bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of exercise on postoperative nitrogen balance
Authors: Freund H. , Yoshimura N. , Fischer J. E.
Published: December 2017

This study was designed to investigate whether exercise, when used as an adjunct to parenteral nutrition, has any influence on postoperative muscle catabolism, amino acid metabolism, and nitrogen balance. Twenty male Sprague-Dawley rats were divided into two groups of exercised and nonexercised animals. All animals underwent laparotomy and jugular vein cannulation, were placed in metabolic cages, and were infused with a dextrose-protein solution at 15 kcal and 0.56 g amino acids/100 g body wt per 24 h for a total of 96 h. The exercised animals were run on a treadmill for 15 min/day for a total of 3 days. There was no difference in nitrogen balance and body weight change between exercised and nonexercised animals, as well as no difference between animals who experienced different degrees of exercise. Total and individual plasma amino acids in the exercised group were 15% lower than in the nonexercised group; the total and individual free amino acids in muscle of the exercised group were 66% higher than in the nonexercised group. This pattern of high levels of amino acids in the muscle, coupled with decreased plasma concentrations, is suggestive of increased amino acid turnover in the muscle of the exercised animals. We suggest that, in the postoperative or postinjury period, exercise has a stimulating effect on amino acid turnover in the skeletal muscle resulting from 1) amino acid (mainly the branched-chain amino acids) consumption for energg metabolism and gluconeogenesis, and 2) protein synthesis. The net balance of both results in nitrogen equilibrium similar to that of a nonexercised control group.
Airway closure and closing volume
Authors: Forkert L. , Dhingra S. , Anthonisen N. R.
Published: December 2017

Using boluses of radioactive Xe we compared regional N2O uptake with regional perfusion distribution during open glottis breath hold in five seated men. Measurements were made near residual volume, at closing volume (CV), above CV and when possible, between CV and residual volume (RV). At low lung volumes basal N2O uptake was small whereas basal blood flow was not. This discrepancy was interpreted as evidence of airway closure and was quantitated. All subjects showed extensive basal closure near RV. At closing volume four of five subjects demonstrated closure and some closure was evident in these subjects at volumes in excess of CV. The increase in airway closure with decreasing lung volume was much greater below CV than above it. Conventional CV tracings were obtained using helium boluses; the height of phase IV was positively correlated with the change in airway closure between CV and RV as assessed by the N2O technique. The slope of phase III did not correlate with the amount of airway closure measured at CV. We concluded that the conventionally measured CV is not the volume at which airway closure begins but that the onset of phase IV reflects an increase in basal airway closure and the height of phase IV reflects the amount of basal closure between CV and RV.
Estimating a distribution's central moments: a specific tidal ventilation application
Authors: Butler J. P. , Mohler J. G.
Published: December 2017

A method is presented for extracting central moments of a distribution from data generated by the distribution over a known kernel. It is applied to the problem of the specific tidal ventilation in the lung in the multiple-breath N2-washout setting, and we found that in estimating the mean and variance, the method accurately recovers from test data those values characteristic of a test distribution. Some preliminary results on normal subjects are shown.
Oxygen tensions measured in cat cerebral cortex under hyperbaric conditions
Authors: Hempel F. G.
Published: December 2017

Pyrenebutyric acid (PBA), the intracellular fluorescent indicator, was used to measure the partial pressure of oxygen (PO2) in the exposed cerebral cortex of anesthetized cats at hyperbaric pressures up to 4 ATA. The validity of the PBA method for determining cortical PO2 was confirmed by demonstrating a precise linear relationship between Pao2 and the reciprocal of the fluorescence of PBA in the brain as the cat was ventilated with sequentially greater oxygen pressures while holding the Paco2 nearly constant. Increments in the Paco2 while the Pao2 was maintained at a high (about 2,000 Torr) level resulted in stepwise greater oxygen tensions in the brain until an oxygenation end point was reached with a Paco2 averaging near 122 Torr. Greater amounts of CO2 did not bring the mean PO2 of the brain, 1,017 Torr, closer to 2,000 Torr. During normocapnia the cortical PO2 was greater than the PO2 of cerebral venous blood collected from the superior sagittal sinus; however, in hypercapnia (PaCO greater than 45 Torr), the PO2 of the sinus blood exceeded the value determined in the cortex. This latter observation is taken as evidence for convective shunting of cerebral arterial blood to venous circulation when hypercapnia is present.
Effects of temperature, relative humidity, and mode of breathing on canine airway secretions
Authors: Man S. F. , Adams G. K. , Proctor D. F.
Published: December 2017

Airway secretions were collected from the upper trachea of eight healthy nosebreathing mongrel dogs under general anesthesia, and the electrolytes and osmolality of these secretions were determined. Compared to plasma, secretions contained 15% higher Na+ and 33% higher Cl-, were 18% higher in osmolality, but had a lower Na+/Cl- throughout the 6-h experiments. When six nose-breathing dogs were exposed to air at 28.5 degrees C and 95% relative humidity, secretion osmolality became lower, but Na+/Cl- remained unchanged. In four other dogs, secretions approached the osmolality of plasma when inspired air was at 36.4 degrees C and 100% relative humidity. These secretions contained 22% higher Cl- and a lower Na+/Cl- than plasma. The differences between airway secretions and interstitial fluid suggest that secretions are formed by active Cl- transport. In another four dogs, secretion osmolality was higher with mouth breathing than breathing through the nose. Inasmuch as humidified and warmed air lowered and mouth breathing raised the osmolality of airway secretions, we postulate that the hyperosmolality of secretions results from water loss from the airway surface during conditioning of inspired air.
Transit-time analysis of the forced spirogram in healthy children and adults
Authors: Macfie A. E. , Harris E. A. , Whitlock R. M.
Published: December 2017

Mean transit time (MTT), coefficient of variation (COV), and index of skewness (IOS) of transit times were measured, with the more conventional derivatives of the forced expiratory spirogram, in 178 healthy people aged 6–71 yr breathing air, and in 18 healthy adults breathing 20% oxygen in helium (O2He) in addition. Breathing O2He very significantly altered MTT and all derivatives with dimensions of flow or time, but altered COV and IOS very little. Between 6 and 30 yr mean MTT, after adjustment for expired volume, remained constant and then increased to 71 yr. Mean COV and IOS increased from 6 to 71 yr, though with an apparent change in rate during the early teens. The results suggest that whereas the resistance of large airways falls in proportion to growth of the lungs, small-airway resistance becomes less uniform during both childhood and adult life.
A continuum mechanics analysis of pulmonary vascular interdependence in isolated dog lobes
Authors: Lai-Fook S. J.
Published: December 2017

The pressure-diameter (PD) behavior of intact pulmonary vessels was measured roentgenographically at several fixed deflation transpulmonary pressures (Ptp). At any constant vascular pressure (Pv), the intact-vessel diameter was larger for higher Ptp. The behavior of the parenchyma was described by a nonlinear analysis. An excised-vessel PD behavior was computed which was consistent with both nonlinear parenchymal behavior and measured intact-vessel PD behavior. Estimates of Px', the difference between the perivascular pressure and the pleural pressure, as a function of Ptp and Pv were obtained. For physiological values of Pv, mean values of Px' for arteries were -1 cmH2O at Ptp of 4 cmH20 and decreased almost linearly to -15 cmH20 at Ptp of 25 cmH2O. Veins showed a similar behavior, but Px' was more positive. Increasing Pv raised Px' and decreasing Pv lowered Px' at all values of Ptp. These results indicate that the interdependence effect is small at functional residual capacity, increases with lung inflation, and is greater for arteries than veins.
Responses of forearm blood flow to graded leg exercise in man
Authors: Johnson J. M.
Published: December 2017

To test whether the cutaneous vascular responses to exercise are influenced by the level of work, three strategies were followed. In each, forearm blood flow and esophageal temperature were measured throughout. In part I, the forearm blood flow-internal temperature relationships from separate sessions of steady-state exercise at different loads were compared. In part II, work load was varied between 50 and 150 W. Work load was raised or lowered 50 W every 5 min over 60–75 min. The third strategy was to examine the immediate change in forearm blood flow accompanying rapid, large increments or decrements in work load. The results do not support a graded response of the cutaneous circulation to exercise. In both the first and second protocols above, the relationship of forearm blood flow to internal temperature was not measurably altered by work load. Multiple linear regression analysis failed to reveal a consistent role for work load in part II. In the third protocol, there was no consistent or sustained response to an abrupt change in work load. Thus over the range of work loads used in this study there appears to be no major role for the level of work in the regulation of forearm skin blood flow other than through the effect on internal temperature.
Body temperature and ventilatory responses to CO2 during chronic respiratory acidosis
Authors: Jennings D. B.
Published: December 2017

During acute hypercapnia (5% carbon dioxide) in resting conscious dogs, ventilation (Ve) attained a new level above control within 5 min, but rectal temperature decreased gradually to reach a steady state lower than control after 40–60 min. At 2 days of breathing 5% carbon dioxide, Ve remained elevated, as in acute hypercapnia, but Paco2 increased and the threshold of the ventilatory response shifted to a higher Paco2. By 2 days of hypercapnia, rectal temperature (Tr) had returned to normal, reflecting an alteration of hypothalamic temperature control that might be expected to result in enhanced respiratory drive. Surprisingly, despite blood acid-base compensation between 2 and 14 days of hypercapnia, Ve did not decrease, whereas Paco2 decreased to the level observed during acute hypercapnia, and the threshold of the ventilatory response returned to normal. Therefore, at 14 days of respiratory acidosis, acid-based compensation resulting from increase in bicarbonate was not associated with reduced respiratory drive. This result could not be accounted for on the basis of a temperature mechanism because temperature adaptation occurred earlier.
Effect of pentobarbital anesthesia on rheology and transport of canine tracheal mucus
Authors: King M. , Engel L. A. , Macklem P. T.
Published: December 2017

Tracheal mucus samples were collected from six tracheostomized dogs before and after induction of pentobarbital anesthesia. The dynamic mechanical properties of the mucus were determined by the magnetic microrheometer technique. In 15 experiments, the mean value of elasticity at 1 rad/s rose from 67 dyn/cm2 before anesthesia to 212 dyn/cm2 in the period 15–90 min after induction. At the same time, mean viscosity at 1 rad/s rose from 24 to 79 P. The mucociliary transportability of some of the mucus samples was assayed by means of in vitro frog palate technique. In 10 experiments, the relative transport rate for dog tracheal mucus went from 98% of frog palate control befor anesthesia to 79% during pentobarbital anesthesia. A negative relationship between from palate transport rate and mucus elasticity was found. A negative correlation between transport and mucus viscosity at constant elasticity was also discovered. Finally, the mucus collection rate was reduced by a factor of about 8 during anesthesia, suggesting a reduction in the average depth of mucus.
Human skin wettedness and evaporative efficiency of sweating
Authors: Candas V. , Libert J. P. , Vogt J. J.
Published: December 2017

Rates of evaporation and sweating were recorded for three acclimatized male subjects in hot humid conditions, the ambient parameters of which were set so that the various imposed evaporative rates required the same skin wettedness at different levels of sweating. Rectal and skin temperatures were measured. Results showed that during steady state occurring during the 2nd h of exposure each subject reached the required evaporative rate by means of increases in skin wettedness regardless of the level of sweating; the sweat evaporative efficiency, defined as the ratio between evaporative rate and sweat rate, decreased as skin wettedness increased, in a range between 0.74 and 1.0 Sweat efficiency fell to 0.67 for fully wet skin. The body temperatures did not increase with time if skin wettedness was less than unity. Evaporative heat transfer coefficient (he), maximum evaporative capacity, and wettedness were estimated on the basis of the observed decrease of sweat efficiency. The relationship between skin wettedness and sweat efficiency was interpreted as a combined effect of differences in local he as well as in local sweat rates.
Cardiac responses of dogs to nonsynchronous and heart synchronous whole-body vibration
Authors: Bhattacharya A. , Knapp C. F. , McCutcheon E. P. , Evans J. M.
Published: December 2017

Changes in cardiac function produced by synchronizing vibration-induced forces with events in the cardiac cycle were compared to those for the nonsynchronous case in eight chronically instrumented, tranquilized dogs. The supine animals received sinusoidal, whole-body vibration (along the spinal +/- Gz axis) at a constant acceleration amplitude (+/- 0.75 G). The vibration frequency (2–3 Hz) was set equal to the paced heart frequency. Synchronization between vibration and cardiac cycles on a beat-by-beat basis produced a specific and sustained cardiovascular response; such a sustained response was not possible with nonsynchronous vibration. With synchronization, relationships could be found and sustained in which changes either exceeded or were below mean nonsynchronous levels, in some cases below previbration values. For the synchronous vs. nonsynchronous states, significant modification of cardiac function was reflected in parameters such as coronary flow (+15% to -34%) and myocardial oxygen consumption (+21% to -51%). Thus, whole-body oscillation acceleration (vibration) is a forcing function that can produce and maintain a particular cardiovascular response.
Information content of the multibreath nitrogen washout
Authors: Wagner P. D.
Published: December 2017

The distribution of ventilation per unit volume (Va/Vol) in the lung is often studied using the multibreath N2 washout test. Most approaches have focused on the determination of a single Va/Vol distribution (consisting of from two compartments to a continuum) compatible with the data, but because the potential number of lung units greatly exceeds the number of breaths measured, many distributions are usually compatible with a given set of washout data. Interpretation of single distributions therefore requires evaluation of the variability among all such compatible distributions. The technique of linear programing is well suited to evaluation of these compatible distributions and its application to the N2 washout is explained. Twelve examples of washout data are analyzed in this way. The results indicate that using the first 20 or so breaths of the washout, narrow distributions of Va/Vol are well specified. Distributions with up to four distinct modes are also well specified, but for broad distributions the shape cannot be adequately defined. Good resolution in the region of high Va/Vol is found to be critically dependent on measuring the first few breaths of the washout.
Effects of pulmonary circulation on blood levels of insulin and glucagon in ambulant dogs
Authors: Geddes D. M. , Blackburn J. P. , Bailey J. S. , Muller F. J.
Published: December 2017

The effect of the lung on insulin and glucagon were studied by comparing aortic and mixed venous levels in ambulant dogs with indwelling catheters. In the resting state ther was no difference for either hormone. After injection of insulin aortic levels exceeded mixed venous for 10 min; mixed venous levels exceeded aortic for the next 36 min. After injection of glucagon mixed venous levels consistently exceeded aortic. Single-pass studied showed an apparent gain in immunoreactive insulin as compared with [14C]inulin and 125I-albumin during passage through the lung; but no effect on glucagon could be demonstrated. A loss of immunoreactive hormone across the lung might be explained by degradation within the capillary lumen be endothelial cell surface peptidases or uptake onto specific receptors. The apparent gain of immunoreactive insulin across the lung might be due to displacement of immunoreactive exogenous hormone competing for receptor sites or modification of exogenous hormone by the lungs with increase in immunoreactivity.
Simple, accurate equations for human blood O2 dissociation computations
Authors: Severinghaus J. W.
Published: December 2017

Hill's equation can be slightly modified to fit the standard human blood O2 dissociation curve to within plus or minus 0.0055 fractional saturation (S) from O less than S less than 1. Other modifications of Hill's equation may be used to compute Po2 (Torr) from S (Eq. 2), and the temperature coefficient of Po2 (Eq. 3). Variations of the Bohr coefficient with Po2 are given by Eq. 4. S = (((Po2(3) + 150 Po2)(-1) x 23,400) + 1)(-1) (1) In Po2 = 0.385 In (S-1 - 1)(-1) + 3.32 - (72 S)(-1) - 0.17(S6) (2) DELTA In Po2/delta T = 0.058 ((0.243 X Po2/100)(3.88) + 1)(-1) + 0.013 (3) delta In Po2/delta pH = (Po2/26.6)(0.184) - 2.2 (4) Procedures are described to determine Po2 and S of blood iteratively after extraction or addition of a defined amount of O2 and to compute P50 of blood from a single sample after measuring Po2, pH, and S.
Effects of extrapulmonary airway distension on breathing in anesthetized dogs
Authors: Lloyd T. C.
Published: December 2017

Anesthetized dogs with open chests were perfused with a pump-oxygenator. We first observed the effects of intermittent periods of sustained inflation of both lungs, of only one lobe, and of an intra-airway balloon on the diaphragm electromyogram (EMG). Lung or lobe inflation with low pressures depressed respiratory frequency (fr) by prolonging expiratory time (TE) in proportion to inflating pressure, but balloon inflation was without effect. We next intermittently inflated one or two lobes after all others were ligated and thereafter inflated all the extrapulmonary airways following total lung excision. Lobe inflation, by varying TE, decreased fr at low pressures and often increased fr at higher pressures. Extrapulmonary airway distension slightly increased fr and the mean rate of rise of the integrated EMG, but decreased inspiratory time and peak EMG amplitude. TE was slightly prolonged by low pressures when using sustained airway pressurization but was shortened by higher pressures when distending cyclically. In comparison to lobe inflation, the effects from isolated airways were small, and the inhibitory effect of lung inflation could not be attributed to them.
Bradycardia during face cooling in man may be produced by selective brain cooling
Authors: Caputa M. , Cabanac M.
Published: December 2017

In human subjects, bradycardia was produced by immersing the subjects' faces in water at 15 degrees C when they were hyperthermic. When they were hypothermic, the same face cooling produced tachycardia. It is suggested that the difference in cardiac response originates in selective brain cooling during hyperthermia, by venous return from the face to the brain, via ophthalmic veins.
Reduced lung volume during behavioral active sleep in the newborn
Authors: Henderson-Smart D. J. , Read D. J.
Published: December 2017

In a previous study of newborn infants we observed overall rib cage collapse during active sleep and postulated that the lungs also could be deflated, leading to reduced oxygen stores and circumstances favoring the rapid development of hypoxemia during apnea. In this study, thoracic gas volume (TGV) has been measured directly by occlusion plethysmography in six normal babies during behavioral quiet and active sleep and related to the different movements of the rib cage and abdomen-diaphragm that occur during each sleep state. TGV was significantly reduced in each baby during active sleep and was associated with rib cage deflation and increased abdomen-diaphragm excursions. The average reduction of TGV was 31% when compared with the volume in quiet sleep and did not depend on the order in which the sleep states were tested. The reduced lung volume in active sleep could have implications for the regulation of breathing in that state. A reduction of lung oxygen stores in active sleep suggests an age-related vulnerability of the young infant to hypoxemia.
Respiratory response to HCl acidosis in dogs after carotid body denervation
Authors: Kaehny W. D. , Jackson J. T.
Published: December 2017

To test the participation of the carotid bodies in the respiratory response to metabolic acidosis, six dogs were infused with HCl for 2 h followed by HCl feeding to prolong the acidosis to 48 h. This protocol was repeated after carotid body denervation (CBD). Mean control PCO2 rose by 7.3 Torr after CBD. PCO2 fell comparably during acidosis before and after CBD at all time periods from 30 to 48 h and returned to control levels by 72 h. The pH ranged from 7.10 to 7.30 during acidosis pre- and post-CBD. The decreases in pH and bicarbonate concentration did not differ significantly at any time interval between the pre- and post-CBD studies. This study indicates that in dogs moderately severe HCl acidosis stimulates ventilation acutely and chronically through a central mechanism in the absence of the carotid bodies.
Transient response of the Geman-Miller respiratory oscillator model
Authors: Engeman R. M. , Swanson G. D.
Published: December 2017

Recent evidence suggests that there is a persistence of elevated respiratory center activity for many respiratory cycles after the cessation of a neural stimulus. To explore the theoretical possibility that this behavior may be a consequence of the neural oscillator that dictates respiratory rhythm, the transient response of a mathematical model of a medullary respiratory oscillator recently described by Geman and Miller was examined using computer simulation. This concept was motivated by the presence of a persistent transient response behavior inherent in oscillators from mathematical physics. The results indicate that a transient persistence effect is evident in the model behavior under some conditions, and this effect as well as the steady-state amplitude is markedly sensitive to the shape of the saturation function that interconnects the neuron populations. Furthermore, this behavior is initiated by either an abrupt decrease in a tonic input or an abrupt decrease in the synaptic weights connecting subpopulations of neurons.
Breathing responses of unanesthetized man and guinea pigs to increased transrespiratory pressure
Authors: Gillespie J. R. , Bruce E. , Alexander J. , Mead J.
Published: December 2017

We compared the breathing responses of unanesthetized men and guinea pigs to externally imposed shifts in lung volume produced by steady pressures applied to the body surface while the mouth remained near atmospheric pressure. Lung inflation caused no consistent or significant changes either in frequency or end-tidal CO2 in the three men. In contrast, during lung inflation the guinea pigs breathed at low frequencies and smaller tidal volumes and showed consistent increases in arterial PCO2 lasting up to 10 min. The changes seen immediately on application of pressure, namely apneic periods followed by breathing in which inspiratory duration was shortened while expiratory duration was substantially increased, indicates that conscious guinea pigs have active inflation reflexes. We concluded that the reflex responses rather than mechanical factors probably account for the underventilation in the guinea pigs and that guinea pigs are not nearly as well equipped as is man to defend gas exchange in the face of nonmetabolic shifts in lung volume.
Human pulmonary resistance: effect of frequency and gas physical properties
Authors: Bhansali P. V. , Irvin C. G. , Dempsey J. A. , Bush R. , Webster J. G.
Published: December 2017

We have investigated a new technique that could be specific for detecting small airway diseases. We measured resistance in nine subjects, evaluating the effect of breathing 80% He-20%O2, air, and 80% SF6–20% O2 at different flow rates (0.25--1.01 l/s) and frequencies (4--12 Hz). To test the sensitivity and specificity of this new technique, we used intravenous histamine infusion to cause peripheral constriction. During histamine infusion six of nine subjects showed the following changes: 1) dynamic compliance decreased; 2) subjects developed frequency dependence of compliance, and 3) there was no significant change in pulmonary resistance or Rrs (respiratory resistance) at 4 Hz. These data suggested a time-constant discrepancy in the periphery due to histamine infusion. These six subjects also developed frequency dependence of resistance (delta Rrs from 4 to 12 Hz), which was significant when breathing air (-22 +/- 6%) and maximal when we used He-O2 (-32 +/- 3%). We conclude that He-O2 can improve the specificity of frequency dependence of Rrs for detecting events occurring in the peripheral airways.
Respiratory impedance and derived parameters in young children by forced random noise
Authors: Williams S. P. , Fullton J. M. , Tsai M. J. , Pimmel R. L. , Collier A. M.
Published: December 2017

The frequency dependence of total respiratory impedance during spontaneous breathing was measured repeatedly in 16 children (3--5 yr old) over a 3-mo period using forced random noise and spectral analysis. Total respiratory resistance, compliance, and inertance, which were calculated fromthe impedance data using regression analysis with a second-order model, had overall mean values +/- SD of 5.61 +/- 0.49 cmH2O.l-1.s, 403 +/- 1.04 ml.cmH2O-1, and 0.0120 +/- 0.0024 cmH2O.l-1.s2, respectively. Linear regression analysis showed that resistance and compliance correlated with either height or forced vital capacity with r values in the range 0.77--0.89. Analysis of measurement variability suggested that resistance measurements had, on the average, a coefficient of variation of 15%; corresponding values for compliance and inertance measurements were 25%.
Distribution of regional volumes and ventilation in excised canine lobes
Authors: Kallok M. J. , Wilson T. A. , Rodarte J. R. , Lai-Fook S. J. , Chevalier P. A. , Harris L. D.
Published: December 2017

A linear elasticity solution for the gravitational deformation of excised lungs was obtained. The accuracy of our solution was examined by comparing predicted and measured displacements of markers glued to the surface of canine lower lobes. The equations describing the strains in a lobe were used to predict the distribution of regional volumes and the slope of phase III (S3) of a single-breath oxygen (SBO2) test. The analysis predicted a negative S3. However, S3 was found to be positive in the five lobes tested, suggesting that factors other than gravity were responsible for the observed pattern of ventilation. In SBO2 tests repeated with increasing delays at end inflation, S3 progressively decreased, became negative, and was eventually abolished. Our equations predicted the most negative observed S3 well. We conclude that continuum mechanics can be used to describe the gravitational deformation of lungs and the resulting effect on ventilation distribution.
Equation of motion of a cyclist
Authors: di Prampero P. E. , Cortili G. , Mognoni P. , Saibene F.
Published: December 2017

Tractional resistance (RT, N) was determined by towing two cyclists on a racing bike in “fully dropped” posture in calm air on a flat track at constant speed (5--16.5 m/s). RT increased with the air velocity (v, m/s): RT = 3.2 + 0.19 V2. The constant 3.2 N is interpreted as the rolling resistance and the term increasing with v2 as the air resistance. For a given posture this is a function of the body surface (SA, m2), the air temperature (T, degree K), and barometric pressure (PB, Torr). The mechanical power output (W, W) can then be described as a function of the air (v) and ground (s) speed: W = 4.5.10(-2) Ps + 4.1.10(-2) SA (PB/T)v2 s, where P is the overall weight in kg. With a mechanical efficiency of 0.25, the energy expenditure rate (VO2, ml/s) is given by: VO2 = 8.6.10(-3) Ps + 7.8.10(-3) SA (PB/T)v2 s (1 ml O2 = 20.9 J). As the decrease of VO2max with altitude is known from the literature, this last equation allows the calculation of the optimal altitude for top aerobic performance. The prediction derived from this equation is consistent with the present 1-h world record.
Effect of inhalate thermal conductivity and high O2 in producing hypothermia
Authors: Beran A. V. , Shinto R. A. , Proctor K. G. , Sperling D. R.
Published: December 2017

The effect of an increase in inhalate thermal conductivity and the fraction of inspiratory O2 (FIO2) on the rate of cooling and rewarming using a surface-inhalate heat exchange method was evaluated. Male New Zealand White rabbits were divided into three groups: those ventilated with air, those with 20% O2 + 80% He, and those with 100% O2. All animals were cooled to an esophageal temperature of 22.5 degrees C (or for 180 min maximum). Following a 15-min exposure to room air, the animals were connected to the humidifying and warming system. He-O2 had the highest thermal conductivity and the animals ventilated with it had the fastest cooling rate. One hundred percent O2 and room air had similar thermal conductivities, but the animals ventilated with 100% O2 had significantly lower cooling rates. These data indicate that, while maintaining a constant surface heart exchange, the rate of heat exchange across the lung can be modified by altering the thermal conductivity of the inhalate gas mixture. Total heat exchange can also be modified by hyperoxemia-induced hemodynamic changes.
A closed lung system study of inert gas absorption
Authors: Johnson T. S. , Swanson G. D. , Sodal I. E. , Reeves J. T. , Virtue R. W.
Published: December 2017

The demonstration that the rate of rise of the alveolar fraction of nitrous oxide is enhanced when the inspired N2O concentration is high is termed the “concentration effect.” A similar effect on a second gas has been termed the “second gas effect”. These effects have been observed in open systems and attributed to differential changes between inspired and expired ventilation. The purpose of this investigation is to study these effects in a closed system. A breath-holding maneuver was utilized with a high and a low N2O concentration in argon and oxygen. The results indicate that breath holding with a high N2O concentration “concentrates” both the alveolar fraction of N2O and argon. These results are attributable to alveolar volume shrinkage as a consequence of the large absorption of N2O by the pulmonary blood. A mathematical model verifies this interpretation and suggests that volume shrinkage can be important in breath-holding maneuvers designed for noninvasive measurement of cardiac output and lung tissue volume.
Thoracoabdominal mechanics during relaxed and forced vital capacity
Authors: Siafakas N. M. , Morris A. J. , Green M.
Published: December 2017

Thoracoabdominal configuration, intrathoracic (esophageal), intra-abdominal (gastric), and transdiaphragmatic pressures were studied in six normal upright subjects during relaxed (RVC) and forced vital capacity (FVC). Chest wall configuration showed substantial departure from its relaxation characteristics during FVC. Paradoxical (outward) movement was recorded for a low lateral diameter of the rib cage (on the costal margin) at high volume during RVC and during most of FVC, while the other rib cage dimensions were decreasing. Transdiaphragmatic pressure was positive during most of the FVC, particularly toward RV, reflecting active contraction of the diaphragm. We conclude that diaphragmatic activity modulates forced expiration and that the chest wall may influence the FVC maneuver.
Tolerance of estrogen-treated rats to acute cold exposure
Authors: Fregly M. J. , Kelleher D. L. , Black D. J.
Published: December 2017

Female rats treated chronically with ethynylestradiol (36 micrograms/kg per day) alone, and in combination with the progestational agent, norethynodrel (253 micrograms/kg per day), cooled significantly faster than controls when lightly restrained and exposed to air at 5 degrees C. Rate of cooling of rats given only norethynodrel was similar to that of the control group. In other studies, rate of oxygen consumption was determined for all groups during acute exposure to cold (14 degrees C). All estrogen-treated groups achieved the same maximal rate of oxygen consumption as control and norethynodrel-treated groups during cold exposure, but cooled significantly faster. Two groups of female rats were treated chronically with ethynylestradiol at two separate doses (36 and 61 micrograms/kg per day). An untreated group served as controls. Rate of oxygen consumption of all animals were measured during restraint and exposure to cold (18 degrees C). The estrogen-treated groups again achieved the same maximal rate of oxygen consumption as the control group, but also cooled significantly faster despite the fact that the cold stress was less severe than in the previous experiment. That estrogen-treated rats cooled faster than controls in both studies despite achieving a maximal rate of heat production which did not differ from controls suggests that reduced cold tolerance of estrogen-treated rats may be related to increased heat loss.
Degradation of endogenous protein by rabbit pulmonary macrophages
Authors: Woodside K. H. , Massaro D.
Published: December 2017

Pulmonary macrophages were preincubated for 1 or 20 h with L-[U-14C]phenylalanine and the degradation of labeled proteins studied by reincubating these cells in the presence of 4 mM L-phenylalanine and measuring rates of [14C]phenylalanine released from the cells into the medium. We found that proteins prelabeled in 1 or 20 h were degraded 8.0 and 3.0%.h-1, respectively. Decreases in cell viability reduced the rate of protein degradation. Lack of exogenous glucose slowed the rate of degradation of proteins labeled in 1 h, but not of those labeled in 20 h. Varying amino acids in the medium from normal to 5 times normal rabbit plasma levels had no effect on the degradation of either group of proteins. Rates of degradation of both fast and slowly turning over proteins were inhibited during phagocytosis of polystyrene latex particles by about 62 and 33%, respectively. The time course of the changes in protein degradation suggests they are related to intracellular events in the phagocytic process, rather than particle attachment or uptake.
Mechanical efficiency of fast- and slow-twitch muscle fibers in man during cycling
Authors: Suzuki Y.
Published: December 2017

The influence of different percentages of slow-twitch (ST) and fast-twitch (FT) fibers in vastus lateralis on delta efficiency expressed by delta work (x)/delta energy liberation (y) in y = a + bx was studied in six subjects during cycling on an ergometer at 60 or 100 rpm at work loads below 80% of VO2max. Three subjects had an average of 78% ST fibers (ST group) and the other subjects had an average of 76% FT fibers (FT group). There was no difference between the two groups in delta efficiency at 60 rpm, but at 100 rpm the efficiency of the ST group was significantly lower than that of the FT group (19.6 vs. 28.8%, P less than 0.01). In the ST group respiratory exchange ratio (R) was higher at 100 rpm than at 60 rpm, but the FT group had similar R values at both pedal revolution rates. The most important finding was the reduced efficiency when pedaling frequency was increased from 60 to 100 rpm in the ST group (23.3 to 19.6%). Predominant use of ST fibers at rapid pedal rates may require a substantial increase in energy expenditure.
Frequency dependence of respiratory resistance in healthy children
Authors: Stanescu D. , Moavero N. E. , Veriter C. , Brasseur L.
Published: December 2017

We measured in 130 (61 girls) children aged 3--14 yr respiratory resistance (Rrs), with the oscillation technique, between 4 and 9 Hz. Rrs, at both 4 and 9 Hz, decreased as a function of height (r = 0.74, P less than 0.001). No statistical difference was found between boys and girls. Frequency dependence of resistance (Rrs 4 Hz-Rrs 9 Hz) was found in children at all ages, and decreased with increasing height (r = 0.50, P less than 0.001). We suggest that frequency dependence of resistance in children can be explained on the basis of an increased peripheral resistance, which produces an asynchronous distribution of tidal volume between dead space and lung parenchyma. During growth peripheral resistance decreases and Rrs bcome less frequency dependent to reach at about 15--16 yr independency of frequence.
Dibutyryl cyclic GMP and hyperventilation promote rat lung phospholipid release
Authors: Klass D. J.
Published: December 2017

Ventilation of rats at high inspiratory pressures raises lung tissue content of guanosine 30,5′-cyclic monophosphate (cGMP). Hyperventilation in rabbits augments release of phospholipid into lavage fluid. Can cGMP, in the absence of hyperventilation, increase lung phospholipid release? Sprague-Dawley rats are injected with [14C]palmitate, and after 1.5 h are anesthetized and ventilated for 20 min. Three groups are ventilated at peak inspiratory pressures (PIP) of 10 cmH2O, while saline, dibutyryl adenosine 3′,5′-cyclic monophosphate (DBcAMP), or dibutyryl cGMP (DBcGMP) is infused into the pulmonary artery. In a fourth group, saline is infused into the pulmonary artery, but ventilation is performed with PIP of 25 cmH2O. Lung tissue and lavage fluid are then analyzed for phospholipid (PL) content and for incorporation of [14C]palmitate into lavage and tissue PL fractions. Ventilation at increased pressure and infusion of DBcGMP are associated with increases in release of labeled PL into lavage fraction. The findings suggest that the increase in lavage PL release associated with hyperventilation is, at least in part, mediated by cGMP.
Liver blood flow and oxygen consumption during hypocapnia and IPPV in the greyhound
Authors: Hughes R. L. , Mathie R. T. , Fitch W. , Campbell D.
Published: December 2017

Pentobarbital-anesthetized greyhounds were passively hyperventilated using intermittent positive-pressure breathing (IPPV) and the effects of raised airway pressure, accompanied by hypocapnia and then by normocapnia, on liver blood flow and oxygen consumption were studied. Electromagnetic flowmeters were used to measure hepatic arterial, portal venous, and splenic venous blood flow. Studies were carried out at three levels of raised airway pressure, both at normocapnia and hypocapnia. It was found that hypocapnic hyperventilation produced a decrease in portal venous and hepatic arterial blood flow. Normocapnic hyperventilation resulted in a restoration of portal venous blood flow but with a further decrease in hepatic arterial blood flow. A decrease in oxygen consumption with hypocapnia, returning to control values with normocapnia, was seen. It is suggested that the reduction in liver blood flow and oxygen consumption seen with passive hyperventilation is chiefly an effect of hypocapnia and is largely reversed by restoration of normocapnia.
Effect of rate of change in skin temperature on local sweating rate
Authors: Libert J. P. , Candas V. , Vogt J. J.
Published: December 2017

To evaluate the relative contributions of positive and negative variations of mean skin temperature (+/- dTsk/dt) on thermoregulatory responses, male resting nude subjects were exposed to rapid or slow alterations in air and wall temperatures (28--45 degrees C; Pa = 20.0 mbar). Rates of heating-cooling cycles were equal to dTa/dt = +/- 3.40, 1.13, 0.57, 0.38, or 0.19 degrees C/min. Continuous measurements were made of rectal, oral, ear, and mean skin temperatures and of arm sweating (dew-point hygrometer method). During all exposures the local skin temperature was kept constant (Tsl = 39 degrees C). The results showed that peripheral inputs are a major factor in thermoregulatory processes. Cutaneous receptors produce a positive and a negative rate component within the central thermal integrator. A higher rate threshold was observed for the positive rate component than for the negative one.
In situ perfusion of rat lungs: stability and effects of oxygen tension
Authors: Watkins C. A. , Rannels D. E.
Published: December 2017

A new method for perfusion of rat lungs in situ was developed for metabolic studies. The pulmonary circulation was cannulated without contacting the lungs, which remained in the thoracic cage. Perfusion was continued for up to 4 h with Krebs-Henseleit bicarbonate buffer, equilibrated with 95% O2- 5% CO2 and containing 4.5% bovine serum albumin, 5.6 mM glucose, and levels of amino acids normally found in rat plasma. At an arterial pressure of 20 cmH2O flow remained constant (10.9 ml/min.100 g body wt) and appeared evenly distributed among the lobes. Tidal volume was 1 ml/100 g body wt (72/min); positive end-expiratory pressure was 2 cmH2O. The preparation remained stable and metabolically active for 4 h, as evidenced by a minimal decline in dry-to-wet weight ratio, constant levels of ATP and glycogen, a high ratio of glucose uptake to lactate production, and a linear rate of incorporation of [14C]phenylalanine into protein. The lungs were unaffected when perfusate oxygen was reduced to a more physiological level (20% O2–75% N2–5% CO2). In the presence of 95% N2–5% CO2 dry-to-wet weight ratio, ATP, glycogen, and amino acid incorporation decreased, while lactate production doubled.
Impedance of intrathoracic airway models during low-frequency periodic flow
Authors: Fredberg J. J. , Mead J.
Published: December 2017

The total pulmonary and lower airway impedances of the normal adult lung were simulated from 0.5 to 10 Hz using a distributed parameter model of the complete tracheobronchial tree. The model includes branching asymmetry; distributed representation of gas compliance, inertance, viscous effects, and inertial distortion of velocity profiles; and nonrigid airway walls. The model predicts closely similar resistance and frequency dependence of resistance but substantially greater reactances than observed by Finucane et al. (J. Appl. Physiol. 38: 517--530, 1975). Increases in resistance with frequency could be explained by changes in the distribution of flow among parallel inhomogeneities (47%), inertial distortion of velocity profiles (35%), changes in the serial distribution of flow due to gas compliance (11%), and airway wall compliance (7%). The disparity between measured and simulated reactance is attirbutable to artifact in the previously reported reactance measurement.
Effect of betamethasone on pressure-volume relationship of fetal rhesus monkey lung
Authors: Mitzner W. , Johnson J. W. , Scott R. , London W. T. , Palmer A. E.
Published: December 2017

We have investigated the acceleration of fetal lung maturity following glucocorticoid administration. Air-filling of saline-filling pressure-volume curves were obtained on fetal rhesus monkey lungs after treatment with betamethasone. With air filling there was a marked increase in the total lung capacity (ml air/g at 40 cmH2O) in the treated animals. By normalizing the curves and plotting volume as a percent maximal volume, we examined the shape of deflation curves, a common functional measure of surfactant activity. We found little difference in the shapes between control and steroid-treated animals. With saline filling there was also a similar increase in the lung capacity. As surface tension has a negligible effect on saline pressure-volume curves, we conclude that the primary functional effect of glucocorticoids on the fetal lung may not be an alteration of surface forces. Rather the glucocorticoids seem to accelerate maturity more by increasing lung compliance through structural changes that allow the lung to contain more air for equivalent transpulmonary pressures or pressure changes. This may occur either by increasing the distensibility of already inflatable alveoli or by recruiting new units.
Cage size and exercise affects infarct size in rat after coronary artery cauterization
Authors: Moskowitz R. M. , Burns J. J. , DiCarlo E. F. , Flaim S. F. , Harrison T. S. , Peuler J. , Zelis R.
Published: December 2017

Left coronary occlusion in the rat was performed by cornary artery cauterization. A small amount of myocardial damage at the site of occlusion was noted, and myocardial infarction occurred in the distal distribution of the obstructed coronary. The effects of cage size and level of physical activity on estimated infarct size (as measured by creatine kinase depletion) 48 h after occlusion were determined. Isolation in small cages and moderate treadmill exercise resulted in an approximate doubling of the amount of infarction when compared to grouping of rats in large cages. Mild exercise did not increase infarct size. Total urinary catecholamines in normal rats placed in small cages for 48 h were elevated when compared to unconfined rats in larger cages. Cornary artery occlusion by cauterization is an easily performed technique. Cage size and level of activity (and their effects on sympathoadrenal function) are important independent determinations of infarct extent after coronary occlusion in the rat.
Effects of glycogen depletion and work load on postexercise O2 consumption and blood lactate
Authors: Segal S. S. , Brooks G. A.
Published: December 2017

To study a possible relationship between blood lactate and O2 consumption (VO2) after exercise, 11 male subjects exercised on a bicycle ergometer at moderate and heavy work loads in both normal glycogen and glycogen-depleted states. At rest, glycogen depletion resulted in significantly lowered blood glucose and lactate concentrations, CO2 production (VCO2), respiratory exchange ratio (R), and minute ventilation (VE). With the exception of glucose, these variables changed more in response to heavy exercise (HE: 2 min at a mean of 1,750 kg.m/min) than to moderate exercise (ME: 2 min at a mean of 1,000 kg.m/min). At either work load, VCO2, R, and lactate showed consistently greater responses in the normal glycogen state. The slope of the initial component of the postexercise VO2 curve was unaffected by either work load or lactate. Although the slope of the slow component of the postexercise VO2 curve became significantly more negative after HE, it was unaffected by the level of lactate. These results are inconsistent with the hypothesis of a “lactacid O2 debt.” Exercise intensity was the predominant factor influencing the magnitude and kinetics of postexercise VO2. Glycogen depletion resulted in lower VCO2, R, and blood lactate, but higher VE during heavy exercise. The results suggest that factors, in addition to CO2 flux to the lungs, influence VE during exercise.