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Measurement of rates of oxygen consumption ( Mo 2 ) in small aquatic embryos or larvae (<1 mm) in response to altered environmental conditions has traditionally been challenging. Here, using modifications of a commercially available fluorescent optode flow-through cell (FTC; PreSens FTC-PSt3) and routine laboratory supplies (syringes, stopcocks, tubing), we have constructed a manual intermittent flow respirometer (MIFR) that allows measurement of Mo 2 in small numbers of individuals when sequentially exposed to different environmental conditions (e.g., changes in seawater pH) through a gravity-driven media replacement perfusion system. We first show that the FTC can be used in "static" mode while incubating small numbers of embryos/larvae contained within the planar oxygen sensor (POS) chamber with Nitex filters. We then demonstrate the use of the MIFR by exposing larval echinoderms ( Fellaster zelandiae, Evechinus chloroticus, and Centrostephanus rodgersii) to seawater equilibrated with elevated CO 2 and measured Mo 2 during acute and chronic exposure to hypercapnia. This MIFR method will allow investigators to address questions regarding the respiratory physiology of small aquatic animals, such as the thresholds for metabolic depression in embryonic and larval forms. NEW & NOTEWORTHY A manual intermittent flow respirometer (MIFR), allowing media exchange in a flow-through cell containing small aquatic organisms, permits repeated measurement of Mo 2 of individuals not only in a single medium (e.g., technical replication), but also in different media (here, high CO 2 -equilibrated seawater), enabling measurement of acute physiological responses to changed conditions. This versatile technique has wide-ranging implications for the study of the Mo 2 response of aquatic organisms in the face of climate change.

A sedentary lifestyle and lack of physical activity are well-established risk factors for chronic disease and adverse health outcomes. Thus, there is enormous interest in measuring physical activity in biomedical research. Many consumer physical activity monitors, including Basis Health Tracker, BodyMedia Fit, DirectLife, Fitbit Flex, Fitbit One, Fitbit Zip, Garmin Vivofit, Jawbone UP, MisFit Shine, Nike FuelBand, Polar Loop, Withings Pulse O 2 , and others have accuracies similar to that of research-grade physical activity monitors for measuring steps. This review focuses on the unprecedented opportunities that consumer physical activity monitors offer for human physiology and pathophysiology research because of their ability to measure activity continuously under real-life conditions and because they are already widely used by consumers. We examine current and potential uses of consumer physical activity monitors as a measuring or monitoring device, or as an intervention in strategies to change behavior and predict health outcomes. The accuracy, reliability, reproducibility, and validity of consumer physical activity monitors are reviewed, as are limitations and challenges associated with using these devices in research. Other topics covered include how smartphone apps and platforms, such as the Apple ResearchKit, can be used in conjunction with consumer physical activity monitors for research. Lastly, the future of consumer physical activity monitors and related technology is considered: pattern recognition, integration of sleep monitors, and other biosensors in combination with new forms of information processing., (Copyright © 2017 the American Physiological Society.)

One of the most effective ways of engaging students of physiology and medicine is through laboratory demonstrations and case studies that combine 1) the use of equipment, 2) problem solving, 3) visual representations, and 4) manipulation and interpretation of data. Depending on the measurements made and the type of test, laboratory demonstrations have the added benefit of being able to show multiple organ system integration. Many research techniques can also serve as effective demonstrations of integrative human physiology. The "Duffin" hyperoxic rebreathing test is often used in research settings as a test of central respiratory chemosensitivity and cerebrovascular reactivity to CO2. We aimed to demonstrate the utility of the hyperoxic rebreathing test for both respiratory and cerebrovascular responses to increases in CO2 and illustrate the integration of the respiratory and cerebrovascular systems. In the present article, methods such as spirometry, respiratory gas analysis, and transcranial Doppler ultrasound are described, and raw data traces can be adopted for discussion in a tutorial setting. If educators have these instruments available, instructions on how to carry out the test are provided so students can collect their own data. In either case, data analysis and quantification are discussed, including principles of linear regression, calculation of slope, the coefficient of determination (R(2)), and differences between plotting absolute versus normalized data. Using the hyperoxic rebreathing test as a demonstration of the complex interaction and integration between the respiratory and cerebrovascular systems provides senior undergraduate, graduate, and medical students with an advanced understanding of the integrative nature of human physiology., (Copyright © 2016 The American Physiological Society.)

Since its inception in 19th-century Germany, the physiology laboratory has been a complex and expensive research enterprise involving experts in various fields of science and engineering. Physiology research has been critically dependent on cutting-edge technological support of mechanical, electrical, optical, and more recently computer engineers. Evolution of modern experimental equipment is constrained by lack of direct communication between the physiological community and industry producing this equipment. Fortunately, recent advances in open source technologies, including three-dimensional printing, open source hardware and software, present an exciting opportunity to bring the design and development of research instrumentation to the end user, i.e., life scientists. Here we provide an overview on how to develop customized, cost-effective experimental equipment for physiology laboratories.

In the present study, a practical activity is proposed to adopt an experimental approach to demonstrate the relationship between the equilibrium potential for K(+) and transmembrane electrical potential without glass micropipettes. A conventional setup for recording contractile activity of isolated smooth muscle preparations was used based on the events elegantly described by Somlyo and Somlyo in the 1960s. They showed that, in response to a given stimulus, smooth muscle cells may contract, recruiting electromechanical or pharmacomechanical coupling by mechanisms that involve, or not, changes in transmembrane potential, respectively. By means of contractions and relaxations of a ring-like preparation from the rat mesenteric artery, it is possible to observe the functional consequences of handling K(+) concentration in the extracellular compartment and the effects caused by opening K(+) channels in that preparation, which are significant when the cell membrane establishes an electrical potential difference between intra- and extracellular compartments (driven mainly by K(+) permeability under resting conditions). The effects observed by students fit well with values predicted by Nernst and Goldman-Hodgin-Katz equations, and we demonstrated that the activity is able to improve students' comprehension regarding basic principles of bioelectricity.

The Einthoven triangle is central to the field of electrocardiography, but the concept of cardiac vectors is often a difficult notion for students to grasp. To illustrate this principle, we constructed a device that recreates the conditions of an ECG reading using a battery to simulate the electrical vector of the heart and three voltmeters for the main electrocardiographic leads. Requiring minimal construction with low cost, this device provides hands-on practice that enables students to rediscover the principles of the Einthoven triangle, namely, that the direction of the cardiac dipole can be predicted from the deflections in any two leads and that lead I + lead III = lead II independent of the position of heart's electrical vector. We built a total of 6 devices for classes of 30 students and tested them in the first-year Human Physiology course at the University of California-Davis School of Medicine. Combined with traditional demonstrations with ECG machines, this equipment demonstrated its ability to help medical students obtain a solid foundation of the basic principles of electrocardiography.

The Virtual Physiology of Exercise Laboratory (VPEL) program was created to simulate the test design, data collection, and analysis phases of selected exercise physiology laboratories. The VPEL program consists of four modules: 1) cardiovascular, 2) maximal O(2) consumption (Vo(2max)), 3) lactate and ventilatory thresholds, and 4) respiratory exchange ratio. The purpose of this investigation was to compare student learning from the VPEL program with that from traditional "hands-on" exercise physiology laboratory activities. Student participants from the spring 2009 Integrated Fitness Programming course were randomly assigned to either experimental group 1 or group 2. Group 1 completed a hands-on version of a typical Vo(2max) laboratory activity, whereas group 2 completed the VPEL Vo(2max) module. Both groups then completed the same assessment to evaluate their understanding of Vo(2max) laboratory concepts. Group 1 then completed the VPEL lactate and ventilatory threshold module, whereas group 2 completed a hands-on version of that same activity. Both groups then completed the same assessment to evaluate their understanding of lactate and ventilatory threshold laboratory concepts. Mean Vo(2max) assessment scores were 86.39 +/- 4.13 and 85.64 +/- 6.72 and mean lactate and ventilatory threshold assessment scores were 85.50 +/- 8.05 and 86.15 +/- 6.45 for groups 1 and 2, respectively. These findings lend additional support to the following conclusion of similar investigations (2, 4, 6): that virtual laboratories instruct students as effectively as hands-on laboratories.

Students generally approach topics in physiology as a series of unrelated phenomena that share few underlying principles. However, if students recognized that the same underlying principles can be used to explain many physiological phenomena, they may gain a more unified understanding of physiological systems. To address this concern, we developed a simple, inexpensive, and easy to build model to demonstrate the underlying principles regarding Starling's Law of the Heart as well as lung and arterial elastic recoil. A model was chosen because models significantly enhance student understanding. Working with models also encourages research-oriented learning and helps our students understand complex ideas. Students are drawn into discussion by the power of learning that is associated with manipulating and thinking about objects. Recognizing that the same underlying principles can be used to explain many physiological phenomena may help students gain a more complete understanding of physiological systems.

Accelerometers are often used to quantify the acceleration of the body in arbitrary units (counts) to measure physical activity (PA) and to estimate energy expenditure. The present study investigated whether the identification of types of PA with one accelerometer could improve the estimation of energy expenditure compared with activity counts. Total energy expenditure (TEE) of 15 subjects was measured with the use of double-labeled water. The physical activity level (PAL) was derived by dividing TEE by sleeping metabolic rate. Simultaneously, PA was measured with one accelerometer. Accelerometer output was processed to calculate activity counts per day (AC(D)) and to determine the daily duration of six types of common activities identified with a classification tree model. A daily metabolic value (MET(D)) was calculated as mean of the MET compendium value of each activity type weighed by the daily duration. TEE was predicted by AC(D) and body weight and by AC(D) and fat-free mass, with a standard error of estimate (SEE) of 1.47 MJ/day, and 1.2 MJ/day, respectively. The replacement in these models of AC(D) with MET(D) increased the explained variation in TEE by 9%, decreasing SEE by 0.14 MJ/day and 0.18 MJ/day, respectively. The correlation between PAL and MET(D) (R(2) = 51%) was higher than that between PAL and AC(D) (R(2) = 46%). We conclude that identification of activity types combined with MET intensity values improves the assessment of energy expenditure compared with activity counts. Future studies could develop models to objectively assess activity type and intensity to further increase accuracy of the energy expenditure estimation.

Lower body negative pressure (LBNP) is an established and important technique used to physiologically stress the human body, particularly the cardiovascular system. LBNP is most often used to simulate gravitational stress, but it has also been used to simulate hemorrhage, alter preload, and manipulate baroreceptors. During experimentation, the consequences of LBNP and the reflex increases in heart rate and blood pressure can be manipulated and observed in a well-controlled manner, thus making LBNP an important research tool. Numerous laboratories have developed LBNP devices for use in research settings, and a few devices are commercially available. However, it is often difficult for new users to find adequately described design plans. Furthermore, many available plans require sophisticated and expensive materials and/or technical support. Therefore, we have created an affordable design plan for a LBNP chamber. The purpose of this article was to share our design template with others. In particular, we hope that this information will be of use in academic and research settings. Our pressure chamber has been stress tested to 100 mmHg below atmospheric pressure and has been used successfully to test orthostatic tolerance and physiological responses to -50 mmHg.

The synchronization of cardiac and locomotor rhythms has been suggested to enhance the efficiency of arterial delivery to active muscles during rhythmic exercise, but direct evidence showing such a functional role has not been provided. In this study, we tested the hypothesis that the heartbeat is coupled with intramuscular pressure (IMP) changes so as to time the delivery of blood through peripheral tissues when the IMP is lower. To this end, we developed a computer-controlled, dynamic, thigh cuff occlusion device that enables bilateral thigh cuffs to repeatedly inflate and deflate, one side after the other, to simulate rhythmic IMP changes during bipedal locomotion. Nine healthy subjects were examined, and three different occlusion pressures (50, 80, and 120 mmHg) were applied separately to the thigh cuffs of normal subjects while they were sitting. Alternate occlusions of the bilateral thigh cuffs administered at the frequency of the mean heart rate produced significant phase synchronization between the cardiac and cuff-occlusion rhythms when 120 mmHg pressure was applied. However, synchronization was not observed when the occlusion pressure was 50 or 80 mmHg. During synchronization, heartbeats were most likely to occur in phases that did not include overlap between the peak arterial flow velocity in the thigh and elevated cuff pressure. We believe that phase synchronization occurs so that the cardiac cycle is timed to deliver blood through the lower legs when IMP is not maximal. If this can be extrapolated to natural locomotion, synchronization between cardiac and locomotor activities may be associated with the improved perfusion of exercising muscles.

Using Bluetooth wireless technology, we developed an implantable telemetry system for measurement of the left ventricular pressure-volume relation in conscious, freely moving rats. The telemetry system consisted of a pressure-conductance catheter (1.8-Fr) connected to a small (14-g) fully implantable signal transmitter. To make the system fully telemetric, calibrations such as blood resistivity and parallel conductance were also conducted telemetrically. To estimate blood resistivity, we used four electrodes arranged 0.2 mm apart on the pressure-conductance catheter. To estimate parallel conductance, we used a dual-frequency method. We examined the accuracy of calibrations, stroke volume (SV) measurements, and the reproducibility of the telemetry. The blood resistivity estimated telemetrically agreed with that measured using an ex vivo cuvette method (y=1.09x - 11.9, r2= 0.88, n=10). Parallel conductance estimated by the dual-frequency (2 and 20 kHz) method correlated well with that measured by a conventional saline injection method (y=1.59x - 1.77, r2= 0.87, n=13). The telemetric SV closely correlated with the flowmetric SV during inferior vena cava occlusions (y=0.96x + 7.5, r2=0.96, n=4). In six conscious rats, differences between the repeated telemetries on different days (3 days apart on average) were reasonably small: 13% for end-diastolic volume, 20% for end-systolic volume, 28% for end-diastolic pressure, and 6% for end-systolic pressure. We conclude that the developed telemetry system enables us to estimate the pressure-volume relation with reasonable accuracy and reproducibility in conscious, untethered rats.

Convective fluid motion through artery walls aids in the transvascular transport of macromolecules. Although many measurements of convective filtration have been reported, they were all obtained under constant transmural pressure. However, arterial pressure in vivo is pulsatile. Therefore, experiments were designed to compare filtration under steady and pulsatile pressure conditions. Rabbit carotid arteries were cannulated and excised from male New Zealand White rabbits anesthetized with pentobarbitol sodium (30 mg/kg i.v. administered). Hydraulic conductance was measured in cannulated excised rabbit carotid arteries at steady pressure. Next, pulsatile pressure trains were applied within the same vessels, and, simultaneously, arterial distension was monitored using Optical coherence tomography (OCT). For each pulse train, the volume of fluid lost through filtration was measured (subtracting volume change due to residual distension) and compared with that predicted from steady pressure measurements. At 60- and 80-mmHg baseline pressures, the experimental filtration volumes were significantly increased compared with those predicted for steady pressure (P < 0.05). OCT demonstrated that the excess fluid volume loss was significantly greater than the volume that would be lost through residual distension (P < 0.05). After 30 s, the magnitude of the excess of fluid loss was reduced. These results suggest that sudden onset of pulsatile pressure may cause changes in arterial interstitial hydration.

A simple, noninvasive, and economical home-made respirometer has been used to determine the standard metabolism of goldfish. The apparatus has been tested on several fishes and has proved its accuracy in determining a mass effect on standard metabolism. The apparatus can be made easily by middle school, high school, and undergraduate students and can be used to introduce them to basic concepts in animal physiology and in biological statistics.

Human bioartificial muscles (HBAMs) are tissue engineered by suspending muscle cells in collagen/MATRIGEL, casting in a silicone mold containing end attachment sites, and allowing the cells to differentiate for 8 to 16 days. The resulting HBAMs are representative of skeletal muscle in that they contain parallel arrays of postmitotic myofibers; however, they differ in many other morphological characteristics. To engineer improved HBAMs, i.e., more in vivo-like, we developed Mechanical Cell Stimulator (MCS) hardware to apply in vivo-like forces directly to the engineered tissue. A sensitive force transducer attached to the HBAM measured real-time, internally generated, as well as externally applied, forces. The muscle cells generated increasing internal forces during formation which were inhibitable with a cytoskeleton depolymerizer. Repetitive stretch/relaxation for 8 days increased the HBAM elasticity two- to threefold, mean myofiber diameter 12%, and myofiber area percent 40%. This system allows engineering of improved skeletal muscle analogs as well as a nondestructive method to determine passive force and viscoelastic properties of the resulting tissue.

Demonstrating action potentials during class experiments is very educational for science students. It is not easy, however, to obtain a stable intracellular recording of action potentials from the conventionally used skeletal muscle cells, because the tip of a glass microelectrode often comes out or breaks due to muscle contraction. Here, I present a much simpler recording method using a flexible polyethylene electrode with a wide orifice (approximately 1 mm) for a bullfrog heart beating on automaticity. Extracellular recordings of action potentials (electrocardiogram) can be obtained by placing an electrode on the cardiac surface, and transmembrane potentials can be obtained by rupturing the membrane with negative pressure, i.e., whole cell configuration. Once attached to the heart by suction, the polyethylene electrode does not easily come off during contraction of the heart. Perfusion of the heart via the postcaval vein offers us opportunities for observing the effects of either changing ionic compositions of solutions or applying drugs. The techniques shown here provide a simple and convenient way to perform a variety of class experiments.

In the midbrain sound localization pathway of the barn owl, a map of auditory space is synthesized in the external nucleus of the inferior colliculus (ICX) and transmitted to the optic tectum. Early auditory experience shapes these maps of auditory space in part by modifying the tuning of the constituent neurons for interaural time difference (ITD), a primary cue for sound-source azimuth. Here we show that these adaptive modifications in ITD tuning correspond to changes in the pattern of connectivity within the inferior colliculus. We raised owls with an acoustic filtering device in one ear that caused frequency-dependent changes in sound timing and level. As reported previously, device rearing shifted the representation of ITD in the ICX and tectum but not in the primary source of input to the ICX, the central nucleus of the inferior colliculus (ICC). We applied the local anesthetic lidocaine (QX-314) iontophoretically in the ICC to inactivate small populations of neurons that represented particular values of frequency and ITD. We measured the effect of this inactivation in the optic tecta of a normal owl and owls raised with the device. In the normal owl, inactivation at a critical site in the ICC eliminated responses in the tectum to the frequency-specific ITD value represented at the site of inactivation in the ICC. The location of this site was consistent with the known pattern of ICC-ICX-tectum connectivity. In the device-reared owls, adaptive changes in the representation of ITD in the tectum corresponded to dramatic and predictable changes in the locations of the critical sites of inactivation in the ICC. Given that the abnormal representation of ITD in the tectum depended on frequency and was likely conveyed directly from the ICX, these results suggest that experience causes large-scale, frequency-specific adjustments in the pattern of connectivity between the ICC and the ICX.

Inhaled concentration (C), minute volume (MV), and exposure duration (T) are factors that may affect the uptake of ozone (O(3)) within the respiratory tract. Ten healthy adult nonsmokers participated in four sessions, inhaling 0.2 or 0.4 ppm O(3) through an oral mask while exercising continuously to elicit a MV of 20 l/min for 60 min or 40 l/min for 30 min. In each session, fractional absorption (FA) was determined on a breath-by-breath basis as the ratio of O(3) uptake to the inhaled O(3) dose. The mean +/- SD value of FA for all breaths was 0.86 +/- 0.06. Although C, MV, and T all had statistically significant effects on FA (P < 0.0001, P = 0.004, and P = 0.026, respectively), the magnitudes of these effects were small compared with intersubject variability. For an average subject, a 0. 05 change in FA would require that C change by 1.3 ppm, MV change by 46 l/min, or T change by 1.7 h. It is concluded that inhaled dose is a reasonable surrogate for the actual dose delivered to a particular subject during O(3) exposures of <2 h, but it is not a reasonable surrogate when comparisons are made between individuals.

The device described in this study uses functionally variable dead space to keep effective alveolar ventilation constant. It is capable of maintaining end-tidal PCO(2) and PO(2) within +/-1 Torr of the set value in the face of increases in breathing above the baseline level. The set level of end-tidal PCO(2) or PO(2) can be independently varied by altering the concentration in fresh gas flow. The device comprises a tee at the mouthpiece, with one inlet providing a limited supply of fresh gas flow and the other providing reinspired alveolar gas when ventilation exceeds fresh gas flow. Because the device does not depend on measurement and correction of end-tidal or arterial gas levels, the response of the device is essentially instantaneous, avoiding the instability of negative feedback systems having significant delay. This contrivance provides a simple means of holding arterial blood gases constant in the face of spontaneous changes in breathing (above a minimum alveolar ventilation), which is useful in respiratory experiments, as well as in functional brain imaging where blood gas changes can confound interpretation by influencing cerebral blood flow.

Although several factors are known to influence nonuniformity of ventilation, including lung mechanical properties (regional structure and compliance), external factors (chest wall, pleural pressure, heart), and ventilatory parameters (tidal and preinspiratory volume, flow rate), their relative contributions are poorly understood. We studied five excised, unperfused, canine right-middle lobes under varied levels of tidal volume (VT), thus eliminating many factors affecting heterogeneity. Multiple-breath washouts of N(2) were analyzed for anatomic dead space volume (VD(anat)), nonuniformity of N(2) washout, and nonuniformity between joined acinar regions vs. that occurring between larger joined regions. Approximately 80% of ventilation heterogeneity was found among joined acinar regions at resting levels of VT, but increasing VT reduced intra-acinar heterogeneity to about 25% of that found at resting levels. Increasing VT had essentially no effect on VD(anat) and heterogeneity among larger joined regions. The results indicate that the magnitude of VT is a major influence on the dominant intra-acinar component of ventilation heterogeneity and that VT effects on VD(anat) are likely due to perfusion and/or influences normally external to the lobar structure.

An open-circuit (OpCirc) acetylene uptake cardiac output (QT) method was modified for use during exercise. Two computational techniques were used. OpCirc1 was based on the integrated uptake vs. end-tidal change in acetylene, and OpCirc2 was based on an iterative finite difference modeling method. Six subjects [28-44 yr, peak oxygen consumption (VO(2)) = 120% predicted] performed cycle ergometry exercise to compare QT using OpCirc and direct Fick methods. An incremental protocol was repeated twice, separated by a 10-min rest, and subsequently subjects exercised at 85-90% of their peak work rate. Coefficient of variation of the OpCirc methods and Fick were highest at rest (OpCirc1, 7%, OpCirc2, 12%, Fick, 10%) but were lower at moderate to high exercise intensities (OpCirc1, 3%, OpCirc2, 3%, Fick, 5%). OpCirc1 and OpCirc2 QT correlated highly with Fick QT (R(2) = 0.90 and 0.89, respectively). There were minimal differences between OpCirc1 and OpCirc2 compared with Fick up to moderate-intensity exercise (<70% peak VO(2)); however, both techniques tended to underestimate Fick at >70% peak VO(2). These differences became significant for OpCirc1 only. Part of the differences between Fick and OpCirc methods at the higher exercise intensities are likely related to inhomogeneities in ventilation and perfusion matching (R(2) = 0.36 for Fick - OpCirc1 vs. alveolar-to-arterial oxygen tension difference). In conclusion, both OpCirc methods provided reproducible, reliable measurements of QT during mild to moderate exercise. However, only OpCirc2 appeared to approximate Fick QT at the higher work intensities.

In this investigation a simplified variable-pressure paired neck chamber was developed as a practical alternative to traditional neck collar designs used to study the arterial baroreceptor reflex in humans. The purpose of this new design was to extend the use of the noninvasive neck chamber method of baroreceptor investigation to teachers of physiology. Performance tests indicate that these new chambers are capable of delineating the stimulus-response relationship for both the blood pressure baroreflex [sensitivity = 0.425 +/- 0.13 mmHg mean arterial pressure (MAP)/mmHg neck chamber pressure (NCP); range = 24.9 +/- 4.6 mmHg MAP] and the heart rate baroreflex (sensitivity 0.273 +/- 0.12 beats.min-1.mmHg NCP-1; range = 16.7 +/- 6.8 beats/min). This was achieved by applying localized positive and negative air pressures to the carotid sinuses throughout the range from +60 to -60 mmHg in steps of 20 mmHg. This simplified neck chamber method offers distinct methodological advantages over traditional neck collars, making it a valuable tool for demonstrating baroreflex regulation of the circulation.

It has been observed for nearly 100 years that visually guided human movements appear to be composed of submovements, intermittently executed overlapping segments. This paper presents experiments to investigate the pervasiveness of movement intermittency and, in particular, whether it is exclusively due to visual feedback. With and without visual feedback, human subjects were asked to 1) move with constant velocity and 2) draw elliptical figures on a phase-plane display (showing velocity vs. position) that required cyclic movements at different frequencies. In both tasks, we found that removal of visual feedback did not significantly change movement intermittency. Subjects were unable to generate movements at constant speed. In addition, subjects moved less smoothly when drawing slower phase-plane ellipses. Furthermore, elliptical phase-plane figures were not always drawn at the frequency suggested by the center of the display. Instead, subjects moved more slowly than the tall (fast) ellipse displays suggested, and faster than the wide (slow) displays suggested. These results show that 1) movement intermittency is not exclusively due to visual feedback and 2) may in fact be a fundamental feature of movement behavior.

We describe and use a CO2 diffusion pipette to produce a quickly reversible focal acidosis in the retrotrapezoid nucleus region of the rat brain stem. No tissue injection is made. Instead, artificial cerebrospinal fluid (aCSF) equilibrated with CO2 circulates within the micropipette, providing a source for continued CO2 diffusion into the tissue from the pipette tip. Tissue pH electrodes show the acidosis is limited to 500 micron from the tip. In controls (aCSF equilibrated with air), 1-min pipette perfusions increased tissue pH slightly and decreased phrenic nerve amplitude. In moderate- and high-CO2 groups (aCSF equilibrated with 50 or 100% CO2), 1-min perfusions significantly decreased tissue pH and increased phrenic nerve amplitude in a dose-dependent manner. The responses developed and reversed within minutes. Compared with our prior use of medullary acetazolamide injections to produce a focal acidosis, in this approach the acidosis 1) arises and reverses quickly and 2) its intensity can be varied. This allows study of sensitivity and mechanism. We conclude from this initial experiment that retrotrapezoid nucleus region chemoreceptors operate within the normal physiological range of CO2-induced tissue pH changes.

A new forced-swimming apparatus for determining maximum swimming time in mice was devised for use in the evaluation of the endurance capacity of Std and ddY and CDF1 mice after various diet and drug treatments. With the apparatus, a water current is generated by circulating water with a pump in a swimming pool. A spout and suction slit were contrived to generate a constant current while the strength of the current is regulated by a valve. The decrease in the leg-kicking intervals of mice accompanying the increase in the current speed confirmed that the workload is adjustable by regulation of the current speed. Compared with the number of forelimb strokes, that of the hindlimb kicks was greater. The swimming time until fatigue was observed to decrease with increasing current speed in the two strains of mice. As biochemical indexes, the blood lactate and muscle glycogen levels corroborated the correlation between current speed and increase in workload. These results indicate that the apparatus employed in the present study is suitable for the evaluation of the endurance capacity of mice and that is useful for detecting the effects of dietary differences and drug pretreatments on this capacity.

We have applied the phosphorescence lifetime technique (Vanderkooi, J. M., G. Maniara, T. J. Green, and D. F. Wilson. J. Biol. Chem. 262: 5476-5482, 1987) to determine oxygen tension in single capillaries of the hamster retractor muscle. Palladium meso-tetra(4-carboxyphenyl)porphine (10 mg/ml, pH 7.40, bound to bovine serum albumin) was used as the phosphorescent oxygen sensor. Our measurement system consisted of a microscope configured for epi-illumination, a strobe flash lamp, a 430-nm bandpass excitation filter, and a 630-nm cut-on emission filter. A rectangular diaphragm was used to limit the illumination field to 10 microns x 10 microns, and an end-window photomultiplier tube was used to detect the phosphorescence signal, which was then input to an analog-to-digital board in a personal computer. In vitro calibrations were carried out at 37 degrees C on samples flowing through a glass capillary tube (diameter, 300 microns) at four different O2 concentrations (0, 2.5, 5, and 7.5%). In vivo tests were carried out on arterioles, capillaries, and venules of the retractor muscle of anesthetized hamsters. The phosphorescent compound was administered by injection into a jugular vein (20 mg/kg). Phosphorescence decay curves were analyzed by a new model of heterogeneous oxygen distribution in the excitation/emission volume. Mean Po2 values and the local Po2 gradients within the excitation/ emission volume were calculated from phosphorescence life-times obtained from individual decay curves. The time course of Po2 obtained during 0.5-s measurement periods (5 decay curves at 0.1-s intervals) at a given site along a capillary indicated the presence of a gradient in Po2 within the plasma space between and near red blood cells. Similar Po2 gradients were also detected in arterioles and venules. Mean Po2 values for arterioles, capillaries, and venules over the 0.5-s observation period were 27 +/- 5, 14 +/- 2, and 11 +/- 3 (SD) mmHg, respectively. The magnitude of the Po2 gradient in the arterioles, capillaries, and venules was 6 +/- 1, 4 +/- 1, and 2 +/- 1 mmHg/micron, respectively.

Cyclic strain is known to influence many aspects of vascular cell biology, including macromolecular biosynthesis, cell proliferation, and cell morphology. The simulation of the cyclic strain associated with the vasculature in situ has been carried out mostly using devices that manipulated flat membranes on which the cells of choice are cultured. The purpose of this work was to create an apparatus wherein cyclic strains consistent with those found in native blood vessels could be applied to intact three-dimensional (tubular) specimens perfused ex vivo. The cyclic strain protocols using our apparatus may be any combination of axial stretch and twist. Concurrently, the perfusion flow and shear stress are controlled as desired. Vessel diameter, intraluminal pressure, volume flow, and regional strain are measured and stored on line. To illustrate the application of the device, we present hemodynamic and kinematic data collected from a human saphenous vein segment perfused under steady-flow conditions while subjected to cyclic stretch and twist.

This paper describes a method for measuring the increase in halide permeability of isolated airway epithelial cells induced by adenosine 3',5'-cyclic monophosphate (cAMP). Suspensions of isolated cells, known to contain the cystic fibrosis transmembrane conductance regulator (CFTR), were placed in the upper part of a Swinnex filter holder containing a filter with pores of 0.65 micron diameter. Medium was perfused over the cells at room temperature and collected at minute intervals following its passage through the filter. Experiments were performed on Calu-3 and T84 cells (human lung and colonic epithelial cell lines), primary cultures of dog and human tracheal epithelium, and Swiss 3T3 fibroblasts stably transfected with CFTR. In all cell types, addition of agents that elevate cAMP led to increases in the rates of loss of 36Cl and 125I. However, in human tracheal epithelial cells, warming the medium from room temperature to 37 degrees C was a more effective way of stimulating tracer efflux. Increases in efflux in response to either temperature or cAMP-elevating agents were inhibited by diphenylamine-2-carboxylate, a blocker of CFTR. Reproducible increases in tracer efflux were seen with as few as 10(6) cells. Cells that had been trypsinized off their culture dishes responded better than cells that had been scraped off, although treatment of scraped cells with trypsin enhanced their responsiveness to cAMP-elevating agents. Cystic fibrosis is characterized by the lack of a cAMP-activated Cl conductance in the apical membrane of airway epithlia.(ABSTRACT TRUNCATED AT 250 WORDS)

Although techniques for the short-term control of end-tidal gases exist, the lack of a satisfactory technique for longer-term control of the end-tidal gases has limited protracted physiological experiments of this nature. We have constructed a chamber in which subjects can be comfortable for many hours while having their end-tidal gas composition monitored and controlled. The system for controlling the end-tidal gas composition is based on a principle described by Swanson and Bellville (J. Appl. Physiol. 39: 377-385, 1975) in which end-tidal PO2 (PETO2) and PCO2 (PETCO2) are monitored and deviations of the actual PETO2 and PETCO2 (PETCO2) are monitored and deviations of the actual PETO2 and PETCO2 from the desired values are corrected by a feedback mechanism that adjusts the inspired gas composition accordingly. End-tidal and inspired gas tensions are measured via a nasal catheter connected to a mass spectrometer. A computer averages the end-tidal and inspired gas tensions and, at 5-min intervals, adjusts the gas composition inside the chamber. During 8 h of isocapnic hypoxia, the system held the 5-min average value for PETO2 within 2 Torr of the desired value (55 Torr) and the value for PETCO2 within 0.35 Torr of the desired value (the resting value for each subject) in four subjects.

To examine the effect of shear stress on hydraulic conductivity (Lp) of bovine aortic endothelial cell monolayers grown on polycarbonate filters, we developed a rotating disk system, which imposed a defined shear stress while Lp was measured. A 10-cmH2O pressure differential was applied to monolayers, and baseline Lp was established between 1.65 +/- 0.85 and 4.94 +/- 1.05 x 10(-7) cm.s-1.cmH2O-1. One-hour exposure to 10 dyn/cm2 shear stress caused a significant (P < 0.05) increase in Lp by 2.16-fold (+/- 0.42), and Lp remained elevated when shear stress was removed. Three-hour exposure to shear stresses between 0.1 and 20.0 dyn/cm2 revealed a threshold for shear-induced increase in Lp of 0.5 dyn/cm2. At 20 dyn/cm2, Lp initially decreased by 30% (+/- 13.4%, P < 0.05) and then increased to a level 3.76-fold (+/- 0.83, P < 0.05) greater than baseline Lp at 3 h. The shear-induced increase in Lp was reversed with dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP, 1 mM) and could be significantly (P < 0.05) inhibited when monolayers were preincubated with 0.3 mM DBcAMP, a concentration that did not significantly affect baseline Lp. Furthermore, preincubation with a general phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (1 mM), completely blocked the shear-induced increase in Lp. On the basis of these results, we conclude that shear stress alters endothelial Lp through a cellular mechanism involving signal transduction, not by a purely physical mechanism.

The accuracy of transit-time ultrasonic flow probes for measurement of regional blood flow and cardiac output was evaluated after long-term implantation in sheep. Transit-time flow probes (3, 4, 6, and 20 mm) accurately measured flow in vitro. Recalibration in vivo demonstrated that this accuracy was maintained after 1-9 mo of implantation on the left circumflex coronary (3-mm probe), cranial mesenteric (6-mm probe), left renal (4-mm probe), and left external iliac (6-mm probe) arteries of sheep. The flow probes also showed good zero stability. However, a transit-time flow probe (20 mm) chronically implanted on the pulmonary trunk significantly underestimated cardiac output compared with thermodilution or timed collection of blood. Although this flow probe underestimated flow, the response was linear. Bilateral carotid occlusion caused mesenteric, renal, and iliac vasoconstrictions, confirming that innervation of these vascular beds was undamaged. For experimental purposes, regional blood flow was measured with transit-time flow probes and cardiac output was measured with electromagnetic flow probes calibrated against thermodilution. In summary, transit-time flow probes reliably and accurately measure regional blood flow over many months in adult sheep, but, to measure cardiac output in sheep, the probes must be calibrated in vivo against another reference technique.

The rate of metabolic energy expenditure during locomotion (Mloco) is proportional to body weight (Wb) divided by the time during each stride that a single foot contacts the ground (tc) (Nature Lond. 346: 265-267, 1990). Using this knowledge, we developed an electronic foot contact monitor. Our objective was to derive and cross-validate an equation for estimation Mloco from Wb/tc. Twelve males were tested [age = 19.4 +/- 1.4 (SD) yr, Wb = 78.4 +/- 8.0 kg] during horizontal treadmill walking (0.89, 1.34, and 1.79 m/s) and running (2.46, 2.91, and 3.35 m/s). Measured Mloco was defined as the total rate of energy expenditure, measured by indirect calorimetry, minus the estimated rate of resting energy expenditure. The equation to estimate Mloco was derived in six randomly selected subjects: Mloco = 3.702.(Wb/tc) - 149.6 (r2 = 0.93). Cross-validation in the remaining six subjects showed that estimated and measured Mloco were highly correlated (r2 = 0.97). The average individual error between estimated and measured Mloco was 0% (range -22 to 29%). In conclusion, Mloco can be accurately estimated from Wb and measurements of tc made by an ambulatory foot contact monitor.

Recently, we were charged with providing a learning opportunity for high school students participating in the Upward Bound Regional Math and Science Program, a program designed to stimulate interest in mathematics and science for students from disadvantaged environments. Our challenge was to introduce students to the joys, excitement, and mystery of physiology and to stimulate their interest for future study. To this end, we developed a laboratory experience that examined basic physiological concepts in an animal model. This opportunity introduced students to how their bodies work and the importance of the use of animals in research. The students left the experience confident, motivated, and excited about learning.

A short-circuit current experiment on epithelial ion transport is described that is suitable for student classes in human and animal physiology. Segments of late distal colon from either pig or cow are obtained from the slaughterhouse depending on the animals' daily schedule. Initial tissue preparation already in the slaughterhouse, cold storage, and proper choice of bath solutions are essential prerequisites for success. Students monitor spontaneous transepithelial voltage and short-circuit current (Isc) by use of manually operated voltage clamp units. Two main transport mechanisms are studied, electrogenic Na+ absorption and Cl- secretion. Electrogenic Na+ absorption is studied by measuring the Isc drop after amiloride. Then Cl- secretion is stimulated by theophylline and subsequently inhibited by furosemide. In some experiments K+ secretion can be detected by the blocking effect of mucosal Ba2+. Response of tissues from pig and cow is qualitatively similar but quantitatively different. The equipment is sturdy and inexpensive, can be provided by most departmental workshops, and has been tested for 3 yr in regular lab courses. Observations made during these experiments are closely related to clinical states, such as secretory diarrhea, cystic fibrosis, and hyperaldosteronism, as well as to the mechanisms of clinically used diuretics.

A versatile, inexpensive, easily constructed suction electrode system is described that can be used for routine exercises by the student on, or for demonstrations of, the electrophysiology of frog sciatic nerve and gastrocnemius and sartorius muscles. A disposable plastic syringe and a disposable pipette with Ag-AgCl wire comprise the suction electrode. Six readily manipulable electrodes are installed in the walls of the Plexiglas preparation bath, and an arbitrary number of additional "free" electrodes can be placed where desired. An optional small chamber, formed from a disposable plastic culture dish and Gootch rubber tubing, provides for "barrier" recording within the larger chamber. Interpretations are given of the electrical responses of nerve and muscle in terms of longitudinal currents along the preparation within the suction electrode tubes.

A teaching laboratory is described that demonstrates two principles of the somatosensory system: 1) the "spot-like" nature of skin sensitivity and 2) tactile acuity. This laboratory has been used for a large medical school class (140-160 students). One reason for the success of this laboratory is the ability to provide a sufficient number of stimulating apparatuses. The two-point discrimination device used to measure tactile acuity can be made easily and cheaply. In addition, two other demonstrations are described that are suitable for smaller classes or that students can do on their own. Although this lab was designed for medical students, the content makes it suitable for undergraduate or high school students.

We developed a chronic rat preparation in which a flow probe is placed around the ascending aorta and arterial catheters are implanted in the systemic and pulmonary circulations. This preparation was used to continuously monitor cardiac output (CO), systemic arterial pressure (Psa), and pulmonary arterial pressure (Ppa). More than 80% of the instrumented animals appeared healthy and continued to gain weight for longer than 2 wk. Stable CO, Psa, and Ppa were observed throughout this period. The effects of angiotensin II and hypoxia on the systemic and pulmonary circulations were studied, and possible adverse effects on the heart of long-term implantation of the flow probe were examined. This rat model provides a physiological small-animal preparation for short- and long-term hemodynamic and therapeutic studies on both the systemic and pulmonary circulations.

A comparatively simple apparatus allows even beginning students to observe action potentials in the cockroach leg. The recordings are made extracellularly by impaling the leg on two insect pins. Deflection of large spines on the leg, which are each innervated by one sensory neuron, initiates the action potentials. Using this technique, students observe the all-or-nothing nature of action potentials, their coding of information by frequency, and sensory adaptation.

Regulation of feeding is a fundamental element of homeostasis. This is reflected in the similarity of control mechanisms in a wide range of animals, including insects and humans. A close examination of feeding behavior can illuminate the physiological processes driving regulation. A simple, inexpensive method for recording fine details of feeding by caterpillars is described. Possible experiments, interpretation of the data, and the relationship of observations to the underlying physiology, are outlined.

Two methods of measurement of splenic and hepatic vascular capacitance responses were compared in cats anesthetized with pentobarbital. For the spleen, measurements using ultrasonic crystals were compared with recordings of splenic weight. The cube of the relative change in thickness at one point on the longitudinal axis of the spleen was closely correlated with the overall change in spleen weight. For the liver, measurements by ultrasonic crystals were compared with plethysmographic recordings of liver volume. Individual measurements of cubed relative thickness did not correlate well with plethysmographic volume, and two sets of crystals on the same liver lobe gave different estimates of relative liver volume. However, averaged measurements for a group of animals showed similar means by the two methods. We conclude that ultrasonic crystals, when appropriately attached, can reliably monitor changes in splenic volume, but that for the liver, the variability in thickness responses at different sites on different livers is high. Unless a large number of observations are made, the results will be unreliable.

Epicardial porous disks were used to estimate left ventricular interstitial fluid adenosine in the isolated guinea pig heart perfused at constant flow. To validate this technique, adenosine was infused with 0.5 microM dipyridamole and 5 microM erythro-4-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA) to inhibit adenosine uptake and deamination, respectively. Under these conditions, with 6 or 12 microM adenosine in the arterial infusate, the venous and steady-state left ventricular disk adenosine values equaled those of the perfusion fluid, reflecting the expected equilibration between vascular and left ventricular interstitial fluid (disk) compartments. The concentration of endogenous adenosine in the interstitial fluid as estimated by the epicardial disks under control conditions was 0.28 +/- 0.03 microM with a concomitant coronary sinus concentration of 0.004 +/- 0.001 microM. We conclude that a marked adenosine gradient exists between the interstitial fluid and the vascular space and that disk adenosine measurements provide a useful index of left ventricular interstitial fluid adenosine.

A method for continuous servo-controlled infusion of sodium chloride to dogs is reported. The servo system consists of a sodium-sensitive electrode, a modified commercial flowmeter, a thermistor, a control unit, and a pump. Based on analog inputs from electrode, flowmeter, and thermistor, the control unit generates appropriate numbers of voltage steps, which drive the pump infusing a concentrated solution of sodium chloride. Inputs from the thermistor are necessary to correct for the influence of fluctuations in urine temperature. The sodium servo system has been tested together with a weight servo mechanism in conscious water-diuretic dogs. Furosemide (1 microgram.kg-1.min-1) was infused to change the rate of sodium excretion by a factor of 17 from 3 +/- 1 to 50 +/- 15 mumols/min. Within this range, the apparatus replaced the sodium losses with great accuracy. From seven experiments the average system response in micromoles per minute (NaIn) measured in 10-min periods against mean renal excretion of sodium (NaEx) was NaIn = 0.98.NaEx - 1.37. The servo system provides a tool for accurate maintenance of body sodium irrespective of large changes in the rate of sodium excretion.

The autoregulating vascular bed of the isolated canine extensor digitorum longus muscle was investigated for the possible existence of two positive zero-flow pressure axis intercepts, a tone-dependent one and a tone-independent one. An isolated preparation, perfused with autologous blood, was used to exclude effects of collateral flow and nervous and humoral regulation while autoregulation was left intact [mean autoregulatory gain 0.50 +/- 0.24 (SD)]. In a first series of experiments, the steady-state (zero flow) pressure axis intercept [mean 8.9 +/- 2.6 (SD) mmHg, tone independent] and the instantaneous (zero flow) pressure axis intercept [mean 28.5 +/- 9.9 (SD) mmHg, tone dependent] were determined as a function of venous pressure (range: 0-45 mmHg) and were independent of venous pressure until the venous pressure exceeded their respective values. Beyond this point the relations between the venous pressure and the steady-state and instantaneous pressure axis intercept followed the line of identity. The findings agree with the predictions of the vascular waterfall model. In a second series it was shown by means of administration of vasoactive drugs that the instantaneous pressure axis intercept is tone dependent, whereas the steady-state pressure axis intercept is not. It is concluded that there is a (proximal) tone-dependent zero-flow pressure at the arteriolar level and a (distal) tone-independent zero-flow pressure at the venous level.

We investigated the hypothesis that an increase in cytoplasmic calcium ion concentration, [Ca2+]i, is one of the mechanisms responsible for increased microvessel permeability. We loaded the cells forming the walls of individually perfused microvessels in frog mesentery with fura-2 and measured [Ca2+]i in the control state and after adding the Ca2+ ionophore ionomycin to the perfusate. [Ca2+]i in the control state was 65 +/- 6 nM and increased to an initial peak of 285 +/- 29 nM after 1-3 min. After 4, 6, and 10 min, [Ca2+]i was 199 +/- 18, 163 +/- 16, and 129 +/- 9 nM, respectively. [Ca2+]i fell back to 77 +/- 7 nM after ionophore was removed. In similar experiments, hydraulic conductivity (Lp) increased to a peak of 9.5 times control after 1-3 min, then fell to 2.0 times control after 6 min. Lp remained elevated at this level for as long as ionophore was present in the perfusate. [Ca2+]i modulates the initial and sustained phases of the permeability increase. Both processes depend on external Ca2+ influx. Our experiments provide the first direct measurement of [Ca2+]i during a change in the permeability of an intact microvessel.

A device is described for measuring dew-point temperature and water vapor pressure in small confined areas. The method is based on the deposition of water on a cooled surface when at dew-point temperature. A small Peltier module lowers the temperature of two electrically conductive plates. At dew point the insulating gap separating the plates becomes conductive as water vapor condenses. Sensors based on this principle can be made small and rugged and can be used for measuring directly the local water vapor pressure. They may be installed within a conventional ventilated sweat capsule used for measuring water vapor loss from the skin surface. A novel application is the measurement of the water vapor pressure gradients across layers of clothing worn by an exercising subject.

A method is described for breath-by-breath measurement of alveolar gas exchange corrected for changes of lung gas stores. In practice, the subject inspires from a spirometer, and each expired tidal volume is collected into a rubber bag placed inside a rigid box connected to the same spirometer. During the inspiration following any given expiration the bag is emptied by a vacuum pump. A computer monitors inspiratory and expiratory tidal volumes, drives four solenoid valves allowing appropriate operation of the system, and memorizes end-tidal gas fractions as well as mixed expired gas composition analyzed by mass spectrometer. Thus all variables for calculating alveolar gas exchange, based on the theory developed by Auchincloss et al. (J. Appl. Physiol. 21: 810-818, 1966), are obtained on a single-breath basis. Mean resting and steady-state exercise gas exchange data are equal to those obtained by conventional open-circuit measurements. Breathing rates up to 30 X min-1 can be followed. The breath-to-breath variability of O2 uptake at the alveolar level is less (25-35%) than that measured at the mouth as the difference between the inspired and expired volumes, both at rest and during exercise up to 0.7 of maximum O2 consumption.