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Biomedical subjects

F L Powell

Publications and source records attributed to F L Powell.

66 records · Page 4Linked to original sources
PubMed1982

Measurement of continuous distributions of ventilation-perfusion in non-alveolar lungs.

We modified the multiple inert gas elimination technique, which was originally developed for alveolar lungs, to measure continuous distributions of V/Q in the cross-current lungs of birds. In theory, the method is also applicable to counter-current gas exchangers. The algorithms for inferring essentially continuous V/Q distributions from a limited number of measurements and the least-squares approach for dealing with experimental error are independent of the model of gas exchanger being studied. A Monte-Carlo procedure was used to predict the expected frequency of occurrence of given magnitudes of experimental error for each model. If the observed frequency distribution of error exceeds the predicted, then this indicates an incorrect choice of model (analogous to chi-square tests). Thirty-four data sets from 8 geese indicate that: (1) the assumptions of the technique are adequately met; (2) the alveolar model is not appropriate for birds, but the cross-current model is; and therefore; (3) the cross-current modification of the multiple inert gas elimination technique can be used to assess V/Q inequality in avian lungs.

Animals↗
PubMed1982

Ventilation-perfusion inequally in avian lungs.

We assessed ventilation-perfusion inequality in 8 anesthetized, tidally ventilated geese in terms of continuous V/Q distributions using the multiple inert gas elimination technique modified for cross-current avian lungs (Powell and Wagner, 1982). Thirty-four data sets were collected. Allowing for differences in solubility, high molecular weight gases (Enflurane, SF6) were not retained in the blood to any greater extent than the other gases, suggesting that diffusion in the gas phase is functionally complete. Shunt averaged only 0.4 +/- 0.1% (SEM) of cardiac output and areas of low V/Q were seldom seen. Twenty-nine of the 34 data sets had bimodal V/Q distributions with 10.6 +/- 1.4% of expired ventilation and 0.3 +/- 0.1% of cardiac output in a high V/Q mode; the physiological basis of the high mode is unknown. The log-standard deviation of the main Q mode averaged 0.56 or slightly greater than that for healthy men, dogs, or earlier estimates from unidirectionally ventilated birds. It is predicted that CO2 will be more impaired by such V/Q inequality than O2, but that increased ventilation will overcome the CO2 impairment more easily than that of O2 transport.

Animals↗
PubMed1982

Intrapulmonary CO2 receptors and control of breathing in ducks: effects of prolonged circulation time to carotid bodies and brain.

The role of intrapulmonary chemoreceptors in the breath-to-breath control of spontaneous breathing was studied in anesthetized ducks by stimulating these receptors with changes in mixed venous CO2 loads during prolonged circulation time to the carotid bodies and brain by vascular loops placed in both brachiocephalic arteries. Blood equilibrated with gas mixtures of high (85% CO2-15% O2) or low CO2 (air) was infused into the right ventricle at 100 ml . min-1, while simultaneously withdrawing blood from the entrance of the right atrium at the same rate. A variety of cardiopulmonary and blood gas variables were measured. Infusing blood of high PCO2 increased both respiratory frequency and tidal volume long before the altered blood could have reached the carotid bodies or brain. The increase in ventilation was not enough to prevent a rise in PaCO2. Infusing blood of low PCO2 decreased both respiratory frequency and tidal volume. Again, the changes in respiration occurred before the infused blood had reached the carotid bodies or the brain. Infusion of blood similar in PCO2 to mixed venous blood did not significantly alter ventilation or arterial blood gases. The rapidity of the ventilation response to a change in mixed venous CO2 load led us to conclude that the intrapulmonary chemoreceptors can detect changes in mixed venous CO2 loads and that they initiate a ventilatory change appropriate to minimize alterations in PaCO2. These receptors, thus, can control breathing on a breath-to-breath basis in birds.

Animals↗
PubMed1982

Diffusion in avian lungs.

Arterial PO2 in resting, normoxic avian lungs in not at the level of predicted for an ideal crosscurrent lung. In contrast to healthy alveolar lungs, such a reduction in efficiency of O2 exchange from optimal levels cannot be totally explained by ventilation/perfusion inequality, and the discrepancy is most likely related to diffusion resistances. The diffusing capacity of avian lungs (DLO2) will depend on: 1) stratification in the air capillaries, 2) blood-gas barrier morphology, 3) O2-Hb kinetics ( theta ), and 4) diffusive/perfusive conductance (D/ beta bQ) matching. Stratification in air capillaries, the membrane diffusing capacity, and time available in pulmonary capillaries for arterialization do not appear to be limiting at rest. D/ beta bQ inequality is expected in normoxic avian lungs but predictive models show that this should not limit O2 uptake. However, these resistances may interact in crosscurrent lungs or there may be other unknown diffusion limitations (e.g., theta ) to reduce PaO2 in birds. Recent morphologic evidence suggests DLO2 may increase in birds during exercise and V/Q and D/ beta bQ inequality would be expected to have less of an effect during hypoxia. Together, these factors may reconcile the relatively low PaO2 in resting birds at sea level and their ability to exercise at high altitudes.

Animals↗
PubMed1981

Airflow in the avian respiratory tract: variations of O2 and CO2 concentrations in the bronchi of the duck.

Variations of CO2 and O2 concentrations within a respiratory cycle were recorded at various sites in the bronchial system of anesthetized, spontaneously ventilating ducks, using small metal cannulae introduced into the main bronchus (MB), a medioventral (MV) or mediodorsal (MD) secondary bronchus and connected to a mass spectrometer for continuous gas analysis. The following results were obtained and conclusions drawn. (1) Since during inspiration, CO2 concentration (FCO2) was close to zero all along MB and since FCO2 was nearly constant throughout the respiratory cycle in MV, it must be inferred that on inspiration, no significant amount of air passes directly either from MV to MB or in the opposite direction, there being thus a complete functional valving of the MV orifices. In particular the Hazelhoff loop mechanism (inspiratory reflux of lung gas into the MB) is not operative. (2) During expiration, FCO2 in MV was only slightly higher than that in the trachea, but substantially above FCO2 deep in MB. This suggests that most of the expiratory flow from caudal air sacs is diverted through the paleopulmo and only little exits directly through MB. It is shown that the functional valving of bronchial air flow is advantageous for gas exchange as it reduces air shunts and provides a nearly steady lung ventilation.

Animals↗
PubMed1980

Ventilatory response to the PCO2 profile in chicken lungs.

We investigated the influence of intrapulmonary chemoreceptors (IPC) on ventilatory movements in anesthetized chickens when PCO2 profiles along the parabronchi were changed. In all experiments the right lung was denervated, both lungs unidirectionally ventilated, and PaCO2 kept constant. In series 1 (7 birds), gas flow and the PCO2 profile in the left lung were reversed. PaCO2, PECO2 and ventilatory movements did not change. In Series 2 (4 birds), PCO2 in caudal regions of the innervated lung was elevated by increasing gas flow and P1CO2 from 0 to 21 Torr. Ventilatory movements did not change. In Series 3 (4 birds), either lung was over-ventilated with 7 or 49 Torr P1CO2, alternating the gases between lungs every 100 sec. Ventilatory movements changes with P1CO2 but much less than predicted from P1CO2 effects in the non-perfused, innervated lung. From the longitudinal distribution of IPC and PCO2 profiles in the lung we predicted moderate to large changes in ventilatory movements in all series. The discrepancy between predicted and observed results in Series 1 and 2 indicates that IPC in caudal regions of the lung have little effect on ventilation under the conditions examined. In Series 3, observed ventilatory movements were less sensitive to P1CO2 than predicted, indicating that IPC sense a different PCO2 than the PCO2 profile in the parabronchial lumen and that IPC have a significant sensitivity to pulmonary blood PCO2.

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↗
PubMed1976

Response to CO2 of intrapulmonary chemoreceptors in the emu.

We studied discharge frequencies of 12 intrapulmonary chemoreceptors in the paleopulmonic lung of an emu (Dromiceius novaechollandiae) during unidirectional, artificial ventilation when step changes and static CO2 concentrations were given. Discharge frequency in afferent neurons from the receptors increased as intrapulmonary CO2 decreased. The response of the receptors to various static intrapulmonary CO2 concentrations was similar to that previously demonstrated for the duck and chicken. The median sensitivity of the emu receptors at one-half maximal discharge was 4.6 imp-(sec-0.01 F1CO2)-1. Discharge frequencies altered phasically in nine of 12 receptors when step changes in CO2 of 3.3% at 1.6 Hz were given in the unidirectional gas stream while four of 12 modulated their discharge when the CO2 changes were as rapid as 3.2 Hz. Hence, some receptors can respond to rapid fluctuations in CO2 in their microencironment. We conclude that intrapulmonary chemoreceptors in the paleopulmonic lung of the emu exhibit similar characteristics to those in birds that possess varying amounts of neopulmonic parabronchi, such as the duck and chicken.

Animals↗
PubMedDate not supplied

Effects of normobaric and hypobaric hypoxia on ventilation and arterial blood gases in ducks.

We measured ventilation (V1) and arterial blood gases in awake Pekin ducks exposed to normoxia at sea level, normobaric hypoxia achieved by lowering FIO2 at normal barometric pressure (NORMO), and hypobaric hypoxia achieved with a low pressure chamber and 21% O2 (HYPO). Average normoxic values were: V1 = 0.46 L . (kg.min)-1, PaO2 = 99.7 Torr, PaCO2 = 30.1 Torr. At PIO2 = 90 Torr, NORMO and HYPO measurements were not significantly different (P greater than 0.05). At PO2 = 46 Torr, NORMO V1 was less than HYPO V1 but blood gases were not significantly different: VI = 1.00 vs 1.45 L . (kg.min)-1; PaO2 = 31.3 vs 33.0 Torr; PaCO2 = 11.5 vs 10.6 Torr. Although both tidal volume (VT) and respiratory frequency (fR) were greater in HYPO, similar blood gases with NORMO and HYPO suggest similar parabronchial ventilation. The results suggest increased physiologic dead space, caused by reduced efficacy of aerodynamic valving, with reduced gas density in hypobaria.

Air Pressure↗