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Biomedical subjects

K Rehder

Publications and source records attributed to K Rehder.

At least 73 records · Page 4Linked to original sources
PubMed1987

Muscarinic M1 receptors mediate the increase in pulmonary resistance during vagus nerve stimulation in dogs.

The physiologic roles of the 2 muscarinic receptors (M1 and M2) in the vagal control of pulmonary resistance were studied by comparing the effects of pirenzepine (PZ, M1-blocker), gallamine (GAL, M2-blocker), and atropine (AT, M1- and M2-blocker) on the increase in pulmonary resistance (RL) and on the reduction in heart rate (HR) during bilateral cervical vagus nerve stimulation in 18 anesthetized (chloralose and urethane) and paralyzed (vecuronium) dogs. PZ, AT, and GAL all inhibited the reduction in HR during vagus nerve stimulation, although the inhibition required relatively high doses of PZ and GAL. AT and PZ inhibited the increase in RL during vagus nerve stimulation. The ratio of the dose needed to inhibit by 50% the HR response to the dose needed to inhibit by 50% the RL response was approximately 45:1 for PZ, 12:1 for AT, and less than 0.4:1 for GAL. Thus, compared with AT, PZ is a more selective blocker of vagally induced increases in RL, indicating that M1 receptors are present in the airway smooth muscle of intact anesthetized dogs. In the same dose range as that which caused the inhibition of the HR response, GAL had no consistent effect on the increase in RL during vagus nerve stimulation, indicating that M2 receptors do not mediate the increase in RL in intact anesthetized dogs.

Airway Resistance↗
PubMed1987

Body position and ventilation-perfusion relationships in unilateral pulmonary disease.

The effect of positional change (right vs left lateral decubitus) on the distribution of ventilation and perfusion ratios was determined in four patients with respiratory failure and chest roentgenographic findings of unilateral pulmonary disease. In these patients with a unilateral interstitial pattern, improvement in oxygenation which occurred when the "good" side was dependent (down) was associated with changes in the patterns of ventilation-perfusion distribution; two patients showed a predominant decrease in right-to-left intrapulmonary shunt, and two showed an improvement in ventilation-perfusion equality. Therefore, when unilateral interstitial pulmonary disease was present, positional change resulted in changes in right-to-left intrapulmonary shunt or low ventilation-perfusion ratios or both. Variability between patients can be explained by the nonhomogeneity of pulmonary disease in patients with respiratory failure.

Aged↗
PubMed1986

High-frequency, small-volume ventilation during thoracic surgery.

Surgical conditions during conventional mechanical ventilation (CMV) and pulmonary gas exchange were compared with those during high-frequency ventilation (HFV) in 24 patients undergoing anesthesia for intrathoracic surgery. HFV at an oscillatory frequency of 3 Hz and a delivered gas volume of 1.3-1.9 ml/kg provided excellent surgical conditions for peripheral lung procedures. However, surgical conditions for procedures on the major airways or mediastinal structures were unsatisfactory during HFV. Adequate pulmonary gas exchange was achieved with HFV when the chest was open. Further evidence is presented for expiratory flow limitation during HFV. Expiratory flow limitation seems to occur particularly in patients with chronic obstructive airway disease, leading to increased lung volume. Currently, the authors do not recommend HFV for routine use during anesthesia for thoracic surgery.

Adult↗
PubMed1986

Resonant amplification of delivered volume during high-frequency ventilation.

The volume of gas delivered from a high-frequency ventilation (HFV) circuit was measured with an ultrasonic flowmeter. The measurements were done in vitro (20-liter air-filled glass bottle) and in vivo (9 anesthetized dogs lying supine) at oscillation frequencies ranging from 4 to 23 Hz and stroke volumes of the pump ranging from 36 to 150 ml. We varied the length and diameter of the tube connecting the pump with the endotracheal tube, the length and diameter of the bias outflow tube, the diameter of the endotracheal tube, and the stroke volume of the pump. Both in vitro and in vivo, there was resonant amplification of the delivered gas volume; i.e., the delivered gas volume exceeded the stroke volume at certain frequencies. Altering the dimensions of connecting tube, endotracheal tube, bias outflow tube, or stroke volume, i.e., changing the resistance to gas flow, gas compliance, and/or gas inertance in these elements, altered the ratio of gas delivered to stroke volume that could be predicted by an electric analog. These data indicate that the delivered gas volume during HFV depends critically on the configuration of the HFV circuit, the size of the endotracheal tube, the oscillation frequency, and the pump stroke volume. Knowledge of the delivered gas volume during HFV and appreciation of the phenomenon of resonant amplification of the delivered gas volume will permit a more accurate description of factors contributing to gas transport during HFV.

Animals↗
PubMed1986

Differences in regional vascular conductances in isolated dog lungs.

The distribution of pulmonary blood flow is influenced by gravity, regional lung expansion, and hypoxic pulmonary vasoconstriction. However, these factors cannot completely explain the three-dimensional distribution of blood flow in the lung. The present study was designed to see whether anatomically related factors could contribute. Regional blood pressure vs. flow curves were determined in 100-230 small parenchymal samples (0.3-0.4 ml) from 12 isolated perfused dog lungs held at constant inflation pressure. In each region four blood flows were measured using radioactively labeled microspheres, and the four corresponding regional perfusion pressures were determined by correcting the measured perfusion pressure for hydrostatic effects. There were considerable differences in the slopes of the pressure vs. flow curves among lung regions. Dorso-caudal regions of the lung had higher vascular conductances than ventrocephalad regions, independent of the vertical orientation of the lung or the inflation volume during injections of microspheres. Thus the distributions of regional vascular conductances were related to the anatomic location and were not related to gravity, nor were they caused by nonuniformities in regional lung expansion or by hypoxic vasoconstriction or edema.

Animals↗
PubMed1986

Simulation of the vertical gradient of transpulmonary pressure by stable foams.

We describe a simulation of the vertical gradient of transpulmonary pressure (VGTP) using a stable foam, which is suitable for use in studies of the effect of the VGTP on excised lungs. We generated foams that produced linear hydrostatic pressure gradients (HPGs) from 0.18 to 0.44 cmH2O/cm depth, which were stable over time and were reproducible. The HPG was similar under static and dynamic conditions. The foam did not affect lung elastic properties or cause histological changes. We conclude that these stable foams provide a practical, inexpensive simulation of the VGTP and should be useful in studying the effects of the VGTP on regional lung behavior.

Animals↗
PubMed1985

High-frequency small-volume ventilation in anesthetized humans.

Pulmonary gas exchange during conventional mechanical ventilation (CMV) (tidal volume 10 ml/kg, rate 8-10 breaths/min) was compared with that during high-frequency small-volume ventilation (HFV) in 67 patients undergoing anesthesia for various surgical procedures. HFV was studied at oscillation frequencies ranging from 3 to 18 Hz with stroke volumes of 0.8 to 2.2 ml/kg. Adequate pulmonary gas exchange was achieved with CMV and HFV, and the efficiency of oxygenation, that is, (A-a)DO2, was similar in the two conditions. During HFV, the lung volume was higher than during CMV in most patients. Muscle paralysis did not significantly change either PaCO2 or PaO2. In general, increasing fresh gas flow into the HFV system above approximately 10 1/min resulted in little reduction in PaCO2, but reduction of fresh gas flow below approximately 6 1/min increased PaCO2 progressively. Currently, we do not recommend HFV at 12-18 Hz for routine use during anesthesia for orthopedic or abdominal surgery.

Adult↗
PubMed1984

Ventilation-perfusion relationship during high-frequency ventilation.

The efficiency of oxygenation and the uniformity of the distribution of regional ventilation (Vr) to regional perfusion (Qr) along the vertical and horizontal axes was compared in anesthetized dogs between conventional mechanical ventilation (CMV) and high-frequency ventilation (HFV) at 5.8, 15.0, and 29.8 Hz. Both CMV and HFV were adjusted to result in similar arterial CO2 tensions. The distribution of Vr/Qr during HFV at 5.8 Hz tended to be more uniform than during HFV at 15.0 or 29.8 Hz or during CMV. Consistent with this observation, arterial O2 tension (PaO2) tended to be higher during HFV at 5.8 Hz (means +/- SD, 90 +/- 9 Torr) than during HFV at 15.0 Hz (83 +/- 9 Torr) or 29.8 Hz (78 +/- 10 Torr); PaO2 was significantly higher during HFV at 5.8 Hz than during CMV (83 +/- 7 Torr).

Animals↗
PubMed1984

High-frequency ventilation: lymph flow, lymph protein flux, and lung water.

The effects of high-frequency oscillatory (HFV) ventilation on lung fluid balance and microvascular permeability to macromolecules were measured in open-chest dog lungs. Prenodal lung lymph flow, concentration of total plasma proteins in lymph and plasma, pulmonary arterial and left atrial pressure, cardiac output, and blood-free lung wet-to-dry weight ratios were measured for conventional mechanical ventilation (CMV, 12/min, 200-300 ml tidal volume) and HFV of 15 Hz and a stroke volume of 40-50 ml for normal and elevated left atrial pressures. HFV increased both lymph flow and lung water (68 and 20%, respectively), and lymph-to-plasma ratios of total plasma proteins remained unchanged. When left atrial pressure was increased, an analysis of lymph protein flux indicates that the lung microvascular permeability was not altered by HFV. The increase in lymph flow and lung water associated with HFV may reflect an increased microvascular exchange surface area or a change in interstitial fluid pressure.

Animals↗
PubMed1984

Gas transport and pulmonary perfusion during high-frequency ventilation in humans.

Regional pulmonary 133Xe clearances, regional 133Xe washins, regional distribution of pulmonary blood flow, and pulmonary gas exchange were determined during high-frequency small-volume ventilation (HFV, oscillation frequencies 12 or 18 Hz, stroke volumes 1.2-0.8 ml/kg) in six healthy anesthetized-paralyzed volunteers lying supine. Adequate pulmonary gas exchange was maintained by HFV; the efficiency of oxygenation during HFV did not differ significantly from that during conventional mechanical ventilation at similar mean lung volumes. During HFV regional pulmonary clearances and washins of tracer gas were different among regions. Apical nondependent lung regions cleared faster and had greater regional longitudinal gas conductances than did basal nondependent or dependent regions. The vertical gradient for pulmonary perfusion was preserved during HFV. Apparently the rate of interregional gas mixing is small during HFV at 12 and 18 Hz in anesthetized-paralyzed humans.

Adult↗
PubMed1983

Sedation and respiratory mechanics in man.

The effects of sedation with halothane, enflurane or midazolam on respiratory mechanics and lung volumes were studied in young healthy volunteers, in the supine position. Functional residual capacity increased with halothane sedation, but was unchanged with sedation produced by enflurane or midazolam. Sedation with halothane and enflurane, but not midazolam, tended to increase lung static recoil pressure. Total lung capacity was decreased during sedation with midazolam. No evidence was found that sedation with these three agents increased airway resistance. These findings imply that changes in respiratory mechanics induced by the residual effects of anaesthetic agents are unlikely to contribute significantly to the impairment in pulmonary gas exchange which may occur in the period immediately after operation.

Adult↗
PubMed1983

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.

Animals↗
PubMed1983

Gas mixing in the airways of dog lungs during high-frequency ventilation.

Washout of insoluble inert test gases of different diffusivity (He and SF6 or He and Ar) from dog lungs was studied during high-frequency ventilation (HFV). Test gas equilibrium and subsequent washout were performed with HFV, succeeding measurements being performed at different stroke volumes (1.5-2.5 ml/kg body wt), oscillation frequencies (10-30 Hz), and with different lung volumes (32-74 ml X kg-1). Test gas concentrations were continuously measured by a mass spectrometer. The time course of washout could be described as the sum of two exponentials. There were no consistent differences in the time courses of washout between He and SF6 or between He and Ar. It is concluded that gas mixing in the airways during HFV is not significantly limited by diffusion, and this is suggested to apply during HFV to steady-state transport of respiratory gases (e.g., O2 and CO2) as well as to the transient state of inert gas washout.

Animals↗
PubMed1983

Long-term high-frequency ventilation in dogs.

The lungs of 11 anesthetized dogs (with or without preexisting lung disease) were ventilated for 36 h by high-frequency, small-volume ventilation (HFV) to determine the effects of HFV on pulmonary gas exchange, mechanical properties of the respiratory system, and function of the cardiovascular system. For comparison, the lungs of 5 other anesthetized dogs without preexisting lung disease were ventilated with conventional mechanical ventilation (CMV) for a similar period. All dogs without preexisting lung disease whose lungs were ventilated with either HFV or CMV maintained satisfactory respiratory and cardiovascular functions for the duration of the study. After 36 h of HFV, no evidence for changes in the mechanical behavior of the lungs was detected. Small amounts of transudates were observed in the pleural space of all dogs ventilated with HFV; no dog ventilated with CMV had pleural effusions.

Animals↗
PubMed1982

Martin Kirschner.

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Fracture Fixation↗