bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of VCO2 in control of breathing of awake exercising dogs
Authors: Bennett F. M. , Tallman R. D. , Grodins F. S.
Published: December 2017

Steady-state ventilatory responses to CO2 inhalation, intravenous CO2 loading (loading), and intravenous CO2 unloading (unloading) were measured in chronic awake dogs while they exercised on an air-conditioned treadmill at 3 mph and 0% grade. End-tidal PO2 was maintained at control levels by manipulation of inspired gas. Responses obtained in three dogs demonstrated that the response to CO2 loading [average increase in CO2 output (Vco2) of 216 ml/min or 35%] was a hypercapnic hyperpnea in every instance. Also, the response to CO2 unloading [average decrease in Vco2 of 90 ml/min or 15% decrease] was a hypocapnic hypopnea in every case. Also, the analysis of the data by directional statistics indicates that there was no difference in the slopes of the responses (change in expiratory ventilation divided by change in arterial Pco2) for loading, unloading, and inhalation. These results indicate that the increased CO2 flow to the lung that occurs in exercise does not provide a direct signal to the respiratory controller that accounts for the exercise hyperpnea. Therefore, other mechanisms must be important in the regulation of ventilation during exercise.
Ventilatory response to hypercapnia during sleep and wakefulness in cats
Authors: Netick A. , Dugger W. J. , Symmons R. A.
Published: December 2017

Eucapnic breathing and ventilatory responses to hypercapnia were studied in seven cats during sleep and wakefulness. No significant differences were found in minute ventilation (VE), alveolar ventilation (VA), or alveolar PCO2 (PACO2) between wakefulness (W) and non-rapid-eye-movement (NREM) sleep, but VA and VE were less during rapid-eye-movement (REM) sleep than W, and PACO2 declined during REM compared with NREM. To test the hypercapnic response, cats were required to rebreathe from a bag containing 6% CO2 and 94% O2 (to eliminate the hypoxic response). The response curve was displaced to the right during NREM and REM; the slope was reduced only during REM to a value about 75% of W and NREM. Eye movements, quantifying phasic REM, were only slightly correlated (negatively) with the deviation of ventilation from the response curve. The hypercapnic response was diminished, not eliminated, during REM, even during phasic REM. The reduced slope arose principally from the failure of the expiratory time to shorten with hypercapnia as during W and NREM. The cat's hypercapnic response compared with the dog's, measured by others with the same methodology, suggests that differences between species may be more crucial than methodology in explaining earlier contradictory results.
Thermal responses during arm and leg and combined arm-leg exercise in water
Authors: Toner M. M. , Sawka M. N. , Pandolf K. B.
Published: December 2017

Thermal and metabolic responses were examined during exposures in stirred water at approximately 20, 26, and 33 degrees C while subjects were performing 45 min of either arm (A), leg (L), or combined arm-leg (AL) exercise. Eight males immersed to the neck completed a low exercise intensity for A exercise and both a low and high exercise intensity for L and AL exercise. During low-intensity exercise, final metabolic rate (M) for A, L, and AL exercise was not different (P greater than 0.05) between exercise type for each water temperature (Tw). In contrast final rectal temperatures (Tre) for A and AL exercise were significantly lower than L values for each Tw during low-intensity exercise. These findings were supported by both mean weighted skin temperature (Tsk) and mean weighted heat flow (Hc) values, which were greater during A than L for each Tw. During high-intensity exercise, final Tre values were lower (P less than 0.05) during AL compared with L exercise across all Tw. Final Tsk and Hc values were not different between each type of exercise, although M was significantly lower during L exercise in 20 degrees C water. These data suggest a greater conductive and convective heat loss during exercise utilizing the arms when compared with leg-only exercise.
Effect of lung injuries on [14C]urea permeability-surface area product in dogs
Authors: Zelter M. , Lipavsky A. , Hoeffel J. M. , Murray J. F.
Published: December 2017

To determine whether [14C]urea permeability-surface area product (PS) is a reliable indicator of changes in permeability in various injuries and its relationship to indicator-dilution and gravimetric lung water contents, we studied six groups of anesthetized, paralyzed, and mechanically ventilated dogs (5 animals each). The groups consisted of control dogs, those injured by intravenous alloxan, oleic acid, or glass beads, and those exposed to acute hypoxia or increased left atrial pressure from volume loading (Pla). Interanimal variation of PS was large (3.0–15.0 ml/s), but successive hourly values in individual animals were stable for 2 h in experimental groups and for 4 h in controls. The PS increased after alloxan, elevated Pla, and 2 h of hypoxia; PS decreased after oleic acid and microemboli. The gravimetric lung water increased after alloxan, oleic acid, and microemboli, and indicator-dilution lung water increased only after alloxan. We conclude 1) that intersubject variability requires normalization to enable detection of significant deviation from base line, and 2) that decreased PS after oleic acid and microvascular injury occurred because vascular obstruction, which decreased surface area, masked probable coexisting increases in capillary permeability.
EMG activity of slow and fast ankle extensors following spinal cord transection
Authors: Alaimo M. A. , Smith J. L. , Roy R. R. , Edgerton V. R.
Published: December 2017

Transformations of slow-twitch fibers to the fast-twitch type following spinal cord transection are thought to be related to a substantial decrease or virtual absence of neuromuscular activity. In this experiment, spontaneous activity levels in spinalized and normal cats, raised under similar conditions, were assessed by integrated electromyography (I-EMG) recorded for 240 min over 24 h from the slow-contracting soleus (SOL) and the fast-contracting lateral gastrocnemius (LG). In the SOL of the spinalized cats, there was a 75% reduction in total I-EMG and a 66% reduction in the total duration of muscle activity. Conversely, the LG showed no significant change in total I-EMG, but there was a 66% reduction in the total duration of muscle activity. Based on muscle property data published in companion studies, there was no significant correlation between the SOL total I-EMG and the reduction in contraction times or the decrease in the percentage of slow-twitch fibers determined histochemically. We conclude that transformations of slow-twitch fibers following spinal transection may be regulated by several factors, among which is the total level of spontaneous daily activity.
Plasma catecholamines and their effect on blood lactate and muscle lactate output
Authors: Stainsby W. N. , Sumners C. , Andrew G. M.
Published: December 2017

This study was designed to test the hypothesis that epinephrine (E) and norepinephrine (NE) increase net muscle lactate output (L) of in situ gastrocnemius-plantaris muscle group during contractions. Plasma [E] and [NE] were measured before and after the surgical isolation of the muscle and at 10-min intervals during the 60-min experiments. Plasma [E] and [NE] were increased threefold by intravenous infusions of E (n = 3) or NE (n = 3) at a rate of 1.5 micrograms X kg body wt-1 X min-1. Arterial and muscle venous blood samples for O2 and lactate concentrations were also obtained. The infusions began at min 11 and repetitive isometric contractions (4 tw/s) began at min 31. The presurgery plasma [E] and [NE] averaged 0.34 and 0.52 ng/ml, respectively, and rose to 1.12 and 1.19 ng/ml 10 min after surgery. Arterial and venous lactate concentrations (CaL and CvL) increased continuously during E infusion but remained constant during NE infusion. Maximal L during the first 10 min of contractions was significantly increased compared with an identical earlier study without infusions. O2 uptake was not changed by the infusions. It is concluded that E causes CaL to rise and that both E and NE increase maximal net lactate output during contractions.
CO2 elimination as a function of frequency and tidal volume in rabbits during HFO
Authors: Watson J. W. , Jackson A. C.
Published: December 2017

CO2 elimination (VCO2) was monitored during high-frequency oscillation (HFO) over a frequency (f) range of 2–30 Hz in anesthetized and paralyzed rabbits to determine whether effective gas exchange could be achieved in this species, to determine the f and tidal volume (VT) dependence of gas exchange in this species, and to compare these results with those from dog and human studies. We were able to produce VCO2 levels during HFO that exceeded normal steady-state levels of CO2 production with VT's less than the total dead space volume. VCO2 was related to f in a curvilinear fashion, whereas in some rabbits VCO2 became independent of f at higher frequencies. This curvilinear relationship between f and VCO2 is similar to data from humans but contrasts with the linear relationship found in dogs. Evidence is presented indicating frequency-dependent behavior of gas exchange is correlated with a frequency-dependent decrease in respiratory system resistance. We propose that the frequency-dependent mechanical properties of the rabbit lung may also account for the species differences in HFO gas exchange.
Upper airway closing pressures in snorers
Authors: Issa F. G. , Sullivan C. E.
Published: December 2017

We studied 14 subjects who were selected to represent the broad range of severity of snoring: group A, four subjects who gave a history of snoring only when provoked by nasal obstruction or alcohol intake; group B, six subjects who typically snored for long periods each night; and group C, four subjects who snored heavily all night and who typically experienced a few episodes of obstructive apnea (mean apnea index 4 apneas/h). Low levels of nasal continuous positive airway pressure (CPAP) (range, 2.0–6.0 cmH2O; mean, 4.0 cmH2O) prevented snoring. Nasal occlusion caused upper airway closure during inspiratory efforts in all 14 subjects. There was a relationship between the clinical severity of snoring and the upper airway closing pressure (UACP). Upper airway closure occurred at greater suction pressures in group A than in group C but there was overlap between the three categories. The upper airway was consistently more collapsible in rapid-eye-movement sleep than in non-rapid-eye-movement sleep. There was little evidence of breath-by-breath improvement of upper airway stability during sustained asphyxia, the UACP remaining constant despite marked increases in drive to the diaphragm. In five subjects UACP was measured following alcohol intake. Alcohol reduced upper airway stability in all subjects in a dose-dependent manner.
O2 transport in ponies during treadmill exercise
Authors: Pan L. G. , Forster H. V. , Bisgard G. E. , Dorsey S. M. , Busch M. A.
Published: December 2017

We assessed cardiovascular variables and blood O2 contents in order to characterize O2 transport in ponies during treadmill exercise. In normal ponies at 1.8, 3, and 6 mph, respectively, cardiac output (Qc) increased from 12 l/min at rest to maximum levels of 19.7, 28.7, and 39.9 l/min between 30 and 60 s. Qc then decreased to steady-state levels of 18.2, 24.6, and 32.7 l/min by 4 min. Heart rate (HR) showed a similar biphasic response in the 1st min of exercise. Systolic and diastolic arterial blood pressure (BP) decreased at the onset of exercise by 20–25 Torr (P less than 0.05) and then increased to a steady-state by 60 s. Mean right ventricular pressures (MRVBP) increased from approximately 9.7 Torr at rest to 15.9 (1.8 mph), 15.2 (3 mph), and 23.6 Torr (6 mph) by 1 min and then decreased throughout the remainder of the 8 min of exercise (P less than 0.05). At 3 and 6 mph, respectively, arterial O2 content (CaO2) increased from 11.6 vol% at rest to 12.7 and 15.0 vol% by 45 s and 13.1 and 16.6 vol% by 7 min. At 7 min of 9.3 mph exercise, it increased to 20.34 vol%. Hemoglobin (Hb) at 3 mph increased from 9.6 g/100 ml at rest to 10.5 g/100 ml by 45 s and 11.7 g/100 ml by 7 min. At 6 mph, Hb increased to 12 g/100 ml at 45 s and 13.0 g/100 ml by 7 min of exercise. These data demonstrate that the rapid, work load-dependent increase in CaO2 represents an important mechanism to increase O2 transport in exercising ponies.(ABSTRACT TRUNCATED AT 250 WORDS)
Temporal pattern of pulmonary gas exchange during exercise in ponies
Authors: Forster H. V. , Pan L. G. , Bisgard G. E. , Dorsey S. M. , Britton M. S.
Published: December 2017

We characterized the temporal patterns of pulmonary O2 consumption (VO2) and CO2 excretion (VCO2) in exercising ponies. We also assessed the cardiac, ventilatory, and hematologic contributions to the VO2-VCO2 changes during exercise. At five moderate treadmill work loads in normal ponies, VO2 and VCO2 generally increased progressively throughout the 1st min reaching, respectively, approximately 95 and 80% of steady state by 45–60 s. Between 1 and 1.5 min, Vo2 and Vco2 were either stable or they decreased 300–500 ml, but then each increased slightly, reaching steady-state levels between 3 and 5 min. The increases to steady-state VO2 and VCO2 were clearly not monoexponential. Arterial O2 content (CaO2) increased during exercise, presumably because of mobilization of stored splenic erythrocytes. For example, after 1 and 6 min at 6 mph 3% grade, CaO2 had increased above rest by 3.2 and 4.9 vol%, respectively (P less than 0.05). Hyperventilation during exercise decreased arterial CO2 content (CaCO2) below rest. For example, after 1 and 6 min at 6 mph 3% grade, CaCO2 had decreased below rest by 2.8 and 1 vol%, respectively (P less than 0.05). At all work loads, heart rate (HR) and presumably cardiac output increased rapidly during the 1st min, reaching a maximum by approximately 45 s. HR then decreased (P less than 0.05), reaching a steady state by 3 min of exercise. During the first 1.5 min of exercise in carotid body-denervated (CBD) ponies, the changes in VO2, HR, and CaO2 were temporally delayed relative to the normals, whereas the changes in VCO2 and CaCO2 were relatively augmented.(ABSTRACT TRUNCATED AT 250 WORDS)
Physiological dead space during high-frequency ventilation in dogs
Authors: Weinmann G. G. , Mitzner W. , Permutt S.
Published: December 2017

Tidal volumes used in high-frequency ventilation (HFV) may be smaller than anatomic dead space, but since gas exchange does take place, physiological dead space (VD) must be smaller than tidal volume (VT). We quantified changes in VD in three dogs at constant alveolar ventilation using the Bohr equation as VT was varied from 3 to 15 ml/kg and frequency (f) from 0.2 to 8 Hz, ranges that include normal as well as HFV. We found that VD was relatively constant at tidal volumes associated with normal ventilation (7–15 ml/kg) but fell sharply as VT was reduced further to tidal volumes associated with HFV (less than 7 ml/kg). The frequency required to maintain constant alveolar ventilation increased slowly as tidal volume was decreased from 15 to 7 ml/kg but rose sharply with attendant rapid increases in minute ventilation as tidal volumes were decreased to less than 7 ml/kg. At tidal volumes less than 7 ml/kg, the data deviated substantially from the conventional alveolar ventilation equation [f(VT - VD) = constant] but fit well a model derived previously for HFV. This model predicts that gas exchange with volumes smaller than dead space should vary approximately as the product of f and VT2.
Influence of blood flow on cutaneous permeability to inert gas
Authors: Lin Y. C. , Kakitsuba N. , Watanabe D. K. , Mack G. W.
Published: December 2017

A thermally regulated Plexiglas chamber was designed for investigation of transcutaneous diffusion of N2 and helium (He) in the human hand. Influence of cutaneous blood flow in this process was studied simultaneously with gas diffusion measurements. Changes in cutaneous blood flow (Q, in ml X min-1 X 100 ml tissue-1) were effected by altering ambient temperature (T) from 20 to 40 degrees C (Q = 0.08 X 100.07T). We found that the rate of inert gas diffusion through human skin, expressed as conductance (G, in ml STPD X h-1 X m-2 X atm-1), increases exponentially as a function of blood flow, and was indistinguishable between He and N2 (G = 21.19 X 100.0124Q). The permeability, diffusion coefficient per unit diffusion distance (D/h, in cm/h), also rose exponentially as a function of blood flow. But permeability for He (D/h = 0.1748 X 100.0203Q) was greater than that for N2 (D/h = 0.1678 X 100.0114Q). As cutaneous blood flow rises, because of increased temperature, the apparent diffusion distance falls linearly for both N2 and He. The change is more prominent for He than for N2 diffusion. Estimated replacement time for the body stores of N2 by transcutaneous diffusion alone was shortened from 26.8 h at 31 degrees C to 15.1 h at 37 degrees C. It is suggested from this study that beneficial results may be derived during decompression procedure 1) by maintaining an appropriate transcutaneous pressure gradient of inert gases, and 2) by elevating ambient temperature.
Antagonism by taurine of pressure-induced tremor in the guinea pig
Authors: Gilman S. C. , Hallenbeck J. M. , Ackerman M. J. , Bradley M. E.
Published: December 2017

The tremorogenic effect of high pressure was antagonized in guinea pigs by intravenous treatment with taurine in doses of 250 and 500 mg/kg. Also pretreatment with 250 mg/kg taurine suppressed tremor development as evidenced by increased threshold and decreased amplitude. It is hypothesized that antagonism of pressure-induced tremor by taurine may be related to changes in membrane calcium transport.
Frequency dependence of pulmonary compliance and resistance in patients with obstructive lung disease
Authors: Clement J. , Bobbaers H. , Van de Woestijne K. P.
Published: December 2017

The frequency dependence of pulmonary compliance and resistance was investigated in 27 patients with obstructive lung disease. Compliance and resistance were determined either by the conventional zero crossing (Cdyn) and isovolume (RL) technique or by a modified Fourier analysis following a smoothing procedure (auto- and cross-correlation function) yielding an effective compliance and resistance, CL and RL. The latter technique was used to calculate CL and RL from the fundamental and third and fourth harmonics present in the flow and transpulmonary pressure signals. Three breathing frequencies were investigated: 0.5, 1, and 2 Hz. Both Cdyn and CL, calculated from the fundamental component, decreased progressively with frequency. However, Cdyn showed less frequency dependence than CL. CL calculated from the harmonics was significantly smaller than CL from the fundamental at the same breathing frequency. RL, as well as RL calculated from the fundamental, tended to increase with frequency. A decline of resistance with frequency became apparent, however, when RL from the fundamental was compared with RL obtained from the corresponding higher order harmonics. These results suggest that the frequency dependence of resistance can be masked by the usual procedure of breathing at several frequencies. Instead the measurements should be performed at a single frequency, for instance spontaneous breathing, by computing resistance from the higher order harmonics present in the breathing signals.
Direct effects of nitroprusside do not alter gas exchange in canine oleic acid edema
Authors: Angle M. , Ducas J. , Schick U. , Girling L. , Prewitt R. M.
Published: December 2017

The authors investigated why intrapulmonary shunt (QS/QT) increases with sodium nitroprusside (SNP) in canine oleic acid pulmonary edema. To determine the effects of flow alone on QS/QT, a peripheral arteriovenous fistula with a variable resistor was employed to increase cardiac output (Q) 26 and 52% above base line in a stepwise fashion (P less than 0.01). To examine the direct effects of SNP, distinct from changes in flow, the drug was given to produce matched increments in Q in each dog (P less than 0.01). To control for time, base-line measurements were obtained before and after each intervention, the sequence of which was alternated. At each increment in Q, SNP and the arteriovenous fistula increased QS/QT a similar amount. The mixed venous O2 tension (P-vO2) followed Q similarly in each group. Pulmonary vascular resistance (PVR) fell more (P less than 0.01) with SNP than with the arteriovenous fistula at identical Q and P-vO2. The authors conclude that, in this model, a direct pharmacological effect of SNP does not contribute to the deterioration in QS/QT. In fact, SNP exerts a pulmonary vasoactive effect that does not adversely affect gas exchange.
Glycosaminoglycan biosynthesis in the isolated perfused rat lung
Authors: Sampson P. M. , Boyd R. B. , Pietra G. G. , Fishman A. P.
Published: December 2017

The suitability of an isolated lung, perfused under carefully monitored conditions, for the study of the biosynthesis of glycosaminoglycans was examined for the rat lung using either [35S]-sulfate or [6-3H]glucosamine. Metabolic and electron-microscopic studies after 3 h of perfusion showed that under the conditions of this study the isolated lung showed no anatomical or metabolic derangements. All glycosaminoglycans normally synthesized in the intact lung were identified. The predominant glycosaminoglycan was heparan sulfate (40% of total). Approximately 14% of the glucosamine incorporated into the glycosaminoglycans was found in hyaluronic acid. Less than 5% of either label was in heparin. The remainder of the synthesized glycosaminoglycans, with the exception of 10% which could not be identified, consisted of the chondroitin sulfates and dermatan sulfate. The relative proportions of the newly synthesized glycosaminoglycans, including the low amounts of heparin, are similar to those found in isolation of endogenous lung glycosaminoglycans. The isolated perfused rat lung appears to be a useful model for the study of glycosaminoglycan biosynthesis by the intact lung.
Effect of a 42.2-km footrace and subsequent rest or exercise on muscular strength and work capacity
Authors: Sherman W. M. , Armstrong L. E. , Murray T. M. , Hagerman F. C. , Costill D. L. , Staron R. C. , Ivy J. L.
Published: December 2017

This study 1) quantitates the effect of a 42.2-km footrace (marathon) on leg extensor strength (maximal peak torque, MPT) and work capacity (WC, measured during a leg extensor fatigue test), and 2) describes the effect of either a rest or exercise regimen for 1 wk after the marathon on the recovery of MPT and WC. Ten trained male runners performed personal records in a marathon and were then randomly assigned to either a rest or exercise-recovery group. The rest group did not train, whereas the exercise group ran 20-45 min/day at their selected intensity of exercise [50-60% maximal O2 consumption (Vo2max)] during the recovery week. MPT was measured at 1.1, 3.2, and 5.3 rad X s-1. The total work generated during a 50-contraction active extension-passive flexion fatigue test conducted at 3.2 rad X s-1 was defined as WC. Reports of perceived soreness of the quadriceps were obtained before each strength-testing session. These measurements were obtained before the marathon and 15-20 min and 1, 3, 5, and 7 days postmarathon. A significant reduction in MPT and WC resulted and continued 1 day postmarathon. MPT of both groups improved through day 5 postmarathon at 1.1 and 3.2 rad X s-1. MPT of the rest group improved through day 7 postmarathon but remained less than premarathon MPT. Recovery of MPT was impaired in the exercise group through days 5-7 postmarathon after 40-45 min exercise at 60% Vo2max. WC was recovered 3 days postmarathon in the rest group but was still impaired 7 days postmarathon in the exercise group.(ABSTRACT TRUNCATED AT 250 WORDS)
Pharyngeal airway-stabilizing function of sternohyoid and sternothyroid muscles in the rabbit
Authors: Roberts J. L. , Reed W. R. , Thach B. T.
Published: December 2017

The upper airway is vulnerable to collapse from negative intraluminal pressures during inspiration. The tongue muscles, the genioglossi and geniohyoids, by contracting during inspiration, appear to function to resist this collapse. This study supports the hypothesis that two cervical strap muscles, the sternohyoid and sternothyroid, have a similar function. First, phasic inspiratory electromyographic activity was recorded from the sternohyoid and sternothyroid muscles of nine anesthetized rabbits during tidal breathing. Furthermore, each muscle showed a progressive increase in electromyographic activity with airway occlusion. Second, in eight rabbits, by determining the amount of negative pressure required to collapse the upper airway (airway closing pressure determination), it was shown that upper airway stability improved with electrical stimulation of either the paired sternohyoid or sternothyroid muscles. In addition, in 12 freshly killed rabbits, mechanical tension, mimicking the contraction of either the sternohyoid or sternothyroid, improved airway stability. Finally, observations of the pharyngeal lumen utilizing a fiber-optic endoscope, revealed concentric narrowing of the oro- and nasopharynx when airway pressure was lowered and concentric widening when tension was increased in the sternohyoid or sternothyroid muscles. These findings support the hypothesis that phasic inspiratory contraction of the sternohyoid and sternothyroid muscles functions to resist pharyngeal airway collapse due to negative intraluminal pressures.
Temperature regulation during treadmill exercise in the rat
Authors: Shellock F. G. , Rubin S. A.
Published: December 2017

The response of colonic and tail-skin temperatures to treadmill exercise was assessed in female Sprague-Dawley rats using incremental and single-stage exercise protocols to investigate the relationship between deep body temperature and work rate. O2 uptake (VO2) was measured by flow-through technique to evaluate the exercise intensity. Experiments were performed in ambient temperatures below (22-25 degrees C) and above (33-35 degrees C) the thermoneutral zone of the rat. During graded incremental exercise there was a linear relationship between colonic temperature (Tco) and VO2 in both the cooler and warmer ambient temperatures. However, Tco and tail-skin temperature (Tsk) at comparable work rates in the cooler and warmer environments were 40.22 +/- 0.59, 34.84 +/- 1.10 degrees C and 42.04 +/- 0.57, 38.39 +/- 1.54 degrees C, indicating that the rise in Tco was unrelated to the severity of exercise. During single-stage exercise the rats were able to achieve thermal equilibrium but only at low work rates and in the cool environment (22-25 degrees C). There were no significant differences in Tco at the first three levels of single-stage exercise (stage 1, 39.63 +/- 0.34 degrees C; stage 2, 39.67 +/- 0.49 degrees C; stage 3, 39.75 +/- 0.50 degrees C) despite significant differences in VO2 (stage 1, 4.3 +/- 0.7 ml X min-1 X 100 g-1; stage 2, 5.3 +/- 0.6 ml X min X 100 g-1; stage 3, 7.6 +/- 1.2 ml X min-1 X 100 g-1). This demonstrates that there was no relationship between the level of Tco maintained during exercise and the work intensity.(ABSTRACT TRUNCATED AT 250 WORDS)
Epinephrine, norepinephrine, and dopamine during a 4-day head-down bed rest
Authors: Pequignot J. M. , Guell A. , Gauquelin G. , Jarsaillon E. , Annat G. , Bes A. , Peyrin L. , Gharib C.
Published: December 2017

Head-down bed rest at an angle of 6 degrees was used as an experimental model to simulate the hemodynamic effects of microgravity, i.e., the shift of fluids from the lower to the upper part of the body. The sympathoadrenal activity during acute (from 0.5 to 10 h) and prolonged (4 days) head-down bed rest was assessed in eight healthy men (24 +/- 1 yr) by measuring epinephrine (E), norepinephrine (NE), dopamine (DA), and methoxylated metabolite levels in their plasma and urine. Catecholamine (CA) and methoxyamine levels were essentially unaltered at any time of bed rest. Maximal changes in plasma were on the second day (D2): NE, 547 +/- 84 vs. 384 +/- 55 pg/ml; DA, 192 +/- 32 vs. 141 +/- 16 pg/ml; NS. After 24 h of bed rest, heart rate decreased from 71 +/- 1 to 63 +/- 3/min (P less than 0.01). Daily dynamic leg exercise [50% maximum O2 uptake (VO2 max)] used as a countermeasure did not alter the pattern of plasma CA during bed rest but resulted in a higher urinary NE excretion during postexercise recovery (+45% on D2; P less than 0.05). The data indicate no evident relationship between sympathoadrenal function and stimulation of cardiopulmonary receptors or neuroendocrine changes induced by central hypervolemia during head-down bed rest.
Role of tracheal and bronchial circulation in respiratory heat exchange
Authors: Baile E. M. , Dahlby R. W. , Wiggs B. R. , Pare P. D.
Published: December 2017

Due to their anatomic configuration, the vessels supplying the central airways may be ideally suited for regulation of respiratory heat loss. We have measured blood flow to the trachea, bronchi, and lung parenchyma in 10 anesthetized supine open-chest dogs. They were hyperventilated (frequency, 40; tidal volume 30–35 ml/kg) for 30 min or 1) warm humidified air, 2) cold (-20 degrees C dry air, and 3) warm humidified air. End-tidal CO2 was kept constant by adding CO2 to the inspired ventilator line. Five minutes before the end of each period of hyperventilation, measurements of vascular pressures (pulmonary arterial, left atrial, and systemic), cardiac output (CO), arterial blood gases, and inspired, expired, and tracheal gas temperatures were made. Then, using a modification of the reference flow technique, 113Sn-, 153Gd-, and 103Ru-labeled microspheres were injected into the left atrium to make separate measurements of airway blood flow at each intervention. After the last measurements had been made, the dogs were killed and the lungs, including the trachea, were excised. Blood flow to the trachea, bronchi, and lung parenchyma was calculated. Results showed that there was no change in parenchymal blood flow, but there was an increase in tracheal and bronchial blood flow in all dogs (P less than 0.01) from 4.48 +/- 0.69 ml/min (0.22 +/- 0.01% CO) during warm air hyperventilation to 7.06 +/- 0.97 ml/min (0.37 +/- 0.05% CO) during cold air hyperventilation.
Interaction of local and reflex thermal effects in control of forearm blood flow
Authors: Wenger C. B. , Bailey R. B. , Roberts M. F. , Nadel E. R.
Published: December 2017

We measured forearm blood flow (ABF) bilaterally on six subjects during 15-min periods of leg exercise and the first 10 min of recovery. One forearm (control) was kept at about 33 degrees C skin temperature in all experiments. In experiments at ambient temperature (Ta) of 15 degrees C, the other arm (experimental) was kept at about 26, 33, and 40 degrees C, respectively, during three successive cycles of exercise and recovery. ABF in the 26 degrees C forearm was linearly related to and averaged 42% of control. The relation of ABF in the 40 degrees C forearm to control ABF showed a bend at control ABF of 4–5 ml X 100 ml-1 X min-1. Below the bend, experimental ABF average 213% of control. Above the bend, experimental ABF averaged 5.09 ml X 100 ml-1 X min-1 above control. In four subjects, after heating the experimental forearm to 40 degrees C, we measured ABF for 25–30 min at rest in Ta of both 15 and 25 degrees C. At 25 degrees C Ta, ABF in the heated forearms rose gradually, but control ABF showed little change. At 15 degrees C Ta, the effect on ABF of local heating to 40 degrees C was much reduced, apparently due to reflex vasoconstrictor signals.
Influence of the heart on the vertical gradient of transpulmonary pressure in dogs
Authors: Hyatt R. E. , Bar-Yishay E. , Abel M. D.
Published: December 2017

Estimations were made of the vertical gradient of transpulmonary pressure (VGTP) from measurements of esophageal pressure in nine head-up dogs at functional residual capacity (FRC) when alive, when dead, and after total bilateral pneumothorax. The VGTP of 0.4 cmH2O/cm height in the alive state was abolished by pneumothorax, and roentgenograms showed that the heart moved in a caudal-dorsal direction. There was a small but significant increase in the VGTP on going from FRC to near total lung capacity (TLC) in alive head-up dogs. In eight dead head-up dogs heart weight was increased by replacing various amounts of heart blood with Hg. The VGTP was significantly increased from 0.28 to 0.51 cmH2O/cm height. The fractional increase in the VGTP was similar to the fractional increase in heart weight. In five dogs extrapolation to zero heart weight gave an average VGTP of 0.14 cmH2O/cm height. We conclude that the lungs help support the heart in the head-up dog and that the VGTP is in part determined by the pressure distribution required for this support.
Mechanisms of respiratory response to isoproterenol in glomectomized cats
Authors: Eldridge F. L. , Kiley J. P. , Millhorn D. E.
Published: December 2017

Effects of intravenous isoproterenol (2–3 micrograms) on arterial pressure, end-tidal CO2 partial pressure (PCO2), medullary extracellular fluid (ECF) pH, and phrenic activity were studied in 13 anesthetized paralyzed cats whose vagi and carotid sinus nerves were cut. The cats were servo-ventilated to keep PCO2 relatively constant. Injections of Ringer solution were without effect. Isoproterenol caused arterial pressure to fall, a transient small (1 Torr) increase of PCO2, increased venous CO2 return to the lungs, a medullary ECF acidosis, and a stimulation of respiration that continued to be elevated after arterial pressure, PCO2, and medullary ECF pH had returned to control. We show that the ECF acidosis is minimally due to the hypotension and to the small transient rise of PCO2. We also show that the respiratory response cannot be explained solely by the ECF acidosis. We conclude that, in addition to its known stimulation of peripheral chemoreceptors, isoproterenol causes medullary ECF to become acidic probably due to metabolic effects on neural tissue and has a separate direct stimulating effect on neurons in the brain.
Pleural stress pressure as a force to control liquid accumulation and maintain lung expansion
Authors: Harada K. , Mutsuda T. , Saoyama N. , Hamaguchi N. , Shimada Y.
Published: December 2017

Total gas pressure in the pleural space is more subatmospheric than that in the alveolar cavity. This pressure difference minus elastic recoil pressure of the lung was termed stress pressure. We investigated the relationship between stress pressure and a force that would hold the lung against the chest wall to prevent accumulation of liquid. The condition was a pleural space with an enlarged pleural surface pressure. Dogs anesthetized with pentobarbital sodium were placed in a box maintained subatmospherically at approximately -30 cmH2O and breathed atmospheric air for 4 h. Liquid volume in the pleural space of the dogs was measured under conditions of thoracotomy. In the normal group, the volume of the pleural liquid was within the normal range of approximately 2.0 ml and the visceral and the parietal pleura made contact. In the pneumothorax group, established by injecting 50 ml of air into the pleural space, the liquid increased significantly in all cases by a mean value of approximately 12 ml. Thus pleural stress pressure seems to be an important force holding the lung against the chest wall and aiding in the control of accumulation of liquid in a more subatmospheric pleural space.
Effect of cutaneous denervation of face and trunk on thermoregulatory responses to cold in rats
Authors: Heath M. E.
Published: December 2017

The effect of eliminating afferent input from cutaneous thermoreceptors of the face and trunk on the ability of rats to regulate body temperature in cool environments was studied. Thermoregulatory ability in a cool environment was assessed first in a 25 degrees C environment and then during slow (20 min) and rapid (5 min) reductions of ambient temperature (Ta) to 15 degrees C by monitoring rate of heat production, rectal temperature, and skin temperature on the back, ear, and tail. These measurements were made in four rats while they were intact and during the 2 wk after cutaneous denervation. Rats were found to regulate body temperature well even after the cutaneous nerves of the trunk and face were sectioned. In eight rats the metabolic curve was determined before and 7–10 days after cutaneous denervation. Although the minimal resting metabolic rates did not differ in the two conditions, the lower critical temperature was significantly elevated from 26.8 to 28.9 degrees C and the rate of rise in metabolic rate per degrees celsius decrease in Ta was also significantly higher after cutaneous denervation. It appears that the higher rate of heat production is in compensation for an increase in the rate of heat loss in denervated rats.
Thermoelastic properties of uniaxially deformed lung strips
Authors: Karlinsky J. B. , Bowers J. T. , Fredette J. V. , Evans J.
Published: December 2017

We examined the temperature dependence of small degassed hamster lung strip mechanics to develop insights into the molecular basis of lung elasticity. Quasi-static length-tension curves of adapted lung strips were generated at 10, 23, 37, 50, and 80 degrees C; quasi-static tension-temperature plots (QSTT) at strains of 0.5, 0.75, and 1.0 were then formulated. Static tension-temperature (STT) plots at strain 1 were independently generated from other strips. Stress relaxation was evaluated as a function of temperature at different strains; hysteresis ratio was calculated as a parameter of mechanical efficiency. Between 23 and 37 degrees C, the slopes of the QSTT plots at the different strains were close to zero. The slope of the STT plot was slightly positive, indicating that the tension developed by a stretched strip was primarily due to entropic changes with length, suggesting that strips behave like rubber polymers near physiological temperature. Between 10 and 23 degrees C, the slope of the QSTT curve was zero at the two lowest strains but was negative at strain 1; and slope of the STT curve was zero at strain 1. These data indicated that collagen fiber and possibly glycosaminoglycan function was abnormally affected at 10 degrees C. Between 50 and 80 degrees C at strain 1, the slopes of both the QSTT and STT plots at all strains were positive. These data suggested that elastic fiber function was altered between 50 and 80 degrees C such that both internal energetic and entropic contributions to the tension were changed. Stress relaxation and hysteresis data were consistent with these findings.
Reduced training intensities and loss of aerobic power, endurance, and cardiac growth
Authors: Hickson R. C. , Foster C. , Pollock M. L. , Galassi T. M. , Rich S.
Published: December 2017

Twelve subjects participated in an exercise program of cycling and running 40 min/day, 6 days/wk. After 10 wk, they continued to train with either a one-third or two-thirds reduction in work rates for an additional 15 wk. Frequency and duration for the additional training remained the same as during the 10 wk of training. The average increases in maximum O2 uptake (VO2 max) were between 11 and 20% when measured during cycling and treadmill running after 10 wk of training. VO2 max was not maintained at the 6-day/wk training levels with a one-third reduction in training intensity but was still higher than pretraining levels. With a two-thirds reduction in intensity, VO2 max declined to an even greater extent than with the one-third reduction. Short-term endurance (approximately 5 min) was maintained in the one-third reduced group but was markedly reduced in the two-thirds reduced group. Long-term endurance was decreased significantly from training by 21% in the one-third reduced group (184–145 min) and by 30% in the two-thirds reduced group (202–141 min). Calculated left ventricular mass, obtained from echocardiographic measurements, increased approximately 15% after training but returned to control levels after reduced training in both groups. These results demonstrate that training intensity is an essential requirement for maintaining the increased aerobic power and cardiac enlargement with reduced training.
Thermal mapping of the airways in humans
Authors: McFadden E. R. , Pichurko B. M. , Bowman H. F. , Ingenito E. , Burns S. , Dowling N. , Solway J.
Published: December 2017

To characterize the intrathoracic thermal events that occur during breathing in humans, we developed a flexible probe (OD 1.4 mm) containing multiple thermistors evenly spaced over 30.2 cm, that could be inserted into the tracheobronchial tree with a fiberoptic bronchoscope. With this device we simultaneously recorded the airstream temperature at six points from the trachea to beyond the subsegmental bronchi in six normal subjects while they breathed ambient and frigid air at multiple levels of ventilation (VE). During quiet breathing of room air the average temperature ranged from 32.0 +/- 0.05 degrees C in the upper trachea to 35.5 +/- 0.3 degrees C in the subsegmental bronchi. As ventilation was increased, the temperature along the airways progressively decreased, and at a VE of 100+ 1/min the temperature at the above two sites fell to 29.2 +/- 0.5 and 33.9 +/- 0.8 degrees C, respectively. Interval points were intermediate between these extremes. With cold air, the changes were considerably more profound. During quiet breathing, local temperatures approximated those recorded in the maximum VE room-air trial, and at maximum VE, the temperatures in the proximal and distal airways were 20.5 +/- 0.6 and 31.6 +/- 1.2 degrees C, respectively. During expiration, the temperature along the airways progressively decreased as the air flowed from the periphery of the lung to the mouth: the more the cooling during inspiration, the lower the temperature during expiration. These data demonstrate that in the course of conditioning inspired air the intrathoracic and intrapulmonic airways undergo profound thermal changes that extend well into the periphery of the lung.
Effect of expiratory loading on glottic dimensions in humans
Authors: Brancatisano T. P. , Dodd D. S. , Collett P. W. , Engel L. A.
Published: December 2017

We examined the effects of external mechanical loading on glottic dimensions in 13 normal subjects. When flow-resistive loads of 7, 27, and 48 cmH2O X l-1 X s, measured at 0.2 l/s, were applied during expiration, glottic width at the mid-tidal volume point in expiration (dge) was 2.3 +/- 12, 37.9 +/- 7.5, and 38.3 +/- 8.9% (means +/- SE) less than the control dge, respectively. Simultaneously, mouth pressure (Pm) increased by 2.5 +/- 4, 3.0 +/- 0.4, and 4.6 +/- 0.6 cmH2O, respectively. When subjects were switched from a resistance to a positive end-expiratory pressure at comparable values of Pm, both dge and expiratory flow returned to control values, whereas the level of hyperinflation remained constant. Glottic width during inspiration (unloaded) did not change on any of the resistive loads. There was a slight inverse relationship between the ratio of expiratory to inspiratory glottic width and the ratio of expiratory to inspiratory duration. Our results show noncompensatory glottic narrowing when subjects breathe against an expiratory resistance and suggest that the glottic dimensions are influenced by the time course of lung emptying during expiration. We speculate that the glottic constriction is related to the increased activity of expiratory medullary neurons during loaded expiration and, by increasing the internal impedance of the respiratory system, may have a stabilizing function.
Diaphragmatic fatigue in normoxia and hyperoxia
Authors: Pardy R. L. , Bye P. T.
Published: December 2017

Diaphragmatic fatigue was induced in six normal young men inspiring against a variable alinear resistance. Breathing pattern was rigidly controlled (tidal volume 0.75 liter, 12 breaths . min-1). Fatigue was defined as an inability to continue to generate a target transdiaphragmatic pressure (Pdi = 0.65 - 0.84 Pdimax). Diaphragmatic electromyogram (EMG, esophageal electrode) and perceived effort (PE, open-ended scale) were recorded. Subjects were tested on an identical resistance inspiring air or 100% O2 in random order on different days. They were unaware of the gas mixture inspired. Mean endurance time (tlim) +/- SE for air was 4.1 +/- 1.4 min and for O2 was 8.6 +/- 2.7 min (P less than 0.005). The increased tlim in O2 was associated with a delay in onset of EMG changes heralding diaphragmatic fatigue and a decrease in PE at any time during the study compared with the level of PE in air. Arterial O2 saturation (ear oximeter) remained at the resting level of 99.0 +/- 0.2% in O2 and decreased from the resting level of 97.2 +/- 0.2% by 2.8 +/- 0.7% (P less than 0.01) in air. The end-tidal CO2 fraction increased to a similar degree in air and O2 studies. We conclude that when breathing pattern, minute ventilation, and Pdi are held constant during inspiratory resistive loading, breathing O2 delays the onset of diaphragm fatigue and decreases PE.
A new nuclear magnetic resonance property of lung
Authors: Morris A. H. , Blatter D. D. , Case T. A. , Cutillo A. G. , Ailion D. C. , Durney C. H. , Johnson S. A.
Published: December 2017

Inflated lung has a nuclear magnetic resonance (NMR) free-induction decay (FID) which is short compared with that of collapsed lung and those of other body tissues. An almost identically short FID is obtained from a slurry of 5-micron alumina particles in water. Interfaces between air and water in lung and between alumina and water in the slurry appear to be the source of spatial internal magnetic inhomogeneities which produce NMR line broadening and the short FID. Paired images that included lung, taken with paired symmetric and asymmetric NMR spin-echo sequences, permit the generation of an image, by subtraction, of the lung isolated from surrounding tissue. These new lung images are neither proton density, T1 (spin-lattice relaxation time), nor T2 (spin-spin relaxation time) images. They complement current NMR images and provide information about regional lung inflation. This previously unrecognized NMR property of lung tissue has potential application in NMR imaging, in quantitative determination of lung water and its distribution, and in the quantitation of regional lung inflation.
Endotoxin-tolerant rats are still protected from oxygen toxicity by low-dose endotoxin treatment
Authors: Frank L.
Published: December 2017

To determine if we could reduce endotoxin's potential for toxicity, we produced “endotoxin-tolerant” rats by administering progressively increasing daily doses of endotoxin (10 ng, 100 ng, 1 microgram, 10 micrograms/kg). This dosage regimen produced a high degree of tolerance to the toxic actions of endotoxin: whereas only 3/17 (18%) of control rats survived a normally lethal dose of endotoxin (25 mg/kg), survival for the endotoxin-tolerant rats was 16/16. When endotoxin-tolerant rats received a standard protective dose of 500 micrograms/kg endotoxin just before transfer to 96–98% O2, 19/20 survived the 72-h exposure period vs. 20–30% survival for controls. Thus whereas the endotoxin-tolerant state blocked the tested lethal and toxic effects of endotoxin, it did not nullify the O2 protective action of endotoxin. In addition, endotoxin's stimulatory effects on the lung antioxidant enzymes in the 96–98% O2-exposed rats was also not blocked by the endotoxin-tolerant state. Thus the therapeutic ratio (TR) of endotoxin as an experimental pharmacological treatment against O2-induced lung damage has been markedly enhanced (TR = ratio of dose producing beneficial effects to dose producing toxic effects).