Ventilation and gas exchange during treadmill locomotion in the American alligator (Alligator mississippiensis).
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A number of anatomical characters of crocodilians appear to be inconsistent with their lifestyle as sit-and-wait predators. To address this paradoxical association of characters further, we measured lung ventilation and respiratory gas exchange during walking in American alligators (Alligator mississippiensis). During exercise, ventilation consisted of low-frequency, large-volume breaths. The alligators hyperventilated severely during walking with respect to their metabolic demands. Air convection requirements were among the highest and estimates of lung P(CO2) were among the lowest known in air-breathing vertebrates. Air convection requirements dropped immediately with cessation of exercise. These observations indicate that the ventilation of alligators is not limited by their locomotor movements. We suggest that the highly specialized ventilatory system of modern crocodilians represents a legacy from cursorial ancestors rather than an adaptation to a lifestyle as amphibious sit-and-wait predators. (+info)
Pelvic aspiration in the American alligator (Alligator mississippiensis).
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The pelvis of crocodilians is highly derived in that the pubic bones are isolated from the acetabulum and are attached to the ischia via moveable joints. We examined the possible role of this unusual morphology in lung ventilation by measuring ventilation, abdominal pressure and the electrical activity of several abdominal and pelvic muscles in the American alligator (Alligator mississippiensis). We found that the activity of two pelvic muscles, the ischiopubis and ischiotruncus muscles, was correlated with inspiration; these muscles rotate the pubes ventrally and thereby increase abdominal volume. During expiration, contraction of the rectus abdominis and transversus abdominis rotates the pubes dorsally. We suggest that this mechanism facilitates diaphragmatic breathing by creating space for caudal displacement of the viscera during inspiration. Because birds also use a dorso-ventral movement of the pelvis to effect ventilation, some form of pelvic aspiration may be plesiomorphic for archosaurs. (+info)
Physiological variability in neonatal armadillo quadruplets: within- and between-litter differences.
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The role of genetics on neonatal physiological variability was examined in the nine-banded armadillo (Dasypus novemcinctus). Since armadillos give birth to only monozygous quadruplets, the genetic variation within litters is essentially zero. Quadruplets born in captivity were isolated and weighed within 8 h of birth. Oxygen consumption (V.(O2)) was measured in resting neonates by flow-through respirometry, heart rate obtained from an electrocardiogram and ventilation was measured by impedance techniques. Following the measurements, neonates were returned to the mother. Measurements were repeated at 4 and 8 days after birth. Mean heart rate significantly increased from 132 beats min(-1) on the day of birth to 169 beats min(-1) on day 8. Mean ventilation rate significantly decreased from 81 breaths min(-1) on the day of birth to 54 breaths min(-1) on day 8. During this same developmental period, mean mass significantly increased from 100 g to 129 g, and mean mass-specific oxygen consumption significantly decreased from 32.2 ml O(2)kg(-1)min(-1) to 28.6 ml O(2)kg(-1) min(-1). For all variables measured, within-litter variability was always significantly less than between-litter variability, confirming a 'sibling effect' that we attribute to the genetic components determining physiological characters. (+info)
Effects of controlled breathing, mental activity and mental stress with or without verbalization on heart rate variability.
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OBJECTIVES: To assess whether talking or reading (silently or aloud) could affect heart rate variability (HRV) and to what extent these changes require a simultaneous recording of respiratory activity to be correctly interpreted. BACKGROUND: Sympathetic predominance in the power spectrum obtained from short- and long-term HRV recordings predicts a poor prognosis in a number of cardiac diseases. Heart rate variability is often recorded without measuring respiration; slow breaths might artefactually increase low frequency power in RR interval (RR) and falsely mimic sympathetic activation. METHODS: In 12 healthy volunteers we evaluated the effect of free talking and reading, silently and aloud, on respiration, RR and blood pressure (BP). We also compared spontaneous breathing to controlled breathing and mental arithmetic, silent or aloud. The power in the so called low- (LF) and high-frequency (HF) bands in RR and BP was obtained from autoregressive power spectrum analysis. RESULTS: Compared with spontaneous breathing, reading silently increased the speed of breathing (p < 0.05), decreased mean RR and RR variability and increased BP. Reading aloud, free talking and mental arithmetic aloud shifted the respiratory frequency into the LF band, thus increasing LF% and decreasing HF% to a similar degree in both RR and respiration, with decrease in mean RR but with minor differences in crude RR variability. CONCLUSIONS: Simple mental and verbal activities markedly affect HRV through changes in respiratory frequency. This possibility should be taken into account when analyzing HRV without simultaneous acquisition and analysis of respiration. (+info)
Do oral appliances enlarge the airway in patients with obstructive sleep apnoea? A prospective computerized tomographic study.
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This study evaluated the effect of an anterior mandibular positioning appliance (AMPA) on minimum pharyngeal cross-sectional area (MPCSA) in 32 conscious supine obstructive sleep apnoea (OSA) subjects. The change in MPCSA was measured using low dose computerized tomography, with and without an AMPA in situ. The results showed that the mean presenting respiratory disturbance index (RDI) was 26.6 events/hour, with a body mass index of 28.6 kg/m2 and mean age of 51.5 years. There was a statistically significant increase in MPCSA of 28.34 mm2 on appliance insertion (SD = 59.06 mm2; range -145 to +190 mm2; P = 0.011). The mean mandibular displacement was 5.73 mm (SD = 2.51 mm) in protrusion and 8.27 mm (SD = 4.51 mm) inferiorly. A poor correlation was found between the size of the mandibular displacement and the change in MPCSA (protrusion r = 0.268; inferiorly r = 0.240, P > 0.05). In conclusion, the AMPA significantly increased MPCSA, suggesting that it may be an effective therapy for OSA. There was, however, a wide but unpredictable individual variation of response. As a small number of patients may worsen in their condition with temporary mandibular advancement (TMA), it is essential that all patients treated with TMA should be investigated by polysomnography both before and after treatment. (+info)
Analysis of the mechanisms of expiratory asynchrony in pressure support ventilation: a mathematical approach.
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A mathematical model was developed to analyze the mechanisms of expiratory asynchrony during pressure support ventilation (PSV). Solving the model revealed several results. 1) Ratio of the flow at the end of patient neural inspiration to peak inspiratory flow (VTI/V(peak)) during PSV is determined by the ratio of time constant of the respiratory system (tau) to patient neural inspiratory time (TI) and the ratio of the set pressure support (Pps) level to maximal inspiratory muscle pressure (Pmus max). 2) VTI/V(peak) is affected more by tau/TI than by Pps/Pmus max. VTI/V(peak) increases in a sigmoidal relationship to tau/TI. An increase in Pps/Pmus max slightly shifts the VTI/V(peak)-tau/TI curve to the right, i.e., VTI/V(peak) becomes lower as Pps/Pmus max increases at the same tau/TI. 3) Under the selected adult respiratory mechanics, VTI/V(peak) ranges from 1 to 85% and has an excellent linear correlation with tau/TI. 4) In mechanical ventilators, single fixed levels of the flow termination criterion will always have chances of both synchronized termination and asynchronized termination, depending on patient mechanics. An increase in tau/TI causes more delayed and less premature termination opportunities. An increase in Pps/Pmus max narrows the synchronized zone, making inspiratory termination predisposed to be in asynchrony. Increasing the expiratory trigger sensitivity of a ventilator shifts the synchronized zone to the right, causing less delayed and more premature termination. Automation of expiratory trigger sensitivity in future mechanical ventilators may also be possible. In conclusion, our model provides a useful tool to analyze the mechanisms of expiratory asynchrony in PSV. (+info)
Nasal airflow dynamics: mechanisms and responses associated with an external nasal dilator strip.
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The adhesive external nasal dilator strip (ENDS) is widely advocated for prevention of snoring and promotion of nasal breathing during exercise. In the present study, the effects of the ENDS on nasal airflow resistance (Rn) in normal subjects were examined and factors determining individual responses to the ENDS explored. Using posterior rhinomanometry, 20 healthy Caucasian adults (10 males, 10 females; age: 18-56 yrs) were studied during quiet tidal breathing and voluntary hyperpnoea with (ENDS) and without (control) ENDS and with a placebo strip (placebo) before and after application of a topical nasal decongestant (oxymetazoline hydrochloride). During tidal breathing, only nine subjects showed a significantly (p<0.05) decreased inspiratory and/or expiratory Rn with the ENDS ("responders"). During the control, inspiratory Rn (at 0.4 L x s(-1)) was higher in "responders" than "nonresponders" (3.28+/-0.16 versus 2.60+/-0.08 cmH2O x L(-1) x s; p=0.04). The effects of nasal decongestant and the ENDS were additive. During voluntary hyperpnoea, inspiratory Rn (at 1.0 L x s(-1)) and the hysteresis of the inspiratory transnasal pressure/flow curve were decreased with the ENDS in most subjects. It is concluded that the external nasal dilator strip influences nasal airflow dynamics by both dilation of the nasal valve and stabilization of the lateral nasal vestibule walls and may be more effective in subjects with a high resting nasal airflow resistance. (+info)
Aerobic responses of prepubertal boys to two modes of training.
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OBJECTIVE: To investigate the effects of two contrasting eight week training programmes on the aerobic performance of 39 prepubescent boys (mean age 10.1 years). METHODS: All boys were volunteer subjects from three city schools and the schools were matched by a health related behaviour questionnaire. All of the boys were assessed as Tanner stage one for genitalia and pubic hair development. Criterion laboratory tests included peak VO2 as assessed by an incremental discontinuous treadmill test to voluntary exhaustion. Submaximal measurements of heart rate, minute ventilation (VE) and VO2 were also recorded during the treadmill test. One of the schools provided the control group (n = 14), and boys from the other schools followed two contrasting training programmes. The first was a sprint interval running programme (n = 12) comprising 10 second and 30 second sprints, and the second a continuous cycle ergometer programme (n = 13) maintaining a heart rate in the range 80-85% of maximum for 20 minutes on a Monark cycle ergometer. After eight weeks training three times a week, the three groups were retested. RESULTS: There were no significant differences in peak VO2 (p>0.05) with training in either of the groups. Neither were there significant changes in any of the submaximal variables VO2, VE, or heart rate (p>0.05). CONCLUSION: The findings of this study indicate that neither eight week sprint interval running nor continuous cycle ergometer training programmes significantly improve maximal or submaximal indicators of the aerobic performance of prepubertal boys. (+info)