bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential inhibitory effect of isoproterenol on contractions of canine airways
Authors: Russell J. A.
Published: December 2017

We examined the inhibitory effect of isoproterenol on contractions of isolated canine airways induced by histamine, 5-hydroxytryptamine (5-HT), and acetylcholine. Airway contractions were matched by using agonist concentrations that produced approximately 60% of the contractile force generated during a previous exposure to 10(-4) M acetylcholine. Concentrations of isoproterenol causing 50% relaxations of histamine-, 5-HT-, and acetylcholine-induced contractions were 9.9 X 10(-9), 3.6 X 10(-8), and 9.0 X 10(-8) M, respectively. Total relaxation of histamine- and 5-HT-induced contractions occurred at 10(-7) and 10(-6) M isoproterenol, respectively, whereas isoproterenol concentrations greater than or equal to 10(-4) M never totally relaxed airways contracted by acetylcholine. We conclude that isoproterenol inhibits airway contractions induced by histamine and 5-HT much more effectively than those induced by acetylcholine.
Effect of resistive loading on inspiratory work output in anesthetized cats
Authors: Zocchi L. , Luijendijk S. C. , Zin W. A. , Rossi A. , Milic-Emili J.
Published: December 2017

In five spontaneously breathing anesthetized cats, we determined the inspiratory elastic (Wel), resistive (Wres), and total (WI) mechanical work rates (power) during control and first loaded inspirations through graded linear resistances (delta R) by “Campbell diagrams” based on measurement of esophageal pressure. WI did not change with delta R's up to 0.31 cmH2O X ml-1 X s, the concomitant decrease in Wel being balanced by an increase in Wres. The stability of WI in the face of delta R's was due to the vagally mediated prolongation of inspiration and the intrinsic properties of the respiratory system and of the contracting inspiratory muscles. To assess the separate contributions of volume-related and flow-related intrinsic mechanisms to the stability of WI, we made model predictions of the immediate effects of delta R's on inspiratory mechanical work output based on measurements of inspiratory driving pressure waves and passive and active respiratory resistance and elastance on the same five cats. The results suggest that the intrinsic stability of WI in the face of delta R's is provided primarily by the active elastance.
Numerical values of the classical Haldane coefficient
Authors: Gronlund J. , Garby L.
Published: December 2017

Values of the classical Haldane coefficient, i.e, the change in the concentration of total CO2 in whole blood per unit of change in the concentration of total O2 at constant PCO2, have been calculated at different combinations of plasma pH (range 7.25–7.50), erythrocyte 2,3-diphosphoglycerate (DPG) concentration (range 3.5–6.5 mM), PCO2 (range 25.0–65.0 Torr), initial hemoglobin O2 saturation (range 0.50–0.80), and erythrocyte volume fraction (range 0.25–0.55). The principle of the calculations is to utilize the so-called reciprocity relations to determine the amount of protons and CO2 released from hemoglobin on oxygenation and to estimate the resulting change in the concentration of total CO2 from published data on the interaction coefficient for the binding of O2 and protons to hemoglobin, the interaction coefficient for the binding of O2 and CO2 to hemoglobin, the distribution of protons across the erythrocyte membrane, the equilibrium constants for the reactions between CO2 and H2O, and CO2 and oxyhemoglobin, the buffer capacity of oxygenated erythrolysate, and the buffer capacity of plasma. The results show that the concentrations of the allosteric ligands, DPG, protons, and CO2 have a significant influence on the numerical value of the Haldane coefficient. Furthermore, the coefficient depends on the hemoglobin O2 saturation and the erythrocyte volume fraction. The dependency of the Haldane coefficient on the O2 saturation and the PCO2 causes an increase in the O2-linked CO2 flux across the alveolar membrane by more than 30% in patients with respiratory insufficiency.
Limitations of Zilversmit approach to analysis of precursor-product relationships
Authors: Jones M. E. , Nicholas T. E.
Published: December 2017

Recently, a modification of the Zilversmit method has been used to establish the extent to which a precursor-product relationship exists between the phospholipids of the lamellar bodies (PLlb) and those in the alveolar compartment (PLalv) of the rabbit lung. According to this analysis, if a plot of specific activity (sp act) of PLalv vs. the integral with respect to time of (sp act PLlb-sp act PLalv) results in a straight line, then a presumptive precursor-product relationship exists; the slope of this line will indicate the turnover time of the product compartment. We have established analytically and confirmed numerically that collinearity is, in fact, a poor test of precursor-product relationship. We examine some causes of hysteresis and the direction of hysteresis of this plot for compartmental configurations other than precursor product. Finally, we apply the conclusions of our analysis to some of the published data relating to the relationship between PLlb and PLalv, and we indicate where previous conclusions may now be considered premature.
Single-unit pH-sensitive double-barreled microelectrodes for extracellular use
Authors: Javaheri S. , De Hemptinne A. , Leusen I.
Published: December 2017

The purpose of this study is to systematically describe the construction of pH-sensitive double-barreled microelectrodes for extracellular use. The most important advantages of these microelectrodes are as follows: the reference and the pH barrels are next to each other, and therefore the measured pH is not affected by asymmetric or slowly spreading direct current potential. The diameter of the tip of the microelectrodes is between 7 and 35 micron. These pH-sensitive microelectrodes are generally stable and Nernstian. They can be used repeatedly both in vivo and in vitro to measure tissue extracellular fluid pH. Some applications are described.
Measurement of fetal heat production using differential calorimetry
Authors: Power G. G. , Schroder H. , Gilbert R. D.
Published: December 2017

These experiments were undertaken to measure heat production of fetal lambs in utero by using differential calorimetry. We used the principle that fetal heat production, H(fetus), can be calculated from measurements of base-line temperature difference between mother and fetus, delta T(fetus), heat introduced from an external source, H(heater), and the increase in body temperature, delta T(heater), that results, i.e., H(fetus) = H(heater) X delta T(fetus)/delta T(heater). We placed microheaters (1.8 mm diam) in the inferior vena cavae of eight near-term lambs and placed thermistors and catheters into maternal and fetal vessels and amniotic fluid. Five days later, fetal arterial temperature averaged 0.54 +/- 0.02 degrees C (SE) higher than maternal arterial temperature. When the heater was turned on to dissipate 29–103 cal/min, fetal temperature increased to approach 0.1–0.5 degrees C higher than control; the final temperature was estimated using the rate of increase during the first 20 min. Fetal heat production averaged 47.1 +/- 4.1 cal X min-1 X kg-1 during the warming phase in these lambs, which weighed 3.26 +/- 0.36 kg. This value would be 3–4% less if corrected for the increase in metabolic rate caused by heating, assuming a Q10 of 2.5. Fetal heating did not alter fetal heart rate, blood pressure, or blood gas values significantly, nor was hemolysis visible in plasma samples. When heat production was calculated from the decrease in fetal temperature after the heater was turned off, an average value of 41.2 +/- 2.5 cal X min-1 X kg-1 was found. Because this value is comparable to the heating phase, fetal metabolic rate and the insulating properties of the fetal shell are not likely to have been changed by the heating.
Endurance training in older men and women II. Blood lactate response to submaximal exercise
Authors: Seals D. R. , Hurley B. F. , Schultz J. , Hagberg J. M.
Published: December 2017

Seven men and four women (age 63 +/- 2 yr, mean +/- SD, range 61–67 yr) participated in a 12-mo endurance training program to determine the effects of low-intensity (LI) and high-intensity (HI) training on the blood lactate response to submaximal exercise in older individuals. Maximal oxygen uptake (VO2max), blood lactate, O2 uptake (VO2), heart rate (HR), ventilation (VE), and respiratory exchange ratio (R) during three submaximal exercise bouts (65–90% VO2max) were determined before training, after 6 mo of LI training, and after an additional 6 mo of HI training. VO2max (ml X kg-1 X min-1) was increased 12% after LI training (P less than 0.05), while HI training induced a further increase of 18% (P less than 0.01). Lactate, HR, VE, and R were significantly lower (P less than 0.05) at the same absolute work rates after LI training, while HI training induced further but smaller reductions in these parameters (P greater than 0.05). In general, at the same relative work rates (ie., % of VO2max) after training, lactate was lower or unchanged, HR and R were unchanged, and VO2 and VE were higher. These findings indicate that LI training in older individuals results in adaptations in the response to submaximal exercise that are similar to those observed in younger populations and that additional higher intensity training results in further but less-marked changes.
Mean airway pressure and alveolar pressure during high-frequency ventilation
Authors: Simon B. A. , Weinmann G. G. , Mitzner W.
Published: December 2017

Studies and applications of high-frequency ventilation (HFV) are often performed under conditions of controlled mean airway pressure (Paw). In the present study we tested the assumption that controlling Paw adequately controls lung volume during HFV by investigating the relationship between a reliably measured Paw and the mean alveolar pressure (Palv) of the lungs during HFV of healthy dogs. We minimized the errors of Paw measurement due to the Bernoulli effect and various technical factors by appropriate choice of transducers, amplifiers, and measurement site. Palv was estimated by clamping the ventilator tube during oscillation and measuring the equilibration pressure of the lung and airways. Paw and Palv were determined as functions of frequency (8–25 Hz), tidal volume (60–90 ml), Paw (-5 to 12 cmH2O), and position of the animal (supine vs. lateral). We found that Paw could significantly underestimate Palv and that the degree of underestimation increased at higher frequencies, larger tidal volumes, and lower Paw. Shifting the animal from the supine to the lateral position greatly accentuated this effect. The elevation of Palv above Paw was seen to be a function of mean flow and largely independent of the frequency-tidal volume combination which produced the flow. A possible explanation of this pressure difference is that it results from differences in inspiratory and expiratory airway impedances, which in turn depend on airway geometry, compliance, lung volume, and expiratory flow limitation.
Inspiratory airway CO2 loading in the pony
Authors: Shirer H. W. , Orr J. A. , Loker J. L.
Published: December 2017

To determine if CO2-sensitive airway receptors are important in the control of breathing, CO2 was preferentially loaded into the respiratory airways in conscious ponies. The technique involved adding small amounts of 100% CO2 to either the latter one-third or latter two-thirds of the inspiratory air in an attempt to raise CO2 concentrations in the airway dead space independent of the arterial blood. Arterial blood gas tensions (PCO2 and PO2) and pH, as well as respiratory output (minute volume, tidal volume, and respiratory rate), were measured in a series of 20 experiments on 5 awake ponies. Elevation of airway CO2 to approximately 12% by addition of CO2 to the latter portion of the inspiratory tidal volume did not alter either ventilation or arterial blood gases. When CO2 was added earlier in the inspiratory phase to fill more of the airway dead space, a small but significant increase in minute volume (2.1 l X min-1 X m-2) and tidal volume (0.1 l X m-2) was accompanied by an increase in arterial PCO2, arterial PO2, and a fall in pH (0.96 Torr, 10.5 Torr, 0.007 units, respectively). A second series of 12 experiments on 6 awake ponies using radiolabeled 14CO2 determined that the increases in breathing were minimal when compared with the large increase that occurred when these animals inhaled 6% 14CO2 (12.7 l X min-1 X m-2). Also, stimulation of systemic arterial or central nervous system chemoreceptors cannot be eliminated from the response since significant amounts of 14CO2 were present in the arterial blood when this marker gas was added to the latter two-thirds of the inspiratory tidal volume. The results, therefore, provide no evidence for CO2-sensitive airway receptors that can increase breathing when stimulated during the latter part of the inspiratory cycle.
Effect of intravenous midazolam on breathing pattern and chest wall mechanics in human
Authors: Morel D. R. , Forster A. , Bachmann M. , Suter P. M.
Published: December 2017

Breathing pattern, thoracoabdominal motion, and separate end-expiratory positions of the rib cage and abdomen were measured noninvasively in eight healthy subjects before and after intravenous administration of either placebo or midazolam, a short-acting benzodiazepine. Compared with placebo, midazolam produced a significant (P less than 0.01) decrease in mean inspiratory flow of 29% from preinjection values, resulting in a 39% reduction in tidal volume (VT). This ventilatory depression was partly compensated by a 35% decrease in expiratory time producing an increase in respiratory rate (+39%). The fall in VT was almost entirely (91%) mediated by a reduction of the abdominal contribution to tidal breathing while sparing rib cage motion. This fact contrasts with the effects of inhalational anesthetics or morphine, which preferentially depress rib cage expansion, indicating that thoracoabdominal motion may selectively be depressed by different pharmacological agents. In addition, continuous recording of end-expiratory levels showed a significant transient fall in the rib cage's end-tidal position 2 min after midazolam administration associated with the occurrence of central apneas.
Dynamic maintenance of end-expiratory lung volume in full-term infants
Authors: Kosch P. C. , Stark A. R.
Published: December 2017

We recorded airflow, tidal volume, respiratory muscle electromyogram (EMG), and chest wall configuration in eight normal newborn infants to investigate the determination of end-expiratory lung volume (EEV). The expiratory flow-volume representation was nearly linear and EMG evidence of respiratory muscle activity was absent during the latter part of expiration in both supine and upright postures, consistent with passive expiration. Occasional breaths were associated with marked retardation of expiratory airflow (braking). During unobstructed apnea, expiration proceeded to the relaxation volume (Vr) with no change in slope of the flow-volume curve. During breathing, EEV was greater than Vr observed during apnea. We calculated the difference between EEV and Vr estimated by extrapolation of the linear portion of the expiratory flow-volume curve as 14.4 +/- 5.4 ml (supine) and 11.8 +/- 2.4 ml (upright). When infants were tilted from supine to upright, expiratory duration (TE) and the expiratory time constant (tau) increased significantly. Since the increases in tau and TE offset each other, the EEV-Vr difference was similar in both postures. We propose that while braking plays a major role in the early part of expiration, as long as the final portion of expiration is passive, the dynamic maintenance of EEV above Vr depends on the relative values of tau and TE. Expiratory braking mechanisms interact with the passive mechanical properties of the respiratory system to modulate the balance between tau and TE. These mechanisms provide a neonatal breathing strategy to maintain EEV above a low Vr until the chest wall stiffens with maturity.
Response of nasal blood flow to neurohormones as measured by laser-Doppler velocimetry
Authors: Druce H. M. , Bonner R. F. , Patow C. , Choo P. , Summers R. J. , Kaliner M. A.
Published: December 2017

A new simple but general estimation method for survival time in a hot environment is presented in this study. Even in heat-tolerant rats showing a triphasic heat response, an accurate estimation of survival time (ST) is possible. Rat groups, which included some heat-tolerant individuals, were exposed to 42.5 degrees C, 40% rh. Colonic temperature (Tco) was measured continuously by copper-constantan thermocouple. The ST (Y) of male and female rats were expressed as a linear function of time (X) until the Tco of 42.5 degrees C was reached: Y = 0.976X + 30.6 and Y = 0.968X + 31.6, respectively. A Tco of 42.5 degrees C at rest was just below the maximum survivable body temperature and above the steady-state equilibrium Tco levels during the second phase of the triphasic heat-response curve. Heat-tolerant individuals showed lower equilibrium temperatures than heat-intolerant rats. All 140 rats survived the Tco of 42.5 degrees C and lived for more than 8 wk, thus enabling them to be used for future experiments on thermoregulation. The heat survivors were able to reproduce, and their genetically controlled offspring could be used for thermoregulatory experiments.
High-speed bubble-segmented blood sampler for the rat
Authors: Graham M. M. , Abbott G. L.
Published: December 2017

An arterial blood sampler for use in the conscious rat is described. With this apparatus it is possible to obtain small (10 microliter) whole-blood or plasma samples as frequently as 1/s and to derive accurate arterial time-concentration curves in the first 60–120 s after compounds are injected for regional blood flow or pharmacokinetic measurements. The blood is withdrawn from an implanted arterial catheter into polyethylene tubing at a constant rate while bubbles are introduced at regular intervals via a side channel into the column of blood. Although some dispersion of blood samples occurs as the tubing is traversed, this can be mathematically corrected. However, correction is unnecessary if the information of interest is the area under the time-concentration curve.
Lack of effect of exercise on platelet activation and platelet reactivity
Authors: Mant M. J. , Kappagoda C. T. , Quinlan J.
Published: December 2017

The effects of brief maximal exertion on platelet activation and reactivity have been studied in normal subjects. Although initial studies in seven subjects showed apparent exercise-induced platelet activation and enhanced platelet reactivity, these findings could not be confirmed in 13 subjects studied subsequently. There was no change in the platelet aggregate ratio, platelet fluorescent granule number or the plasma platelet factor 4 (PF4) or beta-thromboglobulin, although transient and significant increases in the platelet count and plasma heparin neutralizing activity (HNA) occurred. These results were reproducible in subjects studied more than once. It is postulated that in vitro platelet activation, most likely associated with blood collection, explained the initial results. It is concluded from the subsequent studies that in normal subjects brief maximal exercise causes neither platelet activation nor altered platelet reactivity but does cause a transient increase in the platelet count. The increase in HNA with exertion, without any accompanying increase in the PF4, demonstrates that these assays measure different substances and that the increase in HNA following exertion is most unlikely to be derived from platelets.
Effect of lymphatic cannula outflow height on lung microvascular permeability estimations
Authors: Laine G. A. , Drake R. E. , Zavisca F. G. , Gabel J. C.
Published: December 2017

Estimates of the pulmonary microvascular membrane reflection coefficient (sigma) and permeability-surface area product (PS) are frequently made with the assumption that a percent change in transmicrovascular fluid flux (Jv) will be represented by an equal percent change in the lymph flow rate (QL) from a single cannulated lung lymph vessel. To test this, we measured QL in seven anesthetized dogs with the outflow end of the lymph cannula set at several heights (H) above and below the lung hilus. The left atrial pressure was then elevated to increase Jv, and QL was again measured at several H's. The percent increase in QL at elevated left atrial pressure depended on H. We used the QL data and lymph and plasma protein concentrations to estimate sigma and PS with a modified form of the Kedem and Katchalsky equations. The calculated values varied considerably with H. Our results indicate that changes in Jv are not represented by equal changes in QL. Therefore, techniques for estimating permeability that depend upon QL as an estimate of Jv may lead to erroneous estimates of sigma and PS.
Blood lactate disappearance at various intensities of recovery exercise
Authors: Dodd S. , Powers S. K. , Callender T. , Brooks E.
Published: December 2017

Numerous studies have reported that following intense exercise the rate of blood lactate (La) disappearance is greater during continuous aerobic work than during passive recovery. Recent work indicates that a combination of high- and low-intensity work may be optimal in reducing blood La. We tested this hypothesis by measuring the changes in blood La levels following maximal exercise during four different recovery patterns. Immediately following 50 S of maximal work, subjects (n = 7) performed one of the following recovery treatments for 40 min: 1) passive recovery (PR); 2) cycling at 35% maximal O2 uptake (VO2 max) (35% R); 3) cycling at 65% VO2 max (65% R); 4) cycling at 65% for 7 min followed by cycling at 35% for 33 min (CR). The treatment order was counterbalanced with each subject performing all treatments. Serial blood samples were obtained throughout recovery treatments and analyzed for La. The rate of blood La disappearance was significantly greater (P less than 0.05) in both the 35% R and CR when compared with either the 65% R or PR. No significant difference (P greater than 0.05) existed in the rate of blood La disappearance between the 35% R and CR. These data do not support the hypothesis that exercise recovery at a combination of intensities is superior to a recovery involving continuous submaximal exercise in lowering blood La following maximal work.
Related and unrelated changes in response to exercise and cold in rats: a reevaluation
Authors: Harri M. , Dannenberg T. , Oksanen-Rossi R. , Hohtola E. , Sundin U.
Published: December 2017

Groups of rats were subjected to various treatments: continuous exposure to cold (5 degrees C); exercise by running; intermittent cold exposure, -20 degrees C daily for 60 min; and in some experiments combined influence of cold acclimation and exercise for at least 6 wk. The resulting adaptive changes can be grouped in three different categories. Cold-specific changes included increased food intake, an increase in both mass and metabolic activity of brown adipose tissue leading to an increased capacity for nonshivering thermogenesis, and maintenance of the stores of ascorbic acid and muscle glycogen during cold exposure. These changes were associated with an improved resistance to cold with which the rats were able to maintain their body temperature in both cold air and water were typical of rats previously exposed to cold. Training-specific changes typically included increased activities of aerobic muscle enzymes and decreased activity of lactate dehydrogenase and a higher O2 uptake and shivering activity during cold exposure as compared with sedentary control rats. These changes were observed for trained rats only and were not associated with an improved resistance to cold. Other adaptive changes were found, to a variable extent, for all treated rat groups. These included cardiac hypertrophy, reduced urinary catecholamine excretion during and after stress situations, increased tail skin temperature response to isoproterenol, and a higher tail skin temperature during exposure to cold. There were no systematic differences between groups in changes of blood glucose, glycerol, or lactate concentrations during cold exposure.(ABSTRACT TRUNCATED AT 250 WORDS)
VO2 kinetics of constant-load exercise following bed-rest-induced deconditioning
Authors: Convertino V. A. , Goldwater D. J. , Sandler H.
Published: December 2017

The purpose of this study was to determine the effects of bed-rest-induced deconditioning on changes in O2 uptake (VO2) kinetics, O2 deficit, steady-state VO2, and recovery VO2 during the performance of constant-load exercise. Five male subjects (36–40 yr) underwent 7 days of continuous bed rest (BR) in the head-down (-6 degrees) position. Two days before (pre) and the day after (post) BR each subject performed one submaximal exercise test in the supine and one in the upright position consisting of 5 min of rest, 5 min of cycle ergometer exercise at 700 kg.m/min, and 10 min of recovery from exercise. VO2 was measured continuously in all tests from 2-liter aliquot gas samples collected every 30 s. Following BR steady-state VO2 was unchanged in supine and upright exercise. In the supine position BR did not change total exercise VO2, O2 deficit, or total recovery VO2. However, compared with pre-BR, total exercise VO2 decreased (P less than 0.05) from 7.41 +/- 0.11 to 7.23 +/- 0.17 liters, O2 deficit increased (P less than 0.05) from 1.15 +/- 0.05 to 1.41 +/- 0.07 liters, and total recovery VO2 increased (P less than 0.05) from 5.17 +/- 0.11 to 5.47 +/- 0.17 liters during the post-BR upright test. Despite the ability to attain similar steady-state VO2 within 5 min, bed-rest-induced deconditioning resulted in a reduction of total VO2 capacity and an increase in the O2 deficit during submaximal constant-load exercise. This change in VO2 kinetics is found only with exercise in the upright rather than supine position implicating orthostatic mechanisms in the delayed response to submaximal exercise.
A low-cost modular oxygen-consumption device for small animals
Authors: Arundel P. A. , Holloway B. R. , Mellor P. M.
Published: December 2017

This paper describes a simple apparatus enabling the O2 consumption of small animals to be monitored. The system consists of a sensitive solid-state pressure transducer linked via a relay to a small peristaltic pump. While the animal breathes air in its closed chamber the CO2 expired is removed by an absorber; hence the pressure falls. The signal is sensed by the transducer triggering the pump to deliver a set volume of O2 to the chamber. The number of pump operations per unit time necessary to keep the system equilibrated is a measure of the O2 consumption rate. Each device is built as a module, up to four being mounted in one assembly controlled by a microcomputer. A balance control, priming switch, pump-volume setting, and electromagnetic counter are built into each front panel. Calibration is achieved be removing a known volume of air from the system with no animal present and counting the number of operations to return the chamber to equilibrium.
Modification of lymph by sheep caudal mediastinal node: effect of intranodal endotoxin
Authors: Adair T. H. , Montani J. P. , Guyton A. C.
Published: December 2017

Postnodal lymph from the sheep caudal mediastinal node (CMN) is used by many investigators to assess lung vascular protein permeability. We explored the possibility that damage to the CMN blood-lymph barrier could produce increases in postnodal lymph flow and lymph-to-plasma protein concentration ratio (L/P) characteristic of lung vascular damage. Escherichia coli endotoxin (0.049 micrograms/min) was infused into a prenodal lymph vessel to the CMN in the conscious sheep, and postnodal lymph was collected for the next 7 h. Intranodal endotoxin caused an 80% increase in postnodal lymph flow and a 30% increase in postnodal L/P. Because there was no indication that the endotoxin had exerted a systemic effect, the lymph response to endotoxin was attributed to a direct effect of endotoxin on the blood-lymph barrier of the CMN. We conclude that significant increases in postnodal lymph flow and L/P characteristic of lung vascular damage can occur when the blood-lymph barrier of the CMN becomes damaged.
Alveolar gas exchange during exercise: a single-breath analysis
Authors: Allen C. J. , Jones N. L. , Killian K. J.
Published: December 2017

Changes in expired alveolar O2 and CO2 were measured breath-by-breath in six healthy male subjects (mean age 30 yr, mean weight 80 kg) at rest, 600 kpm/min, and 1,200 kpm/min. Changes were expressed in relation to expired volume (liters) and time (s) and separated into an initial dead-space component using the Fowler method applied to expired CO2 and O2, and alveolar slope. The alveolar slopes with respect to time (dPACO2, dPAO2, Torr/s) increased in relation to CO2 output (VCO2, 1/min, STPD) and O2 intake (VO2, 1/min, STPD) but were reduced by increasing tidal volume (VT, liters, BTPS): dPACO2 = 2.7 + 4.6(VCO2) - 1.9(VT) (r = 0.97); and dPAO2 = 2.3 + 5.5(VO2) - 1.9(VT) (r = 0.96). From the alveolar slopes, tidal volume, and airway dead-space volume, mean expired alveolar PO2 and PCO2 (PAO2, PACO2) were calculated. There was no change in arterialized capillary PCO2 (PaCO2) between rest (38.9 +/- 0.66 Torr) and heavy exercise (38.2 +/- 2.18 Torr), but mean PACO2 rose from 36.7 +/- 0.55 to 40.8 +/- 1.67 Torr during heavy exercise. There was no change in arterialized capillary (mean = 84.3 +/- 0.7 Torr) or alveolar (mean = 107.2 +/- 1.03 Torr) PO2. Exercise increases the fluctuations in alveolar gas composition leading to discrepancies between the PCO2 in mean alveolar gas and arterial blood to an extent that is dependent on VCO2 and VT.
Modulation of pulmonary stretch receptors and airway resistance by parasympathetic efferents
Authors: Richardson C. A. , Herbert D. A. , Mitchell R. A.
Published: December 2017

Recording from pulmonary stretch receptors in the intact cervical vagus nerve revealed a novel interaction between stretch receptors and smooth muscle in the lungs of anesthetized paralyzed cats. Firing rates of pulmonary stretch receptors were modulated in step with the inflation-deflation cycle of the mechanical respirator, as expected. Firing rates of most slowly adapting receptors, but not rapidly adapting receptors, were also strongly modulated in step with the phrenic nerve activity even when the respirator was turned off and the cat motionless. The modulation of some receptors' firing rates by the inspiratory motor output was as great as the change in firing-rate in response to a lung inflation of 20 ml of air (one tidal volume). Atropine blocked the inspiratory-related modulation of slowly adapting/receptor firing rates; it did not block the inflation-related modulation. Pulmonary resistance was modulated in step with the inspiratory activity on the phrenic nerve. Hyperventilation to neural apnea (no phrenic nerve activity) reduced pulmonary resistance to its lowest level, a level equal to that produced by an injection of isoproterenol or atropine. Hypoxia during hypocapnic apnea caused bursts of inspiratory activity on the phrenic nerve accompanied by one-to-one increases in airway resistance. We conclude that the intrathoracic airway smooth muscle contracts with each neural inspiration, that the modulation of the pulmonary stretch receptors is due to a mechanical interaction with the intrathoracic airway smooth muscle, and that through the mechanical link with airway smooth muscle, stretch receptor sensitivity depends on inspiratory output, a closed loop.
Total deposition of ultrafine sodium chloride particles in human lungs
Authors: Blanchard J. D. , Willeke K.
Published: December 2017

The total deposition of monodisperse, 0.026-0.19 micron (dry volume equivalent diameter) sodium chloride particles in the lungs of five healthy subjects, who breathed orally, was measured. For a tidal volume of 1,000 ml and flow rate of 500 ml/s, the percentages deposited were: 37.2 +/- 8.4% (mean +/- SD) for 0.026 micron, 23.8 +/- 3.3% for 0.051 micron, 22.8 +/- 3.1% for 0.096 micron, and 31.8 +/- 6.2% for 0.19 micron particles. The deposition minimum corresponded to a particle size of approximately 0.08 micron. Deposition did not correlate with measures of lung volume or body size but did correlate with forced expired flow rate after 75% of forced vital capacity (FVC) exhaled (FEF 75%/FVC) and with percent-predicted values for FEF 25-75% and FEF 75%. Lengthening the breathing period from 4 to 8 s/breath while maintaining flow rate at 500 ml/s caused an additional 11.3 +/- 3.1% of the inhaled particles to deposit. Sedimentation and diffusion were found to be the principal deposition mechanisms. These hygroscopic particles deposited according to sizes they would attain in air with a relative humidity between 96 and 100%.
Characterization by stimulation of medullary mechanisms underlying gasping neurogenesis
Authors: St John W. M. , Bledsoe T. A. , Tenney S. M.
Published: December 2017

Our purpose was to evaluate the hypothesis that neurons in the lateral tegmental field of the medulla comprise a pattern generator for neurogenesis of gasping. Stimulations in this area produced changes characteristic of pattern generators in other systems. These included shifts in gasping rhythm and refractory periods for eliciting gasps; the latter varied inversely with spontaneous gasping frequency. These responses were recorded from activities of phrenic and hypoglossal nerves of decerebrate, cerebellectomized, vagotomized, paralyzed, and ventilated cats. Gasping followed freezing the brain stem between pons and medulla. In addition to lateral tegmental loci, gasps were elicited by stimulating areas extending lateral to the nucleus ambiguus and medial to the contralateral medulla. These areas are envisaged to contain axons to or from the pattern generator of lateral tegmental field. Finally, stimulations in sites approximating nucleus tractus solitarius and nucleus ambiguus delayed spontaneous gasps and terminated ongoing gasps. Current required to terminate gasps fell during neural inspiration. Our data are consistent with the lateral tegmental field of medulla comprising a central pattern generator for gasping and pacemaker elements being a component of this pattern generator.
Reflex effects and receptor responses to upper airway pressure and flow stimuli in developing puppies
Authors: Fisher J. T. , Mathew O. P. , Sant'Ambrogio F. B. , Sant'Ambrogio G.
Published: December 2017

We studied the changes in breathing pattern due to pressure and airflow stimuli applied to isolated upper airway in nine 1- to 14-day-old and six 29- to 35-day-old anesthetized puppies breathing through a tracheostomy. Negative-pressure and flow, both inspiratory and expiratory, altered the breathing pattern only in the 1- to 14-day-old puppies, whereas positive pressure was ineffective in both age groups. Negative pressure caused apnea in 12% of the trials, expiratory flow in 18%, and inspiratory flow in 21%. When apnea did not occur there was a significant prolongation of inspiratory and expiratory time and a decrease of tidal volume of the first breath following the application of negative pressures. Section of the superior laryngeal nerves abolished the responses to pressure and flow. In nine 1- to 14-day-old and four 29- to 35-day-old puppies we recorded the activity of single units of the superior laryngeal nerves. We identified specialized receptors responding to pressure (68.5%), flow (2.7%), and contraction of upper airway muscles (drive, 28.8%). All types of receptors had a prevalent inspiratory-related activity. In the younger age group the discharge rate of pressure receptors at comparable negative pressures was lower than in older puppies. The strong inhibitory influences originating from the upper airway in the early stages of development presumably reflect different integrative properties of the central nervous system.
A theory of diffuse light scattering by lungs
Authors: Butler J. P. , Suzuki S. , Oldmixon E. H. , Hoppin F. G.
Published: December 2017

We present a theoretical treatment of backscattered light from the interior of a lung illuminated by a thin beam of light normally incident on the pleural surface. An approximate formula is developed describing how the backscattered intensity varies with distance from the point of light entry. This is shown to depend markedly on the optical mean free path and on the effective extinction coefficient. We attempt to relate the optical mean free path to the mean alveolar size. This relationship is found to depend primarily on septal reflection and refraction. Reflection is treated quantitatively. Refraction is much more difficult and may have to be approached empirically. We present here the rudiments of a technique with implications for the possibility of dynamic stereology.
Evaluation of phase correction and low gas density to improve thoracic gas volume measurement
Authors: Begin P. , Peslin R. , Hannhart B. , Gallina C.
Published: December 2017

We investigated two methods of decreasing the error on plethysmographic determinations of thoracic gas volume (TGV) related to cheeks movements during panting maneuvers: lowering gas density in the airways with an 80% He-20% O2 mixture and computing TGV from the in-phase component of the plethysmographic signal (TGVr). The methods were tested by measuring how TGV estimates varied when panting frequency was raised from 0.8 to 2.5 Hz during the same occlusion. The measurements were performed in 6 normal subjects and 12 patients with chronic bronchitis with and without cheeks support and when the airway was connected to an external device simulating an increased cheeks compliance. A small negative frequency dependence of TGV (delta TGV/delta f = -1.2 +/- 0.8%/Hz with cheeks support), most probably unrelated to upper airway walls, was found in normal subjects. Delta TGV/delta f was positive and algebraically larger in patients than in normals, reaching 2.2 +/- 3.4%/Hz without cheeks support and 11.8 +/- 8.0%/Hz with the additional cheeks. The latter value was only 20% smaller when computed on the basis of TGVr, demonstrating the limited usefulness of the phase-based correction. In contrast, breathing He-O2 decreased delta TGV/delta f to approximately 50% of its air value (P less than 0.01) and appears as an effective way to diminish the error in obstructive patients.
Differential effects of CO2 and H+ as central stimuli of respiration in the cat
Authors: Shams H.
Published: December 2017

Effects of H+ and CO2 as independent stimuli of central respiratory chemoreceptors were studied in anesthetized cats in which pH and PCO2 on the ventral surface of the medulla (pHe and PeCO2) could be monitored in response to intravenous acid infusion or CO2 inhalation or to a combination of CO2 inhalation and base infusion that allowed PeCO2 to vary at constant pHe. Respiratory responses to these changes were monitored by measuring tidal volume (VT), respiratory frequency (f), and total ventilation. Respiratory acidosis stimulated ventilation by increasing both VT and f. Mild metabolic acidosis (decrease in pHe less than 0.05) exerted similar effects, but more severe metabolic acidosis failed to produce further stimulation. Increasing or decreasing PeCO2 at constant pHe caused pronounced increases or decreases in respiration mediated both by VT and f. For the same change in PeCO2 the respiratory effects were, however, less pronounced when pHe was kept constant than when pHe was allowed to change with PeCO2. The results suggest that both CO2 and H+ exert independent effects on respiration via central chemoreceptors.
Chronic exercise and left ventricular structure and function in healthy human subjects
Authors: Wolfe L. A. , Martin R. P. , Watson D. D. , Lasley R. D. , Bruns D. E.
Published: December 2017

Twelve healthy well-trained participants in a supervised exercise program (mean age, 41.3 yr) were compared with 12 sedentary control subjects (mean age, 38.9 yr) with physical characteristics similar to the exercised group (EG) before training. Resting echocardiograms revealed significantly lower heart rates (HR) in the EG compared with control group (CG) but no evidence for cardiac structural differences between groups. Radionuclide angiograms performed at rest and during two levels of supine cycling (HR targets: 120 and 140 beats X min-1) resulted in increases in background-corrected end-diastolic counts [EDC(bc)] and confirmed use of the Frank-Starling mechanism in the majority of subjects. Mean values (+/- SD) for ejection fraction (EF) and normalized peak systolic ejection rate (PSER) (P greater than 0.05 between groups) were the following. (Formula: see text) The results suggested that fitness training does not induce significant cardiac enlargement as apparent from measurements at rest or important changes in contractile state during exercise. Increases in exercise stroke volume with such training may be the result of an increased end-diastolic volume.
Effects of exercise training on plasma lipids and lipoproteins in rats
Authors: Pels A. E. , White T. P. , Block W. D.
Published: December 2017

We studied the effects of exercise training on plasma lipid and lipoprotein concentrations of rats on a high-fat and high-cholesterol diet. Twelve weeks of training occurred at moderate [Mod-Exer, 70% peak O2 consumption (VO2)] and high (High-Exer, 82% peak VO2) intensities. The duration of daily training sessions was adjusted to maintain equivalent energy expenditure between groups. Following training, body weight and lean body mass were 10% lower in the High-Exer group than the Mod-Exer or control groups. Compared with control values, carcass fat content was 33% lower for both trained groups. The oxidative capacity of skeletal muscle was approximately 30% greater in the trained groups compared with the control group. Total cholesterol, high density lipoprotein cholesterol, and total triglyceride concentrations in plasma were not different between the trained groups, but were 33–47% lower compared with the control group. The exercise-induced changes in plasma lipid and lipoprotein concentrations may be a result of a change in preferred substrate utilization in skeletal muscle toward a greater oxidation of lipid.
Fiber number, area, and composition of mouse soleus muscle following enlargement
Authors: Timson B. F. , Bowlin B. K. , Dudenhoeffer G. A. , George J. B.
Published: December 2017

Muscle fiber number, cross-sectional area, and composition were studied in response to enlargement produced by synergistic ablation in the mouse soleus muscle. The effect of the location of a histological section on the number of fibers that appear in the section was also studied using the mouse soleus muscle. Enlargement was produced in the soleus muscle of 15 male and 15 female mice by ablation of the ipsilateral gastrocnemius muscle. Fiber counts, using the nitric acid digestion method, revealed no difference between control and enlarged muscles in male and female mice. Mean fiber area, determined by planimetry, was 49.1 and 34.5% greater following enlargement in male and female mice, respectively. Increase in muscle weight could be totally accounted for by the increase in fiber area following enlargement. A transformation of type II to type I fibers occurred following enlargement for both sexes. Counts of fibers from histological sections revealed that there was a progressive decrease in the fiber number as the section was moved from the belly to the distal end of the muscle. The results of these studies indicate that muscle enlargement in the mouse soleus muscle is due to hypertrophy of the existing muscle fibers.
Effect of respiratory alkalosis on skeletal muscle metabolism in the dog
Authors: Brice A. G. , Welch H. G.
Published: December 2017

These experiments were conducted to determine whether changes in skeletal muscle metabolism contribute to the previously reported increase in whole-body O2 uptake (VO2) during respiratory alkalosis. The hind-limb and gastrocnemius-plantaris preparations in anesthetized and paralyzed dogs were used. VO2 of the hindlimb and gastrocnemius muscle was calculated from measurements of venous blood flow and arterial and venous O2 concentrations (Van Slyke analysis). Whole-body VO2 was measured by the open-circuit method. Minute ventilation (hence blood gases and pH) was controlled by a mechanical respirator. Whole-body, hind-limb, and gastrocnemius muscle VO2 increased 14, 19, and 20%, respectively, during alkalosis (P less than 0.05). In all experiments, arterial lactate concentration increased significantly (P less than 0.05) during alkalosis. A positive venoarterial lactate difference across muscle during alkalosis indicated that skeletal muscle is a source of the elevated blood lactate. We concluded that VO2 of resting skeletal muscle is increased during states of respiratory alkalosis and that this increase can account for much of the increase in whole-body VO2.
Neonatal endotracheal flowmeter for tidal volume, airway pressure, and end-tidal gas
Authors: Brady J. P. , Deming D. D. , McCann E. M.
Published: December 2017

We have designed a new endotracheal flowmeter to measure tidal volume, phasic and mean airway pressures, inspiratory time, and end-tidal PCO2 and PO2 in intubated infants. The flowmeter is light (11 g) and adds minimal dead space (1.0 ml) and resistance (2 cmH2O X 100 ml- X s) to the infant's airway. The volume signal (less than or equal to 10 ml) is linear to 7 Hz, and end-tidal gases can be measured at respiratory rates of 90 breaths/min. This flowmeter is particularly valuable for evaluation of rapid mechanical ventilation of very low birth weight infants.
Decreased brain levels of ascorbic acid in rats exposed to high pressures
Authors: Obrenovitch T. P. , Gillard J. L.
Published: December 2017

Ascorbic acid was repeatedly monitored in vivo in the striatum of rats subjected to an increasing pressure (100 bar/h compression rate; 0.5 bar partial pressure of O2 He-O2 mixture, up to 120 bar (121 ATA), to which they were exposed for 1 h. Measurements were performed using differential pulse voltammetry and carbon fiber microelectrodes. High-pressure-exposed animals exhibited a dramatic decrease of striatal ascorbic acid. This decrease was detectable at pressures as low as 50 bar and significant over 70 bar (75% of the control level), and the lower level (25% of the control level) was reached shortly after the end of the compression period. This finding is discussed in relation to the physiological role of ascorbic acid in the brain, e.g., its participation in the defense mechanisms against reactive O2 intermediates and lipid peroxidations and its probable involvement in neurotransmission. Emphasis is placed on a possible increased sensitivity of nerve cell membrane phospholipids to peroxidation under stressful hyperbaric situations.