Biomedical subjects

J R Torre-Bueno

Publications and source records attributed to J R Torre-Bueno.

10 recordsLinked to original sources

PubMed1992

Colour thresholding and objective quantification in bioimaging.

Computer imaging is rapidly becoming an indispensable tool for the quantification of variables in research and medicine. Whilst its use in medicine has largely been limited to qualitative observations, imaging in applied basic sciences, medical research and biotechnology demands objective quantification of the variables in question. In black and white densitometry (0-256 levels of intensity) the separation of subtle differences between closely related hues from stains is sometimes very difficult. True-colour and real-time video microscopy analysis offer choices not previously available with monochrome systems. In this paper we demonstrate the usefulness of colour thresholding, which has so far proven indispensable for proper objective quantification of the products of histochemical reactions and/or subtle differences in tissue and cells. In addition, we provide interested, but untrained readers with basic information that may assist decisions regarding the most suitable set-up for a project under consideration. Data from projects in progress at Tulane are shown to illustrate the advantage of colour thresholding over monochrome densitometry and for objective quantification of subtle colour differences between experimental and control samples.

Animals↗

PubMed1986

Pulmonary gas exchange in humans exercising at sea level and simulated altitude.

In a previous study of normal subjects exercising at sea level and simulated altitude, ventilation-perfusion (VA/Q) inequality and alveolar-end-capillary O2 diffusion limitation (DIFF) were found to increase on exercise at altitude, but at sea level the changes did not reach statistical significance. This paper reports additional measurements of VA/Q inequality and DIFF (at sea level and altitude) and also of pulmonary arterial pressure. This was to examine the hypothesis that VA/Q inequality is related to increased pulmonary arterial pressure. In a hypobaric chamber, eight normal subjects were exposed to barometric pressures of 752, 523, and 429 Torr (sea level, 10,000 ft, and 15,000 ft) in random order. At each altitude, inert and respiratory gas exchange and hemodynamic variables were studied at rest and during several levels of steady-state bicycle exercise. Multiple inert gas data from the previous and current studies were combined (after demonstrating no statistical difference between them) and showed increasing VA/Q inequality with sea level exercise (P = 0.02). Breathing 100% O2 did not reverse this increase. When O2 consumption exceeded about 2.7 1/min, evidence for DIFF at sea level was present (P = 0.01). VA/Q inequality and DIFF increased with exercise at altitude as found previously and was reversed by 100% O2 breathing. Indexes of VA/Q dispersion correlated well with mean pulmonary arterial pressure and also with minute ventilation. This study confirms the development of both VA/Q mismatch and DIFF in normal subjects during heavy exercise at sea level. However, the mechanism of increased VA/Q mismatch on exercise remains unclear due to the correlation with both ventilatory and circulatory variables and will require further study.

Adult↗

PubMed1985

Ventilation-perfusion inequality in normal humans during exercise at sea level and simulated altitude.

To investigate the effects of both exercise and acute exposure to high altitude on ventilation-perfusion (VA/Q) relationships in the lungs, nine young men were studied at rest and at up to three different levels of exercise on a bicycle ergometer. Altitude was simulated in a hypobaric chamber with measurements made at sea level (mean barometric pressure = 755 Torr) and at simulated altitudes of 5,000 (632 Torr), 10,000 (523 Torr), and 15,000 ft (429 Torr). VA/Q distributions were estimated using the multiple inert gas elimination technique. Dispersion of the distributions of blood flow and ventilation were evaluated by both loge standard deviations (derived from the VA/Q 50-compartment lung model) and three new indices of dispersion that are derived directly from inert gas data. Both methods indicated a broadening of the distributions of blood flow and ventilation with increasing exercise at sea level, but the trend was of borderline statistical significance. There was no change in the resting distributions with altitude. However, with exercise at high altitude (10,000 and 15,000 ft) there was a significant increase in dispersion of blood flow (P less than 0.05) which implies an increase in intraregional inhomogeneity that more than counteracts the more uniform topographical distribution that occurs. Since breathing 100% O2 at 15,000 ft abolished the increased dispersion, the greater VA/Q mismatching seen during exercise at altitude may be related to pulmonary hypertension.

Acclimatization↗

PubMed1985

Diffusion limitation in normal humans during exercise at sea level and simulated altitude.

The relative roles of ventilation-perfusion (VA/Q) inequality, alveolar-capillary diffusion resistance, postpulmonary shunt, and gas phase diffusion limitation in determining arterial PO2 (PaO2) were assessed in nine normal unacclimatized men at rest and during bicycle exercise at sea level and three simulated altitudes (5,000, 10,000, and 15,000 ft; barometric pressures = 632, 523, and 429 Torr). We measured mixed expired and arterial inert and respiratory gases, minute ventilation, and cardiac output. Using the multiple inert gas elimination technique, PaO2 and the arterial O2 concentration expected from VA/Q inequality alone were compared with actual values, lower measured PaO2 indicating alveolar-capillary diffusion disequilibrium for O2. At sea level, alveolar-arterial PO2 differences were approximately 10 Torr at rest, increasing to approximately 20 Torr at a metabolic consumption of O2 (VO2) of 3 l/min. There was no evidence for diffusion disequilibrium, similar results being obtained at 5,000 ft. At 10 and 15,000 ft, resting alveolar-arterial PO2 difference was less than at sea level with no diffusion disequilibrium. During exercise, alveolar-arterial PO2 difference increased considerably more than expected from VA/Q mismatch alone. For example, at VO2 of 2.5 l/min at 10,000 ft, total alveolar-arterial PO2 difference was 30 Torr and that due to VA/Q mismatch alone was 15 Torr. At 15,000 ft and VO2 of 1.5 l/min, these values were 25 and 10 Torr, respectively. Expected and actual PaO2 agreed during 100% O2 breathing at 15,000 ft, excluding postpulmonary shunt as a cause of the larger alveolar-arterial O2 difference than accountable by inert gas exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1984

A theoretical method for selecting space craft and space suit atmospheres.

A theoretical method for selecting space craft and space suit atmospheres assumes that gas bubbles cause decompression sickness and that the risk increases when a critical bubble volume is exceeded. The method is consistent with empirical decompression exposures for humans under conditions of nitrogen equilibrium between the lungs and tissues. Space station atmospheres are selected so that flight crews may decompress immediately from sea level to station pressure without preoxygenation. Bubbles form as a result of this decompression but are less than the critical volume. The bubbles are absorbed during an equilibration period after which immediate transition to suit pressure is possible. Exercise after decompression and incomplete nitrogen equilibrium are shown to increase bubble size, and limit the usefulness of one previously tested stage decompression procedure for the Shuttle. The method might be helpful for evaluating decompression procedures before testing.

Decompression Sickness↗

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↗

PubMed1978

The metabolic cost of flight in unrestrained birds.

Oxygen consumption and carbon dioxide production were measured during flight in unrestrained starlings by a new method. Mean RQ after the first 30 min of flight was 0.69 +/- 0.08 (+/- S.D.). Mean rate of carbon dioxide production was 19.7 +/- 2.2 ml CO2/min, which corresponds to a metabolic rate of 8.9 +/- 1 W. Metabolic rate during flight did not change significantly over a range of air speeds from 8 to 18 m/s and birds would not fly at speeds outside of this range. Current theories of bird flight predict a large change in metabolic rate over the same range of speeds. Wingbeat frequency was constant at 12 +/- 0.5 Hz. Wingbeat amplitude reached a minimum at a speed of 14 m/s and increased at both higher and lower speeds. Angle between the body and horizontal was least at high speeds and increased at low speeds. As existing theories do not take into account the change of drag resulting from changes in body attitude, this may be a cause of the discrepancies between theory and observation.

Animals↗

PubMed1978

Evaporative cooling and water balance during flight in birds.

The rate of evaporative cooling was calculated from the rate of mass loss in starlings (Sturnus vulgaris) during 90 min flights in a wind-tunnel. Evaporative heat loss ranged from 5% of the metabolic rate at -5 degrees C to 19% of the metabolic rate at 29 degrees C. Radiation and convection accounted for the balance of the heat loss. On average, starlings dehydrated during flights at all temperatures above 7 degrees C. The comparison of these results with data from field studies, which indicate that long-distance migrants do not dehydrate, suggests that migrants may maintain water balance by ascending to colder air in which convection carries off most of the heat produced.

Animals↗

PubMed1976

Temperature regulation and heat dissipation during flight in birds.

Core and skin temperature were measured by radiotelemetry in starlings (Sturnus vulgaris) during 30 min flights in a wind tunnel. Core temperature was independent of ambient temperature from 0 to 28 degrees C. The temporal mean of the monitored core temperature during flight was 42-7 degrees C in one bird and 44-0 degrees C in another. These temperatures are 2-4 degrees C higher than the resting temperature in starlings, and are among the highest steady-state temperatures observed in any animal. Skin temperature on the breast was within a few degrees of core temperature. In some locations skin temperature was higher at low ambient temperatures than at intermediate ambient temperatures. An analysis of the data shows that a high core temperature does not function as an aid to head dissipation. On the contrary, insulation is adjusted to maintain a high temperature, presumably because it is necessary for flight. The increase in skin temperature at low ambient temperatures is believed to be a result of a decrease in heat flow through the breast feathers brought about by feather adjustments, to compensate for an unavoidable increase in heat flow in unfeathered or poorly feathered parts of the body.

Animals↗

PubMed1975

Reactions of migrating birds to lights and aircraft.

Midair collsions between birds and aircraft pose a hazard for both. While observing migrating birds with a tracking radar, we find that birds often react, by taking evasive maneuvers, at distances of 200-300 m to both searchlight beams and the approach of a small airplane with its landing lights on. Appropriately arranged lights on aircraft should decrease the hazard of collisions with birds.

Aircraft↗