Cardiorespiratory effects of conventional and high frequency ventilation in rabbits with bilateral pneumothoraces and surfactant depleted lungs

We compared high frequency ventilation (HFV) to conventional mechanical ventilation (CMV) under normoxic and normocapnic condition in surfactant depleted rabbits with bilateral pneumothoraces. We hypothesized that lower airway pressures would be required with HFV under these conditions. We applied CMV and HFV in 8 anaesthetized rabbits with a prototype ventilator at frequencies of 30, 100, 200, and 300 cycles/min. A positive end-expiratory pressure (PEEP) just below the pressure sufficient to open the air leak from the pneumothoraces was applied at all frequencies. Airway pressures, gas exchange, heart rate, and mean arterial pressure were recorded. Peak airway pressure decreased significantly from 2.50 to 2.10 kPa when the frequency of ventilation was increased from 30 to 300 cycles/min. There were no significant changes in mean airway pressure, PaO2, arterial pH, heart rate, and mean arterial pressure when HFV was compared to CMV. In conclusion, during HFV peak airway pressures measured at the mouth were decreased. Our ability to maintain adequate gas exchange in the face of ongoing pulmonary air leaks may reflect lower alveolar pressures.     

Restoration of endothelial cell function by chronic cicletanine treatment in Dahl salt-sensitive rats with salt-induced hypertension

Various modes of high-frequency ventilation (HFV) have been developed to avoid the disadvantages of conventional mechanical ventilation. In the present study, we examined the hypothesis that high-frequency oscillation (HFO) is superior to high-frequency positive pressure ventilation (HPPV) and combined high-frequency ventilation (CHFV) in surfactant-deficient rabbits. The aim of the ventilator strategy was to adjust the mean airway pressure to 2 cm above critical opening pressure of the inflation limb of the respiratory system pressure volume (P/V) curve, achieve a normal tidal volume (VT) (5 ml/kg body weight) and apply repeated sustained inflations. We studied the effect of these HFV modes on oxygenation, lung mechanics and lung histology in 15 New Zealand White rabbits during a 6-hour experiment. Statistically, the HFO group demonstrated significantly better oxygenation (P < 0.05), lung mechanics (lung stability index: P < 0.05), and better lung tissue histology compared to the HPPV and CHFV groups. In contrast to the HPPV and CHFV groups, the P/V curves of the HFO group showed significant recovery over the 6-hour period after lavage. The lungs of the HFO-treated group had a more uniform distribution of alveoli and less overdistention than the HPPV group (P < 0.002), and less atelectasis than the CHFV group (P < 0.05). The HFO group had less lung injury than the CHFV groups (P < 0.01) and its lungs contained significantly less water than both other groups (P < 0.05). We conclude that the relationship between mean and end-expiratory pressures impacts strongly on both oxygenation and the progression of injury during HFV at the same mean airway pressures. The HFO group showed less acute lung injury than the other ventilatory groups.     

AANA journal course: update for nurse anesthetists--advances in ventilating the patient with severe lung disease

Mechanical ventilation has become commonplace in critical care environments and a number of improvements designed to improve the interface between patient and machine are finding their way into the operating room as well. Strategies which are discussed include differential lung ventilation, inspiratory pause, inverse ratio ventilation, mandatory minute volume, pressure support ventilation, and airway pressure release ventilation. These strategies are discussed individually in terms of both their theoretical and clinical utility. A user-friendly classification of ventilatory approaches based on the rate of breathing is also provided as is treatment of the issue of the cardiovascular effects of positive end-expiratory pressure. Conditions which increase ventilatory demand in mechanically ventilated patients are reviewed, as these require consideration when caring for the patient receiving mechanical ventilation. While conventional positive pressure approaches are suitable for the majority of patients who present for anesthesia and surgery, patients with significant pulmonary dysfunction should be availed the newer approaches to management when possible. This will only become feasible when practitioners recognize the importance and application of these approaches and urge their introduction into operating room based equipment.     

The control over the new obtaining procedeum of indomethacin

Acute respiratory distress syndrome (ARDS) is a severe condition that has a high mortality. Mechanical ventilation is required and concepts have evolved over the last few decades as to the methods and principles guiding such ventilatory support. In particular, volutrauma as a feature of ventilator-associated lung injury has been well documented, leading to pressure-limited strategies with consequent permissive hypercapnia. Such an approach is in direct contrast to traditional ventilatory teaching of high tidal volumes and normal PaCO2. Current strategies therefore emphasis lower tidal volumes, adequate positive end-expiratory pressure (PEEP), minimum FiO2, and the use of pressure-control modes (plus or minus inverse-ratio ventilation). Hypercapnia is allowed to develop, and adjunctive methods are employed to improve oxygenation in order to minimise the "pressure-cost" of maintaining adequate oxygenation. With such an approach, overall mortality is reported to be around 40%.     

Expiratory flow limitation during exercise in competition cyclists

In some trained athletes, maximal exercise ventilation is believed to be constrained by expiratory flow limitation (FL). Using the negative expiratory pressure method, we assessed whether FL was reached during a progressive maximal exercise test in 10 male competition cyclists. The cyclists reached an average maximal O2 consumption of 72 ml. kg-1. min-1 (range: 67-82 ml. kg-1. min-1) and ventilation of 147 l/min (range: 122-180 l/min) (88% of preexercise maximal voluntary ventilation in 15 s). In nine subjects, FL was absent at all levels of exercise (i.e., expiratory flow increased with negative expiratory pressure over the entire tidal volume range). One subject, the oldest in the group, exhibited FL during peak exercise. The group end-expiratory lung volume (EELV) decreased during light-to-moderate exercise by 13% (range: 5-33%) of forced vital capacity but increased as maximal exercise was approached. EELV at peak exercise and at rest were not significantly different. The end-inspiratory lung volume increased progressively throughout the exercise test. The conclusions reached are as follows: 1) most well-trained young cyclists do not reach FL even during maximal exercise, and, hence, mechanical ventilatory constraint does not limit their aerobic exercise capacity, and 2) in absence of FL, EELV decreases initially but increases during heavy exercise.     

Role of tidal volume, FRC, and end-inspiratory volume in the development of pulmonary edema following mechanical ventilation

Mechanical ventilation with high peak inspiratory pressure and large tidal volume (VT) produces permeability pulmonary edema. Whether it is mean or peak inspiratory pressure (i.e., mean or end-inspiratory volume) that is the major determinant of ventilation-induced lung injury is unsettled. Rats were ventilated with increasing tidal volumes starting from different degrees of FRC that were set by increasing end-expiratory pressure during positive-pressure ventilation. Pulmonary edema was assessed by the measurement of extravascular lung water content. The importance of permeability alterations was evaluated by measurement of dry lung weight and determination of albumin distribution space. Pulmonary edema with permeability alterations occurred regardless of the value of positive end-expiratory pressure (PEEP), provided the increase in VT was large enough. Similarly, edema occurred even during normal VT ventilation provided the increase in PEEP was large enough. Furthermore, moderate increases in VT or PEEP that were innocuous when applied alone, produced edema when combined. The effect of PEEP was not the consequence of raised airway pressure but of the increase in FRC since similar observations were made in animals ventilated with negative inspiratory pressure. However, although permeability alterations were similar, edema was less marked in animals ventilated with PEEP than in those ventilated with zero end-expiratory pressure (ZEEP) with the same end-inspiratory pressure. This "beneficial" effect of PEEP was probably the consequence of hemodynamic alterations. Indeed, infusion of dopamine to correct the drop in systemic arterial pressure that occurred during PEEP ventilation resulted in a significant increase in pulmonary edema. In conclusion, rather than VT or FRC value, the end-inspiratory volume is probably the main determinant of ventilation-induced edema. Hemodynamic status plays an important role in modulating the amount of edema during lung overinflation but does not fundamentally modify the characteristics of this edema which is consistently associated with major permeability alterations. These results may be relevant for ventilatory strategies during acute respiratory failure.     

Mechanical ventilation of patients with acute lung injury

Ventilatory management of patients with acute lung injury (ALI), particularly its most severe subset, acute respiratory distress syndrome (ARDS), is complex. Newer lung protective strategies emphasize measures to enhance alveolar recruitment and avoid alveolar overdistention, thus minimizing the risk of ventilator-induced lung injury (VILI). Key components of such strategies include the use of smaller-than-conventional tidal volumes which maintain peak transpulmonary pressure below the pressure associated with overdistention, and titration of positive end-expiratory pressure to promote maximal alveolar recruitment. Novel techniques, including prone positioning, inverse ratio ventilation, tracheal gas insufflation, and high frequency ventilation, are considerations in severe ARDS. No single approach is best for all patients; adjustment of ventilatory parameters to individual characteristics, such as lung mechanics and gas exchange, is required.     

Effects of surfactant distribution and ventilation strategies on efficacy of exogenous surfactant

The effects of both surfactant distribution patterns and ventilation strategies utilized after surfactant administration were assessed in lung-injured adult rabbits. Animals received 50 mg/kg surfactant via intratracheal instillation in volumes of either 4 or 2 ml/kg. A subset of animals from each treatment group was euthanized for evaluation of the exogenous surfactant distribution. The remaining animals were randomized into one of three ventilatory groups: group 1 [tidal volume (VT) of 10 ml/kg with 5 cmH2O positive end-expiratory pressure (PEEP)]; group 2 (VT of 5 ml/kg with 5 cmH2O PEEP); or group 3 (VT of 5 ml/kg with 9 cmH2O PEEP). Animals were ventilated and monitored for 3 h. Distribution of the surfactant was more uniform when it was delivered in the 4 ml/kg volume. When the distribution of surfactant was less uniform, arterial PO2 values were greater in groups 2 and 3 compared with group 1. Oxygenation differences among the different ventilation strategies were less marked in animals with the more uniform distribution pattern of surfactant (4 ml/kg). In both surfactant treatment groups, a high mortality was observed with the ventilation strategy used for group 3. We conclude that the distribution of exogenous surfactant affects the response to different ventilatory strategies in this model of acute lung injury.     

Adaptive lung ventilation (AVL). Evaluation of new closed loop regulated respiration algorithm for operation in the hyperextended lateral position

The lateral decubitus position is the standard position for nephrectomies. There is a lack of data about the effects of this extreme position upon respiratory mechanics and gas exchange. In 20 patients undergoing surgery in the nephrectomy position, we compared a new closed-loop-controlled ventilation algorithm, adaptive lung ventilation (ALV), which adapts the breathing pattern automatically, to the respiratory mechanics with conventionally controlled mandatory ventilation (CMV). The aims of our study were (1) to describe positioning effects on respiratory mechanics and gas exchange, (2) to compare ventilatory parameters selected by the ALV controller with traditional settings of CMV, and (3) to assess the individual adaptation of the ventilatory parameters by the ALV controller. The respirator used was a modified Amadeus ventilator, which is controlled by an external computer and possesses an integrated lung function analyzer. In a first set of measurements, we compared parameters of respiratory mechanics and gas exchange in the horizontal supine position and 20 min after changing to the nephrectomy position. In a second set of measurements, patients were ventilated with ALV and CMV using a randomized crossover design. The CMV settings were a tidal volume of 10 ml/kg body weight, a respiratory rate of 10 breaths/min, an I:E ratio of 1:1.5, and an end-inspiratory pause of 30% of inspiratory time. With both ventilation modes F1O2 was set to 0.5 and PEEP to 3 cm H2O. During ALV a desired alveolar ventilation of 70 ml/ kg KG.min was preset. All other ventilatory parameters were determined by the ALV controller according to the instantaneously measured respiratory parameters. Positioning induced a reduction of compliance from 61.6 to 47.9 ml/cm H2O; the respiratory time constant shortened from 1.2 to 1.08 s, whereas physiological dead space increased from 158.9 to 207.5 ml. On average, the ventilatory parameters selected by the ALV controller resembled very closely those used with CMV. However, an adaptation to individual respiratory mechanics was clearly evident with ALV. In conclusion, we found that the effects of positioning for nephrectomy are minor and may give rise to problems only in patients with restrictive lung disease. The novel ALV controller automatically selects ventilatory parameters that are clinically sound and are better adapted to the respiratory mechanics of ventilated patients than the standardized settings of CMV are.     

The laryngeal mask airway and positive-pressure ventilation

BACKGROUND: The utility of the laryngeal mask airway during positive-pressure ventilation has yet to be determined. Our study was designed to assess whether significant leaks occurred with positive-pressure ventilation and if leaks were associated with gastroesophageal insufflation. METHODS: Forty-eight patients undergoing elective surgery were studied. After induction of anesthesia and paralysis, controlled ventilation was used with four different peak pressure settings in each patient (15, 20, 25, and 30 cmH2O). The order of ventilator pressure settings was assigned from a randomized block schedule. Data collected included inspiratory and expiratory volumes, qualitative assessments of gastroesophageal insufflation, and leak at the neck. After data collection during laryngeal mask use, the anesthesiologist intubated the trachea and measurements were repeated for tracheal tube ventilation. Leak was calculated by subtracting the expiratory from the inspiratory volume and expressed as a fraction of the inspiratory volume. RESULTS: Ventilation with the laryngeal mask airway was adequate at all ventilation pressures and comparable with tracheal tube ventilation. Leak fraction (mean +/- SD) at 15, 20, 25, and 30 cmH2O for laryngeal mask ventilation were 0.13 +/- 0.15, 0.21 +/- 0.18, 0.25 +/- 0.16 and 0.27 +/- 0.17, respectively, and 0.03 +/- 0.03, 0.05 +/- 0.03, 0.05 +/- 0.03 and 0.04 +/- 0.03, respectively, for tracheal tube ventilation. Leak fractions for ventilation with the laryngeal mask were consistently greater than those measured for tracheal tube ventilation at similar ventilation pressures. Leak fraction with laryngeal mask ventilation increased with increasing airway pressures, whereas leak with tracheal tube ventilation remained unchanged. The frequency of gastroesophageal insufflation ranged from 2.1% at a ventilation pressure of 15 cmH2O to 35.4% at 30 cmH2O. CONCLUSIONS: Ventilation using the laryngeal mask appears to be adequate if airway resistance and pulmonary compliance are normal. Gastroesophageal insufflation of air will become a problem in the presence increased ventilation pressure.     

Current aspects of acute respiratory distress syndrome in children

Acute respiratory distress syndrome (ARDS) is a frequent condition in pediatric intensive care units. The mortality remains high despite advances in conventional mechanical ventilation and aetiological treatment. Several animal studies have documented lung injury during mechanical ventilation with high tidal volume, and clinical investigations have shown that in human ARDS, most ventilation is distributed to the small areas of remaining aerated lung resulting in overdistension of these areas and lung injury ("baby lung" theory). Nevertheless the usefulness of extrapulmonary gas exchange remains much debated. New ventilatory strategies have been developed in order to reduce ventilator-induced lung injury and to improve systemic oxygenation but multicentric randomized clinical trials are needed before these strategies can be validated.     

Experimental changes in the alveolo-capillary barrier induced by artificial ventilation

Mechanical ventilation can have deleterious effects on the lungs. Extra-alveolar escape of air, such as pneumothorax or subcutaneous emphysema, are complications which have long been known. New experimental studies have clearly shown that mechanical ventilation can also result in pathologic changes to the air/blood barrier. Mechanical ventilation with high end-inspiratory pressure and high volume causes lung edema in whose origin abnormal permeability of the alveolo-capillary barrier plays a major role. The abnormalities are in fact the result of pulmonary distention and not of elevated air pressure; this justifies the term "volume traumatism". The presence of a previous acute pulmonary injury considerably increases the deleterious effects of mechanical ventilation on the lungs. Although the clinical implications of these experimental studies are difficult to assess, they have nevertheless resulted in major changes in ventilation strategy for acute lung diseases such as the acute respiratory distress syndrome of the adult.     

Effect of global inspiratory muscle fatigue on ventilatory and respiratory muscle responses to CO2

We evaluated the effect of global inspiratory muscle fatigue on ventilation and respiratory muscle control during CO2 rebreathing in normal subjects. Fatigue was induced by breathing against a high inspiratory resistance until exhaustion. CO2 response curves were measured before and after fatigue. During CO2 rebreathing, global fatigue caused a decreased tidal volume (VT) and an increased breathing frequency but did not change minute ventilation, duty cycle, or mean inspiratory flow. Both esophageal and transdiaphragmatic pressure swings were significantly reduced after global fatigue, suggesting decreased contribution of both rib cage muscles and diaphragm to breathing. End-expiratory transpulmonary pressure for a given CO2 was lower after fatigue, indicating an additional decrease in end-expiratory lung volume due to expiratory muscle recruitment, which leads to a greater initial portion of inspiration being passive. This, combined with the reduction in VT, decreased the fraction of VT attributable to inspiratory muscle contribution; therefore the inspiratory muscle elastic work and power per breath were significantly reduced. We conclude that respiratory control mechanisms are plastic and that the respiratory centers alter their output in a manner appropriate to the contractile state of the respiratory muscles to conserve the ventilatory response to CO2.     

Liquid assisted ventilation: an alternative ventilatory strategy for acute meconium aspiration injury

Evidence of surfactant inactivation by meconium has led to the use of exogenous surfactant therapy in the management of meconium aspiration syndrome (MAS). Liquid assisted ventilation has been shown to improve the cardiopulmonary function in lungs with high surface tension. We compared exogenous surfactant therapy with liquid assisted ventilation in the management of experimental acute meconium aspiration injury. Thirty-two newborn lambs were ventilated at peak inspiratory pressures of 13-16 cm H2O, positive end expiratory pressure of 3-4 cm H2O, fractional inspired oxygen concentration (FiO2) of 1.0, and a respiratory frequency range between 30 and 35 breaths/min. Baseline arterial blood gases, pulmonary function, and arterial blood pressure measurements were taken. All lambs were given 2-3 ml/kg of an unfiltered 25% meconium solution. Lambs were then randomized into either gas-ventilated meconium control, or one of three treatment groups: 1) surfactant; 2) partial liquid ventilation (PLV); or 3) total liquid ventilation (TLV) for 4 hours after meconium injury. All treated groups demonstrated a significant increase in arterial oxygenation (P < 0.05); surfactant and PLV-treated lambs demonstrated significantly decreased arterial PCO2 (P < 0.05). Compliance in all groups increased compared with injury values; compliance of the TLV group increased more than in all other treatment groups (P < 0.05). In addition, lung histology of the TLV group demonstrated clear, intact alveolar epithelium and homogeneously expanded alveoli, while no such improvement was evident in the other groups. These data suggest roles for both exogenous surfactant therapy and liquid assisted ventilation techniques in the management of MAS.     

Development, characterization and application of an antibody against 5-fluoro-2''deoxyuridine-5''monophosphate, the active metabolite of 5-fluorouracil

To assess the distribution of ventilation to each lung, we measured ventilation and maximum negative airway pressure during occluded inspiratory effort (Pmax) of the individual lungs in eight male patients immediately before and after right upper lobectomy using a double-lumen endotracheal tube at a constant depth of enflurane anesthesia (end-tidal concentration 1.7%). Compared with the breathing pattern observed immediately before surgery, minute ventilation, Pmax, and respiratory frequency significantly increased immediately after the surgery, whereas tidal volume was unchanged. Bronchospirometry revealed that tidal volumes on the nonoperated side significantly increased after the operation. In contrast, tidal volumes on the operated side significantly decreased after the operation and were associated with significantly smaller Pmax obtained from unilateral airway than those of the nonoperated side postoperatively. These results indicate that there are considerable differences in ventilatory function between the lungs on the operated side and nonoperated side. The lung on the nonoperated side can partially compensate for the impaired ventilatory function on the operated side.     

Assessment of insulin sensitivity in glucokinase-deficient subjects

Mechanical ventilation using a modified endotracheal tube, allowing bypass and washout of the endotracheal dead space (McETV), was compared with conventional controlled mechanical ventilation (CMV) in healthy and in surfactant-depleted rabbits. In healthy animals, shifting from CMV to McETV led to an increase in PaO2 (89 +/- 16 versus 104 +/- 13 mm Hg; p < 0.05) and a decrease in PaCO2 (41.5 +/- 3 versus 30 +/- 3 mm Hg; p < 0.05). As a result of reducing the peak inspiratory pressure (PIP) from 21 +/- 2 to 12 +/- 2 cm H2O (p < 0.05), it was possible in McETV mode to maintain comparable ventilation to that achieved by CMV. In surfactant-depleted animals, compared with CMV, McETV produced a rise in PaO2 without change in thoracic volume (from 100 +/- 40 to 150 +/- 60 mm Hg, p < 0.05) and a fall in PaCO2 (from 46 +/- 5 to 37 +/- 4 mm Hg, p < 0.05). After 4 h of ventilation, the surfactant-depleted animals from the CMV group developed thoracic overdistension quicker (at hour 1, p < 0.05) and, consequently, more animals died from pneumothorax compared with the McETV group (five versus two). We concluded that McETV ensured adequate gas exchanges with lower insufflation pressures and could diminish positive pressure ventilation-induced injury.     

Negative pressure ventilation vs. spontaneous assisted ventilation during rigid bronchoscopy. A controlled randomised trial

BACKGROUND: Ventilation during interventional rigid bronchoscopy (IRB) under general anaesthesia (jet ventilation, positive pressure ventilation and spontaneous assisted ventilation) may offer some difficulties. This study compares the effectiveness during IRB of intermittent negative pressure ventilation (INPV) and spontaneous assisted ventilation (SAV). METHODS: Thirty-eight patients submitted to IRB were randomised into two groups: SAV or INPV. All patients received a total intravenous anaesthesia; INPV patients were paralysed. Pre- and intra-operative arterial blood gases and O2 flow through a rigid bronchoscope were assessed. The endoscopist applying a subjective score evaluated the operating conditions. RESULTS: Patients of the INPV group, as compared to the SAV group, required a lower dosage of fentanyl (2.6 +/- 1.8 micrograms.kg-1.h-1 vs. 6.6 +/- 4.8 micrograms.kg-1.h-1), a lower O2 supply (3.3 +/- 2.8 l/min vs. 11.6 +/- 3.4 l/min), a shorter recovery time (5.4 +/- 2.9 min vs. 9.8 +/- 7.1 min) and no manually assisted ventilation (0 +/- 0 vs. 1 +/- 1.1 n degree/procedure). Intraoperative PaCO2 was higher in the SAV (8.1 +/- 1.3 kPa) than in the INPV group (5.0 +/- 1.6 kPa) and intraoperative pH differed in the two groups (7.26 +/- 0.05, SAV vs. 7.47 +/- 0.08, INPV). Operating conditions, as assessed by a subjective score, were considered better with INPV than with SAV (4.9 vs. 4.3). CONCLUSIONS: As compared to SAV, INPV in paralysed patients during IRB reduces administration of opioids, shortens recovery time, prevents respiratory acidosis, excludes the need for manually assisted ventilation, reduces O2 need and affords optimal surgical conditions. INPV appears a safe, non-invasive and effective ventilatory management during IRB.     

Function of the diaphragm during exercise]

We evaluated the effect of global inspiratory muscle fatigue (GF) on respiratory muscle control during exercise at 30%, 60%, and 90% of maximal power output in normal subjects. Fatigue was induced by breathing against a high inspiratory resistance until exhaustion. Respiratory pressures, breathing pattern, and perceived breathlessness were measured. Induction of GF had no effect on the ventilatory parameters during mild and moderate exercise. It altered, however, ventilatory response to heavy exercise by increasing breathing frequency and minute ventilation, with minor changes in tidal volume. This was accompanied by an increase in perceived breathlessness. GF significantly increased both the tonic and phasic activities of abdominal muscles that allowed 1) the diaphragm to maintain its function while developing less pressure, 2) the same tidal volume with lesser shortening of the rib cage inspiratory muscles, and 3) relaxation of the abdominal muscles to contribute to lung inflation. The increased work performed by the abdominal muscles may, however, lead to a reduction in their strength. GF may impair exercise performance in some healthy subjects that is probably not related to excessive breathlessness or other ventilatory factors. The respiratory system is remarkably adaptable in maintaining ventilation during exercise even with impaired inspiratory muscle contractility.     

Regulation of ventilatory capacity during exercise in asthmatics

In asthmatic and control subjects, we examined the changes in ventilatory capacity (VECap), end-expiratory lung volume (EELV), and degree of flow limitation during three types of exercise: 1) incremental, 2) constant load (50% of maximal exercise capacity; 36 min), and 3) interval (alternating between 60 and 40% of maximal exercise capacity; 6-min workloads for 36 min). The VECap and degree of flow limitation at rest and during the various stages of exercise were estimated by aligning the tidal breathing flow-volume (F-V) loops within the maximal expiratory F-V (MEFV) envelope using the measured EELV. In contrast to more usual estimates of VECap (i.e., maximal voluntary ventilation and forced expiratory volume in 1 s x 40), the calculated VECap depended on the existing bronchomotor tone, the lung volume at which the subjects breathed (i.e., EELV), and the tidal volume. During interval and constant-load exercise, asthmatic subjects experienced reduced ventilatory reserve, higher degrees of flow limitation, and had higher EELVs compared with nonasthmatic subjects. During interval exercise, the VECap of the asthmatic subjects increased and decreased with variations in minute ventilation, due in part to alterations in their MEFV curve as exercise intensity varied between 60 and 49% of maximal capacity. In conclusion, asthmatic subjects have a more variable VECap and reduced ventilatory reserve during exercise compared with nonasthmatic subjects. The variations in VECap are due in part to a more labile MEFV curve secondary to changes in bronchomotor tone. Asthmatics defend VECap and minimize flow limitation by increasing EELV.     

Another view of schizophrenia subtypes. A report from the international pilot study of schizophrenia

We studied respiratory mechanics in young volunteers before and after 5-wk training programs limited to the ventilatory muscles. Four strength trainers (S) performed repeated static maximum inspiratory and expiratory maneuvers against obstructed airways. Four endurance trainers (E) performed voluntary normocarbic hyperpnea to exhaustion. Subjects spent 30-45 min each day in these exercises, 5 days a week. Four control subjects (C) did no training. We attempted to minimize the effect of learning. S increased pressure maximums by about 55%, but vital capacity and total lung capacity by only about 4%. Initially all subjects could sustain hyperpnea at about 81% of their control 15-s maximum voluntary ventilation (MVV) for 15 min; E increased this to about 96% and increased their MVV by 14% as well. No other statistically significant changes were recognized in any group. We conclude that ventilatory muscle strength or endurance can be specifically increased by appropriate ventilatory muscle training programs.