Respiratory mechanics in patients with tense cirrhotic ascites

Lung volumes are decreased by tense ascites and increase after large volume paracentesis (LVP). The overall effect of ascites and LVP on the respiratory function is poorly understood. We studied eight cirrhotic patients with tense ascites before and after LVP. Inspiratory muscle force (maximal transdiaphragmatic pressure (Pdi,max), and the lowest pleural pressure (Pp1,min)) was assessed while the patients were seated. Rib cage and abdominal volume displacements, as well as pleural and gastric pressures were measured during quiet breathing while the patients were supine. Pdi,max and Ppl,min were normal and did not change after LVP (from 84.2+/-19.7 to 85.2+/-17.0 cmH2O and from 68.3+/-19.7 to 74+/-15.9 cmH2O, respectively). The abdominal contribution to the generation of tidal volume was greater than that of the rib cage (79 vs 21%), a pattern which did not change after LVP (73 and 27%). Before LVP, tidal swings both of pleural pressure (Ppl,sw) and transdiaphragmatic pressure (Pdi,sw) were large (15.3+/-4.3 and 18.5+/-3.9 cmH2O, respectively) and the load on inspiratory muscles was increased as a consequence of elevated dynamic elastance of the lung (El,dyn) (11.4+/-2.6 cmH2O x L(-1)) and ("intrinsic") positive end-expiratory pressure (PEEPi) (4.3+/-3.5 cmH2O). LVP reduced the load on the inspiratory muscles, as shown by the significant decrease in Ppl,sw (10.6+/-2.0 cmH2O), Pdi,sw (12.8+/-3.0 cmH2O), El,dyn (10.0+/-2.0 cmH2O x L(-1)) and PEEPi (1.1+/-1.3 cmH2O). The amount of fluid removed was closely related to changes in Ppl,sw and PEEPi. We conclude that the strength of the inspiratory muscles is normal or reduced in seated cirrhotic patients. In the supine position, tense ascites results in an increase in lung elastic load and development of positive end-expiratory pressure, with a consequent overload and increased activation of inspiratory muscles. Large volume paracentesis decreases overloading and activation, but does not change the strength of the inspiratory muscles.     

Alveolar oxygen uptake and femoral artery blood flow dynamics in upright and supine leg exercise in humans

We tested the hypothesis that the slower increase in alveolar oxygen uptake (VO2) at the onset of supine, compared with upright, exercise would be accompanied by a slower rate of increase in leg blood flow (LBF). Seven healthy subjects performed transitions from rest to 40-W knee extension exercise in the upright and supine positions. LBF was measured continuously with pulsed and echo Doppler methods, and VO2 was measured breath by breath at the mouth. At rest, a smaller diameter of the femoral artery in the supine position (P < 0. 05) was compensated by a greater mean blood flow velocity (MBV) (P < 0.05) so that LBF was not different in the two positions. At the end of 6 min of exercise, femoral artery diameter was larger in the upright position and there were no differences in VO2, MBV, or LBF between upright and supine positions. The rates of increase of VO2 and LBF in the transition between rest and 40 W exercise, as evaluated by the mean response time (time to 63% of the increase), were slower in the supine [VO2 = 39.7 +/- 3.8 (SE) s, LBF = 27.6 +/- 3.9 s] than in the upright positions (VO2 = 29.3 +/- 3.0 s, LBF = 17.3 +/- 4.0 s; P < 0.05). These data support our hypothesis that slower increases in alveolar VO2 at the onset of exercise in the supine position are accompanied by a slower increase in LBF.     

Proinsulin: recent observations and controversies

INTRODUCTION: Defibrillation thresholds (DFTs) usually are determined with the patient in the supine position. However, patients may be in the upright position when a shock is delivered during follow-up, which may explain some first shock failures observed clinically. This study investigated whether body posture affects defibrillation energy requirements of nonthoracotomy implantable cardioverter defibrillators with biphasic shocks. METHODS AND RESULTS: Using a step up-down protocol, DFTs were compared intraindividually in 52 patients ("active-can" sytems in 41 patients, two-lead systems in 11 patients) for the supine and upright positions as achieved by a tilt table. The mean DFT was 7.3 +/- 4.2 J in the supine versus 9.2 +/- 4.8 J in the upright position (P = 0.002). Repeated comparison in reversed order 3 months after implantation in 22 patients revealed thresholds of 6.2 +/- 2.5 J (supine) versus 8.4 +/- 3.7 J (upright; P < 0.03) 1 week and 4.4 +/- 2.4 J (supine) versus 6.2 +/- 4.1 J (upright; P < 0.04) 3 months after implantation. DFTs decreased significantly for both body positions from 1 week to 3 months after implantation (P < 0.04). CONCLUSION: (1) DFTs for biphasic shocks delivered by nonthoracotomy defibrillators are higher in the upright compared to the supine body position. (2) Differences remain significant 3 months after implantation. For both body positions, DFT decreases significantly from 1 week to 3 months after implantation. These findings have important implications for programming first shock energy to lower than maximal values or for development of devices with lower maximal stored energy.     

Continuous ambulatory radionuclide monitoring of left ventricular function: effect of body position during ergometer exercise

We assessed the reliability of a continuous ambulatory radionuclide monitoring system (the VEST system, Capintec, Inc., Ramsey, NJ) for measurement of left ventricular performance during exercise in the upright and supine positions. METHODS: Sixteen healthy male volunteers (aged 32-46 yr; mean age 37 +/- 4 yr) were studied. All volunteers underwent ergometer exercise testing in both the upright and supine positions, and left ventricular performance was determined with the VEST system. RESULTS: The resting heart rate, systolic blood pressure, pressure rate product, relative end-diastolic volume, relative end-systolic volume and left ventricular ejection fraction (LVEF) all showed no differences between the upright and supine positions. At peak exercise, the heart rate, systolic blood pressure and pressure rate product showed no differences between the upright and supine positions. In the upright position at peak exercise the relative end-diastolic volume was increased (83% +/- 9% to 91% +/- 11%, p < 0.001); the relative end-systolic volume remained unchanged (34% +/- 3% to 33% +/- 15%), and LVEF was significantly increased from 58% +/- 6% to 66% +/- 11% (p < 0.01). In the supine position at peak exercise, the relative end-diastolic volume remained unchanged (85% +/- 5 to 83% +/- 7%), the relative end-systolic volume was increased (35% +/- 5% to 43% +/- 13%, p < 0.01), and LVEF was decreased from 58% +/- 5% to 48% +/- 17% (p < 0.01). These results indicated inferior data collection by the VEST system in the supine position. CONCLUSION: Since the detector of the VEST system may be too small, the data collection is impaired during exercise in the supine position by shifting the heart with deep respiration. The VEST system is very useful for determining left ventricular performance when applied in the sitting or upright position. However, in the supine position during exercise, the use of the VEST system should be avoided because it might indicate an artifactual deterioration of left ventricular performance.     

Alveolar oxygen uptake and blood flow dynamics in knee extension ergometry

The relationship was studied between the increase in oxygen uptake (VO2) measured breath-by-breath at the mouth, and the increase in femoral artery blood flow measured continuously with pulsed and echo Doppler methods. Five men exercised at 50 W on a knee extension ergometer in both the supine and the upright posture. The kinetics of the responses were determined by curve fitting to obtain the mean response time (MRT = 63% of the time required to achieve steady state). In the upright position, the increase in blood flow (MRT = 12.4 +/- 9.4 s, mean +/- SD) was faster than the increase in VO2 (29.6 +/- 9.3 s). Likewise in the supine position, blood flow increased more rapidly (25.1 +/- 9.7 s vs. 36.7 +/- 9.6 s). It should be noted that the increase in blood flow appeared to be faster than VO2, yet when blood flow adapted more slowly in the supine posture, it had an impact on the adaptation of VO2. This suggests that blood flow might have important effects on metabolism at the onset of submaximal exercise.     

Isolation and partial characterization of chromoprotein from the larval hemolymph of the Japanese oak silkworm (Antheraea yamamai)

OBJECTIVES: To investigate by urodynamic study position-related changes in uroflowmetry and postvoid residual urine volume (PVR) in men because altered bladder function in the supine position may be a predisposing factor for urinary tract infections in the institutionalized elderly. METHODS: Two healthy men, 34 and 59 years of age and living at home, and 53 nursing home residents (mean age 71.8 years, range 46 to 92) were evaluated with uroflowmetry in the standing and recumbent positions (lying on the left or right side); corresponding PVRs were measured by transabdominal ultrasonic bladder scanning. The two healthy men were monitored longitudinally with multiple recordings in both voiding positions, and the nursing home residents were subjected to two observations: one measurement of the variable parameters in either position. Differences were considered to be significant at P < 0.05. RESULTS: The 34-year-old man performed 51 3 flows (368 standing and 145 recumbent). The mean of all the peak flow rates in the upright (28.2 +/- 4.2 mL/s) versus the recumbent (16.8 +/- 4.1 mL/s) position revealed a highly significant difference (P = 0.0001). Sixteen urinary flows and corresponding PVRs were completed by this subject in either voiding position. The difference between PVRs in the standing (13.1 +/- 14.7 mL) versus recumbent (15.3 +/- 17.5 mL) position was not statistically significant. The 59-year-old man completed 156 flows (128 standing and 28 recumbent). A highly significant difference was noted between the mean of all peak flows in the upright (18.9 +/- 4.1 mL/s) versus recumbent (12.6 +/- 2.0 mL/s) position (P = 0.0001). Thirty-seven urinary flows and corresponding PVRs were completed by this individual (10 PVRs were determined after voiding in the standing and 27 after voiding in the recumbent position). No significant difference was noted between PVRs in the standing (24.6 +/- 34.4 mL) versus recumbent (16.5 +/- 60.0 mL) position. In the nursing home residents, the difference between the mean peak flow rates in the standing (14.5 +/- 8.6 mL/s) versus recumbent (12.4 +/- 6.7 mL/s) position also reached statistical significance (P = 0.0084). The difference between PVRs in the standing (60.5 +/- 125.6 mL) versus recumbent (84.8 +/- 186.2 mL) position barely reached statistical significance (P = 0.0497). CONCLUSIONS: The urinary flow rate decreases in the recumbent position. Bedridden residents may be predisposed to urinary tract infections because of alterations in voiding dynamics in the supine position. This area needs further study.     

Time and frequency domain analyses of heart rate variability during orthostatic stress in patients with neurally mediated syncope

The role of autonomic balance during upright tilt in patients with neurally mediated syncope is unclear. To assess the characteristics of autonomic tone during orthostatic stress, 15 patients (mean age 32 years) with recurrent episodes of syncope (> or = 2) and a positive response to a 30-minute 60 degrees upright tilt were compared with the following control groups: (1) 15 patients (mean age 33.5 years) with > or = 2 episodes of recurrent syncope and a negative tilt response, and (2) 15 age- and sex-matched healthy volunteers (mean age 34 years) with no previous history of presyncope or syncope. Time domain measurements assessed were mean RR interval, standard deviation of normal RR intervals, and percentage of normal consecutive RR intervals differing by > 50 ms. Frequency domain measurements of the low-frequency (LF) and high-frequency (HF) bands were obtained, and the LF/HF ratio was also calculated. All variables were calculated in the supine position and during the first 5 minutes of upright tilt. No significant difference was observed in the time and frequency domain variables in the supine position between control groups with a negative head-up tilt response and the group with a positive response. The percentage of normal consecutive RR intervals differing by > 50 ms during the first 5 minutes of head-up tilt was significantly higher in the group with positive tilt tests than in the controls (25 +/- 12% vs 7 +/- 4%, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Autonomic regulation of nasal vessels during changes in body position

The effects of postural changes on nasal airflow and nasal capillary blood flow were investigated in 15 healthy volunteers. Measurements were performed following nasal application of saline solution (control), the alpha-1 receptor antagonist prazosin, the alpha-2 receptor antagonist yohimbine, and after application of both prazosin and yohimbine. Nasal airflow in the control experiments did not significantly differ in the upright (362 +/- 166 ml/s), dorsally recumbent (350 +/- 167 ml/s) and 70 degrees head down position (311 +/- 167 ml/s). Following application of prazosin, nasal airflow was reduced to 223 +/- 121 ml/s in the upright position. Prazosin treatment significantly reduced nasal airflow to 177 +/- 111 ml/s when subjects were placed in dorsally recumbent positions and to 117 +/- 104 ml/s in 70 degrees head down positions (P < 0.001). Following application of yohimbine, nasal airflow remained stable when subjects were turned from upright (348 +/- 165 ml/s) to supine position (352 +/- 186 ml/s), whereas it was reduced to 199 +/- 137 ml/s in the head-down position. Application of both prazosin and yohimbine significantly increased nasal capillary blood flow in laser Doppler flowmetry measurements (P < 0.05). Changes in body position with or without application of the active drugs did not alter nasal capillary blood flow. These findings suggest that nasal congestion due to increased filling pressure in nasal capacitance vessels following postural changes is mainly prevented by alpha-1 adrenergic mechanisms.     

Influence of body position on diaphragmatic and scalene activation during hypoxic rebreathing

We measured electromyographic activity of the diaphragm (EMGdi) and scalene (EMGsc) during isocapnic progressive hypoxic ventilatory responses in five normal males in the supine and upright seated positions. The slope of the regression line relating EMGdi expressed as a percentage of maximum to percent fall in arterial oxyhemoglobin saturation was 93% steeper upright than supine (P < 0.005), whereas the slope of EMGdi activity to minute volume of ventilation was 73% higher upright than supine (P < 0.05). In addition, the slope of EMGsc activity relative to percent fall in arterial oxyhemoglobin saturation and minute ventilation was greater upright than supine (151%, P < 0.001 and 61%, P = 0.056, respectively). Greater EMGsc activity upright than supine was similar to findings during hypercapnic rebreathing. However, the greater EMGdi activity upright than supine stands in contrast to hypercapnic rebreathing where it was previously shown that EMGdi activity was not affected by a change in body position. We conclude that during hypoxic ventilatory responses both EMGdi and EMGsc activities are more pronounced upright than supine. Diaphragmatic activation during progressive hypoxia in response to a change in body position is different from that seen during progressive hypercapnia.     

Stroke volume measurement during supine and upright cycle exercise by impedance cardiography

This study evaluated impedance cardiography (ZCG) estimates of stroke volume (SV) during exercise. Seven subjects were studied at rest and during progressive cycle exercise in supine and upright positions. SV was determined by ZCG (SVZCG) during exercise and for the first 5 cardiac cycles following exercise. SVZCG was compared with separate measurements of SV by CO2 rebreathing (SVCO2). Static blood resistivity (p) was measured at each level of exercise. No significant differences were found between supine exercise and immediate post-exercise values for the peak of the first derivative of the impedance change (dZ/dtmax), left ventricular ejection time (LVET), or SVZCG. Small differences in dZ/dtmax and SVZCG, but not LVET, were found in exercise to post-exercise cycling in the upright position. Intra-individual SVZCG and SVCO2 were moderately correlated (upright mean r = 0.64, supine r = 0.42) from rest to 70% of peak VO2. Similar correlations were found between Pulse-O2 (VO2/heart rate, used as an index to SV) and both SVZCG (upright r = 0.73, supine r = 0.57) and SVCO2 (upright r = 0.8, supine r = 0.65). The ZCG parameters dZ/dtmax and LVET correlated better with Pulse-O2 (dZ/dtmax: upright r = 0.92, supine r = 0.73; LVET: upright r = -0.9, supine r = -0.9). SVZCG calculated with the Kubicek equation performed as well as SVCO2. ZCG might be a superior method if the inversely correlated parameters, dZ/dtmax and LVET, were not expressed as a product to calculate SV.     

Renal artery stenosis and accessory renal arteries: accuracy of detection and visualization with gadolinium-enhanced breath-hold MR angiography

Extracellular volume (ECV) of arms, trunk, and legs determined from segmental bioimpedance data in 11 healthy men (31.6 +/- 7 yr) obtained at the end of a 30-min equilibration phase in the supine body position was compared with ECV determined from whole body measurements (ECVWB). ECV was calculated from extracellular resistance (RECV) identified from the bioimpedance spectrum for a range of 10 frequencies. Whole body RECV (527.6 +/- 55.6 Omega) was equal to the sum of RECV in the arms, trunk, and legs (241.6 +/- 36. 3, 49.2 +/- 5.1, and 236.3 +/- 25.5 Omega, respectively). The sum of equilibrated ECV in arms (1.31 +/- 0.25 liters), trunk (10.08 +/- 1.65 liters), and legs (2.80 +/- 0.82 liters) was smaller than ECVWB (20.90 +/- 2.59 liters). In six subjects who changed from a standing to a supine body position, ECV decreased in arms (-2.59 +/- 2.51%, P = NS) and legs (-10.96 +/- 3.02%, P < 0.05) but increased in the trunk (+4.2 +/- 3.2%, P < 0.05). ECVWB also decreased (-4.98 +/- 1. 41%, P < 0.05). However, the sum of segmental extracellular volumes remained unchanged (-0.06 +/- 0.07%, P = NS). The sum of segmental ECVs is not sensitive to changes in body position, which otherwise interferes with the estimation of ECV in bioimpedance analysis when ECVWB is used.     

Leptin

INTRODUCTION: The purpose of this study was to test whether radiofrequency (RF) energy could be used to fixate leads to the endocardium. METHODS AND RESULTS: In six dogs we measured the dislodgment force and pacing threshold before and after RF fixation in the coronary sinus (CS) and right ventricle (RV). RF fixation was achieved with a CardioRhythm Atakr ablation unit. The dislodgment force of CS leads fixed with RF energy was 1.63+/-0.65 oz, compared with < 0.1 oz for similar leads placed in the CS of six separate dogs. In the RV, leads fixed with RF energy had a dislodgment force of 1.29+/-0.27 oz, compared with 0.48+/-0.28 oz. for urethane (P < 0.01) and 1.01+/-0.21 oz for silicone (P = 0.41) tined leads. In the CS, the pacing threshold for RF fixed leads increased significantly from 2.2+/-1.1 V (0.5 msec) before fixation to 4.2+/-1.3 V after fixation (P < 0.01), while in the RV, the pacing threshold increased from 0.41+/-0.05 V (0.5 msec) before fixation to a mean of 2.03+/-0.44 V after fixation (P < 0.01). In another group of six dogs studied for 12 weeks, 5 of 6 RF fixed CS leads remained attached, as did 8 of 10 RF fixed RV leads. For the RV leads, the mean pacing threshold was 0.90+/-0.35 V, compared with 0.53+/-0.18 V (0.5 msec) for similar tined leads (P = 0.02) and 1.2+/-0.30 V (0.5 msec) for screw leads (P = 0.18) in the RV. CONCLUSION: We conclude that RF energy can be used to attach leads to the RV and CS endocardium. While the RV pacing thresholds increased acutely, the mean chronic thresholds were not significantly different for RF fixed leads and standard tined or screw leads.     

The effects of ventricular fluid osmolality on bulk flow of nascent fluid into the cerebral ventricles of cats

Transdiaphragmatic pressure (Pdi) and expiratory flow (V) were monitored during vital capacity single breath N2 washouts in 7 seated subjects. Transient increases in V were produced (1) actively, by subjects increasing mouth pressure while expiring through a constant resistance of (2) passively, by the operator transiently decreasing the resistance. Voluntary contraction of the diaphragm (increased Pdi) was achieved when abdominal muscles were tensed while maintaining V constant. In 5 subjects a transient increase in Pdi of 25-150 cm H2O consistently produced a transient increase in expired N2 concentration of 1.80 +/- 0.06% (Mean +/- 1 SE); in 1 subject N2 concentration decreased by 0.8% to 2.7% N2, and in one subject the alveolar plateau was uninfluenced by changes in Pdi. Passive increases in V up to 21/sec had no effect on FEN2 in any of the subjects. Active increase in V changed FEN2 only when associated with increases in Pdi. Qualitatively similar results were obtained during helium (He) bolus washouts. However, whereas diaphragmatic contraction, maintained throughout expiration, had no measurable influence on the N2 washout, it changed the slope of the He alveolar plateau in 6 out of 7 subjects. We conclude that in normal subjects the alveolar N2 plateau is relatively insensitive to flow variations up to 21/sec. The fluctuations in FEN2 observed when the expiratory flow is varied are due to concomittant changes in Pdi. We propose that diaphragmatic contraction changes the pattern of lung emptying by altering the vertical gradient of pleural pressure.     

Functional outcome of patients with chronic obstructive pulmonary disease and exercise hypercapnia

Chronic hypercapnia is associated with a poor prognosis in chronic obstructive pulmonary disease (COPD). Some patients are normocapnic at rest but retain CO2 during exercise. The significance of this abnormality on the course of the disease is unknown. Sixteen stable COPD patients (13 males and 3 females, aged 60 +/- 5 yrs, mean +/- SD) who had previously undergone pulmonary function tests and progressive exercise testing with arterial blood sampling at rest and maximal capacity, entered the study. At first evaluation (E1), subjects were normocapnic at rest (arterial carbon dioxide tension (Pa,CO2): 4.9-5.7 kPa, (37-43 mmHg)) and all presented exercise-induced hypercapnia (end-exercise Pa,CO2 > 5.7 kPa (43 mmHg) with a minimal 0.5 kPa (4 mmHg) increase from resting value). The subjects were re-evaluated 24-54 months later (34 +/- 8 months) (second evaluation (E2)). At E2, forced expiratory volume in one second (FEV1) had decreased from 42 +/- 13 to 38 +/- 15% of predicted values, and mean resting Pa,CO2 had increased from 5.2 +/- 0.3 to 5.7 + 0.4 kPa. Maximal exercise capacity (Wmax) decreased between E1 and E2 from 76 +/- 30 to 56 +/- 22 W. Even if Wmax was lower at E2, end-exercise, Pa,CO2 was higher than at E1 (6.6 +/- 0.8 vs 6.4 +/- 0.5 kPa). At E2, eight subjects presented resting hypercapnia (group H), whilst the others remained normocapnic (Group N). Group H subjects had higher Pa,CO2, at Wmax than Group N and lower Wmax than Group N at E2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characteristics of vascular wall cells subjected to dynamic cyclic strain and fluid shear conditions in vitro

Surfactant bolus instillation may be associated with a drop in blood pressure. Platelet-activating factor (PAF) has been found in surfactant preparations. The aim of this study was to evaluate rapid tracheal infusion of surfactant during 5 min as an alternative to bolus instillation and to examine whether a PAF receptor antagonist is able to prevent the decrease in blood pressure. METHODS: Surfactant deficiency was induced in 16 adult rabbits by lung lavages with saline. Six animals received a bolus of a porcine surfactant preparation (Curosurf (CS); 200 mg/kg), labeled with red microspheres to assess pulmonary distribution. In another 5 rabbits, the same amount of labelled CS was instilled by tracheal infusion within 5 min. A third group of 5 animals received 3 mg/kg body weight of the PAF antagonist WEB 2170 before CS bolus instillation. RESULTS: After CS bolus administration, mean PaO2 increased by 44.7 +/- 8.3 kPa (mean +/- SD) within 2 min and remained at this level. Mean arterial blood pressure dropped transiently by 2.3 +/- 2 kPa within 5 min. Pulmonary distribution of surfactant was even. After infusion, mean PaO2 rose by 22.4 +/- 16.3 kPa within 15 min. Blood pressure dropped by 1.8 +/- 1.1 kPa within 15 min. The distribution was extremely uneven. Blood pressure decreases also occurred after pretreatment with PAF receptor antagonist. CONCLUSION: Rapid tracheal infusion of surfactant results in poorer oxygenation, an inhomogeneous distribution and a similar decrease in blood pressure compared to the bolus instillation method. Blood pressure changes could not be prevented by a PAF receptor-specific antagonist.     

Quanolirones I and II, two new human cytomegalovirus protease inhibitors produced by Streptomyces sp. WC76535

The aim of the study was to assess whether changes in the interposition of body compartments affect the results of body composition measurements by dual-energy x-ray absorptiometry (DEXA) in the fan-beam mode. Thirty healthy subjects underwent two sequential measurements: the first was performed in the supine position as described by the manufacturer, and the second in the prone position. Estimates of body composition were compared between the two measurements. Mean body weight did not differ between measurements ([mean+/-SD] supine vprone, 68.561+/-12.461 v 68.589+/-12.469 kg). Mean bone mineral content (BMC) was lower in the prone position versus the supine position. When the head was excluded, this difference reached statistical significance (supine v prone, 1,738+/-361 v 1,688+/-360 g, P=.0001). The mean fat tissue mass (FTM) was lower and lean tissue mass (LTM) higher in the prone measurements. When the head was excluded, the mean FTM difference between the two measurements became greater (FTM supine v prone, 25.129+/-10.445 v 24.030+/-10.388 kg, P=.0001; LTM supine v prone, 37.309+/-9.357 v 38.246+/-9.150 kg, P=.0001). It is concluded that the positioning of the patient on the examination table affects DEXA body composition measurements by the fan-beam mode. This could imply a lack of accuracy of the method, which may be due to subtle changes in regional tissue depth and fat distribution caused by patient repositioning.     

Influence of upper airway pressure oscillations on soft palate muscle electromyographic activity

Snoring is characterized by high-frequency (30-50 Hz) pressure oscillations (HFPO) in the upper airway (UA). The soft palate is a major oscillating structure during snoring, and soft palate muscle (SPM) activity is an important determinant of velopharyngeal patency. Consequently, we examined the effect of artificial HFPO applied to the UA on the integrated electromyographic (EMG) activity of the SPMs in 11 supine mouth-closed anesthetized (pentobarbital sodium/chloralose) dogs breathing spontaneously via a tracheostomy. The EMGs of the palatinus (Pal; n = 11), levator veli palatini (LP; n = 9), and tensor veli palatini (TP; n = 8) were monitored with intramuscular fine-wire electrodes. Peak inspiratory and peak expiratory EMG activity was measured in arbitrary units (au) as the mean of five consecutive breaths. HFPO [+/- 4.5 +/- 0.4 (SE) cmH2O; 30 Hz] applied at the laryngeal end of the isolated UA increased peak inspiratory EMG from 3.3 +/- 2.0 to 8.4 +/- 1.7 au (P < 0.05) for Pal and from 2.0 +/- 1.1 to 7.3 +/- 2.7 au (P < 0.05) for LP. For the TP, increases were evident in four dogs, but mean values for the group did not change (5.8 +/- 2.4 to 11.0 +/- 4.1 au, P = 0.5). The peak expiratory EMG did not change for any SPM (all P > 0.3). Thus HFPO applied to the UA augments inspiratory SPM activity. Reflex augmentation of SPM activity by HFPO may serve to dilate the retropalatal airway and/or stiffen the soft palate during inspiration in an attempt to stabilize UA geometry during snoring.     

Smaller lungs in women affect exercise hyperpnea

We subjected 29 healthy young women (age: 27 +/- 1 yr) with a wide range of fitness levels [maximal oxygen uptake (VO2 max): 57 +/- 6 ml . kg-1 . min-1; 35-70 ml . kg-1 . min-1] to a progressive treadmill running test. Our subjects had significantly smaller lung volumes and lower maximal expiratory flow rates, irrespective of fitness level, compared with predicted values for age- and height-matched men. The higher maximal workload in highly fit (VO2 max > 57 ml . kg-1 . min-1, n = 14) vs. less-fit (VO2 max < 56 ml . kg-1 . min-1, n = 15) women caused a higher maximal ventilation (VE) with increased tidal volume (VT) and breathing frequency (fb) at comparable maximal VT/vital capacity (VC). More expiratory flow limitation (EFL; 22 +/- 4% of VT) was also observed during heavy exercise in highly fit vs. less-fit women, causing higher end-expiratory and end-inspiratory lung volumes and greater usage of their maximum available ventilatory reserves. HeO2 (79% He-21% O2) vs. room air exercise trials were compared (with screens added to equalize external apparatus resistance). HeO2 increased maximal expiratory flow rates (20-38%) throughout the range of VC, which significantly reduced EFL during heavy exercise. When EFL was reduced with HeO2, VT, fb, and VE (+16 +/- 2 l/min) were significantly increased during maximal exercise. However, in the absence of EFL (during room air exercise), HeO2 had no effect on VE. We conclude that smaller lung volumes and maximal flow rates for women in general, and especially highly fit women, caused increased prevalence of EFL during heavy exercise, a relative hyperinflation, an increased reliance on fb, and a greater encroachment on the ventilatory "reserve." Consequently, VT and VE are mechanically constrained during maximal exercise in many fit women because the demand for high expiratory flow rates encroaches on the airways' maximum flow-volume envelope.     

Ultrasound evaluation of piglet diaphragm function before and after fatigue

Clinically, a noninvasive measure of diaphragm function is needed. The purpose of this study is to determine whether ultrasonography can be used to 1) quantify diaphragm function and 2) identify fatigue in a piglet model. Five piglets were anesthetized with pentobarbital sodium and halothane and studied during the following conditions: 1) baseline (spontaneous breathing); 2) baseline + CO2 [inhaled CO2 to increase arterial PCO2 to 50-60 Torr (6.6-8 kPa)]; 3) fatigue + CO2 (fatigue induced with 30 min of phrenic nerve pacing); and 4) recovery + CO2 (recovery after 1 h of mechanical ventilation). Ultrasound measurements of the posterior diaphragm were made (inspiratory mean velocity) in the transverse plane. Images were obtained from the midline, just inferior to the xiphoid process, and perpendicular to the abdomen. M-mode measures were made of the right posterior hemidiaphragm in the plane just lateral to the inferior vena cava. Abdominal and esophageal pressures were measured and transdiaphragmatic pressure (Pdi) was calculated during spontaneous (Sp) and paced (Pace) breaths. Arterial blood gases were also measured. Pdi(Sp) and Pdi(Pace) during baseline + CO2 were 8 +/- 0.7 and 49 +/- 11 cmH2O, respectively, and decreased to 6 +/- 1.0 and 27 +/- 7 cmH2O, respectively, during fatigue + CO2. Mean inspiratory velocity also decreased from 13 +/- 2 to 8 +/- 1 cm/s during these conditions. All variables returned to baseline during recovery + CO2. Ultrasonography can be used to quantify diaphragm function and identify piglet diaphragm fatigue.     

Atrial distension in humans during microgravity induced by parabolic flights

The hypothesis was tested that human cardiac filling pressures increase and the left atrium is distended during 20-s periods of microgravity (microG) created by parabolic flights, compared with values of the 1-G supine position. Left atrial diameter (n = 8, echocardiography) increased significantly during microG from 26.8 +/- 1.2 to 30.4 +/- 0.7 mm (P < 0.05). Simultaneously, central venous pressure (CVP; n = 6, transducer-tipped catheter) decreased from 5.8 +/- 1.5 to 4.5 +/- 1.1 mmHg (P < 0.05), and esophageal pressure (EP; n = 6) decreased from 1.5 +/- 1.6 to -4.1 +/- 1.7 mmHg (P < 0.05). Thus transmural CVP (TCVP = CVP - EP; n = 4) increased during microG from 6.1 +/- 3. 2 to 10.4 +/- 2.7 mmHg (P < 0.05). It is concluded that short periods of microG during parabolic flights induce an increase in TCVP and left atrial diameter in humans, compared with the results obtained in the 1-G horizontal supine position, despite a decrease in CVP.