Biomedical subjects

G K Prisk

Publications and source records attributed to G K Prisk.

3 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↗