Biomedical subjects

G K Prisk

Publications and source records attributed to G K Prisk.

8 recordsLinked to original sources

PubMed1992

Avian arterial chemoreceptor responses to steps of CO2 and O2.

The responses of avian arterial chemoreceptor preparations to 44-sec steps of inspired CO2 and O2 were quantified. Anesthetized ducks were unidirectionally ventilated, arterial pH was recorded with a fast responding indwelling electrode, and neural activity was recorded from 28 preparations consisting of dissected filaments of the vagus nerve (23 single-fibered, 5 few-fibered). We analyzed responses using cycle-triggered stimulus histograms of neural discharge, cross correlation analysis, and analysis of variance. Average responses of the chemoreceptor preparations to PaCO2 steps from 24 +/- 1 to 38 +/- 1 Torr were larger (per Torr), occurred faster, and appeared more rate sensitive than the responses to PaO2 steps from 101 +/- 3 to 56 +/- 2 Torr. Average responses to CO2 steps usually appeared more rate sensitive when measured during arterial hypoxia than during arterial normoxia. These characteristics are very much like those reported for mammalian arterial chemoreceptors, except that responses of avian chemoreceptor preparations to repetitive CO2 steps were highly variable according to statistical analysis.

Animals↗

PubMed1992

Pulmonary function in microgravity.

We report the successful collection of a large quantity of human resting pulmonary function data on the SLS-1 mission. Preliminary analysis suggests that cardiac stroke volumes are high on orbit, and that an adaptive reduction takes at least several days, and in fact may still be in progress after 9 days on orbit. It also suggests that pulmonary capillary blood volumes are high, and remain high on orbit, but that the pulmonary interstitium is not significantly impacted. The data further suggest that the known large gravitational gradients of lung function have only a modest influence on single breath tests such as the SBN washout. They account for only approximately 25% of the phase III slope of nitrogen, on vital capacity SBN washouts. These gradients are only a moderate source of the cardiogenic oscillations seen in argon (bolus gas) and nitrogen (resident gas), on such tests. They may have a greater role in generating the normal CO2 oscillations, as here the phase relationship to argon and nitrogen reverses in microgravity, at least at mid exhalation in those subjects studied to date. Microgravity may become a useful tool in establishing the nature of the non-gravitational mechanisms that can now be seen to play such a large part in the generation of intra-breath gradients and oscillations of expired gas concentration. Analysis of microgravity multibreath nitrogen washouts, single breath washouts from more physiological pre-inspiratory volumes, both using our existing SLS-1 data, and data from the upcoming D-2 and SLS-2 missions, should be very fruitful in this regard.(ABSTRACT TRUNCATED AT 250 WORDS)

Gravitation↗

PubMed1991

Maximum expiratory flow-volume curves during short periods of microgravity.

To elucidate the effect of normal gravitation on the shape of the maximum expiratory flow-volume (MEFV) curve, we studied nine normal subjects in a National Aeronautics and Space Administration microgravity research aircraft. They performed multiple MEFV maneuvers at 0, 1, and approximately 2 G. The MEFV curves for each subject were filtered, aligned at residual volume, and ensemble averaged to produce an average MEFV curve for each state, allowing differences to be studied. Most subjects showed a decrease in the forced vital capacity at 0 G, which we attribute to an increased intrathoracic blood volume. In most of these subjects, the mean lung volume associated with a given flow was lower at 0 G over about the upper half of the vital capacity. This is similar to the change previously reported during headout immersion and is consistent with the known effect of engorgement of the lung with blood on elastic recoil. There were also consistent but highly individual changes in the position and magnitude of detailed features of the curve, the individual patterns being similar to those previously reported on transition from the erect to the supine position. This supports the idea that the location and motion of choke points that determine the detailed individual configuration of MEFV curves can be significantly influenced by gravitational forces, presumably via the effects of change in longitudinal tension on local airway pressure-diameter behavior and thus wave speed.

Adult↗

PubMed1988

Influence of collateral ventilation on single-breath washout curves.

To examine the relationship between airway closure and collateral ventilation, Ar bolus single-breath washout tests were performed in the supine position in 10 mature dogs (animals with a well-developed collateral ventilation). Transpulmonary pressure was measured simultaneously to obtain the volume above residual volume of the inflection point in the pressure-volume curve (VIP). In pigs, closing volume (CV/VC%, mean 27.4%, where VC is vital capacity) equaled the volume of inflection (VIP/VC%, mean 35.1%) when the dead space (0.07 liter) was accounted for, indicating simultaneous onset. In dogs, closing volume (CV/VC%, mean 48.1%) was greater than the volume of inflection (VIP/VC%, mean 27%). Furthermore, as closing volume increased, so did the volume exhaled between closing volume and the volume of inflection [(CV-VIP)/VC%]. These increases were strongly age related, with the oldest dogs showing the greatest differences between closing volume and volume of inflection. These results support the previous suggestion that this difference is a measure of the degree of collateral ventilation. We defined a concavity index (CI) of phase IV by measuring the ratio of the end-to-mid phase IV height above extrapolated phase III (no concavity implies CI = 2). Whereas pigs had a low CI (mean 3.3), dogs had a high CI (mean 10.6). In dogs, the CI correlated well with closing volume (CV/VC%) and the volume exhaled between closing volume and volume of inflection [(CV-VIP)/VC%]. Again, this relationship was strongly dependent on age, suggesting that the CI is also a valid indication of the degree of collateral ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1988

Gravitational independence of single-breath washout tests in recumbent dogs.

To examine the mechanisms of lung filling and emptying, Ar-bolus and N2 single-breath washout tests were conducted in 10 anesthetized dogs (prone and supine) and in three of those dogs with body rotation. Transpulmonary pressure was measured simultaneously, allowing identification of the lung volume above residual volume at which there was an inflection point in the pressure-volume curve (VIP). Although phase IV for Ar was upward, phase IV for N2 was small and variable, especially in the prone position. No significant prone to supine differences in closing capacity for Ar were seen, indicating that airway closure was generated at the same lung volumes. The maximum deflections of phase IV for Ar and N2 from extrapolated phase III slopes were smaller in the prone position, suggesting more uniform tracer gas concentrations across the lungs. VIP was smaller than the closing volume for Ar, which is consistent with the effects of well-developed collateral ventilation in dogs. Body rotation tests in three dogs did not generally cause an inversion of phase III or IV. We conclude that in recumbent dogs regional distribution of ventilation is not primarily determined by the effect of gravity, but by lung, thorax, and mediastinum interactions and/or differences in regional mechanical properties of the lungs.

Animals↗

PubMed1987

A modeling approach to the estimation of CO diffusing capacity.

Standard methods of measuring the diffusing capacity of the lung for CO are susceptible to inhomogeneity and to errors in the performance of a breathing maneuver by the subject. A mathematical model of CO uptake from a single alveolar lung is developed and used as the basis for an estimation procedure to measure both lung volume and diffusing capacity during a rebreathing maneuver. Because this estimator-model uses the exact flow generated by the subject, errors in such factors as breath-hold times or depth of inspiration do not result. The estimator-model was tested using simulated data from uniformly and nonuniformly ventilated models and was found to be insensitive to noise and inhomogeneity, in contrast to the diffusing capacity of the lungs for CO (exhaled). The estimator-model makes greater use of the available data than traditional methods by utilizing both the slope of the alveolar plateaus for CO and the relative heights of such plateaus in a rebreathing experiment.

Capillaries↗

PubMed1987

Estimation of amount of stationary pulmonary blood from carbon monoxide uptake measurements.

A mathematical model of CO uptake from a single alveolus is modified to include stationary pulmonary blood arising from a pulmonary vascular obstruction. From this model an estimator model is developed that produces simultaneous estimations of the diffusing capacity of the lung for CO and the fraction of the pulmonary capillary blood that is stationary. The estimator model was tested using simulated data from uniform and non-uniform simulators and found to be only mildly sensitive to noise and incorrect values for the pulmonary capillary blood volume. Both the estimator model and breath-to-breath changes in the diffusing capacity of the lung for CO (exhaled) were found to be greatly affected by inhomogeneity of diffusing capacity and ventilation. At times both returned false positive results that limit their use as a screening test for stationary pulmonary blood. Although changes in CO uptake may at times indicate the presence of stationary pulmonary blood, the confounding effects of inhomogeneity of ventilation and diffusing capacity make the use of such changes impractical under most circumstances.

Animals↗

PubMed1987

Carbon dioxide response and breath-hold times in underwater hockey players.

Competitive underwater hockey play demands frequent and prolonged breath-hold dives. To see whether participants were physiologically adapted to breath-hold diving we studied the ventilatory response to carbon dioxide (CO2) and the breath-hold times of 34 male, underwater hockey players (divers) and compared them to 28 male, dry-land sportsmen (athletes). The divers showed an increased tolerance to CO2, the mean (+/- SD) slope of the CO2 response curve being 1.08 (+/- 0.55) liter.min-1.mmHg CO2(-1) when measured by the rebreathing method. This was significantly less (P less than 0.005) then that of the athletes 1.68 (+/- 0.72) liter.min-1.mmHg CO2(-1). The breath-hold times measured at 2 lung volumes did not differ significantly between the 2 groups. A subgroup of 8 international underwater hockey players exhibited prolonged breath-hold times but were otherwise similar to the rest of the divers in the other measured parameters.

Adult↗