Size,temperature, and scaphognathite frequency-dependent variations of ventilation volumes in Carcinus maenas (L.)

There is a direct, linear relationship between scaphognathie beat frequency and absolute ventilation volume in Carcinus maenas (L). The absolute ventilation volume is directly proportional to the size of the animals. At all scaphognathie frequencies small animals have a greater relative ventilation volume than large animals. The absolute stroke volume (ml/beat) is greater in large animals than in small animals. The majority of the available evidence suggests that, whilst the force of the scaphognathie stroke may be variable, the amplitude of its excursion remains constant at all beat frequencies.     

Respiratory units of motor production and song imitation in the zebra finch

Juvenile male zebra finches (Taeniopygia guttata) learn a stereotyped song by imitating sounds from adult male tutors. Their song is composed of a series of syllables, which are separated by silent periods. How acoustic units of song are translated into respiratory and syringeal motor gestures during the song learning process is not well understood. To learn about the respiratory contribution to the imitation process, we recorded air sac pressure in 38 male zebra finches and compared the acoustic structures and air sac pressure patterns of similar syllables qualitatively and quantitatively. Acoustic syllables correspond to expiratory pressure pulses and most often (74%) entire syllables are copied using similar air sac pressure patterns. Even notes placed within different syllables are generated with similar air sac pressure patterns when only segments of syllables are copied (9%). A few of the similar syllables (17%) are generated with a modified pressure pattern, typically involving addition or deletion of an inspiration. The high similarity of pressure patterns for like syllables indicates that generation of particular sounds is constrained to a narrow range of air sac pressure conditions. Following presentation of stroboscope flashes, song was typically interrupted at the end of an expiratory pressure pulse, confirming that expirations and, therefore, syllables are the smallest unit of motor production of song. Silent periods, which separate syllables acoustically, are generated by switching from expiration to inspiration. Switching between respiratory phases, therefore, appears to play a dominant role in organizing the stereotyped motor program for song production.     

Gas exchange and air flow in the lung of the snake,Pituophis melanoleucus

Summary Gas samples from various regions of the lung were obtained throughout the breathing cycle inPituophis melanoleucus. Changes in CO₂ concentration during the interbreath period differed markedly along the length of the lung. In general, the largest and most rapid increases in CO₂ tension were measured at the cranial end of the vascular lung. Further caudad in the vascular lung, the increase was slower and did not reach mixed venous CO₂ tension before exhalation. In animals exhibiting the lowest breathing frequencies and presumably larger tidal volumes, the region of gas exchange extended into the cranial portion of the air sac. There was little or no change in gas tensions within the remaining caudal regions of the air sac. Measurement of exhaled CO₂ and O₂ tensions at the nares confirmed the longitudinal gradient in gas exchange and also demonstrated the sequential emptying of the lung. Large regional differences in the ratio of blood flow to alveolar volume are probably responsible for the gradients in lung gases.Interpretation of N₂ clearance curves in terms of two freely communicating compartments demonstrated the presence of a ventilation inequality. Consistent with this was the lack of body wall contractions between breaths while animals were resting. However, just prior to and during activity body wall contractions not associated with breathing often occurred and resulted in pressure excursions in the lung of ca. five mm H₂O. In addition, the heart beat results in a pressure change within the lung of ca. 0.2 mmH₂O which may be significant in gas mixing.     

Pericardium modulates left and right ventricular stroke volumes to compensate for sudden changes in atrial volume

The pericardium may modulate acute compensatory changes in stroke volumes seen with sudden changes in cardiac volume, but such a mechanism has never been clearly demonstrated. In eight open-chest dogs, we measured left and right ventricular pressures, diameters, stroke volumes, and pericardial pressures during rapid (approximately 300 ms) systolic infusions or withdrawals of approximately 25 ml blood into and out of the left atrium and right atrium. Control beats, the infusion/withdrawal beat, and 4-10 subsequent beats were studied. With infusions, ipsilateral ventricular end-diastolic transmural pressure, diameter, and stroke volume increased. With the pericardium closed, there was a compensatory decrease in contralateral transmural pressure, diameter, and stroke volume, mediated by opposite changes in transmural end-diastolic pressures. The sum of the ipsilateral increase and contralateral decrease in stroke volume approximated the infused volume. Corresponding changes were seen with blood withdrawals. This direct ventricular interaction was diminished when pericardial pressure was <5 mmHg and absent when the pericardium was opened. Pericardial constraint appears essential for immediate biventricular compensatory responses to acute atrial volume changes.     

Tracheal length changes during zebra finch song and their possible role in upper vocal tract filtering

Sounds produced in the avian vocal organ may be modified by filter properties of the upper vocal tract. Possible mechanisms to actively control filter characteristics include movements of the beak, tongue, and larynx and adjustments of tracheal length. We investigated whether length changes of the trachea are a likely mechanism for adjusting upper vocal tract filter properties during song in the zebra finch (Taeniopygia guttata). Tracheal length was monitored at the basal end using sonomicrometry and was recorded together with subsyringeal air sac pressure and acoustic output. Tracheal shortening occurred at the onset of song bouts, and during each motif the tracheal length decreased during expiratory pressure pulses and increased during the short inspirations. A bilateral tracheal syringeal nerve cut confirmed that the initial shortening at the onset of the song bout is an active shortening of the trachea (i.e., mediated by syringeal muscle activity). The modulation of length during the motif was not affected by the denervation and is most likely driven by the pressurization of the interclavicular air sac. The absolute length change during the motif was small (<0.2 mm) and not clearly related to acoustic features of the song. For example, some high-frequency syllables, which are generated during inspiration, were accompanied by tracheal elongation. Because this elongation shifts tube resonances to lower frequencies, it is inconsistent with an active adjustment of length to enhance high frequency sounds. The small magnitude and inconsistent nature of dynamic tracheal length changes during song make it unlikely that they significantly affect vocal tract filter properties if the trachea is modeled as a rigid tube.     

Measurement of tidal lung volumes in neonates during high-frequency oscillation

High-frequency oscillation (HFO) has been used clinically to ventilate infants with respiratory distress. However, there are problems in monitoring the effects on the respiratory system and in particular in measuring the volumes delivered; this is important information in terms of safety and mechanisms of action of HFO. We have validated two sizes of respiratory jacket for measuring oscillatory volume changes of 0.25–5 ml at frequencies of 2–25 Hz, the volume delivered from a purpose-built oscillator having first been validated. Different combinations of volume and frequencies were then oscillated into each jacket, while it was being worn by a well preterm baby. Studies were performed with each jacket on five babies with weights between 0.82 and 1.86 kg. The results showed that at any given frequency there was a linear relationship between the pressure oscillations measured from a side port of the jacket and the delivered volume. Both jackets showed the same pattern of frequency response, overreading at < 10 Hz and underreading at 10–25 Hz. When appropriately calibrated, the respiratory jacket can be used as a non-invasive method of measuring volumes delivered by HFO.     

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is ± 5 parts in 10⁷. Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH₂F₂, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO₂ pump laser, and strength.     

Chest wall impedance partitioned into rib cage and diaphragm-abdominal pathways

We measured chest wall "pathway impedances" (ratios of pressure changes to rates of volume displacement at the surface) with esophageal and gastric balloons and inductance plethysmographic belts around the rib cage and abdomen during forced volume oscillations (5% vital capacity, 0.5-4 Hz) at the mouth of five relaxed, seated subjects. Volume displacements of the total chest wall surface, measured by summing the rib cage and abdominal signals, approximated measurements using volume-displacement, body plethysmography over the entire frequency range. Resistance (R) and elastance (E) of the diaphragm-abdomen pathway were several times greater than those of the rib cage pathway, except at the highest frequencies where diaphragm-abdominal E was small. R and E of the diaphragm-abdomen pathway and of the rib cage pathway showed the same frequency dependencies as that of the total chest wall: R decreased markedly as frequency increased, and E (especially in the diaphragm-abdomen) decreased at the highest frequencies. These results suggest that the chest wall can be reasonably modeled, over the frequency range studied, as a system with two major pathways for displacement. Each pathway seems to exhibit behavior that reflects nonlinear, rate-independent dissipation as well as viscoelastic properties. Impedances of these pathways are useful indexes of changes in chest wall mechanical behavior in different situations.     

Dynamic image analysis applied to the study of ciliary beat on cultured ciliated epithelial cells from rabbit trachea

We have developed an automated image analysis method to study the ciliary beat frequency of ciliated cells of the primary culture from rabbit trachea. The ciliated outgrowth image is digitized and the variation in optical density is automatically calculated for each selected area of interest. 32 measurements of ciliary beat frequency are, in this way, calculated simultaneously in 6 min. With this reliable device, some studies on baseline frequency of control culture have been carried out. There was no variation in the mean frequencies of ciliated cells of the primary culture of different tracheas in our culture conditions. Moreover, the values of ciliary beat frequency at the starting point of the outgrowth were similar to those at the periphery of the outgrowth. There is nevertheless a slow decrease in frequencies versus the duration of culture. We have also established that the frequency of ciliary beat of some cells fluctuates in a periodic pattern whereas the majority of the ciliated population beat in a stable way. The image analysis process allows us to perform a cartography of frequencies on the video display. It also allows us to have access to the frequency of one cilium. Our method therefore seems to be reliable and furthermore simple in the evaluation of the potential effect of inhaled toxic compounds on ciliated cells of mammalian respiratory tract.     

The blood circulatory function of the dorsal aorta ligament in Rainbow trout (Salmo gairdneri)

An elastic longitudinal ligament stretched under considerable tension lies within the dorsal aorta of Rainbow trout.
Experiments with mechanically simulated swimming movements in an artificial model demonstrate that such a ligament can act as a pump mechanism. The output of the pump increases with tail beat frequency up to a certain point where the mechanism tends to break down. Investigations on the trout dorsal aorta show that pump breakdown probably takes place at relatively low output pressures.
Fundamental blood flow considerations indicate that a fully effective dorsal aorta pump over the full range of swimming speeds is undesirable. It is concluded that the dorsal aorta ligament can act as a pump which automatically increases circulation during swimming particularly to the body musculature. The output pressure is small but may be of significance in causing reflex increase in cardiac output.     

Beak gape dynamics during song in the zebra finch

Bird song is a complex communication behavior that requires the coordination of several motor systems. Sound is produced in the syrinx and then modified by the upper vocal tract, but the specific nature and dynamics of this modification are not well understood. To determine the contribution of beak movements to sound modification, we studied the beak gape patterns in zebra finches (Taeniopygia guttata). Subsyringeal air sac pressure and song were recorded together with changes in beak gape, which were monitored with a magneto-sensitive transducer. Beak gape was positively correlated with fundamental frequency, peak frequency, and subsyringeal air sac pressure in all but one bird. For harmonic stacks, peak frequency increased with increasing beak gape, and the relationship between fundamental frequency and beak gape was no longer significant. Experimentally holding the beak open or closed had acoustic consequences consistent with the model in which beak movements change upper vocal tract length and, thus, the filter properties. Beak gape was positively correlated with sound amplitude in all but two birds. The relationship between beak aperture and amplitude may, however, be indirect because air sac pressure is correlated with amplitude and beak gape. The beak is opened quickly and to its widest aperture immediately prior to the onset of sound and at rapid transitions in sound, suggesting that beak movements may affect vibratory behavior of the labia.     

Automated measurement of ciliary beat frequency

Measurements of ciliary beat frequency using video images are dependent on observer interpretation. To obtain objective estimates of ciliary beat frequency from video-image sequences, a computer-based method was developed. Regions of interest of video-image sequences were selected and digitized. Variations in numerical values representing light intensity resulting from cilia beating were extracted and analyzed using autocorrelation techniques. The ciliary beat frequencies obtained for 14 in vitro experiments on ciliated cells or epithelium from the frog palate (Rana catesbeiana) over the range of frequencies 2-25 Hz correlated well with independent observer measurements (r = 0.979). The addition of such computer-based methods to video observer-based systems allows more objective and efficient determinations of ciliary beat frequency.     

Divergent changes in the rate of development of pressure in the left ventricle and in the performance of the heart as a pump.

Dog hearts were prepared in situ so that heart rate (HR), left ventricular end diastolic pressure (LVEDP) and mean aortic pressure (MAP) could be controlled separately during computation of left ventricular dP/dt max and external stroke work (SW). Progressive increases in HR consistently raised dP/dt max over a wide range, and consistently lowered SW except at low rates. Progressive increases in LVEDP or MAP consistently raised both dP/dt max and SW. Infusion of noradrenaline consistently raided both dP/dt max and SW, except at very high HR when only dP/dt max was consistently raised. Our results lead us to question the validity of equating changes in pre-ejection measurements with changes in performance of the heart as a pump under abnormal conditions and in the assessment of inotropic agents.     

Gas transport during high-frequency ventilation

During high-frequency small-volume ventilation (HFV), the transport rate of gas from the mouth to a lung region is a function of two conductances (conductance is the transfer rate of a gas divided by its partial pressure difference): regional longitudinal gas conductance along the airways (Grlongi) and gas conductance between lung regions (Ginter). Grlongi per unit regional lung (gas) volume [Grlongi/(Vr beta g)] was determined during HFV in 11 anesthetized paralyzed dogs lying supine. The distribution of Grlongi/(Vr beta g) was nearly uniform during HFV when stroke volumes were less than approximately two-thirds of the Fowler dead-space volume. By contrast, the distribution of Grlongi/(Vr beta g) was nonuniform when the stroke volume exceeded approximately two-thirds of the Fowler dead-space volume and the oscillation frequency was 5 Hz. Gas conductance along the airways per unit lung gas volume [average Glongi/(V beta g)], for the entire lung, increased with stroke volume at all frequencies, but for a given product of oscillation frequency and stroke volume, the average Glongi/(V beta g) was greater when stroke volume was large and oscillation frequency was low. The average Glongi/(V beta g) increased with frequency up to a maximal value; the frequency at which the maximum occurred depended on the kinematic viscosity of the inspired gas mixture.     

Dynamic baroreflex control of blood pressure: influence of the heart vs. peripheral resistance

The aim in the present experiments was to assess the dynamic baroreflex control of blood pressure, to develop an accurate mathematical model that represented this relationship, and to assess the role of dynamic changes in heart rate and stroke volume in giving rise to components of this response. Patterned electrical stimulation [pseudo-random binary sequence (PRBS)] was applied to the aortic depressor nerve (ADN) to produce changes in blood pressure under open-loop conditions in anesthetized rabbits. The stimulus provided constant power over the frequency range 0-0.5 Hz and revealed that the composite systems represented by the central nervous system, sympathetic activity, and vascular resistance responded as a second-order low-pass filter (corner frequency approximately 0.047 Hz) with a time delay (1.01 s). The gain between ADN and mean arterial pressure was reasonably constant before the corner frequency and then decreased with increasing frequency of stimulus. Although the heart rate was altered in response to the PRBS stimuli, we found that removal of the heart's ability to contribute to blood pressure variability by vagotomy and beta(1)-receptor blockade did not significantly alter the frequency response. We conclude that the contribution of the heart to the dynamic regulation of blood pressure is negligible in the rabbit. The consequences of this finding are examined with respect to low-frequency oscillations in blood pressure.     

Estimation of alveolar pressure during forced oscillation of the respiratory system.

A method for obtaining a continuous estimate of alveolar pressure (PAlv) during periodic flow is described; it was developed to improve the precision of measurements of airway and respiratory tissue impedance using the improved resolution of relatively high-frequency (approximately 5 Hz) singlas. The respiratory system was modulated with a piston pump, and lung volume and the volume change due to compression and expansion of alveolar gas were measured plethysmorgraphically; these signals and an analog divider were used to obtain a continuous solution of Boyle's law during flow. The plethysmorgraph was of the "flow" type; with it volume changes at frequencies up to 10 Hz and with rates of change up to 6 l/s were measured without amplitude or phase distortion. The method permits control of frequency and flow amplitude during PAlv measurement and calibration of PAlv in the absence of an active chest wall. However, it is technically complex.     

Vascular endothelial growth factor-C stimulates the lymphatic pump by a VEGF receptor-3-dependent mechanism

Vascular endothelial growth factor (VEGF)-C plays an important role in lymphangiogenesis; however, functional responses of lymphatic vessels to VEGF-C have not been characterized. We tested the hypothesis that VEGF-C-induced activation of VEGF receptor (VEGFR)-3 increases lymphatic pump output. We examined the in vivo pump activity of rat mesenteric collecting lymphatics using intravital microscopy during basal conditions and during treatment with 1 nM recombinant VEGF-C, the selective VEGFR-3 agonist VEGF-Cys(156)Ser mutation (C156S; 1 nM), or 0.1 nM VEGF-A. Their specific responses were also analyzed during selective inhibition of VEGFR-3 with MAZ-51. Contraction frequency, end-diastolic diameter, end-systolic diameter, stroke volume index, pump flow index, and ejection fraction were evaluated. We also assessed arteriolar diameter and microvascular extravasation of FITC-albumin. The results show that both VEGF-C and VEGF-C156S significantly increased contraction frequency, end-diastolic diameter, stroke volume index, and pump flow index in a time-dependent manner. VEGF-A caused a different response characterized by a significantly increased stroke volume after 30 min of treatment. MAZ-51 (5 muM) caused tonic constriction and decreased contraction frequency. In addition, 0.5 and 5 muM MAZ-51 attenuated VEGF-C- and VEGF-C156S-induced lymphatic pump activation. VEGF-A caused vasodilation of arterioles, whereas VEGF-C and VEGF-C156S did not significantly alter arteriolar diameter. Also, VEGF-A and VEGF-C caused increased microvascular permeability, whereas VEGF-C156S did not. Our results demonstrate that VEGF-C increases lymphatic pumping through VEGFR-3. Furthermore, changes in microvascular hemodynamics are not required for VEGFR-3-mediated changes in lymphatic pump activity.     

Colour polymorphism in the salt-marsh isopod,Sphaeroma rugicauda; Evidence for stable equilibrium frequencies

Summary If morph frequencies in a polymorphic population are maintained at stable equilibria, then if the frequencies are perturbed they should return to their equilibrium values. Artificial populations of the isopod were set up in cages on the salt-marsh with varying frequencies of the pattern morph. The cages were left undisturbed for five months over the breeding season. In the control cages the initial frequency of pattern (0.15) was the same as in the natural population. At the end of the experiment the frequency had not changed significantly, and was not significantly different from the frequency of pattern in the natural population (at the end of the experiment). High frequency cages started with pattern at a frequency of 0.5, showed significant decreases in frequency towards the control values, from which they were not significantly different by the end of the experiment. The average frequency in low frequency cages (started with pattern at 0.06) rose only slighly and was still significantly lower than the average control frequency by the end of the experiment. It is suggested that in these cages the restoring force may have been opposed by random processes, since pattern was lost entirely from some of the cages. The results indicate that the polymorphism is at a stable equilibrium, although the nature of the restoring forces were not identified.     

Partitioning of pulmonary resistance in dogs: effect of tidal volume and frequency

To determine the sensitivity of pulmonary resistance (RL) to changes in breathing frequency and tidal volume, we measured RL in intact anesthetized dogs over a range of breathing frequencies and tidal volumes centering around those encountered during quiet breathing. To investigate mechanisms responsible for changes in RL, the relative contribution of airway resistance (Raw) and tissue resistance (Rti) to RL at similar breathing frequencies and tidal volumes was studied in six excised, exsanguinated canine left lungs. Lung volume was sinusoidally varied, with tidal volumes of 10, 20, and 40% of vital capacity. Pressures were measured at three alveolar sites (PA) with alveolar capsules and at the airway opening (Pao). Measurements were made during oscillation at five frequencies between 5 and 45 min-1 at each tidal volume. Resistances were calculated by assuming a linear equation of motion and submitting lung volume, flow, Pao, and PA to a multiple linear regression. RL decreased with increasing frequency and decreased with increasing tidal volume in both isolated and intact lungs. In isolated lungs, Rti decreased with increasing frequency but was independent of tidal volume. Raw was independent of frequency but decreased with tidal volume. The contribution of Rti to RL ranged from 93 +/- 4% (SD) with low frequency and large tidal volume to 41 +/- 24% at high frequency and small tidal volume. We conclude that the RL is highly dependent on breathing frequency and less dependent on tidal volume during conditions similar to quiet breathing and that these findings are explained by changes in the relative contributions of Raw and Rti to RL.     

Intrinsic difference in beat frequency between the two flagella of Chlamydomonas reinhardtii

The flagellar beat frequency of the biflagellated green alga Chlamydomonas reinhardtii was measured by fast Fourier transform analysis of the light intensity fluctuation in microscope images of swimming cells. Live cells had a mean beat frequency of 48-53 Hz at 20 degrees C. However, detergent-extracted "cell models," when reactivated in the presence of 1 mM ATP, appeared to have two different beat frequencies of about 30 and 45 Hz. Measurements in cell models in which only one of the two flagella was beating indicated that the lower and higher frequencies most likely represented the beat frequency of the flagellum nearer to the eyespot (the cis-flagellum) and that of the flagellum farther from it (the trans-flagellum), respectively. In live cells also, the trans-flagellum beat at a frequency about 30% higher than that of the cis-flagellum when the cells were rendered uniflagellated by mechanical treatment, whereas both flagella beat at the frequency of the cis-flagellum under normal conditions. These observations suggest that the two flagella of Chlamydomonas have different intrinsic beat frequencies but that they are somehow synchronized when beating together on a live swimming cell.