PubMed Health⌕ Search

Biomedical subjects

H J Guy

Publications and source records attributed to H J Guy.

27 records · Page 2Linked to original sources
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

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↗
PubMed1982

Phase V of the single-breath washout test.

A downward-deflecting phase V is often seen following the phase IV terminal rise in the single-breath N2 washout test (SB N2). This phase V was studied in eight normal nonsmoking subjects aged 27-41, using both the SB N2 test and single-breath washouts of boluses of inert tracer gas slowly inhaled from residual volume (RV). All of the subjects showed a distinct phase V in both tests. Expiratory flow rates between 0.1 and 2.0 1/s were used; at each flow rate phase V appeared shortly after expiration became flow limited. Thus the volume above RV at which phase V began increased with increasing expiratory flow rate. The difference between the exhaled volumes at which flow became limited and phase V appeared was shown to be approximately equal to the anatomic dead space. This behavior is predicted by a model of lung emptying in a gravitational field. As expiration proceeds, flow limitation occurs first in the (tracer-poor) lower lung regions and then progresses toward the (tracer-rich) upper lung regions causing phase IV. When all lung regions have finally become flow limited, the amount of flow from the upper regions decreases relative to that of the lower regions, thereby causing phase V.

Adult↗
PubMed1980

DALE--a system for developing computer-aided biomedical experiments.

The implementation of new computer-aided biomedical experiments usually requires a high level of computing expertise and a significant amount of time. Acquiring this knowledge and devoting the necessary time may result in the inefficient use of a researcher's own particular skills. A number of software aids for laboratory experimentation have been developed, but it is considered that none adequately satisfies the user's requirements. DALE (direct access to laboratory equipment) has been designed as a user-oriented software system, and consists of a menu-based interactive subsystem, with which experiments are defined, and a table-driven interpreter to execute the experiment. Little computing knowledge or development time is required to implement new experiments, and experience has indicated that DALE is a useful tool for biomedical experimentation.

Computers↗
PubMed1976

Computerized, noninvasive tests of lung function. A flexible approach using mass spectrometry.

The design, operation, and some applications of a computerized pulmonary function testing system built around a mass spectrometer are described. The test sequence, performed in 10 to 20 min, includes spirometry, a single-breath N2 washout, and measurement of the diffusing capacity of the lung for CO. Secondary tests, an integral part of the sequence, include rebreathing estimates of lung volume and cardiac output, and a breath-by-breath analysis of over-all gas exchange. These secondary tests lead to computer modeling of a one-compartment lung closely matched to the subject's lungs. Differences between alveolar plateau slopes in the model and real lung provide information about the degree of ventilation-perfusion mismatch in the subject. It is expected that the combination of tests will be useful in the early detection of lung disease.

Computers↗