PI Max Research Articles

Effect of expiratory resistive loading on the noninvasive tension-time index in COPD.

Expiratory resistive loading (ERL) is used by chronic obstructive pulmonary disease (COPD) patients to improve respiratory function. We, therefore, used a noninvasive tension-time index of the inspiratory muscles (TT(mus) = I/PI(max) x TI/TT, where I is mean inspiratory pressure estimated from the mouth occlusion pressure, PI(max) is maximal inspiratory pressure, TI is inspiratory time, and TT is total respiratory cycle time) to better define the effect of ERL on COPD patients. To accomplish this, we measured airway pressures, mouth occlusion pressure, respiratory cycle flow rates, and functional residual capacity (FRC) in 14 COPD patients and 10 normal subjects with and without the application of ERL. TT(mus) was then calculated and found to drop in both COPD and normal subjects (P<0.05). The decline in TT(mus) in both groups resulted solely from a prolongation of expiratory time with ERL (P<0.001 for COPD, P<0.05 for normal subjects). In contrast to the COPD patients, normal subjects had an elevation in I and FRC, thus minimizing the decline in TT(mus). In conclusion, ERL reduces the potential for inspiratory muscle fatigue in COPD by reducing TI/TT without affecting FRC and I.

Assessment of respiratory drive and muscle function in the pediatric intensive care unit and prediction of extubation failure.

Extubation failure can result from poor respiratory drive, impaired respiratory muscle function, or excessive inspiratory load. Measurement of airway pressure changes either during tidal breathing or after end-expiratory occlusion allows assessment of respiratory drive and muscle function. To determine whether the results of airway pressure measurements characterized children who subsequently failed extubation and identify which test's results had the highest predictive performance. A prospective study. Pediatric intensive care unit. A sample of 42 stable intubated pediatric patients who were judged clinically ready for extubation. A pneumotachograph was placed between the endotracheal tube and ventilator circuit. Airway pressure was measured from the pneumotachograph. The flow and pressure signals were amplified and displayed in real time on a laptop computer. During a temporary disconnection from the ventilator, the airway was occluded at end-expiration and the occlusion maintained for at least five breaths. From the first inspiratory effort during the occlusion, the pressure generated after 0.1 sec of occlusion (P0.1) and the largest negative pressure (PI) were calculated. From the series of breaths during the occlusion, the maximum P0.1 (P0.1 max) and maximum PI (PI max) were determined and P0.1/P0.1 max, PI/PI max and P0.1/PI max calculated. From spontaneous, tidal breaths during ventilatory support the pressure time product was calculated. Thirty-six (84%) of the children were successfully extubated. The children who failed extubation were characterized by a lower median P0.1 (p <.06), P0.1/P0.1 max, p <.05 and P0.1/PI max (p <.02). P0.1 and P0.1/P0.1 max and performed best in predicting extubation failure (areas under the receiver operator characteristic curves, 0.76 and 0.77 respectively). Assessment of P0.1 was the most useful airway pressure measurement in predicting extubation failure. Assessment of P0.1 may help to characterize children likely to fail extubation.

Influence of body weight on the severity of dyspnea in chronic obstructive pulmonary disease.

A substantial number of patients with COPD are underweight (UW); they comprise the clinical subtype of "dyspneic" or emphysematous. To determine whether these patients are more dyspneic than normal weight (NW) patients with COPD, we quantitated the severity of dyspnea, using a modified Medical Research Council (MRC) dyspnea scale, in 33 UW and 57 NW patients and compared their pulmonary function tests (PFTs), arterial blood gases (ABGs), and respiratory muscle strength as estimated by maximum static inspiratory (PI(max)) and expiratory (PE(max)) mouth pressures (all as means +/- SEM). Body mass index was 18.7 +/- 1.2 and 24.5 +/- 1.8 kg/m(2) in UW and NW patients, respectively (p < 0.0001). The MRC dyspnea scale was 3. 1 +/- 0.9 in UW and 2.5 +/- 1.2 in NW groups (p = 0.035). All PFT and ABG parameters were similar in the two groups except for DCO (36 +/- 11% in UW and 57 +/- 17% in NW, p < 0.001) and PI(max) (55 +/- 18 mm Hg in UW and 66 +/- 19 mm Hg in NW, p = 0.020). In a stepwise multiple regression model, %DCO and %MVV combined were the best predictors of dyspnea severity (R(2) = 0.30, p = 0.001). We conclude that UW patients with COPD are more dyspneic than NW patients. Although the origin of dyspnea in COPD is multifactorial, changes in DCO and respiratory muscle strength may contribute to its intensity.

Respiratory muscle recruitment and exercise performance in eucapnic and hypercapnic severe chronic obstructive pulmonary disease.

If chronic hypercapnia in patients with severe COPD occurs as a consequence of respiratory muscle (RM) weakness or fatigue, we would expect that ventilatory muscle recruitment (VMR) and exercise performance in stable hypercapnic patients would differ from those in eucapnic patients. We evaluated exercise performance and RM function at rest and during exercise in 19 eucapnic (PCO(2) 40 +/- 3 mm Hg), and 13 hypercapnic (PCO(2) 52 +/- 10 mm Hg) patients with severe COPD. A metabolic cart was used to determine V E, V O(2), V CO(2), and HR. Gastric (Pg) and esophageal (Ppl) balloons were used to measure Pg, Ppl, and Pdi. Ventilatory muscle recruitment pattern (VMR) was partitioned using end-inspiratory and end-expiratory Pg and Ppl. Hypercapnic patients had lower FEV(1) (0.60 +/- 0.24 versus 0.95 +/- 0.31 L, p < 0.001), MVV (28 +/- 11 versus 41 +/- 13 L, p < 0.001), resting PO(2) (61 +/- 11 versus 70 +/- 11 mm Hg, p < 0.001), peak PO(2) (60 +/- 20 versus 75 +/- 22 mm Hg, p < 0.005), and V E(max) (24 +/- 10 versus 32 +/- 12 L/min, p < 0.001). Patients in both groups had similar FRC (5.7 +/- 1.6 versus 5.0 +/- 1.5 L), V O(2)max (0.58 +/- 0.30 versus 0.76 +/- 0.32 L/min), Watts (45 +/- 48 versus 71 +/- 59), V E/MVV (88 +/- 33 versus 79 +/- 14), and HRmax (117 +/- 17 versus 128 +/- 18 beats/min). PI(max) (67 +/- 28 versus 65 +/- 32 cm H(2)O) and PE(max) (98 +/- 34 versus 96 +/- 40 cm H(2)O) were also similar in both groups. VMR (DeltaPg/DeltaPpl) at rest (-0.28 +/- 0.51 versus 0 +/- 0.35) and during exercise (0.4 +/- 0.2 versus 0.39 +/- 0.15) was equally affected in both groups. We conclude that exercise capacity and ventilatory muscle recruitment are similarly impaired in eucapnic and hypercapnic patients with severe COPD. These findings make inability of the lung to increase ventilation and not respiratory muscle dysfunction a more attractive explanation for CO(2) retention in stable hypercapnic patients.

Sniff nasal pressure: A sensitive respiratory test to assess progression of amyotrophic lateral sclerosis

Impairment of pulmonary function is a major prognostic indicator in amyotrophic lateral sclerosis (ALS). Forced vital capacity (FVC) and maximal voluntary ventilation (MVV) decline linearly and are commonly used to assess disease progression. The aim of this study was to evaluate the usefulness of testing respiratory muscle strength in ALS with a novel test, sniff nasal pressure (Pn(sn)), in parallel with more classic tests such as maximal inspiratory pressure (PI(max)) and maximal expiratory pressure (PE(max)). Sixteen patients with ALS were examined monthly over a period of 18 +/- 10 months. At the time of inclusion in the study, values were normal for FVC (107% of predicted value) and MVV (87% of predicted value) but abnormally low for Pn(sn) (67% of predicted value), PI(max) (69% of predicted value), and PE(max) (54% of predicted value). Late in the course of ALS, all patients could perform Pn(sn) whereas 6 could not perform PI(max) and 7 could not perform PE(max). The rate of deterioration was most often linear and similar for FVC (-4.1% of predicted value per month), MVV (-4.3% of predicted value per month), and Pn(sn) (-4.2% of predicted value per month). We conclude that Pn(sn) was the single respiratory test combining linear decline, sensitivity in mild disease, and feasibility in advanced disease. Being easy to perform and inexpensive, Pn(sn) appears well suited to assess the decline of respiratory muscle strength in ALS.

Inspiratory muscle training protocol using a pressure threshold device: Effect on dyspnea in chronic obstructive pulmonary disease

Objective: To evaluate the ability of patients with chronic obstructive pulmonary disease (COPD) to accomplish 6 weeks of inspiratory muscle training (IMT) using a pressure threshold device, and to observe how the training affected inspiratory muscle strength and dyspnea. Design: Pilot study comparing baseline values with posttest values. Subjects: Four adults with severe COPD (the mean of the forced expiratory volume in 1 second [FEV 1] was 28% of predicted value). Methods: Daily IMT sessions of 5 to 30 minutes' duration and weekly training load increments of −2 to −4cmH 2O over a 6-week period with the training device at loads of >30% of baseline maximal inspiratory pressure (PI max). Outcome Measures: Dyspnea measures were Mahler's Baseline and Transition Dyspnea Index and the Borg categoryratio scale administered during a submaximal exercise protocol. Results: All subjects tolerated the training load, improved their inspiratory muscle strength, and reported reduced dyspnea. Conclusion: Using a constant-load pressure threshold device to attain loads of >30% of the patient's baseline PI max is a feasible way to accomplish inspiratory muscle training in adults with severe COPD.

Ventilatory and mouth occlusion pressure responses to hypercapnia in chronic tetraplegia

Objective: To compare the ventilatory response to hypercapnia and the mouth occlusion pressure measured at 0.1 second following inspiration (P 0.1) in hypercapnia between chronic tetraplegic and normal subjects. Design: A case-control study with an uneven sample size for the study of clinical disorders. Setting: Patients were recruited from the outpatient clinic of a rehabilitation department. Participants: Seven normal men and 9 men with tetraplegia who had cervical cord injuries (C5–C8), with a mean injury duration of 9.7 yrs. Interventions: Pulmonary function tests were performed during resting, whereas minute ventilation (V E) and P 0.1 were measured during CO 2 rebreathing. Results: The maximal voluntary ventilation (MVV), vital capacity (VC), and maximal respiratory muscle strength in the tetraplegic subjects were significantly less than in the normal subjects. Both the ventilatory and P 0.1 responses to hypercapnia were significantly reduced in tetraplegic as compared with normal subjects, but the reductions were eliminated by normalizing with maximal ventilatory performance (MVV or VC) and maximal inspiratory muscle strength (PI max), respectively. Conclusions: Chronic tetraplegic persons have diminished ventilatory and P 0.1 responses to hypercapnia. Respiratory muscle weakness may be a primary factor contributing to the diminished ventilatory response observed in these patients.

Inertial-load method determines maximal cycling power in a single exercise bout.

A cycle ergometer was modified to measure power (P) with resistance provided solely by the moment of inertia (I) of the flywheel. P was calculated as the product of I, angular velocity (omega), and angular acceleration (alpha). Flywheel omega and alpha were determined by means of an optical sensor and a micro-controller based computer interface which measured time (+/- 1 microsecond) and allowed P to be calculated instantaneously (PI) every 3 degrees of pedal crank rotation or averaged over one complete revolution of the pedal cranks (PREV). Values for maximum P were identified from each bout (PI max and PREV max). Mechanical calibration of torque via a resistive strap proved this method to be both valid and accurate. Thirteen active male subjects performed four bouts of maximal acceleration lasting approximately 3-4 s with 2 min resting recovery. The mean coefficient of variation for PREV max was 3.3 +/- 0.6% and the intraclass correlation was 0.99. PREV max averaged 1317 +/- 66 W at 122 +/- 2 rpm, and PI max averaged 2137 +/- 101 W at 131 +/- 2 rpm. PREV max and PI max were highly correlated (r = 0.86 and r = 0.80 respectively, P < 0.002) with estimated lean thigh volume. Therefore, the inertial-load method provides a valid and reliable determination of cycling power in one short exercise bout.

Selective resection of the phrenic nerve roots in rabbits: Part II: Respiratory effects

This study evaluates the delayed respiratory consequences of selective resection of one or several roots of the right phrenic nerve in rabbits. A total of 50 animals were operated on according to five modalities of root resection. A total of 11 animals served as control. The breathing pattern was analysed 8 weeks after surgery. Transdiaphragmatic pressure was measured during transjugular supramaximal stimulation of the phrenic nerve, unilaterally or bilaterally and during prolonged tracheal occlusion (PI max). No difference was observed between the esophageal pressure observed during bilateral phrenic nerve stimulation (BilPeso) in control animals when compared to animals with resection of the highest root of the right phrenic nerve (16.2±1.0 versus 14.5±1.0 cmH 2O (mean±SE). Resection of the two highest or of the two lowest roots of the right phrenic nerve resulted in a similar BilPeso (11.3±0.8 versus 11.1±1.2 cmH 2O). Preservation of only the accessory phrenic nerve (APN) resulted in a low value of BilPeso (9.8±1.0 cmH 2O) similar to that obtained with complete denervation of the right hemidiaphragm. Ventilation and PI max were not different between the denervated or intact rabbits during quiet breathing. We conclude that in rabbits: (1) Diaphragmatic function is preserved after resection of the highest root of the phrenic nerve. (2) Diaphragmatic function is altered if only the APN is preserved.

Pulmonary function abnormalities in Prader-Willi syndrome

Objective: To determine whether individuals with Prader-Willi syndrome (PWS) have abnormalities in pulmonary function as a result of thoracic muscle weakness. Design: Testing of spirometry, flow-volume curves, lung volumes, and static respiratory pressures was performed in patients with PWS who are followed at the University of Connecticut. All tests were performed in triplicate on two or more occasions. Only reproducible tests were accepted. Established normative data were applied for all test results. Results: A total of 18 male subjects (age, 17.9 ± 10.2 years (mean ± SD); range, 5-39 years) and 17 female subjects (age, 23.5 ± 13.0 years; range, 5-54 years) completed the tests. Forced vital capacity and forced expiratory volume in 1 second were reduced; the forced expiratory volume in 1 second/forced vital capacity ratio was normal, total lung capacity was in the low normal range, and residual volume was elevated. Maximum inspiratory (PI max) and expiratory (PE max) pressures were markedly reduced in 32 subjects tested. Fifteen subjects had PE max values and 20 subjects had PI max values <60 cm H 2O, respectively. There was a linear correlation between forced expiratory volume in 1 second and both PI max and PE max ( r = 0.71; r = 0.62, respectively), and between forced vital capacity and both PE max and PI max ( r = 0.62 and r = 0.74, respectively). There was an inverse relationship between both PI max and PE max, and residual volume ( r = 0.47 and r = 0.72, respectively). Conclusion: Children and adults with PWS have restrictive ventilatory impairment primarily as a result of respiratory muscle weakness. Efforts to improve thoracic muscle strength may be useful in improving pulmonary function in individuals with PWS. ( J PEDIATR 1995;126:565-70)

EMG recordings of the respiratory muscles during unilateral and bilateral chest expansion

Respiratory muscle (RM) EMG was recorded in 10 healthy adults during bilateral and voluntary unilateral inspiration. Each performed bilateral and unilateral inspiration at 50, 75 and 100 per cent of maximal inspiration (PI max) measured with a mouth pressure gauge. The obliquus externus abdominus (EAO) EMG was also recorded in five subjects. Results showed that RM and EAO activity on the expanding side was similar during all levels of effort. The RM activity on the non-contracting side during most submaximal efforts was higher than that on the same side during bilateral efforts but not during maximal effort. The increase in EMG could be due to cross-talk from EAO and latissimus dorsi, or co-activation of the internal intercostal muscles. Because RM activity at PI max was similar for unilateral and bilateral efforts, it was concluded that voluntary unilateral RM inhibition may not be possible during maximal effort.

An exactly solvable self-avoiding walks model: II. Triangular and honeycomb lattices

A modified self-avoiding walks model previously proposed for the square lattice is applied to the triangular and honeycomb lattices. In the model, the walker is restricted not to take any turn which will put the walker in a direction rotated by more than a certain angle, Phi max, from any of the directions previously taken. The generating functions are obtained, and various quantities are evaluated exactly. For all three (square, triangular and honeycomb) lattices, it is found that the model exhibits the characteristics reminiscent of one-dimensional self-avoiding walks in all directions, while strongly retaining the anisotropic effect of the direction of the first step. For the honeycomb lattice, the authors have studied the model for Phi max= pi (A-model) and Phi max=3/2 pi (B-model). Unlike other walks, the B-model exhibits a special property: the oscillations between even and odd steps in various quantities such as the number of N-step walks do not decay as the number of steps increases.

Respiratory failure and sleep in neuromuscular disease.

Sleep hypoxaemia in non-rapid eye movement (non-REM) and rapid eye movement (REM) sleep was examined in 20 patients with various neuromuscular disorders with reference to the relation between oxygen desaturation during sleep and daytime lung and respiratory muscle function. All the patients had all night sleep studies performed and maximum inspiratory and expiratory mouth pressures (PI and Pemax), lung volumes, single breath transfer coefficient for carbon monoxide (KCO), and daytime arterial oxygen (PaO2) and carbon dioxide tensions (PaCO2) determined. Vital capacity in the erect and supine posture was measured in 14 patients. Mean (SD) PI max at RV was low at 33 (19) cm H2O (32% predicted). Mean PE max at TLC was also low at 53 (24) cm H2O (28% predicted). Mean daytime PaO2 was 67 (16) mm Hg and PaCO2 52 (13) mm Hg (8.9 (2.1) and 6.9 (1.7) kPa). The mean lowest arterial oxygen saturation (SaO2) was 83% (12%) during non-REM and 60% (23%) during REM sleep. Detailed electromyographic evidence in one patient with poliomyelitis showed that SaO2% during non-REM sleep was maintained by accessory respiratory muscle activity. There was a direct relation between the lowest SaO2 value during REM sleep and vital capacity, daytime PaO2, PaCO2, and percentage fall in vital capacity from the erect to the supine position (an index of diaphragm weakness). The simple measurement of vital capacity in the erect and supine positions and arterial blood gas tensions when the patient is awake provide a useful initial guide to the degree of respiratory failure occurring during sleep in patients with neuromuscular disorders. A sleep study is required to assess the extent of sleep induced respiratory failure accurately.

Role of a sulfhydryl group in gastric lipases. A binding study using the monomolecular-film technique.

Native human and rabbit gastric lipases (HGL and RGL, respectively) were inactivated after modification of one sulfhydryl group/enzyme molecule. HGL and RGL were covalently labeled using 5,5'-dithiobis(2-nitro-[14C]benzoic acid) and the interaction of 2-nitro-5-thio-[14C]benzoic-acid-labeled lipases ([14C]Nbs-lipases) with monomolecular lipid films was investigated. Our results show that [14C]Nbs-lipases bind to lipid films as efficiently as native HGL or RGL. The critical surface pressure pi c and the maximal surface pressure (delta pi max) of [14C]Nbs-lipases were enhanced in comparison with those of native RGL and HGL. These changes in behavior were probably due to an increase in hydrophobicity brought about, directly or indirectly, by the binding of the Nbs radical. This chemical modification thus blocks the hydrolysis site and reinforces the hydrophobic character of the gastric lipases.

Airway pressures during crying in healthy infants.

Maximal inspiratory and expiratory airway pressures (PI max and PE max) were measured in 100 healthy infants (51 males, 49 females; age range, 0.06-3.76 years) by occluding the airway with a suitable face mask during a crying effort. Mean values +/- SD for PI max and PE max were 118 +/- 21 cm H2O and 125 +/- 35 cm H2O, respectively. Maximal inspiratory pressure was independent of age, sex, and anthropometrics, while maximal expiratory pressure showed a low but statistically significant positive correlation with body weight (P less than 0.001).

FATIGUE OF THE INSPIRATORY MUSCLES OF THE RIB CAGE IN HUMANS

Studies on respiratory muscle fatigue have focused on the diaphragm (DIA). We have found, however, that maximal static inspiratory pleural pressure (Pi max) is limited by the strength of the inspiratory muscles of the rib cage (RC). Failure to maintain Pi max during inspiratory endurance tasks might therefore result from fatigue of the RC muscles rather than DIA. To test this hypothesis, 5 trained subjects repeated maximal inspiratory efforts (duty cycle, 0.5) until Pi max could not be maintained. Subjects performed such efforts with a minimum of abdominal muscle recruitment. Before and after inspiratory efforts, DIA muscle strength was evaluated by measuring the transdiaphragmatic pressure generated during maximal expulsive efforts with an open glottis (Pdi max). (During expulsive efforts the DIA is maximally activated; thus, the Pdi obtained is a true index of DIA strength). Results (x±SD, *p<.01, paired t): We conclude that (1) Pi max is not limited by DIA strength, and (2) because DIA strength was unchanged, failure to maintain Pi max in these subjects appeared to be due to fatigue of the inspiratory muscles of the RC. RC muscle fatigue may be important in the pathogenesis of respiratory muscle failure. Supported by HL 07633.

Inhibition of lipases by proteins. A kinetic study with dicaprin monolayers.

We report further investigations on protein inhibition of pancreatic and microbial lipases carried out with the monolayer technique. When beta-lactoglobulin A, melittin, serum albumin, myoglobin, and a protein inhibiting lipase from soybean were preincubated with a dicaprin film at a surface pressure of 35 dynes/cm, no activity was detected with horse pancreatic or Rhizopus delemar lipases. By contrast, Rhizopus arrhizus and Geotrichum candidum lipase activities were not impaired under the same conditions. Experiments using mixed lipid-protein film transfer clearly show that the inhibition of pancreatic lipase is due to the protein associated with lipid and not caused by direct protein-enzyme interaction in the aqueous phase. Three parameters were used to determine the surface properties of the various proteins at the dicaprin/water interface; namely, the initial rate of surface pressure increase, (delta pi/delta t)t = 0, the maximal surface pressure increase, delta pi max, and the critical surface pressure, pi c. A positive correlation was observed between values of (delta pi/delta t)t = 0 of proteins and their respective capacity to inhibit pancreatic and R. delemar lipases. By contrast, there was no apparent correlation with the two other parameters, delta pi max or pi c.

Upwelling in the Southern Benguela Current

This survey of the southernmost significant upwelling site in the Benguela Current showed that the oceanography is dominated by the seasonal wind cycle of predominant S-E winds in summer and N-W winds in winter. In the upwelling season, extending from September to March, a semi-permanent plume is isolated by a pronounced oceanic front whose position varies in the short-term and is related to wind direction. Surface waters change immediately and deeper waters more slowly to fluctuations in wind. The rate of upwelling was statistically related to wind data. A maximum rate of 32 m day −1 was found. In spring low temperature and salinity water flows northward on the shelf while between late summer and later winter oxygen-depleted water, rich in nutrients, flowed south at an estimated rate of 7–21 × 10 4 m 3 s −1 in a counter current to the Good Hope Jet. Local depletion of oxygen occurs due to phytoplankton decomposition caused, in autumn, by falling light levels and, in summer in calm periods, by nitrate depletion (<1 μg-at N 1 −1). Primary productions is estimated at 3.7 kg C m −2 yr −1 with a maximum growth rate ( PI max) = 17.4–19.0 mg C mg chlorophyll a −1 hr −1 and half-saturation constant ( K S) = 0.4–1.1 μg-at N 1 −1. Nutrients were utilized and oxygen produced: ΔP: ΔN: ΔSi: ΔO=1:19.1 to 23.3:17.5 to 23.3:−227 to −293. High N:Si ratios (maximum 4.28) were found in oxygen-depleted water produced locally while that coming from the north had low ratis, due to resolution of silica from the sediments and nitrate reduction. The mean zooplankton standing stock, 2.3 g dry weight m −2, was 12% of the phytoplankton crop. In summer stocks were maximal 40–100 km and minimal 20–50 km from the coast while in winter they were maximal inshore. Little vertical migration occurred and the waters above the thermocline contained the majority of the population.

Dialysis-induced changes in muscle strength.

Little is known about the acute effects of hemodialysis on muscle strength. Rapid changes in hemodynamic and biochemical parameters are known to occur during dialysis and may alter muscle performance. Ten patients maintained on chronic hemodialysis had measurements of quadriceps muscle and handgrip strength performed before and after dialysis. In seven of these patients maximum static inspiratory and expiratory pressures (PI max and PE max respectively) were similarly determined. Quadriceps muscle strength improved in 6 patients, decreased in 3 and remained unchanged in 1. Handgrip strength increased in 5 patients, decreased in 3, and remained unchanged in 1. PI max decreased in 6 patients and increased in 1, and PE max decreased in 4 patients and increased in 3. No significant correlation was found between the changes in strength of the tested muscle groups and the serum concentrations of sodium, potassium, calcium, phosphorus, urea nitrogen, and creatinine, changes in blood pressure of fluid balance. The dialysis-induced changes in biochemical parameters may exert opposing effects on neuromuscular performance. This may explain the diversity of the results obtained in this study.

Relationship of static respiratory muscle pressure and maximum voluntary ventilation in normal subjects.

40 normal subjects performed spirometry, maximum voluntary ventilation (MVV), and tests of static inspiratory (Pi max) and expiratory (Pe max) respiratory muscle pressure. Forced expiratory volumes in 0.5 (FEV0.5), in 0.75 (FEV0.75), and 1 sec (FEV1) correlated significantly with MVV (r = 0.805, 0.804, 0.779, respectively). When Pi max was considered as a second independent variable, the probability of predicting MVV from timed forced expiratory volumes was enhanced (r = 0.914, 0.900 and 0.872 for FEV0.5, FEV0.75, and FEV1, respectively). Statistical analysis indicated that multiple regression with Pi max was superior to regression with timed forced expiratory volume alone in the prediction of MVV. For any given FEV1, however, Pi max was widely dispersed (range: -60 to -200 cm H2O). MVV values, expressed as percentage difference between largest and smallest value, varied less than did Pi max. Pe max, vital capacity, height and age did not enhance the ability of timed forced expiratory volumes to predict MVV. These data indicate that while respiratory muscle strength is important for sustaining maximal ventilation, the MVV is not a sensitive indicator of respiratory muscle strength.