Direct measurement of static chest wall compliance in animal and human neonates

The measurement of pulmonary mechanics has been developed extensively for adults, and these techniques have been applied directly to neonates and infants. However, the compliant chest wall of the infant frequently predisposes to chest wall distortion, especially when there is a low dynamic lung compliance (CL,dyn). We describe a technique of directly measuring the static chest wall compliance (Cw,st), developed initially in the newborn lamb and subsequently applied to the premature neonate with chest wall distortion. The mean CL,dyn in seven intubated newborn lambs in normoxia was 2.45 +/- 0.41 ml.cmH2O-1.kg-1, whereas Cw,st was 11.81 +/- 0.25 ml.cmH2O-1.kg-1. These values did not change significantly in seven animals breathing through a tight-fitting face mask or with hypercapnia-induced tachypnea. For the eight premature infants the mean CL,dyn was 1.35 +/- 0.36 ml.cmH2O-1.kg-1, whereas the mean Cw,st was 3.16 +/- 1.01 ml.cmH2O-1.kg-1. This study shows that, under relaxed conditions when measurements of static compliance are performed, the chest wall is more compliant than the lung. The measurement of Cw,st may thus be used to determine the contribution of the respiratory musculature in stabilizing the chest wall.     

Compliances of the liquid-filled lungs and chest wall during development in fetal sheep.

Our aim was to measure the compliance of the liquid-filled lungs (CL), and the compliance of the chest wall (CW) in fetal sheep in utero. CL and CW were measured in 6 fetuses. The compliance of the lungs and chest wall combined (respiratory system, Crs) was measured in 9 fetuses. Pressure differences across the lungs (PL), chest wall (PW) and respiratory system (Prs) were measured while the lungs were deflated and inflated with liquid from their resting lung liquid volume (V1). V1 was measured using an indicator dilution technique. Specific compliance values were obtained by normalizing the values of CL, CW and Crs with respect to values of V1. From values obtained during stepwise inflation from V1, specific compliances (ml/cm H2O/ml of lung liquid) were: lungs, 0.22 +/- 0.02; chest wall, 0.41 +/- 0.07; respiratory system, 0.13 +/- 0.01. Specific compliances of the lungs, chest wall and respiratory system did not change significantly with advancing gestational age from 120 to 143 days. Our baseline data will be valuable in assessing the in utero progress of the structural development of the lungs following manipulations known to cause altered lung growth.     

One- and two-dimensional echocardiography in bodybuilders using anabolic steroids

The object of this study was to investigate the possible concentric increase in the left ventricular (LV) wall thickness by intensive strength training and to differentiate between the specific effect of the strength training itself and the influence of anabolic drugs. In this study 21 top-level bodybuilders [users of anabolic steroids (A): n = 14; non-users (N): n = 7] underwent one-dimensional and two-dimensional echocardiography as well as a cycle ergometer test. In both groups blood pressure at rest and during ergometric exercise was within the normal range. In spite of the same amount of time being spent on training, A showed significantly better power results than N. Total heart volume (A = 11.3 +/- 0.9 ml.kg-1; N = 11.9 +/- 0.9 ml.kg-1) and LV muscle mass were almost identical in A and N and correlated significantly with body weight and lean body mass respectively. The body dimension-related diastolic LV diameter was significantly lower in A (0.567 +/- 0.062 mm.kg-1) than in N (0.639 +/- 0.040 mm.kg-1). An increase in the LV posterior wall (p less than 0.01) and septum thickness (ns) resulted in increased LV wall thickness:diameter (p less than 0.01) and LV muscle mass:volume (p less than 0.05) ratios in A (0.458 +/- 0.590; 1.38 +/- 0.25 g.ml-1) in comparison to N (0.356 +/- 0.077; 1.16 +/- 0.17 g.ml-1). The septal:posterior wall thickness ratio was similar for both groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Predictors of sweat loss in man during prolonged exercise

Nineteen healthy male subjects, differing in training status and Vo2max (52 +/- 1 ml.min-1.kg-1, mean +/- SEM; 43-64 ml.min-1.kg-1, range), exercised for 1 h at an absolute workload of 192 +/- 8 W (140-265 W); this was equivalent to 70 +/- 1% Vo2max (66-74%). Each exercise test was performed on an electrically braked cycle ergometer at a constant ambient temperature (22.5 +/- 0.0 degrees C) and relative humidity (85 +/- 0%). Nude body weight was recorded prior to and after each exercise test. Absolute sweat loss (body weight loss corrected for respiratory weight loss) during each test was 910 +/- 82 g (426-1665 g); this was equivalent to 1.3 +/- 0.1% (0.7-2.2%) of pre-exercise body weight (relative sweat loss). Weighted mean skin temperature and rectal temperature increased after 5 min of exercise from 30.5 +/- 0.3 degrees C and 37.2 +/- 0.1 degrees C respectively to 32.5 +/- 0.2 degrees C and 38.8 +/- 0.1 degrees C respectively, recorded immediately prior to the end of exercise. Bivariate linear regression and Pearson's correlation demonstrated absolute sweat loss was related to Vo2max (r = 0.72, p less than 0.001), absolute exercise workload (r = 0.66, p less than 0.01), body surface area (r = 0.62, p less than 0.01), weight (r = 0.60, p less than 0.01) and height (r = 0.53, p less than 0.05). Relative sweat loss was related to VO2max (r = 0.77, P less than 0.001) and absolute exercise workload (R = 0.59, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of tidal volume on respiratory compliance in anesthetized infants and young children

Recent studies have suggested a close association between total respiratory compliance (Crs) and tidal volume in anesthetized paralyzed infants who are being artificially ventilated. To investigate this further, the multiple occlusion technique was used to measure Crs in 20 anesthetized infants and young children (aged 1-25 mo) before elective surgery. Measurements were made after intubation 1) during spontaneous breathing (SB), 2) after administration of a non-depolarizing muscle relaxant with tidal volume and frequency mimicking that during SB, and 3) with the child still paralyzed but tidal volume approximately double that during SB. Compared with values obtained during SB, there was no significant change in Crs after paralysis when ventilation matched the child's own pattern (P greater than 0.2). When ventilated with the larger tidal volumes, the infants showed a highly significant increase in Crs (mean 62%, range 14-158%, P less than 0.0001). These results may have implications not only for studies performed during anesthesia but also when infants were monitored in the intensive care setting. Values of Crs obtained in ventilated infants may reflect both the mechanical behavior of the respiratory system and the pattern of ventilation at the time of measurement.     

Ventilatory CO2 response in endurance-trained rats

A CO2 rebreathing technique was used to assess possible changes in the ventilatory response to CO2 in rats following a 14-week swim training program. Over the final 9 weeks, the rats swam 1 hr per day with a weight of 2.5% of the body weight attached to the tail. Ventilation was measured by a barometric method in awake, restrained rats in a total body plethysmography at CO2 concentrations of 0, 2, 4, 6, and 8%, with an initial O2 concentration of approximately 100%. Ventilation increased in the trained rats with increasing CO2 from 775ml . min-1 . kg-1 at 0% CO2 to 1,387 ml . min-1 . kg-1 at 8% CO2. This increase was a consequence of a 34% increase in tidal volume and a 32% increase in breathing frequency. In comparison with a group of sedentary control rats, there was a significantly higher ventilation and tidal volume at 0% CO2; however, this difference disappeared with increasing levels of CO2. A significantly lower resting heart rate was observed in the exercised (296 +/- 44 beats . min-1, mean +/- SD) compared to the sedentary control rats 380 +/- 42). It was concluded that, while the normal training response of resting bradycardia was observed following this duration and intensity of training, endurance swimming had no significant effect on the ventilatory response to CO2 in the rat.     

Power spectra of inspiratory nerve activity with lung inflations in cats

To investigate the effect of lung inflations on the high-frequency synchrony (70-122 Hz) observed in the inspiratory activity of respiratory motor nerves of decerebrate cats, I applied a step increase in lung inflation pressure at fixed delays into the inspiratory phase and computed power spectra of phrenic neurograms before and during inflation. In 25 decerebrate paralyzed cats the frequency of the high spectral peak was 92.3 +/- 11.1 Hz before and 105.3 +/- 12.1 Hz during the step in inflation pressure, shifting upward by 13.0 +/- 6.0 Hz. For 8 of the 25 cats, the recurrent laryngeal and phrenic neurograms were recorded simultaneously. The high spectral peak was present during inspiration in the recurrent laryngeal power spectra and coherent with the high peak in the phrenic power spectra. In response to lung inflation, the high peak disappeared from the power spectra of the recurrent laryngeal nerve as the inspiratory activity was inhibited; a shift upward in frequency was not detectable. Comparing inspiratory times (TI, based on the phrenic neurograms) for breaths with no lung inflations to those for breaths with lung inflations, I found that lung inflations early in inspiration caused a decrease in TI, lung inflations at intermediates times had no effect on TI, and lung inflations late in inspiration caused an increase in TI. Despite lung inflation decreasing, not affecting, or increasing inspiratory duration and amplitude of the phrenic neurogram, lung inflation always caused a shift upward in the high-frequency peak of the phrenic power density. The fact that lung inflation, a powerful respiratory stimulus, affected the frequency of the high peak in a consistent manner suggests that the high-frequency synchrony is an important and robust feature of the central respiratory pattern generator.     

Lung impedance in healthy humans measured by forced oscillations from 0.01 to 0.1 Hz

Lung impedance was measured from 0.01 to 0.1 Hz in six healthy adults by superimposing small-amplitude forced oscillations on spontaneous breathing. Measurements were made with an almost constant-volume input (160-180 ml) or with an almost constant-flow input (20-30 ml.s-1). No significant difference was found between the two conditions. Lung resistance (RL) sharply decreased from 0.97 kPa.l-1.s at 0.01 Hz to 0.27 kPa.l-1.s at 0.03 Hz and then mildly to 0.23 kPa.l-1.s at 0.1 Hz. Lung effective compliance (CL) decreased slightly and regularly from 0.01 Hz (2.38 l.kPa-1) to 0.1 Hz (1.93 l.kPa-1). The data were analyzed using a linear viscoelastic model adapted from Hildebrandt (J. Appl. Physiol. 28:365-372, 1970) and complemented by a Newtonian resistance (R): RL = R + B/(9.2f); CL = 1/(A + 0.25B + B.log2 pi f), where f is the frequency and B/A is an index of lung tissue viscoelasticity. A good fit was generally obtained, with an average difference of 10% between the observed and predicted values. The ratio B/A was not affected by the breathing and was 10.6 and 13.6% in the constant-volume and constant-flow conditions, respectively, which agrees with Hildebrandt's observations in isolated cat lungs. R was systematically larger than the plethysmographic airway resistance, suggesting that lung tissue resistance might also include a Newtonian component.     

Ontogeny of respiratory control and pulmonary mechanics in newborn rabbits

Maturation of the respiratory pattern and the active and passive mechanical properties of the respiratory system were assessed in 19 tracheotomized rabbits (postnatal age range: 1-26 days) placed in a body plethysmograph. With maturation both minute ventilation and tidal volume significantly increased, whereas respiratory frequency decreased. When normalized for body weight (kg) both the passive (Rrs X kg) and active (R'rs X kg) resistances of the respiratory system significantly increased with age, whereas the corresponding passive (Crs X kg-1) and active (C'rs X kg-1) compliances significantly decreased. At any given age R'rs X kg only slightly exceeded Rrs X kg, whereas C'rs X kg-1 was significantly lower than Crs X kg-1. Moreover, the maturational increases in Rrs X kg and R'rs X kg exceeded the corresponding decreases in Crs X kg-1 and C'rs X kg-1, resulting in significant age-related increases in both the passive (tau rs) and active (tau'rs) time constants of the respiratory system. Due to the age-related increases in tau'rs, producing a delayed volume response to any given inspiratory driving pressure, the relative volume loss obtained at any time during inspiration was greater in the maturing rabbit. On the other hand, because of concomitant compensatory changes in respiratory pattern, evidenced by increases in inspiratory duration with age, the end-inspiratory tidal volume loss in the maturing animal was maintained generally less than 10% at all postnatal ages. Thus maturational changes in respiratory pattern appear coupled to changes in the active mechanical properties of the respiratory system. The latter coupling serves to optimize the transduction of inspiratory pressure into volume change in a manner consistent with establishing the minimum inspiratory work of breathing during postnatal development.     

Effects of ageing and exogenous melatonin on pituitary responsiveness to GnRH in rats

The effect of age and melatonin on the activity of the neuroendocrine reproductive system was studied in young cyclic (3-5 months-old), and old acyclic (23-25 month-old) female rats. Pituitary responsiveness to a bolus of GnRH (50 ng per 100 g body weight) was assessed at both reproductive stages in control and melatonin-treated (150 micrograms melatonin per 100 g body weight each day for 1 month) groups. After this experiment, female rats were treated for another month to study the influence of ageing and melatonin on the reproductive axis. Plasma LH, FSH, prolactin, oestradiol and progesterone were measured. A positive LH response to GnRH was observed in both control groups (cyclic and acyclic). However, a response of greater magnitude was observed in old acyclic rats. Melatonin treatment reduced this increased response in acyclic rats and produced a pituitary responsiveness similar to that of young cyclic rats. FSH secretion was independent of GnRH administration in all groups, indicating desynchronization between LH and FSH secretion in response to GnRH in young animals and during senescence. No effect on prolactin was observed. Significantly higher LH (3009.11 +/- 1275.08 pg ml(-1); P < 0.05) and FSH concentrations (5879.28 +/- 1631.68 pg ml(-1); P < 0.01) were seen in acyclic control rats. After melatonin treatment, LH (811.11 +/- 89.71 pg ml(-1)) and FSH concentrations (2070 +/- 301.62 pg ml(-1)) decreased to amounts similar to those observed in young cyclic rats. However, plasma concentrations of oestradiol and progesterone were not reduced. In conclusion, the results of the present study indicate that, during ageing, the effect of melatonin is exerted primarily at the hypothalamo-pituitary axis rather than on the ovary. Melatonin restored the basal concentrations of pituitary hormones and pituitary responsiveness to similar values to those observed in young rats.     

Thermoregulation in hyperhydrated men during physical exercise

The influence of hyperhydration on thermoregulatory function was tested in 8 male volunteers. The subjects performed cycle exercise in the upright position at 52% Vo2max for 45 min in a thermoneutral (Ta = 23 degrees C) environment. The day after the control exercise the subjects were hyperhydrated with tap water (35 ml X kg-1 of body weight) and then performed the same physical exercise as before. Total body weight loss was lower after hyperhydration (329 +/- 85 g) than during the control exercise (442 +/- 132 g), p less than 0.05. The decrease in weight loss after hyperhydration was probably due to a decrease in dripped sweat (58 +/- 64 and 157 +/- 101 g, p less than 0.05). With hyperhydration delay in onset of sweating was reduced from 5.8 +/- 3.2 to 3.7 +/- 2.0 min (p less than 0.05), and rectal temperature increased less (0.80 +/- 0.20 and 0.60 +/- 0.10 degrees C, p less than 0.01). The efficiency of sweating was higher in hyperhydrated (81.4%) than in euhydrated subjects (57.1%), p less than 0.01. It is concluded that hyperhydration influences thermoregulatory function in exercising men by shortening the delay in onset of sweating and by decreasing the quantity of dripped sweat. As a result, the increases in body temperature in hyperhydrated exercising men are lower than in normally hydrated individuals.     

Forced oscillatory impedance of the respiratory system at low frequencies

Respiratory mechanical impedances were determined during voluntary apnea in five healthy subjects, by means of 0.25- to 5-Hz pseudo/random oscillations applied at the mouth. The total respiratory impedance was partitioned into pulmonary (ZL) and chest wall components with the esophageal balloon technique; corrections were made for the upper airway shunt impedance and the compressibility of alveolar gas. Neglect of these shunt effects did not qualitatively alter the frequency dependence of impedances but led to underestimations in impedance, especially in the chest wall resistance (Rw), which decreased by 20-30% at higher frequencies. The total resistance (Rrs) was markedly frequency dependent, falling from 0.47 +/- 0.06 (SD) at 0.25 Hz to 0.17 +/- 0.01 at 1 Hz and 0.15 +/- 0.01 kPa X l-1 X s at 5 Hz. The changes in Rrs were caused by the frequency dependence of Rw almost exclusively between 0.25 and 2 Hz and in most part between 2 and 5 Hz. The effective total respiratory (Crs,e) and pulmonary compliance were computed with corrections for pulmonary inertance derived from three- and five-parameter model fittings of ZL. Crs,e decreased from the static value (1.03 +/- 0.18 l X kPa-1) to a level of approximately 0.35 l X kPa-1 at 2-3 Hz; this change was primarily caused by the frequency-dependent behavior of chest wall compliance.     

Enhanced protein breakdown after eccentric exercise in young and older men

The effects of eccentric exercise on whole body protein metabolism were compared in five young untrained [age 24 +/- 1 yr, maximal O2 uptake (VO2max) = 49 +/- 6 ml.kg-1.min-1] and five older untrained men (age 61 +/- 1 yr, VO2max = 34 +/- 2 ml.kg-1.min-1). They performed 45 min of eccentric exercise on a cycle ergometer at a power output equivalent to 80% VO2max (182 +/- 18 W). Beginning 5 days before exercise and continuing for at least 10 days after exercise, they consumed a eucaloric diet providing 1.5 g.kg-1.day-1 of protein. Leucine metabolism in the fed state was measured before, immediately after, and 10 days after exercise, with intravenous L-[1-13C]leucine as a tracer (0.115 mumol.kg-1.min-1). Leucine flux increased 9% immediately after exercise (P less than 0.011) and remained elevated 10 days later, with no effect of age. Leucine oxidation increased 19% immediately after exercise and remained 15% above baseline 10 days after exercise (P less than 0.0001), with no effect of age. In the young men, urinary excretion of 3-methylhistidine per gram of creatinine did not increase until 10 days postexercise (P less than 0.05), but in the older men, it increased 5 days after exercise and remained high through 10 days postexercise (P less than 0.05), averaging 37% higher than in the young men. These data suggest that eccentric exercise produces a similar increase in whole body protein breakdown in older and young men, but myofibrillar proteolysis may contribute more to whole body protein breakdown in the older group.     

Reduced feeding response to neuropeptide Y in senescent Fischer 344 rats

The anorexia of aging syndrome in humans is characterized by spontaneous body weight loss reflecting diminished food intake. We reported previously that old rats undergoing a similar phenomenon of progressive weight loss (i.e., senescent rats) also display altered feeding behavior, including reduced meal size and duration. Here, we tested the hypothesis that blunted responsiveness to neuropeptide Y (NPY), a feeding stimulant, occurs concurrently with senescence-associated anorexia/hypophagia. Young (8 mo old, n = 9) and old (24-30 mo old, n = 11) male Fischer 344 rats received intracerebroventricular NPY or artificial cerbrospinal fluid injections. In response to a maximum effective NPY dose (10 microg), the net increase in size of the first meal after injection was similar in old weight-stable (presenescent) and young rats (10.85 +/- 1.73 and 12.63 +/- 2.52 g/kg body wt (0.67), respectively). In contrast, senescent rats that had spontaneously lost approximately 10% of body weight had significantly lower net increases at their first post-NPY meal (1.33 +/- 0.33 g/kg body wt (0.67)) than before they began losing weight. Thus altered feeding responses to NPY occur in aging rats concomitantly with spontaneous decrements in food intake and body weight near the end of life.     

Increased oxygen consumption associated with breathing activity in fetal lambs

To examine the relationship between fetal O2 consumption and fetal breathing movements, we measured O2 consumption, umbilical blood flow, and cardiovascular and blood gas data before, during, and after fetal breathing movements in conscious chronically catheterized fetal lambs. During fetal breathing movements, O2 consumption increased by 30% from a control value of 7.7 +/- 0.7 (SE) ml X min-1 X kg-1. Umbilical blood flow was 210 +/- 21 ml X min-1 X kg-1 before fetal breathing movements; in 9 of 16 samples it increased by 52 +/- 12 ml X min-1 X kg-1, while in the other 7 it decreased by 23 +/- 9 ml X min-1 X kg-1. Umbilical arterial and venous O2 partial pressures and pH fell during fetal breathing movements, and the fall was greater when umbilical blood flow was decreased. Partial CO2 pressure rose in both vessels, and again the increase was greatest when umbilical blood flow fell during fetal breathing movements. Also associated with a fall in umbilical blood flow was the transition from low-amplitude irregular to large-amplitude regular fetal breathing movements. It is concluded that fetal breathing movements increase fetal O2 demands and are associated with a transient deterioration in fetal blood gas status, which is most severe during large-amplitude breathing movements.     

Dietary protein requirements and body protein metabolism in endurance-trained men

The effects of regular submaximal exercise on dietary protein requirements, whole body protein turnover, and urinary 3-methylhistidine were determined in six young (26.8 +/- 1.2 yr) and six middle-aged (52.0 +/- 1.9 yr) endurance-trained men. They consumed 0.6, 0.9, or 1.2 g.kg-1.day-1 of high-quality protein over three separate 10-day periods, while maintaining training and constant body weight. Nitrogen measurements in diet, urine, and stool and estimated sweat and miscellaneous nitrogen losses showed that they were all in negative nitrogen balance at a protein intake of 0.6 g.kg-1.day-1. The estimated protein requirement was 0.94 +/- 0.05 g.kg-1.day-1 for the 12 men, with no effect of age. Whole body protein turnover, using [15N]glycine as a tracer, and 3-methylhistidine excretion were not different in the two groups, despite lower physical activity of the middle-aged men. Protein intake affected whole body protein flux and synthesis but not 3-methylhistidine excretion. These data show that habitual endurance exercise was associated with dietary protein needs greater than the current Recommended Dietary Allowance of 0.8 g.kg-1.day-1. However, whole body protein turnover and 3-methylhistidine excretion were not different from values reported for sedentary men.     

Vagal afferent activity and body temperature in 3 to 10-day-old and adult rats

This study examined the possible contribution of vagal stretch receptor activity to the increased power of the Hering-Breuer reflex in hyperthermia in rats during the early postnatal period. Experiments were performed on 10 anesthetized (pentobarbital 40 mg/kg, i.p.) 3 to 10-day-old (body weight of 16 +/- 1 g; SE) and, for comparison, 18 adult Sprague-Dawley rats (body weight of 336 +/- 35 g). Animals were tracheostomized and artificially ventilated with oxygen. The left vagus nerve was cut. In adult animals, single receptor fibers or a bundle of a few fibers were recorded using a bipolar stainless-steel electrode under mineral oil. In the young rats, a suction electrode filled with normal saline was used. Positive pressure of either 5 or 10 cmH2O was applied to the trachea when the respirator was turned off. The vagal activity was amplified and monitored on a storage oscilloscope for calculation of the frequency of vagal afferent activity during a given pressure application at different rectal temperatures (T(R); range 28 to 42 degrees C). In total, 30 and 31 sets of vagal activity in the young and adult rats, respectively, were analyzed. In all cases, an increase in tracheal pressure (P(TR)) from 5 to 10 cmH2O increased the frequency of vagal firing. The increase was greater in the adult versus the young animals; at 36 degrees C the increase was 49 +/- 11% and 16 +/- 3% in the adult and young rats, respectively (P < 0.01). In all animals, vagal receptors showed temperature-sensitivity, but less so in the young than in the adult rats (P < 0.0004 and P < 0.003; for P(TR) of 5 and 10 cmH2O, respectively). In addition, the relationship between temperature-sensitivity and T(R) had significant slopes (P < 0.001 for both inflation pressures) in the adults but not in the young rats, indicating that in the latter the temperature-sensitivity of vagal receptors is independent of TR. These results imply that temperature-sensitivity of vagal receptors could have contributed to the increased power of the Hering-Breuer reflex in rats during the early postnatal period in the warmer environment.     

Whole-body systemic transcapillary filtration rates, coefficients, and isogravimetric capillary pressures in Bufo marinus and Rana catesbeiana

Whole-body and organ-level transcapillary filtration rates and coefficients are virtually unexamined in ectothermal vertebrates. These filtration rates appear to be greater than in mammals when plasma volume shifts and lymphatic function are analyzed. Gravimetric techniques monitoring whole-body mass changes were used to estimate net systemic filtration in Bufo marinus and Rana catesbeiana while perfusing with low-protein Ringer's and manipulating venous pressure. Capillary pressures were estimated from arterial and venous pressures after measuring the venous to arterial resistance ratio of 0.23. The capillary filtration coefficient (CFC) for the two species was 25.2+/-1.47 mL min-1 kg-1 kPa-1. Isogravimetric capillary pressure (Pci), the pressure at which net fluid is neither filtered nor reabsorbed, was 1.12+/-0.054 kPa and was confirmed by an independent method. None of these variables showed a significant interspecific difference. The anuran CFC and Pci are significantly higher than those found using the same method on rats (7.6+/-2.04 mL min-1 kg-1 kPa-1 and 0.3+/-0.37 kPa, respectively) and those commonly reported in mammals. Despite the high CFC, the high Pci predicts that little net filtration will occur at resting in vivo capillary pressures.     

Catheterization of pulmonary artery in rats with an ultraminiature catheter pressure transducer

Utilizing new materials and miniaturization techniques, an ultraminiature catheter pressure transducer for catheterization of the pulmonary artery (PA) has been developed and applied in intact, spontaneously breathing, anesthetized rats. The catheter arrangement consists of three components: 1) an SPR-671 ultraminiature pressure transducer (measuring catheter), 2) a plastic introducer (sheath) that is slipped over the measuring catheter, and 3) an external wire mounted on the outside of the introducer for bending its tip. The measuring catheter is first inserted through the right jugular vein into the right ventricle. The introducer is then slipped over it. The tip of the introducer is bent so that there is an angle of approximately 90 degrees or less to the shaft. The measuring catheter is advanced across the pulmonary valve into the PA. Measurements of pulmonary arterial pressure were made in five male Long Evans (364 +/- 7 g body wt) and five female Sprague-Dawley (244 +/- 7 g body wt) rats under control conditions. The effects of infusion of norepinephrine (0.1 mg.kg(-1).h(-1) iv for 20-min duration) were tested in Long Evans rats. Pulmonary arterial systolic pressure measurements were 34.0 +/- 0.8 and 29.5 +/- 0.4 mmHg, and diastolic pressure values were 23.6 +/- 0.8 and 18.1 +/- 0.6 mmHg in male Long Evans and female Sprague-Dawley rats, respectively. Norepinephrine induced an increase in pulmonary arterial systolic (40.8 +/- 0.1 mmHg) and diastolic (28.6 +/- 0.4 mmHg) pressures and an elevation in pulmonary vascular resistance from a control value of 0.093 +/- 0.003 to 0.103 +/- 0.004 mmHg.kg.min.ml(-1).     

Partitioning of airway responses to inhaled methacholine in the rat

We measured the changes in upper and lower airway resistance after inhalation of aerosols of methacholine (MCh) in doubling concentrations (16, 32, 64, and 128 mg/ml) in 11 anesthetized nonintubated spontaneously breathing rats. Upper airway resistance (Ru) increased from a control value of 0.48 +/- 0.04 cmH2O X ml-1 X s (mean +/- SE) to 0.85 +/- 0.15 after 128 mg/ml MCh, whereas lower airway resistance (Rlo) increased from 0.11 +/- 0.03 to 0.21 +/- 0.04. However, there was no correlation between the magnitudes of the changes in Ru and Rlo. In a further seven anesthetized spontaneously breathing rats aerosols of MCh were delivered into the lower airways via a tracheostomy and resulted in increases in Rlo from a control value of 0.20 +/- 0.03 to 0.66 +/- 0.12 after 128 mg/ml MCh. Ru also increased to approximately double its control value. We conclude that inhaled MCh causes narrowing of both Ru and Rlo in the anesthetized rat, the changes in Ru and Rlo are not correlated, and changes in Ru can occur when MCh deposition occurs only in the lower airways.