bluuebunny/crossref_metadata_2025 huggingface dataset:
Circadian variations in concentrations of plasma thyroxine and triiodothyronine in man
Authors: Balsam A. , Dobbs C. R. , Leppo L. E.
Published: December 2017

The plasma concentrations of thyroxine (T4), triiodothyronine (T3), and total protein (Pr) were measured at 2-h intervals in 8 male subjects during two 24-h periods. Plasma T4 and T3 levels varied significantly during the day. T4 values were highest at 0900 hours and thereafter declined rapidly reaching lowest levels at 1500–1700 hours (mean decrement, 13.2% of 0.00-hour value). Plasma T3 was highest at 0900 hours and lowest at 1700–1900 hours (mean decrement, 16.7% of 0900-hour value). Fluctuations observed in Pr were not significant. Variations in plasma T4 and T3 appeared concordant with respect to time, since no significant variation was detected in T3:T4 plasma concentration ratios. In view of previous studies that have demonstrated circadian variations in the binding of thyroid hormones by plasma proteins, it is suggested that the observed temporal variations in plasma concentrations of T3 and T4 reflect parallel changes in the capacity or affinity of specific plasma binding proteins of these iodothyronines.
Step changes in end-tidal CO2: methods and implications
Authors: Swanson G. D. , Bellville J. W.
Published: December 2017

A dynamic end-tidal forcing technique for producing step changes in end-tidal CO2 with end-tidal O2 held constant independent of the ventilation response or the mixed venous return is introduced for characterizing the human ventilation response to end-tidal CO2 step changes for both normoxic (PAO2 = 125 Torr) and hypoxic (PAO2 = 60 Torr) conditions. The ventilation response approaches a steady state within 5 min. In normoxia, the on-transient is faster than the off-transient, presumably reflecting the action of cerebral blood flow. The hypoxic step response is faster than the normoxic response presumably reflecting the increased contribution from the carotid body. The delay in the ventilation response after the change in end-tidal CO2 is less in hypoxia than in normoxia and reflects the action of a transport delay and that of a virtual delay. These delays are interpreted with respect to the high-frequency phase shift data for the same subject, generated using sinusoidal end-tidal forcing. The methods of others for experiments utilizing step changes in inspired CO2 are considered with respect to our methods.
Maximum expiratory flow-volume studies on monkeys exposed to bituminous coal dust
Authors: Moorman W. J. , Lewis T. R. , Wagner W. D.
Published: December 2017

To assess early ventilatory responses at the 2 mg/m3 bituminous coal dust standard, 23 cynomolgus monkeys were exposed by inhalation to Pennsylvania and Utah coal dust. Ten controls were utilized. Pennsylvania coal was selected from a field having a high prevalence of coal workers' pneumoconiosis while the Utah coal was selected from a low prevalence area. After 24 mo of exposure, a pattern of pulmonary impairment consistent with peripheral airway obstruction was demonstrated. Reductions were observed in the forced expiratory volume in 1 s, maximum midexpiratory flow rate, and especially maximum expiratory flow at small lung volumes. Hyperinflation (RV/TLC) was observed in both coal treatments; however, no specific lung volumes differed significantly from controls. No differences were found between the Pennsylvania and Utah treatments. Design and specifications for a new hydraulically operated plethysmograph-respirator are included.
Ventricular function following acute carbon monoxide exposure
Authors: Cramlet S. H. , Erickson H. H. , Gorman H. A.
Published: December 2017

Cardiac output function curves were used to investigate the effects of carbon monoxide on the heart in the conscious dog. Each dog was briefly exposed to 1,500 ppm carbon monoxide through a permanent tracheostomy. Immediately upon attaining either 10%, 20%, or 30% HbCO a rapid infusion of Ringer's lactate was given to test cardiac capabilities. The combined effects of carbon monoxide and infusion produced significant increases in cardiac output, heart rate, mean left ventricular pressure, dP/dt and (dP/dt)/IP. Cardiac output was sufficient to prevent peripheral hypoxia at all HbCO levels; however, there was evidence of impending cardiac depression beginning at 20% HbCO.
Mucociliary tracheal transport rates in man
Authors: Yeates D. B. , Aspin N. , Levison H. , Jones M. T. , Bryan A. C.
Published: December 2017

A new method for measuring mucociliary tracheal transport rates (MTTR's) is described. An aqueous aerosol containing albumin microspheres labeled with 99mTc was inhaled in such a manner that it was deposited in local concentrations in the large airways. These boli of microspheres were transported up the trachea and their MTTR's measured using a gamma camera. MTTR's were measured in 42 healthy nonsmoking adults (32 men and 10 women, mean age 28 yr). The mean MTTR's appeared to be log normally distributed with a geometric mean of 3.6 mm/min and a coefficient of variation of 75%. The MTTR's of men and women were similar. Each individual's short-term coefficient of variation was 25%. Twenty-two repeat studies 1 wk to 15 mo apart showed the variation within individuals was less than between individuals. The parasympatholytic drug, atropine (0.6 mg iv) decreased MTTR's for at least 3 h. Inhalation of the sympathomimetic drug, Th1165a increased MTTR's. Chronic and acute smoking did not appreciably change the MTTR'S.
Determination of plasma volume by 113min-labeled transferrin
Authors: Horowitz M. , Beer G. , Loewinger E.
Published: December 2017

The binding property of ionic indium (In3+) with plasma transferrin was utilized for determination of plasma volumes (PV) of whole body and individual organs in small animals. Plasma transferrin from a donor rat was labeled with 15–17 muCi 113mIn/ml plasma and injected into the tested rats. PV were determined either by extrapolation to the dilution at time zero (for whole animals) or by calculation of the ratio, organ radiation: radiation of a plasma unit volume (for organs). The reliability of the method for determination of whole-body PV was ascertained by comparing the results obtained with those obtained simultaneously by the Evans blue dilution method. Whole body PV values obtained by the two methods were similar, with a correlation coefficient (r) of 0.997. The short half life of 113mIn enables it to be used with other nuclides which have similar or different energies in the same sample; indium radiation was counted first and after it had disappeared the activity of the other nuclide could be measured.
Frequency response of the chest: modeling and parameter estimation
Authors: Peslin R. , Papon J. , Duviver C. , Richalet J.
Published: December 2017

The frequency response of the respiratory system was studied in the range from 3 to 70 Hz in 15 normal subjects by applying sinusoidal pressure variations around the chest and measuring gas flow at the mouth. The observed input-output relationships were systematically compared to those predicted on the basis of linear differential equations of increasing order. From 3 to 20 Hz the behavior of the system was best described by a 3rd-order equation, and from 3 to 50 Hz by a 4th-order one. A mechanistic model of the 4th order, featuring tissue compliance (Ct), resistance (Rt) and inertance (It), alveolar gas compressibility (Cg) and airway resistance (Raw), and inertance (Iaw) was developed. Using that model, the following mean values were found: Ct = 2.08–10(-2)1-hPa-1 (1 hPa congruent to 1 cm of water); Rt = 1.10-hPa-1(-1)-s; It = 0.21–10(-2)hPa-1(-1)-s2; Raw = 1.35-hPa-1(-1)-s; Iaw = 2.55–10(-2)hPa-1(-1)-s2. Additional experiments devised to validate the model were reasonably successful, suggesting that the physical meaning attributed to the coefficients was correct. The validity of the assumptions and the physiological meaning of the coefficients are discussed.
Effect of maternal malnutrition on surface activity of fetal lungs in rats
Authors: Faridy E. E.
Published: December 2017

The effects of maternal malnutrition on fetal lung growth and surface forces were studied in albino rats. Pregnant albino rats were subjected to one of the following diets: rat chow ad lib. (controls), partial food deprivation (intake one-half that of the controls), complete food deprivation for 4 days (on gestation day 3–7, 9–13, or 17–21), low protein (8%), and fat free. The fetal lungs were studied on the 21st day of gestation (delivered by cesarean section) or at birth (gestation day 22). Fetuses and neonates after maternal food deprivation (FD) on the 17–21 day of pregnancy, and after a low-protein (LP) diet during pregnancy, had significantly smaller body weight and lung wet or dry weight/body weight ratio (hypocellular lungs). The minimum surface tension (gamma min) of fetal lung extracts was significantly increased with FD and LP. This was associated with a reduction of about 35% in lung lecithin content, expressed per lung DNA. The earlier in pregnancy the rat was subjected to 4-day food deprivation the less the effect on the fetus. At birth the gamma min and the lung lecithin content reached control values. This recovery occurred after birth (at age 4–10 h) and prior to first feeding. However, the lungs remained small and hypocellular. The results indicate that the nutritional status of the pregnant rat influences the surface activity and the growth of the fetal lung.
Body composition and Vo2max of exceptional weight-trained athletes
Authors: Fahey T. D. , Akka L. , Rolph R.
Published: December 2017

The maximal oxygen uptake and body composition of 30 exceptional athletes who have trained extensively with weights was measured. The sample included 3 world record holders, 8 other world class athletes, and 19 national class competitors. The sports represented were shot-putting, discus throwing, body building, power lifting, wrestling, and olympic lifting. Vo2max as determined on a bicycle ergometer by the open-circuit method was 4.6 +/- 0.7 1-min-1 (mean +/- SD) (48.8 +/- 7 ml-kg-1., 56.4 +/- 8.6 ml-(kg LBW)-1). The mean maximal heart rate was 185.3 +/- 11.6 beats-min-1. The subjects attained a work rate of 1,728.2 +/- 223 kpm-min-1 on a continuous progressive bicycle ergometer test and had mean maximal ventilations of 152.5 +/- 27.7 1-min-1 BTPS. Body composition was determined by densitometry. Body weight averaged 96.0 +/- 14.9 kg, with mean percent fat of 13.8 +/- 4.5. The results of this study indicate that exceptional weight-trained athletes are within the normal college-age population range in body fat and of somewhat higher physical working capacity.
Relationship between respiratory nerve and muscle activity and muscle force output
Authors: Eldridge F. L.
Published: December 2017

To demonstrate the most satisfactory way of using electrical activities of respiratory nerves and muscles, activities of phrenic nerve and external intercostal muscle (ICM) and the airway pressure changes generated by respiratory muscle contraction were recorded in anesthetized cats during complete airway occlusion. Electrical activities were rectified, integrated and processed in terms of peak and average inspiratory rates per 0.1 s and of total activity per breath. Peak rate of phrenic nerve activity exhibited a high linear correlation (r = 0.974) with peak inspiratory pressure. Average phrenic rate showed a similar high correlation (r = 0.973). Peak rate of external ICM was linearly related to peak pressure but the correlation was less good (r = 0.915). Total phrenic activity per breath was too dependent upon inspiratory duration to be a satisfactory correlate (r = 0.674). In this experiment occlusion pressure was an index of muscle force generation and respiratory control system output. It is concluded that peak or average rates of phrenic activity provide an electrical index of output changes. On theoretical grounds, peak rate is probably better.
Local control of pulmonary resistance and lung compliance in the canine lung
Authors: Coon R. L. , Rattenborg C. C. , Kampine J. P.
Published: December 2017

Local control of pulmonary resistance and lung compliance was studied in the in situ left lower lobe of the canine lung. Recirculation of blood through the lobe while the Pco2 of the ventilatory gas was varied resulted in an increase in resistance and a decrease in compliance only when the pulmonary venous pH was greater than 7.42. Alternating sodium bicarbonate and lactic acid infusion while alveolar Pco2 was maintained below 5 mmHg demonstrated the dependence of the hypocapnic response on the acid-base status of the blood perfusing the respiratory airways. The increase in resistance and decrease in compliance observed at a pulmonary venous pH of 7.64 was comparable to that observed after lobar pulmonary artery occlusion. Varying degrees of hypoxia did not significantly affect bronchomotor tone, nor was the bronchoconstriction following lobar pulmonary artery occlusion affected by the hypoxia. Vagal stimulation superimposed on a stepwise increase in pulmonary venous pH from 7.32 to 7.62 resulted in an increase in resistance which paralleled the increase in resistance when pulmonary venous pH alone was increased. Compliance was not significantly affected by vagal stimulation at any level of pulmonary venous pH.
Strontium-85 extraction during transcapillary passage in tibial bone
Authors: Cofield R. H. , Bassingthwaighte J. B. , Kelly P. J.
Published: December 2017

Indicator dilution experiments were done to determine the extraction of 85Sr during a single passage through capillaries of the tibial diaphysis. Extraction was estimated by injection of 85SrCl2 and a nonpermeant, reference tracer, T-1824-labeled albumin, into the nutrient artery and recording of the effluent venous dilution curves (femoral vein). The mean (+/- SD) maximal instantaneous extraction was 0.53 +/- 0.08 (N = 12). Net retention after 10 min, estimated from venous curves, was 0.41 +/- 0.06 (N = 12), which appeared not substantially different from the retention estimated by direct isotope counting of the tibias for 85Sr, 0.35 +/- 0.06 (N = 12). In a second set of experiments in intact animals, tibial 85Sr extraction after intravenous injection was apparently higher, 0.53 +/- 0.28 (N = 15). Values of tibial diaphyseal blood flow, estimated from washout curves for iodoantipyrine after tibial nutrient artery injection, were 1.47 +/- 0.63 ml/min per 100 g (N = 27). The extraction was not much diminished by higher flows. The estimates of permeability-surface area product (PS) for bone capillaries did increase with flow, suggesting recruitment of more capillaries at higher flows. PS values averaged 0.63 +/- 0.29 (N = 12); we conclude that the capillary membrane is a primary barrier to the passage of 85Sr and presumably other small hydrophilic solutes.
Man's physiologic response to long-term work during thermal and pollutant stress
Authors: Gliner J. A. , Raven P. B. , Horvath S. M. , Drinkwater B. L. , Sutton J. C.
Published: December 2017

Metabolic, temperature, and cardiorespiratory responses of 19 healthy males, age range 18–30 yr for one group and 40–55 yr for another, were studied during 210 minutes submaximal work at 35% Vo2 max. The subjects were exposed to four different pollutant gas mixtures at two different temperatures, 25 degrees C and 35 degrees C (relative humidity 30%). The four gas mixtures were filtered air (FA), 50 ppm carbon monoxide in filtered air (CO), 0.24 ppm peroxyacetyl nitrate in filtered air (PAN), and a combination of all three mixtures (PANCO). In the CO exposure, the heart rate was significantly greater than that observed during FA conditions (P less than 0.05). Metabolic and thermoregulatory responses to long-term work were not different in the various pollutant environments. Significant decreases in stroke volume and increases in heart rate were observed during the course of the 25 degrees C exposures with no alteration in cardiac output. Heart rates were higher during 35 degrees C exposures while cardiac output remained at the same level with a consequent further reduction in stroke output.
Predicting the carboxyhemoglobin levels resulting from carbon monoxide exposures
Authors: Peterson J. E. , Stewart R. D.
Published: December 2017

Data from a series of human exposures to carbon monoxide (CO) were analyzed to determine the fit to the theoretical Coburn-Forster-Kane (CFK) equation which describes CO absorption and excretion. The equation was found to predict carboxyhemoglobin (HbCO) saturations for both men and women at exercise rates ranging from sedentary to 300 kpm/min when they were exposed to steady CO concentrations of 50, 100, and 200 ppm for 0.33–5.25 h. Methods for determining values of each of the variables in the CFK equation were collected and a rational, efficient procedure for solving the equation by trial and error was outlined. The CFK equation was then used to prepare a graph, relating HbCO saturation to exposure duration and concentration, and also to describe the effect of several variables on the rate of CO uptake and equilibrium HbCO levels, important considerations in the determination of permissible public, occupational, and experimental exposure to CO.
D2 18O (deuterium oxide) method for CO2 output in small mammals and economic feasibility in man
Authors: Lifson N. , Little W. S. , Levitt D. G. , Henderson R. M.
Published: December 2017

A test of the validity of the isotopic steady state relationships of the doubly labeled water (H2O) method has been carried out with D2 18O in small mammals (three chipmunks and one mouse). CO2 outputs calculated just from 1) the rate of water intake and 2) the ratios of the isotopic concentrations in the body water to the intake water agreed satisfactorily with observed values. Moreover, reconstructed energy and material balances agreed reasonably with similar balances reconstructed for an immediately succeeding period on the same animals studied by the previously validated decay procedure. We conclude from an error analysis that by expressing the isotopic specific activities as abundances in excess of the body water of a subject on a given regimen, the decay procedure is economically feasible in the human with available accuracy of isotopic analyses and the present cost of H2 18O. The method therefore appears to be a useful tool ready for application to the field of human energy metabolism.
Effect of continuous postive-pressure ventilation (CPPV) on edema formation in dog lung
Authors: Caldini P. , Leith J. D. , Brennan M. J.
Published: December 2017

The effect of CPPV on edema formation in lungs perfused at constant blood flow was studied in whole dogs and in isolated dog lungs. In intact animals, subjected to an increase in left atrial pressure relative to pleural pressure of 40 Torr, pulmonary shunts correlate inversely (r = -0.82) with the level of end-expiratory pressure (PEE). CPPV had no significant effect on total extravasation of liquid even though PEE higher than 20 Torr was effective in preventing liquid from accumulating in the airways. In isolated lobes, perfused at constant blood flow and at a venous pressure of zero, accumulation of liquid occurred when PEE was increased above 8–10 Torr. At comparable levels of pulmonary arterial pressure, an increase in PEE resulted in lesser accumulation of liquid than when pulmonary venous pressure was elevated. Morphometric measurements revealed no significant difference in the distribution of accumulated liquid within the lung parenchyma between lobes made edematous either by raising venous pressuure or by raising PEE. It would appear that CPPV, while beneficial in improving arterial oxygen tension in pulmonary edema, does not prevent extravasation of liquid in lungs perfused at constant blood flow. High levels of PEE appear to damage the lung by favoring accumulation of liquid in the extravascular spaces of the lung.
Effect of chest strapping on regional lung function
Authors: Sybrecht G. W. , Garrett L. , Anthonisen N. R.
Published: December 2017

We studied lung mechanics and regional lung function in five young men during restrictive chest strapping. The effects on lung mechanics were similar to those noted by others in that lung elastic recoil increased as did maximum expiratory flow at low lung volumes. Chest strapping reduced the maximum expiratory flow observed at a given elastic recoil pressure. Breathing helium increased maximum expiratory flow less when subjects were strapped than when they were not. These findings indicated that strapping decreased the caliber of airways upstream from the equal pressure point. Regional lung volumes from apex to base were measured with xenon 133 while subjects were seated. The distribution of regional volumes was measured at RV, and at volumes equal to strapped FRC and strapped TLC; no change due to chest strapping was observed. Similarly, the regional distribution of 133Xe boluses inhaled at RV and strapped TLC was unaffected by chest strapping. Closing capacity decreased with chest strapping. We concluded that airway closure decreased during chest strapping and that airway closure was not the cause of the observed increase in elastic recoil of the lung. The combination of decreased slope of the static pressure-volume curve and unchanged regional volumes suggested that strapping increased the apex-to-base pleural pressure gradient.
Glottal aperture during panting with voluntary limitation of tidal volume
Authors: Jackson A. C. , Gulesian P. J. , Mead J.
Published: December 2017

A disadvantage of the forced oscillatory technique for measuring total respiratory resistance (namely, that it is usually done during quiet breathing or breathing holding--breathing patterns where the glottic aperture may be highly variable) was overcome by making the measurement during panting. The imposed forced oscillations (Hz) were distinguished from the spontaneous quiet breathing and panting frequencies by ensemble averaging. However, when panting was voluntary restricted so as to standardize the quiet breathing and panting flow amplitudes, resistance values frequently increased. The suggestion that partial glottal closure occurred during voluntarily restricted panting was confirmed by simultaneous inspection of the glottis with a fiberoptic bronchoscope. Thus, maximal opening of the glottis is assured only during unrestricted panting.
A device for testing mechanical properties of biological materials--the "Biodyne"
Authors: Pinto J. G. , Price J. M. , Fung Y. C. , Mead E. H.
Published: December 2017

An electromechanical servo-controlled device has been developed. This device can be used to test the mechanical behavior of a wide variety of biological soft tissues. Control and execution of material testing procedures such as stress-strain, vibration, relaxation, creep etc. can be performed by manual operation of the device or by interfacing it with a laboratory type minicomputer. Experiments on excitable tissues such as muscle can also be executed. The design details and system performance are discussed.
Sodium kinetics in aorta of spontaneously hypertensive rats
Authors: Llaurado J. G. , Madden J. A.
Published: December 2017

Transport rate constants (kij) for Na exchanges in isolated aorta of normotensive and spontaneously hypertensive rats (SHR) were determined with the use of 33Na as a tracer and the aid of digital computer simulation. A three-compartment model consisting of 1) extracellular, 2) intracellular, and 3) “endointracellular” spaces (compartments) was found to describe adequately the kinetics of 22Na. Results show that in SHR: I) K01, which is related to the overall Na outflow from tissue, was increased by 41%; ii) k12, describing Na movements from intra- to extracellular compartment, was increased by 67%; iii) k21, representative of Na movements from extra-to intracellular compartment, was decreased by 39%. These results indicate a faster turn-over of Na and a relative accumulation or translocation of Na into the extracellular space in aorta of SHR. The findings are interpreted in the light of recent reports on the role of Na in contractile response or reactivity of arteries. A humoral mechanism operative at the arterial wall level for the development of hypertension is at the arterial wall level for the development of hypertension is suggested. The main significance of the methodology employed in this work is that the values found for the kij are not subject to fluctuations intrinsic to auxiliary indicators of extracellular space.
Ontogeny of tracheal fluid, pulmonary surfactant, and plasma corticoids in the fetal lamb
Authors: Mescher E. J. , Platzker A. C. , Ballard P. L. , Kitterman J. A. , Clements J. A. , Tooley W. H.
Published: December 2017

We examined fetal plasma corticoids and flow rate, electrolyte composition, and surfactant content of tracheal fluid in chronic experiments with eight fetal lambs. From 120 to 148 days of gestation the rate of fluid production was 4.5 ml/kg per h, and there was no change in mean fluid sodium (147.8 meq/1), chloride (153.1 meq/1), calcium (2.2 mg/100 ml), and pH (6.23). Tracheal fluid potassium increased from 4.3 meq/1 at 120–130 days to 8.9 meq/1 at term, while plasma sodium, chloride, calcium, pH, and potassium were constant at 146.1 meq/1, 110.0 meq/1, 12.1 mg/100 ml, 7.39, and 4.0 meq/1, respectively. Plasma corticoids were less than 1.5 mug/100 ml total (0.3 mug/100 ml free) until 130 days, when they increased rapidly to 10.5 total (3.2 free) at 148 days. Surfactant was first detected in tracheal fluid between 124 and 133 days and its secretion increased rapidly after 135 days to a value of 125 mug/kg per h at 148 days. A sudden increase in fetal plasma corticoids does not seem to be the stimulus for appearance of surfactant in the lamb, although these hormones may induce the rapid accumulation of surfactant prior to delivery.
Continuous positive-pressure ventilation and choledochoduodenal flow resistance
Authors: Johnson E. E. , Hedley-Whyte J.
Published: December 2017

Resistance to flow through the choledochoduodenal junction was measured during constant perfusion (0.8 ml saline/min). In eight dogs, intermittent positive-pressure ventilation (IPPV) and continuous positive-pressure ventilation (CPPV) were compared. Pressure in the common bile duct was always higher during JPPV than IPPV. With the first application of CPPV the rate of intravenous fluid was adjusted to maintain constant Hct. Mean hepatic venous pressure (Phv) increased from 6.6 to 11.5 cmH2O (P less than 0.001). Mean pressure in the common bile duct increased (P less than 0.001) from 11.6 to 14.1 cmH2O. The average increase in resistance was 21%. Changes reversed with return to IPPV. During the second application of CPPV, intravenous fluid was increased to maintain constant arterial pressure. Phv increased to 12.8 cmH2O and pressure in the common bile duct increased to 15.0 cmH2O (30% increase). In four additional dogs, choledochoduodenal resistance during continuous CPPV was reduced by intravenous vasopressin, intravenous norepinephrine and intraducta phenylephrine. CPPV increases resistance to flow through the choledochoduodenal junction, probably by vascular engorgement.
Hydrogen ion concentration and oxygen uptake in an isolated canine hindlimb
Authors: Harken A. H.
Published: December 2017

Oxygen utilization (VO2) and lactate production by an isolated perfused canine hindlimb was evaluated at various hydrogen ion concentrations. A membrane lung perfusion system was established such that blood flow and temperature could be fixed at normal levels. Oxygen, nitrogen, and carbon dioxide (CO2) gas flows to the membrane lung were independently regulated to provide a fixed arterial oxygen content (CaO2). By changing CO2 flow, the pH of the arterial blood was varied between 6.9 and 7.6 at 10-min intervals. The mean O2 delivery (CaO2 X blood flow) was between 16.3 ML O2/min and 20.5 ml O2/min. Standard error of the mean in each dog, however, was less than 0.4 ml O2/min. VO2 was linearly related to the pH of the perfusing blood: VO2% = 100.1 pH - 643 (r = 0.866). Oxygen consumption was inversely related to PCO2: VO2% = -0.62 PCO2 + 124, but the correlation was less good (r = 0.729). Lactate production was linearly related to the pH of the perfusing blood (above a pH of 7.4): lactate produced = 22.5 pH - 162.5 (r = 0.75). At a pH below 7.4, lactate was not produced. Oxygen consumption of skeletal muscle appears critically dependent on extracellular fluid pH. A change in pH of 0.1 alters VO2 almost exactly 10%. Alkalosis is a potent stimulus to lactic acid production by skeletal muscle.
Central neural stimulation of respiration in unanesthetized decerebrate cats
Authors: Eldridge F. L.
Published: December 2017

A previously reported central neural respiratory control process was restudied in unanesthetized decerebrate cats during spontaneous breathing, and during conditions of constant chemical stimulation where phrenic nerve activity was used to quantitate respiratory output. Respiration was increased by carotid sinus nerve stimulation. The pattern of respiration was examined at the cessation of such stimulation. In spontaneously breathing animals, active hyperventilation (HV) was followed by hyperpnea for up to 30 s and never by apnea. Passive HV was always followed by apnea. In animals with controlled chemical conditions, the transient at the end of stimulation consisted of two components, the first an immediate decrease in respiratory output and the second a slow decrease with a period of over 5 m. It is suggested that a facilitatory feedback process, probably located in the reticular activating system, maintains respiratory output for some time after cessation of a stimulus. This study duplicates the results of previous studies and shows that no area of the brain above the pons is required for the mechanism's operation.
Measurement of cardiac output by electrical impedance at rest and during exercise
Authors: Denniston J. C. , Maher J. T. , Reeves J. T. , Cruz J. C. , Cymerman A. , Grover R. F.
Published: December 2017

A comparison was made between cardiac output values determined by the dye dilution and electrical impedance methods in ten subjects at rest and during graded exercise on a bicycle ergometer. The cardiac output values determined by the two methods were linearly related and significantly (P less than 0.001) correlated (r = 0.90). Movement artifact associated with exercise at maximum or near-maximum work loads caused severe distortion of the dZ/dt wave form and prevented calculation of impedance cardiac output at these levels of work. Use of the lowest value of L (distance between mean value of L in the impedance stroke volume equation (SV = p(L2/ZO2) (dZ/dt)mt), resulted in nearly identical values for the least-squares line and equalvalue line of impedance and dye cardiac outputs. Although absolute values of cardiac output determined by the two methods were not identical in all subjects the changes in cardiac output were nearly identical during the different levels of exercise. The data support the validity of the impedance method as a noninvasive, atraumatic measure of cardiac output at rest and during graded exercise.
Synchronization of respiratory frequency by somatic afferent stimulation
Authors: Iscoe S. , Polosa C.
Published: December 2017

In cats anesthetized with chloralose-urethan, vagotomized, paralyzed, and artifically ventilated, superficial radial (cutaneous) and hamstring (muscle) nerve afferents were stimulated while phrenic nerve electrical activity was recorded. The results obtained with both types of nerves were similar. Stimulation in mid and late expiration advanced the onset of the next inspiration, shortening its duration. Stimulation in early inspiration advanced, while that in late inspiration delayed, the onset of the next expiration. These effects were often accompanied by changes in phrenic motoneuron firing patterns (earlier recruitment, increased discharge frequency, increased slope of integrated phrenic neurogram). Repetitive somatic afferent stimulation produced sustained increases in respiratory frequency in all cats and in half of them entrainment of respiratory frequency to the frequency of stimulation occurred at ratios such as 4:3, 4:5, 1:2, 1:3, 1:4, and 1:7. The lowest stimulus intensity required for evoking these phase shifts was between 5 and 10T (threshold of most excitable fibers) for muscle afferents and between 1 and 2T for cutaneous afferents. These results demonstrate the existence of a reflex mechanism capable of locking respiratory frequency to that of a periodic somatic afferent input. They also provide an experimental basis for the hypothesis that reflexes are resposible for the observed locking between step or pedal frequency and respiratory rate during exercise in man.
Respiratory volume-time relationships during resistive loading in the cat
Authors: Zechman F. W. , Frazier D. T. , Lally D. A.
Published: December 2017

The first-breath (neural) effects of graded resistive loads added separately during inspiration and expiration was studied in seven anesthetized cats before and after bilateral vagotomy. Additions of airflow resistance during inspiration reduced the volume inspired (VI) and increased inspiratory duration (TI). The duration of the ensuing unloaded expiration (TE) was unchanged. Vagotomy eliminated the TI modulation with inspiratory loads. Tracheal occlusion at the onset of inspiration yielded TI values similar to the fixed values observed following vagotomy. Resistive loads added during expiration produced similar results. Expired volume (VE) decreased and (TE) increased approaching the values obtained after vagotomy. Unlike the inspiratory resistive loads, loading during expiration results in an upward shift in the functional residual capacity (FRC). The FRC shift produces a time lag between the onset of diaphragmatic (EMG) activity and the initiation of airflow of the next (unloaded) inspiration. These studies suggest separate volume-time relationships for the inspiratory and expiratory phases of the breathing cycle. Both relationships are dependent upon vagally mediated volume feedback.
Effects of hypoxia, heat, and humidity on physical performance
Authors: Lahiri S. , Weitz C. A. , Milledge J. S. , Fishman M. C.
Published: December 2017

The effects of hot, humid environment were compared with the effects of high altitude on the physical performance capacity of Ne-palese residents by measuring oxygen uptakes and heart rates at various work rates. The following groups of men were selected: 66 residents of a hot and humid environment in the Terai at sea level; 24 residents and 16 sojourners at 3,8000 m. The maximal oxygen uptake of the sea-level residents was, on the average, 2.55 1.min-1, at which a maximal heart rate of about 200 beats/min was reached. The sojourners at 3,800 m showed a higher maximal oxygen uptake (2.94 1. min-1) at their maximal heart rate of about 175 beats/min. The residents of 3,800 m achieved a similiar oxygen uptake as the sojourners, but did not show a similar maximal heart rate limitation, suggesting that they were capable of achieving a higher maximal oxygen uptake. This study shows that hot, humid environment at sea level is as much incapacitating as is hypoxia at high altitude.
Growth and physical training with reference to heredity
Authors: Weber G. , Kartodihardjo W. , Klissouras V.
Published: December 2017

Identical male twins (four sets aged 10 yr, four sets aged 13 yr, and four sets aged 16 yr) were divided so that one twin underwent strenuos endurance training for 10 wk, while his brother served as a control without training. Intrapair comparisons of the training-period changes in aerobic, anaerobic, and cardiorespiratory responses to maximum work on a bicycle ergometer disclosed that 1) 10-yr-old trained twins improved more than untrained twins did in VO2max,2) 16-yr-old trained twins increased their VO2max, O2 pulse, blood lactate, ventilation, and respiratory rate and decreased their maximal heart rates more than their untrained counterparts did, and 3) the trained and the untrained 13-yr-old twins changed commensurately. Further, interage comparisons of the intrapair differences showed that both the 10- and 16-yr olds improved their VO2max more than did the 13-yr olds. In view of this evidence, the old hypothesis that more may be gained by introducing extra exercise at the time when the rate of growth is greatest is not tenable.
Construction of picoliter-nanoliter self-filling volumetric pipettes
Authors: Quinton P. M.
Published: December 2017

A technique is described whereby-volume, self-filling micropipettes can be constructed with minimal time and effort. The delivery volumes of such pipettes may range from several picoliters to more than 100 nl. The delivery of a given pipette of even the smallest volume is precise, generally yielding standard deviations much less than 1% of the mean volume as measured by liquid-scintillation counting of isotope dilutions. The technique offers considerable advantage to previously described techniques for constructing small constant-volume pipettes.
On-line cardiac output by digital computer
Authors: Huber F. , Sodal I. E. , Weil J. V.
Published: December 2017

Many devices for fast cardiac output calculations employ special assumptions and departures from the Stewart-Hamilton method. These assumptions and departures can cause substantial errors. This publication describes an on-line computer system for evaluating dye-dilution curves according to the classical Stewart-Hamilton method. Dilution curves are smoothed, using a digital filter to eliminate heartbeat noise. Recirculation is removed using the constant ratio property of exponentials. The quality of the curves is evaluated by determining the length of the base line, the extent and the fit to an exponential downslope, and a figure of merit based on the five tanks-in-series model. Dilution curves, the logarithmic form, and the exponential ratios are displayed on a CRT for visual checks. Comparison of cardiac outputs obtained by this on-line system with results obtained by hand calculations showed a mean difference of 150 ml. Repeated evaluation of one electronically simulated dye curve resulted in SD = 10 ml for computer results and SD = 200 ml for hand calculations.
Human lung mechanics during water immersion
Authors: Prefaut C. , Lupi-h E. , Anthonisen N. R.
Published: December 2017

We measured lung volumes, static deflation pressure-volume curves of the lung, maximum expiratory flow-volume curves, and closing capacities in five men standing immersed to the neck in water. FRC was decreased 27%, while other lung volumes did not change significantly. At high lung volumes immersion tended to increase lung elastic recoil while recoil was decreased at low lung volumes, changes compatible with vascular congestion. Maximum expiratory flow was increased at high lung volumes, probably because of hydrostatic pressure. At low lung volumes maximum expiratory flow was decreased. This was probably due to decreased recoil since the relationship between elastic recoil and maximum flow was unchanged. Closing capacities by the N2 technique were unchanged but the slope of the alveolar plateau and the amplitude of cardiogenic oscillations were decreased in some individuals. Static and dynamic lung properties were unchanged by 5 min of immersion with tidal volume restricted to 0.5 liter. Though immersion produced volume restriction comparable with that reported with chest strapping, it did not produce similar changes in lung mechanics.
Reflex and mechanical circulatory effects of graded Valsalva maneuvers in normal man
Authors: Korner P. I. , Tonkin A. M. , Uther J. B.
Published: December 2017

In 17 normal subjects we studied the changes evoked by five levels of expiratory pressure (EP) ranging from 2.5 to 30 mmHg in a number of circulatory variables during the last 10 s of a 30-s Valsalva maneuver. Variables studied included mean arterial (MAP) and pulse (PP) pressures; right atrial (RAP) and peripheral vein (PVP) pressures; cardiac output (CO); total peripheral resistance (TPR) and heart rate (HR). EP-circulatory response curves were obtained in each subject a) before autonomic block; b) after cardiac effector block (atropine + propranolol); c) after “total” autonomic block (atropine + propranolol; guanethidine + phentolamine). Mechanical effects were determined from results during “total” autonomic block. They included EP-related rises in RAP and PVP each to about 0.7 mmHg/mmHg applied EP, and falls in CO, MAP, and PP to levels of approximately 50%, 70%, and 80% of resting respectively at EP 30 mmHg, but no changes in TPR and HR. Reflex effects included EP-related rises in HR and in TPR and in MAP, to levels of 160%, 160%, and 115% of resting respectively at EP 30 mmHg. The afferent input profile is probably complex, and the role of the different receptor groups may vary at the different levels of EP.
An intact globe technique for electrophysiological studies on cornea
Authors: Graves C. N. , Sanders S. S. , Shoemaker R. L. , Rehm W. S.
Published: December 2017

An intact globe method was developed to determine the characteristics of the cornea of the bullfrog, Rana catesbeiana. With this method the anterior chamber could be perfused and the transcorneal potential difference (PD) and electrical resistance determined. It was found for the endothelium plus stroma (epithelium scraped) that the PD was essentially zero and the electrical resistance was only a small fraction of that of the intact cornea. Elevation of K+ or decrease in Cl- concentration in the anterior chamber produced in intact corneas a large and rapid change in PD while with the epithelium scraped (stroma and endothelium intact) these elevations produced a negligible change in PD. It is concluded that ions can rapidly move across the endothelium and stroma of the cornea.
Total and regional cerebral blood flow measurement with 7-10-, 15-, 25-, and 50-mum microspheres
Authors: Marcus M. L. , Heistad D. D. , Ehrhardt J. C. , Abboud F. M.
Published: December 2017

Cerebral arteriovenous shunting of 7–10-, 15-, 25-, and 50-mum labeled microspheres was studied in 12 anesthetized dogs. Approximately 8% of the 7–10-mum spheres were shunted to cerebral venous blood, whereas less than 2% of the 15-, 25-, and 50-mum spheres were shunted. Cerebral vascular dilatation induced by hypoxia or hypercapnia did not alter the shunting. The calculated total cerebral flow was 10–15% lower with 7–10-mum microspheres as compared with simultaneous flows measured with the larger microspheres which also suggests that 7–10-mu spheres were shunted through the brain. The calculated distribution of cerebral flow was similar with 7–10- and 15-mum spheres but markedly altered when 50-mum spheres were used. Repeated injections of 15-mum spheres were used. Repeated injections of 15-mum microspheres given under stable conditions yielded total cerebral blood flows which averaged +/- 6% of their respective mean and the regional distribution of flow was highly reproducible. These data suggest that, in dogs, 15-mum spheres are an appropriate size to use to measure cerebral blood flows, since shunting is minimal, the distribution is not artifactually distorted, and the measurements are reproducible.
Oral administration of radioactive sulfate to measure extracellular fluid space in man
Authors: Bauer J. H.
Published: December 2017

Radioactive sulfate-35 (35S) was administered to eight human subjects intravenously and orally, to compare respective kinetics of distribution. Intravenously administered 35S attained equilibration within 60–90 min. Orally administered 35S attained equilibration within 60–105 min and thereafter achieved plasma activity equivalent to the intravenously administered tracer. Eighty percent or greater of the 35S dose was recovered in the 24-h urine, following either intravenous or oral administration. The mean extracellular fluid space demonstrated less than 9% mean difference between routes of administration. It is concluded that 35S is completely absorbed at tracer doses, and may be administered orally as a reliable substitute for intravenously administered 35S for measuring extracellular fluid space.
Limiting factors to oxygen transport on Mount Everest
Authors: Cerretelli P.
Published: December 2017

The effect of a sudden increase of the inspired oxygen tension on the maximal aerobic performance was studied on 23 subjects acclimated to high altitude (5,350–8,848 m above sea level) in the course of a 4-mo expedition to Mt. Everest. Inhalation of 100% O2 at 390 mmHg or a rapid descent (20 min) by helicopter to 2,850 m (Pio2 = 117 mmHg) raised maximal oxygen consumption (Vo2 max) from an average 0.7 of the control sea-level value, respectively, to 0.92 and 0.97. The failure of acclimated subjects to increase markedly or even to resume the preexisting sea-level Vo2mxa while breathing O2 in the presence of a 40% increase of blood Hb concentration and of a limited reduction of maximal cardiac output (Qmax), is attributed to changes in the peripheral circulation. These may consist of a) a hindrance of O2 diffusion due to erythrocytes packing secondary to increased hematocrit (Hct up to 70%); b) a bypass of arterial blood from the high-resistance working areas of the body aimed at reducing the load on the heart caused by increased blood viscosity. A 11.6% increase above normal controls of Hb concentration still found in 13 subjects 25 days after leaving altitude does not increase significantly maximum O2 consumption.
Effect of neck versus chest cooling on responses to work in heat
Authors: Shvartz E.
Published: December 2017

Six young men performed bench-stepping at a load of 40 W, once at room temperature of 23 degrees C and 3 times in heat (39.5 degrees C db, 30.3 degrees C wb). Two of the heat exposures included cooling of either the neck or chest by circulating cool water having an inlet temperature of 8.3 degrees C. The heat exchanges for the neck and chest were of equal size and they consisted of PVC tubes, having a total length of 3m each, which covered 2.2% of the body surface area. Heat exchange between the tubing assemblies and the environment was prevented by proper insulation. As compared with no cooling in heat, each method of cooling resulted in no change in heart rate, a decrease of 0.5 degrees C in rectal temperature, small and insignificant decreases in skin temperature and 16–22% decreases in sweat rates. Heat removed from the neck and chest equalled 63.1 and61.9 W-m-2, respectively. This large heat removal and the substantial decreases in rectal temperature and sweat rate as a result of cooling 2.2% of the body surface area were explained in terms of the powerful effect of conductive cooling and the particular regions which were cooled.
Frequency response analysis of the diaphragm in vivo
Authors: Evanich M. J. , Lourenco R. V.
Published: December 2017

Frequency response analysis was used to determine the dynamic response characteristics of cat diaphragm under isovolumetric conditions at functional residual capacity (FRC) and at lung volumes above and below FRC. In apneic cats, sinusoidally modulated pulse rate patterns were applied to both phrenic nerves. Modulation frequencies over the range of 0.05–4 Hz were used. Amplitude ratio vs. frequency plots obtained at FRC for intratracheal, intraesophageal, and intragastric pressures were essentially flat at low frequencies but decreased at higher frequencies. Intratracheal and intraesophageal pressure responses were altered by changes in resting lung volume while intragastric pressure was not. The amplitude ratio was decreased at lung volumes above FRC but increased at volumes below FRC. Thus, lung volume significantly affected the input-output relations between phrenic nerve input and diaphragm muscle output. In all preparations studied, significant phase lags were present throughout the entire modulation frequency range. However, in contrast to the effect of lung volume on amplitude ratio, phase lag was not dependent on changes in lung volume.