bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of inspiratory muscle tone in maintenance of FRC in the newborn
Authors: Lopes J. , Muller N. L. , Bryan M. H. , Bryan A. C.
Published: December 2017

The importance of inspiratory muscle tone in the maintenance of functional residual capacity (FRC) in newborns was studied in eight premature infants with birth weights of 1,166 +/- 217 g and gestational age 29 +/- 1.9 wk (mean +/- SD). Rib cage and abdominal anteroposterior diameters were monitored with magnetometers, and electromyograms of the diaphragm and intercostal muscles were recorded with surface electrodes. Sleep state was monitored using electrooculogram and behavioral criteria. We assessed the decrease in tonic activity of the inspiratory muscles and the fall in end-expiratory lung volume during apnea compared with the period just preceding apnea. A total of 98 apneas were analyzed. In all instances a decrease in diaphragmatic and intercostal tone was associated with a decrease in the anteroposterior diameter of both rib cage and abdomen, indicating a fall in FRC. These changes were more marked during quiet sleep than during rapid-eye-movement sleep (P less than 0.01). Our results suggest that inspiratory muscle tone is a major determinant of FRC in the newborn.
Microvascular injury distal to unilateral pulmonary artery occlusion
Authors: Johnson R. L. , Cassidy S. S. , Haynes M. , Reynolds R. L. , Schulz W.
Published: December 2017

We explored three questions: 1) does edema fluid accumulate distal to temporary unilateral pulmonary artery occlusion (TUPAO); 2) if so how rapidly does it accumulate; and 3) how is it affected by positive end-expiratory pressure (PEEP)? Using a tracheal divider we measured pulmonary capillary blood flow (Qc), tissue volume (Vt), and diffusing capacity (DLCO) in each lung with a rebreathing method. After control measurements in 12 dogs, the left pulmonary artery was occluded and measurements were repeated at intervals during 4 h of occlusion and 30 min after release of the occlusion. Six of the dogs were ventilated with 10 cmH2O PEEP. Finally the lungs were removed, weighed, and fixed for histology. TUPAO caused a 29% increase in Vt of the left lung without PEEP and a 59% increase with PEEP. After release of the occlusion, Qc and DLCO in the left lung returned to control levels within 30 min in dogs not on PEEP but remained depressed in dogs ventilated with PEEP even though PEEP was removed. At postmortem the left lung weighed more than expected in both groups of dogs but was significantly heavier in those on PEEP. Histology confirmed bronchovascular cuffing with edema and hemorrhage.
Increased hemoglobin-oxygen affinity does not decrease skeletal muscle oxygen consumption
Authors: Ross B. K. , Hlastala M. P.
Published: December 2017

The importance of hemoglobin-oxygen affinity (HOA) in affecting skeletal muscle oxygen consumption (VO2) was reevaluated using an isolated canine gracilis muscle. HOA of the blood [normal O2 half-saturation pressure of hemoglobin (P50) = 30 Torr] was increased by refrigerated storage (P50 = 22 Torr), incubation in sodium metabisulfite (P50 = 24 Torr), or in sodium cyanate (P50 = 14 Torr). Stored blood caused a significant fall in VO2 to 80% of control, with no change in venous O2 partial pressure (PvO2), substantiating previous studies. However, in contrast, blood incubated in sodium metabisulfite or sodium cyanate resulted in no impairment of VO2, with a fall in PvO2 in the latter case indicating that a critical PvO2 did not cause the reduction in VO2 with stored blood. To substantiate further the lack of existence of a critical PO2, fresh and increased HOA blood was perfused at constant flow rates and varying arterial oxygen saturations. Stored blood showed a marked reduction in VO2 as compared with normal blood over a wide range of saturations. However, carbamylated blood VO2 was identical to fresh blood VO2 values. The data suggest that the position of the oxygen dissociation curve may not be as important as originally thought in determining skeletal muscle oxygen delivery. The drop in VO2 caused by perfusion with stored blood is due to some other factor unrelated to HOA.
Left ventricular function in marathon runners: echocardiographic assessment
Authors: Paulsen W. , Boughner D. R. , Ko P. , Cunningham D. A. , Persaud J. A.
Published: December 2017

Cardiac alterations induced by chronic isotonic exercise were assessed echocardiographically in 8 active male marathon runners aged 29 +/- 7 yr (mean +/- SD) compared with 10 sedentary controls aged 27 +/- 5 yr. The runners had a significantly higher aerobic capacity than the controls (72.8 +/- 6 vs. 41.4 +/- 6 ml . kg-1 . min-1; P less than 0.001). Compared with the controls, the runners had a significantly lower heart rate at rest (49 +/- 3 vs. 73 +/- 9 beats/min; P less than 0.01) and during submaximal supine exercise at a similar absolute work load (115 +/- 11 vs. 124 +/- 12 beats/min; P less than 0.01). Similarly, the runners had a lower pressure-rate product both at rest (5.52 +/- 1.0 x 10(3) vs. 9.43 +/- 1.4 x 10(-3)) and during submaximal exercise (19.7 +/- 3.2 x 10(3) vs. 25.0 +/- 4.2 x 10(3); P less than 0.01). The left ventricular peak velocity of circumferential fiber shortening of the runners relative to that of the controls was significantly reduced both at rest (1.40 +/- 0.08 vs. 1.64 +/- 0.08 circ/s) and during submaximal supine exercise at a similar absolute work load (2.36 +/- 0.15 vs. 2.71 +/- 0.10 circ/s). However, this reduction in V cf was found to be directly related to the lower pressure-rate product of the runners and therefore did not reflect a decreased intrinsic myocardial contractility in the runners relative to the controls.
Venous air emboli in sheep: reversible increase in lung microvascular permeability
Authors: Ohkuda K. , Nakahara K. , Binder A. , Staub N. C.
Published: December 2017

We studied the effects of continuous intravenous air embolization on lung fluid balance in unanesthetized sheep. Following a 2-h base line, we infused 300-micrometers-diam air bubbles into the pulmonary artery at a rate sufficient to increase pulmonary vascular resistance by 60–300% and for periods of 0.25–3 h. Air emboli produced a dose- and duration-dependent increase in lung lymph and protein flow due mainly to an increase in endothelial barrier permeability but also to elevated pressure in the over-perfused microcirculation. When we stopped the air infusion, the vascular resistance fell as the air emboli were reabsorbed. Lung lymph and protein flow increased further and then returned slowly to base line with a half-time proportional to the duration of embolization. Increasing left atrial pressure during air embolization caused an increase in lymph flow and protein clearance and an average decrease of 15 Torr in arterial O2 tension, all changes in excess of that caused by either increased pressure or air emboli alone.
Blood flow response of human calf muscles to static contractions at various percentages of MVC
Authors: Richardson D.
Published: December 2017

Six male subjects within the age range of 20–35 yr consented to perform static calf muscle contractions at 7.5, 15, and 30% of their maximum voluntary contractile strength (MVC) for a period of 2 min each. Isometric contractions were performed in a sitting position by pressing the knee against a solid support plate via plantar flexion. Calf muscle blood flow (BF) was measured periodically before, during, and after each contraction by a Whitney gauge. Average resting BF was 3.9 ml . min-1 . 100 ml-1 of calf volume. During the 7.5, 15, and 30% MVC contractions, BF increased to steady-state levels of 7.2, 7.9, and 5.3 ml . min-1 . 100 ml-1, respectively. The values for 7.5 and 15% MVC were significantly higher than resting BF (P less than or equal to 0.05). The postcontraction hyperemia, measured as the area under the postcontraction BF curve, averaged 4.4, 10.1, and 23.2 ml/100 ml, respectively, for the 7.5, 15, and 30% MVC efforts. Comparison of these values with corresponding hyperemic volumes during contraction showed that the portions of the total BF response that occurred in the postcontraction periods were 41, 57, and 88%, respectively, for the 7.5, 15, and 30% efforts. These results demonstrate that during static calf muscle contractions BF increases by only a modest amount, and at even small forces of contraction a sizable portion of the total flow response occurs in the postcontraction period.
Endurance training in the rat. I. Myocardial mechanics and biochemistry
Authors: Nutter D. O. , Priest R. E. , Fuller E. O.
Published: December 2017

The effects of physical training and detraining on cardiac structure and myocardial mechanics were studied in young and adult male rats trained by graded treadmill running for 12 wk and compared with sedentary controls. Detraining was produced by training for 12 wk followed by 6 sedentary wk. A training effect was demonstrated by increased succinate dehydrogenase activity in skeletal muscle (trained 10.0 +/- 1.2 mumol . g-1 . min-1; sedentary 6.4 +/- 0.8 mumol . g-1 . min-1; P less than 0.05). Although heart weight-to-body weight ratios were increased in trained rats of both ages, left ventricular fiber diameters and myocardial RNA, DNA, and collagen content were unchanged by training. Active and passive mechanics (myocardial contractility and stiffness) were studied in left ventricular papillary muscles and did not differ significantly between groups, with the exception of depressed contractility observed in young trained rats [(e.g., papillary peak developed isometric tension at Lmax (length at peak tension)] was 2.64 +/- 0.24 g/mm2 in trained vs. 3.59 +/- 0.22 g/mm2 in sedentary (P less than 0.01). This difference was abolished by detraining. Papillary muscle contractile responses to calcium, norepinephrine, and hypoxia were not altered by training or detraining. In conclusion, moderate endurance training did not result in significant cardiac hypertrophy, altered myocardial stiffness, or consistent changes in myocardial contractility.
Endurance training in the rat. II. Performance of isolated and intact heart
Authors: Fuller E. O. , Nutter D. O.
Published: December 2017

The effects of isotonic physical training and detraining on cardiac function were studied in young and adult male rats trained by graded treadmill running and compared with sedentary controls. Absolute left ventricular mass was not increased, and ventricular compliance was not altered by training. Ventricular function curves that plotted peak systolic pressure, maximum rate of rise of left ventricular pressure, cardiac output, coronary flow, or stroke work as a function of atrial filling height in the isolated perfused heart did not demonstrate a training effect in either age group. The cardiac response to hypoxia was also comparable in the trained and sedentary rats. The base-line heart rate of anesthetized rats, in which in situ cardiac function was studied, was lower in the trained rats (321 +/- 14 vs. 377 +/- 8, P less than 0.005). Resting hemodynamics and left ventricular function curves generated from pressure-flow data during volume infusion did not differentiate between the hearts of trained and sedentary rats. In conclusion, a moderate level of endurance training did not enhance cardiac contractility when this was assessed under nonexercise conditions in both the isolated perfused heart and intact in situ heart preparations.
Assessment of alveolar-capillary membrane permeability of dogs by aerosolization
Authors: Huchon G. J. , Little J. W. , Murray J. F.
Published: December 2017

We developed a method for measuring an index of alveolar-capillary membrane permeability (PI) by aerosolizing a mixture of 99mTc-diethylenetriaminepentaacetic acid (Tc-DTPA) and 125I-antipyrine (I-AP) and injecting 111In-DTPA (In-DTPA). The I-AP was used to compute the quantity of Tc-DTPA delivered and the In-DTPA the quantity of Tc-DTPA in the body. The PI was the ratio of the uptake of Tc-DTPA per minute to the amount deposited at the end of aerosolization. In 14 anesthetized dogs we measured the volume of distribution of I-AP (0.54 +/- 0.034 l/kg body wt) and/or showed that the volumes of distribution of Tc-DTPA and In-DTPA were similar. We measured PI in four groups of dogs: control (n = 5), oleic acid (n = 5), hydrochloric acid (n = 6), and high left atrial pressure (n = 5). The PI increased significantly in both groups with acid-induced increased permeability compared with the control and high left atrial pressure groups, which did not differ from each other. We conclude that the aerosolization method is suitable for differentiating increased from normal permeability.
Brain and CSF water and ions in newborn puppies during acute hypo- and hypernatremia
Authors: Nattie E. E. , Edwards W. H.
Published: December 2017

We studied the fluid and electrolyte response of the brain and cerebrospinal fluid (CSF) in the lightly anesthetized newborn puppy exposed to acute (1–3 h) mild hyponatremia (12% decrease) and hypernatremia (7% increase). The changes in CSF osmolality, sodium, and chloride were equal to those in plasma. Blood acid-base values and CSF PCO2 remained normal, but in CSF there was a transient dilution acidosis in hyponatremia and contraction alkalosis in hypernatremia. In brain tissue, with hyponatremia, brain water increased in proportion to the osmotic stress (a change which was greater than that previously observed in adults) and the chloride space increased in the puppy (a change that was opposite to that observed in adults). There were no significant changes in dry tissue potassium, sodium, or chloride content. In hypernatremia, brain water decreased less than predicted by the osmotic change, the chloride space was unchanged, dry tissue potassium and chloride increased, and sodium was unchanged. In the newborn puppy, brain cell and extracellular volume regulation is not apparent with acute hyponatremia but is with hypernatremia.
A physiological stimulus to upper airway receptors in humans
Authors: McBride B. , Whitelaw W. A.
Published: December 2017

The regular involuntary inspiratory muscle contractions that occur in normal conscious men during breath holding were quantified by means of the waves of intrathoracic pressure that they produced. A stream of cool air circulated through the nose and mouth reproducibly inhibited the contractions. The degree of inhibition increased with increasing nasal flow in the range of normal resting respiratory flow and with lower temperature of circulating gas. The effect depended on the phase of respiration in which flow occurred and was abolished by local anesthesia of the nose and pharynx. The results demonstrate that the upper airway contains flow-sensitive receptors, the discharge of which can have a marked influence on respiration.
Collateral ventilation may protect against high-altitude pulmonary hypertension
Authors: Kuriyama T. , Wagner W. W.
Published: December 2017

We propose that the pulmonary hypertension developed by cattle and swine at high altitude is associated with their lack of collateral ventilation. We reason that if collateral ventilation helps keep interregional oxygen tensions homogeneous, then in its absence, local ventilation-perfusion balance must rely on arterial constriction; the additional work causes arterial walls to be more muscular at low altitude, a characteristic of cattle and swine that appears prerequisite for the development of pulmonary hypertension at high altitude. In contrast, species with collateral ventilation, e.g., dogs, have thin-walled pulmonary arteries and therefore can not sustain pulmonary vasoconstriction at altitude. Sheep, however, challenge the hypothesis, because their thick lobular septae should block collateral ventilation, yet they have thin pulmonary arteries and resist high-altitude hypertension. We measured collateral ventilation by determining how long it takes air injected into isolated segments to escape. Cattle and swine had no collateral ventilation (time constants greater than 30 s), whereas dogs and sheep had collateral ventilation (time constants less than 0.8 s). These data support the hypothesis that only species without collateral ventilation develop pulmonary hypertension at high altitude.
ACTH and cortisol responses to hypoxia in dogs
Authors: Raff H. , Tzankoff S. P. , Fitzgerald R. S.
Published: December 2017

To determine the role of endogenous ACTH and hyperventilation in the adrenocortical response to hypoxia, pentobarbital-anesthetized dogs equipped with left adrenal venous cannulas for measurement of cortisol secretion rate (CSR) and arterial cannulas for measurement of plasma ACTH were exposed to 20 min of normoxia (group I), spontaneous ventilation, normocapnic hypoxic hypoxia (group II), controlled ventilation, normocapnic hypoxic hypoxia (group III), controlled ventilation, normocapnic carbon monoxide hypoxia (group IV), or hypoxic hypoxia with elevated carboxyhemoglobin (group V). Group I showed no change in ACTH and CSR. Groups II and III greatly increased CSR whereas only group III increased ACTH significantly. Group IV greatly increased ACTH whereas CSR increased but less than group III. Group V showed a significant increase in ACTH but no significant CSR response. In addition, 5 U of ACTh were infused in several animals from groups I, III, and IV. Exogenous ACTH caused increases in CSR that were larger in group I than groups III and IV. The data are consistent with the hypothesis that ACTH in arterial blood is not the sole controller of CSR during hypoxic stress.
Respiratory depression produced by activation of GABA receptors in hindbrain of cat
Authors: Yamada K. A. , Hamosh P. , Gillis R. A.
Published: December 2017

Respiratory responses to activation of gamma-aminobutyric acid (GABA) receptors in the hindbrain were measured in chloralose-anesthetized cats using a Fleisch pneumotachograph. GABA receptors were activated by intracisternal injections of muscimol and GABA. Muscimol (0.05--6.65 micrograms) administered to seven animals caused a depression of respiratory activity with apnea occurring in each animal. Before apnea occurred, a decrease in tidal volume was observed (from 25.7 +/- 0.9 to 14.7 +/- 1.1 ml). Respiratory rate and inspiratory and expiratory durations were unchanged. GABA (0.05--12.15 mg) administered to five animals produced the same effect as muscimol on respiratory activity. Apnea produced by both agents was reversed by intracisternal administration of the GABA-receptor antagonist drug, bicuculline. Administration of bicuculline to four naive animals increased tidal volume (from 31.3 +/- 1.7 to 36.5 +/- 0.7 ml) but had no effect on either respiratory rate or inspiratory duration. These results indicate that activation of GABA receptors causes respiratory depression and suggest that GABA may be an important neurotransmitter in CNS neural pathways involved in regulating respiratory activity.
Response of collateral channels to histamine: lack of vagal effect
Authors: Kaplan J. , Smaldone G. C. , Menkes H. A. , Swift D. L. , Traystman R. J.
Published: December 2017

A new technique using a monodispersed aerosol of histamine delivered to sublobar bronchi through a flexible fiber-optic bronchoscope was used to study the role of the vagus nerve and the effect of anesthesia in the response of collateral channels to exogenous histamine. Studies were performed in paralyzed dogs anesthetized with pentobarbital sodium or alpha-chloralose. Challenges with histamine aerosol were delivered to separate bronchi in each animal before and after bilateral cervical vagotomy. Resistance through collateral channels increased in a reproducible manner following histamine challenge. Vagotomy resulted in no significant change in base-line resistance through collateral channels. The response of collateral channels to exogenous histamine aerosol was not significantly affected by vagotomy or the type of anesthesia used. We conclude that vagal reflexes do not play a significant role in the response of collateral channels to exogenous histamine.
Role of histamine in regulating pulmonary vascular tone and reactivity
Authors: Porcelli R. J. , Ventura D. F. , Mahoney W. A. , Bergofsky E. H.
Published: December 2017

The profile of histamine responsiveness of the pulmonary circulation and the role of endogenous histamine in regulating pulmonary vascular tone and reactivity were studied using the isolated perfused feline pulmonary circulation. Repetitive cumulative dose-response curves demonstrated a progressive decline in the response of the pulmonary circulation to histamine. The present studies also demonstrated elaboration of histamine by the perfused feline lung, and showed that decreasing this elaboration by mast-cell stabilization with cromolyn sodium (disodium cromoglycate, DSCG) had no significant effect on pulmonary vascular tone but resulted in greater lobar vasoconstriction to infused histamine. In contrast, DSCG had no significant effect on the pulmonary pressor response to serotonin, norepinephrine, hypoxia, and hypercapnia. These data suggest that 1) pulmonary; vascular tachyphylaxis occurs with exogenously infused histamine; 2) the withdrawal of endogenous histamine results in greater pulmonary vasoconstriction to exogenously infused histamine; an 3) the histamine release, which was prevented by DSCG, has no role in mediating pulmonary hypoxic or hypercapnic vasoconstriction in the cat.
Shape and regional volume in immersed lung lobes
Authors: Gillett D. , Ford G. T. , Anthonisen N. R.
Published: December 2017

We froze 10 isolated canine lower lobes by immersing them in chlorothene (sp gr 1.4) at -20 degrees C. In six instances the contralateral lower lobe was frozen over dry ice. The lobes were then sliced horizontally, and the volume and weight of each slice were measured so that expansion (specific volume) and the amount of tissue (weight) could be assessed as a function of distance down the lung. Lobes frozen under chlorothene at low [35% total lung capacity (TLC)] and medium [60% TLC] volumes demonstrated a gradient of regional expansion that was about half that predicted on the basis of pleural surface pressure. Lobes frozen under chlorothene at high volumes [80% TLC] did not demonstrate a significant gradient of regional expansion. These results demonstrated tissue interdependence. When lobes frozen under chlorothene were compared with contralateral lobes frozen over dry ice, substantial differences in shape were evident. Chlorothene-frozen lobes had greater vertical height, and a smaller fraction of their weight was present in dependent regions: lobes frozen in chlorothene had half as much tissue over the lower 40% of their vertical height as did lobes frozen over dry ice. We demonstrated two mechanisms by which relative homogeneity of regional expansion was maintained in response to differences in pleural pressure, tissue interdependence and tissue movement from more compressed to less compressed regions.
Vagotomy reverses apnea induced by high-frequency oscillatory ventilation
Authors: Thompson W. K. , Marchak B. E. , Bryan A. C. , Froese A. B.
Published: December 2017

Apnea has been observed in both animals and patients during high-frequency oscillatory ventilation. The effects of vagotomy were studied during periods of oscillator-induced apnea in 11 pentobarbital-anesthetized dogs. The animals were intubated and breathing spontaneously. An arterial cannula was inserted for monitoring blood pressure and blood gases. Intratracheal airway pressure was measured, and respiratory activity was assessed using either an intrapleural catheter or esophageal balloon. The dogs then underwent high-frequency ventilation at 15 Hz. Apnea was induced by appropriate selection of volume displacement of the piston pump and the distal airway pressure in eucapnic animals. Segments of right and left vagus nerves were exposed in the neck, bathed in local anesthetic, and transected. Spontaneous ventilation resumed immediately in nine animals and could not be suppressed at the same CO2 partial pressure despite continuation of oscillation. We conclude that the apnea observed during high-frequency ventilation is mediated by active vagal inhibition of central respiratory activity and is usually reversed by vagotomy.
Hypoxic pulmonary vasoconstriction in dogs: effects of lung segment size and oxygen tension
Authors: Marshall B. E. , Marshall C. , Benumof J. , Saidman L. J.
Published: December 2017

Six pentobarbital-anesthetized dogs were prepared with endobronchial tubes and electromagnetic flow probes. The effects of changing inspired oxygen concentrations (FIO2 = 1, 0.21, 0.15, 0.1, 0.075, 0.05, and 0) were tested on test segments of different size corresponding to left lower lobe, left upper lobe-lingula, left lung, right lung, right lung plus left lower lobe, right lung plus left upper lobe-lingula, and whole lung. In each test the rest of the lung received oxygen. Hypoxic pulmonary vasoconstriction is demonstrated by both diversion of blood flow away from hypoxic test segments and by increased perfusion pressure. Flow diversion (FD%) decreases with the size of the hypoxic test segment (%QSN) from a maximum of 75% for very small segments to zero when the whole lung is hypoxic. FD% increases linearly as alveolar oxygen tension (PAO2) of the test segment is decreased in the range of 130--28 Torr. When mixed venous oxygen tension (PVO2) is less than 45 Torr FD% is reduced. These relationships are described by FD% = [74.99 - 0.0778 (%QSN) - 0.00661 (%QSN)2] [1.268 - 0.0096 (PAO2)] [0.47 + 0.012 (PVO2)], with r = 0.92 and standard error for prediction of 8.4%. Pulmonary perfusion pressure changes (PPH/PPN) increase with the size of the hypoxic test segments from 0 with very small segments to approximately 2.2 for the hypoxic whole lung. For all test segments PPH/PPN increases linearly with PAO2. These relationships are described by PPH/PPN = 1 + [0.0043 (%QSN) + 0.000072 (%QSN)2] [1.234 - 0.0096 (PAO2)], with r = 0.91 and standard error for prediction of 0.3 units. Responses to hypoxic pulmonary vasoconstriction in dogs are therefore shown to be predictable and continuous, and the physiological basis for action of each of the variables is discussed.
Inhibitors of prostaglandin synthesis, tracheal fluid, and surfactant in fetal lambs
Authors: Kitterman J. A. , Liggins G. C. , Clements J. A. , Campos G. , Lee C. H. , Ballard P. L.
Published: December 2017

To study their effects on tracheal fluid (TF) production and surfactant flux, we gave 12-h infusions of prostaglandin synthetase inhibitors (PGSI) on 16 occasions to 10 fetal lambs at gestational ages (GA) of 125--141 days. Results were similar with both sodium meclofenamate (13.9 +/- 3.4 mg.kg-1, 12 studies) and indomethacin (33.6 +/- 8.0 mg.kg-1, 4 studies). All studies were done at least 6 days after surgery and 4 days before spontaneous birth. During infusions of PGSI, there were no changes in fetal arterial blood pressure, pH, PaO2, PaCO2, TF production or its concentration of sodium, potassium, and chloride; calcium concentration in TF increased slightly. We expressed tracheal surfactant flux as micrograms.kg-1.h-1 of saturated phosphatidylcholine (SPC). If control SPC flux was less than 5 micrograms.kg-1.h-1 (10 studies at GA of 125--141 days), it did not change during infusion of PGSI; however, if control was greater than 5 micrograms.kg-1.h-1 (6 studies at GA 132--140 days), SPC flux decreased during the infusions in all studies. The results suggest that prostaglandins do not strongly influence TF production up to 4 days before birth and that prostaglandins are involved in the increased flux of surfactant which occurs in late gestation.
Single-breath nitrogen test in excised human lungs
Authors: Berend N. , Skoog C. , Thurlbeck W. M.
Published: December 2017

Pressure-volume curves and simulated single-breath nitrogen tests were performed on 32 excised left human lungs and the slope of phase III, and phase IV plus minimal volume, expressed as percent of the lung volume at a transpulmonary pressure of 30 cmH2O (closing capacity), was calculated. The lungs were graded as to the degree of emphysema and degree of peripheral airways disease. Peripheral airway dimensions were also measured. The closing capacity expressed as percent predicted in vivo was significantly correlated with the total pathological scores (P less than 0.01) and inflammation scores (P less than 0.01) as well as the transpulmonary pressures at the onset of phase IV (P less than 0.01). Correlations with the emphysema grade were not significant. The slopes of phase III were highly variable even among normal lungs and could not be shown to correlate with airways disease or emphysema.
Effects of alpha -adrenergic blockade during acute anemia
Authors: Chapler C. K. , Cain S. M.
Published: December 2017

Studies were carried out in seven anesthetized paralyzed dogs to examine the importance of alpha -adrenergic tone in the cardiovascular responses during acute anemia. Data were obtained 1) at normal hematocrit (Hct), 2) during anemia produced by isovolemic hemodilution with dextran (Hct, 13–15%), 3) during anemia after alpha -blockade (alpha -bl) with phenoxybenzamine (3 mg/kg), and 4) following volume expansion during anemia with a red blood cell dextran solution. Cardiac output (QT), limb and total body oxygen uptake (VO2), and limb blood flow (QL) were determined. Both QT and QL increased during anemia (P less than 0.01), whereas limb resistance (RL) and total peripheral resistance (TPR) were decreased (P less than 0.01). No further change in either RL or TPR occurred with alpha -blockade anemia, but both QT and QL decreased (P less than 0.01). Whole-body VO2 increased during anemia and then declined with alpha -bl and anemia. Following volume expansion during anemia with alpha -bl, QT, QL, and whole-body VO2 increased. We conclude that alpha -adrenergic sympathetic tone to capacitance vessels is essential for the cardiac output increased during anemia, but has little or no effect on resistance vessels and hence distribution of peripheral blood flow.
Summated circulatory responses of thermal and baroreflexes in humans
Authors: Ebert T. J. , Stowe D. F. , Barney J. A. , Kalbfleisch J. H. , Smith J. J.
Published: December 2017

Baroreceptor and thermal receptor mediated reflexes are important neural control systems that can markedly alter blood pressure in humans. These two systems have different afferent limbs and are integrated at different central sites. Although the circulatory effects of activating these individual reflexes have been examined, the effects of simultaneous activation of two or more separate reflexes have received relatively little attention. We used noninvasive methods in 13 normal men (20–27 yr) to examine the responses mediated by cardiopulmonary and arterial baroreceptors; the reflexes were elicited by alterations in central blood volume [lower body negative pressure (LBNP) and leg elevation (LE)] in the presence or absence of local thermal receptor stimulation induced by hand immersion (HI) in 10 degree C water. During all levels (-10, -25, and -40 Torr) of LBNP and during LE, forearm vascular resistance (FVR) was altered. At the two higher levels of LBNP, stroke volume, cardiac index, and blood pressure (BP) decreased, and heart rate (HR) and total peripheral resistance (TPR) increased. TPR, FVR, and BP increased during HI. Our analyses indicated that responses to combined stimuli, i.e., local cold during LBNP or LE, resulted in simple additive responses in all variables except HR. A central interaction between thermal and baroreflex control of HR is possible.
Physiological action tremor of the ankle
Authors: Pozos R. S. , Iaizzo P. A. , Petry R. W.
Published: December 2017

Comparisons were made between physiological tremor (PT), which is the involuntary oscillation produced when the leg is held in a plantarflexed position, and physiological action tremor (PAT), which is an involuntary oscillation associated with the voluntary slow raising and lowering of the heel. Frequency analysis using spectral techniques revealed a major frequency range of 6–9 Hz for PT and a major frequency range of 4–8 Hz for PAT. Computed root-mean-square (rms) acceleration values for each tremor type showed that the amplitude of PAT was significantly higher (2–5 times) than that of PT. This significant increase in amplitude occurred at specific stages of the voluntary movement. Major peaks in the spectral plots of the demodulated electromyogram signals of the soleus and tibialis anterior muscles corresponded to the frequency peaks seen with PAT.
Effect of interstitial fluid (kerosene) on pressure-volume characteristics of rat lung
Authors: Urmey W. F. , Scharf S. M. , Brown R. , Carlson D. , Song P.
Published: December 2017

Although pulmonary interstitial edema has been estimated to decrease pulmonary compliance (CL), it has been experimentally difficult to demonstrate whether the observed changes in CL are directly due to the presence of interstitial fluid or if they result instead from concomitant pulmonary vascular engorgement and/or alveolar edema. Since kerosene-inflated lungs do not leak, we were able to use kerosene to measure the effect on CL of the accumulation of interstitial fluid (kerosene) in the postmortem rat lung. Pressure-volume (PV) studies of the lung were done during the progressive increase in interstitial fluid (kerosene). Analysis of the deflation limbs of the quasistatic PV curves obtained following serial inflations with kerosene indicated that the maximal volume of kerosene [MV35, equal to the maximum tissue plus airway volume at a transpulmonary pressure (Ptp) of 35 cmH2O] was 3.8 +/- 1.2 ml (31.0 +/- 11.8%) greater than TLC35 [air volume at Ptp of 35 cmH2O prior to kerosene inflation]. The increases in interstitial kerosene volume had no effect on kerosene PV characteristics, as was demonstrated by superimposing lung PV curves obtained at various states of interstitial filling. We conclude that the interstitial compartment is large and very compliant and that the presence of even great amounts of fluid limited to this compartment does not restrict lung expansion.
Computer-assisted method for performing impedance cardiography calculations
Authors: Frey M. A.
Published: December 2017

Impedance cardiography provides a noninvasive technique to monitor stroke volume on a beat-by-beat basis. It correlates well with other techniques at rest, with both cycle and arm-ergometer exercise, and during head-up tilt. It has the advantage that it does not require active subject participation, as does the CO2-rebreathing technique; yet it is still noninvasive. The method described herein facilitates the measurement and calculation of stroke volume, cardiac output, and indices of ventricular function when this technique is used - whether a few or many beats are recorded. This method utilizes a recording of the impedance cardiogram, which may include a simultaneously recorded electrocardiogram and phonocardiogram; a digitizer for reading the coordinates from the recording; a CRT terminal with keyboard for additional data input and for monitoring output; a printer; and a minicomputer for calculation of variables and data analysis. Data related to approximately 100 cardiac beats can be read, calculated, printed, and statistically analyzed in about an hour.
Alveolar epithelium permeability to small solutes: developmental changes
Authors: Goodman B. E. , Wangensteen D.
Published: December 2017

To determine whether alveolar epithelium permeability to small lipid-insoluble solutes changes during development we measured transport across the blood-gas barrier in isolated Ringer-perfused lungs from prenatal, 1-day-old, 4-wk-old, and adult rabbits. Radioactive test molecules, one of which was always sucrose, were dissolved in Ringer solution and instilled into the trachea of degassed lungs. Samples taken from recirculating perfusate were used to calculate permeability-surface area (PS) products. Results were expressed as the ratio (PS)/(PS)sucrose, and as absolute permeability. Lungs from 4-wk-old rabbits were studied most thoroughly; the (PS)/(PS) sucrose ratios obtained are urea 4.0, erythritol 1.3, mannitol 0.98, L-glucose 1.4, and D-glucose 5.6. These and other data imply that the most lipid-insoluble molecules (erythritol, mannitol, L-glucose, and sucrose) are transported by a nonselective bulk process. Urea transport is primarily through lipid membranes; D-glucose seems to involve a special process. Sucrose and L-glucose permeability decreased during development, but their relative permeabilities did not change. Small lipid-insoluble solutes apparently do not cross the alveolar epithelium through small water-filled pores, and their permeability decreases as the animal matures.
A computational model for expiratory flow
Authors: Lambert R. K. , Wilson T. A. , Hyatt R. E. , Rodarte J. R.
Published: December 2017

A mathematical model of maximal expiratory flow was developed. Coupled equations describing the pressure losses in the flow and the pressure-area behavior of the airway were integrated along the airway from the periphery to the flow-limiting site. Equations describing pressure losses in the flow were adapted from studied of bronchial casts. The bronchial anatomy utilized was that described by Weibel. Bronchial mechanical properties were obtained from measurements in excised human lungs for the central airways and by extrapolations of these data for the peripheral airways. The maximal flow for air and helium predicted by the model agrees with that of five lungs from which mechanical properties were obtained. The model predictions agree with published values of density and viscosity dependence of maximal flow. At high and midlung volumes, maximal flow is determined primarily by the wave-speed mechanism. At low lung volumes, maximal flow is primarily determined by the coupling of viscous pressure losses and airway mechanical properties.
Effect of body weight and muscularity on human diaphragm muscle mass, thickness, and area
Authors: Arora N. S. , Rochester D. F.
Published: December 2017

To assess the consequences to the human diaphragm of alterations in body weight and muscularity, we measured the mass, thickness, area, and length of diaphragm muscle at necropsy. Of 33 subjects who were clinically well until sudden death, 27 had sedentary occupations and normal weight (group N), while 6 were nonobese laborers whose average weight was 40% greater than normal (group M). Among 37 patients dying of more prolonged illness, 23 were of normal weight (group W), while 14 weighed 71% of normal (group U). Subjects with obesity, chronic pulmonary disease, or edema were excluded. Disease per se did not significantly affect diaphragm dimensions. However, in group M diaphragm muscle mass, thickness, area, and length were 165, 129, 125, and 117% of normal (P less than 0.005), whereas in group U the corresponding values were 57, 73, 77, and 83% (P less than 0.001). Thus alterations in body weight and muscularity profoundly affect diaphragm muscle mass, causing a nearly threefold variation between muscular normal subjects and underweight patients.
Heat balance of ox steers (Bos taurus) in steady-temperature environments
Authors: McLean J. A. , Downie A. J. , Watts P. R. , Glasbey C. A.
Published: December 2017

Work was undertaken to investigate body heat storage in cattle subjected to steady temperature environments. Heat production (M) of and heat losses (H) from two steers were studied by simultaneous direct and indirect calorimetry over periods of up to 11 days. M and H followed similar trends except after feeding and watering. When the animals stood both M and H leveled approximately 20% higher than when they were lying down. Over 24-h periods total M and H agreed within the limits of experimental error. Heat storage of the calorimeter contents (MH) was calculated from the accumulated difference between M and H. Day-night cycles observed in MH were partly due to the heat of warming food and water and of cooling excreta (FF). The difference (TB = MH - FF) represented calorimetrically determined changes in heat storage in the animal's body. Day-night cycles in TB were small (less than 1 degree C range in equivalent change in mean body temperature) but agreed well with observed changes in body core (carotid artery) temperatures. It is concluded that day-night changes in heat storage in fixed-temperature environments are small but measurable by calorimetry and that the methods used are applicable for future studies with cyclic environmental temperatures.
Ventilatory responses at rest and during exercise in marathon runners
Authors: Mahler D. A. , Moritz E. D. , Loke J.
Published: December 2017

Diminished ventilatory responsiveness to hypercapnia and hypoxia has been reported in athletes, but whether reduced chemosensitivity might lessen hyperpnea during exercise and facilitate performance is unknown. To evaluate ventilatory control and its possible role in athletic performance, we prospectively measured ventilatory responses to hypercapnia and hypoxia at rest and ventilatory equivalents for carbon dioxide (VE/VCO2) and oxygen (VE/VO2) during exercise in 20 accomplished marathon (42.2 km) runners (RUN) and 20 control subjects (CON). The athletes (mean age 27.8, range 18–41 yr) were all experienced runners with a mean best marathon time of 2 h, 36 min (range 2:142:55). There were no significant differences in the ventilatory responses at rest to hypercapnia (RUN, 2.23 +/- 0.73 vs. CON, 2.61 +/- 1.05 l X min-1 X Torr-1) and hypoxia (RUN, 0.57 +/- 0.40 vs. CON, 0.88 +/- 0.72 l X min-1 X 1% desat-1) (mean +/- SD). Similarly, there were no significant differences in VE/VCO2 and VE/VO2 between the two groups. Good correlation (r = 0.68; P less than 0.01) was observed between hypercapnic response at rest and exercise ventilation (VE/VCO2) in RUN. However, both hypercapnic and hypoxic ventilatory responses correlated poorly with marathon running time. These results demonstrate no differences in ventilatory responses at rest and during exercise between marathon runners and control subjects. The range of ventilatory responsiveness observed in this group of marathon runners indicates that a spectrum of ventilatory control is present in well-trained endurance athletes.
Activation of the parasternal intercostals during breathing efforts in human subjects
Authors: De Troyer A. , Sampson M. G.
Published: December 2017

We have tested the possibility that the electromyographic (EMG) activity present in the parasternal intercostal muscles during quiet inspiration was reflexive, rather than agonistic, in nature. Using concentric needle electrodes we measured parasternal EMG activity in four normal subjects during various inspiratory maneuvers. We found that 1) phasic inspiratory activity was invariably present in the parasternal intercostals during quiet breathing, 2) the parasternal EMG activity was generally increased during attempts to perform the tidal breathing maneuver with the diaphragm alone, 3) parasternal EMG activity was markedly decreased or suppressed in the presence of rib cage distortion during diaphragmatic isovolume maneuvers, and 4) that EMG activity could not be voluntarily suppressed during breathing unless the inspired volume was trivial. We conclude that the parasternal EMG activity detected during quiet inspiration in the normal subjects depends on a central involuntary mechanism and is not related to activation of intercostal mechanoreceptors.
Effect of chemical stimuli on nerves supplying upper airway muscles
Authors: Weiner D. , Mitra J. , Salamone J. , Cherniack N. S.
Published: December 2017

Studies of upper airway resistance suggest that the activity of cranial nerves supplying upper airway muscles changes with chemical drive and that imbalances in the activation of these nerves as compared to the phrenic play a role in causing upper airway obstruction. We assessed the effect of hypoxia and hypercapnia on the activity of the hypoglossal nerve, the recurrent laryngeal nerve, and phrenic nerve in paralyzed anesthetized artificially ventilated dogs. Comparison of hypoglossal and phrenic nerves were also repeated after vagotomy. Both hypoglossal and recurrent laryngeal nerves exhibited increased activity with inspiration. Hypoxia and hypercapnia increased phrenic nerve activity as well as the activity of the two cranial nerves. While linear increases occurred in phrenic and recurrent laryngeal nerve activity with both chemical stimuli, the relationship between hypoglossal and phrenic nerve activity was curvilinear. At lower levels of chemical drive, changes in hypoglossal nerve were less than in the phrenic, and the reverse was true at higher levels of chemical stimulation. There were also differences in the response of both cranial nerves and the phrenic to changing vagal stimulation. The dissimilarities observed in the cranial response of the nerves (versus the phrenic) could potentially affect the forces developed during inspiration and lead to obstruction in the upper airway.
Modulation of human sinus node function by systemic hypoxia
Authors: Eckberg D. L. , Bastow H. , Scruby A. E.
Published: December 2017

We studied sinus node responses to mild to moderate systemic hypoxia provoked by nitrogen inhalation in five healthy young men. Volunteers maintained their usual tidal volumes and respiratory frequencies at constant levels. We modified carotid arterial baroreceptor activity by applying neck suction or pressure during held expiration. Arterial oxygen saturation began to decline between 8.0 and 9.6 s after the onset of the first breath of nitrogen. Pulse interval declined in parallel with oxygen saturation. During mild hypoxia cardioacceleration was restricted primarily to the inspiratory phase of respiration. Moderate hypoxia diminished the magnitude of sinus arrhythmia. It did not alter baroreflex responsiveness. Our results suggest that in normal humans, augmentation of chemoreceptor input leads to reduction of cardiac vagal motoneuron output. This effect exhibits a distinct respiratory periodicity (more prominent in inspiration) and appears to be independent of any influence of hypoxia on ventilation or baroreflex responsiveness.
Neural responses of the cat carotid and aortic bodies to hypercapnia and hypoxia
Authors: Fitzgerald R. S. , Dehghani G. A.
Published: December 2017

The response (imp . s-1) of single- or few-fiber preparations from the carotid body (10 experiments) and the aortic body (5 experiments) to various levels of hypercapnia on different backgrounds of hypoxia were analyzed by two statistical techniques--analysis of variance and the Duncan's new multiple-range test. These analyses showed an initial statistically significant increase in the slope of the response to increasing arterial pressure of CO2 (PaCO2) as PaO2 fell. But the slope of the response to carbon dioxide later showed a clear tendency to become less; i.e., no significant increase in imp . s-1 when a PaCO2 rose (substantially) with normoxic (carotid body) and hypoxic (carotid and aortic bodies) backgrounds. The response of the aortic body to hypercapnia showed no statistically significant increase if the background was hyperoxia or normoxia. The characteristic of the chemoreceptor to become saturated in its response to carbon dioxide while still retaining its ability to respond to hypoxia suggests the possibility that at least some of the mechanisms involved in the chemoreception of hypoxia differ from those involved in the chemoreception of hypercapnia.