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PubMed2005

Patient-ventilator interaction during the triggering phase.

Partial patient-controlled mechanical support mode ventilators provide positive pressure assistance whenever a patient's inspiratory effort decreases pressure or flow in the ventilator circuit below the sensitivity set by clinicians; these modes minimize disuse atrophy of the respiratory muscles, can facilitate the weaning process, and usually require lower ventilator pressures. The capability of restoring gas exchange, unloading respiratory muscles, and relieving the patient's dyspnea with partial patient-controlled mechanical support modes depends on matching between the ventilator setting and the patient's ventilatory demand (ie, patient-ventilator interactions).

Airway Resistance↗
PubMed2005

Patient-ventilator interaction: an overview.

During assisted mechanical ventilation, the total pressure applied to respiratory system is the sum of ventilator and muscle pressure. As a result, the respiratory system is under the influence of two pumps, the ventilator pump (ie, Paw), which is controlled by the physician's brain and the capabilities of the ventilator, and the patient's own respiratory muscle pump (Pmus), which is controlled by the patient's brain. The patient-ventilator interaction is mainly an expression of the function of these two brains, which should be in harmony to promote patient-ventilator synchrony. The achievement of this harmony depends exclusively on the physician, who should be aware that during assisted mechanical ventilation the respiratory system is not a passive structure but reacts to pressure delivered by the ventilator via various feedback systems and, depending on several factors both to the ventilator and patient, may modify the function of the ventilator. Finally, the physician should know that the ventilator imposes significant constraints to the respiratory system, the magnitude of which depends heavily on the triggering variable, the variable that controls the gas delivery and the cycling off criterion.

Humans↗
PubMed2005

Retention of ventilation skills of emergency nurses after training with the SMART BAG compared to a standard bag-valve-mask.

BACKGROUND AND PURPOSE: Studies show that nurses retain resuscitation skills poorly and that retention of ventilation skills is particularly difficult. We formed the hypothesis that the SMART BAG (SB, O-Two Medical Technologies Inc., Canada), i.e. a bag-valve-mask device with a pressure/flow responsive valve, would assist nurses in providing more efficient ventilation six months after training. MATERIALS AND METHODS: Prior to training, 39 emergency nurses performed CPR for 2 min, in pairs, using a standard bag-valve-mask device (STBVM, Laerdal, Norway) to assess their base line skills. A CPR training manikin (Simulaids, USA) equipped with a PEEP valve in the oesophagus set at 20 cm H2O was used to measure inspiratory time, tidal volume (Vt), peak pressure and gastric insufflation (GI). Immediately following training they were tested using an O-Two STBVM and a SB. Half of the nurses were retested after three months, the other half after six months. Efficient ventilation was defined as a mean Vt>400 ml and GI<50 ml in 1 min. RESULTS: Before training, only 16% of nurses ventilated efficiently: 63% had GI and 28% had Vt<400 ml. Three months after training the efficiency of the STBVM and the SB was high (81 and 75%, respectively). Six months after training, there was a trend towards higher efficiency for the SB (63%) compared to the STBVM (25%) (p=0.07). For instances with the STBVM producing a Vt>400 ml, those without GI had a lower peak pressure than those with GI (7.8 cm H2O versus 17.7 cm H2O, p=0.0001) and showed a trend towards a longer inspiratory time (1.28 s versus 1.08 s, p=0.08). Of all efficient ventilations with a STBVM, 26% had a Vt>600 ml. CONCLUSIONS: Six months after training, nurses ventilated at least as efficiently with the SB, compared with the STBVM. This illustrates the ability of the SB to compensate for the deterioration over time in skill. On the other hand, training with a STBVM should focus primarily on prolonging the inspiratory time, and therefore the peak pressure, whilst maintaining an adequate Vt.

Adult↗
PubMed2006

Effects of an inspiratory impedance threshold device on blood pressure and short term survival in spontaneously breathing hypovolemic pigs.

BACKGROUND: The inspiratory impedance threshold device (ITD) has been shown to improve hemodynamic variables and survival outcomes during cardiopulmonary resuscitation in animals and humans. We hypothesized that use of an ITD, with a resistance of -10 cm H2O, will improve hemodynamics and short-term survival rates during hypovolemic hypotension in spontaneously breathing pigs. METHODS: Female farm pigs ( approximately 26 kg) were intubated and anesthetized with propofol with the dose adjusted to permit spontaneous respirations. They were bled to 50% of calculated blood volume through an arterial catheter and then prospectively randomized to either treatment with an ITD or observation alone. Arterial and intratracheal pressures as well as arterial blood gases were measured. After 90 min the ITD was removed, normal saline was administered to all surviving animals, the anesthetic was discontinued, and animals were allowed to recover. Statistical analysis was performed with one-way repeated ANOVA and survival rates were calculated with Kaplan-Meier analysis. RESULTS: Treatment with the ITD resulted in lower intratracheal inspiratory pressure in the treatment group (-11+/-0.4 mmHg versus -4+/-0.7 mmHg, respectively, P<0.005). Mean arterial pressure after 30 min of treatment with the ITD was higher in the treatment group (61.1+/-5.5 mmHg versus 37.4+/-2.1 mmHg, respectively, P<0.005). All pigs in the control group died within 65 min of the initial bleed, whereas 7/8 (87%) treated with an ITD survived for >90 min (P<0.001). During the recovery phase, 6/8 (75%) in the ITD group survived for >3h and awoke without neurological deficit; one surviving animal in the ITD group never woke up. Arterial oxygenation was not compromised in the ITD group. CONCLUSIONS: Use of an ITD improved blood pressure and short-term survival rates in a spontaneously breathing porcine model of hypovolemic hypotension.

Animals↗
PubMed2004

The bronchodilatory effect of deep inspiration diminishes with aging.

Deep inspirations have the ability to dilate constricted airways. The impairment of this function has been associated with the occurrence of asthmatic symptoms. We evaluated whether the bronchodilatory effect of deep inspiration (DI) is affected by aging. We tested 25 healthy subjects (median age: 54 yrs, range: 25-83 yrs). Single dose methacholine (Mch) provocations were performed in the absence of DI, which induced at least 15% reduction in inspiratory vital capacity (IVC) from baseline. The post-Mch IVC measurement was followed by 4 DIs and by another IVC (post-DI IVC). The fractional difference between post-DI IVC and post-Mch IVC represented the % bronchodilation by DI. The % bronchodilation significantly diminished with aging (r=0.65, P=0.0005). The bronchodilatory ability of DI was also positively associated with the degree of Mch-induced reduction in IVC (r=0.84, P<0.0001). In multiple regression analysis, where % bronchodilation was the dependent variable, both % reduction in IVC (P<0.0001) and age (P=0.02) entered the model. Our data raise the hypothesis that aging is associated with reduction in DI-induced bronchodilation.

Adult↗
PubMed2006

Deep inspiration-induced changes in lung volume decrease with severity of asthma.

We have previously reported that the magnitude of deep inspiration (DI)-induced bronchodilation is only slightly reduced in mild asthmatics, compared to healthy subjects. The aim of this study was to evaluate whether increased severity of asthma is associated with impairment in the ability of DI to induce changes in lung volume. Thirty-six consecutive asthmatics recruited from the Pulmonary and the Allergy Outpatient Clinics of the Institute of Respiratory Diseases of the University of Palermo were divided into 3 groups: Intermittent (I), Mild Persistent (MP) and Moderate-Severe (MS), based on GINA guidelines. Single dose methacholine (Mch) bronchoprovocations were performed in the absence of DI, to induce at least 15% reduction in inspiratory vital capacity (IVC) from baseline. The post-Mch IVC was followed by 4 consecutive DI and by another IVC, to determine the bronchodilatory effect of DI. The bronchodilatory effect of DI was found to significantly decrease with increasing severity of asthma (I: 68+/-5.4%, MP: 45+/-7.2%, MS: 4+/-15.6%; ANOVA: P<0.0001). Bronchodilation by DI, but not FEV(1) or FEV(1)/FVC, was also inversely correlated to symptom scores (r=-0.42, P=0.01) and to weekly salbutamol usage (r=-0.47, P=0.004). These observations provide support to the hypothesis that the attenuation of the bronchodilatory effect of DI contributes to the severity of the clinical manifestations of asthma.

Adolescent↗
PubMed1999

Effect of internal thoracic artery preparation on blood loss, lung function, and pain.

BACKGROUND: Postoperative blood loss, respiratory distress, and pain after coronary artery operation were assessed in a prospective, randomized, clinical study comparing two techniques of internal thoracic artery preparation. METHODS: In group A (n = 57) the internal thoracic artery was dissected with the entire surrounding connective tissue after opening the pleura, using routine lateral pleural drainage. In group B (n = 55) a venoarterial pedicle was prepared without surrounding muscle leaving the pleura intact. We assessed blood loss, clinical outcome, lung function, location, intensity, and quality of pain 6 days and 3 months after the operation. RESULTS: Significantly higher blood loss was observed in group A (A, 608+/-58 mL; B, 470+/-48 mL; p = 0.027). Forced expiratory volume in 1 second was significantly decreased in group A 6 days after surgery (A, 76.0%+/-1.6%; B, 83.2%+/-1.6%; p = 0.020). The forced expiratory volume in 1 second correlated to inspiratory vital capacity, which confirmed the advantage of the venoarterial technique (A, 0.771+/-0.021; B, 0.832+/-0.020; p = 0.003). Vital capacity was significantly higher in the venoarterial group at 3 months (A, 85.2%+/-2.1%; B, 98.5%+/-1.2%; p = 0.009), but not on postoperative day 6. The incidence of pleural effusion and atelectasis was significantly higher in group A (effusion: A, 52.6%; B, 23.6%; p = 0.002; atelectasis: A, 42.1%; B, 20.0%, p = 0.015). Sternal pain (A, 36.8%; B, 9.1%; p = 0.001) and suspenders pain (A, 33.3%; B, 7.3%; p = 0.001) occurred more often in group A. When using a multidimensional pain score, patients in group A experienced significantly sharper (6 days: A, 6.7+/-0.3; B, 3.3+/-0.2; p = 0.018; 3 months: A, 3.5+/-0.3; B, 1.4+/-0.3; p = 0.046) and more annoying pain (6 days: A, 7.6+/-0.2; B, 2.7+/-0.1; p = 0.036; 3 months: A, 6.6+/-0.3; B, 2.3+/-0.2; p = 0.040). CONCLUSIONS: These results demonstrate that the venoarterial preparation technique is superior to conventional internal thoracic artery preparation regarding postoperative blood loss, lung function, and pain.

Female↗
PubMed2000

Respiratory muscle weakness and respiratory muscle training in severely disabled multiple sclerosis patients.

OBJECTIVE: To evaluate the contribution of respiratory muscle weakness (part 1) and respiratory muscle training (part 2) to pulmonary function, cough efficacy, and functional status in patients with advanced multiple sclerosis (MS). DESIGN: Survey (part 1) and randomized controlled trial (part 2). SETTING: Rehabilitation center for MS. PATIENTS: Twenty-eight bedridden or wheelchair-bound MS patients (part 1); 18 patients were randomly assigned to a training group (n = 9) or a control group (n = 9) (part 2). INTERVENTION: The training group (part 2) performed three series of 15 contractions against an expiratory resistance (60% maximum expiratory pressure [PEmax]) two times a day, whereas the control group performed breathing exercises to enhance maximal inspirations. MAIN OUTCOME MEASURES: Forced vital capacity (FVC), inspiratory, and expiratory muscle strength (PImax and PEmax), neck flexion force (NFF), cough efficacy by means of the Pulmonary Index (PI), and functional status by means of the Extended Disability Status Scale (EDSS). RESULTS: Part 1 revealed a significantly reduced FVC (43% +/- 26% predicted), PEmax (18% +/- 8% predicted), and PImax (27% +/- 11% predicted), whereas NFF was only mildly reduced (93% +/- 26% predicted). The PI (median score, 10) and EDSS (median score, 8.5) were severely reduced. PEmax was significantly correlated to FVC, EDSS, and PI (r = .77, -.79, and -.47, respectively). In stepwise multiple regression analysis. PEmax was the only factor contributing to the explained variance in FVC (R2 = .60), whereas body weight (R2 = .41) was the only factor for the PI. In part 2, changes in PImax and PEmax tended to be higher in the training group (p = .06 and p = .07, respectively). The PI was significantly improved after 3 months of training compared with the control group (p < .05). After 6 months, the PI remained significantly better in the training group. CONCLUSIONS: Expiratory muscle strength was significantly reduced and related to FVC, cough efficacy, and functional status. Expiratory muscle training tended to enhance inspiratory and expiratory muscle strength. In addition, subjectively and objectively rated cough efficacy improved significantly and lasted for 3 months after training cessation.

Body Mass Index↗
PubMed1999

Abdominal weight and inspiratory resistance: their immediate effects on inspiratory muscle functions during maximal voluntary breathing in chronic tetraplegic patients.

OBJECTIVE: To study the immediate effects of maximal voluntary (MV) breathing, with and without abdominal weight (AW) or inspiratory resistance (IR), on inspiratory muscle functions in chronic tetraplegic patients. DESIGN: A crossover trial design. SETTING: Rehabilitation department of a university hospital. PARTICIPANTS: Nine tetraplegic men injured at the C4 to T1 levels, with a mean duration of injury of 72.8 months. INTERVENTIONS: Each subject performed MV breathing without and with AW load (AWMV breathing) and IR load (IRMV breathing) separately. MAIN OUTCOME MEASURES: Electromyographic (EMG) activity of the inspiratory muscles, mouth pressure, inspiratory flow, and inspiratory volume. RESULTS: AWMV breathing evoked greater diaphragmatic EMG activity, inspiratory flow, and inspiratory volume than did IRMV breathing, although the increase of diaphragmatic EMG activity was not statistically significant. Conversely, IRMV breathing produced greater sternocleidomastoid EMG activity and negative mouth pressure than did AWMV breathing. Both AWMV and IRMV breathing evoked greater inspiratory muscle EMG activity than did MV breathing. CONCLUSION: AW and IR loads have differential immediate effects on the inspiratory muscle functions during MV breathing in patients with chronic tetraplegia, suggesting that these two breathing maneuvers may have dissimilar mechanisms of training in such patients. The muscle EMG activity evoked during MV breathing with AW or IR is greater than that without a mechanical load, implying that mechanically loaded training in tetraplegic patients results in load compensatory adjustments via their respiratory motor output to improve respiratory function.

Abdomen↗
PubMed1977

The effect of a low continuous positive airway pressure on the reflex control of respiration in the preterm infant.

The airway occlusion technique was used to measure the strength of the Hering-Breuer inflation reflex before and during the administration of low pressure CPAP. In five of 12 preterm infants studied in the first two weeks of life, CPAP did not alter the inflation reflex. In the other seven premature infants, shortened rather than lengthened inspiratory efforts were observed on occlusion 32 times of CPAP but only twice on CPAP. In seven term infants at 1 to 2.5 hours of age this shortening was noted only twice in 58 occlusions. In the preterm infants exhibiting short responses, the peak inspiratory pressure generated in response to occlusion rose on CPAP from 3.4 to 7.1 cm H2O (p less than 0.005), while respiratory rate fell from 61 to 49 breaths/minute (p less than 0.025). This data suggests that CPAP enhances these infants' ability to adjust to increased respiratory loads, possibly by the elimination of a Hering-Breuer deflation reflex.

Humans↗
PubMed1980

Decreased ventilation response to hypoxia in children with asthma.

We measured the ventilation and inspiratory muscle activity responses to hypoxia and hypercapnia in 18 children with asthma. Ventilation was less efficient in the asthmatic children in that more inspiratory muscle activity per liter of ventilation was required than in normal children. Asthmatic and healthy children had similar ventilation responses to hypercapnia; at all levels of end-tidal Pco2, the inspiratory muscle activity was greater in those with asthma. However, during progressive isocapnic hypoxia, asthmatic patients did not increase their inspiratory muscle activity at a rate greater than normal. Thus, because of inefficient ventilation, they had significantly decreased ventilatory responses to hypoxia. Neither ventilation nor inspiratory muscle activity response to hypoxia was correlated with duration of illness or with the degree of airways obstruction present. These results demonstrate that children with chronic asthma have decreased hypoxic responsiveness and suggest that neither long-term airways obstruction nor intermittent hypoxia associated with asthma is necessary to diminish hypoxic response in asthmatic patients. An asthmatic child with depressed hypoxic responsiveness may be at increased risk of hypoxic complications or respiratory failure during acute asthma.

Airway Obstruction↗
PubMed1981

Prospective clinical comparison of two methods for mechanical ventilation of neonates: rapid rate and short inspiratory time versus slow rate and long inspiratory time.

A prospective comparison was made of the clinical courses of two groups of neonates ventilated according to different protocols: one group at rates of 20 to 40/minute with a one-second IT, and the other at a rate of 60/minute and 0.5 second IT. Other ventilator settings were adjusted within protocol limits to maintain desired blood gas values. Mean starting and highest PIP were lower in the rapid rate group. The results showed no difference in mortality, failure to remain within protocol limits, time requiring respiratory treatment or FiO2 more than 0.6, and incidence of PDA or chronic lung disease. There was a difference (P = 0.011) in number of infants developing pneumothoraces (14% in the rapid group vs 35% in the slow group). Rapid rate ventilation can be used to decrease the incidence of pneumothorax, reserving long IT and higher PIP for infants who cannot be oxygenated or ventilated without them.

Humans↗
PubMed1983

Decreased ventilation in preterm infants during oral feeding.

As respiratory difficulty may accompany nipple feeding in preterm neonates, we studied the effect of oral feeding on ventilation in 23 preterm infants. The infants composed two groups based on their postconceptional age at the time of study: Group A comprised 12 infants 34 to 35.9 weeks of age, and group B, 11 infants 36 to 38 weeks. Ventilation was measured via a nasal mask pneumotachometer, and sucking pressure via a nipple that also permitted milk delivery; transcutaneous PO2 and PCO2 were continuously monitored. The feeding pattern comprised an initial period of continuous sucking of at least 30 seconds, followed by intermittent sucking bursts for the remainder of the feed. When compared with an initial semi-upright control period, minute ventilation (V1) during continuous sucking fell by 52 +/- 6% (P less than 0.001) and 40 +/- 2% (P less than 0.001) in groups A and B, respectively. This was the result of a decrease in respiratory frequency and tidal volume and was associated with a fall in TcPO2 of 13 +/- 4 mm Hg (P less than 0.01) in group A and 10 +/- 2 mm Hg (P less than 0.01) in group B. During intermittent sucking, V1 and TcPO2 recovered partially only in the more mature infants (group B). At the end of the feed, TcPCO2 have risen by 3 +/- 1 mm Hg (P less than 0.001) in group A and by 2 +/- 2 mm Hg (P less than 0.05) in group B. Thus oral feeding results in an impairment of ventilation during continuous sucking and the subsequent recovery during intermittent sucking is dependent on postconceptional age.

Drinking↗
PubMed1988

Ventilatory chemosensitivity in parents of infants with sudden infant death syndrome.

We measured ventilatory responses to progressive isocapnic hypoxia and to hyperoxic hypercapnia (CO2) using rebreathing techniques in 16 parents of infants with autopsy-confirmed sudden infant death syndrome (SIDS) and 18 control parents matched for age, sex, and body size. Response to ventilatory loading was assessed by repeating the CO2 test with an inspiratory flow-resistive load (16 cm H2O/L/sec). During loaded and unloaded CO2 tests, respiratory effort was also assessed by measuring the pressure generated in the first 0.1 second (P0.1) of the subsequent inspiratory effort after brief manual occlusion of the inspiratory line. Ventilatory responses of the parents of victims of SIDS to chemical and mechanical stimulation were not significantly different from those of control parents. Responses in both groups were similar to previously reported normal values. There was a linear increase in ventilation (VE) in response to hypercapnia and hypoxia and in P0.1 in response to hypercapnia. We found expected increases in P0.1/PCO2 and decreases in VE/PCO2 slopes during loaded breathing in all subjects, but no difference between groups. We conclude that parents of SIDS victims have normal ventilatory chemosensitivity and respiratory drive.

Adult↗
PubMed2002

Usefulness of phrenic nerve stimulation to measure upper airway collapsibility in normal awake subjects.

Upper airway (UA) collapsibility can be characterized during sleep by looking at the changes in inspiratory flow limitation (IFL) with changing nasal pressure. IFL can be induced during wakefulness using phrenic nerve stimulation (PNS) applied during exclusive nasal breathing. The aim of the study was to evaluate the possibility of measuring UA critical pressure (Pcrit) in normal awaked subjects using electrical PNS (EPNS) or bilateral anterior magnetic phrenic stimulation (BAMPS). Instantaneous flow, esophageal (Peso) and mask pressures (Pmask), and genioglossal (GG) end-expiratory EMG activity were recorded in 13 normal subjects (4F, 9M) with randomly changing Pmask (0 to -20 cmH2O). For each trial, we examined the relationship between maximal inspiratory flow (Vtmax) of IFL twitches and the corresponding Pmask. Pcrit could be determined in 12 subjects (mean -33.5 +/- 16.3 cmH2O). No difference in Pcrit values was found between the EPNS and BAMPS methods but the strength of the Vtmax/Pmask relationship was higher with BAMPS. GG end-expiratory EMG activity increased with decreasing Pmask but no significant relationship was found between the slope of the GG end-expiratory EMG activity/Pmask relationship and Pcrit. We conclude that: (1) Pcrit can be measured during wakefulness in normal using PNS: (2) Pcrit measurements may be easier and more reliable with BAMPS than EPNS: and (3) Pcrit does not seem to be influenced by the pressure-related changes in GG end-expiratory EMG.

Adult↗
PubMed1998

Assessment of respiratory system viscoelasticity in spontaneously breathing rabbits.

Airflow, volume (V), inspiratory time (TI), tracheal pressure (Ptr), abdomen (Dab) and rib cage diameters (Drc), peak diaphragm (Adi) and parasternal muscle activity (Aic) were measured in thirteen anaesthetized and vagotomized rabbits and in six vagotomized rabbits with cordotomy at T1 during unimpeded inspirations followed by rapid end-inspiratory airway occlusion, relaxation against closed airways, and inspiratory effort. To modify the inspiratory flow pattern, such sequences were performed at different volume, levels of chemical drive, and body temperatures (BT). Under all conditions, Adi, Aic, TI, Drc and Dab at iso-volume were the same for unimpeded and occluded inspirations; end-inspiratory Ptr was lower for occluded than for unimpeded inspirations, the difference (Pdiff) being larger the lower the volume at which occlusions were performed and the higher the chemical drive and BT. After paralysis, the viscoelastic constants of the respiratory system, modelled as a Kelvin body, were assessed according to the rapid airway occlusion method and used together with the inspiratory flow waveform to predict the end-inspiratory viscoelastic pressure (Pvisc) of unimpeded inspirations. Since the slope of the Pdiff vs. Pvisc relationship never differed from unity, Pdiff under the specified conditions should represent the effective Pvisc of unimpeded inspirations.

Animals↗
PubMed1999

Task failure, breathing discomfort and CO2 accumulation without fatigue during inspiratory resistive loading in humans.

Task failure during inspiratory resistive loading has been attributed to inspiratory muscle fatigue. Six subjects breathed at their own rate and duty cycle through an inspiratory resistive load to a target mouth pressure of 80% maximal inspiratory pressure (MIP) until task failure, when breathing discomfort (measured with a modified Borg scale) was maximal. Six protocols were used to vary ventilatory parameters and hence the rate of rise, of end-tidal CO2. MIP did not decline during resistive loading in any protocol, but there were significant increases in end-tidal CO2 (ranging from 1.0 to 3.9). Time to task failure increased in protocols that enabled subjects to reduce the rate of CO2 accumulation. Differences in endurance times between subjects were related to their sense of breathing discomfort with rising CO2 measured in separate rebreathing studies. Task failure was due to breathing discomfort associated with CO2 accumulation and sensations related to the generation of large inspiratory pressures, rather than inspiratory muscle fatigue.

Adult↗