bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of beta-adrenergic blockade during exercise on ventilation and gas exchange
Authors: Brown H. V. , Wasserman K. , Whipp B. J.
Published: December 2017

The ventilatory effects of beta-adrenergic blockade during steady-state exercise were studied in eight normal subjects using intravenous propranolol hydrochloride (0.2 mg/kg). Heart rate decreased in all subjects by an average of 17%. Coincident with the phase of decreasing heart rate was a significant decrease in both minute ventilation (VE) and CO2 output (VCO2), averaging 9.6 and 9.2%, respectively. Both functions returned to prepropranolollevels after heart rate had reached its reduced steady-state value. The change in VE was significantly correlated with the change in VCO2 (r = 0.85, Pless than 0.005), and was associated with negligible changes in endtidal CO2 tensions and ventilatory equivalents for CO2. We interpret these studies as showing that the transient isocapnic hypopnea concomitant with an acute reduction in cardiac output was secondary to a transient decrease in CO2 flux (cardiac output x mixed venous CO2 content). This decrease in VE appearsto be induced by the acute decrease in cardiac output (“cardiodynamic hypopnea”), in fashion similar to the previously described cardiodynamic hyperpnea.
Computer simulation of brainstem respiratory activity
Authors: Geman S. , Miller M.
Published: December 2017

A mathematical model of the medullary respiratory oscillator, composed of two mutually inhibiting populations (inspiratory and expiratory) of computer-simulated neurons, is presented. Each population consists of randomly interconnected subpopulations of excitatory and inhibitory neurons, is presented. Each population consists of randomly interconnected subpopulations ofexcitatory and inhibitory neurons. Neuronal coupling is such that either the inspiratory or expiratory population alone is capable of cyclic activity.Weak inhibitory connections between inspiratory and expiratory populations provide satisfactory reciprocating activity independent of the natural frequency of either population alone. Initiation and persistence of rhythmic activity is dependent on a diffused noncyclic excitatory input. Vagal discharge, simulated by phasic inhibition of inspiratory neurons, results in increased respiratory frequency with decreased inspiratory activity. In the absence of simulated vagal discharge, uniform facilitation of synaptic connections increases averaged activities of inspiratory and expiratory populations, with minor effect on frequency. In the presence of simulated vagal discharge, facilitation of synaptic connections increases both frequency and amplitude. The simulated effects of synaptic facilitation, with and without vagal discharge, mimic the physiological response to CO2 in the intact and vagotimized animal.
Transducer for recording electrical and mechanical chronic intestinal activity
Authors: Lambert A. , Eloy R. , Grenier J. F.
Published: December 2017

An extraluminal displacement transducer has been developed for simultaneously recording the mechanical activity in two perpendicular directions andthe electrical activity of the intestinal serosa. The length variations in two perpendicular directions were measured by means of strain gauges bounded on two pairs of lamellae embedded in a rigid stand. The electrical activity was recorded by means of four electrodes situated at the extremity of these lamellae. The electrical gauges of each pair of lamellae are connected to form a Wheatstone bridge. This device allows establishment of a correlation between the mechanical displacement of the intestinal wall serosa and electrical potentials by means of studies of long duration.
Ventricular dimensions measured noninvasively by echocardiography in the awake dog
Authors: Mashiro I. , Nelson R. R. , Cohn J. N. , Franciosa J. A.
Published: December 2017

A surface echocardiographic technique was employed in 37 mongrel dogs for measurement of left ventricular dimensions. Intracardiac bolus injectionsof dextran were used as an echo contrast material to visualize cardiac chambers, and the identification of intracardiac structures was further confirmed by postmortem examination. The left ventricle could be satisfactorily visualized from both the right and left chest, providing two transverse left ventricular diameters nearly perpendicular to each other. End-diastolic andend-systolic diameter measurements in the two separate transverse planes differed by an average of only 0.07 and 0.1 cm, respectively, and dimensionalmeasurements were reproducible from day to day. Diastolic diameter ranged from 3.0 to 4.7 cm (mean 3.7 cm) and systolic diameter 1.9 to 3.3 cm (mean 2.6 cm). Diameter was directly related to animal weight. Stroke volume calculated from the dimension measurements correlated with stroke volume calculated from indicator-dilution curves in 16 dogs. Ejection fraction averaged 0.67 and 0.54, depending on the formula used to calculate volumes. These results indicate that surface echocardiography can be employed to evaluate left ventricular dimensions in the awake dog.
Method to optimize high-pressure, multicomponent gas mixing
Authors: Scacci R.
Published: December 2017

By use of the equations derived herein, a method is outlined to determine the optimum filing sequence and to obtain the maximum possible pressure when two or more pure high-pressure gases are to be transferred to a receiver cylinder in order to prepare a multicomponent gas mixture. The method is valid for any number of gas components, originating from high-pressure storage cyclinders of arbitrary size and pressure and for a receiver cylinder to contain initially one or more of the component gases. Percentage concentrations within 1% of desired are easily obtained with this method.
Time course of muscular atrophy during immobilization of hindlimbs in rats
Authors: Booth F. W.
Published: December 2017

The hindlimbs of rats were immobilized, in plaster casts, for varying durations, and the time course for atrophy of muscle and of selected proteins in these muscles was determined. In those muscles whose lengths were at less than resting length during the fixation procedures, exponential decay to a new apparent steady state after atrophy was shown by wet and dry muscle weights and by the amounts of biuret protein, cytochrome c, and citrate synthase. The time taken to decrease to one-half of the final decrease at the new apparent steady state level was about 4–6 days for the above parameters which decayed exponentially. In contrast, the myoglobin concentration increased during atrophy and the amount of myoglobin remain unchanged during atrophy. When fixation procedures on limbs were such that muscles were stretched to lengths greater than resting length, then the onset of atrophy was delayed; indeed, in some cases muscles hypertrophied when fixed in the stretched position.
Adrenocortical function in aging exercise-trained rats
Authors: Severson J. A. , Fell R. D. , Tuig J. G. , Griffith D. R.
Published: December 2017

Plasma corticosterone concentrations and in vitro adrenal secretion of corticosterone were determined in exercise-trained rats. Rats, 100, 200, and 300 days of age, were trained for a 10-wk period by treadmill running. Following the training program, rats were subjected to an acute bout of swimming. Acute swimming elevated plasma corticosterone concentrations in all age groups. At 170 days of age, the plasma corticosterone concentration following swimming was higher in exercise-trained rats than in controls. The opposite was true of acutely swum rats at 270 and 370 days of age. Acute swimming elevated the in vitro adrenal gland response to adrenocorticotropic hormone stimulation in control rats at all ages and in trained rats at 170 days of age. The in vivo relationship of epinephrine and the pituitary adrenal system is suggested as a mechanism which could have caused this response. The relationship of secretion rates to plasma corticosterone concentrations indicated that extra-adrenal mechanisms, such as decreased turnover, were also responsible for the elevated plasma corticosterone levels observed in response to acute swimming.
Acoustic helium analyzer for closing volume measurement
Authors: Hamilton L. H. , Christman N. T. , Rickaby D. A.
Published: December 2017

An acoustic gas analyzer was developed to measure helium during the closing volume (CV) test. It is based on the principle that altering the composition of a gas mixture will change the velocity at which sound is transmitted through the gas. The change in transit time for an acoustic burst across an in-line (breathe-through) cell is measured as a function of He concentration in the expired air during the CV test. Although CO2 and H2O vapor affect the signal, so it is not specific for He, the system provides good records of CV. A comparison of measurements in 21 normal subjects demonstrated no differences for CV measured in the same breath by the bolus technique using the acoustic gas analyzer and by the resident gas method using a nitrogen analyzer. Differences in closing volumes measured by the He bolus technique and the resident gas method might exist in patients with some kinds of pulmonary disease, and the suggestion is made that CV measurements by the two methods might assist in describing pulmonary alterations in patients with bronchopulmonary disease.
Fetal cerebral oxygen consumption at different levels of oxygenation
Authors: Jones M. , Sheldon R. E. , Peeters L. L. , Meschia G. , Battaglia F. C. , Makowski E. L.
Published: December 2017

Cerebral oxygen consumption (VCO2) was measured in 10 unanesthetized, chronically catheterized fetal sheep at 130–140 days of gestation. The VCO2 was calculated using cerebral blood flow (QC) measured with radioactive microspheres and the cerebral arteriovenous difference of O2 content (C(a-V)O2) calculated from preductal arterial and sagittal sinus venous blood. The ewe was exposed to varying concentrations of oxygen, resulting in fetal arterial oxygen contents (CaO2) of 0.89–5.58 mM, arterial oxygen tension (PaO2) values of 14–36 Torr, and cerebral venous oxygen tension (PVO2) values of 9–25 Torr. Although there was a clear relationship between the fetal CaO2 and C(a-V)O2, this was shown to be the result of changes in Qc rather than changes in VCO2. There was not a statistically significant correlation between either CaO2 or PVO2 and VCO2 over this range of oxygenation. On the other hand, C(a-V)O2 was highly correlated with Qc. There is no evidence that VCO2 is a function of oxygen tension (PO2) in the unanesthetized fetal sheep as long as the sagittal sinus PO2 is greater than or equal to 9 Torr.
Ventilatory responses to hypercapnia and hypoxia during continuous aspirin ingestion
Authors: Riley D. J. , Legawiec B. A. , Santiago T. V. , Edelman N. H.
Published: December 2017

Hypercapnic and hypoxic ventilatory responses were serially measured in nine normal subjects given 3.9 g aspirin (ASA) per day for 9 days. Minute ventilation (VE), end-tidal carbon dioxide tension (PETCO2), venous bicarbonate concentration [HCO3-], oxygen consumption (VO2), hypercapnic ventilatory response (deltaVE/deltaPCO2), and isocapnic hypoxic ventilatory response (A) were determined before, 2 h after the first dose, and at 72-h intervals during the next 14 days. Serum salicylate levels averaged 18.6 +/- 2.0 mg/dl. VE increased (P less than 0.05, PETCO2 decreased (P less than 0.05), and [HCO3-] did not change significantly during drug ingestion. deltaVE/deltaPCO2 increased gradually to a value 37% greater than control by day 3 and remained constant (P less 0.01). A increased by 251% and VO2 by 18% within 2 h and remained constant for the remainder of the ASA period (P less than 0.01). All values returned to base line within 24 h following cessation of ASA. We conclude that during continuous ASA ingestion there is a gradual increase of hypercapnic ventilatory response. This may reflect slow entrance of ASA into the central nervous system. In contrast, there is a rapid rise in hypoxic ventilatory response which may be mechanically linked to changes in metabolic rate.
Creatine metabolism in skeletal muscle of cold-acclimated rats
Authors: Kurahashi M. , Kuroshima A.
Published: December 2017

Creatine metabolism in skeletal muscle of cold-acclimated rats was studied with the aid of [14C]creatine as a tracer. Creatine contents of all muscles studied were significantly lower in cold-acclimated rats than in controls. Radioactive creatine uptake by soleus of cold-acclimated rats was significantly lower than that of controls, while radioactive creatine uptakes by heart, diaphragm, and gastrocnemius of cold-acclimated rats were not different from those of controls. Urinary creatine dervied from muscle creatine plus urinary creatinine, which corresponds to total creatine release from muscle, increased in the early stage of cold exposure and was restored to control level after completion of cold acclimation. Creatine turnover rate in skeletal muscle was not different between control and cold-acclimated rats. These findings indicate that cold acclimation results in reduced creatine content and uptake of skeletal muscle, and could be interpreted as reflecting enhanced ability of nonshivering thermogenesis in skeletal muscle.
In vivo calibration of flow-dependent blood gas catheters
Authors: Lundsgaard J. S. , Groenlund J. , Einer-Jensen N.
Published: December 2017

In vivo calibration of blood gas catheters is complicated by the fact that their signals are flow dependent. A calibration method is described here, which permits continuous in vivo calibration. The principle is to compensate for flow dependence through simultaneous measurement on an inspired, inert reference gas of known partial pressure. The method is demonstrated by experiments on three anesthetized dogs, in which the arterial oxygen partial pressure was measured in situ with a flow-dependent blood gas catheter. The compensated signal was in good agreement with the partial pressure of oxygen measured with conventional techniques.
Effect of acute and established anemia on O2 transport at rest, submaximal and maximal work
Authors: Woodson R. D. , Wills R. E. , Lenfant C.
Published: December 2017

Effects of acute and maintained isovolemic anemia on oxygen transport was studied during rest and exercise in normal males. Following 34% reduction in hemoglobin concentration (Hb), supine and standing Q rose acutely by 56% and 20%, respectively, but returned nearly to the control value by 10–14 days, producing a decrease in PVO2. Redistribution of blood flow appeared to compensate significantly for the decrease in systemic oxygen transport. 2,3-Diphosphoglycerate rose by 18%, in vivo PO2 at half-saturation of hemoglobin (P50) rose by approximately 2 mm over 7–9 days and probably afforded some compensation. The relationship between VO2 and external work intensity was independent of Hb. During exercise, Q/VO2 and VE/VO2 were increased in acute anemia, but PVO2, for a given VO2, decreased below control levels. After 10–14 days the relative increase in VE with exercise persisted; the increase in Q was less pronounced; and PVO2 was further decreased. With both acute and extablished anemia maximal exercise capacity and maximal VO2 (VO2 max) decreased in proportion to the Hb reduction.
Reliability of noninvlasive methods for measuring cardiac function in exercise
Authors: Wolfe L. A. , Cunningham D. A. , Davis G. M. , Rechnitzer P. A.
Published: December 2017

Externally recorded systolic time intervals (STI's), indirect (CO2 re-breathing) cardiac output, and auscultatory blood pressures were measured during upright bicycle ergometer work in 20 healthy men, aged 24–56 yr. The subjects were studied on 2 separate days at steady-state work loads chosen to represent light (mean heart rate (HR) = 96 beats.min-1), moderate (HR = 118 beats.min-1) and heavy (HR = 147 beats.min-1) exercise. In addition to determinations of cardiac output, systolic time intervals, and blood pressure, the individual's mean systolic ejection rate (stroke volume/left ventricular ejection time) was calculated as a measure of left ventricular function. In general, heart-rate-corrected STI's were found to be reliable and reproducible. Reliability coefficients for total electromechanical systole and left ventricular ejection time ranged from 0.93 to 0.96 while those for the preejection period and its subcomponents were between 0.63 and 0.88. The reliability of cardiac output, stroke volume, mean systolic ejection rate, and systolic blood pressure was also considered to be acceptable but tended to be higher during moderate and heavy work (r = 0.85–0.95) compared to light exercise (r = 0.60–0.83).
Catecholamine-synthesizing enzymes in adrenals of seasonally acclimatized voles
Authors: Feist D. D. , Feist C. F.
Published: December 2017

Tyrosine hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT) activities were assayed in adrenal glands of the following groups of the Alaskan red-backed vole (Clethrionomys rutilus dawsoni): 1) laboratory reared at 20 degrees C and 2) exposed to 5 degrees C for 1, 3, 7, and 28 days; 3) wild, summer acclimatized; 4) wild, fall acclimatized; and 5) wild, winter acclimatized. TH activity in laboratory-acclimated voles exposed to 5 degrees C was increased by 2 times after 3 days and remained elevated after 28 days. PNMT activity in these same voles was increased after 7 days and also remained elevated after 28 days of cold exposure. In wild-acclimatized voles TH activity and PNMT activity in summer were equivalent to levels in 28-day cold-acclimated laboratory voles. In fall, TH activity was increased to 2.5 times the summer value. It decreased by midwinter, but remained elevated above the summer level. In contrast, PNMT activity appeared unchanged from summer through fall and winter. Pregnant summer voles had markedly increased TH activity. Adrenal norepinephrine and epinephrine did not change significantly with cold acclimation or seasonal acclimatization. Thus, acclimatization of wild voles to fall and winter conditions involved aquisition of a greater capacity to synthesize adrenal catecholamines than that produced by exposing laboratory-reared voles to an extended period of cold.
Adaptation of the rat myocardium to endurance training
Authors: Tibbits G. , Koziol B. J. , Roberts N. K. , Baldwin K. M. , Barnard R. J.
Published: December 2017

The purpose of this study was to assess cardiac adaptation to endurance training in rats. After 11 wk of progressive treadmill exercise (1 h/day), gastrocnemius cytochrome c oxidase activity was 38% higher (P less than 0.01) in the trained (n = 20) as compared to control (n = 20) rats. Cardiac Mg2+-stimulated myofibril ATPase activity (0.308 +/- 0.012 vs. 0.324 +/- 0.006 micrometer.mg-1.min-1) did not change nor was there any change in myofibril protein concentration (60.0 +/- 1.12 vs. 59.9 +/- 0.85 mg.g-1). The isolated left ventricular papillary muscle showed no significant change in time-to-peak tension (TPT) or half-relaxation time. Tension output, however, was significantly increased with training, 2.2 +/- 0.3 vs. 1.5 +/- 0.1 g.mm-2 (P less than 0.025). Furthermore, when the papillary preparations were perfused with 0.5 mM lanthanum (La3+) to displace membrane-bound Ca2+, the time course for tension decay was significantly prolonged in the trained muscles (P less than 0.001). We conclude that endurance running of this type does not necessarily increase myofibril ATPase activity or the time course of the isometric twitch of rat papillary muscle. However, tension output per unit area does increase and this appears to be due to a greater amount of Ca2+ being made available to the contractile apparatus.
Regulation of breathing in newborns at high altitude
Authors: Lahiri S. , Brody J. S. , Motoyama E. K. , Velasquez T. M.
Published: December 2017

Resting respiratory parameters and respiratory responses to acute changes in end-tidal O2 and CO2 pressure (PETO2 and PETCO2) were investigated in Peru in 23 newborn and 4 older infants at 3.850 m and in 13 newborns at 800 m. The study was done with the subjects asleep in a thermoneutral environment. The transient increase in ventilation in both high- and low-altitude newborns was followed by a decrease in response to acute hypoxia. During hyperoxia the two groups showed a slight but not clearly significant decrease in ventilation, whereas older high-altitude infants showed a sustained decrease. All subjects showed a prompt and clear response to CO2 inhalation during hyperoxia. We conclude that ventilatory peripheral chemoreflex is not fully developed in newborns regardless of altitude. The weak link in the reflex arc may reside in the afferent component because CO2 response was not impaired. Since hypoxic response became persistent in older infants its blunting in adult high-altitude natives is not a legacy of newborns.
Cardiovascular effects of positive end-expiratory pressure in dogs
Authors: Cassidy S. S. , Robertson C. H. , Pierce A. K. , Johnson R. L.
Published: December 2017

Our purpose was to reexamine the relationship of the fall in cardiac output and blood pressure which occurs during positive end-expiratory pressure (PEEP) to changes in transmural right atrial and left atrial filling pressures. Closed-chest dogs, half with pulmonary edema, were studied during spontaneous breathing and inspiratory positive-pressure breathing (IPPB) with 0–15 cmH2O PEEP. Mean esophageal pressure accurately reflected changes in pericardial pressure and was used to estimate extracardiac pressure. We found that cardiac output fell approximately 50% and blood pressure fell 20% during 15 cmH2OPEEP in spite of well maintained transmural right atrial and left atrial (or pulmonary artery wedge) pressures suggesting a primary or reflex depression of atrial or ventricular function.
Response of the renin-aldosterone system in the camel to acute dehydration
Authors: Finberg J. P. , Yagil R. , Berlyne G. M.
Published: December 2017

Plasma renin activity (PRA), renin substrate concentration (PRS), aldosterone concentration (PA), and cortisol levels were determined in five camels during dehydration (8–10 days complete denial of water) and at timed intervals after rapid rehydration in cool spring and hot summer weather. Plasma sodium concentration increased from 138 +/- 3.7 to 147 +/- 2.5 (mean +/- SE) meq/l during spring dehydration, and from 146 +/- 1.3 to 157 +/- 1.14 meq/l during dehydration in the summer. Plasma sodium concentration returned to control levels over the course of several hours following rapid rehydration. Only minor changes in plasma potassium concentration occurred. The hormonal changes were accentuated in the summer dehydration. PRA increased slightly on dehydration, and returned to control levels over the course of several hours following rehydration. PA increased slightly on dehydration but was markedly elevated 24 h after rehydration. PRS showed a slight increase following rehydration in the spring experiment, but no significant change in the summer experiment. Changes in cortisol were insignificant. The results are consistent with a role for angiotensin and aldosterone in enhancing sodium and water reabsorption from kidney and large intestine on dehydration in this species.
Optimal rate of work for mountaineers
Authors: Nag P. K. , Sen R. N. , Ray U. S.
Published: December 2017

The physiological responses of seven young male highlanders were recorded at high altitude while they were carrying loads (0, 25, 35, 45, and 55 kg) on snow at different speeds, supporting the loads on their backs by circular straps around the forehead. The rates of work calculated from the gross weight (body weight plus actual load in kg) multiplied by the speed of walking, m.min-1, ranged from 4,460 to 8,440 kg.m.min-1. The relationship between the rate of work and energy expenditure was rectilinear within the present range of values. The oxygen consumption (51.6 and 59.7 ml.min-1.kg-1 BW) for 55-kg load (at 4.09 and 4.64 km.h-1) possibly reached maximal aerobic capacity. At higher energy output at high altitude the subjects were exhausted after a short period of work. The proportion of increase of oxygen consumption per kg gross weight carried or per kg.m was almost constant up to a 55-kg experimental load. It is suggested that for day-to-day operations work should not be undertaken at more than 30–40% of maximal work capacity; a rate of work around 4,000 kg.m.min-1 (25–30 kg actual load at 3.0 to 3.5 km.h-1) may be considered as optimal for highlanders and porters at high altitude.
Extravascular water content of heart and lungs after acute myocardial ischemia
Authors: Gee M. H. , Gwirtz P. A. , Spath J. A.
Published: December 2017

We measured the extravascular water content of hearts and lungs of anesthetized dogs subjected to one of the following protocols: a)sham operation, b) circumflex artery ligation, c) increased left atrial pressure (Pla), or d) increased Pla and circumflex artery ligation. After 4 h, extravascular water of the heart and lungs increased significantly in the three experimental groups when compared with values from sham-operated dogs. After circumflex artery ligation, extravascular heart water increased 29% and lung water 8%, although Pla and calculated pulmonary microvascular pressure (Pmv) did not change. Extravascular heart water also rose 30% after increasing Pla from 23 to 37 cm H2O by inflating a left atrial baloon. In these dogs, extravascular lung water increased as a hyperbolic function of Pmv. Increasing Pla to 20 cm H2O in dogs with coronary artery ligation resulted in a 16% increase in heart water. Also at each Pmv, extravascular lung water was greater in dogs with coronary artery ligation than in dogs without. These data indicate that the increased extravascular lung water after coronary artery ligation cannot be explained solely by hemodynamic mechansims. We suggest that acute myocardial ischemia contributes to an increase in vascular permeability in the heart and lungs.
Effect of lung volume on expiratory time in the newborn infant
Authors: Martin R. J. , Okken A. , Katona P. G. , Klaus M. H.
Published: December 2017

The effect of an increased end-expiratory lung volume on inspiratory and expiratory duration was examined in 13 term infants at 4, 30, and 70 h of age. This was accomplished by the administration of a continuous positive airway pressure (CPAP) of 0, 3, and 6 cmH2O by use of a face mask connected to a pneumotachometer, and by measurement of the timing of the respiratory cycle over 1-min intervals. At increasing functional residual capacity (FRC) there was a progressive increase in expiratory time (TE) and fall in respiratory rate, with a variable effect on inspiratory time (TI). As CPAP increased from 0 to 6 cmH2O, the TI/TE ratio fell from 0.75 to 0.62 (P less than 0.01), 0.90 to 0.66 (P less than 0.001), and 0.87 to 0.64 (P less than 0.001) at 4, 30, and 70 h, respectively. We conclude that alterations in end-expiratory lung volume significantly alter expiratory duration in the newborn infant at term. This may be analogous to the vagally mediated tonic control of expiratory time with changing FRC recently described in anesthetized animals.
Effects of time and vasoconstrictor tone on O2 extraction during hypoxic hypoxia
Authors: Cain S. M.
Published: December 2017

To test the role of peripheral vasoconstrictor tone in the efficient use of a limited O2 supply, three groups of anesthetized dogs were ventilated with 9.1% O2 until circulation failed. Two groups were alpha-blocked with phenoxybenzamine and one of those was volume expanded with dextran to restore blood pressure. After O2 utake was lowered in hypoxia, O2 uptake was linearly related to O2 delivery (cardiac output X arterial O2 content) with r = 0.94. The slope of that line was mathematically identical to the extraction ratio and it increased from 0.54 at 10 min to 0.87 at the end of hypoxia (r = 0.99). In both alpha-block groups O2 extraction remained constant with time, and O2 extraction in each alpha-block group was significantly less (P less than 0.01) than in the unblocked group. As further evidence of better O2 extraction, mixed venous partial O2 pressure was significantly less in the unblocked group, 6.2 +/- 3.4 Torr vs. 10.6 +/- 3.2 and 9.9 +/- 2.4 Torr with alpha block (P less than 0.01). Results after alpha-block indicated that a vigorous vasoconstrictor tone during hypoxia conserved O2 by promoting greater extraction by the tissues.
Variability of oxygen affinity of normal blood: an automated method of measurement
Authors: Winslow R. M. , Morrissey J. M. , Berger R. L. , Smith P. D. , Gibson C. C.
Published: December 2017

Oxygen equilibrium curves of 48 healthy adult subjects have been measured by the method of Rossi-Bernardi et al. (Clin. Chem. 21: 1747, 1975), in which H2O2 is gradually added to a sample of deoxygenated blood that contains an excess of catalase. The mean P50 for nonsmokers was 26.9 Torr and the distribution of values was slightly skewed to the right (range 24.2--29.9 Torr). The method differs from others previously available in that pH, PCO2, and HCO3-- are constant during oxygenation. The system for control of the experiment and data collection and processing has been automated by the use of a microprocessor so that the equilibrium curve can be obtained quickly, reproducibly, and relatively simply. With the aid of a digital computer, the parameters of the generalized Adair equation can also be estimated.
Effects of exercise, altitude, and food on blood hormone and metabolite levels
Authors: Stock M. J. , Chapman C. , Stirling J. L. , Campbell I. T.
Published: December 2017

Measurements of blood glucose and plasma free fatty acids (FFA), thyroxine (T4), free thyroxine (FT4), triiodothyronine (T3), and thyroid-stimulating hormone (TSH) were made on samples taken from fed and fasted human subjects while at rest and immediately after 20 min moderate exercise. Six subjects were studied on successive weeks before (LA1), during (HA1, HA2, HA3), and after (LA2) a 3-wk sojourn at high altitude (3,650 m). The subjects and location were the same as those used for the energy expenditure measurements described in the preceding paper (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 45:345--349, 1978). The most marked effect of altitude was to potentiate the rise in FFA due to exercise. This effect was most noticeable in fed subjects during HA1 and HA2. Changes in the plasma levels of the thyroid hormones correlated with the FFA changes and, once again, exercise at altitude caused the greatest increase in circulating levels. Possible causes of the parallel changes in FFA and thyroid hormone levels and their relationship to changes in energy metabolism are discussed.
Regional lung expansion at total lung capacity in intact vs. excised canine lungs
Authors: Chevalier P. A. , Rodarte J. R. , Harris L. D.
Published: December 2017

A computer-based biplane videoroentgenographic recording technique that determines the spatial coordinates of radiopaque lung parenchymal markers was used to compare regional lung expansion at total lung capacity (TLC) in the intact dog (prone and supine) and after removal from the chest. The reproducibility of the technique was examined by repeated determinations of intermarker distances at various static lung volumes during stepwise inflation and deflation of the lungs. Most of the variability in repeated determinations of intermarker distances at any lung volume was due to cardiogenic motion. When marker positions were determined repeatedly at the same phase of the cardiac cycle, the maximum coefficient of variation was less than 3% for a marker pair separated by 16.5 mm. At TLC, distances between all intralobar marker pairs in the intact thorax (prone and supine) and excised were highly linearly related (r = 0.96–0.99), whereas distances between interlobar marker pairs did not correlate as well (r = 0.77–0.86). We conclude that at TLC 1) the intact thorax does not distort the shape of the individual lobes from the state of isotropic expansion, and 2) in different body positions, overall lung shape may be different due to displacementof lobes relative to each other, but individual lobes remain uniformly expanded.
Time course of sympathoadrenal adaptation to endurance exercise training in man
Authors: Winder W. W. , Hagberg J. M. , Hickson R. C. , Ehsani A. A. , McLane J. A.
Published: December 2017

One possible reason for the lower exercise heart rate after endurance exercise training is that the sympathetic drive to the heart is reduced. We have studied the relationship between plasma catecholamines and heart rate during exercise in the course of a 7-wk training program. Six untrained subjects exercised vigorously (on bicycle ergometers and by running) 30--50 min/day for 7 wk. Prior to the beginning of training and at weekly intervals thereafter, participants were subjected to a 5-min strenuous bicycle ergometer test. In the test prior to training, plasma epinephrine increased to 0.5 ng/ml and norepinephrine increased to 3.0 ng/ml. The major proportion of the training-induced decrement in catecholamine response was reached at the end of the 3rd wk when epinephrine increased to 0.17 ng/ml and norepinephrine increased to 1.5 ng/ml in response to the same test. Heart rate during exercise continued to decrease even after the catecholamine response had plateaued, implying that the reduced sympathetic response is not solely responsible for the reduced exercise heart rate.
Effects of pulmonary congestion and of left atrial distention on breathing in dogs
Authors: Lloyd T. C.
Published: December 2017

Prior experiments showed that pulmonary congestion may initiate tachypnea from lung receptors and that left atrial distention has no significant effect on breathing, but in those experiments secondary reflexes could have determined the results. In this study we separately distended the entire pulmonary vascular bed, the arterial compartment, and the left atrium in dogs perfused and oxygenated by an external system while ventilating and while not ventilating the lungs. Distending pressures ranged from 20 to 70 Torr, and as output variables we measured the initial rate of inspiration, peak inspiratory magnitude, inspiratory duration, expiratory duration, and breathing frequency from the diaphragmatic electromyogram. Total vascular congestion caused prolongation of expiration and lowering of frequency without effect on inspiratory duration, its rate or magnitude. A smaller depression was induced from the arterial compartment. Left atrial distention, which failed to occur sufficiently often to be attributable to dogs in general, had much less effect. However, when a related change in breathing did occur, it was limited to a shortening of inspiratory duration.
Plasma volume changes with movement to supine and standing positions
Authors: Hagan R. D. , Diaz F. J. , Horvath S. M.
Published: December 2017

The chronology of hemoconcentration and hemodilution associated with changes in posture, and the reliability of venous hematocrit (Hct), hemoglobin (Hb), and plasma proteins (PP) as indicators in evaluating changes in plasma volume were determined in seven male subjects. Red cell mass was also measured by the CO method at the termination of the erect and supine positions. Movement to and from supine and erect positions produced consistent, rapid, and progressive changes in Hct, Hb, and PP. Thirty-five minutes in a supine position resulted in a 440-ml expansion of plasma volume. Resumption of the standing position resulted in an increase of 10.3 and 10.8% for Hct and Hb, respectively, and an increase in PP of 20.8%. A fluid efflux of 593 ml reduced blood and plasma volume by 9.5 and 16.2%, respectively. Red cell mass was unaffected by changes in posture. The significance of these postures on the reported alterations in plasma volumes consequent to the imposition of stresses on man are discussed.
Evaporative water loss in man in a gravity-free environment
Authors: Leach C. S. , Leonard J. I. , Rambaut P. C. , Johnson P. C.
Published: December 2017

Daily evaporative water losses (EWL) during the three Skylab missions were measured indirectly using mass and water-balance techniques. The mean daily values of EWL for the nine crew members who averaged 1 h of daily exercise were: preflight 1,750 +/- 37 (SE) ml or 970 +/- 20 ml/m2 and inflight 1,560 +/- 26 ml or 860 +/- 14 ml/m2. Although it was expected the EWL would increase in the hypobaric environment of Skylab (one-third atmosphere). an average decrease from preflight sealevel conditions of 11% was measured. The results suggest that weightlessness decreased sweat losses during exercise and possibly reduced insensible skin losses as well. The weightlessness environment apparently promotes the formation of an observed sweat film on the skin surface during exercise by reducing convective flow and sweat drippage, resulting in high levels of skin wettedness that favor sweat suppression.
Cold-induced pulmonary hypertension in cattle
Authors: Will D. H. , McMurtry I. F. , Reeves J. T. , Grover R. F.
Published: December 2017

The frequency with which cattle develop right-heart failure during the winter at high altitude suggested that cold might contribute to hypoxic pulmonary hypertension. Indeed in a preliminary study conducted out-of-doors during early Spring, two calves with known hyperreactive pulmonary vessels showed elevated pulmonary arterial pressures attributed to their prior exposure to nighttime cold (-5 degrees C). In a second study five hyperreactive calves had increases in mean pulmonary arterial pressure from 29 to 45 Torr (+ 55%) during 48 h of exposure to cold (0 to -5 degrees C) in a climatic chamber. Three calves with less reactive lung vessels increased their pressures from 25 to 36 Torr (+ 44%). In a more complete study, six calves selected as potential hyperresponders showed increases in pulmonary arterial pressure (+ 60%), blood flow (+ 18%), and vascular resistance (+ 38%) during 48 h of cold exposure. Arterial PO2 decreased (-10 Torr) and PCO2 rose (+6 Torr) suggesting hypoventilation. Oxygen breathing returned pulmonary pressures and resistance to near control values, suggesting that cold had induced a hypoxic pulmonary vasoconstriction and an increased blood flow. Thus, a cold produced pulmonary hypertension in cattle at the modest altitude of 1,524 m and the pressor responses were greater in calves with more reactive lung vessels.
Lung tissue guanosine 3',5'-monophosphate: effects of ventilation and anesthesia
Authors: Klass D. J.
Published: December 2017

In vivo levels of guanosine 32,52-cyclic monophosphate (cGMP) in rat lung were measured by radioimmunoassay. The basal levels of this agent were found to change depending on the method of killing or anesthesia used. Lowest values were found after microwave irradiation to the head (10.2 fmol/mg wet wt). Values after pentobarbitol anesthesia, with or without atropine, were significantly higher (19–24 fmol/mg). In animals anesthetized with pentobarbital and ventilated at pressures of 7 cmH2O with no end-expiratory pressure, lung cGMP was 42–49 fmol/mg. Ventilation at higher pressures resulted in much higher levels of cGMP (20 cmH2O, 105 fmol/mg; 30 cmH2O, 233 fmol/mg). The response of cGMP to ventilation was not blocked by pretreatment of the animals with atropine. High-pressure ventilation was without effect on lung adenosine 32,52-cyclic monophosphate.
A plethysmograph for long-term measurements of ventilation in unrestrained animals
Authors: Jacky J. P.
Published: December 2017

An apparatus for quantitative measurement of ventilation in unrestrained small animals is described. The subject rests in an environmental chamber, and respiration is indicated by barometric pressure oscillations proportional to tidal volume. The chamber is purged continuously at a relatively high flow rate during studies. Thus, CO2 does not accumulate and long-term measurement can proceed without interruption. Respiratory control studies are especially facilitated since different gas mixtures can be rapidly passed through the chamber. An electronic device also is described which automatically calculates expired minute volumes (VE) from the pressure signal obtained from the plethysmograph.
Slow postcapillary pH changes in blood in anesthetized animals
Authors: Bidani A. , Crandall E. D.
Published: December 2017

To investigate the hypothesis that blood pH and PCO2 continue to change after the blood leaves an exchange capillary, we used a rapidly responding, pressure-insensitive, stopped-flow pH electrode apparatus. Arterial blood from an anesthetized dog or cat is drawn through the apparatus into a syringe. Syringe movement is then suddenly stopped. Temperature and pH of the blood in the electrode assembly are continuously monitored, both before and after blood withdrawal ceases. Hemolysis was reduced by coating all blood contact surfaces with silicone and fasting the animal overnight, anesthetizing it with crystalline pentobarbital sodium, and allowing it to ventilate spontaneously. After stopping withdrawal, pH of blood in the electrode chamber continued to change, rising 0.01 unit with t1/2 of 4.4 s. After lysed blood was returned to the animal to provide carbonic anhydrase to the plasma, no pH change was seen after stopping the flow. The small pH rise occurring in arterial blood in vivo is probably due in large part to disequilibrium of [H+] between red blood cells and plasma at the end of the pulmonary capillary, the equilibration process being rate-limited by the extracellular CO2 hydration-dehydration reaction.
Oxygen toxicity in neonatal and adult animals of various species
Authors: Frank L. , Bucher J. R. , Roberts R. J.
Published: December 2017

Neonatal and adult animals of five species were exposed to 95+% O2. Survival time and changes in lung antioxidant enzyme activity (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GP)) in response to hyperoxia were determined. Adult animals succumbed to O2 lung toxicity in 3--5 days. Neonatal rats, mice and rabbits showed minimal lung changes after 7 days of hyperoxic exposure and these same neonatal animals showed rapid and significant increases in lung antioxidant enzyme activities. In contrast, neonatal guinea pigs and hamsters had no lung antioxidant enzyme response to hyperoxia and these neonates died in 95+% O2 as readily as their respective parent animals. Results from an in vitro hyperoxic exposure system suggest that the lack of enzymic response of the guinea pig (and hamster) neonates to O2 challenge is due to an inherent pulmonary biochemical unresponsiveness rather than to a deficiency of a necessary “serum factor.” The results of this species and age study support the important role of the lung antioxidant enzyme defense system in protection of the lung from O2-induced injury.
Flow dependence of gas distribution and the pattern of inspiratory muscle contraction
Authors: Fixley M. S. , Roussos C. S. , Murphy B. , Martin R. R. , Engel L. A.
Published: December 2017

We measured regional distribution of xenon-133 boli at 0.25, 0.75, and 1.5 l/s in four normal seated subjects during inspirations performed predominantly with intercostal and accessory muscles (IC) or with the diaphragm, accompanied by outward abdominal motion (Ab). In six additional subjects we inferred the topographical distribution of helium boli during similar breaths and flow rates from the slope of the alveolar plateau recorded during a slow expiration (less than 0.5 l/s). Distribution of the helium boli was studied during natural as well as IC and Ab inspirations. At each of the flow rates IC breaths distributed relatively more of the inspired bolus to upper lung regions than did Ab inspirations. Natural breaths at 0.25 l/s resulted in distributions similar to those of Ab inspirations, whereas at 1.5 l/s the distribution approached that of IC inspirations. A three-compartment model, representing upper, middle, and lower lung regions, was used to simulate bolus distribution. The experimental data showed substantial departure from predictions based on regional time constants alone. However, additional small differences in applied pressure (less than 0.50 cmH2O) between the regions satisfactorily accounted for the gas distribution.
Anesthetics inhibit pressure-induced repetitive impulse generation
Authors: Kendig J. J. , Schneider T. M. , Cohen E. N.
Published: December 2017

Repetitive and spontaneous impulse generation appears in nerve axons exposed to high pressure. This phenomenon is a possible basis for high-pressure nervous syndrome (HPNS) or pressure reversal of anesthesia, two examples of an antagonistic interaction between anesthetic drugs and high pressure. In the present study, the interactions between three classes of anesthetic drug (ethyl alcohol, the volatile inhalation agent halothane, and phenobarbital) and repetitive activity were explored. Ethyl alcohol (5% in solution) and halothane (1.3 and 3.4% in oxygen) inhibited pressure-induced repetitive activity. Phenobarbital at 0.25 mM in solution, the maximum concentration obtainable at low temperature, was partially effective. The three drugs produce an unconscious state that is “reversed” at hyperbaric pressure. Halothane and phenobarbital inhibit HPNS, but ethyl alcohol has not been tested for this property. The results thus support a relevance of repetitive activity to HPNS, to pressure reversal of anesthesia, or to both.
Contribution of peripheral pooling to the renal response to immersion in the dog
Authors: Zucker I. H. , Gilmore J. P.
Published: December 2017

The present investigation evaluated the renal and hemodynamic responses to head-out water immersion in dogs. Dogs were immersed in the vertical (seated) position in a 34 degrees C bath. Urine flow (V), osmolar clearance (Cosm), free water clearance (CH2O), sodium excretion (UNa+V), potassium excretion (UK+V), GFR, effective renal plasma flow (ERPF), central venous pressure (CVP), and cardiac output (CO) all increased significantly during immersion. This response was unchanged by bilateral cervical vagotomy or by deoxycorticosterone acetate and antidiuretic hormone administration. The control values of these dogs were low and indicated a state of peripheral vascular pooling which was readjusted to normal by the immersion maneuver. The renal and hemodynamic values during the period of immersion were similar to values of a group of dogs which were recumbent in air. Furthermore, when the latter group of dogs were tilted head down 19 degrees, there was no further increase in any of the measured parameters. These data are consistent with the view that water immersion in the upright dog simply redistributes blood volume back to that level seen in the recumbent dog, a position which is more natural for this species.
Recirculation times in exercising children
Authors: Cumming G. R.
Published: December 2017

Recirculation times were measured with indicator-dilution methods in 19 subjects, aged 5--14 yr, during near-maximal supine bicycle exercise. Recirculation times were as short as 4.5 s and peak recirculation occurred within 10 s. When rebreathing methods are used to measure exercise cardiac output in children, their very rapid recirculation needs to be considered.
Effect of histamine and methacholine on guinea pig tracheal permeability to HRP
Authors: Boucher R. C. , Ranga V. , Pare P. D. , Inoue S. , Moroz L. A. , Hogg J. C.
Published: December 2017

The effects of histamine, methacholine, and ether on the permeability of the respiratory mucosa to macromolecules were investigated employing a radioimmunoassay and histochemical techniques to monitor movement of horseradish peroxidase (HRP) from airway lumen to blood. We found that 0.08% of the dose of HRP instilled into guinea pig tracheas was present in the blood volume at 10 min, and plasma HRP levels increased at a rate of 0.0036% instilled dose/min thereafter. After inhalation challenge, significant increases in plasma rates of accumulation of HRP were recorded for the histamine, methacholine, and ether groups, whereas no change in rate was noted for the control (Tyrode's) group. Electron micrographs of tracheal sections showed HRP penetration into the intercellular spaces of the epithelium after histamine, methacoline, or ether exposure but no penetration in the Tyrode's group. We conclude that, like ether, histamine and methacholine increase tracheobronchial permeability and this effect is most likely mediated by a functional change in the epithelial tight junction.