Inspiratory Pressure-time Product Research Articles

Ventilator performances for non-invasive ventilation: a bench study

IntroductionA wide range of recent ventilators, dedicated or not, is available for non-invasive ventilation (NIV) in respiratory or intensive care units (ICU). We conducted a bench study to compare their...

Inspiratory threshold loading negatively impacts attentional performance.

RationaleThere are growing concerns over the occurrence of adverse physiologic events (PEs) occurring in pilots during operation of United States Air Force and Navy high-performance aircraft. We hypothesize that a heightened inspiratory work of breathing experienced by jet pilots by virtue of the on-board life support system may constitute a “distraction stimulus” consequent to an increased sensation of respiratory muscle effort. As such, the purpose of this study was to determine whether increasing inspiratory muscle effort adversely impacts on attentional performance.MethodsTwelve, healthy participants (age: 29 ± 6 years) were recruited for this study. Participants completed six repetitions of a modified Masked Conjunctive Continuous Performance Task (MCCPT) protocol while breathing against four different inspiratory threshold loads to assess median reaction times (RTs). A computer-controlled threshold loading device was used to set the inspiratory threshold loads. Repeated measures analysis of variances (ANOVAs) were performed to examine: (i) the efficacy of the threshold loading device to impose significantly higher loading at each loading condition; (ii) the effects of loading condition on respiratory muscle effort sensation; and (iii) the influence of hypercapnia on MCCPT scores during inspiratory threshold loading. Generalized additive mixed effects models (GAMMs) were used to examine the potential non-linear effects of respiratory muscular effort sensation, device loading, and hypercapnia, on MCCPT scores during inspiratory threshold loading.ResultsInspiratory threshold loading significantly augmented (P < 0.05) inspiratory effort sensation and the inspiratory pressure-time product (PTP). Our analyses also revealed that median hit RT was positively associated with inspiratory effort sensation during inspiratory loading trials.ConclusionThe findings of this work suggest that it was not increasing inspiratory muscle effort (i.e., PTP) per se, but rather participant’s subjective perception of inspiratory “load” that impacts negatively on attentional performance; i.e., as the degree of inspiratory effort sensation increased, sotoo did median hit RT. As such, it is reasonable to suggest that minimizing inspiratory effort sensation (independent of the mechanical output of the inspiratory muscles) during high-performance flight operations may prove useful in reducing pilot RTs during complex behavioral tasks.

Comparative bench study evaluation of different infant interfaces for non-invasive ventilation

BackgroundTo compare, in terms of patient-ventilator interaction and performance, a new nasal mask (Respireo, AirLiquide, FR) with the Endotracheal tube (ET) and a commonly used nasal mask (FPM, Fisher and Paykel, NZ) for delivering Pressure Support Ventilation (PSV) in an infant model of Acute Respiratory Failure (ARF).MethodsAn active test lung (ASL 5000) connected to an infant mannequin through 3 different interfaces (Respireo, ET and FPM), was ventilated with a standard ICU ventilator set in PSV. The test lung was set to simulate a 5.5 kg infant with ARF, breathing at 50 and 60 breaths/min). Non-invasive ventilation (NIV) mode was not used and the leaks were nearly zero.ResultsThe ET showed the shortest inspiratory trigger delay and pressurization time compared to FPM and Respireo (p < 0.01). At each respiratory rate tested, the FPM showed the shortest Expiratory trigger delay compared to ET and Respireo (p < 0.01). The Respireo presented a lower value of Inspiratory pressure–time product and trigger pressure drop than ET (p < 0.01), while no significant difference was found in terms of pressure-time product at 300 and 500 ms. During all tests, compared with the FPM, ET showed a significantly higher tidal volume (VT) delivered (p < 0.01), while Respireo showed a trend toward an increase of tidal volume delivered compared with FPM.ConclusionsThe ET showed a better patient-ventilator interaction and performance compared to both the nasal masks. Despite the higher internal volume, Respireo showed a trend toward an increase of the delivered tidal volume; globally, its efficiency in terms of patient-ventilator interaction was comparable to the FPM, which is the infant NIV mask characterized by the smaller internal volume among the (few) models on the market.

Limited predictability of maximal muscular pressure using the difference between peak airway pressure and positive end-expiratory pressure during proportional assist ventilation (PAV).

BackgroundIf the proportional assist ventilation (PAV) level is known, muscular effort can be estimated from the difference between peak airway pressure and positive end-expiratory pressure (PEEP) (ΔP) during PAV. We conjectured that deducing muscle pressure from ΔP may be an interesting method to set PAV, and tested this hypothesis using the oesophageal pressure time product calculation.MethodsEleven mechanically ventilated patients with oesophageal pressure monitoring under PAV were enrolled. Patients were randomly assigned to seven assist levels (20–80%, PAV20 means 20% PAV gain) for 15 min. Maximal muscular pressure calculated from oesophageal pressure (Pmus, oes) and from ΔP (Pmus, aw) and inspiratory pressure time product derived from oesophageal pressure (PTPoes) and from ΔP (PTPaw) were determined from the last minute of each level. Pmus, oes and PTPoes with consideration of PEEPi were expressed as Pmus, oes, PEEPi and PTPoes, PEEPi, respectively. Pressure time product was expressed as per minute (PTPoes, PTPoes, PEEPi, PTPaw) and per breath (PTPoes, br, PTPoes, PEEPi, br, PTPaw, br).ResultsPAV significantly reduced the breathing effort of patients with increasing PAV gain (PTPoes 214.3 ± 80.0 at PAV20 vs. 83.7 ± 49.3 cmH2O•s/min at PAV80, PTPoes, PEEPi 277.3 ± 96.4 at PAV20 vs. 121.4 ± 71.6 cmH2O•s/min at PAV80, p < 0.0001). Pmus, aw overestimates Pmus, oes for low-gain PAV and underestimates Pmus, oes for moderate-gain to high-gain PAV. An optimal Pmus, aw could be achieved in 91% of cases with PAV60. When the PAV gain was adjusted to Pmus, aw of 5–10 cmH2O, there was a 93% probability of PTPoes <224 cmH2O•s/min and 88% probability of PTPoes, PEEPi < 255 cmH2O•s/min.ConclusionDeducing maximal muscular pressure from ΔP during PAV has limited accuracy. The extrapolated pressure time product from ΔP is usually less than the pressure time product calculated from oesophageal pressure tracing. However, when the PAV gain was adjusted to Pmus, aw of 5–10 cmH2O, there was a 90% probability of PTPoes and PTPoes, PEEPi within acceptable ranges. This information should be considered when applying ΔP to set PAV under various gains.

A Bench Study of 2 Ventilator Circuits During Helmet Noninvasive Ventilation

To compare helmet noninvasive ventilation (NIV), in terms of patient-ventilator interaction and performance, using 2 different circuits for connection: a double tube circuit (with one inspiratory and one expiratory line) and a standard circuit (a Y-piece connected only to one side of the helmet, closing the other side). A manikin, connected to a test lung set at 2 breathing frequencies (20 and 30 breaths/min), was ventilated in pressure support ventilation (PSV) mode with 2 different settings, randomly applied, of the ratio of pressurization time to expiratory trigger time (T(press)/T(exp-trigger)) 50%/25%, default setting, and T(press)/T(exp-trigger) 80%/60%, fast setting, through a helmet. The helmet was connected to the ventilator randomly with the double and the standard circuit. We measured inspiratory trigger delay (T(insp-delay)), expiratory trigger delay (T(exp-delay)), T(press)), time of synchrony (T(synch)), trigger pressure drop, inspiratory pressure-time product (PTP), PTP at 300 ms and 500 ms, and PTP at 500 ms expressed as percentage of an ideal PTP500 (PTP500 index). At both breathing frequencies and ventilator settings, helmet NIV with the double tube circuit showed better patient-ventilator interaction, with shorter T(insp-delay), T(exp-delay), and T(press); longer T(synch); and higher PTP300, PTP500, and PTP500 index (all P < .01). The double tube circuit had significantly better patient-ventilator interaction and a lower rate of wasted effort at 30 breaths/min.

The Effect of Ventilator Performance on Airway Pressure Release Ventilation

Using a model lung connected to six different ventilators, with each ventilator in the airway pressure release ventilation mode, we measured differences in intrinsic positive end-expiratory pressure (PEEPi) during the expiratory phase and calculated the inspiratory and expiratory pressure time product (PTP) as an index of work of breathing during the inspiratory phase. We compared 6 ventilators: Puritan-Bennett 840, Evita XL, Servo i, Avea, Hamilton G5, and Engström. With a constant inspiratory pressure level of 25 cm H(2)O and expiratory pressure level of 0 cm H(2)O, PEEPi was measured as the expiratory time was decremented from 1.0 second to 0.2 second in steps of 0.1 second. The inspiratory and expiratory PTPs were measured during the ventilator's inspiratory phase by simulating spontaneous breathing with a tidal volume of 300 mL, with a respiratory rate of 30 breaths/min and with expiratory flow rates of 0.5 L/s, 1.0 L/s, and 1.5 L/s. In all ventilators, the progressive diminution of the expiratory time caused a significant increase in PEEPi (P< 0.001). With a 0.2-second expiratory time, PEEPi ranged from 9.4± 0.07 cm H(2)O for the Servo i to 15.7± 0.04 cm H(2)O for the Avea. The Servo i had a significantly lower inspiratory PTP than did the other ventilators (P< 0.001). When the expiratory flow rate was 0.5 L/s and 1.0 L/s, the expiratory PTP was lower with the Servo i and Evita XL than with the other ventilators (P< 0.001). PEEPi varied significantly among ventilators. Inspiratory and expiratory work of breathing varied between ventilators when spontaneous breathing occurred during the ventilator's inspiratory phase.

Effects of Spontaneous Breathing During Airway Pressure Release Ventilation on Respiratory Work and Muscle Blood Flow in Experimental Lung Injury

To evaluate the effects of spontaneous breathing at ambient airway pressure (Paw) and during airway pressure release ventilation (APRV) on respiratory work and respiratory muscle blood flow (RMBF) in experimental lung injury. Prospective experimental study. Research laboratory of a university hospital. Twelve hemodynamically stable, analgosedated, and tracheotomized domestic pigs. Respiratory work was estimated by the inspiratory pressure time product (PTPinsp) of esophageal pressure, and RMBF was measured with colored microspheres. Lung injury was induced with IV boli of oleic acid. The first set of measurements was performed before induction of lung injury while pigs were breathing spontaneously at ambient Paw, the second after induction of lung injury while breathing spontaneously at ambient Paw, and the third with lung injury and spontaneous breathing with APRV. After induction of lung injury PTPinsp increased from 138 +/- 14 to 214 +/- 32 cm H2O s/min when pigs breathed spontaneously at ambient Paw (p < 0.05) and returned to 128 +/- 27 cm H2O s/min during APRV. While systemic hemodynamics and blood flow to the psoatic and intercostal muscles did not change, diaphragmatic blood flow increased from 0.34 +/- 0.05 before to 0.54 +/- 0.08 mL/g/min after induction of lung injury and spontaneous breathing at ambient Paw (p < 0.05) and returned to 0.32 +/- 0.05 mL/g/min during APRV (p < 0.05 vs spontaneous breathing at ambient Paw [lung injury]). Respiratory work and RMBF are increased in acute lung injury when subjects breathe spontaneously at ambient Paw. Supporting spontaneous breathing with APRV decreases respiratory work and RMBF to physiologic values.

Ventilation therapy for patients with COPD

Acute ventilatory failure in COPD is caused by impaired respiratory mechanics and an imbalance of capacity and load of the respiratory muscles. Continuous positive airway pressure (CPAP), pressure support ventilation (PSV), proportional assist ventilation (PAV) or controlled mechanical ventilation (CMV) are effective in unloading the respiratory pump. CPAP reduces the inspiratory pressure time product by reducing the elastic work of breathing due to intrinsic PEEP (PEEPi). PSV and PAV reduce the work of breathing and additionally improve alveolar ventilation and CO2 elimination. In spontaneous breathing patients these modes of ventilation should be applied non invasively by using a face mask. In CMV, hyperinflation should be avoided by choice of low tidal volumes and long exspiratory times (low respiratory rate, I:E ratio 1:3, 1:4). In the weaning from CMV, PSV or PAV and CPAP is used. There seems to be a beneficial effect in nocturnal intermittent nonivasive ventilation (NPPV) in chronic hypercapnic stable COPD patients with documented hypoventilation during the night, which is reversible by NPPV.

Proportional Assist Ventilation Reduces the Work of Breathing during Exercise at Moderate Altitude

Reducing the work of breathing (WOB) during exercise and thus the oxygen required solely for ventilation may be an option to increase the oxygen available for nonventilatory physiological tasks at altitude. This study evaluated whether pressure support ventilation (PSV) and proportional assist ventilation (PAV) may partially reduce WOB during exercise at altitude. Seven volunteers breathing with either PSV or PAV or without support (control) were examined for WOB, inspiratory pressure time product (iPTP), and (O(2)) before and during pedaling at 160 W for 4 min on an ergometer at an altitude of 2860 m, where barometric pressure and oxygen partial pressure are approximately 30% less than at sea level. PSV and PAV reduced WOB from 4.5 +/- 0.9 J/L(-1)/min(-1) during unsupported breathing to 3.7 +/- 0.4 (p < 0.05) and 3.2 +/- 0.7 (p < 0.01), respectively. iPTP was reduced during PAV (570 +/- 151 cm H(2)O/sec/min(-1), p < 0.01), but not during PSV (727 +/- 116, p = 0.58) compared with unsupported ventilation during exercise (763 +/- 90). During PSV and PAV breathing, higher arterial oxygen saturations (84 +/- 2%, p < 0.05, and 86 +/- 1%, p < 0.01, respectively) were observed compared with control (80 +/- 3%), indicating that PSV and PAV attenuated hypoxemia during exercise at altitude. Total body (O(2)), however, was not reduced during PSV or PAV. In conclusion, both PSV and PAV reduced the WOB during exercise at altitude, but only PAV reduces iPTP. Both modes reduce hypoxemia, which may be due to higher alveolar ventilation or decreased ventilation-perfusion heterogeneity compared to unsupported breathing.

Effects of tracheotomy on respiratory mechanics in spontaneously breathing patients.

Tracheotomy is a method of intubating the trachea, which is employed in several clinical settings, including the treatment of head and neck neoplasms. Tracheotomy is believed to facilitate weaning through changes in respiratory mechanics. Existing information concerning functional changes associated with tracheotomy are limited to comparisons with orotracheal intubation. In this study, respiratory mechanics were monitored in seven spontaneously breathing patients, before and after an elective tracheotomy was performed for surgical treatment of cancer. Campbell diagrams were constructed by plotting pressure, obtained with an oesophageal balloon catheter, against volume, obtained from a pneumotachograph placed at the airway opening. Work of breathing was calculated as the internal area of the Campbell diagram and was partitioned into its elastic and inspiratory and expiratory resistive components. Oesophageal pressure was also used to quantify intrinsic positive end-expiratory pressure (PEEPi) and the pressure-time product (PTP), which is considered to be proportional to the oxygen cost of breathing. PTP was divided into its resistive and elastic components. Inspiratory resistive work, PEEPi, inspiratory PTP, as well as its resistive and elastic components were significantly reduced by tracheotomy. Tracheotomy significantly reduces work of breathing and pressure-time product in spontaneously breathing patients.

Continuous positive airway pressure in new-generation mechanical ventilators: a lung model study.

A number of new microprocessor-controlled mechanical ventilators have become available over the last few years. However, the ability of these ventilators to provide continuous positive airway pressure without imposing or performing work has never been evaluated. In a spontaneously breathing lung model, the authors evaluated the Bear 1000, Drager Evita 4, Hamilton Galileo, Nellcor-Puritan-Bennett 740 and 840, Siemens Servo 300A, and Bird Products Tbird AVS at 10 cm H(2)O continuous positive airway pressure. Lung model compliance was 50 ml/cm H(2)O with a resistance of 8.2 cm H(2)O x l(-1) x s(-1), and inspiratory time was set at 1.0 s with peak inspiratory flows of 40, 60, and 80 l/min. In ventilators with both pressure and flow triggering, the response of each was evaluated. With all ventilators, peak inspiratory flow, lung model tidal volume, and range of pressure change (below baseline to above baseline) increased as peak flow increased. Inspiratory trigger delay time, inspiratory cycle delay time, expiratory pressure time product, and total area of pressure change were not affected by peak flow, whereas pressure change to trigger inspiration, inspiratory pressure time product, and trigger pressure time product were affected by peak flow on some ventilators. There were significant differences among ventilators on all variables evaluated, but there was little difference between pressure and flow triggering in most variables on individual ventilators except for pressure to trigger. Pressure to trigger was 3.74 +/- 1.89 cm H(2)O (mean +/- SD) in flow triggering and 4.48 +/- 1.67 cm H(2)O in pressure triggering (P < 0.01) across all ventilators. Most ventilators evaluated only imposed a small effort to trigger, but most also provided low-level pressure support and imposed an expiratory workload. Pressure triggering during continuous positive airway pressure does require a slightly greater pressure than flow triggering.

Effort and work of breathing in neonates during assisted patient-triggered ventilation.

OBJECTIVE: This study compares patient-ventilator synchrony, work of breathing and patient effort in neonates during different modes of patient-triggered ventilation. DESIGN: Clinically stable neonates received intermittent mandatory ventilation (IMV), synchronized intermittent mandatory ventilation (SIMV), pressure assist/control ventilation (A/C), and pressure support ventilation (PSV) in a random order for 20 mins. With each mode patient-ventilator synchrony, work of breathing, and patient effort were evaluated. SETTING: Neonatal level III intensive care unit of a university hospital. Measurements and RESULTS: Seven clinically stable neonates (31.4 +/- 2 wks gestation, weighing 1.49 +/- 0.38 kg) were randomly ventilated with the above four modes using a Bird VIP ventilator. Esophageal pressure, airway pressure, and flow were measured using a CP-100 neonatal monitor (Bicore). Data for five consecutive breaths in each mode were analyzed. Patient effort and work of breathing differed significantly among modes of ventilation. The inspiratory pressure time product was least with A/C (0.54 +/- 0.29 cm H(2)O.sec) and increased with PSV (0.60 +/- 0.39 cm H(2)O.sec), SIMV (1.46 +/- 0.55 cm H(2)O.sec), and IMV (2.74 +/- 1.05 cm H(2)O.sec) (p <.05). A similar trend was observed for work of breathing, with work least during A/C (0.07 +/- 0.04 joules per liter [J/L]), followed by PSV (0.17 +/- 0.14 J/L), SIMV (0.33 +/- 0.13 J/L), and IMV (0.41 +/- 0.16 J/L) (p <.05). Marked dyssynchrony between patient-initiated and ventilator-initiated inspiration occurred only during IMV. CONCLUSION: Asynchrony can be avoided by the use of assisted, patient triggered modes of ventilation and, of the available modes, pressure A/C results in the least effort and work of breathing for clinically stable neonates.

Pathophysiologic basis of acute respiratory distress in patients who fail a trial of weaning from mechanical ventilation.

To determine the mechanisms of acute respiratory distress and failure in patients with chronic obstructive pulmonary disease (COPD), we studied 17 ventilator-supported patients who failed a trial of spontaneous breathing and 14 patients who tolerated such a trial and were successfully extubated. Immediately before the weaning trials, maximal inspiratory pressure was not statistically different between the two groups (p = 0.48). On discontinuation of the ventilator, the failure group immediately developed rapid shallow breathing, and higher values of dynamic lung elastance (EdynL) (p < 0.01) and intrinsic positive end-expiratory pressure (PEEPi, p < 0.03) than did the success group. Between the onset and end of the trial, the failure group developed further increases in EdynL (p < 0.0001) and PEEPi (p < 0.0001), and increases in inspiratory resistance (p < 0.009) and inspiratory pressure-time product (PTP) (p < 0.0001). Partitioning of PTP at the end of the trial revealed a 111% increase in the PEEPi component, a 33% increase in the non-PEEPi elastic component, and a 42% increase in the resistive component (all p < 0.0001). Despite the increase in PTP, 13 of the failure patients developed an increase in PaCO2. The product of PTP and PaCO2, an index of inefficient CO2 clearance, was more than twice as high in the failure group than in the success group at the end of the trial (p < 0.0005). Thus, development of acute respiratory distress during a failed weaning attempt was due to worsening of pulmonary mechanics, which in conjunction with rapid shallow breathing led to inefficient clearance of CO2.

Variability of patient-ventilator interaction with pressure support ventilation in patients with chronic obstructive pulmonary disease.

In 12 patients with chronic obstructive pulmonary disease (COPD) receiving pressure support ventilation (PSV), we studied the variability of respiratory muscle unloading and defined its physiologic determinants using a modified pressure-time product (PTP). Inspiratory PTP/min decreased as PSV was increased (p < 0.001), but there was considerable interindividual variation: coefficients of variations of up to 96%. On multiple linear regression analysis, 73 to 83% of the variability in inspiratory PTP was explained by inspiratory resistance, minute ventilation, and intrinsic positive end-expiratory pressure. Taking an inspiratory PTP/min of < 125 cm H2O.sec/min to represent a desirable level of inspiratory effort during PSV, a respiratory frequency of < or = 30 breaths/min was more accurate than a tidal volume > 0.6 L in predicting this threshold (p < 0.001). At PSV of 20 cm H2O, expiratory effort, quantitated by an expiratory PTP, was clearly evident in five patients before the cessation of inspiratory flow, signifying that the patient was "fighting" the ventilator; of note, these five patients had a frequency of < or = 30 breaths/min. In conclusion, patient-ventilator interactions in patients with COPD are complex, and events in expiration need to be considered in addition to those of inspiration.