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Biomedical subjects

P Scheid

Publications and source records attributed to P Scheid.

At least 145 records · Page 8Linked to original sources
PubMed1980

Tracheal volume in the pupa of the Saturniid moth Hyalophora cecropia determined with inert gases.

Tracheal volume (VTr) was measured in pupae of the Giant silkworm moth Hyalophora cecropia (Saturniidae, Lepidoptera, Insecta) using inert gas wash-out techniques. The animal was placed in a small vessel that was continuously ventilated (rate, V) by a gas mixture containing 20% O2 in N2; the inflowing (F1) and outflowing gas fractions (FE) of the vessel could be continuously measured by a respiratory mass spectrometer. At the onset of a spiracular constriction period, which was evidenced from the FECO2 trace, the mixture was rapidly replaced by pure Ar. At the subsequent burst, the amount of N2 emerging from the animal, MN2, was calculated from V and the difference (FE--F1)N2. VTr was calculated from MN2 and the N2 concentration in the tracheal system before constriction (assumed to equal that in the ventilating gas before replacement by Ar). Measurements were repeated with N2 and Ar replacing each other. VTr average 48 microliter . g-1 (range 39 to 59) for animals of 5.8 g average body weight (range 3.4 to 9.9), when inert gas solubility in body fluids was accounted for. Both size and stage in pupal development appear to affect VTr. These values show reasonable agreement with literature data, mostly obtained by emptying the tracheal gas space by mechanical compression.

Animals↗
PubMed1980

Alveolar-capillary equilibration kinetics of 13CO2 in human lungs studied by rebreathing.

Blood/gas equilibration of CO2 in lungs was studied in man by a rebreathing technique, in which the rate of uptake of the stable isotope 13CO2 in low concentration (inspired concentration about 0.07%) was measured at blood/gas equilibrium of the abundant CO2 isotope. The results were expressed in terms of overall conductance for alveolar gas-pulmonary blood equilibration (DCO2, pulmonary diffusing capacity for CO2). The following mean values of DCO2 were found in 3 healthy young men (in mmol . min-1 . Torr-1): rest, 8.0; during exercise (75 Watts), 13.7. Comparison with DO2 measured by rebreathing in the same conditions suggests equilibration of the CO2/HCO3(-)/H+ system in blood, rather than diffusion of CO2, as the limiting process in capillary/alveolar CO2 transfer. The term 'equilibration capacity' is thus suggested for DCO2. Calculations based on the experimental results show that the overall limitation of pulmonary CO2 exchange function resulting from this finite DCO2 is slight at rest, but of considerable extent in heavy exercise.

Carbon Dioxide↗
PubMed1980

Single-exhalation method for study of lobar and segmental lung function by mass spectrometry in man.

A single-exhalation method, based on a modification of the conventional single-breath technique, was applied to study lung function in normal subjects during fiberoptic bronchoscopy. After a single inspiration of a test gas mixture (1% He, 1% C2H2, 0.07% C18O in air), the test gas concentrations were continuously monitored during subsequent slow exhalation, using a respiratory mass spectrometer that sampled either at the lips (Whole-lung test) or, through the bronchoscope, at various sites within the bronchial tree (Regional test). Changes in concentrations of the test gases with time allowed estimation of alveolar ventilation (Va), blood flow (Q), and diffusing capacity (DLCO), per unit accessible lung volume (Va). In the Whole-lung test, both DLCO and Q agreed closely with values obtained in the same subject by a rebreathing method. No differences were observed between the upright and the lateral decubitus positions. In teh Regional test, VA/VA, DLCO/VA and Q/VA were larger in the dependent than in the upper lung, when sampling was from the main bronchi in the lateral decubitus positions. Sampling from lobar bronchi in the upright position revealed an increase from top to bottom in VA/VA, DLCO/CA and Q/VA, this being most marked for Q. These results are compatible with the regional variations that have been shown by radioactive techniques and have been attributed to gravitational forces. The method appears to be suitable for the study of lobar and segmental lung function in patients with lung disease.

Bronchoscopy↗
PubMed1980

Incomplete gas mixing in air sacs of the duck.

During normal breathing, the CO2 concentration in caudal air sacs of birds is higher, and the O2 concentration lower, than expected on the basis of the known air flow pattern. We have experimentally tested two hypotheses which could explain this finding: (1) Preferential shunting of re-inspired dead space gas into caudal air sacs; (2) Incomplete mixing of inspired and residential air sac gas. - Different portions of the inspired air in anesthetized ducks were labeled by injecting a small bolus of argon (Ar) into the trachea. The resulting Ar concentration was recorded continuously in the caudal thoracic air sac at the ostium and in deeper regions.-The amount of Ar entering the sac was found to be independent of the volume inspired prior to injection of the label, and hypothesis (1) thus dismissed. However, during inspiration and subsequent expiration the Ar bolus was found to be neither perfectly mixed within the inspired gas nor with the air sac residential gas. More than 10 sec of breath-hold were necessary for air sac gas to approach an equilibrium value. Gas layering (stratification) in caudal air sacs gas is proposed to cause the high CO2 and low O2 levels during steady state breathing, as air sac residential gas equilibrates with a layer of dead space gas that enters the air sac on each breath and contains a higher CO2 and lower O2 concentration than the mixed inspirate.

Animals↗
PubMed1980

Solubility of acetylene in human blood determined by mass spectrometry.

To measure the acetylene solubility (alpha C2H2) in human blood, a blood sample, which had been equilibrated with a gas mixture containing C2H2, was injected into an airtight acetylene-free vessel, and the gas partial pressure was measured by mass spectrometry after reequilibration. The system was calibrated by injecting into the vessel a known volume of the equilibrating gas mixture. At 37 degrees C, alpha C2H2 averaged 0.768 +/- 0.004 (SD) ml STPD.ml blood-1.atm-1, which is only slightly above the data from the literature.

Acetylene↗
PubMed1980

Solubility of helium, argon, and sulfur hexafluoride in human blood measured by mass spectrometry.

A method has been developed to measure the solubility coefficients of gases in liquids by respiratory mass spectrometry. A sample (2.5 ml) pf the test liquid, equilibrated with a test gas mixture, is injected into a sealed flask (approximately 140 ml) for extraction by equilibration. The reequilibrated gas phase in the flask is analyzed by a mass spectrometer. Separately, an equal volume (2.5 ml) of the equilibrating test gas mixture is injected into a larger sealed flask (approximately ll liter) where it is mixed and then analyzed by the mass spectrometer. Solubility in the liquid is calculated from the ratio of mass spectrometer readings in both flasks and the ratio of flask volumes. The ratio of volumes of the small and the large flasks is made similar to the gas/liquid partition coefficient whereby the mass spectrometer readings in both become similar. With this approach, errors due to amplifier and mass spectrometer nonlinearity are greatly attenuated. The method was used to measure the solubility of helium, argon, and sulfur hexafluoride in distilled water, human plasma, and human blood.

Argon↗
PubMed1979

Measurement of the distensibility of the parabronchi in duck lungs.

Air flow resistance in the parabronchial lung of the duck was measured at various pressure differences between the lung and the body surface (Prs) using a body plethysmograph. One lung of the anesthetized animal was ventilated at a steady flow rate, from trachea, through the parabronchial lung, and out via a cannula in the caudal thoracic air sac (Tr leads to CS flow), or vice versa (CS leads to Tr flow), all flow being directed over the parabronchi (Pb) by blocking the main bronchus between the medioventral (MV) and mediodorsal secondary bronchi (MD). Pressure differences were measured between MV and MD (Ptot), and between the clavicular air sac and MD giving the pressure drop along the parabronchial tubes (PPb). The pressure drop along MV, PVb, was derived as Ptot-PPb. Air flow resistances, Rtot, RPb, RVb, were calculated from the ratio of the corresponding pressure difference to the flow rate. Results show: (1) All resistances decreased with increasing distending pressure (Prs) from -20 to +20 cm H2O this change being most pronounced around Prs = 0; (2) The flow resistance of these structures depended on the flow direction, being smaller with Tr leads to CS flow during distension than in the opposite direction; (3) Arterial blood gases did not significantly change with varying distending pressure, suggesting unimpaired gas exchange even when the lung is significantly compressed. The results indicate that the parabronchi and the secondary bronchi of the duck lung have a finite compliance but that changes in intrapulmonary pressure, compression of the lung, do not result in significant collapse of the air capillaries with ensuing impairment of gas exchange.

Airway Resistance↗
PubMed1979

Gas exchange in the parabronchial lung of birds: experiments in unidirectionally ventilated ducks.

Pulmonary exchange of O2 and CO2 was measured in unidirectionally ventilated ducks in an attempt to determine lung O2 diffusing capacity, DO2. Perfusion shunt (= venous admixture) was estimated from O2 exchange in hyperoxia, and the ventilation shunt (ventilation of non-perfused parallel lung units) was estimated from exchange of the highly soluble inert gas, chloroform. Differences in the ventilation/perfusion ratio of parallel lung units were assessed from measurement of CO2 exchange using a parallel two-compartment model. DO2 values were calculated accounting for ventilation shunt, perfusion shunt, and inhomogeneity. Perfusion shunt averaged 2.7% and ventilation shunt, 9.4%. The ventilation/perfusion ratio in the two compartments differed on the average by a factor of 2.6. The uncorrected values of DO2, not accounting for lung inhomogeneities, progressively declined with increasing inspired PO2, but this dependence was less pronounced after correcting for lung inhomogeneities. The corrected value of DO2 averaged 100 mumol . min-1 . torr-1 for ducks of 1.8 kg mean body weight. DO2 did not differ when nitrogen was replaced by helium in the ventilatory gas indicating that diffusion within the air capillaries did not contribute a significant resistance to O2 uptake. The results suggest that neither functional inhomogeneities nor diffusion between lung gas and blood limit O2 uptake of the resting duck. Under conditions of elevated metabolism, however, these parameters may become rate-limiting for O2 supply.

Animals↗
PubMed1979

On the boundary conditions used in calculations of gas mixing in alveolar lungs.

The lung boundaries exhibit a tight barrier for any insoluble gas; hence boundary conditions for lung gas mixing have to account for the absence of both diffusive and convective fluxes across the lung walls. Scrimshire et al. (1978) have, in contrast, used the less rigid boundary condition that only the net flux be zero. As we believe this boundary condition to be inappropriate for the study of insoluble gases, the results derived appear to have no physiological significance.

Humans↗
PubMed1979

Arterial-expired PCO2 differences in the dog during acute hypercapnia.

A recent report (J. Appl. Physiol. 38: 382-388, 1975) suggests that negative blood-gas CO2 partial pressure (PCO2) differences exist in the dog during hypercapnia, as mean expired PCO2 exceeded arterial PCO2 by more than 10 Torr when the CO2 fraction in inspired gas (FICO2) was 0.1. We have reinvestigated this problem in anesthetized dogs breathing spontaneously room air or hypercapnic mixtures (FICO2 = 0.05 or 0.10). During steady state, arterial blood samples were analyzed with electrodes, care being taken to keep the electrode temperature within +/- 0.2 degrees C at the actual aortic temperature of the animal. Respired gas was measured at the tracheostomy by a sensitive low-noise respiratory mass spectrometer. During room air breathing, the arterial-end-expired PCO2 difference, P(a-E')CO2, averaged +5 Torr and decreased to +0.9 Torr and to +0.1 Torr with FICO2 = 0.05 and 0.1, respectively. Hypoxia (FIO2 = 0.10) had no apparent effect on the P(a-E')CO2 difference. We ascribe the decrease in P(a-E')CO2 with hypercapnia to the diminishing effects of alveolar dead space, whereby end expired PCO2 approached arterial PCO2. We then conclude that in blood-gas equilibration lungs, PCO2 in end-capillary blood comes close to alveolar PCO2, and that the negative blood-gas PCO2 differences reported earlier are probably caused by deficiencies in the techniques used.

Animals↗
PubMed1978

Bohr effect induced by CO2 and fixed acid at various levels of O2 saturation in duck blood.

The Bohr factor, phi = delta log Po2/deltapH, was determined at various levels of hemoglobin O2 saturation (SO2) in fresh whole blood of the duck. Plasma pH was varied by either changing PCO2 of the blood at constant base excess (CO2 Bohr factor, phiCO2) or by addition of NaHCO3 and HCl at constant PCO2 (fixed acid BOHR factor, phiAH). No differences were found between phiCO2 and phiAH at SO2 levels between 20 and 85%, and there was no saturation dependence of the Bohr factor, its average value being -0.44. It is concluded that in whole blood of this bird species CO2 exerts no direct effect on the O2 affinity of hemoglobin.

Animals↗
PubMed1978

Ventilatory response to CO2 in birds. I. Measurements in the unanesthetized duck.

Ventilation and blood gases were measured in unanesthetized ducks at various levels of inspired CO2 partial pressure (PICO2). Ventilation was markedly augmented with increasing PICO2, whereas arterial and mixed venous PCO2 stayed essentially constant up to a PICO2 of about 20 torr and changed only slightly between that and the highest level tested (34 torr). After carbonic anhydrase had been blocked, blood PCO2 was elevated at all levels of PICO2 but the ventilatory response to increases in PICO2 were attenuated. The response to CO2 in the normal bird (before administration of acetazolamide) shows similarities to that in mammals. Qualitative differences between both classes of vertebrates after blockade of carbonic anhydrase may, however, suggest differences in their systems that control ventilation.

Acetazolamide↗
PubMed1978

Ventilation response to CO2 in birds. II. Contribution by intrapulmonary CO2 receptors.

The CO2 sensitivity of intrapulmonary CO2 receptors (IPC) in the duck was studied, before (Control) and after blockade of carbonic anhydrase by Diamox, by recording single unit afferent activity in the vagus nerve. During Control, IPC activity decreased with increasing airway CO2 concentration. After Diamox administration, the discharge from IPC was higher at all levels of airway PCO2, and the receptors' CO2 sensitivity was markedly attenuated. Comparing these results with measurements on ventilation and blood gases of the duck under similar experimental conditions (Powell et al., 1978b) suggests that IPC play a role in the adjustment of ventilation to altered concentrations of inspired CO2; IPC may thus be a significant component in the control of breathing under physiological conditions.

Acetazolamide↗
PubMed1978

Response of intrapulmonary chemoreceptors in the duck to changes in PCO2 and pH.

We have estimated the relative importance of changes in blood PCO2 and pH in determining activity of intrapulmonary chemoreceptors (IPC) in the unidirectionally ventilated duck. The response of single unit vagal afferents from IPC to changing lung gas PCO2 was tested before and after changing blood pH by intravenous infusion of NaHCO3. Using multiple linear regression analysis, we calculated how much of the change in IPC activity for a given change in PCO2 was due to the changing PCO2 at constant pH (CO2 sensitivity) or to the change in pH concomitant with the change in PCO2 (H+ sensitivity). For 10 IPC, the CO2 sensitivity was on the average 2.3 times larger than the H+ sensitivity. Changes in pH as well as PCO2 of lung blood should be considered in assessing the role of IPC in control of breathing.

Action Potentials↗