Stock optimizing in choice when a token deposit is the operant.

Each of 2 monkeys typically earned their daily food ration by depositing tokens in one of two slots. Tokens deposited in one slot dropped into a bin where they were kept (token kept). Deposits to a second slot dropped into a bin where they could be obtained again (token returned). In Experiment 1, a fixed-ratio (FR) 5 schedule that provided two food pellets was associated with each slot. Both monkeys preferred the token-returned slot. In Experiment 2, both subjects chose between unequal FR schedules with the token-returned slot always associated with the leaner schedule. When the FRs were 2 versus 3 and 2 versus 6, preferences were maintained for the token-returned slot; however, when the ratios were 2 versus 12, preference shifted to the token-kept slot. In Experiment 3, both monkeys chose between equal-valued concurrent variable-interval variable-interval schedules. Both monkeys preferred the slot that returned tokens. In Experiment 4, both monkeys chose between FRs that typically differed in size by a factor of 10. Both monkeys preferred the FR schedule that provided more food per trial. These data show that monkeys will choose so as to increase the number of reinforcers earned (stock optimizing) even when this preference reduces the rate of reinforcement (all reinforcers divided by session time).

Natural choice in nonhuman primates.

In 5 experiments, 4 monkeys and 1 ape chose between 2 food sources, each held in 1 of the experimenter's hands while he stood in front of a cage. When choosing between 2 sources of the same food that differed in amount, preference for the larger amount decreased as the size of each good proportionately increased. A second finding was that subjects were indifferent between a 2-food mixture and a single food that was part of the mixture if the single food was the preferred food of the mixture, a result suggesting the less preferred food had no value. Experiment 6 replicated these effects in 4 additional monkeys. These effects may be incompatible with previous theorizing about animal choice and may reflect a cognitive difference between nonhuman primates and humans.

Effects of morphine and pancuronium on lung volume and oxygenation in premature infants with hyaline membrane disease.

To determine the effect of analgesia and paralysis on lung volume and oxygenation in premature infants supported by mechanical ventilation because of hyaline membrane disease, functional residual capacity (FRC), and arterial/alveolar oxygen tension ratio were measured in nine premature infants with hyaline membrane disease before and after the administration of morphine sulfate and pancuronium bromide. Without a change of positive end-expiratory pressure, ventilator rate and peak inspiratory pressure were increased before the first set of measurements to minimize the contribution of the infants' own respiratory effort to total ventilation. These ventilator settings were then held constant (except fraction of inspired oxygen) before and after the administration of the drugs. The FRC was measured with a multiple-breath N2 washout technique by means of whole-body plethysmography to measure airway flow. The FRC and the ratio of arterial to alveolar oxygen tension decreased in seven of nine patients after treatment with morphine and pancuronium. The decrease in FRC for all patients was significant (2.4 +/- 2.9 ml/kg; p < 0.05), and a significant correlation was demonstrated between the change in the arterial/alveolar oxygen tension ratio and the change in FRC (r = 0.82; p < 0.01). Gestational age, birth weight, postnatal age, severity of lung disease, and time after the administration of morphine and pancuronium were not significantly correlated with the change in FRC. We believe that a decrease in oxygenation caused by alveolar derecruitment occurred even though the ventilator settings had been increased before the first set of measurements. The decrease in FRC in these infants, who are thought to have alveolar instability because of surfactant deficiency, may have resulted from the loss of expiratory braking mechanisms. We conclude that analgesia and paralysis should be used with caution under these circumstances.

The physiologic effects of surfactant treatment on gas exchange in newborn premature infants with hyaline membrane disease.

To describe the physiologic effects of surfactant treatment on gas exchange in human premature infants with hyaline membrane disease, functional residual capacity (FRC), tidal volume (VT), the alveolar portion of tidal volume (VA), alveolar ventilation (VA), nitrogen clearance index, effective breath fraction calculated as VA/VT, compliance of the respiratory system, and arterial oxygen and carbon dioxide tensions were measured in 17 patients before and 0.5, 2, and 6 h after the administration of a single dose of either a synthetic surfactant (SS), Exosurf (n = 10), or a bovine surfactant (BS), Survanta (n = 7). By 2 h, treatment with either BS or SS was followed by an increase in the arterial/alveolar ratio of PO2 (a/A) and in FRC (p < 0.01 for both a/A and FRC). The a/A and FRC improved sooner (p < 0.001) and to a greater extent (p < 0.01) after BS than after SS. Compliance of the respiratory system and VT were decreased after either BS or SS at 0.5 h (p < 0.01) and remained decreased after SS at 2 h (p < 0.01). There was no significant change in VA or VA after either BS or SS. Because FRC and a/A increased without an accompanying increase in VA, VA, or compliance of the respiratory system, we believe that the immediate increase in FRC in this study was caused by stabilization of gas exchange units already being ventilated in addition to recruitment of new units.(ABSTRACT TRUNCATED AT 250 WORDS)

Odor matching and odor memory in the rat.

To assess olfactory matching-to-sample learning, rats were exposed to two odors separated by a 1-s presentation of clean air. If, and only if, the odors were identical, a response produced a water reinforcer. High levels of performance were maintained over a series of 10 novel three-odor matching-to-sample problems on this conditional go/no-go discrimination procedure. In general, performance accuracy improved over problems and errorless or near errorless performance on many stimulus combinations, particularly near the end of training, indicated acquisition of a learning set. There was little decrement in performance when the interstimulus interval was increased gradually from 1 to 10 s and matching-to-sample was not disrupted when a novel odor was presented during the interstimulus interval. These results demonstrate that rats readily learn an olfactory matching-to-sample task, maintain high levels of performance even with delays of 10-s between stimuli, and can acquire a matching-to-sample learning set. The outcomes are in agreement with prior studies demonstrating exceptional learning of instrumental tasks by rats when they are provided with odor cues.

Stock optimizing: maximizing reinforcers per session on a variable-interval schedule.

In Experiment 1, 2 monkeys earned their daily food ration by pressing a key that delivered food according to a variable-interval 3-min schedule. In Phases 1 and 4, sessions ended after 3 hr. In Phases 2 and 3, sessions ended after a fixed number of responses that reduced food intake and body weights from levels during Phases 1 and 4. Monkeys responded at higher rates and emitted more responses per food delivery when the food earned in a session was reduced. In Experiment 2, monkeys earned their daily food ration by depositing tokens into the response panel. Deposits delivered food according to a variable-interval 3-min schedule. When the token supply was unlimited (Phases 1, 3, and 5), sessions ended after 3 hr. In Phases 2 and 4, sessions ended after 150 tokens were deposited, resulting in a decrease in food intake and body weight. Both monkeys responded at lower rates and emitted fewer responses per food delivery when the food earned in a session was reduced. Experiment 1's results are consistent with a strength account, according to which the phases that reduced body weights increased food's value and therefore increased subjects' response rates. The results of Experiment 2 are consistent with an optimizing strategy, because lowering response rates when food is restricted defends body weight on variable-interval schedules. These contrasting results may be attributed to the discriminability of the contingency between response number and the end of a session being greater in Experiment 2 than in Experiment 1. In consequence, subjects lowered their response rates in order to increase the number of reinforcers per session (stock optimizing).

Theoretic analysis of middle ear gas composition under conditions of nonphysiologic ventilation.

As gas flows in and out of the nasopharynx, the pressure in that region fluctuates. It drops below or rises above atmospheric pressure, which is itself not constant but is subject to changes in altitude and weather. Such pressure changes in the nasopharynx produce a pumping of gas into and out of the middle ear. The net amount of middle ear gas transferred from or to the nasopharynx will, component for component, in steady state exactly equal the amount of middle ear gas transferred to or from the microcirculation by means of diffusional absorption by (or release from) the mucosa. In the case of a permanently patulous eustachian tube, a single parameter, characteristic of the rate of ventilation through the open eustachian tube, is found to determine the gas composition in the middle ear, whereas in the case of a middle ear ventilated by tympanostomy, two rate-of-ventilation parameters, one for gas flow through the ventilation tube and one for flow through a periodically open eustachian tube, determine the steady state gas composition. A high rate of ventilation favors absorption of oxygen and venting of carbon dioxide from the middle ear in both cases.

Nonlinear pressure/volume relationship and measurements of lung mechanics in infants.

We examined the effects of within-breath changes in compliance (C) upon the accuracy of measurements of compliance and resistance (R) by linear regression analysis and by Mead and Wittenberger's method. These effects were illustrated by a computer model and by lung models with linear and nonlinear pressure/volume relationships, and were also studied in 14 normal spontaneously breathing premature infants (mean +/- SD, BW 1,290 +/- 200 g, GA 29.9 +/- 2.7 weeks, age 7.4 +/- 2.1 days). Flow was measured by pneumotachography and tidal volume was derived as digitally integrated flow, and transpulmonary pressure as airway minus esophageal pressure. We found that C and R calculated from the equation of motion is accurate only if C and R remain constant throughout the respiratory cycle. Calculated compliance depends more on C at the end than at the beginning of inspiration. A decreasing C leads to underestimation or R, while an increasing C leads to an overestimation of inspiratory R. Calculated total R may be accurate, but with low r values for measurement points. Mead and Wittenberger's method and the regression method are similarly affected by changing C; however, since the regression method is based on many more measurement points and therefore allows the detection and analysis of within-breath changes of C and R, it is less prone to erroneous results secondary to signal artifacts than Mead and Wittenberger's method.

Effects of reinforcer delays on choice as a function of income level.

Three rats earned their daily food ration by responding during individual trials either on a lever that delivered one food pellet immediately or on a second lever that delivered three pellets after a delay that was continuously adjusted to ensure substantial responding to both alternatives. Choice of the delayed reinforcer increased when the number of trials per session was reduced. This result suggests that models seeking closure on choice effects must include a parameter reflecting how preference changes with sessionwide income. Moreover, models positing that reinforcer probability and immediacy (1/delay) function equivalently in choice are called into question by the finding that probability and immediacy produce opposing effects when income level is changed.

Transient pressure changes in the middle ear.

Transient increases in total pressure in the ear (1) during sleep, after hypoventilating in a supine position with a closed eustachian tube, and (2) after the partial pressures in middle-ear gas are lowered by a total pressure decrease and the eustachian tube is voluntarily maintained closed can be accounted for quantitatively on the basis of the standard mucosal gas exchange model and the following data: (1) partial pressures in tissue: pN2* = 573 mm Hg (7621 decaPascals [daPa]), pO2* = 40 mm Hg (532 daPa), pCO2* = 46 mm Hg (612 daPa), and pH2O* R = 47 mm Hg (625 daPa); (2) partial pressures in the nasopharynx: pN2' = 566 mm Hg (7528 daPa), pO2' = 120 mm Hg (1596 daPa), pCO2' = 27 mm Hg (359 daPa), and pH20' = 47 mm Hg (625 daPa); (3) a middle-ear gas space of 2 x 10(-5) m3; (4) an absorption rate for nitrogen, when the partial pressure difference is 1 atm, of 3 x 10(15) molecules per second; and (5) mucosal absorption rates for oxygen and carbon dioxide 1.8 and 34 times larger, respectively, than for nitrogen.

Human choice on concurrent variable-interval variable-ratio schedules.

Each of 5 adult male humans sat in a 4 degrees C room where they could warm themselves by illuminating six heat lamps for 10-second periods according to a concurrent variable-interval variable-ratio schedule. Left-button presses on a response panel switched between the schedules and started a 2-second changeover delay. Right-button presses illuminated the heat lamps if assigned by the associated schedule and if the changeover delay had timed out. Panel lights identified the schedule in effect and each effective right-button press. A discrimination procedure--either a multiple variable-interval variable-ratio schedule or the presentation of each schedule individually on alternate days--preceded exposure to the choice procedure for some subjects. For subjects not exposed to a discrimination procedure prior to exposure to choice, or if such exposure failed to result in higher rates to the ratio than to the interval schedule, relative response rates matched relative reinforcement rates. However, if subjects responded at higher rates to the ratio schedule than to the interval schedule during a prior discrimination procedure, relative rates on a subsequent choice procedure deviated from matching in the direction of reinforcement-rate maximizing. In eight of 11 conditions, choice appeared to be governed by maximizing processes. In all cases, human concurrent ratio-interval performances differed from those of nonhumans in that matching was never obtained with local ratio-interval rate differences.

Lung volume, gas mixing, and mechanics of breathing in mechanically ventilated very low birth weight infants with idiopathic respiratory distress syndrome.

We assessed pulmonary function in 14 mechanically ventilated newborn very low birth weight infants with idiopathic respiratory distress syndrome by means of a face-out, volume displacement body plethysmograph and nitrogen washout analyses. Specially designed computer programs were used for calculations of lung volumes, ventilation, gas mixing efficiency, and mechanical parameters. In addition to very low compliance and moderately elevated resistance of the respiratory system, there were considerably impaired gas mixing efficiency and low functional residual capacity (FRC). No correlations between positive end-expiratory pressure and mean airway pressure versus compliance, resistance, or FRC could be found. Neither could correlations be found between FRC and compliance or FRC and the calculated right to left shunt.

A plethysmographic method for assessment of lung function in mechanically ventilated very low birth weight infants.

We have developed and tested a plethysmographic method for assessment of lung function in mechanically ventilated very low birth weight infants during intensive care. Information about the mechanics of the respiratory system is obtained from the respiratory flow as measured by volume displacement plethysmography and from airway pressure measured in the artificial airway. Data on lung volumes, ventilation, and distribution of ventilation is obtained simultaneously by combining the respiratory flow measurements with nitrogen concentration analyses of the respiratory gas. No significant differences were found when the estimations of mechanical parameters and FRC were compared with reference methods and when determinations of the same parameters were repeated in the same subjects. The plethysmograph was shown to be safe and convenient to use, even in studies lasting several hours.

Polyelectrolytes at the endothelial cell surface.

It is recalled that the tension in a stretched polyelectrolyte chain mechanically compensates both the coulomb interaction and the hydrostatic pressure increase around the chain in a compromise which minimises the free energy and keeps water chemical potential constant throughout. Stretching strongly favors parallel cylinder nematic order in polyelectrolyte brushes on a surface or in the slit between two surfaces when the polyelectrolyte chains function as bridges. Strong, stiffly stretched chains result when the molarity of the fixed charge distribution is larger than the molarity of the neutral salt solution with which the brushes are in equilibrium. The relevance of these two systems to the endothelial cells which cover the walls of blood vessels is discussed.

Origin of cardiac-related thoracic electrical impedance variations in lambs.

Cardiac-related deflections in thoracic electrical impedance have been thought to correlate sufficiently well with cardiac stroke volume to be used as the basis for a noninvasive estimation of cardiac output. To determine more precisely the physiological origin of the impedance deflection (DZ), we regarded right ventricular stroke volume (SVa) as the sum of two components: 1) that part of SVa responsible for the transient increment in pulmonary blood volume within a cardiac cycle, SVa-v and 2) the remaining part of SVa, (SVa-SVa-v). SVa-v was measured in lambs by integration of the difference between pulmonary arterial and pulmonary venous flow. SVa and its components were varied experimentally by opening and closing an aorticocaval shunt or by inflating and deflating a cuff implanted around the pulmonary artery. DZ was measured using a tetrapolar disk electrode system. Multivariate linear regression analysis revealed that SVa-v had a significant positive effect on DZ, and, at the same time, (SVa-SVa-v) had a significant negative effect on DZ. In the pulmonary artery occluder model, the positive effect of SVa-v dominated the opposing negative effect of (SVa - SVa-v) so that the net effect of SVa on DZ was positive and significant. In the aorticocaval shunt model, these effects opposed each other to the extent that there was no significant correlation between SVa and DZ. These results shed new light on the physiological origin of DZ. They also demonstrate that use of DZ to measure acute changes in cardiac output may yield misleading results. Changes or the lack of changes in thoracic electrical impedance do not necessarily reflect cardiac output status.

Olfactory learning and odor memory in the rat.

Rats were trained on a series of 9 tasks, each of which required discrimination among 8 different and unique odors. Discrimination accuracy improved across successive problems and, by the end of training, most rats made few errors after their initial exposure to each new odor. Despite the number of stimuli to be discriminated, this acquisition of a learning set was not appreciably different from that demonstrated in an earlier study that used only 2 odors per task. In subsequent retention tests, most rats also showed excellent memory for odors used in prior problems.

Surfactant improves gas mixing and alveolar ventilation in preterm lambs.

Prophylactic treatment with ovine surfactant was evaluated in preterm lambs at risk for development of hyaline membrane disease. Eight mechanically ventilated newborn lambs were treated before delivery and 10 served as controls (gestational age 129-131 d). Lung mechanics, functional residual capacity, alveolar ventilation, efficiency of ventilation, and distribution of ventilation were tested using pressure, flow, and nitrogen elimination (nitrogen washout during 100% oxygen breathing) measurements in the endotracheal tube. The surfactant-treated animals showed significantly improved gas mixing efficiency in the lung with improved alveolar ventilation. Single exponential washout pattern dominated in both groups. Adequate functional residual capacity was established earlier after birth in the treated lambs than in the control animals. Lung mechanics in the treated group showed significant improvement in dynamic lung compliance. Surfactant treatment also improved gas exchange and reduced respirator pressure requirement. We speculate that the main functional effect of surfactant treatment in preterm lambs at risk to develop hyaline membrane disease is to maintain the patency of the peripheral airways in the lung, which improves diffusive gas mixing, alveolar ventilation, and gas exchange. The techniques used in this study should also be useful to evaluate lung function in preterm human infants after specific adaptation of the equipment size.