bluuebunny/crossref_metadata_2025 huggingface dataset:
Difference between the He bolus and N2 technique for measuring closing volume
Authors: Stanescu D. , Veriter C. , Brasseur L.
Published: December 2017

We measured closing volume in sixteen healthy subjects simultaneously and separately with a bolus of He (using a rapid catharaometer) and with the N2 technique. In another group of 35 active workers (some with airway obstruction), closing volume was measured separately with those two methods. In both groups the He closing volume was significantly higher than the N2 closing volume. We attribute this difference to a less marked vertical N2 concentration gradient, leading to a less clearly defined separation between phase III and IV and resulting in an underestimation of the N2 closing volume. Indeed, increasing the N2 gradient in the lung, by inspiring O2 from a higher than residual volume level, increased the N2 closing volume which became comparable to the He closing volume. We also found, for both He and N2 tracings, a significant between-observers difference in reading of the closing volume. However, the difference in reading of ts difference in reading of the closing volume. However, the difference was less important for He closing volumes. We conclude that the bolus method improves the resolution of closing volume and decreases the interobserver variability.
Photography of peripheral pulmonary airway expansion as affected by surfactant
Authors: Enhorning G.
Published: December 2017

Edges of excised lungs from twenty 27-day-old rabbit fetuses were photographed as tracheal pressure was raised and air entered alveoli. Lungs from two littermates were expanded simultaneously with pressure up to 50 cmH2O. The effect of surfactant (SA) on peripheal airway expansion was assessed by depositing 25 mul of SA suspension in the trachea of one pair of lungs. The suspension was obtained by washing the lungs of young adult rabbits and concentrating the SA by centrifugation. In 9 of the 10 experiments, the SA-treated lung was the first to become expanded. When pressure was lowered to 10 or 0 cmH2O, peripheral airways of treated lungs usually maintained expansion; air in control lung alveoli disappeared, or was trapped. High surface tension tended to collapse the cylindrical respiratory bronchiole rather than the spherical alveolus, causing air trapping, if the radius of the cylinder was less than half of the sphere. SA lessened collapsing tendency in the respiratory bronchiole.
Effects of exercise on fluid exchange and body composition in man during 14-day bed rest
Authors: Greenleaf J. E. , Bernauer E. M. , Juhos L. T. , Young H. L. , Morse J. T. , Staley R. W.
Published: December 2017

To determine the cause of the body weight loss during bed rest (BR), fluid balance and anthropometric measurements were taken from seven men (19–21 yr) during three 2-wk BR periods which were separated by 3-wk ambulatory recovery periods. Caloric intake was 3,073 +/- 155 (SD) kcal/day. During two of the three BR periods they performed supine isotonic exercise at 68% of VO2max on the ergometer for 1 h/day; or supine isometric exercise at 21% of maximal leg extension force for 1 min followed by a 1-min rest for 1 h/day. No prescribed exercise was given during the other BR period. During BR, body weight decreased slightly with no exercise (-0.43 kg, NS), but decreased significantly (P less than 0.05) by -0.91 kg with isometric and by -1.77 kg with isotonic exercise. About one-third of the weight reduction with isotonic exercise was due to fat loss (-0.69 kg) and, the remainder, to loss of lean body mass (-0.98 kg). It is concluded that the reduction in body weight during bed rest has two major components: First, a loss of lean body mass caused by assumption of the horizontal body position that is independent of the metabolic rate. Second, a loss of body fat content that is proportional to the metabolic rate.
Diaphragmatic contraction and the gradient of alveolar expansion in the lateral posture
Authors: Roussos C. S. , Martin R. R. , Engel L. A.
Published: December 2017

Using 133Xe we measured the vertical distribution of regional volume in four subjects in the lateral decubitus posture at 20, 40, 60, and 80% of vital capacity (VC). To study the influence of diaphragmatic tone, all measurements were performed either when transdiaphragmatic pressure (Pdi) was low, i.e., diaphragm was “relaxed” (RD) or during voluntary diaphragmatic contraction (VDC). The latter was achieved by tensing the abdominal muscles while keeping the glottis open. Under both conditions the gradient of alveolar expansion tended to be curvilinear, with a discontinuity at the level of the mediastinum. At all lung volumes the difference in regional volume between dependent and nondependent lung regions was less during VDC than during RD. At 70% total lung capacity (TLC) this difference, expressed as percent of regional TLC (%TLCr), decreased from 19.7 +/- 1.7 (mean +/- 1 SE) %TLCr during RD to 3.9 +/- 1.5% TLCr during VDC. It is likely that diaphragmatic tension influences the pleural pressure gradient and regional volume distribution 1) by modifying the transmission of the abdominal hydrostatic pressure gradient to the thorax, and 2) by an upward displacement of the mediastinum.
Role of tissue hypermetabolism in stimulation of ventilation by dinitrophenol
Authors: Levine S.
Published: December 2017

Several authors have hypothesized that tissue hypermetabolism accounts for increases in ventilation (VE) elicited by 2,4-dinitrophenol. However, some data in the literature indicate that stimulation of VE by isomers of dinitrophenol is unrelated to tissue metabolic rate. To test this latter concept, we compared three different isomers of dinitrophenol (i.e., 2,4-dinitrophenol (2,4-DNP), 2,5-dinitrophenol (2,5,-DNP), 2,6-dinitrophenol (2,6-DNP) with respect to stimulation of VE and with respect to stimulation of oxygen consumption (VO2). In all experiments, 3–4 mg/kg of one dinitrophenol isomer was administered to chloralose anesthetized dogs by intra-arterial infusion. 2,4-DNP elicited large increments in both VE and VO2, 2,6-DNP elicited moderate increments in both VE and VO2, whereas 2,5-DNP elicited small increments in both VE and VO2. These observations demonstrate a correlation between ventilatory and metabolic changes affected by isomers of dinitrophenol. Accordingly, these results are consistent with the hypothesis that ventilatory stimulation by congeners of dinitrophenol is related to tissue hypermetabolism.
Time, rate, and temperature factors in the onset of high-pressure convulsions
Authors: Brauer R. W. , Beaver R. W. , Lahser S. , Mansfield W. M. , Sheehan M. E.
Published: December 2017

An interrupted compression profile technique was used to develop data to separate the effects of time and pressure factors governing increase of high-pressure neurological syndrome (HPNS) convulsion threshold pressures (the compression rate effect) during different compression profiles. A single differential equation fits all data available to date for compression rate effect on convulsion thresholds of CD-1 mice (three distinct types of compression profile; mean compression rates 12–1,000 atm/h). The process leading to increase in HPNS convulsion pressure is initiated at the very beginning of compression, proceeds at increasingly rapid rates as higher pressures are attained, and approaches a limiting upper convulsion pressure. The convulsion threshold pressure in any given experiment is independent of the compression rate prevailing during the time immediately preceding onset of the seizure. The magnitude of the compression rate effect in the CD-1 mouse is independent of chamber temperature over a range of 27–36 degrees C, and rectal temperatures of 29.2–37.5 degrees C. The bearing of these results on the design of optimal compression schedules and on the analysis of the neurological mechanisms underlying the HPNS is discussed.
High pressure and intravenous steroid anesthesia in rats
Authors: Bailey C. P. , Green C. J. , Halsey M. J. , Wardley-Smith B.
Published: December 2017

Anesthesia produced by the intravenous steroid agent, Althesin, was studied in Sprague-Dawley rats with and without high pressure of helium gas up to 100 atmospheres absolute (ATA). There were no cumulative or adaptive changes in Althesin requirement at normal pressures over 6-h periods. However, the apparent potency of the agent was reduced by 43% by the addition of 68 ATA helium. Subanesthetic doses of Althesin protected against the onset of convulsions and coarse tremors associated with the high pressure neurological syndrome. It is concluded that the steroid anesthetics may have a place in human diving technology and that the mechanisms associated with the anesthetic-pressure interactions are consistent with the critical volume or lipid bilayer fluidity hypothesis.
Interaction of central nervous system effects of high pressures with barbiturates
Authors: Beaver R. W. , Brauer R. W. , Lahser S.
Published: December 2017

The interactions of phenobarbital, barbital, and pentobarbital with high pressures of heliox were explored. Principal features of the complex results include: double peaks in the time course of convulsion thresholds (Pc); an early peak and a shoulder in the time course of pressures reversing anesthesia (Pa); far steeper dose-response curves for Pa than for Pc; selectively greater anticonvulsant effect for phenobarbital than for the other barbiturates; and enhancement of Pa with simultaneous depression of Pc by reserpine in phenobarbital-pretreated mice. The data indicate the existence of at least two discrete sites of interaction between barbiturates and high pressure, reflected by Pc and Pa. The implications of the data for the development of biophysical theories of pressure reversal of anesthesia and anti-high-pressure neurological syndrome action of anesthetics are discussed, together with implications for the experimental study of convulsant and anticonvulsant agents, and their applications to underwater physiology.
Cytochrome P450-linked p-nitroanisole O-demethylation in the perfused lung
Authors: Itakura N. , Fisher A. B. , Thurman R. G.
Published: December 2017

Oxidative demethylation of p-nitroanisole, a cytochrome P450-linked mixed-function oxidation, was evaluated in isolated perfused rat and rabbit lungs. The product, p-nitrophenol, was monitored continuously in the lung effluent by spectrophotometric measurement. Pulmonary p-nitrophenol production in mumol/h per g dry wt was 6.2+/-0.4 by rabbits and 2.0+/-0.3 by rats (mean+/-SE). Maximal activity of the reaction required pulmonary perfusion rates in excess of 60–80 ml/min per g of dry lung. The half-maximal rate of p-nitrophenol production was observed with p-nitroanisole concentration of 13 micron. Pretreatment of rabbits with chlorpromazine increased p-nitroanisole O-demethylation activity by 63% but phenobarbital pretreatment had no effect. Ventilation with 75% carbon monoxide plus 20% O2 reversibly inhibited the reaction. Specific activity of p-nitroanisole demethylase in the microsomal fraction was 0.5 nmol/min per mg protein in rabbit lungs and 0.1 nmol/min per mg protein in rat lungs. Other rabbit lung subcellular fractions compared with microsomes had significantly lower specific activity. This study demonstrates that p-nitroanisole O-demethylation can be continuously monitored in the intact lung and describes conditions necessary for maximal activity of this pathway.
Penetration of inhaled He and SF6 into alveolar space at low tidal volumes
Authors: Worth H. , Adaro F. , Piiper J.
Published: December 2017

To study mixing of inspired gas with lung gas, penetration of simultaneously inspired helium (He) and sulfur hexafluoride (SF6) into alveolar space was determined in normal subjects at low tidal volumes (from 50 to 500 ml) and at varied lung volumes and speeds of inspiration/expiration. The volume of inspired gas reaching the alveolar space, termed alveolar-tidal volume, VTA, was calculated from preinspiratory lung volume, inspired volume, and inspired and expired alveolar test gas concentrations. The difference between the VTA values calculated for He and SF6, VTA(He) - VTA(SF6), was influenced by tidal volume, lung volume, and the speed of inspiration/expiration, but it was always positive. The results are qualitatively explainable on the basis of easier diffusive mixing of He in lung airways compared with SF6. Since Taylor dispersion would produce deeper penetration, and therefore higher VTA, for a less diffusible gas the results provide no evidence for its implication in pulmonary gas exchange.
Control of liver size in heat-acclimated hamsters
Authors: Chayoth R. , Krauthammer N. , Winikoff J. , Sod-Moriah U. A.
Published: December 2017

In the hamster, heat acclimation reduces liver weight more than it does body weight. Therefore, liver weight constitutes a lower percentage of body weight during exposure to high ambient temperature. This change is not a result of dehydration since water content of the whole body and of the liver is not altered during heat acclimation. However, changes in lactic dehydrogenase isozyme proportions indicate a higher rate of liver degradation during the first 2 wk of heat exposure. These changes are accompanied by enhancement of DNA synthesis which is found to be elevated during the early period of heat exposure and later to fall to the control levels. The enhanced DNA synthesis might be a result of a high rate of tissue regeneration which probably takes place in the organ following the commencement of the degradative processes as was suggested in partial hepatectomy. Since the activity of DNA synthesis is negatively correlated with cyclic AMP levels, it is suggested that cyclic AMP plays some role in controlling hepatic DNA synthesis during heat acclimation.
Temperature and CO2 effect on phrenic activity and tracheal occlusion pressure
Authors: Trippenbach T. , Milic-Emili J.
Published: December 2017

The present investigation was undertaken to study the interaction of CO2 and body temperature on phrenic activity (moving average) and tracheal occlusion pressure. Studies were performed on spontaneously ventilated cats anesthetized with pentobarbital sodium at different body temperatures (32–41 degrees C) while breathing room air, 2 and 4% CO2 in 50% O2. At any given chemical drive, increased body temperature caused a similar increase in rate of phrenic activity and tracheal occlusion pressure, while their peak values remained virtually unchanged. At any given body temperature, increased chemical drive caused an increase in both rate of rise and peak values of phrenic activity and tracheal occlusion pressure. These results confirm previous findings that body temperature affects the rate of rise of the central inspiratory activity (CIA), but not the inspiratory “off-switch” threshold, while CO2 increases both the rate of rise of CIA and off-switch threshold. In addition the results indicate that tracheal occlusion pressure provides a similar index of CIA as “integrated” phrenic activity.
Behavior of artificially produced holes in lung parenchyma
Authors: Lai-Fook S. J. , Hyatt R. E. , Rodarte J. R. , Wilson T. A.
Published: December 2017

Spherical and cylindrical holes were cut in the parenchyma of isolated dog lung lobes. The holes were insufflated with tantalum dust and the hole diameters were measured along the deflation limb of the lobe pressure-volume curve from transpulmonary pressures of 20 to 0 cmH2O. Hole volume as a fraction of lobe volume was found to be independent of transpulmonary pressure. The hole volume relative to the amount of tissue removed was used to determine the displacement at the hole boundary. A comparison of this displacement with the displacement predicted by a continuum mechanics analysis provides evidence for the applicability of the methods of continuum mechanics and further evidence that the shear modulus of the parenchyma is relatively small.
Potentiation of pulmonary vasoconstrictor response with repeated intermittent hypoxia
Authors: Unger M. , Atkins M. , Briscoe W. A. , King T. K.
Published: December 2017

To determine the consistency of the pulmonary vasoconstrictor response to hypoxia, dogs were anesthetized, intubated, and ventilated alternately with air and 10% oxygen. Catheters were placed in the pulmonary artery for measurement of pulmonary artery pressure (PAP), pulmonary capillary wedge pressure, and cardiac output and in the femoral artery for monitoring systemic blood pressure and arterial blood gases. Arterial PCO2 and pH were kept at steady levels throughout by ventilating the dogs with a respirator so that only the isolated effect of hypoxia on the pulmonary vasculature was studied. It was found that there was a progressive rise in the PAP with repeated exposure to the same hypoxic stimulus. In 12 dogs, the mean increase in the PAP was 28% above the base line on the 1st hypoxic exposure, rising to 99% by the 10th exposure over the course of 5 h. It was concluded that interpretation of action of agents blocking or enhancing the hypoxic response must take into account this inherent potentiation of the response on repeated exposure to hypoxia.
Biochemical adaptation of human skeletal muscle to heavy resistance training and immobilization
Authors: MacDougall J. D. , Ward G. R. , Sale D. G. , Sutton J. R.
Published: December 2017

Nine healthy subjects were studied under control conditions and following 5 mo of heavy resistance training and 5 wk of immobilization in elbow casts. Needle biopsies were taken from triceps brachii and analyzed for adenosine triphosphate (ATP), adenosine diphosphate (ADP), creatine (C), creatine phosphate (CP, and glycogen concentrations. Training resulted in an 11% increase in arm circumference and a 28% increase in maximal elbow extension strength. Immobilization resulted in decreases in arm circumference and elbow extension strength of 5% and 35%, respectively. Training also resulted in significant increases in resting concentrations of muscle creatine (by 39%), CP (by 22%), ATP (by 18%), and glycogen (by 66%). Conversely, immobilization significantly reduced CP concentration by 25% and glycogen concentration by 40%. It was concluded that heavy-resistance training results in increases in muscle energy reserves which may be reversed by a period of immobilization-induced disuse.
Lung surface tension and air space dimensions from multiple pressure-volume curves
Authors: Valberg P. A. , Brain J. D.
Published: December 2017

Pressure-volume (PV) curves of excised cat, dog, rabbit, and rat lungs were determined in a sequence of three conditions: 1) normal-surface, air-filled; 2) saline-filled; and 3) polyoxyethylene (20) sorbitan monolaurate-(Tween 20) surface, air-filled. Since the surface tension of lung washings containing 2% Tween 20 is constant, the Tween-surface air-filled lungs presumably exhibit the pressure-volume behavior of lungs with constant surface tension. These data along with the assumption of equivalent geometry in the three conditions permit calculation of the variation of surface tension in the normal lung as a function of volume without assuming a specific surface area vs. volume function or a maximum surface tension. The calculated surface tension dropped during deflation from a high of 50 dyn/cm total lung capacity (TLC) to a low of 4 dyn/cm (less than 25% TLC) with the species being roughly similar. The PV behavior of Tween-surface lungs appears to fit a simple model of alveolar expansion. Air dimensions calculated for the four species on the basis of this model are ordered in the same sequence as morphological measurements, but larger in magnitude.
Instrumentation for measuring functional residual capacity in small animals
Authors: Koen P. A. , Moskowitz G. D. , Shaffer T. H.
Published: December 2017

A system for measuring functional residual capacity (FRC) by the dilution method was evaluated to determine its suitability for use in neonates and small animals. The system makes use of rapid, automatically triggered valves for precise closure at end expiration. Results of a theoretical error analysis and experimental in vitro tests are presented and indicate that the measuring error in FRC is related to the FRC-to-initial rebreathing bag volume ratio. With a 200-ml bag volume one standard deviation of the calculated error was 16% for a 50-ml, 9.1% for a 100-ml, and 5.8% for a 200-ml FRC.
Factors relating to the strength of male adolescents
Authors: Watson A. W. , O'Donovan D. J.
Published: December 2017

Factors relating to the strength of 53 postpubertal adolescent males have been examined. A strength index, composed of left and right handgrip and back strengths, was related to the following: anthropometric measurements and their derivatives; level of habitual activity; body shape as characterized by Heath-Carter and Sheldonian somatotype ratings; and anthropometric ratios. Strength was found to be positively related to all anthropometric measurements with the exception of skinfold thicknesses. When body weight was held constant, strength was positively related to arm circumference, bicondylar diameters of the humerus and femur, thigh volume, and biacromial diameter, and negatively related to percentage of fat. Strength was not related to the level of habitual activity. The relative contributions of overall body size and body shape to predictions of strength are approximately 57 and 47%. Measures of overall size appear to make no independent contribution to strength, beyond that contributed by limb segment volumes, or a combination of linear limb dimensions and measures of body shape.
Aerobic work capacity in chronically undernourished adult males
Authors: Barac-Nieto M. , Spurr G. B. , Maksud M. G. , Lotero H.
Published: December 2017

Maximal O2 consumption (VO2max) and maximal endurance time at 80% Vo2max (T80) were determined in 49 subjects with varying degrees of nutritional compromise. Vo2max was lover by 21% and 52% in subjects with moderate and severe undernutrition, respectively, when compared to men with mild nutritional compromise. Most (80%) of the change in Vo2max could be related to the estimated differences in muscle cell mass (MCM). A significant reduction (-18%) in the Vo2max per unit of MCM was found in the severely undernourished subjects, indicating basic physiological changes. Total body hemoglobin showed the highest correlation with Vo2max (r = 0.709) and at constant MCM (partial r = 0.796). A multiple regression equation was derived to estimate the Vo2max of populations on the basis of simple anthropometry and blood hemoglobin levels. T80 (93–103 min) and estimated maximum sustained 8-h percent effort (32%) in mild, intermediate, or severe undernutrition were not significantly different; by contrast, endurance at a given absolute work load was markedly lower in severe undernutrition (8 vs. 1.5 h) due presumably to the difference in Vo2max.
Closing capacity in awake and anesthetized-paralyzed man
Authors: Juno J. , Marsh H. M. , Knopp T. J. , Rehder K.
Published: December 2017

Functional residual capacity (FRC), closing capacity (CC), and (FRC--CC) were determined in 61 supine patients using the 133Xe bolus test. In 28 of the 61 patients measurements were made both while the patients were awake and during anesthesia-paralysis. Both FRC and CC decreased significantly after induction of anesthesia-paralysis. The magnitude of the reduction in CC, but not of FRC, was dependent on the relationship between FRC and CC in the awake state. Patients whose FRC was larger than their CC while awake (group I) showed less decrease in CC than FRC, i.e., (FRC--CC) decreased. By contrast, those patients whose CC was larger than their FRC while awake (group II) showed a greater decrease in CC than in FRC, i.e., (FRC--CC) became less negative. The reduction in CC after induction of anesthesia-paralysis may result from an increased elastic recoil of the lung. The larger reduction in CC in group II patients may have been due to a larger increase in elastic recoil, possibly due to the development of atelactasis.
Adrenergic influences on histamine-mediated bronchoconstriction in the guinea pig
Authors: Drazen J. M.
Published: December 2017

Intravenous infusion of histamine results in a fall in dynamic pulmonary compliance (Cdyn) in the unanesthetized guinea pig. During a prolonged infusion of histamine (30–200 s) a minimum value of Cdyn is reached and sustained after 30 s. Propranolol (10 mg/kg) enhanced this steady-state response in both normal and adrenally ablated guinea pigs to the same degree. After the infusion was terminated, normal guinea pigs recovered briskly, whereas guinea pigs whose adrenals had been ablated recovered slowly. Propranolol prolonged the recovery from the histamine-mediated fall in Cdyn in normal guinea pigs, but had no significant effect on the pattern of recovery in adrenally ablated animals. These experiments suggest that during a histamine infusion nonadrenal adrenergic factors modify the histamine response, but the brisk recovery from histamine is under the influence of adrenal factors.
Rat locomotory muscle fiber activity during trotting and galloping
Authors: Sullivan T. E. , Armstrong R. B.
Published: December 2017

This study was designed to investigate the hypothesis that the trot-gallop transition in running guadrupeds occurs when active cross-sectional areas of muscles or fiber populations within muscles, reach some critical point as animals increase speed within trotting. Rats (Rattus norvegicus) were used as experimental animals, and glycogen depletion was used to estimate patterns or fiber activity. Our results indicate that 1) the contribution to power output by the front limb muscles was less than that of the hind limb muscles during trotting and galloping; 2) the active cross-sectional area of plantaris muscles peaked immediately prior to the transition in gait; 3) the ankle plantar flexor group of muscles as a whole did not attain a maximum active cross-sectional area during fast trotting; and 4) no major discontinuities in whole muscle or fiber type glycogen depletion rates occurred across the gait change. Although these findings do not prove the hypothesis, they support the concept that the trop-gallop transition follows the attainment of peak active muscle cross-sectional areas as animals increase trotting speed.
Pulse rate-rectal temperature relationships during prolonged work
Authors: Kuhlemeier K. V. , Miller J. M.
Published: December 2017

Forty-six industrial workers performed a total of 653 1-h work bouts over a wide range of work rates )142–273 W/m2) and environmental temperatures (11–35 degrees C corrected effective temperature) in the summer and winter seasons. Simultaneous measurements of heart rates and rectal temperatures were made at the end of each work period, and the relationship between heart rate and rectal temperature was computed with standard multiple linear regression techniques. The overall regression equation is: heart rate (beats/min) = 29.3 (beats/min. degrees C) x rectal temperature (degrees C) - 988.6 (beats/min). The relationship is significantly altered by work rate and job- and season-acquired acclimatization of the subjects. These data suggest that the average heart rates of industrial workers during prolonged work can be predicted from rectal temperatures with a reasonable degree of confidence if the degree of acclimatization and work rates are known. For a rectal temperature of 38.0 degrees C the expected heart rate during prolonged work ranges from 109 beats/min in acclimatized men working at low rates to 143 for unacclimatized men working at heavy rates.
Efficiency of anaerobic work
Authors: Gladden L. B. , Welch H. G.
Published: December 2017

This study was undertaken to compare the efficiency of aerobic and anaerobic work. Nine subjects worked at approximately 100% VO2 max for 2 min while inspiring gas mixtures with O2 fractions ranging from 0.13 to 0.21. Exercise O2 uptake, recovery O2 uptake, and blood lactate concentration were measured. Steady level O2 uptake was measured in normoxia at submaximal loads of about 30, 50, and 70% of VO2 max. Fast recovery O2 uptake did not change as PIO2 was varied. Exercise O2 uptake and blood lactate concentrations were linearly related to PIO2. The ratio of the slopes of these lines provided an empirical expression of the O2 equivalent of blood lactate. This ratio was constant, suggesting that it is not less efficient to use ATP synthesized anaerobically. Energy input from lactate was calculated using this factor. Efficiency decreased as power output increased even at the submaximal work rates. This may result from either 1) a decrease in muscle efficiency, 2) an increase in metabolism that is not directly related to the external work, or 3) some combination of 1 and 2.
Lung volumes in man immersed to the neck: dilution and plethysmographic techniques
Authors: Robertson C. H. , Engle C. M. , Bradley M. E.
Published: December 2017

Previous studies of lung volumes during immersion have utilized dilution techniques for residual volume. We have compared lung volumes obtained by the use of a dual inert gas dilution technique with those determined by the Boyle's law technique in a plethysmograph designed to allow measurements in air and submersed to the neck in water. Both techniques gave similar results dry, but during immersion the dilution residual volume (RV) was 0.200 liter (16%) lower than the plethysmographic value (P greater than 0.001), which suggests that there is a significant amount of gas trapping during immersion due to breathing at low lung volumes and the central shift of blood. The unchanged RV due to hydrostatic force on the chest wall is balanced by the tendency to increase RV due to vascular congestion, which increases closing volume and stiffens the lung to compression.
Heat-injured rats: pathochemical indices and survival time
Authors: Francesconi R. P. , Mager M.
Published: December 2017

Rats were exercised on a treadmill (9.14 m/min) in a hot environment (34.5 degrees C, 30% rh) until a rectal temperature of 42.0--42.5 degrees C was reached. Analysis of plasma constituents in subsequent serial blood samples demonstrated a highly significant inverse correlation between lactate concentration (P less than 0.001) and potassium levels (P less than 0.005) in blood samples taken immediately postexercise when both of these were correlated to survival time. Alternatively, plasma creatine phosphokinase (CPK) activity in these samples, although significantly elevated over control levels (P less than 0.001), was not correlated with either survival time or lactate-potassium concentrations. When fluid was administered prior to the run and immediately thereafter to repress pathological effects, there occurred no changes in plasma lactate and potassium levels between the postrun sample and a second sample taken 60 min later, while CPK levels were significantly reduced (P less than 0.01) in the second sample. However, levels of all three indices were significantly elevated (P less than 0.01) in a third sample taken terminally despite the fact that the animals were restrained and sedentary during this interval. These findings indicate that the hyperthermic injury may have had fundamental pathological effects on metabolism and membrane integrity producing lactacidemia and hyperkalemia of sufficient magnitude to compromise cardiovascular performance.
Characteristics of inspiratory inhibition by phasic volume feedback in cats
Authors: Younes M. K. , Remmers J. E. , Baker J.
Published: December 2017

The dependence of phrenic efferent discharge on vagal-volume feedback was examined in barbiturate-anesthetized, paralyzed cats ventilated by a phrenic-driven servo respirator. The characteristics of the respiratory were altered for a single breath, and the resulting change in phrenic activity was quantitated by comparison with phrenic activity without phasic volume feedback. The relation between volume feedback and phrenic inhibition was determined both when inspiratory termination occurred during the rising phase of phrenic discharge and during the plateau observed with barbiturate-induced apneusis. Inhibition of inspiratory activity occurred only when lung volume exceeded a time-dependent threshold. Above this threshold, andextending over a substantial volume range, volume feedback caused graded and reversible inhibition of phrenic discharge. The threshold for graded inhibition declined progressively during the inspiratory phase, showing no obvious relation to the level of inspiratory activity. At any particular time, the relation between volume and phrenic inhibition was convex to the volume axis, and the slope of the relationship increased with inspiratory time. The results indicate that a) volume feedback inhibits inspiration in a graded manner, b) partial inhibition of phrenic activity renders it more susceptible to additional inhibition, and c) inhibitory effectiveness of volume feedback increases with time.
Changes in ventilatory pattern induced by intravenous anesthetic agents in human subjects
Authors: Gautier H. , Gaudy J. H.
Published: December 2017

The tidal volume-inspiratory duration relationship was studied during air breathing and rebreathing in conscious and anesthetized human subjects using three different intravenous agents. The results observed have been compared with similar experiments carried out in cats. Its has been shown that anesthesia provokes an increase in breathing rate associated with a decrease in tidal volume in human subjects; an opposite effect on breathing rate was observed in cats. Thus, the tidal volume-inspiratory duration relationship, although very similar in the conscious cat or human subject, is very different under anesthesia. The results were quite consistent in a given species whatever the nature of the drug used. It is suggested that modifications of the breathing rate by anesthesia, related to animal species, are caused by central effects of the drug. These effects are probably mediated by different actions on inputs to the inspiratory –off-switch” mechanisms in the two species.
Behavior of the human pulmonary circulation during head-up tilt
Authors: Lewis M. L. , Christianson L. C.
Published: December 2017

Pulmonary blood volume (PBV), flow, and pressures were measured in 15 cardiopulmonary normal subjects, while supine and at 60 degrees head-up passive tilt. PBV, cardiac index (CI), right ventricular diastolic volume (VDVR), and mean pulmonary arterial (Ppa), venous (Pv), and mean right atrial (Pra) pressures all decreased during the first 4 min of tilting, with little subsequent change thereafter, to 30 min. Relative changes of CI, PBV, and VDVR were of similar magnitude (25--30%; mean Ppa and Pv fell 3.2 and 2.3 Torr, respectively. From measurements of thoracic dimensions and changes in intravascular pressures, we calculate that 11% of the pulmonary vascular bed falls into zone I condition, 34% goes from zone III to zone II, and 55% remains in zone III condition during tilt. A highly significant correlation exists between PBV and CI (P less than 0.001), with no significant change in pulmonary mean transit time during tilt. Significant correlations also exist between PBV and Pra (P less than 0.001), Pv (P less than 0.01), and Ppa (P less than 0.05). We conclude that outflow pressure plays a significant role in determining PBV during head-up tilt, but the major determinant is venous return to the right heart.
Pulmonary and systemic vasodilator effects of the newly discovered prostaglandin, PGI2
Authors: Kadowitz P. J. , Chapnick B. M. , Feigen L. P. , Hyman A. L. , Nelson P. K. , Spannhake E. W.
Published: December 2017

The effects of the newly discovered bicyclic prostaglandin, prostacyclin (PGI2), on the pulmonary and systemic vascular beds were investigated in the anesthetized dog. PGI2 decreased systemic and pulmonary arterial pressures in a dose-related manner when injected into the vena cava in doses of 1--30 microgram. Since left ventricular end-diastolic, left atrial, and right atrial pressures were unchanged, and since cardiac output was increased or unchanged, pulmonary and systemic vascular resistances were decreased. PGI2 was 10 times more potent than prostaglandins E1 or E2 in decreasing aortic pressure when injected intravenously, and the effects of PGI2 on the systemic vascular bed were similar when injected into the vena cava or the left atrium. These data indicate that inactivation of PGI2 is minimal in the lung. The stable prostacyclin metabolite, 6-keto-PGF1alpha, had little hemodynamic effects, suggesting that responses to PGI2 were not due to formation of this metabolite. PGI2 produced dose-dependent increases in blood flow in the mesenteric and renal vascular beds. These data demonstrate that PGI2 has marked vasodilator activity in the pulmonary and systemic vascular beds and suggest that prostacyclin is the only known metabolite of arachidonic acid that dilates the pulmonary and systemic circulations.
Effects of lung inflation on pulmonary arterial pressure in dogs with pulmonary edema
Authors: Murray J. F.
Published: December 2017

The effects of lung inflation from positive airway pressure (Paw) on pulmonary arterial pressure (Ppa) and the slope deltaPpa/deltaPaw were studied in normal dogs and dogs with pulmonary edema. Under base-line zone 2 conditions with the lungs perfused at constant flow (100 ml/kg per min) and vascular pressures measured relative to pleural (atmospheric) pressure, the slope deltaPpa/deltaPaw was nearly one (at Paw greater than or equal to 5 cmH2O). Pulmonary edema from high capillary pressure and oleic acid caused deltaPpa/deltaPaw and Ppa to decrease at high lung volumes and Ppa to increase at low lung volumes. These changes were not simulated by vasoactive drugs (adenosine and norepinephrine) but were reproduced by instilling dextran into the lungs and, in part, by occluding the right intermediate bronchus. In pulmonary edema the increased Ppa at low lung volumes is caused by the effects of decreases in the caliber of extra-alveolar vessels, by trapped air or liquid raising alveolar pressure, or by both; the decreased deltaPpa/deltaPaw and Ppa at high volumes is caused mainly by nonuniform distribution of driving pressures and blood flow.
Exercise ventilation correlates positively with ventilatory chemoresponsiveness
Authors: Martin B. J. , Weil J. V. , Sparks K. E. , McCullough R. E. , Grover R. F.
Published: December 2017

To determine the relationship of ventilatory responsiveness to hypoxia and hypercapnia to exercise hyperpnea, these responses and steady-state exercise ventilation (VE) were measured in 16 athletes during light (1/3 VO2 max) and heavy (2/3 VO2 max) exercise. Both the hypoxic and hypercapnic ventilatory responses correlated positively with VE per unit metabolic rate (VE/VCO2) at both exercise levels (P less than 0.05). The contribution of the hypoxic response to normoxic exercise VE was quantified by comparing VE in normoxia to VE during a brief (1 min) exposure to high O2 (PAO2 = 200 Torr). High O2 reduced normoxic exercise VE by a mean of 20% at either exercise intensity. Among individuals this reduction was directly dependent upon the intensity of the hypoxic response, and ranged from 7 to 42% of normoxic VE. After the variable reduction of normoxic VE by hyperoxia, all correlations of ventilatory response with exercise VE were lost except for the correlation of hypercapnic response with heavy exercise VE/VCO2. These findings indicate that the extent of VE in light or heavy exercise is modified by the strength of the hypoxic ventilatory response, and that the hypercapnic response independently correlates with VE during heavy exercise.
Responses of isolated canine airways to electric stimulation and acetylcholine
Authors: Russell J. A.
Published: December 2017

Contractility of tracheal smooth muscle strips and spiral strips of intrapulmonary airways 5 mm and 1.5 mm in diameter was studied in organ baths. Acetylcholine (ACh) sensitivity of canine airways closely resembled that of other species, and concentration-response curves for this drug were similar for all three preparations. Electric field stimulation (ES) elicited sustained contractions and, in contrast to guinea pig and human airways, never produced relaxations below the base line. Atropine antagonized the responses to both ES and exogenous ACh whereas tetrodotoxin abolished the response to supramaximal ES without altering ACh concentration-response curves. Thus, ES contracts airway smooth muscle via release of neurotransmitter from autonomic nerve endings whereas exogenous ACh acts directly on smooth muscle cells. The ratio of maximal force produced by ES to that produced by ACh decreased significantly from the trachea to the 1.5-mm airways. The latter result suggested that either the innervation of airway smooth muscle or the type of smooth muscle intercellular contacts, or both, vary depending on location within the tracheobronchial tree.
Airway responses to histamine and methocholine in Ascaris suum-allergic rhesus monkeys
Authors: Michoud M. C. , Pare P. D. , Boucher R. , Hogg J. C.
Published: December 2017

We performed dose-response curves to inhaled histamine (H) and methacholine (MC) in a group of eight rhesus monkeys, with and without natural allergy to Ascaris suum antigen (AA). The animals were anesthetized with pentobarbital sodium, 25 mg/kg im and studied in a volume-displacement body plethysmograph. The dose of H or MC producing a 50% increase in pulmonary resistance (RL) was used to determine sensitivity to these agents and the increase in RL at a given dose was employed as a measure of reactivity. Sensitivity and reactivity to H and MC were then compared with AA responsiveness. A wide range of responses was observed but allergic animals were not more sensitive or reactive to H or MC than nonallergic animals. In addition, we studied the changes in breathing pattern that occurred during the inhalation of AA, H, and MC in four AA-sensitive animals. AA and H produced rapid shallow breathing within 30 s of starting inhalation, but MC, despite causing an equal degree of bronchoconstriction, did not produce alterations in breathing pattern.
Distribution of pulmonary ventilation and perfusion during short periods of weightlessness
Authors: Michels D. B. , West J. B.
Published: December 2017

Information on the distributions of pulmonary ventilation and perfusion was obtained from four subjects on board a Learjet during 112 weightless periods lasting up to 27 s each. Zero gravity (G) was obtained during all or part of each test by varying the aircraft flight profile. Single-breath N2 washouts were performed with the test inspiration containing an initial bolus of argon at residual volume (RV). When the test inspiration was at 0 G, and the washout at 0 G or greater, the terminal rises and the cardiogenic oscillations in both N2 and argon were small and often absent. If instead the test inspiration was at 1 G with the washout at 0 G, the terminal rises were again small or absent but the cardiogenic oscillations remained. The terminal rise and the cardiogenic oscillations for N2, but not argon, were also nearly eliminated by performing just the preliminary exhalation to RV at 0 G with the test inspiration and washout following at 1 G. Aleveolar plateaus for N2 sloped upward at 0 G apparently due to nontopographical inequalities of ventilation. In further tests during air breathing, recordings were made of expired partial pressure of oxygen PO2) and carbon dioxide (POO2) following a brief hyperventilation and a 15-s breath hold. These recordings revealed marked cardiogenic oscillations in PO2 and PCO2 at 1 G that were enhanced at 2 G but almost eliminated at 0 G. The results suggest that virtually all the topographical inequality of ventilation, blood flow, and lung volume seen under 1-G conditions are abolished during short periods of 0 G.
A neuromuscular mechanism maintaining extrathoracic airway patency
Authors: Brouillette R. T. , Thach B. T.
Published: December 2017

The ability of the extrathoracic airway (ETA) to remain open when exposed to negative pressure was investigated in rabbits. Postmortem, the ETA collapsed at -6.3 +/- 0.6 cmH2O whereas, during airway occlusion maneuvers in lightly anesthetized animals, it remained patent at pressures as low as -80 cmH2O. This discrepancy suggested that a neuromuscular mechanism maintains ETA patency. Four findings indicated that the genioglossus and geniohyoid muscles, which pull the tongue and hyoid bone anteriorly, help maintain ETA patency: 1) anterior movement of the hyoid bone increased the negative pressure at which the ETA collapsed postmortem, 2) ETA closure during occluded inspirations occurred after 12th nerve section abolished electromyographic activity in these muscles and 3) after deep anesthesia depressed such activity, and 4) closing pressure was linearly related to peak integrated electromyograms of the two muscles. After 12th nerve section, ETA closing pressure became more negative with progressive asphyxia greatly exceeding postmortem closing pressure, which suggests that other muscles also help maintain ETA patency. Blood gas tensions, respiratory system mechanoreceptors, and depth of anesthesia appear to influence genioglossus and geniohyoid activity.
Fatigue of inspiratory muscles and their synergic behavior
Authors: Roussos C. , Fixley M. , Gross D. , Macklem P. T.
Published: December 2017

The time (tlim) required to produce inspiratory muscle fatigue was measured in five normal subjects breathing at functional residual capacity (FRC) against a variety of high inspiratory resistive loads. In every breathing test the subjects generated with each inspiration a mouth pressure (Pm) that was a predetermined fraction of maximum Pm (Pmmax). They continued breathing until they were unable to generate this Pm. The Pm/Pmmax that could be generated indefinitely (Pmcrit) was around 60%. The inspiratory power output at that level of breathing was 6.6 kg.m/min (Wcrit). In three of those subjects the same experiment was conducted at an end-expiratory volume of FRC + one-half inspiratory capacity (1/2IC). The higher lung volume was actively maintained by the subjects watching end-expiratory transpulmonary pressure on an oscilloscope. For any fraction of the maximum mouth pressure at FRC + 1/2IC (Pm'max), tlim was shorter than FRC. Pmcrit decreased to 30% Pm'max and Wcrit to 2.6 kg.m/min. Monitoring the abdominal pressure revealed that the contribution of the diaphragm and intercostal accessory muscles alternated in time, possibly postponing the onset of fatigue.
Decay of inspiratory muscle activity in chronic airway obstruction
Authors: Citterio G. , Agostoni E. , Del Santo A. , Marazzini L.
Published: December 2017

Relative decay rate of inspiratory muscle electrical activity (RDRI) in patients with chronic airway obstruction increased with decreasing expiratory time (TE), being faster than in normal subjects for a given TE. Time course of decay was similar in shape to that of normal subjects, whereas persistence time of activity during expiration was about half. Hence, braking action of inspiratory muscles in patients was smaller than in normal subjects. No tonic activity of inspiratory muscles was found in patients, even when frequency was increased and hyperinflation enhanced. Hence tonic activity of inspiratory muscles found by others in asymptomatic asthmatic or normal subjects after histamine inhalation seems elicited by histamine. In normal subjects breathing under resistive load, RDRI became similar to that of patients for a given TE: tonic activity of extradiaphragmatic inspiratory muscles occurred only if frequency was voluntarily increased at least three times, an unphysiological condition with resistive load. Under discontinuous inspiratory elastic load, RDRI of patients decreased or did not change, whereas previously that of normal subjects was found to increase.