Determinants of maximal inspiratory pressure in chronic obstructive pulmonary disease

Inspiratory muscle strength in COPD could be reduced either because of mechanical disadvantage consequent to increased lung volume or because respiratory muscles share in generalized muscle weakness. To assess the relative contributions of these factors, we measured maximal inspiratory and expiratory pressures (Pimax, Pemax, cmH2O) at RV and TLC, respectively, in 32 patients with COPD. The TLC, RV, and diaphragm length index at RV (DLI, cm/cm height) were determined roentgenographically and compared with values from 22 normal subjects studied at comparable lung volume. Half the patients with COPD had normal and half had low values of Pemax, but both groups had similar values of TLC, RV, and DLI. In patients with COPD, Pimax correlated (p less than 0.001) with Pemax (r = 0.73) and DLI (r = 0.64). The slope of the Pimax-DLI relationship was essentially the same in both groups of patients with COPD as it was in the normal subjects. However, at any value of DLI, Pimax was in the normal range in patients with normal Pemax, but significantly lower in patients with low Pemax (p less than 0.001). Expressing Pimax as a combined function of Pemax and DLI yielded the highest correlation (r = 0.84, p less than 0.001), with Pemax explaining 46% and DLI explaining 35% of the variance in Plmax not explained by the other variable alone (p less than 0.001). The PaCO2 was elevated in 13 of 18 patients whose Pimax was less than 55 cm H2O, and inversely correlated with Pimax (r = -0.66, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Orthopnea and tidal expiratory flow limitation in chronic heart failure

BACKGROUND: Tidal expiratory flow limitation (FL) is common in patients with acute left heart failure and contributes significantly to orthopnea. Whether tidal FL exists in patients with chronic heart failure (CHF) remains to be determined. PURPOSES: To measure tidal FL and respiratory function in CHF patients and their relationships to orthopnea. METHODS: In 20 CHF patients (mean [+/- SD] ejection fraction, 23 +/- 8%; mean systolic pulmonary artery pressure [sPAP], 46 +/- 18 mm Hg; mean age, 59 +/- 11 years) and 20 control subjects who were matched for age and gender, we assessed FL, Borg score, spirometry, maximal inspiratory pressure (Pimax), mouth occlusion pressure 100 ms after the onset of inspiratory effort (P(0.1)), and breathing pattern in both the sitting and supine positions. The Medical Research Council score and orthopnea score were also determined. RESULTS: In the sitting position, tidal FL was absent in all patients and healthy subjects. In CHF patients, Pimax was reduced, and ventilation and P(0.1)/Pimax ratio was increased relative to those of control subjects. In the supine position, 12 CHF patients had FL and 18 CHF patients claimed orthopnea with a mean Borg score increasing from 0.5 +/- 0.7 in the sitting position to 2.7 +/- 1.5 in the supine position in CHF patients. In contrast, orthopnea was absent in all control subjects. The FL patients were older than the non-FL patients (mean age, 63 +/- 8 vs 53 +/- 12 years, respectively; p < 0.03). In shifting from the seated to the supine position, the P(0.1)/Pimax ratio and the effective inspiratory impedance increased more in CHF patients than in control subjects. The best predictors of orthopnea in CHF patients were sPAP, supine Pimax, and the percentage change in inspiratory capacity (IC) from the seated to the supine position (r(2) = 0.64; p < 0.001). CONCLUSIONS: In sitting CHF patients, tidal FL is absent but is common supine. Supine FL, together with increased respiratory impedance and decreased inspiratory muscle force, can elicit orthopnea, whom independent indicators are sPAP, supine Pimax and change in IC percentage.     

Impact of impaired inspiratory muscle strength on dyspnea and walking capacity in sarcoidosis

BACKGROUND: Dyspnea and fatigue are frequent but poorly understood symptoms in sarcoidosis patients. This study was aimed at assessing the clinical impact of inspiratory muscle impairment on dyspnea and exercise tolerance. This is the first study using nonvolitional tests that are independent of the patient's cooperation and motivation in addition to volitional tests of inspiratory muscle strength in patients with sarcoidosis. METHODS: Peak maximal inspiratory mouth pressure (Pimaxpeak), maximal inspiratory pressure sustained for 1.0 s (Pimax1.0), twitch mouth pressure (TwPmo), lung function test results, blood gas measurements, 6-min walking distance (6MWD), and Borg dyspnea scale (BDS) scores were assessed in 24 male sarcoidosis patients and 24 healthy male control subjects matched for age and body mass index. RESULTS: Mean (+/- SD) Pimaxpeak (95.2 +/- 25.3% vs 124.6 +/- 23.4% predicted, respectively; p < 0.001) and Pimax1.0 (85.6 +/- 31.4% vs 125.8 +/- 26.8% predicted, respectively; p < 0.001) were lower in sarcoidosis patients compared to control subjects. TwPmo tended to be lower in sarcoidosis patients, and there were three patients who had TwPmo values of < 1.0 kPa, which is a strong indicator of inspiratory muscle weakness. The mean 6MWD was 582 +/- 97 m in sarcoidosis patients and 638 +/- 65 in control subjects (p = 0.025). The mean BDS score was higher in sarcoidosis patients (3.3 +/- 1.7 vs 0.2 +/- 0.5, respectively; p < 0.001). Compared to maximal inspiratory pressure, lung function parameters, and blood gas levels, TwPmo was the strongest predictor for 6MWD (r = 0.663; p = 0.003) and BDS score (r = 0.575; p = 0.012) in sarcoidosis patients following multiple linear regression analysis. CONCLUSIONS: Impairment of inspiratory muscle strength occurs in sarcoidosis patients, and has been suggested to be an important factor causing dyspnea and reduced walking capacity, but this is only reliably detectable when using nonvolitional tests of inspiratory muscle strength.     

Inspiratory muscle function in patients with severe kyphoscoliosis

In 9 patients with severe kyphoscoliosis we studied inspiratory muscle function by measuring transdiaphragmatic pressure (Pdi) and its components: gastric (Pga) and esophageal (Pes) pressures during quiet breathing. Maximal Pdi and maximal inspiratory mouth pressure (Pimax) were also measured. The results showed that Pimax and Pdimax were significantly lower in patients than in normal subjects. During quiet breathing, all patients had positive swings in Pga, indicating an active contraction of the diaphragm, but Pes was significantly more negative, suggesting the recruitment of intercostal and accessory inspiratory muscles. We did not find significant correlations between Pimax, Pdimax, delta Pga/delta Pes, FVC, PaO2, or PaCO2 and the degree of spinal deformity. The FVC tended to correlate with Pimax (r = 0.63) and with Pdimax (r = 0.53). The Pdi correlated with PaO2 (r = 0.66) and with PaCO2 (r = -0.76; p less than 0.05). A significant correlation was also observed between Pimax and PaO2 (r = 0.785; p less than 0.05) and between Pimax and PaCO2 (r = -0.86; p less than 0.01). We conclude that impairment of inspiratory muscle function is related to the development of ventilatory failure in kyphoscoliosis.     

The value of sniff esophageal pressures in the assessment of global inspiratory muscle strength

Esophageal pressure generated during a maximal sniff (sniff Pes) was compared with mouth pressure generated during a maximal inspiration against a closed airway (Pimax) as a measure of global inspiratory muscle strength in 61 patients referred for investigation of respiratory muscle function. Transdiaphragmatic pressure (Pdi) was also measured during both maneuvers to compare maximal diaphragmatic strength. Sniff Pes (males, 68 +/- 27 cm H2O; normal greater than 53; females, 66 +/- 21; normal greater than 48) was greater than Pimax (males, 45 +/- 24 cm H2O; normal greater than 42; females, 42 +/- 24; normal greater than 17) in 55 of the 61 patients, both in absolute values and as a percentage of normal. In 36 patients Pimax and sniff Pes were both normal (mean +/- 2 SD), whereas in 13 patients they were both low. In 11 patients, Pimax was low, but sniff Pes was normal. One patient had a reduced sniff Pes but a Pimax at the lower limit of normal. In the 36 patients in whom both Pimax and sniff Pes were normal, Pdi was also normal or only moderately reduced, and in the 13 patients in whom both Pimax and sniff Pes were reduced, Pdi was very low. However, in the group of 11 patients with a low Pimax but a normal sniff Pes, Pdi was normal or only moderately reduced, suggesting that Pimax was falsely low, perhaps because of difficulties with the technique. Conversely, in the single patient with a low sniff Pes but a Pimax just within the normal range, Pdi was very low. We conclude that measurement of esophageal pressure during a maximal sniff is a useful test of inspiratory muscle strength and overcomes the difficulty some patients have in carrying out the Pimax maneuver.     

Inspiratory muscle weakness in diastolic dysfunction

OBJECTIVES: To test the hypothesis that patients with well-documented diastolic dysfunction (DD) in the setting of normal systolic function will have inspiratory muscle weakness when compared to normal control subjects, and will experience dyspnea and tachypnea during exercise. BACKGROUND: Respiratory muscle weakness has been described in patients with (systolic) congestive heart failure; however, whether or not patients with DD may present with the findings of congestive heart failure is not known. METHODS: We selected for study 14 patients with DD previously referred for cardiopulmonary evaluation whose diagnosis had been confirmed by data obtained at cardiac catheterization. Seven control subjects matched for age, sex, and weight were recruited from the hospital community. Subjects performed both basic pulmonary function tests and tests of muscle strength: handgrip strength (Hgr), and maximal subatmospheric static inspiratory muscle pressure (Pimax). Subjects then performed a graded exercise test on a bicycle ergometer. Minute ventilation, oxygen consumption, carbon dioxide production, and heart rate were monitored continuously. Echocardiography was performed three times: before exercise, at a selected submaximal exercise level (20% of a predicted maximal workload), and at maximal exercise. Subjects rated their degree of dyspnea using the Borg scale at the same three time intervals. RESULTS: Pimax was - 102 +/- 17 cm H(2)O in control subjects, and - 77 +/- 19 cm H(2)O in patients with DD (p = 0.013) [mean +/- SD]. Hgr was similar between the groups. At the selected submaximal exercise level, patients with DD rated dyspnea to be 2.6 +/- 2.2 Borg scale units (control subjects, 0.5 +/- 0.8 Borg scale units). Hey plots described a rapid, shallow breathing pattern in patients with DD during exercise. Patients with DD and control subjects achieved similar maximal work loads. CONCLUSION: Patients with DD have diminished Pimax, adopt a rapid, shallow breathing pattern during exercise, and experience dyspnea at low work loads when compared to matched control subjects.     

Corticosteroid therapy and respiratory muscle function in humans

We examined the effects of prednisone administration on respiratory muscle function in humans using a double-blind study with a placebo control group. A total of 16 normal subjects were randomized to receive 20 mg prednisone daily (n = 8) or placebo daily (n = 8) for 2 wk. Inspiratory muscle strength (Pimax), expiratory muscle strength (PEmax), diaphragmatic strength (Pdimax), and inspiratory muscle endurance were measured at the beginning and end of the study. There was no significant change with treatment for Pimax (-145 +/- 7 to -138 +/- 6 cm H2O), PEmax (171 +/- 17 to 169 +/- 14 cm H2O), Pdimax (194 +/- 11 to 196 +/- 12 cm H2O), or endurance (76 +/- 3 to 77 +/- 4%) for the prednisone group and no significant difference between the two groups. We conclude that prednisone in moderate dosage has no significant effect on respiratory muscle function in humans, at least in the short term.     

Pulmonary function in individuals with a history of poliomyelitis

We examined the relationship between the lung function of 74 individuals with a history of poliomyelitis and reports of shortness of breath during activities of daily living, and the presence of post-polio sequelae risk factors. First, we studied the spirometry of 60 individuals (group 1) and second, we studied the relationship between the spirometry of an additional 14 individuals (group 2) and their respiratory muscle strength (Pimax and Pemax). In both groups, we examined the relationship between factors associated with post-polio sequelae including ventilation at polio-onset, having contracted polio after the age of 10, and having had polio for over 35 years; and lung function. In group 1, the FEV1 and FVC were lower for individuals with shortness of breath than individuals without (p less than 0.01). With respect to risk factors, FEV1 and FVC were lower in individuals who were ventilated at polio-onset, in individuals who contracted polio over 10 years of age, and in individuals who had had polio for less, rather than more than 35 years (p less than 0.05). The results for group 2 were comparable to group 1. In addition, the observed Pimax and Pemax were significantly lower than predicted values (p less than 0.05). Although FEV1 and FVC were positively correlated with both Pimax and Pemax (p less than 0.05), Pemax was disproportionately impaired compared to Pimax (40 +/- 12.1 and 82 +/- 38.8 percent predicted respectively). We conclude that individuals with a history of poliomyelitis can have compromised lung function irrespective of shortness of breath, that risk factors such as ventilation at polio-onset and polio-onset after 10 years of age can help predict those at risk of respiratory compromise, and that the measurement of respiratory muscle strength and of Pemax in particular, can augment the assessment of lung function of these individuals. Such assessment may avert respiratory complications in the post poliomyelitis population including those secondary to health care interventions.     

Measurement of maximal static respiratory pressures at the mouth with different air leaks

The effect of two different circuit leaks on the measurement of maximal static inspiratory and expiratory pressures at the mouth (Pimax, Pemax) was assessed in 70 patients with respiratory disease. Patients were divided into three groups with similar anthropometric and spirometric characteristics. The first group (30 patients) had their Pmax measured with a leak of 2.0 mm internal diameter (ID) and 37 mm length (as proposed by T. Ringqvist) and repeated with a second leak of 1.0 mm ID and 15 mm length (as recommended by J. L. Clausen). The two measurements were done in random order. Measurements for the other two groups (20 patients each) were taken with one or another, the two leaks randomly alternated with no leak. Pimax measurements obtained with Ringqvist's leak were 17 percent (p less than 0.005) lower than those with Clausen's leak and 22 percent (p less than 0.005) lower than those with no leak. Pemax measurements performed with Ringqvist's leak in place were 11 percent (p less than 0.005) lower than those with Clausen's leak and 11 percent (p less than 0.005) lower than those obtained with no leak. The comparison between Clausen's leak and no leak showed no statistically significant difference. We conclude that whenever the effect of pressure generated in the mouth is to be avoided in the measurement of respiratory Pmax, a leak of the size proposed by Ringqvist is to be preferred.     

Airway pressures during crying: an index of respiratory muscle strength in infants with neuromuscular disease

The purpose of this study was to assess the strength of the respiratory muscles in 12 infants with neuromuscular disease (age range: 0.17-2.08 years) by measuring the maximal inspiratory and expiratory airway pressures (Pimax and PEmax) during crying efforts. Infants were divided into two groups according to their respiratory history. Group A included six infants in stable condition without clinical evidence of respiratory abnormalities, and Group B included six infants with severe generalized muscle weakness and previous respiratory failure. The infants in Group B had been weaned from mechanical ventilation 6 to 14 days before being studied. For infants of Group A, Pimax and PEmax values were 77 +/- 28 cmH2O and 62 +/- 18 cmH2O, respectively; for infants of Group B, they were 38 +/- 8 cmH2O and 34 +/- 8 cmH2O, respectively. A positive correlation was found between PEmax and body mass percentile. No infant had hypercapnia at the time of the study, and Pao2 values in infants of Group B were significantly lower than those of Group A. These results suggest that measurements of airway pressures during crying may provide an index of respiratory muscle strength in infants with generalized muscle weakness.     

Inspiratory muscle strength in asthma

Augmentation of inspiratory muscle strength (Pimax) represents an adaptive response to airway obstruction. We explore the possibility that respiratory muscle weakness may herald hospital admission during acute bronchospasm. The Pimax measured 81 +/- 25 percent of a predicted value in 20 patients with acute bronchospasm (forced expiratory volume in one second, 36 +/- 17 percent predicted). Pimax was related to both hyperinflation (functional residual capacity, as percent predicted) and body weight (subjects were 122 +/- 29 percent ideal body weight), but not to the degree of airway obstruction per se. Furthermore, measurements of axial (craniocaudal) motion of the rib cage and asynchrony of rib cage and abdominal motions during tidal breathing did not correlate with either the degree of air flow obstruction or Pimax. We conclude that little if any respiratory muscle weakness occurs with bronchospasm. Furthermore, Pimax does not correlate with the degree of airway obstruction and does not explain abnormalities of rib cage and abdominal motion associated with asthma.     

Closing capacity and gas exchange in chronic heart failure

BACKGROUND: Although it is commonly assumed that pulmonary congestion and edema in patients with chronic heart failure (CHF) promotes peripheral airway closure, closing capacity (CC) has not been measured in CHF patients. PURPOSES: To measure CC and the presence or absence of airway closure and expiratory flow limitation (FL) during resting breathing in CHF patients. METHODS: In 20 CHF patients and 20 control subjects, we assessed CC, FL, spirometry, blood gas levels, control of breathing, breathing pattern, and dyspnea. RESULTS: The patients exhibited a mild restrictive pattern, but the CC was not significantly different from that in control subjects. Nevertheless, airway closure during tidal breathing (ie, CC greater than functional residual capacity [FRC]) was present in most patients but was absent in all control subjects. As a result of the maldistribution of ventilation and the concurrent impairment of gas exchange, the mean (+/- SD) alveolar-arterial oxygen pressure difference increased significantly in CHF patients (4.3 +/- 1.2 vs 2.7 +/- 0.5 kPa, respectively; p < 0.001) and correlated with systolic pulmonary artery pressure (r = 0.49; p < 0.03). Tidal FL is absent in CHF patients. Mouth occlusion pressure 100 ms after onset of inspiratory effort (P0.1) as a percentage of maximal inspiratory pressure (Pimax) together with ventilation were increased in CHF patients (p < 0.01 and p < 0.005, respectively). The increase in ventilation was due entirely to increased respiratory frequency (fR) with a concurrent decrease in Paco2. Chronic dyspnea (scored with the Medical Research Council [MRC] scale) correlated (r2= 0.61; p < 0.001) with fR and P0.1/Pimax. CONCLUSIONS: In CHF patients at rest, CC is not increased, but, as a result of decreased FRC, airway closure during tidal breathing is present, promoting the maldistribution of ventilation, ventilation-perfusion mismatch, and impaired gas exchange. The ventilation is increased as result of increased fR, and Pimax is decreased with a concurrent increase in P0.1, implying that there is a proportionately greater inspiratory effort per breath (P0.1/Pimax). These, together with the increased fR, are the only significant contributors to increases in the MRC dyspnea score.     

Respiratory muscle dysfunction in idiopathic pulmonary arterial hypertension.

Idiopathic pulmonary arterial hypertension (IPAH) is a pulmonary vasculopathy of unknown aetiology. Dyspnoea, peripheral airway obstruction and inefficient ventilation are common in IPAH. Data on respiratory muscle function are lacking. This prospective single-centre study included 26 female and 11 male patients with IPAH in World Health Organization functional classes II-IV. Mean+/-SD pulmonary artery pressure was 48.6+/-16.9 in females and 53.1+/-22.9 mmHg in males; cardiac output was 3.7+/-1.3 and 4.2+/-1.7 L x min(-1). Maximal inspiratory pressure (PI,max) was lower in the female patients than in 20 controls (5.3+/-2.0 versus 8.2+/-2.0 kPa). In the male patients, PI,max was lower than in 25 controls (6.8+/-2.2 versus 10.5+/-3.7 kPa). Maximal expiratory pressure (PE,max) was lower in the female patients than in controls (6.2+/-2.6 versus 9.5+/-2.1 kPa), and in male patients as compared to controls (7.1+/-1.6 versus 10.3+/-3.9 kPa). There was no correlation between PI,max or PE,max and parameters of pulmonary haemodynamics or exercise testing. The ratio of mouth occlusion pressure within the first 0.1 s of inspiration and PI,max was higher in IPAH than in controls (females 0.067+/-0.066 versus 0.021+/-0.008; males 0.047+/-0.061 versus 0.023+/-0.016). In conclusion, this study provides the first evidence of inspiratory and expiratory muscle weakness in idiopathic pulmonary arterial hypertension. The pathomechanisms and the prognostic significance should be further investigated.     

Relationship of upper-limb and thoracic muscle strength to 6-min walk distance in COPD patients

STUDY OBJECTIVES: This study was developed to investigate the influence of thoracic and upper-limb muscle function on 6-min walk distance (6MWD) in patients with COPD. DESIGN: A prospective, cross-sectional study. SETTING: The pulmonary rehabilitation center of a university hospital. PATIENTS: Thirty-eight patients with mild to very severe COPD were evaluated. MEASUREMENTS AND RESULTS: Pulmonary function and baseline dyspnea index (BDI) were assessed, handgrip strength, maximal inspiratory pressure (Pimax), and 6MWD were measured, and the one-repetition maximum (1RM) was determined for each of four exercises (bench press, lat pull down, leg extension, and leg press) performed on gymnasium equipment. Quality of life was assessed using the St. George Respiratory Questionnaire (SGRQ). We found statistically significant positive correlations between 6MWD and body weight (r = 0.32; p < 0.05), BDI (r = 0.50; p < 0.01), FEV(1) (r = 0.33; p < 0.05), Pimax (r = 0.53; p < 0.01), and all values of 1RM. A statistically significant negative correlation was observed between 6MWD and dyspnea at the end of the 6-min walk test (r = - 0.29; p < 0.05), as well as between 6MWD and the SGRQ activity domain (r = - 0.45; p < 0.01) and impact domain (r = - 0.34; p < 0.05) and total score (r = - 0.40; p < 0.01). Multiple regression analysis selected body weight, BDI, Pimax, and lat pull down 1RM as predictive factors for 6MWD (R(2) = 0.589). CONCLUSIONS: The results of this study showed the importance of the skeletal musculature of the thorax and upper limbs in submaximal exercise tolerance and could open new perspectives for training programs designed to improve functional activity in COPD patients.     

Dyspnea and respiratory muscle strength in end-stage liver disease

AIM: To investigate the prevalence of chronic dyspnea and its relationship to respiratory muscle function in end-stage liver disease. METHODS: Sixty-eight consecutive, ambulatory, Caucasian patients with end-stage liver disease, candidates for liver transplantation, were referred for preoperative respiratory function assessment. Forty of these (29 men) were included in this preliminary study after applying strict inclusion and exclusion criteria. Seventeen of 40 patients (42%) had ascites, but none of them was cachectic. Fifteen of 40 patients (38%) had a history of hepatic encephalopathy, though none of them was symptomatic at study time. All patients with a known history and/or presence of co-morbidities were excluded. Chronic dyspnea was rated according to the modified medical research council (mMRC) 6-point scale. Liver disease severity was assessed according to the Model for end-stage liver disease (MELD). Routine lung function tests, maximum static expiratory (Pemax) and inspiratory (Pimax) mouth pressures were measured. Respiratory muscle strength (RMS) was calculated from Pimax and Pemax values. In addition, arterial blood gases and pattern of breathing (V_E: minute ventilation; V_T: tidal volume; V_T/T_I: mean inspiratory flow; T_I: duration of inspiration) were measured. RESULTS: Thirty-five (88%) of 40 patients aged (mean ± SD) 52 ± 10 years reported various degrees of chronic dyspnea (mMRC), ranging from 0 to 4, with a mean value of 2.0 ± 1.2. MELD score was 14 ± 6. Pemax, percent of predicted (%pred) was 105 ± 35, Pimax, %pred was 90 ± 29, and RMS, %pred was 97 ± 30. These pressures were below the normal limits in 12 (30%), 15 (38%), and 14 (35%) patients, respectively. Furthermore, comparing the subgroups of ascites to non-ascites patients, all respiratory muscle indices measured were found significantly decreased in ascites patients. Patients with ascites also had a significantly worse MELD score compared to non-ascites ones (P = 0.006). Significant correlations were found between chronic dyspnea and respiratory muscle function indices in all patients. Specifically, mMRC score was significantly correlated with Pemax, Pimax, and RMS (r = -0.53, P < 0.001; r = -0.42, P < 0.01; r = -0.51, P < 0.001, respectively). These correlations were substantially closer in the non-ascites subgroup (r = -0.82, P < 0.0001; r = -0.61, P < 0.01; r = -0.79, P < 0.0001, respectively) compared to all patients. Similar results were found for the relationship between mMRC vs MELD score, and MELD score vs respiratory muscle strength indices. In all patients the sole predictor of mMRC score was RMS (r = -0.51, P < 0.001). In the subgroup of patients without ascites this relationship becomes closer (r = -0.79, P < 0.001), whilst this relationship breaks down in the subgroup of patients with ascites. The disappearance of such a correlation may be due to the fact that ascites acts as a “confounding” factor. PaCO₂ (4.4 ± 0.5 kPa) was increased, whereas pH (7.49 ± 0.04) was decreased in 26 (65%) and 34 (85%) patients, respectively. PaO₂ (12.3 ± 0.04 kPa) was within normal limits. V_E (11.5 ± 3.5 L/min), V_T (0.735 ± 0.287 L), and V_T/T_I (0.449±0.129 L/s) were increased signifying hyperventilation in both subgroups of patients. V_T/T_I was significantly higher in patients with ascites than without ascites. Significant correlations, albeit weak, were found for PaCO₂ with V_E and V_T/T_I (r = -0.44, P < 0.01; r = -0.41, P < 0.01, respectively). CONCLUSION: The prevalence of chronic dyspnea is 88% in end-stage liver disease. The mMRC score closely correlates with respiratory muscle strength.     

Relationship between upper airway and inspiratory pump muscle force in obstructive sleep apnea

BACKGROUND: Upper airway (UA) patency during inspiration is determined by the balance between dilating forces generated by UA dilator muscle activity and collapsing forces related to the decreased intraluminal pressure that accompanies flow generated by inspiratory muscle activity. It is possible that the relative strengths of UA dilator and inspiratory pump muscles could be an important determinant of the susceptibility to UA collapse during sleep (ie, obstructive sleep apnea [OSA]). METHODS: Measurements of tongue protrusion (TP) force and maximum inspiratory pressure (Pimax) were obtained in 94 patients admitted for overnight polysomnography for suspected OSA, quantified by apnea-hypopnea index (AHI). RESULTS: There was a direct linear relationship between TP force and Pimax (r(2) = 0.37, p < 0.001). A high ratio of TP force to Pimax (greater than group 90th percentile, 0.027 kg/cm H(2)O) appeared to protect against OSA, as moderate-to-severe OSA (AHI > 20/h) was not observed in any individual with a ratio above this threshold. AHI was not linearly related to TP force, Pimax, or the ratio of TP force to Pimax. CONCLUSIONS: UA muscle strength is linearly related to inspiratory pump muscle strength. The ratio of UA muscle strength (TP force) and inspiratory pump muscle strength (Pimax) was not different between individuals with and without OSA; however, a high wakeful ratio of TP force to Pimax appears to be associated with a reduced propensity to moderate-to-severe OSA.     

Inspiratory muscle weakness and dyspnea in chronic heart failure.

Dyspnea is a common, disabling symptom in chronic heart failure, yet the underlying mechanisms remain unknown. The respiratory muscle pump is composed of skeletal muscles whose strength directly influences the pump's performance. Respiratory muscle weakness is important in the dyspnea experienced by some patients with pulmonary disease; however, the role of the respiratory muscle pump in the dyspnea of chronic heart failure has not previously been examined. To assess respiratory muscle strength and its relation to dyspnea during daily activity, we measured maximum inspiratory and expiratory mouth pressures as indices of respiratory muscle strength and the baseline dyspnea index in nine stable, chronic cardiac pump failure patients who had no evidence of primary lung disease, and in nine age- and sex-matched healthy control subjects. The chronic heart failure patients, when compared with their matched control subjects, had reduced inspiratory and expiratory muscle strength, and both inspiratory and expiratory muscle strength were significantly correlated with dyspnea during daily activity (r2 = 0.80, p = 0.001 and r2 = 0.45, p = 0.05, respectively). Inspiratory muscle strength accounted for all of the variance in dyspnea that was correlated with respiratory muscle strength when the relative contributions of inspiratory and expiratory muscle strength were examined. There was no correlation between lung volumes or spirometry and dyspnea in the heart failure patients. These findings indicate that patients with stable chronic heart failure have inspiratory and expiratory muscle weakness and further suggest that the respiratory muscle pump significantly contributes to the dyspnea during the activities of daily living.     

Sniff and Muller manoeuvres to measure diaphragmatic muscle strength

We hypothesized that peak values of oesophageal (Poes) and transdiaphragmatic pressure (Pdi) swings during a maximal sniff manoeuvre and a maximal static inspiratory manoeuvre (Muller manoeuvre) are comparable or give complementary information for assessing diaphragmatic and global inspiratory muscle strength. We studied 98 patients with suspected diaphragmatic dysfunction. Poes and Pdi swings were measured during maximal sniff manoeuvres (sniff), maximal Muller manoeuvres (max), and cervical magnetic phrenic nerve stimulation (cervical Tw). Eighty eight patients were able to perform both volitional manoeuvres. Among them, mean Poes sniff was significantly higher than mean Poes max (48.7+/-28.7 cm H(2)O vs. 42.9+/-27.4 cm H(2)O, p<0.05) and mean Pdi sniff was higher than mean Pdi max (49.2+/-35.1cm H(2)O vs. 42.9+/-33.3 cm H(2)O, respectively, p=0.05). Cervical Pdi Tw correlated better with Pdi sniff (p<0.0001, r=0.62) than with Pdi max (p<0.0001, r=0.44). Poes and Pdi swings were greatest during the sniff manoeuvre in 42 patients (48%) and during the Muller manoeuvre in 29 patients (33%). Among the 17 remaining patients, nine had the greatest Poes swing during a maximal sniff manoeuvre and the greatest Pdi swing during a maximal static inspiratory manoeuvre; the opposite occurred in the other eight patients. The combination of Muller manoeuvre and sniff manoeuvre increased the diagnosis of normal diaphragmatic strength from 18 patients (20%) to 21 patients (24%), and the additional analysis of cervical Pdi Tw further increased the diagnosis of normal diaphragmatic strength to 27 patients (31%). In conclusion, though sniff manoeuvre gave significantly higher values than Muller manoeuvre, both volitional manoeuvres and cervical Pdi Tw are complementary and should be used in combination to evaluate diaphragmatic muscle strength.     

Noninvasive assessment of the tension-time index of inspiratory muscles at rest in obese male subjects

OBJECTIVE: The aim of this study was to investigate the effect of excessive mechanical load caused by obesity on the inspiratory muscle performance in obese men at rest. METHODS: We therefore measure at rest spirometric flows and the noninvasive tension time index of inspiratory muscle (TTmus = PI/PImax x TI/TTOT) in eight obese male subjects (body mass index (BMI) > 30) and 10 controls. RESULTS: Spirometric flow (FEV1% pred, FVC% pred) and maximal inspiratory pressure (PImax) were significantly lower in obese subjects compared to controls (P < 0.001). The mean TTmus was significantly higher in obese subjects than in controls (0.136 +/- 0.003 vs 0.045 +/- 0.01). The increase in TTmus was primarily due to an increase in the ratio of mean inspiratory pressure to maximal inspiratory pressure (PI/PImax) and the duty cycle (TI/TTOT). We found a significant negative relationship between PImax and BMI (r = -0.74, P < 0.001), a positive correlation between TTmus and BMI (r = 0.80, P < 0.001) and a negative correlation between TTmus and forced expiratory volume in 1 s (r = -0.85, P < 0.001). CONCLUSION: Excessive mechanical load caused by obesity imposes a great burden on the inspiratory muscle, which may predispose such subjects to respiratory muscle weakness at rest.