Termination of inspiration through graded inhibition of inspiratory activity.
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Animals↗
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Influence of Muller's maneuver on mitral valve prolapse: correlation with external carotid pulse tracing and echocardiogram.
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Adult↗
The alveolar air equation abbreviated.
The alveolar air equation is not widely used in clinical medicine, probably because of the complicated appearance of its classic forms. The following shorter form has been derived: formula: see text (where PAO2, PEO2, and PIO2 are the partial pressures of oxygen in alveolar, expired, and inspired, gas, respectively, and VD/VT is the ratio of physiologic dead space over tidal volume). This shorter form is an algebraic identity of the classic equation. The shorter form involves the same assumptions and requires the same measurements as the traditional expressions but is more compact and easier to use in circumstances where VD/VT is measured routinely.
Air↗
Control of breathing in obstructive sleep apnea.
We studied the responses of ventilation and occlusion pressure (P100) to hypercapnia, with and without the application of an inspiratory flow-resistive load (12 cm H2O/L/sec), in eight control subjects and in eight subjects with obstructive sleep apnea who did not retain carbon dioxide while awake. The hypercapnic response was assessed by a modification of the Read rebreathing technique. For a given endtidal carbon dioxide, ventilation in control subjects was the same with or without load, and P100 was increased with loading. In contrast, the subjects with sleep apnea decreased their ventilation during loading and did not increase their P100 in response to loading. Relationships between ventilation and P100 were similar in the two groups both with and without load. We conclude that patients with occlusive sleep apnea do not exhibit the normal increase in neural drive to compensate for inspiratory flow-resistive loading.
Adult↗
The inspiratory work of breathing during assisted mechanical ventilation.
We quantified the mechanical work of breathing in six normal subjects during assisted mechanical ventilation. Using two volume-cycled ventilators of different design, we investigated the influence of minute ventilation (VE) and machine settings of trigger sensitivity and flow during CO2-driven hyperventilation to moderate and high levels (12-24 L/min). Work estimates were derived from plots of esophageal and airway pressure against inflation volume. Peak flow and trigger sensitivity were important determinants of the energy expended, and for each combination of machine settings the work done by the subject per liter of ventilation increased with VE. During assisted ventilation the subject expended energy equivalent to 33-50 percent of the work of passive inflation, even under the most favorable conditions of VE, sensitivity and flow. Under the least favorable conditions of VE, sensitivity and flow, the subject's inspiratory work of breathing substantially exceeded the energy needed by the ventilator to inflate the passive thorax. These observations imply that exertion of the respiratory muscles continues throughout inflation during assisted mechanical ventilation and call attention to the possibility that inappropriate selection of ventilatory mode or machine settings may contribute to respiratory muscle fatigue and dyspnea.
Adult↗
Work of breathing and airway occlusion pressure during assist-mode mechanical ventilation.
We determined the effect of varying ventilator tidal volume (VT) and inspiratory flow (V) on the inspiratory muscle work (WI) during assist-mode mechanical ventilation (AMV) in four healthy subjects. In another four subjects, under constant chemoreceptor input, we determined the responses of neuromuscular output as assessed by the mouth occlusion pressure (P0.1) to alteration in WI. During AMV, the inspiratory external work of breathing is partitioned between WI and ventilator work. With a constant ventilator trigger sensitivity, we calculated WI (joules/L of volume) as the difference between the area subtended by the airway pressure-inspiratory volume curves and the ordinate of the assisted breaths subtracted from that of the controlled breaths at ventilator V of 40, 60 and 80 L/min and ventilator VT of 100, 125 and 150 percent spontaneous breathing VT. At all ventilator settings, WI was less than inspiratory muscle work of spontaneous breathing (SB) and was a function of both ventilator VT and V (p less than 0.05), but ventilator V has more effect on WI. Under isocapnia and hyperoxia, we measured P0.1 and WI during AMV at ventilator VT of 125 percent of spontaneous breathing VT and ventilator V of 60, 80 and 100 L/min. End-expiratory lung volume remained constant. P0.1 during AMV was similar to that of the SB. Although WI decreased with increasing ventilator V, P0.1 did not decrease significantly. We conclude that during AMV, both ventilator V and to a less extent ventilator VT determine W. In healthy subjects changes in WI do not affect P0.1.
Airway Resistance↗
Efficiency of work of inspiratory muscles in standing and in exercising dogs.
The objective of this study was to elucidate the resistive, elastic, and total inspiratory muscle work and mainly the efficiency of the inspiratory muscle work in still standing and in exercising dogs. In 180 experiments with nine mongrel dogs, respiratory and circulatory functions were recorded at rest and during a 1.5-mph walk on a treadmill belt which was inclined by 9 degrees. Each dog had been trained and surgically prepared before the series of experiments started. An electronic pressure transducer together with a fluid-filled catheter was attached to the ribs at the midthoracic level. Airflow was monitored with a pneumotachygraph attached to a face mask. Aortic flow was monitored with an electromagnetic flow transducer. Catheters in the atria, the ventricles, and the pulmonary and systemic vessels were used to determine hemodynamic parameters and blood gas levels. All recorded and all derived functions were evaluated by a dedicated computer. At rest, resistive inspiratory work (0.98 kg cm) was smaller than elastic work (1.36 kg cm). Elastic work did not change with exercise but resistive work increased to 1.46 kg.cm. The increase of total work from 2.33 kg.cm at rest to 2.79 kg.cm during exercise did not reach significance. Inspiratory power increased with exercise. Estimated diaphragmatic oxygen consumption increased from 2.23 ml/min at rest to 3.64 ml/min during exercise. It was 1.6 percent of the total oxygen consumption at rest and 1.7 percent of the total oxygen consumption during exercise. The estimated efficiency of the work of inspiratory muscles was 15.8 percent at rest and 25.8 percent during exercise. These values did not vary substantially between different animals.
Animals↗
Ventilatory muscle support in respiratory failure with nasal positive pressure ventilation.
Long-term intermittent mechanical ventilation results in improvements in ventilatory performance and clinical status between ventilation sessions in patients with chronic respiratory failure. The application of intermittent positive pressure ventilation through a nasal mask (NPPV) is a simple, noninvasive method for the provision of chronic intermittent ventilatory support. We investigated the effects of NPPV on inspiratory muscle activity in three normal subjects and nine patients with acute or chronic ventilatory failure due to restrictive (four subjects) or obstructive (five subjects) respiratory disorders. NPPV resulted in reductions of phasic diaphragm electromyogram amplitude to 6.7 +/- 0.7 percent (mean +/- SEM) of values obtained during spontaneous breathing in the normal subjects, 6.4 +/- 3.2 percent in the restrictive group, and 8.3 +/- 5.1 percent in the obstructive group. Simultaneous decreases in activity of accessory respiratory muscles were observed. The reductions in inspiratory muscle activity were confirmed by the finding of positive intrathoracic pressure swings on inspiration in all subjects. With NPPV, oxygen saturation and PCO2 remained stable or improved as compared with values obtained during spontaneous breathing. These results indicate that NPPV can noninvasively provide ventilatory support while reducing inspiratory muscle energy expenditure in acute and chronic respiratory failure of diverse etiology. Long-term assisted ventilation with NPPV may be useful in improving ventilatory performance by resting the inspiratory muscles.
Adult↗
Isoflurane therapy for status asthmaticus in children and adults.
Two adults and two children with life-threatening asthma refractory to maximal standard therapy were treated with the inhalational anesthetic agent isoflurane. In each case, the temporal response to the initiation of therapy was striking. All patients survived and none experienced adverse reactions attributable to the drug. Rapid therapeutic benefit, minimal side effects, absence of cumulative toxicity, and ease of administration are factors supporting the use of isoflurane for patients with severe asthma.
Adolescent↗
Effects of inspiratory loading on 31phosphorus magnetic resonance (PMR) spectroscopy of the inspiratory intercostal muscles in normal humans.
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Humans↗
Combined nasal intermittent positive-pressure ventilation and rocking bed in chronic respiratory insufficiency. Nocturnal ventilatory support of a disabled person at home.
The use of intermittent positive-pressure ventilation via nasal mask with a rocking bed provided the necessary ventilatory support for a person with quadriplegia living at home. This option was required to maintain an independent life-style of choice. The combination of techniques and the linkage of devices demonstrated an effective use of simple available technology for respiratory care at home and the adaptation of the respiratory prescription to the total needs of each person: medical, social, and financial. The further use of nasal mask ventilation in selected cases is encouraged by clinical research protocol.
Beds↗
Predictive risk factors for pulmonary oxygen transfer in patients undergoing coronary artery bypass grafting.
UNLABELLED: The ratio of arterial oxygen tension to inspired oxygen fraction (PaO2/FiO2) is a useful indicator for weaning patients from mechanical ventilation and a reliable predictor of pulmonary dysfunction after cardiac surgery. The aim of this study was to elucidate the patient characteristics and variables that affect the PaO2/FiO2 ratio. Between 1994-1998, 167 patients who underwent coronary artery bypass grafting (CABG) were examined retrospectively. Spearman's correlation coefficients were calculated between the PaO2/FiO2 ratio and intubation period, and length of ICU stay. Patients were then divided into two groups with a PaO2/FiO2 ratio < 350 and PaO2/FiO2 ratio > or = 350. Univariate analysis of the putative risk factors was performed. A logistic regression model was developed to evaluate factors that would influence the PaO2/FiO2 ratio. A significant correlation was observed between the PaO2/FiO2 ratio and intubation period, and length of ICU stay. Univariate predictors of a PaO2/FiO2 ratio < 350 were low body weight, low preoperative PaO2 long operation time, high FiO2, low postoperative PaO2 history of smoking, hypertension and opening of pleura (p < 0.05). Excellent prediction was found with a model consisting of preoperative PaO2 and hypertension. CONCLUSION: The results of this study suggest that patients with a low preoperative PaO2 or hypertension may need more careful peri- and postoperative management since these factors are closely associated with the PaO2/FiO2 ratio.
Adult↗
Paraquat poisoning: an experimental model of dose-dependent acute lung injury due to surfactant dysfunction.
Since the most characteristic feature of paraquat poisoning is lung damage, a prospective controlled study was performed on excised rat lungs in order to estimate the intensity of lesion after different doses. Twenty-five male, 2-3-month-old non-SPF Wistar rats, divided into 5 groups, received paraquat dichloride in a single intraperitoneal injection (0, 1, 5, 25, or 50 mg/kg body weight) 24 h before the experiment. Static pressure-volume (PV) curves were performed in air- and saline-filled lungs; an estimator of surface tension and tissue works was computed by integrating the area of both curves and reported as work/ml of volume displacement. Paraquat induced a dose-dependent increase of inspiratory surface tension work that reached a significant two-fold order of magnitude for 25 and 50 mg/kg body weight (P < 0.05, ANOVA), sparing lung tissue. This kind of lesion was probably due to functional abnormalities of the surfactant system, as was shown by the increase in the hysteresis of the paraquat groups at the highest doses. Hence, paraquat poisoning provides a suitable model of acute lung injury with alveolar instability that can be easily used in experimental protocols of mechanical ventilation.
Animals↗
Activities of superior pharyngeal constrictor and levator veli palatini muscles related to respiration in dogs.
OBJECTIVE: This study, using mongrel dogs, attempted to delineate the respiratory activity of two closure muscles of the velopharynx, the levator veli palatini (LVP) and superior pharyngeal constrictor (PC) muscles. METHOD: Fifteen mongrel dogs were given tracheotomies, with intratracheal tubes being connected to their respiratory circuits. Activities of the PC and LVP muscles were recorded electromyographically, and the effects of PaO2 and PaCO2 were analyzed along with the effects of lung inflation intratracheally with O2 and N2. RESULTS: Under hypoxic conditions, expiratory LVP activity was observed while PC activity diminished. The effects of lung inflation on both LVP and PC activities were also studied. The activities of both muscles were enhanced by lung inflation. CONCLUSION: It was thus suggested that the roles of both muscles during velopharyngeal closing movements are not the same.
Administration, Inhalation↗
Inspiratory muscle training: integrative review.
This article provides a critical review of inspiratory muscle training (IMT) in chronic obstructive pulmonary disease (COPD). Although extensive research on IMT has accumulated, its benefits have been debated, primarily because of methodological limitations of studies. Using relevant key words, multiple databases were searched from 1966. Selected studies used PImax (maximal inspiratory pressure) as an outcome variable. Overall, research demonstrated that a standard protocol of 30% or higher for a duration of 20 to 30 minutes per day for 10 to 12 weeks improves dyspnea and inspiratory strength and endurance with either inspiratory resistive or inspiratory threshold training. Regardless of method, IMT protocols for people with COPD and inspiratory muscle weakness and dyspnea are generally safe, feasible, and effective. Patient selectivity and study of subgroups are recommended.
Activities of Daily Living↗
Evaluation of peak inspiratory pressure and respiratory rate during ventilation of an infant lung model with a self-inflating bag.
OBJECTIVE: To evaluate the peak inspiratory pressure and ventilation rate achieved by physicians when using a neonatal self-inflating bag on a lung model. METHODS: Fifteen physicians ventilated full term and preterm infant lung simulators while the outcomes were captured by a ventilation monitor. RESULTS: Median peak pressures in cmH(2)O for full term and preterm lungs were 23 (interquartile range: 15-47) and 26 (interquartile range: 14-51), being less than 20 in 41.2 and 35.8% of the pressure curves analyzed, more than 40 in 29.7 and 33.6%, and between 27 and 33 cmH(2)O in 8.2 and 6.5% of the curves, respectively. Median ventilation rates were 45 (interquartile range: 36-57) and 48 (interquartile range: 39-55.5) cycles per minute, being more than 30 in 9.3 and 6.7% of pressure curves and more than 60 in 12 and 13.3% of pressure curves, for the full term and preterm lungs, respectively. The differences between these medians were not statistically significant. CONCLUSIONS: Ventilation rates achieved with the self-inflating bag were adequate in approximately 80% of pressure curves analyzed, but the physicians were unable to provide ventilation with minimal pressure variation, producing pressures that diverged from those defined by the neonatal resuscitation training course in 70% of the curves. This was irrespective of whether they were ventilating the lung model analogous to preterm or full term infant lungs.
Cardiopulmonary Resuscitation↗
Pulmonary function, ventilator management, and outcome of dogs with thoracic trauma and pulmonary contusions: 10 cases (1994-1998).
OBJECTIVE: To document pulmonary function, ventilator management, and outcome of dogs with thoracic trauma that required mechanical ventilation because of severe pulmonary contusions. DESIGN: Retrospective study. ANIMALS: 10 dogs that required mechanical ventilation because of severe pulmonary contusions caused by blunt thoracic trauma. PROCEDURE: Signalment, historical data, arterial blood gas values, oxygen tension-based indices, ventilator settings, peak inspiratory pressure, positive end-expiratory pressure, tidal volume, and minute ventilation values were retrieved from medical records. RESULTS: All 10 dogs required positive-pressure ventilation because of dyspnea following trauma and had severely abnormal pulmonary function. Survival rate to discharge was 30%. Dogs were categorized into 2 groups; group A included 5 dogs in which pulmonary function improved during ventilation, whereas group B included 5 dogs that were euthanatized because of progressive lung dysfunction (n = 4) or cardiac arrest (1). Mean +/- SD body weight of group-A dogs (30.9 +/- 15.9 kg [68 +/- 35 lb]) was significantly greater than that of group-B dogs (7.6 +/- 1.8 kg [16.7 +/- 4 lb]). Dogs with improved lung function had peak inspiratory pressure that decreased progressively, whereas lung compliance deteriorated in dogs in group B. CONCLUSIONS AND CLINICAL RELEVANCE: Dyspneic dogs with severe pulmonary contusions may require and benefit from positive-pressure ventilation Prognosis is better for dogs that weigh > 25 kg (55 lb).
Animals↗
Constancy of individual exponents for category production of inspired lung volume.
Individual exponents for production of inspired lung volume were compared both within experimental sessions (after a delay of 5 to 10 min.) and between sessions (after a delay of 1 yr.). Reliable correlations were observed between pairs of individual exponents regardless of the time elapsed between repetitions of the task. Constancy of exponents may reflect a propensity for subjects to respond in characteristic ways to psychophysical scaling tasks.
Adult↗