bluuebunny/crossref_metadata_2025 huggingface dataset:
Indices of thermoregulatory strain for moderate exercise in the heat
Authors: Gonzalez R. R. , Berglund L. G. , Gagge A. P.
Published: December 2017

The effect of varying humidity and dry bulb temperatures was studied on five normal male unclothed subjects while exercising (40–45 min) at 28% VO2max. Air movement was 0.75 m.s-1. The initial test and the 16th test on each subject both done at 50 degrees C and 30 Torr (32% rh). Each subject did the intervening 14 experiments twice per day at varying ambient temperature (Ta) and water vapor pressure (Pa) levels, so selected to progressively increase skin wettedness levels. Mean skin temperature (Tsk) and esophageal temperature (Tes), heart rate (HR), skin evaporative heat loss (Esk), and warm discomfort were continuously observed. Skin wettedness (w) was evaluated as the ratio of the observed Esk to the maximum evaporative capacity of the environment. A rational effective temperature (ET) is defined as the dry bulb temperature at 50% rh in which the total heat exchange from skin surface would be the same as in the test environment, described by the observed Ta and Pa. The results showed that 1) during steady state both HR and Tes were unaffected by Ta from 26 to 41 degrees C responding to the level of exercise intensity, when Pa less than or equal to 20 Torr; 2) both mean body temperature, found by weighting Tsk:Tes by 1:9, and ET were each significant indicators of physiological strain when Pa greater than 20 Torr; 3) a level of strain, caused by skin wettedness values greater than 0.5, is suggested as a primary condition necessary for inducing heat acclimation.
Cerebrospinal fluid acid-base balance during muscular exercise
Authors: Bisgard G. E. , Forster H. V. , Byrnes B. , Stanek K. , Klein J. , Manohar M.
Published: December 2017

Ventilation, metabolism, arterial blood gases, and blood and cerebrospinal fluid (CSF) acid-base status were measured in exercise studies on seven ponies during mild, moderate, and near-maximal treadmill exercise. CSF and arterial blood were sampled via indwelling catheters. Generally measurements were made during the 3rd, 6th, and 9th minute of steady-state exercise, with CSF sampled only during the 9th minute. Alveolar ventilation (VA) and metabolic rate (VO2) increased proportionately during exercise below the anaerobic threshold, but above this threshold, VA increased at a faster rate than VO2. The similarity of these response to those observed in man suggests the pony is a suitable animal model for study of exercise hyperpnea. No change in CSF acid-base balance occurred with light-to-moderate work; however, with near-maximal work a fall in CSF carbon dioxide partial pressure due to hyperventilation caused CSF to become alkaline (pH = 7.380) relative to rest (pH = 7.330). CSF lactate increased slightly with exercise but had no effect on CSF [HCO3-], which remained constant from rest to severe exercise. We conclude that it is unlikely the hyperpnea at any intensity of exercise results from an increased H+ stimulation at the medullary chemoreceptor.
Role of physical effort in the etiology of rat heatstroke injury and mortality
Authors: Hubbard R. W. , Matthew W. T. , Criss R. E. , Kelly C. , Sils I. , Mager M. , Bowers W. D. , Wolfe D.
Published: December 2017

A total of 171 untrained, unacclimatized, and unanesthetized rats were used to evaluate the effects of sedentary and work-induced hyperthermia on the incidence of mortality and cellular injury, 24 h postexposure. Cellular injury was defined as serum transaminase activity (SGPT and SGOT) exceeding 1,000 IU/l (heatstroke levels). Both the percent mortality and the percentage of 24-h survivors with transaminase levels above 1,000 IU/l were plotted against maximum core temperatures. Exertion-induced hyperthermia produced a significantly higher incidence of cellular injury and heatstroke death at lower core temperatures than hyperthermia alone. With hyperthermia only, the SGPT and SGOT dose-response curves were identical. When work was combined with hyperthermia, there was a greater incidence of elevated SGOT at lower core temperatures. These curves bore a striking resemblance to curves reflecting heat- and/or work-induced mortality in humans. The results suggest a direct role of physical effort in causing heatstroke injury and mortality.
Intracellular pH and bicarbonate concentration in human muscle during recovery from exercise
Authors: Sahlin K. , Alvestrand A. , Brandt R. , Hultman E.
Published: December 2017

Eight subjects exercised on an ergometer until exhaustion. Femoral venous blood was analyzed for lactate, pyruvate, protein, electrolytes, and acid-base parameters. Muscle samples taken during the recovery period from m. quadriceps femoris were analyzed for water, electrolytes, lactate, and acid-labile CO2. Water content in the muscle biopsy sample was increased after exercise to 78.7 +/- 0.5% compared with the normal 76.7 +/- 0.8% at rest. The distribution of water between the extra- and intracellular space was calculated by the chloride method. In spite of elevated PCO2 in femoral venous blood the content of acid-labile CO2 was decreased in muscle after exercise. One minute after termination of exercise muscle CO2 was about half of the normal content at rest. During the recovery period muscle CO2 increased but was 20 min after termination of exercise still significantly below the value at rest. Intracellular pH (pHi) and bicarbonate concentration ([HCO3-]i) in muscle have been calculated. The validity of the assumptions underlying the calculations are thoroughly discussed. pHi decreased from the normal value at rest, 7.00 +/- 0.06 (mean +/- SD), to about 6.4 after exercise. [HCO3-] decreased from 10.2 +/- 1.2 mmol/l at rest to about 3 mmol/l after exercise. The changes are the greatest so far reported for an in vivo situation. After 20 min recovery pHi was almost the same as at rest, whereas bicarbonate was still well below.
Waking and ventilatory responses to laryngeal stimulation in sleeping dogs
Authors: Sullivan C. E. , Murphy E. , Kozar L. F. , Phillipson E. A.
Published: December 2017

We studied waking and ventilatory responses to laryngeal stimulation during sleep in three dogs. The dogs breathed through an endotracheal tube inserted caudally into the trachea through a tracheostomy. Laryngeal stimulation was produced either by inflating a small balloon that was positioned in the rostral tracheal segment, or by squirting water onto the larynx through a catheter inserted through the tracheostomy. Airflow was measured with a pneumotachograph, and sleep state was determined by behavioral, electroencephalographic, and electromyographic criteria. We found that the degree of laryngeal stimulation required to produce arousal and coughing was higher in rapid-eye-movement (REM) sleep than in slow-wave sleep (SWS). Stimuli that failed to cause arousal from SWS often produced a single expiratory effort, or brief apnea (1--2 s) and bradycardia. In contrast, during REM sleep subarousal stimuli often resulted in prolonged apnea (greater than 10 s) and marked bradycardia. We conclude that during REM sleep arousal responses to laryngeal stimulation are depressed, but ventilatory and cardiac responses are intact.
Lung volumes after antigen infusion in the guinea pig in vivo: effects of vagal section
Authors: Drazen J. M. , Loring S. H. , Venugopalan C.
Published: December 2017

The effects of intravenous antigen infusion on lung volumes and quasi-static deflationary pulmonary compliance in guinea pigs previously sensitized to ovalbumin were studied in vivo. Ovalbumin infusion significantly increased minimal gas volume to a similar extent in animals with intact or cut vagi. Total lung capacity fell only in animals with intact vagi. Quasi-static compliance fell in both groups of animals, but the fall was significantly greater in animals with intact vagi. These data demonstrate that immediate hypersensitivity reactions alter lung volumes and the elastic properties of the lung by both vagal dependent and vagal independent mechanisms.
Effect on body water of running 10 miles
Authors: Colt E. W. , Wang J. , Pierson R. N.
Published: December 2017

Despite a 2.3% weight loss in 10 men who ran 10 miles, extracellular water (ECW) increased by 3.5%. Total body water (TBW) measured as tritium space increased by 2.4%, and intracellular water (ICW), inferred as the difference between TBW and ECW, increased by 1.8%. The increase in tritium space probably represents increased nonaqueous hydrogen exchange in the postexercise period ond casts doubt on the validity of TBW and ICW when measured immediately after exercise.
Electromyogram pattern of diaphragmatic fatigue
Authors: Gross D. , Grassino A. , Ross W. R. , Macklem P. T.
Published: December 2017

We studied the effect of breathing at various levels of transdiaphragmatic pressure (Pdi) on the EMG power spectrum of the diaphragm. The diaphragmatic EMG was measured simultaneously with a bipolar esophageal electrode (EE) and surface electrode (SE) placed on the ventral portion of the sixth and seventh intercostal spaces in five normal subjects breathing at functional residual capacity (FRC) against an inspiratory resistance. During each fatigue run the subjects generated a Pdi, with each inspiration, that was 25, 50, or 75% of maximum Pdi (Pdimax) for a period up to 15 min. During runs at 50 and 75% of the Pdimax, which are known to produce fatigue, we found for both EE and SE a progressive increase in the amplitude of the low-frequency (L = 20-46.7 Hz) and a decrease in the high-frequency (H = 150-350 Hz) component of the EMG. These changes were not seen at 25% of Pdimax. The diaphragmatic H/L ratio was independent of Pdi when the diaphragm was not fatigued. H/L fell while the diaphragm performed fatiguing work and this was more rapid at higher Pdi's. It was thus concluded that frequency spectrum analysis of the EMG can detect diaphragmatic fatigue reliably, prior to the time when the diaphragm fails as a pressure generator.
Role of respiratory heat exchange in production of exercise-induced asthma
Authors: Deal E. C. , McFadden E. R. , Ingram R. H. , Strauss R. H. , Jaeger J. J.
Published: December 2017

We have hypothesized that it is the total heat flux in the tracheobronchial tree during exercise that determines the degree of postexertional obstruction in asthma, and have developed quanititative expressions that relate these two events. We tested this hypothesis by comparing the observed responses to exercise, while our subjects inhaled dry air at various temperatures ranging from subzero to 80 degrees C in a random fashion, to those that we predicted would occur based upon calculations of respiratory heat exchange. We further determined if heat could be transferred from the inspired air to the mucosa so as to offset evaporative losses from the airways. The observed responses fell as air temperature was increased from -11 to +37 degrees C and exactly matched theoretical predictions. Above 37 degrees C, the observed response exceeded predictions, indicating that it was not possible to provide sufficient heat per se in the air to offset the vaporization of water. However, when small amounts of water vapor were added to the inspirate at high temperatures, bronchospasm was virtually abolished and the response again closely matched theoretical expectations. We conclude that the magnitude of exercise-induced asthma is directly proportional to the thermal load placed on the airways and that this reaction is quantifiable in terms of respiratory heat exchange.
Effect of static or slowly flowing blood on carbon monoxide diffusion in dog lungs
Authors: Holden W. E. , Hallenborg C. P. , Menzel T. E. , Dozor R. , Graf P. D. , Nadel J. A.
Published: December 2017

During temporary left pulmonary artery occlusion (TLPAO) in dogs, blood in pulmonary capillaries downstream from the occlusion is static or flowing slowly. In such areas, the uptake of carbon monoxide (CO) and diffusing capacity (DLCO) should decrease with time as carboxyhemoglobin concentration increases. We measured DLCO during exhalation of five sequential breaths in anesthetized dogs using a modification of a technique recently described in our laboratory (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 43: 617--625, 1977). During TLPAO, the decrease in DLCO was greatest at low lung volumes, suggesting that the occluded lung was emptying later in exhalation, a conclusion supported by measurements of DLCO during TLPAO with the right mainstem bronchus occluded. In addition. DLCO decreased with each breath as the backpressure to diffusion increased in static capillary blood. Inhalation of 4% CO accelerated the rate of decrease in DLCO. Measurement of DLCO during exhalation over multiple breaths may help detect pulmonary vascular obstruction.
Comparison of phrenic motoneuron responses to hypercapnia and isocapnic hypoxia
Authors: St John W. M. , Bartlett D.
Published: December 2017

This study was undertaken to compare phrenic motoneuron responses to hypercapnia and isocapnic hypoxia. Efferent activity of single phrenic nerve fibers was recorded with that of the contralateral phrenic nerve in decerebrate cats which were vagotomized, paralyzed, and artificially ventilated. At normocapnia in hyperoxia, single phrenic fibers were distributed into approximately equal “early” and “late” populations according to their onset of activity relative to the period of the phrenic burst. Elevations of PACO2 or diminutions of PAO2 resulted in progressive increases in the number of spikes per respiratory cycle and decreases in the modal interspike interval for both early and late units. Moreover, either stimulus caused an onset of late unit activity at progressively earlier portions of inspiration. At equivalent levels of peak integrated phrenic discharge achieved at normocapnia or hypercapnia as compared to normoxia or hypoxia, there were no differences in activity patterns for either early or late units. It is concluded that hypoxia-induced alterations in the activity of single phrenic motoneurons are identical to those changes resulting from hypercapnia.
Mechanism of rapid, shallow breathing after ozone exposure in conscious dogs
Authors: Lee L. Y. , Dumont C. , Djokic T. D. , Menzel T. E. , Nadel J. A.
Published: December 2017

In 10 experiments on 3 conscious dogs exercising on a treadmill, we studied the effect of ozone on base-line ventilation and on ventilatory responses to inhaled bronchoconstrictor drugs. Prior to ozone exposure, inhalation of histamine diphosphate aerosol (1%; 5 breaths) increased respiratory frequency (f) by 86 +/- 11% (mean +/- SE), and inhalation of prostaglandin F2 alpha (PGF2 alpha) aerosol (0.1%; 5 breaths) increased f by 74 +/- 16%. Immediately after ozone exposure %0.65 ppm; 2 h), steady-state base line f was increased by 120 +/- 18% and tidal volume (VT) was decreased by 43 +/- 5%. When conduction in the cervical vagus nerves (that were exteriorized permanently in skin loops) was blocked by cooling, these changes caused by ozone were abolished (P greater than 0.05). The increased responses to both histamine and PGF2 alpha aerosols after ozone were unaffected by pretreatment of isoproterenol aerosol (0.5%; 15 breaths), but were completely abolished by vagal cooling. Our studies indicate that ozone-induced rapid, shallow breathing and the increased ventilatory responses to inhaled histamine and PGF2 alpha aerosols are mediated through vagal afferent pathways.
Carotid chemoreceptors in ventilatory responses to changes in venous CO2 load
Authors: Phillipson E. A. , Bowes G. , Townsend E. R. , Duffin J. , Cooper J. D.
Published: December 2017

We examined the role of the carotid chemoreceptors in the ventilatory response to changes in venous CO2 load in 12 awake sheep using a venovenous extracorporeal perfusion circuit and two carbon dioxide membrane lungs (CDML). Three of the sheep had undergone surgical denervation of the carotid bodies (CBD). In the nine intact sheep, as CO2 was removed from or added to the peripheral venous blood through the CDML under normoxic conditions, there was a linear relationship between the rate of pulmonary CO2 excretion (VCO2) and the resulting rate of ventilation over a VCO2 range of 0--800% of control, so that arterial PCO2 remained close to isocapnic. In contrast, in the three CBD sheep, the ventilatory response to changes in VCO2 was significantly decreased under normoxic conditions, resulting in marked hypercapnia. The results indicate that the carotid chemoreceptors exert a major influence on the ventilatory response to changes in venous CO2 load.
Mechanism by which positive end-expiratory pressure increases cerebrospinal fluid pressure in dogs
Authors: Luce J. M. , Huseby J. S. , Kirk W. , Butler J.
Published: December 2017

We investigated possible mechanisms by which positive end-expiratory pressure (PEEP) increased cerebrospinal fluid pressure (PCSF) in anesthetized mechanically ventilated dogs. In part I of the study, PEEP was applied in 5 cmH2O increments each lasting 1–2 min, before and after a snare separated the spinal from the cerebral subarachnoid space in each animal. Next, with the spinal cord still ligated, the dogs were ventilated without PEEP while superior vena cava pressure (PSVC) was raised in 5 cmH2O increments by means of a fluid reservoir connected with the superior vena cava. Cerebrospinal fluid pressure in the cisterna magna increased immediately and in parallel with PEEP before and after the spinal subarachnoid space was occluded and also increased when PSVC was raised independently; in all circumstances the increase in PCSF correlated closely with PSVC (r = 0.926). In part II of the study, arterial blood gases were drawn before and after PEEP was applied in the same increments and for the same duration as in part I. Cerebrospinal fluid pressure measured with a hollow skull screw again rose in parallel with PEEP, whereas arterial carbon dioxide tension rose only slightly at 60 s. In part III of the study, mean arterial pressure (Pa) was allowed to decrease with PEEP or was held constant by distal aortic obstruction and volume infusion. Cerebrospinal fluid pressure increased regardless of Pa, but the increase was greater when Pa was held constant than when it fell with PEEP. We conclude that PEEP increases PCSF primarily by increasing PSVC and decreasing cerebral venous outflow. This effect is augmented if cerebral arterial inflow is increased as well.
Biochemical properties of overloaded fast-twitch skeletal muscle
Authors: Baldwin K. M. , Valdez V. , Herrick R. E. , MacIntosh A. M. , Roy R. R.
Published: December 2017

Previous studies suggest that fast-twitch skeletal muscle overloaded by surgical removal of synergists contains a greater percent of slow-twitch fibers than normal muscle. Therefore we examined subcellular systems known to represent biochemical properties of slow-twitch skeletal muscle by measuring myosin ATPase, Ca2+ regulation of myofibril ATPase, Ca2+ uptake of sarcoplasmic reticulum (SR), and marker enzymes of glycogenolysis in normal soleus (NS) and in normal (NP) and surgically overloaded (OP) plantaris muscles of adult female rats. The OP muscles were 65% larger than NP muscles (P less than 0.001). Specific activity of myosin and myofibril ATPase was approximately 25% lower in OP compared with NP muscle (P less than 0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of myosin revealed the presence of more slow and less fast myosin light-chain components in OP muscles. Although SR of NP muscle took up more Ca2+ than OP muscle during the initial for both groups. Marker regulatory enzymes of glycogenolysis collectively were reduced by 40% in OP compared with NP muscle (P less than 0.001). Collectively the data are consistent with the concept that some muscle fiber types were converted from “fast” to “slow” in the OP muscle.
Pulmonary gas exchange during high-frequency ventilation
Authors: McEvoy R. D. , Davies N. J. , Mannino F. L. , Prutow R. J. , Schumacker P. T. , Wagner P. D. , West J. B.
Published: December 2017

Gas exchange was investigated in normal anesthetized dogs during high-frequency, low-tidal volume ventilation (HFV) using the multiple inert gas elimination method. The pattern of inert gas elimination was initially normal during conventional mechanical ventilation. During HFV there was an increase in the difference between the excretion values of acetone and its less soluble neighboring gases, enflurane and ether, but elimination was independent of molecular weight. This pattern was consistent with a major degree of parallel ventilation-perfusion inequality with 49.4 +/- 1.7% of alveolar ventilation being distributed to lung units with VA/Q ratios greater than 20. Additional experiments, however, showed insufficient change in pulmonary blood flow distribution during HFV to account for these apparently poorly perfused lung units. Instead, it was found that the flux from the lung of the most soluble gas, acetone, per unit concentration difference along the airways was approximately twice that for other gases. Experiments using a simple airway model suggested that this enhanced transport of high-solubility gases during HFV is dependent on the wet luminal surface of conducting airways. A reciprocating exchange of gas between the lumen and airway lining layer is proposed as the most likely explanation for these results.
Pulmonary surfactant
Authors: King R. J.
Published: December 2017

Pulmonary surfactant reduces the surface tension of the alveolar air-liquid interface, thereby providing mechanical stability and preventing alveolar atelectasis. More than 50% of surfactant is dipalmitoyl phosphatidylcholine, a material that is capable of reducing the surface tension of the alveolar interface to uniquely low values. The functions of the remaining 25% unsaturated phosphatidylcholines, 5–10% phosphatidylglycerol, 5% cholesterol, and 8–10% protein are unknown. Surfactant is synthesized by alveolar epithelial type II cells and is probably secreted as a lipoprotein complex. Lamellar bodies, which distinguish type II cells, are likely to be intracellular sites of transport of processing. The catabolism of surfactant after it is secreted into the alveolar lumen is complicated and involves different turnover times for the phosphatidylcholines, phosphatidylglycerol, and the proteins. The metabolic events are under hormonal control and may involve an interplay between beta-adrenergic agonists cAMP, and prostaglandins. In disease, such as the neonatal and adult respiratory distress syndromes, derangements in the metabolic processes may produce surfactant that is abnormal with respect to its chemical and physical properties.
Synergism of hyperoxia and high helium pressures in the causation of convulsions
Authors: Brauer R. W. , Beaver R. W.
Published: December 2017

Hyperoxia beyond 1.8 ATA results in a striking reduction of high-pressure neurological syndrome (HPNS) type I convulsion threshold pressures but is without measurable effect on type II convulsions. The synergism is partially or completely reversed by increasing alveolar or tissue CO2 levels. High total pressures (PI) result in striking reductions in the duration of hyperoxic exposure preceding seizure onset (tc). The interaction of hyperoxia and high pressure gives rise to three zones on the PO2-Pt plane. In zone I, Pt less than 30 ATA, the duration of hyperoxia prior to convulsion onset is given by the equation PO2 -- PO2 lim = K/(tc -- tc lim), where PO2 lim and tc lim both decrease with increasing total pressure. Zone II, Pt = 30–50 ATA and PO2 1.8–2.3 ATA, is characterized by a sharp drop in tc, as Pt is increased beyond 30 ATA, to a value near 15 min that is constant within the PO2 limits given. In zone III, Pt greater than 50 ATA and PO2 greater than 0.2 ATA, tc is of the order of 2 min, and the seizures are essentially HPNS seizures only slightly modified by hyperoxia. The data are interpreted as suggesting that zone I represents hyperoxic seizures facilitated by high pressures, whereas zone II represents HPNS type I seizures facilitated by hyperoxia.
Reduced training duration effects on aerobic power, endurance, and cardiac growth
Authors: Hickson R. C. , Kanakis C. , Davis J. R. , Moore A. M. , Rich S.
Published: December 2017

Thirteen subjects participated in an exercise program of bicycling and running 40 min/day, 6 days/wk. After 10 wk they continued to train either 26 of 13 min/day for an additional 15 wk. Intensity and frequency for the additional 15 wk remained the same as the last 3 wk of training. This study was undertaken to gain further insights into whether the increases in maximum uptake (VO2 max), endurance, and cardiac size can be maintained with reduced training durations. The average increases in VO2 max in response to 10 wk training were between 10 and 20% during the bicycle and treadmill testing. After reduced training, VO2 max continued to remain at the training levels in both groups. Short-term endurance (approx 5 min) was also maintained by both groups. Long-term endurance (2 h or more) remained the same in the 26-min group but decreased significantly (10%, 13913;123 min) in the 13-min group. Calculated left ventricular mass increased 15–20% after training and remained elevated after reduced training in both groups. We conclude that it is possible to maintain almost all of the performance increases with up to a two-thirds reduction of training duration. Nevertheless, the data provide initial evidence that all aspects of the endurance-trained state may not be regulated uniformly in reduced training, particularly since VO2 max and short-term endurance were maintained, but long-term endurance decreased in the 13-min group.
Effect of heating rate on evaporative heat loss in the microwave-exposed mouse
Authors: Gordon C. J.
Published: December 2017

Male CBA/J mice were administered heat loads of 0–28 J X g-1 at specific absorption rates (SARs) of either 47 or 93 W X kg-1 by exposure to 2,450-MHz microwave radiation at an ambient temperature of 30 degrees C while evaporative heat loss (EHL) was continuously monitored with dew-point hygrometry. At an SAR of 47 W X kg-1 a threshold heat load of 10.5 J X g-1 had to be exceeded before EHL increased. An approximate doubling of SAR to 93 W X kg-1 reduced the threshold to 5.2 J X g-1. Above threshold the slopes of the regression lines were 1.15 and 0.929 for the low- and high-SAR groups, respectively. Thus the difference in threshold and not slope attributes to the significant increase in EHL when mice are exposed at a high SAR (P less than 0.02). In separate experiments a SAR of 47 W X kg-1 raised the deep body temperature of anesthetized mice at a rate of 0.026 degrees C X s-1, whereas 93 W X kg-1 raised temperature at 0.049 degrees C X s-1. Hence the sensitivity of the EHL mode of heat dissipation is directly proportional to the rate of heat absorption and to the rate of rise in body temperature. These data contradict the notion that mammals have control over whole-body heat exchange only (i.e., thermoregulation) but instead indicate that the EHL system is highly responsive to the rate of heat absorption (i.e., temperature regulation).
Measurement of energy expenditure in humans by doubly labeled water method
Authors: Schoeller D. A. , van Santen E.
Published: December 2017

The utility of the doubly labeled water method for the determination of energy expenditure and water output was investigated in humans. Approximately 10 g of 18O and 0.5 g of 2H as water was orally administered to four healthy adults. Total body water was determined from the isotope dilution, and the ensuing 18O and 2H disappearance rates from body water were determined for 13 days by mass spectrometric isotope ratio analysis of the urinary water. During this period, subjects were maintained on a measured diet to determine energy and water intake. The energy expenditure from the doubly labeled water method differed from dietary intake plus change in body composition by an average of 2%, with a coefficient of variation of 6%. The water outputs determined by the two methods differed by 1%, with a coefficient of variation of 7%. The doubly labeled water method is noninvasive, and the subjects could maintain their daily activities without restriction.
Volume and protein concentration of epithelial lining liquid in perfused in situ postnatal sheep lungs
Authors: Stephens R. H. , Benjamin A. R. , Walters D. V.
Published: December 2017

Previous methods of estimating the volume of epithelial lining liquid (ELL) in the air-filled lung may be said to have suffered from some theoretical and practical deficiencies. To estimate the ELL volume (VELL) more accurately, a known amount of artificial lung liquid (LL) containing the impermeant tracer 125I-albumin was instilled intraluminally in 56 in situ perfused postnatal sheep lungs (aged 36 h to 12 wk), and the rate of change of LL volume was measured by changes in the tracer concentration. Linear regression of LL volume against time allowed calculation of the VELL at the time of instillation; it was found to be 0.37 +/- 0.15 ml/kg body wt, which is equivalent to a film of 0.15 +/- 0.06 micron mean depth. The median ELL protein concentration was 36.8 mg/ml ELL, i.e., 0.60 times the plasma concentration, which agrees with previously published estimates and which is similar to the interstitial protein concentration. We conclude that the VELL is very small and that there is unlikely to be a protein osmotic gradient across the pulmonary epithelium.
Hypothyroid-mediated changes in adult rat diaphragm muscle contractile properties and MHC isoform expression
Authors: Gosselin L. E. , Zhan W. Z. , Sieck G. C.
Published: December 2017

The purpose of the present study was to examine the effect of acute hypothyroidism on myosin heavy chain (MHC) isoform composition and contractile properties in the adult rat diaphragm muscle. Hypothyroidism was induced by the addition of propylthiouracil (0.05%) in the drinking water for a period of 3 wk. MHC isoform composition of control and hypothyroid diaphragm muscles was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In vitro isometric contractile properties of midcostal diaphragm muscle segements were measured at 26 degrees C, whereas the maximal unloaded shortening velocity was measured at 15 degrees C with the "slack test" method. Serum triiodothyronine and thyroxine values were significantly lower in the hypothyroid compared with the control group. A small but significant increase in the percentage of slow MHC isoform in the diaphragm was observed with acute hypothyroidism, whereas the percentage of the fast MHC isoforms (2A, 2X, and 2B) did not significantly differ between groups. Peak twitch force did not differ between groups. However, twitch contraction and half-relaxation times were significantly prolonged in the hypothyroid group compared with control. Maximal specific force was reduced in the hypothyroid compared with the control group, averaging 15.7 and 19.8 N/cm2, respectively (P < 0.05). The maximal unloaded shortening velocity averaged 4.3 and 8.2 muscle lengths/s in the hypothyroid and control groups, respectively (P < 0.05). We conclude that acute hypothyroidism results in alterations in adult diaphragm muscle contractile properties that cannot be attributed solely to changes in MHC isoform composition.
Water balance and acute mountain sickness before and after arrival at high altitude of 4,350 m
Authors: Westerterp K. R. , Robach P. , Wouters L. , Richalet J. P.
Published: December 2017

The present study is a first attempt to measure water balance and its components at altitude by using labeled water and bromide dilution and relating the results with acute mountain sickness (AMS). Water intake, total water output, and water output in urine and feces were measured over a 4-day interval before and a subsequent 4-day interval after transport to 4,350 m. Total body water and extracellular water were measured at the start and at the end of the two intervals. There was a close relationship between energy intake and water intake, and the relationship was unchanged by the altitude intervention. Subjects developing AMS reduced energy intake and water intake cor respondingly. The increase in total body water (TBW) in subjects developing AMS was accompanied by a reduction in total water loss. They did not show the increased urine output, compensating for the reduced evaporative water loss at altitude. Subjects showed a significant increase in TBW after 4 days at altitude. Subjects with AMS showed the biggest shifts in extracellular water relative to TBW. In conclusion, fluid retention in relation to AMS is independent of a change in water requirements due to altitude exposure. Subjects developing AMS were those showing a fluid shift of at least 1 liter from the intracellular to the extracellular compartment or from the extracellular to the intracellular compartment.
A mechanism of nitric oxide-induced surfactant dysfunction
Authors: Hallman M. , Bry K. , Lappalainen U.
Published: December 2017

Inhaled nitric oxide (NO) may modify surfactant either by interacting with the surfactant complex or by changing the capacity of the proteins of the epithelial lining fluid to inhibit the surface activity. Natural surfactant was exposed to NO (80 parts/million) in air in vitro while the gas-liquid surface was cycled. In the presence or absence of oxidants (Fe2+, xanthine, xanthine oxidase), surfactant exposed to NO retained the high surface activity significantly better than control surfactants exposed to air. Two surfactant inhibitors, hemoglobin (Hb) and albumin, were separately exposed to NO. In contrast to albumin, NO-exposed Hb and methemoglobin (MetHb; 16-125 micrograms/ml) decreased the surface activity at low surfactant concentrations, whereas native Hb had no effect. Surfactant recovered by sedimentation after exposure to MetHb had decreased surface activity and contained MetHb, whereas Hb did not bind to surfactant. Acidic phospholipid phosphatidylglycerol increased the binding of MetHb to surfactant. The MetHb-induced decrease in surface activity was elicited in the presence of surfactant proteins, including a peptide mimicking surfactant protein B. MetHb (but not Hb) added to a low dose of exogenous surfactant decreased the efficacy of surfactant to improve the lung compliance of premature rabbits. We propose that inhaled NO promotes the surface activity of surfactant during tidal ventilation and that, in high-permeability lung edema and surfactant deficiency, inhaled NO increases the inhibition of surface activity by converting Hb to MetHb in the alveolar space.
Airway closure and reopening assessed by the alveolar capsule oscillation technique
Authors: Otis D. R. , Petak F. , Hantos Z. , Fredberg J. J. , Kamm R. D.
Published: December 2017

An alveolar capsule oscillation technique was used to determine 1) the lobe pressure and volume at which airways close and reopen, 2) the effect of expiration rate on closing volume and pressure, 3) the phase in the breathing cycle at which airway closure occurs, and 4) the site of airway closure. Experiments were conducted in excised dog lobes; closure was detected by an abrupt increase in the input impedance of surfacemounted alveolar capsules. Mean transpulmonary pressure (Ptp) at closure was slightly less than zero (Ptp = -2.3 cmH2O); the corresponding mean reopening pressure was Ptp = 14 cmH2O. The expiration rate varied between 1 and 20% of total lobe capacity per second and had no consistent effect on the closing volume and pressure. When lung volume was cycled up to frequencies of 0.2 Hz, closure generally occurred on expiration rather than inspiration. These observations support the conclusion that mechanical collapse, rather than meniscus formation, is the most likely mechanism producing airway closure in normal excised dog lungs. Analysis of measured acoustic impedances and reopening pressures suggests that closure occurs in the most peripheral airways. Reopening during inspiration was often observed to consist of a series of stepwise decreases in capsule impedance, indicating a sequence of opening events.
Density of the fat-free mass and estimates of body composition in male weight trainers
Authors: Modlesky C. M. , Cureton K. J. , Lewis R. D. , Prior B. M. , Sloniger M. A. , Rowe D. A.
Published: December 2017

The purpose of this study was to determine whether the assumed density and composition of the fat-free mass (FFM) and estimates of percent fat (%Fat) from body density by use of the Siri equation (%Fatd) are valid in weight trainers with high musculoskeletal development. Measures of body density by underwater weighing (Db), body water by deuterium dilution, and bone mineral by whole body dual-energy X-ray absorptiometry were obtained in young white men: 14 weight trainers with high musculoskeletal development and 14 non-weight-training controls with average musculoskeletal development. %Fatd was significantly higher (P < or = 0.05) than %Fat estimated from body density, water, and mineral (%Fatd,w,m) by use of a four-component model in weight trainers (17.3 +/- 4.6 vs. 13.2 +/- 5.1%) but not in controls (14.8 +/- 3.1 vs. 14.2 +/- 3.6%). The greater discrepancy between %Fatd and %Fatd,w,m was explained by lower density of fat-free mass (Dffm) in weight trainers (1.089 +/- 0.005 g/ml) than in controls (1.099 +/- 0.007 g/ml). The lower Dffm in the weight trainers was due to higher water (74.8 +/- 1.2 vs. 72.6 +/- 20%) and lower mineral (5.3 +/- 0.6 vs. 5.9 +/- 0.4%) and protein (19.9 +/- 1.4 vs. 21.5 +/- 1.9%) fractions of the FFM. We conclude that, in young white men with high musculoskeletal development, Dffm is lower than the assumed value of 1.1 g/ml and %Fat is overestimated from Db by use of the Siri equation.
Effects of medium-chain triglyceride ingestion on fuel metabolism and cycling performance
Authors: Van Zyl C. G. , Lambert E. V. , Hawley J. A. , Noakes T. D. , Dennis S. C.
Published: December 2017

On three occasions separated by 10 days, six endurance-trained cyclists rode for 2 h at 60% of peak O2 uptake and then performed a simulated 40-km time trial (T-trial). During the rides, the subjects ingested a total of 2 liters of a [U-14C]glucose-labeled beverage containing a random order of either 10% glucose [carbohydrate (CHO)], 4.3% medium-chain triglycerides (MCTs); or 10% glucose + 4.3% MCTs (CHO+MCT). Although replacing CHO with MCTs slowed the T-trials from 66.8 +/- 0.4 (SE) to 72.1 +/- 0.6 min (P < 0.001), adding MCTs to CHO improved the T-trials from 66.8 +/- 0.4 to 65.1 +/- 0.5 min (P < 0.05). Faster T-trials in the CHO+MCT trial than in the CHO trial were associated with increased final circulating concentrations of free fatty acids (0.58 +/- 0.09 vs. 0.36 +/- 0.06 mmol/l; P < 0.05) and ketones (1.51 +/- 0.25 vs. 0.51 +/- 0.07 mmol/l; P < 0.01) and decreased final circulating concentrations of glucose (5.2 +/- 0.2 vs. 6.3 +/- 0.3 mmol/l; P < 0.01) and lactate (1.9 +/- 0.4 vs. 3.7 +/- 0.5 mmol/l; P < 0.05). Adding MCTs to ingested CHO reduced total CHO oxidation rates from 14 +/- 1 to 10 +/- 1 mmol/min at 2 h and from 17 +/- 1 to 14 +/- 1 mmol/min in the T-trial (P < 0.01), without affecting the corresponding approximately 5 and approximately 7 mmol/min rates of [14C]glucose oxidation. These data suggest that MCT oxidation decreased the direct and/or indirect (via lactate) oxidation of muscle glycogen. A reduced reliance on CHO oxidation at a given O2 uptake is similar to an endurance-training effect, and that may explain the improved T-trial performances.
Mitochondrial enzymes increase in muscle in response to 7-10 days of cycle exercise
Authors: Spina R. J. , Chi M. M. , Hopkins M. G. , Nemeth P. M. , Lowry O. H. , Holloszy J. O.
Published: December 2017

Endurance exercise training induces a significant increase in the respiratory capacity of skeletal muscle. This is reflected by a training-induced increase in mitochondrial enzyme activity. One consequence of this adaptation is that there is a decreased reliance on carbohydrate utilization with a concomitant increase in fat utilization, resulting in an improvement in endurance capacity. Recently it has been reported that 7-14 days of cycle ergometer exercise training does not induce an increase in mitochondrial enzyme levels in skeletal muscle but, nevertheless, results in smaller decreases in phosphocreatine and glycogen and smaller increases in Pi and lactate in muscle in response to the same exercise after compared with before training. However, previous studies in rats have shown that an adaptive increase in mitochondrial enzymes is already evident after only 2 days of exercise training. In view of this discrepency, the present study was performed to reevaluate the effect of short-term training (7-10 days) on mitochondrial enzymes in skeletal muscle of humans. Twelve subjects [6 men and 6 women, 27 +/- 5 (SE) yr old] underwent 7 (n = 5) or 10 days (n = 7) of cycle ergometer exercise for 2h/day at 60-70% of peak O2 consumption. Peak O2 consumption was increased by 9% (from 2.97 +/- 0.16 to 3.24 +/- 0.17 l/min) in response to training. Blood lactate levels were lower at the same absolute work rates after than before training. The activities of citrate synthase, beta-hydroxyacyl-CoA dehydrogenase, mitochondrial thiolase, and carnitine acetyltransferase were increased by approximately 30% in response to training. The results of the present study provide evidence that in humans, as in rats, the adaptive increase in mitochondrial enzymes in skeletal muscle occurs fairly rapidly in response to exercise training. They provide no support for the claim that this adaptive response is delayed for > 2 wk after the onset of training.
Nonspiking interneurons in walking system of the cockroach
Authors: Pearson K. G. , Fourtner C. R.
Published: December 2017

Intracellular recordings were made from the neurites of interneurons and motoneurons in the metathoracic ganglion of the cockroach, Periplaneta americana. Many neurons were penetrated which failed to produce action potentials on the application of large depolarizing currents. Nevertheless, some of them strongly excited and/or inhibited slow motoneurons innervating leg musculature, even with weak depolariziing musculature, even with weak depolarizing currents. Cobalt-sulfide-straining of these nonspiking neurons showed them to be interneurons with their neurites contained entirely within the metathoracic ganglion. Two further characteristics of these interneurons were rapid spontaneous fluctuations in membrane potential and a low resting membrane potential. One nonspiking neuron, interneuron I, when depolarized caused a strong excitation of the set of slow levator motoneurons which discharge in bursts during stepping movements of the metathoracic leg. During rhythmic leg movements the membrane potential of interneuron I oscillated with the depolarizing phases occurring at the same time as bursts of activity in the levator motorneurons. No spiking or any other nonspiking neuron was penetrated which could excite these levator motoneurons. From all these observations we conclude that oscillations in the membrane potential of interneuron I are entirely responsible for producing the levator bursts, and thus for producing stepping movements in a walking animal. During rhythmic leg movements, bursts of activity in levator and depressor motoneurons are initiated by slow graded depolarizations. The similarity of the synaptic activity in these two types of motoneurons suggests that burst activity in the depressor motoneurons is also produced by rhythmic activity in nonspiking interneurons. The fact that no spiking neuron was found to excite the depressor motoneurons supports this conclusion. Interneuron I is also an element of the rhythm-generating system, since short depolarizing pulses applied to it during rhythmic activity could reset the thythm. Long-duration current pulses applied to interneuron I in a quiescent animal did not produce rhythmic activity. This observation, together with the finding that during rhythmic activity the slow depolarizations in interneuron I are usually terminated by IPSPs, suggests that interneuron I alone does not generate the rhythm. No spiking interneurons have yet been enccountered which influence the activity in levator motoneurons. Thus, we conclude that the rhythm is generated in a network of nonspiking interneurons. The cellular mechanisms for generating the oscillations in this network are unknown. Continued.
Organization and receptive fields of primate spinothalamic tract neurons
Authors: Applebaum A. E. , Beall J. E. , Foreman R. D. , Willis W. D.
Published: December 2017

A technique is described for recording from axons belonging to the spinothalamic tract of the monkey. The axons arose from cell bodies located within the spinal cord since the latency of orthodromic activation by afferents within the dorsal funiculus was short. The axons were antidromically activated from the ipsilateral diencephalon. The spectrum of conduction velocities indicates that the recordings favored large-diamter axons. However, all of the classes of spinothalamic tract units described from soma-dendritic recordings were represented in the sample. When the locations of the axons in the ventrolateral white matter were mapped, there was virtually complete overlap in the distributions of hair-activated, low-, and high-threshold spinothalamic tract axons, suggesting that the "lateral spinothalamic tract" conveys tactile, as well as pain and temperature, information. The only segregated population of axons were those belonging to units activated by receptors in deep tissues, including muscle. These were in a band along the ventral surface of the cord. The stimulus points for antidromically activating spinothalamic cells of axons were in the known diencephalic course of the spinothalamic tract, including the ventral posterior lateral nucleus. Stimulus point locations were similar for high-threshold and other categories of units. Receptive-field sizes were smaller for high-threshold spinothalamic cells or axons than for hair-activated or low-threshold units. Receptive-field size was correlated with position on the hindlimb. The smallest fields belonged to cells in lamina I, with progressively larger sizes for cells in laminae IV and V. Receptive-field shape was evaluated by the length/width ratio, which was smallest for high-threshold units and progressively larger for low-threshold and hair-activated units. The receptive-field positions of spinothalamic tract axons were related to the locations of the axons. There was a rough somatotopic representation in the tract, with the most caudal dermatomes represented dorsolaterally, and the most rostral ventromedially.