificantly depressed (P less than 0.01) during chronic hypoxia, and returned to control values following descent to low altitude. Likewise, stroke volume following saline infusion was decreased at high altitude and returned to control values following descent. Acute relief of hypoxia at high altitude by administration of 100% oxygen by mask did not reverse the depressedVmax. These findings indicate that chronic hypobaric hypoxia produces a depression of myocardial function which is reversible by chronic but not acuterelief of hypoxia.
Mechanics of the canine diaphragm
Authors: Kim M. J. , Druz W. S. , Danon J. , Machnach W. , Sharp J. T.
Published: December 2017

Diaphragmatic force-length behavior was assessed in anesthetized dogs using two techniques. One employed measurements in a diaphragm strip with intact nerve and blood supply; the second related transdiaphragmatic pressure (Pdi) to direct estimates of diaphragmatic tension from strain gauge archesduring bilateral, tetanic, supramaximal phrenic nerve stimulation. In strippreparations the diaphragm exerted active force at lengths as short as 40% of resting in situ length (Lo), and maximal force was registered at a length averaging 25% greater than Lo. This suggested a broader effective length range for the diaphragm as compared to other skeletal muscles. In the intact preparation both Pdi and directly measured diaphragmatic tension were inversely related to lung volume and when they were used to calculate the diaphragm's effective radius of curvature (r), r was found to change little or decrease at large lung volumes rather than increase as theory wouldpredict. These findings suggest that length tension characteristics outweighgeometric considerations in explaining the diaphragm's function in normal dogs and probably normal men.
Ventilation-perfusion ratio obtained by a noninvasive frequency response technique
Authors: Zwart A. , Seagrave R. C. , Van Dieren A.
Published: December 2017

Results of animal experiments using sinusoidal changes in inspired halothane concentration showed that the ratio of variation in end-expired concentration to the variation in inspired concentration reached a plateau in theBode diagram. With the help of an uptake and distribution model, the interpretation of the results showed that the level of the plateau is determined by the overall ventilation-perfusion ratio. With a good selection of input frequency, tracer agent, and known ventilation, the ventilation-perfusion ratio and the lung perfusion can be consequently obtained noninvasively. Mean ventilation-perfusion ratio was determined with 20 human voluteers. At rest a mean ratio was found of 0.87 +/- 0.28 (SD). At a work load of 90 W a mean ratio was found of 1.19 +/- 0.19 (SD). In two individuals reproducibility and influence of CO2 was studied. At rest without additional CO2 the ventilation-perfusion ratio was 0.71 +/- 0.06 (SD) obtained with a constant breathing rate of 10/min. At an end-expired CO2 level of 6% the ventilation-perfusion ratio was increased almost 2.5 times. The calculated perfusion with and without increased end-expired CO2 levels under the same work load were well reproducible.
Electrochemical sensor for continuous transcutaneous PCO2 measurement
Authors: Beran A. V. , Huxtable R. F. , Sperling D. R.
Published: December 2017

A sensor suitable for continuous transcutaneous PCO2 measurements is described. The sensor consists of an antimony-antimony oxide electrode in combination with a silver-silver chloride reference electrode, bathed in an electrolyte and covered by a Teflon membrane. A servo-controlled heater unit was used to maintain the sensor's temperature and to produce local hyperemia. The resulting oxidation-reduction potential under constant temperature isa linear function of the logarithm PCO2. Response time (95%) to stepchanges in PCO2 from 27 to 70 mmHg was 2.7 +/- 0.3 min. Following a 12-h “aging”time, the electrode exhibited a minimal drift of 5.2 +/-2.2 mV for 16 h, representing an average PCO2 drift of 0.5 mmHg/h. This sensor was applied onthree rabbits and on five human volunteers, and found satisfactory under normal physiological conditions.
Cyclic hypoxic pulmonary vasoconstriction induced by concomitant carbon dioxide changes
Authors: Benumof J. L. , Mathers J. M. , Wahrenbrock E. A.
Published: December 2017

We examined the stability of acute lobar hypoxic pulmonary vasoconstriction. In 12 mongrel dogs the left lower lobe (LLL) was selectively ventilated with a constant minute molume with nitrogen and the electromagnetically measured fraction of the cardiac output perfusing the LLL and the LLL end-tidal CO2 concentration were observed for 1 h. We found that both the fraction of the cardiac output perfusing the LLL and the LLL end-tidal CO2 concentration initially decreased during LLL hypoxia and then oxcillated in a progressively damped fashion. When LLL end-tidal CO2 was kept constant by CO2 infusion during LLL hypoxia or when LLL hypoxia was induced by LLL atelectasis, no oscillations were observed. We conclude that if minute ventilation of a hypoxic area of lung is kept constant, then decreased regional blood flow decreases regional alveolar PCO2. As a consequence of these two opposinginfluences, blood flow to an acutely hypoxic area will be oscillatory.
Premotion silent period in rapid voluntary movement
Authors: Yabe K.
Published: December 2017

The silent period in the agonist prior to rapid voluntary movement (premotion silent period) was observed in the lower limb muscles. The subject was asked to respond to the flashing light by performing a vertical jump as quickly as possible. The most consistent results were obtained in the extensors, particularly the quadriceps. The frequency of the silence of six subjects was 53% in the rectus femoris, 61% in the vastus medialis, and 72% in the vastus lateralis. A neural switching mechanism, directing excitation from preparation phase of jumping into rapid contraction phase, seemed to be attributable to the occurrence of the premotion silent period.
Effect of posture on the single-breath oxygen test in normal subjects
Authors: Cortese D. A. , Rodarte J. R. , Rehder K. , Hyatt R. E.
Published: December 2017

The effect of posture on phase III (alveolar nitrogen plateau) and phase IV (closing capacity) of the single-breath oxygen test was examined in 10 normal people. In part 1 of the study, subjects inspired and expired in the standing, supine, prone, and right lateral decubitus positions; there was no effect of posture on phase IV but slopes of phase III were higher when subjects were in the supine and lateral positions. In part 2, subjects inspired in the standing position and expired in one of the recumbent positions. Phase IV occurred infrequently except in the prone position (6 of 10 subj); slopes of phase III in part 2 were not consistently altered by changing posture. It is difficult to explain the failure of posture to alter phase IV solely on a model requiring a linear gradient of pleural pressure. The slope of phase III appears to depend more on the emptying patterns of small regions with widely varying volume-to-ventilation ratios than on gravity-dependent sequences of emptying. Finally, the data suggest a considerable similarity between the upright and prone positions in terms of lung filling and emptying.
In vivo measurement of pyridine nucleotide fluorescence from cat brain cortex
Authors: Harbig K. , Chance B. , Kovach A. G. , Reivich M.
Published: December 2017

A modification of the methods is described which makes it possible to measure pyridine nucleotide fluorescence from the brain cortex in vivo without interference from movement and hemodynamic artifacts. Movement artifacts were eliminated by the use of a window technique. Fluorescence changes due to changes in hemoglobin oxygenation have been eliminated by measuring fluorescence at an isobestic wavelength of the hemoglobin-oxyhemoglobin reaction. The interference due to changes in red blood cell concentration has beenstudied by simultaneous measurements of fluorescence and ultraviolet reflection. Hemodilution revealed a linear relationship between the fluorescencefrom the pyridine nucleotide and reflected ultraviolet light. The ratio between the light absorption changes was approximately unity under the particular optical geometry employed in this study. This method has been used to measure fluorescence changes produced by nitrogen anoxia. The technique is discussed in relation to previous methods and the effects of anoxia are compared to previous findings.
Effect of water temperature during cold exposure on thermogenic drinking in rats
Authors: Fregly M. J. , Kaplan B. J. , Brown J. G. , Nelson E. L. , Tyler P. E.
Published: December 2017

Availability of water at temperatures higher than ambient (15, 25, 35 degrees C) failed both to affect the ratio of water to food intake during exposure to cold air (5 degrees C) and to influence the thermogenic (postcold exposure) drinking response of rats which characteristically occurs immediately after removal from cold air. Thus, availability of warm water during exposure to cold appeared to have no influence on cold-induced dehydration in rats. A specially constructed drinking apparatus was used in this study. It was designed to maintain water at temperatures greater than ambient during exposure to cold. Details for construction of the apparatus are provided.
Metabolic cost of grade running in dogs
Authors: Raab J. L. , Eng P. , Waschler R. A.
Published: December 2017

Dogs (Canis familiaris) were run up and down 7.4, 11.8, and 20.4% gradesas well as on the horizontal at speeds of 3 and 6 km/h while their steady-state oxygen comsumption was measured. On positive grades the metabolism wasdirectly dependent on both grade and speed. On the negative grades the metabolic rates were dependent only on speed and for each dog were depressed about the same amount below the metabolism needed for horizontal running ateach speed. The clustering of the metabolic rates for the downhill slopes means that to cover a given distance gorizontally and downhill the dog will use the minimum energy if it descends via the gentlest grade. This is so because such a route allows the animal to maintain the lowest metabolism for the longest time. There is no best uphill route. The grade metabolism of the dogs was an almost exact duplicate of that found for humans running on grades which implies similarity of mechanical and biochemical aspects of running.
Cerebellar pressor response in the dog
Authors: Dormer K. J. , Stone H. L.
Published: December 2017

A fastigial pressor response has been elicited in the anesthetized mongrel dog. Stimulation within the rostral portions of this nucleus results in mean arterial pressure rises up to 150 mmHg above control. A proportional tachycardia is simultaneously evoked which may rapidly attain heart rates of190 beats/min above control levels. Peak tachycardias immediately suside and often the heart rate declines below control values during stimulation while arterial pressure remains elevated. When either the carotid sinuses wereisolated by ligation or a bilateral vagotomy was performed, the fastigial tachycardia was sustained. Thresholds for the response are near 0.05 mA and the stimulus intensity curve is linear to 0.4 mA whereupon the pressure rise and tachycardia begin to approach a plateau value. The response could still be attained when submaximal doses of alpha-chloralose anesthesia or highlevels of barbiturates (30–40 mg/kg) were given. Both portions of the response result from widespread sympathetic activation; however, buffering of the response through the baroreceptor reflexes is only demonstrated in the cardiac segment of the response.
Modeling of the relationship between volume variations at the mouth and chest
Authors: Peslin R. , Jardin P. , Hannhart B.
Published: December 2017

A model was developed to interpret the difference between volume variations at the mouth and at the chest observed by body plethysmography during inspiration in normal subjects breathing ambient air. The mechanical phenomena were characterized, as usual, by a time constant alpha, the product of airway resistance and alveolar gas compressibility. In contrast to other models, the change in temperature and water vapor pressure of the inspired gaswas not considered to be instantaneous but rather a first-order process characterized by a thermal time constant tau. Experimental curves obtained in eight subjects were analyzed by use of parameter estimation techniques. Thevalues of alpha were in agreement with those obtained by conventional plethysmography and tau averaged 63+/-24 ms. The results of additional experiments devised to test the physical meaning of the coefficients and the influence of neglected factors support the validity of the model. It was shown that tau cannot be neglected when breathing air at room temperature.
Human cardiovascular and respiratory responses to graded muscle ischemia
Authors: Rowell L. B. , Hermansen L. , Blackmon J. R.
Published: December 2017

Responses of heart rate (HR), mean arterial blood pressure (MAP) ventilation (VE), and forearm blood flow (FBF) to different degrees of leg muscle ischemia were measured in eight subjects in a four-part experiment. Part I.Total circulatory occlusion (OCCL) of resting legs for 15 min had little or no effect on HR, MAP, VE, or FBF. Part II. OCCL of the legs for 3 min immediately after exercise at 50–250 W did not affect HR or end-tidal CO2; it lowered VO2 and VE and prevented recovery of MAP. Part III. OCCL beginning at end and 10, 20, 30 s before end of 7-min exercise (100–150 W) and continuing 3 min into recovery period produced sustained and gradedincrements (5–10 mmHg) in MAP, only small changes in HR, and accelerated recovery of VE while end-tidal CO2 remained constant. Part IV. OCCL atend and 30 s before end of exercise increased FBF 2.5–3.5 times; bothskin and muscle vasodilated. Thus muscle ischemia preceded by exercise can raise MAP without affecting VE, whereas baroreflexes may lower HR and raiseFBF. The results suggest the presence of muscle chemoreceptors whose major effect is on MAP.
Effect of heat acclimatization on intravascular responses to acute heat stress in man
Authors: Bonner R. M. , Harrison M. H. , Hall C. J. , Edwards R. J.
Published: December 2017

The effects of a 185-min exposure to 48 degrees C db/33 degrees C wb, onintravascular volume and osmolarity and on intravascular electrolyte, aldosterone, and cortisol concentrations have been studied in five male subjectsbefore and after acclimatization to heat. Changes in the hematocrit and plasma protein concentration indicated that a hemodilution occurred during thefirst 35 min of the heat exposures, and that this was followed by a hemoconcentration. Although these changes in intravascular volume were not affected by acclimatization, the plasma volume after heat acclimatization was 6.7%greater than before. This increase in plasma volume was associated with an elevation in the ratio [Na]/[K]. However, since plasma osmolarity decreasedthe intravascular expansion could not be explained in terms of elevated electrolyte levels. Plasma aldosterone and cortisol levels were not affected by heat acclimatization, although both were elevated following exercisein the heat. It is concluded that the adrenal cortex is not an important factor in maintaining a state of heat acclimatization once a salt balance hasbeen achieved.
New device for automatic recording and processing AV transmission intervals of the heart
Authors: Akiyama S. , Oshima T. , Saito Y. , Matsuda K.
Published: December 2017

The principle and construction of a device made for the purpose of displaying the interrelationship between two sets of cardiac intervals is described. Electrical signals derived from the atrium and ventricle of the experimental animal are fed to the input of the device where a special switch andan integrated circuit logic gate select the two sets of cardiac intervals to be measured, e.g., AA and VV or AA and AV intervals. These intervals are converted into electrical square pulses having voltages proportional to therespective intervals. Besides simply comparing the two cardiac intervals byrecording them simultaneously against time, the interrelationship of the two is displayed in an X-Y configuration on-line on a cathode-ray oscilloscope. This latter method, if used only for the occasionally induced premature excitations with varied coupling time, facilitates the measurement of the functional refractory periods for atrioventricular conduction. The mode of operation of the device is presented with examples of experiments.
System analysis of heart rate control in man
Authors: Sato I. , Hasegawa Y. , Hotta K.
Published: December 2017

The dynamic property of the heart rate response to exercise was determined and expressed in the frequency domain to establish a method of examiningcardiovascular control function. The response of heart rate to a stimulus was measured at 5-s intervals in nine healthy young volunteers. The stimulusconsisted of several runs of two-step exercise practiced in semirandom sequence for 19 min. The weight function of the system was estimated from autocorrelation function of the input signal and cross-correlation function between the input and output signals. The weight function was transformed into a transfer function and its Bode plot diagram was drawn. From the diagram, four dynamic parameters were determined. These parameters are as follows: Kis a constant showing the theoretical steady-state increment of heart rate,and T1, T2, T3 are time constants. The values obtained in the present experiment with the healthy young males were: K 46.0 +/- 14.6 beats, T1, 2.12 +/- 0.44, T2, 1.12 +/- 0.16, and T3 0.70 +/- 0.07 min.
Impedance cardiography for determination of stroke index
Authors: Keim H. J. , Wallace J. M. , Thurston H. , Case D. B. , Drayer J. I. , Laragh J. H.
Published: December 2017

Stroke index obtained by impedance cardiography was compared with valuesobtained by dye-dilution technique in 17 subjects in 122 determinations made within 2 min of each other. Fifty of these determinations were done afterdrug administration, postural change, or saline infusion. All values obtained by both methods correlated significantly, but with wide scatter (r=0.49,n = 122, P less than 0.001). The series of determinations within each subject, however, correlated only in one subject significantly; thus any changesof stroke index measured by both techniques were not commensurate. In addition, the impedance stroke index values were significantly lower than the dye-dilution technique, impedance cardiography presently does not determine reliably absolute values of stroke index and is not suitable to evaluate changes of stroke index.
Effect of altitude exposure on thermoregulatory response of man to cold
Authors: Blatteis C. M. , Lutherer L. O.
Published: December 2017

The thermoregulatory responses to 10 degrees C (for 3 h) were investigated in 1) 12 natives from sea level (lowlanders) at 150 m, and on arrival at 3,350 and 4,340 m; 2) 6 of these during a 6-wk sojourn at 4,360 m, and on return to sea level; and 3) 5 natives from each of the two altitudes (highlanders) in their respective habitat, and after descent to 150 m. The cold-induced increase in the rate of O2 consumption (Vo2) of the lowlanders was significantly smaller at both altitudes than at sea level. It did not recover substantially during the 6 wk at altitude, but was restored to its initial rate on return to sea level. By contrast, visible shivering activity was augmented on arrival at altitude. It persisted throughout the 6 wk there, but was greatly depressed on return to sea level, despite the increased Vo2. Mean skin temperatures (Tsk) stabilized in the cold at significantly higher values at altitude. Rectal temperature (Tre) decreased similarly at all altitudes. Vo2 of the highlanders in the cold was significantly greater at sea level than at their resident altitudes, although shivering activity was less intense; Tsk stabilized at significantly lower levels at 150 m than at either altitude. These results indicate that altitude exposure reduces the calorigenic response of man to cold, and that this effect is not moderated by acclimatization to altitude, yet is reversible immediately on descent to sea level. The component of cold thermogenesis which appeared to be reduced by altitude exposure was nonshivering thermogenesis rather than visible shivering.
Ventilatory control in peripheral chemoreceptor-denervated ponies during chronic hypoxemia
Authors: Forster H. V. , Bisgard G. E. , Rasmussen B. , Orr J. A. , Buss D. D. , Manohar M.
Published: December 2017

The present study was designed to provide further insight into the role of the carotid and aortic chemoreceptors in ventilatory (VE) acclimatization during sojourn at altitude. Measurements were made: 1) on 10 ponies near sea level(SL, 740 Torr) under normal conditions, 2) on 6 of these at SL following chemoreceptor denervation (CD), and 3) subsequently on all 10 during 4 days of hypobaric hypoxia (PaO2 = 40–47 Torr). CD resulteo in hypoventilation at SL (deltaPaCO2 = d8 Torr, P less than 0.05), and it prevented hyperventilation normally observed with injection of NaCN and acute exposure to hypoxia (less than 1 h). In contrast, hyperventilation was evidentin normal ponies during acute hypoxia (deltaPaCO2 = -6.7 Torr). Ventilationincreased in both groups between the 2nd and 8th h of hypoxia (deltaPaCO2 from 1 h = -4 Torr, P less than 0.05). This change, a common characteristic of acclimatization, persisted throughout 4 days of hypoxia in the normal ponies. However, in the CD ponies this change was evident consistently only through the 12th h and after the 44 h hyperventilation was no longer evident.We conclude that the peripheral chemoreceptors are essential in ponies for normal VE acclimatization to this degree of hypoxemia. Two additional findingsin CD ponies suggest the presence of a CNS inhibitory influence on theVEcontrol center during chronic hypoxemia. First, acute hyperoxygenation on the 4th day of hypoxemia induced hyperventilation (deltaPaCO2 = -5 Torr, P less than 0.05). Second, again on the 4th day and during hyperoxygenation, VE responsiveness to CO2 and doxapram HCl was greater than at sea level.