Biomedical subjects

D L Kilgore

Publications and source records attributed to D L Kilgore.

At least 19 recordsLinked to original sources

PubMed2005

Spike firing allometry in avian intrapulmonary chemoreceptors: matching neural code to body size.

Biological rates in small animals are usually higher than those in large animals, yet the maximal rate of action potential (spike) generation in sensory neurons encoding rate functions is similar in all animals, due to the conserved genetics of voltage-gated ion channels. Therefore, sensory signals that vary at rates approaching maximal spike generation rate, as might occur in animals of diminished body size, may require specialized spike coding to convey this information. To test whether spike coding scales allometrically in sensory neurons monitoring signals that change frequency with body size, we recorded action potentials from 70 avian intrapulmonary chemoreceptors (IPC), respiratory neurons that detect lung CO2 changes during breathing, in five different avian species ranging in size from body mass Mb=0.045 kg (lovebirds) to 5.23 kg (geese). Since breathing frequency scales approximately to Mb-1/4 (higher in small birds, lower in large birds), we reasoned that IPC discharge frequencies may also scale to maintain spike information transmission within each breath. We found that phasic action potential discharge pattern, as quantified by the peak discharge rate and the magnitude of spike frequency adaptation, scaled between Mb-0.22 and Mb-0.26, like breathing rate (P<0.05). Previously published values of peak discharge rate in IPC also fit this allometric relationship. We suggest that mass-dependent scaling of neural coding may be necessary for preserving information transmission with decreasing body size.

Action Potentials↗

PubMed2001

Effects of embryonic CO2 exposure on the adult ventilatory response in quail: does gender matter?

To test the hypothesis that the adult ventilatory response to CO2 can be modified by exposure to CO2 during development, we exposed Japanese quail (Coturnix japonica) from two populations to 2% CO2 throughout embryonic development. The ventilatory response to 6% CO2 was subsequently measured in control and CO2-exposed quail following a 6-9 week deacclimation period. In one population of quail, CO2-exposed female, but not male, quail had a reduced ventilatory response to 6% CO2 as adults (P<0.001). Although control and CO2-exposed quail had similar ventilation while breathing air, CO2-exposed females exhibited a 26% reduction in mean ventilation at 6% CO2, primarily due to a reduced tidal volume. In contrast, the identical incubation treatment had no effect on the ventilation of either gender in a second population of quail. It appears that developmental plasticity in the hypercapnic ventilatory response may generally be greater in females, although this conclusion may vary depending on genetic factors.

Aging↗

PubMed1999

In vivo blood oxygen binding in hypoxic lesser spear-nosed bats: relationship to control of breathing.

The hypoxic ventilatory threshold of many mammals correlates with their hemoglobin-oxygen affinity (P50). Yet, in some small mammals ventilation actually declines, rather than increases, with exposure to decreasing PaO2; their air convection requirement (V(E)/V(O2)), however, is elevated in hypoxia. We propose that the threshold of the hypoxic V(E)/V(O2) of small mammals coincides with the inflection ('knee') of their in vivo O2 equilibrium curve (O2EC). In vivo blood gas and pH data were obtained from normoxic and hypoxic lesser-spear nosed bats, Phyllostomus discolor; in vitro blood O2EC were also generated for normoxic bats at 32 and 37 degrees C and at three P(CO2)'s. The hypoxic V(E)/V(O2) threshold of P. discolor occurs at PaO2 = 39 Torr; the corresponding in vivo O2 saturation is 0.70, approximating the inflection of the O2EC. This animal has a high blood O2 affinity (P50 = 27.5 Torr at pH 7.40 and 37 degrees C; P50 = 30.8 Torr at in vivo pH of 7.31 and TB of 37.4 degrees C). As PaO2 is reduced, a pronounced hypoxia-induced respiratory alkalosis and hypothermia help maintain SaO2 near the O2EC inflection (0.64-0.70 S(O2)).

Acid-Base Equilibrium↗

PubMed1998

Ventilatory, cardiovascular and metabolic responses to hypoxia and hypercapnia in the armadillo.

Armadillos have a low resting metabolic rate and high hemoglobin affinity for their size, a rigid carapace and a semi-fossorial life style. These characteristics could contribute to unusual respiratory responses to hypoxia and hypercapnia which were investigated in this study. Ventilatory and oxygen consumption responses of six adult unanesthetized armadillos to 15, 12, 10 and 8% O2 and 1.5, 3, 5 and 7% CO2 were measured by barometric plethysmography and flow-through respirometry. A significant increase in ventilation occurred in response to 10 and 8% O2 but a decline in oxygen consumption only occurred at 8% inspired O2. The convection requirement response has a threshold at a PaO2 of approximately = 28 Torr which corresponds to a Hb saturation of approximately 70%. Ventilation increased in response to 3% and higher levels of CO2, with no change in oxygen consumption. The magnitude of the ventilatory response to CO2 was similar to other semi-fossorial mammals and less than that of nonburrowing species. However, the pattern of the response was unique in being largely a frequency response with little change in tidal volume, contrary to the tidal volume dominated response to hypercapnia typical of mammals. This feature, not shared by another Xenarthran, the sloth, who lacks a carapace, is likely attributable to the low respiratory system compliance and increased airway resistance resulting from the rigid carapace and small lungs of armadillos and emphasizes the importance of respiratory mechanics in determining breathing pattern.

Animals↗

PubMed1998

How stiff is the armadillo? A comparison with the allometrics of mammalian respiratory mechanics.

Static respiratory mechanics were examined in the armadillo (Dasypus novemcinctus) and compared with allometric relationships newly derived for adult mammals from values in the literature. Normalised by body weight, chest wall compliance (Cw) in the armadillo is lower than predicted. Lung compliance (Cl) is also low in the armadillo, however it is appropriately matched to the resting lung volume (Vr) (ie. Cl/Vr infinity Mass0.0) and the ratio of Cw/Cl is appropriate for the size of the animal. Respiratory system resistance is high in the armadillo, presumably because of smaller airways associated with the small lung. The power of breathing in the armadillo is comparatively high, mainly due to the high resistive forces. Indeed, the oxidative cost of breathing is approximately double that of a mammal with similar Vr. Hypoxia or hypercapnia are known to invoke an attenuated ventilatory response in the armadillo and one that relies more on changes in frequency rather than volume. While such a breathing pattern helps to reduce the power of breathing it also compromises the degree of hyperventilation achieved.

Airway Resistance↗

PubMed1996

Ventilatory and metabolic responses of a bat, Phyllostomus discolor, to hypoxia and CO2: implications for the allometry of respiratory control.

The ventilatory and metabolic responses of lesser spear-nosed bats to hypoxia and hypercapnia were measured to determine whether these corresponded to preliminary allometries and a positive relationship between hypoxic ventilatory threshold and P50. Ventilatory responses of lesser spear-nosed bats to 3, 5 and 7% CO2 differed significantly from ventilation on air and each other. The magnitude of their ventilatory response to CO2 is consistent with the prediction of a smaller ventilatory response to hypercapnia in small compared to large mammals [% delta V varies MB0.130; Williams et al. (1994)]. Among 12, 10 and 8% O2 treatments only the ventilatory response to 8% O2 differed significantly from ventilation on air or the other treatments. Metabolic rate was significantly reduced at both 10 and 8% O2. The hypoxic ventilatory response of these bats does not support the prediction of a greater response in small compared to large mammals [% delta V veries MB0.273; Boggs and Tenney (1984)]. Their metabolic response is consistent with the hypoxic hypometabolism typical of small mammals, though not of comparable magnitude. The response, expressed as percent change in convection requirement (V/VO2), is also less than that observed in other small mammals. This relative insensitivity to hypoxia may be associated with this bat's unusually high affinity hemoglobin (P50 = 27.5 torr).

Anaerobiosis↗

PubMed1995

Scaling of hypercapnic ventilatory responsiveness in birds and mammals.

The possible relationship between CO2 responsiveness and body mass in birds was explored using newly acquired ventilatory data from the barn swallow, Hirundo rustica, and the pigeon, Columbia livia, and that from the literature on four other species. Ventilatory responsiveness (% delta V) of birds to 5% inspired CO2 is scaled to body mass to the 0.145 power (% delta V alpha Mb 0.145). A similar allometric relationship exists for data on 7 species of eutherian mammals taken from the literature (% delta V alpha Mb0.130). The The reduced responsiveness to CO2 in small birds and mammals may be related to an elevated hypoxic ventilatory sensitivity, as demonstrated in mammals (Boggs and Tenney, Respir. Physiol. 58: 245-251, 1984). These scaling relationships may reflect a mechanism for minimizing the inhibition of ventilation resulting from excessive loss of CO2 which thereby permits a higher hypoxic ventilatory response in small species. Other mechanisms, however, could include size related differences in mechanics or alveolar ventilation.

Animals↗

PubMed1992

Chemosensitivity and breathing pattern regulation of the coatimundi and woodchuck.

An analysis of breathing pattern regulation was carried out on the coatimundi and woodchuck who represent two different volume-time patterns. It was found that the coati, with a short expiratory time as a fraction of total breath time, TE/TTOT, has a greater sensitivity to CO2 as represented by the slope and threshold of its ventilatory response. Breathing air the coati maintains post-inspiratory inspiratory activity (PIIA) of the posterior cricoarytenoid (PCA) through 51% of expiration, while the woodchuck, who is less sensitive to CO2 and has a long TE/TTOT, exhibits no PIIA of the PCA. The woodchuck also has a greater incidence and duration of end-expiratory pauses (or delayed inspiratory onset). The woodchuck does not demonstrate the usual inverse relationship between VT and TE in response to 5% CO2 and does not recruit PIIA of the PCA at this level of CO2. These data confirm the importance of CO2 chemosensitivity in regulation of TE. It is further demonstrated that interspecific differences in chemosensitivity among three mammals of the same size are reflected in regulation of TE but not in inspiratory 'drive' (as indicated by mean inspiratory flow, VT/TI).

Animals↗

PubMed1992

Ontogenetic modification of the hypercapnic ventilatory response in the zebra finch.

We investigated the effect of exposure to CO2 during development on the adult ventilatory response to CO2 of zebra finches. Developing zebra finches were exposed to chronic hypercapnic respiratory environments as embryos, as nestlings or during both developmental periods. Their responsiveness to CO2 was then measured following a 125-135 day post-fledging deacclimation period. At a FICO2 of 0.06, mean ventilation of adult finches in the three groups was 74.8, 61.3 and 65.8%, respectively, of that of finches reared under normocapnic conditions. These data indicate that adult acute ventilatory responsiveness to CO2 in birds may be in part determined by CO2 exposure during early development and may help explain the observation that fossorial and semifossorial species of birds and mammals, that naturally encounter high CO2 conditions in their burrows, have a blunted hypercapnic ventilatory response.

Animals↗

PubMed1990

Temperature regulation and basal metabolic rate in the spotted skunk, Spilogale putorius.

1. Metabolic rate, body temperature, and evaporative water loss of six spotted skunks were measured at air temperatures between 8 and 40 degrees C. 2. The mean metabolic rate of spotted skunks at thermoneutral air temperatures was 30.5% below that predicted by body mass. 3. Thermal conductance, body temperature, and rates of evaporative water loss were like those of similar sized mammals. 4. The non-elongate body form, omnivorous diet, and low level of activity of spotted skunks distinguish them from other mustelids and may account for their lower-than-expected basal metabolism.

Animals↗

PubMed1989

Blood oxygen binding properties for the burrowing owl, Athene cunicularia.

Isocapnic O2 equilibrium curves (O2ECs) were generated for whole blood of 4 adult burrowing owls (Athene cunicularia) using thin film techniques. At in vivo pHa (7.49 +/- 0.02; mean +/- 1 SEM) and 41 degrees C, the PO2 at half saturation (P50) was 42.3 +/- 0.8 Torr. CO2 and fixed acid (H+) Bohr slopes (delta log P50/delta pH) were -0.46 +/- 0.01 and -0.42 +/- 0.02, respectively, demonstrating a small specific CO2 effect. CO2 and H+ Bohr slopes were saturation-independent between 0.1 and 0.9 S. Hill plots for Athene blood were non-linear; the Hill coefficient (n) increased from 2.6 below 0.4 S to 3.4 above 0.6 S. Owl equilibrium data were accurately described by the equation: S = [(7.7 x 10(6]/(P4 + 44P3 - 108P2 + 3.5 x 10(4)P) + 1]-1. This complex O2EC shape may result from Hb heterogeneity; isoelectric focusing showed 4 isoHbs with a molar ratio of 9:1:1:1. This study revealed no apparent adaptations of Athene blood for hypoxic and hypercapnic conditions. We conclude that the observed blood O2 binding properties promote tissue O2 delivery during periods of surface activity. While occupying its burrow, the owl compensates for moderate alterations in inspired gas composition partly through increased ventilation.

Acid-Base Equilibrium↗

PubMed1987

Effects of hypoxia and hypercapnia on VT, f, and VI of nestling and adult bank swallows.

The effects of hypoxia, hypercapnia, and hypoxic hypercapnia on ventilation, and breathing pattern in adult and nestling bank swallows (Riparia riparia) were assessed. The CO2 threshold above which inhaled minute volume (VI) increased significantly in adults and nestlings was 0.045. At each level of fractional concentration of inspired CO2 (FICO2), ventilation in nestlings was lower than that in adults. At a FICO2 of 0.09, VI of adults increased by 284%, whereas VI in nestlings changed 238%. Adult bank swallows also showed a blunted ventilatory response to hypoxia, and the nestling's response was similar to other birds. Adults exhibited greater changes in VI at all levels of hypoxic hypercapnia compared with nestlings. Combined hypoxic and hypercapnic stimuli had an additive effect on ventilation in both groups. Chronic exposure of nestlings to the hypercapnia and hypoxia within burrows seems to significantly alter their ventilatory response to these respiratory stimuli.

Animals↗

PubMed1985

Blood flow distribution during hypocapnic hypoxia in Pekin ducks and bar-headed geese.

The purpose of this study was to determine the effects of hypocapnic hypoxia on regional blood flow in birds. Regional blood flow was measured using the radioactive microsphere method in unanesthetized Pekin ducks (Anas platyrhynchos) and bar-headed geese (Anser indicus) breathing 21, 10 and 5% O2. In both birds, arterial PO2 was reduced from about 96 Torr during normoxia to about 28 Torr during severe hypoxia. Severe hypocapnic hypoxia produced a change in the pattern of blood flow in ducks; blood flow to some organs increased (brain, adrenal glands, heart, and eyes) while flow to other organs decreased (liver, spleen, small intestine, shell gland). Compared with ducks, bar-headed geese were able to provide higher levels of O2 delivery to their tissues since blood flow to a variety of organs and skeletal muscles was either unchanged or increased during severe hypoxia. The redistribution of blood flow in Pekin ducks during severe hypocapnic hypoxia may help to support large increases in cerebral and coronary blood flow but may also contribute to the development of a metabolic acidosis.

Animals↗

PubMed1985

Ventilatory and intrapulmonary chemoreceptor sensitivity to CO2 in the burrowing owl.

We measured the ventilatory response of anesthetized, unidirectionally ventilated pigeons and burrowing owls to changes in intrapulmonary CO2 concentration and the static CO2 sensitivity of intrapulmonary chemoreceptors (IPC) in these species and the domestic goose. Compared with pigeons, burrowing owls showed a significantly reduced respiratory frequency and amplitude response to increases in FICO2 from 0.05 to 0.10, which corroborates similar findings in intact, awake individuals of the same species. The average static CO2 sensitivity of IPC in geese, pigeons, and burrowing owls, as reflected by the average slope of the linear regressions of receptor discharge frequency on ln(PICO2), was -7.96, -11.1 and -6.87 imp/sec . ln(PICO2), respectively. The sensitivities of individual receptors were normally distributed in geese and pigeons, but skewed in burrowing owls. Therefore, the median CO2 sensitivity [-5.50 imp/sec . ln(PICO2)] is a more appropriate measure of the typical CO2 sensitivity of IPC in burrowing owls. The static CO2 sensitivity of IPC in burrowing owls is the lowest reported for euthermic birds with a normal acid-base balance and may materially contribute to the blunted ventilatory response of these birds to the elevated CO2 levels they encounter in nature.

Animals↗

PubMed1984

Oxygen delivery to the heart and brain during hypoxia: Pekin duck vs. bar-headed goose.

To investigate mechanisms that may allow birds to tolerate extreme high altitude, we acutely exposed unanesthetized bar-headed geese (Anser indicus) and Pekin ducks (Anas platyrhynchos) to 0.21, 0.10, and 0.05 inspired fractional concentrations of O2 (FIO2). In both birds, arterial O2 partial pressure (PaO2) was about 95 Torr at 0.21 FIO2, 45 Torr at 0.10 FIO2, and 28 Torr at 0.05 FIO2. Hyperventilation occurred at both levels of hypoxia, with PaCO2 decreasing to about 7 Torr at 28 Torr PaO2. At 28 Torr PaO2, arterial O2 content (CaO2) in geese (10.4 vol%) was significantly higher than in ducks (4.1 vol%). As PaO2 declined from about 95 to 28 Torr, both cerebral and coronary blood flow (determined by using the radioactive microsphere method) increased more than fivefold in ducks but less than threefold in geese. At both levels of hypoxia, O2 delivery (flow X CaO2) to the heart and brain of geese was the same as or higher than that of ducks. The unique control of cerebral and coronary O2 delivery exhibited by both species of birds may be related to their remarkable tolerance to severe hypocapnic hypoxia.

Adaptation, Physiological↗

PubMed1984

Attenuated pulmonary pressor response to hypoxia in bar-headed geese.

We determined the pulmonary pressor response during hypoxia in bar-headed geese (Anser indicus), a species that flies at altitudes up to 9,000 m, and Pekin ducks (Anas platyrhynchos), a non-flyer. Mean pulmonary arterial blood pressure (PAP) and arterial O2 partial pressure (PaO2) were measured in unanesthetized birds acutely exposed to 21, 10, 5, and, in geese only, 4% O2. PAP in geese did not change as PaO2 was reduced from 95 to 46 Torr and rose only 3 mmHg when PaO2 was reduced to 28 Torr. The same PaO2 decline in ducks (99 to 29 Torr) resulted in an 11-mmHg rise in PAP. The data suggest that very little or no increase in pulmonary vascular resistance occurs in these geese during hypoxia. This bird may provide a unique model in which to study pulmonary vascular control mechanisms.

Animals↗

PubMed1983

Blood characteristics, tracheal volume and heart mass of burrowing owls (Athene cunicularia) and bobwhite (Colinus virginianus).

1. Measurements of certain hematological and morphological characteristics were made in burrowing owls and bobwhite in search of features that could be associated with the previously described ventilatory adaptations of the burrowing owl to hypoxia and hypercarbia. 2. Values for burrowing owls and bobwhite, respectively, were: P50 = 44.9, 46.0 torr; Hct = 36.6, 38.8 vol%, Hb = 12, 12.3 (g/100 ml); RBC = 2.72 X 10(6), 3.02 X 10(6); log P50/pH = -0.412, -0.485; delta log PCO2/delta pH = -1.39, -1.585. 3. The owls had greater heart weights and smaller tracheal volumes than the bobwhite or the predicted value. 4. No hematological characteristics of the burrowing bird distinguish it from the non-burrowing bird.

Animals↗

PubMed1981

Brain temperatures in running quail.

Hypothalamic (Tb) and colonic (Tc) temperatures of adult bobwhite (colinus virginianus) were measured simultaneously while the birds were resting and running on a motor-driven treadmill at fixed belt speeds ranging from 0.42 to 0.75 m.s-1 at two air temperatures, room and 30 degrees C. For comparison, Tb and Tc were also recorded simultaneously in resting bobwhite exposed to air temperatures of 30 to 45 degrees C. Hypothalamic temperatures of both environmentally heat-stressed and running bobwhite were consistently below colonic temperatures. The mean magnitude of this body-to-brain temperature difference in birds running at the highest speeds (i.e., with the greatest exercise heat loads) and at a high air temperature (30 degrees C) was similar to that of extremely heat-stressed resting birds [ambient temperature (Ta) = 45 degrees C]. Furthermore, the body-to-brain temperature difference in quail running at 30 degrees C increases with running speed. That these birds running at maximum speeds can maintain their Tb nearly constant while Tc increases suggests enhanced heat transfer in the rete mirabile ophthalmicum, an extracranial site of arteriovenous heat exchange.

Animals↗