Effects of Intermittent Negative Pressure Ventilation on Effective Ventilation in Normal Awake Subjects

doi:10.1378/chest.122.1.99

Chest

Volume 122, Issue 1, July 2002, Pages 99-107

https://doi.org/10.1378/chest.122.1.99 Get rights and content

Rationale

Previous studies have shown that an increase in inspiratory pressure during nasal intermittent positive pressure ventilation (IPPV) does not result in increased effective minute ventilation ( $\dot{V}$ e) due to glottic interference.

Study objectives

To test the consequences of increases in negative pressure ventilation (NPV) on $\dot{V}$ e.

Material and methods

Eight healthy awake subjects underwent NPV delivered by an iron lung. First, NPV was started at a respirator frequency (f) of 15 cycles per minute with an inspiratory negative pressure (INP) of − 15 cm H₂O (F15-P15). Then, f was increased to 20 cycles per minute and INP was kept at − 15 cm H₂O. Next, f was kept at 20 cycles per minute and INP was reduced to − 30 cm H₂O (F20-P30). Finally, f was decreased to 15 cycles per minute and INP was kept at − 30 cm H₂O. At each step and for each breath, effective tidal volume (Vt), $\dot{V}$ e, and end-tidal carbon dioxide pressure were measured. In three subjects, the glottis width was assessed using fiberoptic bronchoscopy.

Results

From spontaneous breathing to the first step of NPV (F15-P15), we observed an inhibition of the phasic inspiratory diaphragmatic electromyogram concomitant to a significant increase in $\dot{V}$ e (p < 0.0005). For the group as a whole, the increase in mechanical ventilation (from F15-P15 to F20-P30) resulted in significant increases in Vt and $\dot{V}$ e leading to hypocapnia (p < 0.0005). Moreover, the glottis width did not decrease with the increase in mechanical ventilation.

Conclusions

We conclude that in normal awake subjects, NPV allowed a significant increase in $\dot{V}$ e. These results differ from those previously obtained with nasal IPPV in which the glottic width interferes with the delivered mechanical ventilation.

Section snippets

Subjects

Eight healthy medical students (four men and four women) were studied during NPV. They were 21 to 23 years of age (body mass index, 22.5 ± 1.7; range, 21.2 to 25.2) and were without evidence of cardiorespiratory diseases. All subjects were habituated to NPV during one or two previous training sessions when they learned to relax their respiratory muscles and perform the isovolume maneuvers used to calibrate the respiratory inductive plethysmograph.²⁷²⁸ No precise explanation on the aim of this

Results

Eight subjects were included in the study. Their anthropometric characteristics are reported in Table 1. In each subject, data were available for SB and the four steps of NPV. For SB, an average of 22 ± 13 breaths were analyzed per subject. For each step of NPV, periods that were analyzed breath by breath had a mean duration of 1.5 ± 0.5 min (26 ± 9 breaths per period).

Discussion

The main result of this study is that during NPV generated by an iron lung, increases in f and/or INP result in high levels of Vt and effective $\dot{V}$ e, leading to low levels of Petco₂ in spite of a large increase in Rinsp.

Some technical aspects of this study merit consideration. As the analysis of diaphragmatic muscle activity by surface electrodes is known to be fraught with difficulties, we also used a bipolar esophageal electrode that is considered the “gold standard” to assess the

ACKNOWLEDGMENT

The authors thank Dr. N. Mustfa of the Department of Respiratory Medicine, King's College Hospital, London, UK, for editing the revised manuscript.

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A study on rabbits demonstrated that NPV resulted in superior oxygenation that was unrelated to lung perfusion, which may have been due to an improved inflation of lung volume during both inspiration and expiration.9 Previous research also discovered that in normal awake human subjects, NPV allowed a significant increase in minute ventilation.10 Negative pressure differs from nasal intermittent positive pressure ventilation, in which the glottic width interferes with the delivered mechanical ventilation; thus NPV may offer potentially more effective ventilation.
For patients with bronchiectasis, the mechanical mobilization of secretion constitutes a key therapeutic approach. However, the effectiveness of lung expansion therapy to mobilize secretion in bronchiectasis patients has not been investigated extensively. This study compares patients' exercise tolerance and physical assessment outcomes after secretion clearance using intermittent positive pressure breathing (IPPB) or negative pressure ventilation (NPV) as adjuncts to postural drainage.
This prospective, randomized crossover study examined the data for 18 stable outpatients with bronchiectasis. The outcomes were compared for four treatment sessions of either IPPB or NPV, used as adjuncts to postural drainage. The short-term outcomes involved pulmonary functions and a six-minute walk test (6MWT). We also assessed pulmonary functions and physical clinical signs as immediate treatment effects.
Patients' forced vital capacity (FVC), forced expiratory volume in the first second (FEV₁), and cough efficacy did not change significantly after individual postural drainage sessions using either IPPB or NPV. However, a reduction in the use of accessory muscles was noted after NPV; patients with low baseline FVC might benefit particularly from this reduction (r = 0.699, p < 0.05). No significant differences between two techniques were found for the patient's walking distance. However, the pulse rate after 6MWT was significantly (p < 0.05) lower in the NPV group.
NPV may provide as an effective adjunct to postural drainage as IPPB in weekly lung expansion therapy for outpatients with bronchiectasis. The benefits of NPV might include a reduction in the use of accessory muscles during lung expansion.
The travels of a pulmonologist through the upper airway
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La ventilation non invasive (VNI) est actuellement largement utilisée en cas de détresse respiratoire aiguë afin d’éviter le recours à l’intubation endotrachéale. Cependant, le comportement de la glotte lors des différents modes ventilatoires de VNI peut influencer la ventilation minute effective. La ventilation en pression positive intermittente par voie nasale (VPPIn) en mode volumétrique induit une adduction des cordes vocales responsable d’une diminution de la proportion de ventilation minute insufflée parvenant réellement à l’échangeur pulmonaire (VMe). En mode barométrique contrôlé, la réponse glottique à la VPPIn et donc la VMe sont variables et moins prédictibles. En mode barométrique spontané, la glotte n’interfère pas sur la VMe qui augmente avec les niveaux de pression inspiratoire, essentiellement au-dessus de 20 cmH₂O. Lors de la ventilation en pression négative intermittente (VPNI), l’augmentation de la ventilation ne s’accompagne pas d’une fermeture des cordes vocales permettant d’obtenir des niveaux de VMe supérieurs à ceux observés en VPPIn. Ainsi, les paramètres ventilatoires optimaux sont les suivants : en mode contrôlé barométrique, une fréquence respiratoire (Fr) de 20 cycles par minute, un rapport I/E de 1/1, une pression inspiratoire positive à 15 cmH₂O, et une pression expiratoire aussi faible que possible ; en mode volumétrique : un volume courant de 13 ml/kg , une Fr de 20 cycles par minute, un débit inspiratoire de 0,56–0,85 l par seconde ; en VPNI : une pression négative de –30 cmH₂O et une Fr de 20 cycles par minute. Par ailleurs, durant le sommeil, la réponse glottique à la VNI est différente de celle observée chez le sujet éveillé. Les paramètres ventilatoires « adaptés à l’éveil » peuvent donc être inadéquats pendant le sommeil du fait de la réduction du calibre glottique en sommeil lent. Ces données rappellent donc que le système respiratoire ne peut être considéré comme un modèle à un seul compartiment sous VNI, à l’inverse de la ventilation mécanique endotrachéale.
Nowadays, noninvasive ventilation (NIV) is widely used for the treatment of acute respiratory failure in order to avoid endotracheal intubation. However, the glottis can influence the effective minute ventilation. Nasal intermittent positive pressure ventilation (nIPPV) using volumetric ventilators results in an adduction of the vocal cords leading to a decrease in the percentage of the delivered minute ventilation effectively reaching the lungs (VE). During NIV using a two-level positive-pressure ventilator in the controlled mode, the behaviour of the glottis and thus VE are less stable and predictable. In spontaneous mode, the glottis does not play a role in the control of VE that increases with increasing inspiratory pressures, significantly above 20 cmH₂O. During negative pressure ventilation (NPV), the increase in mechanical ventilation does not result in a narrowing of vocal cords, allowing to achieve levels of VE higher than those observed during nIPPV. Thus, the best setting are as follows: in the controlled mode with barometric ventilators: a respiratory frequency (f) around 20 breaths per minute; an I/E ratio of 1/1; 15 cmH₂O of inspiratory positive airway pressure and an expiratory positive airway pressure as low as possible; during nIPPV with volumetric ventilators: a tidal volume of 13 ml/kg; a f of 20 breaths per minute; an inspiratory flow of 0.56–0.85 l per second; during NPV: a negative inspiratory pressure of –30 cmH₂O and a f of 20 breaths per minute. Moreover, in sleeping subjects, the glottic behaviour during NIV is different from that observed in awake subjects. The best settings established during wakefulness can be not suitable during sleep as observed a glottic narrowing during NREM sleep. Thus, by contrast with endotracheal mechanical ventilation, the respiratory system does not behave like an one-compartment model during NIV.
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: This work was performed at the Pneumology and EEG Units, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, 1200 Brussels, Belgium.

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Chest

Clinical InvestigationsNoninvasive VentilationEffects of Intermittent Negative Pressure Ventilation on Effective Ventilation in Normal Awake Subjects

Rationale

Study objectives

Material and methods

Results

Conclusions

Section snippets

Subjects

Results

Discussion

ACKNOWLEDGMENT

Chest

Chest

Chest

Lancet

Am J Med

Chest

Chest

Chest

Noninvasive ventilation for acute exacerbations of chronic obstructive pulmonary disease

N Engl J Med

Domiciliary nocturnal nasal intermittent positive pressure ventilation in COPD: mechanisms underlying changes in arterial blood gas tensions

Eur Respir J

Treatment of respiratory failure during sleep in patients with neuromuscular disease

Am Rev Respir Dis

Effect of 8 weeks of intermittent negative pressure ventilation on exercise parameters in patients with severe chronic obstructive lung disease [abstract]

Am Rev Respir Dis

Effects of intermittent negative pressure ventilation on respiratory muscle function in patients with severe chronic obstructive pulmonary disease

Am Rev Respir Dis

Evaluation of intermittent long-term negative-pressure ventilation in patients with severe chronic obstructive pulmonary disease

Am Rev Respir Dis

Weekly cuirass ventilation improves blood gases and inspiratory muscle strength in patients with chronic air-flow limitation and hypercapnia

Am Rev Respir Dis

Controlled trial of external negative pressure ventilation in patients with severe chronic airflow obstruction

Am Rev Respir Dis

Reversal of sleep-induced hypoventilation and chronic respiratory failure by nocturnal negative pressure ventilation in patients with restrictive ventilatory impairment

Am Rev Respir Dis

Electromyogram pattern of diaphragmatic fatigue

J Appl Physiol

Nasal mask pressure waveform and inspiratory muscle rest during nasal assisted ventilation

Am J Respir Crit Care Med

Effects of nasal positive-pressure hyperventilation on glottis in normal awake subjects

J Appl Physiol

Effects of nasal positive-pressure hyperventilation on glottis in normal sleeping subjects

J Appl Physiol

Clinical Investigations
Noninvasive Ventilation
Effects of Intermittent Negative Pressure Ventilation on Effective Ventilation in Normal Awake Subjects