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H I Modell

Publications and source records attributed to H I Modell.

At least 19 recordsLinked to original sources
PubMed2000

How to help students understand physiology? Emphasize general models.

Students generally approach topics in physiology as a series of unrelated phenomena that share few underlying principles. In many students' view, the Fick equation for cardiac output is fundamentally different from a renal clearance equation. If, however, students recognize that these apparently different situations can be viewed as examples of the same general conceptual model (e.g., conservation of mass), they may gain a more unified understanding of physiological systems. An understanding of as few as seven general models can provide students with an initial conceptual framework for analyzing most physiological systems. The general models deal with control systems, conservation of mass, mass and heat flow, elastic properties of tissues, transport across membranes, cell-to-cell communication, and molecular interaction.

Cardiovascular Physiological Phenomena↗
PubMed2000

Helping undergraduates repair faulty mental models in the student laboratory.

Over half of the undergraduate students entering physiology hold a misconception concerning how breathing pattern changes when minute ventilation increases. Repair of this misconception was used as a measure to compare the impact of three student laboratory protocols on learning by 696 undergraduate students at 5 institutions. Students were tested for the presence of the misconception before and after performing a laboratory activity in which they measured the effect of exercise on tidal volume and breathing frequency. The first protocol followed a traditional written "observe and record" ("cookbook") format. In the second treatment group, a written protocol asked students to complete a prediction table before running the experiment ("predictor" protocol). Students in the third treatment group were given the written "predictor" protocol but were also required to verbalize their predictions before running the experiment ("instructor intervention" protocol). In each of the three groups, the number of students whose performance improved on the posttest was greater than the number of students who performed less well on the posttest (P < 0.001). Thus the laboratory protocols helped students correct the misconception. However, the remediation rate for students in the "instructor intervention" group was more than twice that observed for the other treatment groups (P < 0.001). The results indicate that laboratory instruction is more effective when students verbalize predictions from their mental models than when they only "discover" the outcome of the experiment.

Exercise↗
PubMed1996

Preparing students to participate in an active learning environment.

Most students have spent the majority of their school career in passive learning environments in which faculty were disseminators of information, and students were required to memorize information or use specified algorithms to "solve problems." In an active learning environment, students are encouraged to engage in the process of building and testing their own mental models from information that they are acquiring. In such a learner-centered environment, faculty become facilitators of learning, and students become active participants, engaging in a dialogue with their colleagues and with the instructor. To create a successful active learning environment, both faculty and students must make adjustments to what has been their respective "traditional" roles in the classroom. For the instructor who is committed to promoting active learning, the challenge lies in helping students understand the necessity of becoming active colleagues in learning. This process can be facilitated if the curriculum includes exercises to direct students' attention to a number of issues that impact their learning. This paper describes four such exercises designed to help students form appropriate course expectations, recognize the need for seeking clarification when communicating, recognize the role of personal experience in building mental models, and become familiar with study aids for building formal models.

Communication↗
PubMed1991

Influence of anticholinesterase on distribution of ventilation and gas exchange.

This project was designed to titrate the influence of pyridostigmine injected intraarterially on pulmonary resistance and gas exchange in pigs and dogs. Pyridostigmine at 1 mg/kg reduced red blood cell cholinesterase activity 28-35% that was not significantly reduced further with doses up to 9 mg/kg. Plasma cholinesterase was reduced by 80% in the dog and 40% in the pig with 1 mg/kg of pyridostigmine and with 3 mg/kg it was reduced to 40% in the pig and 10% in the dog. Higher doses had no further significant effect. Breathing resistance (cm H2O/l/s) in the pig was doubled as a linear function with 9 mg/kg pyridostigmine. In the dog, breathing resistance went to a maximum of 8 cm H2O/l/s from a control value of 1 cm H2O/l/s with 3 mg/kg of pyridostigmine but did not go higher with doses up to 9 mg/kg. PaO2 was reduced by approximately 20% in the pig and 15% in the dog with pyridostigmine doses of 6-9 mg/kg. These experiments indicate that significant alterations in pulmonary function do not occur until acute dosages in the range of 3-6 mg/kg are reached. Furthermore, acute administration of large doses of pyridostigmine results in salivation and gastrointestinal stimulation well in advance of any impairment of respiratory function.

Airway Resistance↗
PubMed1990

Localization of inflammation with 111In IgG and 99Tcm albumin colloid labelled leukocytes in a rabbit model.

Localization of inflammation with two recently described radiotracers, 111In-labelled polyclonal IgG and 99Tcm albumin colloid labelled leukocytes (Tc-WBC), was studied. Accumulation of activity was compared with 111In-labelled leukocytes (In-WBC) using 131I human serum albumin as a control. Ratios of activity in a chemically induced abscess in the thigh of rabbits compared with normal muscle tissue were measured. The results showed that all agents localize in inflammation but Tc-WBC consistently localizes to a greater degree than the other agents. At 2 h the inflammed-to-normal ratios for Tc-WBC were 4, IgG 2.1, albumin 1.9 and In-WBC 1.7. The pattern of the ratios remained similar over the 18 h period of the study. The short time in which leukocytes can be labelled and the quality of the images obtained suggest that Tc-WBC imaging is the method of choice for this model.

Animals↗
PubMed1989

Can technology replace live preparations in student laboratories?

We have seen a trend in recent years toward reduction or elimination of student laboratories in many physiology curricula. Some departments have sought "alternatives" to live preparations in an attempt to retain an active learning experience for students. However, it seems as if few departments have seriously examined the specific educational objectives of their student laboratories to determine whether alternatives exist that will allow these objectives to be met. Technology certainly offers a variety of ways to provide active learning experiences. In some instances, technological approaches can be used to address the same educational objectives as traditional laboratories, while in others these objectives may be partially met by use of technology. However, it is important to recognize that some educational objectives can only be achieved through first-hand experience with live preparations.

Computer Simulation↗
PubMed1985

Influence of G-suit abdominal bladder inflation on gas exchange during +GZ stress.

Available data relating duration of +GZ stress to blood gas exchange status is limited. Furthermore, studies focusing on pulmonary gas exchange during +GZ stress when abdominal restriction is imposed have yielded conflicting results. To examine the time course of blood gas changes occurring during exposure to +GZ stress in dogs and the influence of G-suit abdominal bladder inflation on this time course, seven spontaneously breathing pentobarbital-anesthetized adult mongrel dogs were exposed to 60 s of up to +5 GZ stress with and without G-suit abdominal bladder inflation. Arterial and mixed venous blood were sampled for blood gas analysis during the first and last 20 s of the exposure and at 3 min postexposure. Little change in blood gas status was seen at +3 GZ regardless of G-suit status. However, with G-suit inflation, arterial PO2 fell by a mean of 14.7 Torr during the first 20 s at +4 Gz (P less than 0.01, t test) and 20.6 Torr at +5 GZ (P less than 0.01). It continued to fall an additional 10 Torr during the next 40 s at both +4 and +5 GZ. Arterial PO2 was still 5-10 Torr below control values (P less than 0.05) 3 min postexposure. A second series of experiments paralleling the first focused on blood gas status during repeated exposure to acceleration. Blood gas status was assessed in five dogs during the late 20 s of two 60-s exposures separated by 3 min at 0 GZ. No significant differences between the initial and repeated exposures were detected. The data indicate that G-suit abdominal bladder inflation promotes increased venous admixture.

Acceleration↗
PubMed1984

Influence of the chest wall on regional intrapleural pressure during acceleration (+Gz) stress.

The purpose of this study was to determine the influence of altered chest wall compliance, chest wall shape, and G-suit abdominal bladder inflation on regional intrapleural pressure (Ppl) during +Gz stress. Experiments were conducted in two species (9 dogs, 10 pigs) so that data relating to a spectrum of chest wall characteristics could be obtained. Anesthetized animals were exposed to +Gz levels ranging from 1 to + 5 Gz. Regional Ppl was monitored at 2-4 sites during spontaneous breathing with and without G-suit abdominal bladder inflation and after removal of active chest wall muscular tone by sacrificing the animal. In the dog, Ppl became more negative in the upper and middle thoracic regions with +Gz stress (-1.63 and -1.66 cm H2O.G-1, respectively), but, in the lower thorax, Ppl increased slightly (0.05 cm H2O.G-1). When active muscular tone was removed, the rate of Ppl change increased in the upper thorax (-2.55 cm H2O.G-1), but not in more dependent regions. In the pig, Ppl became more negative with +Gz stress (upper = -3.3; middle = -1.99; lower = -2.16 cm H2O.G-1), and without active muscular tone, the rate of Ppl change tended to increase in all regions (upper = -4.3; middle = -3.47; lower = -2.97 cm H2O.G-1). With G-suit application in both species, Ppl increased toward or exceeded control values at all levels. Results indicate that chest wall characteristics play a significant role in determining regional Ppl during +Gz stress.

Acceleration↗
PubMed1982

Limitations of Kr-81m for quantitation of ventilation scans.

Predictions of Kr-81m behavior in the lungs have been based on a single-compartment model of well-mixed gas. To determine the validity of this model, anesthetized, paralyzed dogs were ventilated mechanically over a wide range of ventilations with Kr-81m in the inspirate. Averaged data obtained from 1.5- to 2-min images were compared with the model's predictions. Krypton-81m concentration appeared more linearly related to ventilation than the model predicts. This suggests that the Kr-81m may not be distributed to the entire resident gas volume or that its distribution changes with lung volume. Estimation of end-expiratory volume (FRC)--based on the tidal volume and the maximum-to-minimum count ratio over the lung during gated acquisitions--underestimated the true FRC by about 40%. The magnitude of error depended upon the combination of tidal volume and frequency and the inspiratory time. Thus, Kr-81m does not mix well with resident lung gas, and the well-mixed, single-compartment model is not a good predictor of Kr-81m behavior in the lung.

Animals↗
PubMed1981

Functional aspects of canine bronchial-pulmonary vascular communications.

Experiments in anesthetized open-chest dogs indicated that blood from the canine bronchial circulation may drain into both the arterial and venous sides of the alveolar drain into both the arterial and venous sides of the alveolar vessel bed. Evan's blue dye injected into the systemic circulation appeared in the effluent from a left lower lobe pulmonary arterial segment in which inflow was stopped with a snare and outflow through the alveolar vessel bed was stopped by maintaining zone 1 conditions. To determine the influence of mean systemic arterial pressure on lobar bronchial flow, flows from arterial and venous cannulas were measured at different mean systemic arterial pressures (lung volume history constant). Influence of lung volume and transpulmonary pressure (Ptp) change were each examined utilizing the hysteresis characteristics of the lung pressure-volume curve. Mean total flows ranged from 2.26 to 5.26 ml/min with 43.61% draining through the arterial side. Flow decreased with lower systemic arterial pressure, high Ptp, and higher lung volume. Distribution of flow was influenced only by lung volume changes. Results indicate that the communication sites contributing to the arterial drainage are located within the alveolar vessel bed. Since bronchial flow drains to both sides of the alveolar vessel bed, it must be considered when interpreting results from "isolated" pulmonary circulation preparations.

Animals↗
PubMed1979

Effects of inspiratory flow pattern on gas exchange in normal and abnormal lungs.

To study the influence of inspiratory flow pattern on gas exchange in normal and abnormal lungs, 15 dogs were mechanically ventilated with the ascending or descending half of a rectified sine-wave flow pattern during pentobarbital anesthesia. Blood-gas status and cardiac output were monitored during each pattern. Pulmonary injury was induced in 9 animals by prior injection of oleic acid into the right atrium. Ventilation was with room air and zero end-expiratory pressure. Although no significant difference was seen between the patterns in animals with normal lung function (PaO2 greater than 85 Torr on the ascending pattern), the descending pattern resulted in a rise in PaO2 of about 10% (P less than 0.01) in animals with abnormal lung function (PaO2 less than 70 Torr on the ascending pattern). No significant difference in PaCO2 or cardiac output was detected when flow pattern was changed in any of the animals. We conclude that inspiratory flow pattern is not a significant factor when ventilating normal lungs, but may improve gas exchange significantly when severe ventilation-perfusion maldistributions exist.

Animals↗