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Biomedical subjects

D F Boggs

Publications and source records attributed to D F Boggs.

At least 19 recordsLinked to original sources
PubMed2005

Activity of three muscles associated with the uncinate processes of the giant Canada goose Branta canadensis maximus.

The activity of three muscles associated with the uncinate processes, (i) external intercostal, (ii) appendicocostalis and (iii) external oblique, were examined using patch and sew-through electrodes during sitting, standing and moderate speed treadmill running in the giant Canada goose. The external intercostal muscles demonstrated no respiratory activity, being active only during running, suggesting they play some role in trunk stabilisation. The appendicocostalis and external oblique muscles are respiratory muscles, being active during inspiration and expiration, respectively. The activity of the appendicocostalis muscles increased during sitting, suggesting that the uncinate processes in birds play an important role in facilitating lateral flaring of the rib cage when sternal rocking is prevented. We suggest that the uncinate processes in birds facilitate movements of the ribs and sternum during breathing and therefore are integral to the breathing mechanics of birds.

Animals↗
PubMed2001

The influence of locomotion on air-sac pressures in little penguins.

Air-sac pressures have been reported to oscillate with wing beat in flying magpies and with foot paddling in diving ducks. We sought to determine the impact on air-sac pressure of wing beats during swimming and of the step cycle during walking in little penguins (Eudyptula minor). Fluctuations averaged 0.16+/-0.06 kPa in the interclavicular air sacs, but only 0.06+/-0.04 kPa in the posterior thoracic sac, generating a small differential pressure between sacs of 0.06+/-0.02 kPa (means +/- S.E.M., N=4). These fluctuations occurred at approximately 3 Hz and corresponded to wing beats during swimming, indicated by electromyograms from the pectoralis and supracoracoideus muscles. There was no abdominal muscle activity associated with swimming or exhalation, but the abdominal muscles were active with the step cycle in walking penguins, and oscillations in posterior air-sac pressure (0.08+/-0.038 kPa) occurred with steps. We conclude that high-frequency oscillations in differential air-sac pressure enhance access to and utilization of the O(2) stores in the air sacs during a dive.

Abdominal Muscles↗
PubMed2000

Pulmonary vascular response of the coati to chronic hypoxia.

The unusually muscular pulmonary arteries normally present in cattle and swine residing at low altitude are associated with a rapid development of severe pulmonary hypertension when those animals are moved to high altitude. Because these species lack collateral ventilation, they appear to have an increased dependence on hypoxic vasoconstriction to maintain normal ventilation-perfusion balance, which, in turn, maintains thickened arterial walls. The only other species known to lack collateral ventilation is the coati, which, similarly, has thick-walled pulmonary arteries. We tested the hypothesis that coatis will develop severe high-altitude pulmonary hypertension by exposing six of these animals (Nasua narica) to a simulated altitude of 4,900 m for 6 wk. After the exposure, pulmonary arterial pressures were hardly elevated, right ventricular hypertrophy was minimal, there was no muscularization of pulmonary arterioles, and, most surprising of all, there was a decrease in medial thickness of muscular pulmonary arteries. These unexpected results break a consistent cross-species pattern in which animals with thick muscular pulmonary arteries at low altitude develop severe pulmonary hypertension at high altitude.

Altitude Sickness↗
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↗
PubMed1998

Differential air sac pressures in diving tufted ducks Aythya fuligula.

The air in the respiratory system of diving birds contains a large proportion of the body oxygen stores, but it must be in the lungs for gas exchange with blood to occur. To test the hypothesis that locomotion induces mixing of air sac air with lung air during dives, we measured differential pressures between the interclavicular and posterior thoracic air sacs in five diving tufted ducks Aythya fuligula. The peak differential pressure between posterior thoracic and interclavicular air sacs, 0.49+/-0.13 kPa (mean +/- s.d.), varied substantially during underwater paddling as indicated by gastrocnemius muscle activity. These data support the hypothesis that locomotion, perhaps through associated abdominal muscle activity, intermittently compresses the posterior air sacs more than the anterior ones. The result is differential pressure fluctuations that might induce the movement of air between air sacs and through the lungs during dives.

Abdominal Muscles↗
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↗
PubMed1993

Collateral ventilation and pulmonary arterial smooth muscle in the coati.

Collateral ventilation can participate in ventilation-perfusion regulation by shifting normoxic gas into hypoxic lung regions. In species lacking collateral pathways, such as cattle and swine, ventilation-perfusion balance must rely heavily on hypoxic vasoconstriction, which may explain why their muscular pulmonary arteries are much thicker than those of other animal species. The presence of these unusually muscular vessels in turn may account for the vigorous pressor response to acute hypoxia in these species. The only other species known to lack collateral ventilation is the coati. To determine whether coatis fit the pulmonary circulatory pattern of cattle and swine, we measured pulmonary arterial wall dimensions and pulmonary vascular responsiveness to acute airway hypoxia in 11 adult coatis. Hypoxia caused impressive pulmonary arterial hypertension [normoxia = 17 +/- 1 (SE) Torr, hypoxia = 40 +/- 2 Torr, cardiac output unchanged]. The medial thickness of muscular pulmonary arteries (50-300 microns) was 17.1 +/- 1.8% (SD) of external diameter, a thickness unprecedented in normotensive adult mammals. We conclude that coatis fit the pattern of other species lacking collateral ventilation, since they have thick-walled pulmonary arteries and a vigorous pressor response to hypoxia.

Animals↗
PubMed1992

Respiratory mechanics of the coatimundi and woodchuck.

The coatimundi breathes with a large tidal volume and relatively short TE/TTOT while the woodchuck has a relatively long TE/TTOT compared to other mammals. Hence, the respiratory mechanics of the coatimundi and woodchuck were studied to determine whether mechanics play any role in the differences in breathing pattern observed in these two mammals of similar body size. Although static respiratory system compliance was less and lower airway resistance was greater in the woodchuck compared to the coati there was no significant difference in deflationary time constant that could contribute to the difference in expiratory time. Both species exhibit less compliant chest walls than would be predicted for animals this size (4.5 and 5 kg) and the coati lung compliance is greater than that of the woodchuck or the prediction. The large tidal volume in the coati may be attributed in part to the large lung volume of this species (2.2 times the allometric prediction). The differences in breathing pattern are more likely related to differences in the control of breathing (i.e. regulation of expiratory airflow and inspiratory onset) than to differences in respiratory mechanics.

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↗
PubMed1989

Cardiorespiratory responses of the woodchuck and porcupine to CO2 and hypoxia.

The burrow-dwelling woodchuck (Marmota monax) (mean body wt. = 4.45 +/- 1 kg) was compared to a similar-sized (5.87 +/- 1.5 kg) but arboreal rodent, the porcupine (Erithrizon dorsatum), in terms of its ventilatory and heart rate responses to hypoxia and hypercapnia, and its blood characteristics. VT, f, T1 and TE were measured by whole-body plethysmography in four awake individuals of each species. The woodchuck has a longer TE/TTOT (0.76 +/- 0.03) than the porcupine (0.61 +/- 0.03). The woodchuck had a higher threshold and significantly smaller slope to its CO2 ventilatory response compared to the porcupine, but showed no difference in its hypoxic ventilatory response. The woodchuck P50 of 27.8 was hardly different from the porcupine value of 30.7, but the Bohr factor, -0.72, was greater than the porcupine's, -0.413. The woodchuck breathing air has PaCO2 = 48 (+/- 2) torr, PaO2 = 72 (+/- 6), pHa = 7.357 (+/- 0.01); the porcupine blood gases are PaCO2 = 34.6 (+/- 2.8), PaO2 = 94.9 (+/- 5), pHa = 7.419 (+/- 0.03), suggesting a difference in PaCO2/pH set points. The woodchuck exhibited no reduction in heart rate with hypoxia, nor did it have the low normoxic heart rate observed in other burrowing mammals.

Animals↗
PubMed1984

Scaling respiratory pattern and respiratory 'drive'.

We tested three predictions regarding the relationship between body size and respiratory 'drive' and timing in mammals. Mechanical considerations had led to the prediction that TE/TTOT and probably TI/TTOT would be interspecific constants. In eleven species of mammals, ranging in size from 0.033 kg to 520 kg, TE/TTOT during awake quiet breathing was an interspecific constant with a value of 0.65 (+/- 0.004); TI/TTOT was 0.345 (+/- 0.004). Given that VT is directly proportional to BW1.0 (Stahl, 1967), if TE and TI are directly proportional to BW0.28 (Bennett and Tenney, 1982), and if VT/TI is an index of respiratory 'drive', then 'drive' should be directly proportional to BW0.72, following the same proportionality with body size as does basal metabolic rate (VO2). Data for the same eleven species gave the relationship VT/TI BW0.74. Testing further the notion that 'drive', on a weight specific basis, is proportional to BW-0.26, we studied the response, % delta VI, in eleven species to approximately 12% inspired O2. This 'output' of the system in response to a hypoxic stimulus was found to scale with BW-0.27. The question whether this reflects a higher set 'gain' of the respiratory controller of smaller animals and/or some feature of the innervation, or intrinsic properties of the respiratory muscles that varies with body size is discussed.

Animals↗
PubMed1984

Effect of perinatal hypercapnia on the adult ventilatory response to carbon dioxide.

Burrowing mammals show a reduced ventilatory response to CO2 and CO2 retention. We examined whether this reduced responsiveness could be due to modification of chemoreceptors by persistent hypercapnia during development. Mice and rats were exposed to 6.0% CO2 throughout gestation and/or weaning and then removed to normocapnic air for a minimum of 6 weeks. Mouse gas pocket O2 and CO2 tensions and hematocrits were analyzed and compared with normocapnically raised controls. The ventilatory and blood gas and pH response to CO2 were compared in chronically cannulated test and control rats. Hematocrits and gas pocket CO2 and O2 tensions of mice and rat ventilatory and arterial blood CO2 and O2 tensions and pH responses were not different in test and control groups. There appears to be little or no developmental affect of CO2 suggesting that the reduced CO2 response seen in burrowers is genetically determined.

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↗
PubMed1982

Chemical specificity of a laryngeal apneic reflex in puppies.

In neonatal mammals the introduction of water and some other fluids into the larynx causes prolonged reflex apnea by stimulation of afferents in the superior laryngeal nerve (SLN). We have studied the chemical specificity of this reflex in 1- to 9-day-old anesthetized puppies. The laryngeal lumen was perfused with a variety of substances while ventilation through a tracheal cannula was recorded. Water consistently elicited apnea, which was terminated by 150 mM NaCl. Sucrose and urea solutions (100-500 mM) also elicited apnea, suggesting that osmolarity is not a critical factor. Phosphate buffer solutions containing NaCl and ranging in pH from 4.5 to 8.7 did not elicit apnea nor did cation substitutions in 150 mM chloride salts, with the exception of K+. Anion substitutions in 150 mM sodium salts indicated that anions of relatively large hydrated size (F-, acetate, formate, gluconate, tartrate, SO2-4, diatrizoate, IO-3, BrO-3, H2PO-4, HCO-3, borate, CO2-3) do induce apnea, whereas small anions (NO-3, ClO-3, SCN-, I-, Br-) similar to Cl- in size do not. Large anion salts and the nonelectrolytes sucrose, urea, and milk ceased to be effective stimuli in the presence of Cl- in concentrations of 80 or more meq/l. The principal stimulus for this apneic reflex is thus the absence or reduced concentration of Cl- (or small anions that can functionally replace Cl-) in the laryngeal fluid. Single fibers in the SLN were responsive to all the substances found capable of eliciting apnea and unresponsive to those not capable of doing so.

Age Factors↗