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Biomedical subjects

B E Shykoff

Publications and source records attributed to B E Shykoff.

9 recordsLinked to original sources
PubMed1991

Phrenic neural output during hypoxia in dogs: constant-flow ventilation vs. spontaneous breathing.

We studied the effects of removing cyclic pulmonary afferent neural information on respiratory pattern generation in anesthetized dogs. Phrenic neural output during spontaneous breathing (SB) was compared with that occurring during constant-flow ventilation (CFV) at several levels of eucapnic hypoxemia. Hypoxia caused an increase in both the frequency and the amplitude of the moving time average (MTA) phrenic neurogram during both SB and CFV. The change in frequency as arterial saturation was reduced from 90 to 60% during SB was significantly higher than that during CFV [SB, 32.3 +/- 10.9 (SD) breaths/min; CFV, 10.3 +/- 5.8 breaths/min; P = 0.001]. By contrast, the increase in the amplitude of the MTA phrenic neurogram was smaller (SB, 0.62 +/- 0.68 units; CFV, 1.35 +/- 0.81 units; P = 0.01). The changes in frequency with hypoxia during both modes of ventilation resulted primarily from a shortening of expiratory time. Both inspiratory time and expiratory time were greater during CFV than during SB, but their change in response to hypoxia was not significantly different. We conclude that the amplitude response of the MTA phrenic neurogram to hypoxia is similar to that seen during hypercapnia; in the presence of phasic afferent feedback the MTA amplitude response is decreased and the frequency response is increased relative to the response observed in the absence of phasic afferents.

Afferent Pathways↗
PubMed1991

Respiratory sinus arrhythmia in dogs. Effects of phasic afferents and chemostimulation.

We examined the hypothesis that respiratory sinus arrhythmia (RSA) is primarily a central phenomenon and thus that RSA is directly correlated with respiratory controller output. RSA was measured in nine anesthetized dogs, first during spontaneous breathing (SB) and then during constant flow ventilation (CFV), a technique whereby phasic chest wall movements and thoracic pressure swings are eliminated. Measurements of the heart rate and of the moving time averaged (MTA) phrenic neurogram during these two ventilatory modes were made during progressive hypercapnia and progressive hypoxia. RSA divided by the MTA phrenic amplitude (RSAa) showed a power-law relationship with both arterial carbon dioxide partial pressure (PaCO2) and oxygen saturation (SaO2), but with different exponents for different conditions. However, the power-law relation between RSAa and respiratory frequency had an exponent indistinguishable from -2 whether hypoxia or hypercapnia was the stimulus for increased respiratory drive, and during both CFV and spontaneous breathing (-1.9 +/- 0.4, hypoxia, SB; -1.8 +/- 0.7, hypoxia, CFV; -2.1 +/- 0.8, hypercapnia, SB; -1.9 +/- 0.7, hypercapnia, CFV). We conclude that respiratory sinus arrhythmia is centrally mediated and directly related to respiratory drive, and that changes in blood gases and phasic afferent signals affect RSA primarily by influencing respiratory drive.

Afferent Pathways↗
PubMed1988

Interpretation of the krypton-81m dynamic series: the distribution of a tidal breath.

Lung scans during cyclic breathing of krypton-81m, an isotope with a 13-s half-life, were acquired in "list mode," where both temporal and spatial information are preserved. Subjects in the left lateral decubitus position breathed with two tidal volumes at each of two frequencies. Profiles of total activity over the acquisition period were examined. They showed little effect of frequency or tidal volume on the distribution of air between dependent and non-dependent regions. Dynamic series for ensemble-averaged breaths were constructed. The regional flow per unit volume was shown to correspond to the time derivative of the regional activity of the dynamic series divided by the corresponding activity. Both the relative timing of the gas flow to different lung regions and the flow per unit volume as a function of time were obtained from the dynamic series. The dependent lung was seen to be better ventilated throughout the respiratory cycle except for brief periods at the start of inspiration and the end of expiration. Most of the dead-space gas can be construed to enter and leave the dependent lung.

Female↗
PubMed1988

Airflow and normal lung sounds.

The relationship between total air flow and normal breath sounds recorded at 2 sites on the chest was investigated. Sounds were measured during rhythmic breathing, during flow rate tracking, and during flow rate tracking against an external resistance by subjects seated and in the left lateral decubitus position. The sound amplitude during inspiration varied directly with the square of the air flow at the mouth. Changes in subject position and breathing pattern altered the gain between the square of the flow and the sound amplitude but not the functional relationship.

Adult↗
PubMed1987

A model-free method for mass spectrometer response correction.

A new method for correction of mass spectrometer output signals is described. Response-time distortion is reduced independently of any model of mass spectrometer behavior. The delay of the system is found first from the cross-correlation function of a step change and its response. A two-sided time-domain digital correction filter (deconvolution filter) is generated next from the same step response data using a regression procedure. Other data are corrected using the filter and delay. The mean squared error between a step response and a step is reduced considerably more after the use of a deconvolution filter than after the application of a second-order model correction. O2 consumption and CO2 production values calculated from data corrupted by a simulated dynamic process return to near the uncorrupted values after correction. Although a clean step response or the ensemble average of several responses contaminated with noise is needed for the generation of the filter, random noise of magnitude less than or equal to 0.5% added to the response to be corrected does not impair the correction severely.

Cardiac Output↗
PubMed1982

Effects of unequal pressure swings and different waveforms on distribution of ventilation: a non-linear model simulation.

In an attempt to understand the role of unequal pleural pressure swings and of different waveforms of pleural pressure variation in the distribution of ventilation during cyclic breathing, a mathematical model simulation was performed. The computer model which incorporates non-linear resistances and compliances as well as sinusoidal, square, and triangular waveforms of pleural pressure variations indicates that the distribution of ventilation is insensitive to the waveform of the pleural pressure. The distribution is also little changed by the depth of breathing (amplitude), but it is affected significantly by the pattern of different pressures over the regions of the model. For sinusoidal, triangular, and low amplitude square wave pleural pressures with equal amplitudes on both compartments, air was distributed preferentially to the lower compartment under the influence of the static pressure difference. With unequal amplitudes, more air flowed to the compartment experiencing the larger pressure swing. This was virtually independent of the waveform and of the amplitudes of the pleural pressure variation. Comparison of the present results with a constant flow model reveals that the overall distribution of tidal air during cyclic breathing is very different from the results obtained in constant rate inspiration experiments or in bolus distribution experiments. New experiments performed under cyclic breathing conditions are thus indicated.

Humans↗